Applies To Product(s): SewerGEMS, WaterGEMS, WaterCAD, HAMMER, SewerCAD, StormCAD, CivilStorm Version(s): 10.00.xx.xx, 08.11.xx.xx Area: Data Input and Model Creation Original Author: Jesse Dringoli, Bentley Technical Support Group Problem When attempting to open a model, one of the following errors occurs: 'Unsupported dataset type schema' 'Object Reference not set to an instance of an object' 'Unexpected Numeric Presentation Formatter' 'Expecting: Numeric Formatter or Station Formatter' Solution This error typically indicates that the model was created in a newer version of product. To find out what version the model was last saved in, open the .WTG or .STSW file (depending on the product) in a text editor such as Wordpad or Notepad and look for "ProductVersionLastModified=" near the top. This wiki provides an explanation of how to do that . You will need to install a version that is equal to or greater than this in order to open the model. If that is not possible, there are a few workarounds that you can try. Option 1 If you are using a version that is equal to or greater than the version last used to modify the model, then the issue could be related to one of the supporting files (eg. .out). Try copying the model file (.stsw, .wtg) and database file (.mdb, .SQLite) to a new folder. Then try to open the model from the new location (without using the supporting files). Option 2 If you have a Water products (HAMMER, WaterCAD, and WaterGEMS), export the model to the standard EPANET format (File > Export > EPANET). This format can be opened in most older versions by going to File > Import > EPANET. Note that there are limitations with this method such as only being able to export one scenario, and other items described in this wiki article related to EPANET importing and exporting. For SewerGEMS and CivilStorm, export the model to the EPA SWMM format (File > Export > SWMM v5). After that the SWMM file can then be opened by most older version of the software (File > Import > SWMM v5). As with the EPANET for the water products, you may also run into some limitations or have the potential to lose some information in the process of the export/import. In SewerCAD and StormCAD, you can export the model to the LandXML format (File > Export > LandXML) and import the LandXML file into the older version of SewerCAD or StormCAD. As with the water products, there may be some limitations to this workflow. Option 3 The other workaround would be to export all elements in your model to shapefiles and then import those shapefiles with the older version of the software using Modelbuilder. This method also will take some work though and can be tedious. The first thing you need to do if you are using this method would be to make sure your FlexTables have all the information you input for the properties of each element and then export each element to a shapefile. Export your elements to shapefiles is described in this wiki . After you do this you would need to use the ModelBuilder tool in the older version of the software (Tools > Modelbuilder) to import all those elements back in. Using ModelBuilder to construct a network is described in this wiki found below and there is also information in our Help documentation on how to use ModelBuilder See Also Can a model to saved down or back to an older version? Error opening old model file: Database format not recognized or read-only "Unexpected drawing version..." error when opening model

Applies To Product(s): WaterCAD, WaterGEMS, HAMMER, SewerCAD, SewerGEMS, StormCAD, CivilStorm Version(s): 08.11.XX.XX Area: Other Original Author: Mark Pachlhofer, Bentley Technical Support Group Error or Warning Message "Unexpected drawing version: 39" (or similar) error or "Object reference not set to an instance of an object" error when opening the software. Explanation This error can occur when you are trying to open a model created in a more recent version of the software than the version that you have, or when one of the supporting files (such as output or DWH drawing file) is corrupt. Resolution First, check if the version that you're using is greater than or equal to the version that the model was created in (look at See Also section below) . You will need to upgrade to the version of the software used for this issue or upgrade to the latest version of the software if you are using an older version. If you're using a version of the software that's greater than or equal to the version that the model was last saved in, check the support files. In the same folder as the model (or in the results file path specified under Tools > Options > Project), you may see several files beside the main project files. To ensure that they are not the cause of the problem, copy the main two project files (either .wtg and .wtg.sqlite or .wtg and .wtg.mdb, depending on your version) to a different folder and try opening it from there. We have seen cases where the . DWH file can sometimes be the issue and it can safely be deleted because it is regenerated when reopening the model. You should make sure that you have the latest patch set applied to the software. You can find directions on how to do that here . If the above does not work you can also try to import that database file by going to File > Import > WaterCAD database See Also Locating the version number of the software a model was created using Errors when opening model: "Unsupported dataset type schema" "Object Reference..." etc

Applies To Product(s): WaterCAD, WaterGEMS, SewerGEMS, SewerCAD, StormCAD, CivilStorm, PondPack, FlowMaster Version(s): 08.XX.XX.XX Area: Other Original Author: Mark Pachlhofer, Bentley Technical Support Group These are the directions to locate the version number of the software your model file was created using. Background There are some cases where you have error messages such as, "Unsupported dataset type schema", where it helps to know what version of the software was used to create a model. Steps to Accomplish WaterGEMS/CAD/HAMMER will be used as an example here. Note that the file extension for the other programs is different, but you will only be opening the non-database project file (.stsw, .ppc, .swg, .swc, .csd, .fm8, or .stmc). Browse to the location/folder of the file that you want to view Right click on the .wtg file and select "Open with..." Now select some type of text editing software such as Notepad, Wordpad, Notepad ++, etc... Look for the third line of the file where it says, "ProductVersionLastModified =" and note the number of the software. See Also How do I download the latest versions of the Bentley hydraulics and hydrology products? "Unexpected drawing version..." error when opening model Errors when opening model: "Unsupported dataset type schema" "Object Reference..." etc

Example model showing the use of the Hydropneumatic tank in Bentley HAMMER.

Applies To Product(s): Bentley HAMMER Version(s): V8i, CONNECT Edition Area: Modeling Original Author: Jesse Dringoli, Bentley Technical Support Group Overview This TechNote explains how the Hydropneumatic Tank element works and its typical application in HAMMER. It also provides an example model file for demonstration purposes. Background The Hydropneumatic Tank element in HAMMER represents a cylindrical or spherical pressure vessel containing fluid at the bottom and an entrapped gas (usually air or nitrogen) overlying the liquid. It is sometimes referred to as a Gas Vessel, air chamber or pressurized surge tank. When the hydropneumatic tank is being filled (usually from a pump), the water volume increases and the air is compressed. When the pump is turned off, the compressed air maintains pressure in the system until the water drains and the pressure drops. This storage of energy as compressed air allows for a high hydraulic grade to be achieved in a relatively small tank, whereas the traditional, unpressurized surge tank would need to be constructed as high as the hydraulic grade you need to achieve. This is because the hydraulic grade in a hydropneumatic tank is the elevation plus the water level PLUS the pressure head of the gas above it, whereas in a surge tank, it is the water surface elevation. Thus, a surge tank is typically not practical for a high head system. 3 So, If the hydropneumatic tank contains enough (pressurized) gas to prevent water columns from separating, it can be a very effective way to avoid or reduce pressure surges. The most common use of a hydropneumatic tank for surge protection is for controlling transients caused by rapid pump start up and shut down. In a typical emergency pump shutdown scenario, the low pressure 'downsurge' can cause severe subatmospheric pressure. Column separation can occur and severe high pressure 'upsurges' can occur upon vapor pocket collapse. So, protective equipment is often necessary to provide water and head to the system upon downsurge and also to bleed water out of the system upon upsurge. Most often the best protection for this situation is either a surge tank or hydropneumatic tank, since they can provide this water and head during a transient event. The hydraulic grade provided by a surge suppressing hydropneumatic tank must be high, and typically will operate at normal pipeline pressure. This means the normal pressure at the tank is the same pressure that would occur if the tank were not installed at all. This is different from 'normal' hydropneumatic tanks in water distribution systems, which typically cycle quickly based on hydraulic grade pump controls. Note: Adding surge-control equipment or modifying the operating procedures may significantly change the dynamic behavior of the water system, possibly even its characteristic time. Selecting appropriate protection equipment requires a good understanding of its effect, for which HAMMER V8i is a great tool, as well as the good judgment and experience you supply. Modeling Considerations If you have decided to model a hydropneumatic tank for surge protection, there are several considerations for its design. Each of these can impact the effectiveness and cost of the device and must be carefully evaluated. For further guidance on sizing of the hydropneumatic tank, we suggest the book 'Fluid Transients in Pipeline Systems' by A. Thorley. Location A hydropneumatic tank is typically installed just downstream of a pump station, so as to keep the water column moving upon pump shutdown. It is typically installed inside an enclosed building and is sometimes 'twinned' (two of the same tank side by side) for maintenance and redundancy purposes. 3 If the hydropneumatic tank location is uncertain or if more than one may be required, you can compute the transient simulation without any protection and check your results (such as the min/max pressure envelope in the Transient Results Viewer.) By viewing these results, you can see critical areas of the pipeline and potentially find a good location candidate for the hydropneumatic tank(s). You can then add your hydropneumatic tank(s), re-compute the transient simulation, re-check the results and make adjustments as necessary. Note: Sometimes a tank may be required on the suction side of a pump station as well, to prevent cavitation upon pump shutdown/startup. Be sure to check the minimum pressure results upstream of the pump for your transient simulation. The pipe connecting from the main pipeline to the hydropneumatic tank can be modeled in HAMMER either implicitly or explicitly. Basically, when laying out the hydropneumatic tank, it can be modeled at a 'Tee' by laying out the connecting pipe, or can be modeled directly on the main line. When modeling on the main line (the typical approach), the influence of the short piping between the main and the tank can be represented by means of the tank inlet diameter and minor loss coefficient fields. Although explicitly entering the short connecting pipes to the vessel is not incorrect in principle, it may lead to excessive adjustments in pipe length or wave speed which in turn may have an impact on the results. This adjustment commonly occurs with short pipes, due to the fact that HAMMER must have a wave be able to travel from one end of the pipe to the other end in even multiples of the time step. So, since you can model the connecting pipe head losses via the minor loss coefficient field, it is often best to model the tank inline. However, you must also consider the effects of water momentum. For example if you're modeling large flows and large diameter pipes, the effects of accelerating that relatively large volume of water (in the connecting pipe) upon emergency pump shut down may be significant. If you are simulating an emergency pump shutdown event, it may be possible to have a condition where a single hydropneumatic tank at the pump station cannot provide adequate protection. For example, if there is an intermediate high point between the pump and the downstream boundary tank/reservoir, even if your initial hydropneumatic tank pressure is high, it will eventually drain down to a hydraulic grade that causes sub-atmospheric pressure at the high point. So, it is important to also consider the length of time that the pump will be shut down. You will likely want to simulate the worst case scenario though, so in this situation you may need additional protection, such as an air valve or additional tank near the high point. For example, consider the following pipeline profile with an emergency pump shutdown: Dark black line = physical elevation. Dashed black line = steady state / initial conditions head. As you can see, the addition of a hydropneumatic tank (gas vessel) just downstream of the pump station does not offer enough protection. Sub-atmospheric pressure occurs at the downstream end of the system, due to the high point. Even with an air valve at the high point, the longer the pump is off, the more air will be introduced into the system. The addition of a surge tank at said high point does well at alleviating this problem. Note: It is important to note that using air chambers and surge tanks in treated drinking water systems can result in water quality deterioration and loss of disinfectant residual. These devices should be equipped with a mechanism for circulating the water to keep it fresh. A further complication occurs when the tanks are located in cold climates where the water can freeze. If freezing is an issue, smaller air chambers that can be housed in heated buildings are preferable. 1 Size Although the total size of the hydropneumatic tank is important, it is not directly used in HAMMER unless you're using a bladder (which is covered later in this TechNote). Instead, you define the initial hydraulic grade and corresponding gas volume, then view the transient results to see how much the gas expanded. Basically your hydropneumatic tank needs to be large enough so that it does not become empty during the transient simulation. HAMMER assumes that the water volume in the tank is enough so that this does not happen. In the Transient Analysis Output Log (Under Report > Transient Analysis Reports), you will see the maximum volume of gas that is needed during the transient analysis. You will then need to provide a hydropneumatic tank that will be able to accommodate that maximum volume of gas and still not become empty of water (assuming that you don't want it to become empty of course.) When you're not using the bladder option, you must enter a total volume for the hydropneumatic tank (the "Volume (Tank)" field), but this is for reference purposes during the transient simulation. If the volume of gas during the transient simulation exceeds the total tank volume that you entered, you'll encounter a User Notification about the maximum gas volume being greater than the entered tank volume. However, HAMMER will still compute gas volumes above the total tank volume, based on the gas law. Not only will this indicate that there is something wrong, but it will also indicate by how much. Meaning, the user can view the maximum gas volume required (in the text output log) with the current tank configuration, make the necessary adjustments, then re-run the simulation. For example, a user entered 500 L as the initial gas volume and 1500 L as the total tank volume, but the output log shows a maximum gas volume of 1640 L. This means that during the transient simulation, the head dropped so low that the expanded gas volume occupied more than 1500 L. It tells the user that their desired tank is almost big enough, but not quite. In case this situation occurs, it's important to realize that the total tank size is not necessarily the only factor. For example, if the initial gas volume at the steady state hydraulic grade was smaller, the maximum gas volume during the transient may be less and within the desired total tank size. Other things such as a differential orifice can also influence the effectiveness of a tank that is a certain size. So, just because the reported gas volume is higher than the tank size you'd like, it doesn't necessarily mean that you need a bigger tank. You may be able to control the maximum gas volume by changing other parameters, therefore allowing the same tank size to be used. Since you may be limited (due to cost, physical space or other reasons) in terms of the largest tank size you can provide, adjustment of these other things may be necessary. With HAMMER, you can easily test different configurations of your tank to find the optimized protection for your pipeline. In some cases, you may have a requirement stating that a certain percentage of the tank volume must be liquid in the steady state conditions. You may also have a limit on the total tank size, maximum pressure, bladder pre-charge pressure, etc. So, you'll need to design around these requirements. Differential Orifice The piping connection between the hydropneumatic tank and the system should be sized to provide adequate hydraulic capacity when the chamber is discharging, as well as to cause a head loss sufficient to dissipate transient energy and prevent the chamber from filling too quickly. Both of these requirements are met through the use of a piping bypass as depicted below. 1 In HAMMER, the headlosses associated with this can be modeled by using the "Minor Loss Coefficient", "Ratio Of Losses" and "Diameter (Tank Inlet Orifice)" attributes of the hydropneumatic tank. This is referred to as the differential orifice, because the ratio of losses allows you to have the inflow headlosses different from the outflow headlosses. In the above illustration, you can see that the check valve causes inflows to undergo larger headlosses as water passes through the bypass. So, the ratio of losses attribute is usually larger than 1.0 and applies to inflows. The "minor loss coefficient" that you enter is used for tank outflows. For tank inflows, the minor loss coefficient is multiplied by the "ratio of losses" and the resulting coefficient is used. The effect of a differential orifice can be large for some systems. Note: you may consider adjusting the minor loss coefficient to represent multiple losses through the tank assembly. For example you may have minor losses from bends, fittings, the tank inlet itself and the differential orifice assembly. In this case, you can set the "minor loss coefficient" value to represent all those losses, but remember that the velocity used to calculate them is based on the area of the "diameter (tank inlet)". Also, you'll need to set up the ratio of losses such that the losses through the entire tank assembly appropriately accounts for the additional loss through the bypass of the differential orifice. Consider the below profile, showing the maximum transient head for a pipeline during an emergency pump shutdown event. The inlet orifice size was decreased by 75 mm and a minor loss coefficient of 1.5 was used, with a ratio of 2.5. As you can see, it helps reduce the maximum transient pressures in the system. This could also mean a possible reduction in total required tank size. Bladder A flexible and expandable bladder is sometimes used to keep the gas and fluid separate in the hydropneumatic tank. Since there is no contact between the compressed air and the water, there is no dissolution. There is thus no requirement for a permanent regulation system such as an air compressor, which is otherwise typically required (since the gas slowly dissolves into the water). 2 When using a bladder, a 'pre-charge' pressure is first applied, before the tank is connected to the system and submitted to pipeline pressure. Transient protection performance when using a bladder-type tank tends to be sensitive to the pre-charge pressure, since it determines the initial gas volume and sensitivity to pressure changes. Sometimes you may have a requirement on the pre-charge pressure, such as being 5% of the normal pipeline pressure. Otherwise, you may need to use trial and error to find the best pre-charge pressure. When using the bladder tank option, prior to and during a transient computation: HAMMER assumes the bladder is at the pre-set pressure but isolated from the system. HAMMER assumes a (virtual) isolation valve is opened, such that the (typically higher) system pressure is now felt by the bladder. HAMMER computes the new (typically smaller) volume of the air inside the bladder. When the transient occurs, HAMMER expands or contracts the volume inside the bladder accordingly. After the simulation is complete, you can look in the text output files to see what the preset pressure, pre-transient volume (at system pressure) and subsequent variations in pressure and volume have occurred. Pump Check Valve When using a hydropneumatic tank just downstream of a pump station, check valve slam is a common concern. This is because after the low pressure transient from a pump shutdown event, the tank maintains a high downstream hydraulic grade, which quickly causes the check valve downstream of the pump to close. So, a non-slam check valve is typically used in these cases. The user must carefully model the check valve by considering its behavior. By default, the check valve node element and check valve property of a pipe assume an instantaneous closure upon first detection of reverse flow. This means no reverse velocity will build up before closure occurs. If this doesn't match the behavior of your check valve, be sure to use the "Open Time", "Closure Time" and "Pressure Threshold" options for the check valve node element. This allow you to model the delay in opening and closing of a check valve. Initial Conditions Behavior As with any transient simulation, a model with a hydropneumatic tank must begin in a steady state condition. HAMMER uses the WaterGEMS hydraulic engine to compute the steady state initial conditions, which are used as the starting point for the transient simulation. For a hydropneumatic tank, the initial conditions provide a hydraulic grade and inflow/outflow to the transient calculation engine. Steady State vs. EPS Typically the initial conditions are computed as a steady state (by selecting "steady state" as the "time analysis type" in the steady state/EPS solver calculation options, which is the default.) If you must compute an Extended Period Simulation (EPS), be aware that you will need to select a time step for the transient calculation to use as its initial conditions (Using the "initialize transient run at time" transient calculation option). You will also likely need to use a small hydraulic time step (selected in the steady state/EPS solver calculation options), since a hydropneumatic tank typically cycles relatively quickly. With EPS, you will likely also need to set up controls for your pump based on the tank hydraulic grade. Lastly, the change in HGL/volume during the EPS is calculated using either a constant area approximation or the gas law, depending on the selection of "tank calculation model." However, when modeling a hydropneumatic tank that is meant for transient surge protection, it typically operates under 'line' pressure, so you usually don't need to analyze changes during EPS. The typical approach is to use a steady state simulation as the initial conditions and select "true" for the "treat as junction" attribute (see below). Treat as Junction? As mentioned above, in many cases a hydropneumatic tank may be implemented only for transient protection. During a steady state condition, the tank may simply operate under the corresponding normal / steady state head ("line pressure"). So, for simplification, it is sometimes preferable to select "true" for the "treat as junction" attribute in the tank properties. Doing this allows the initial conditions solver to compute a hydraulic grade at the tank location, and the user simply assumes that the tank has already responded to the hydraulic grade and the air volume has expanded or contracted accordingly. In this case, the user only needs to enter the initial volume of gas under the "transient" section of the tank properties that corresponds to that initial conditions hydraulic grade (unless using a bladder). It's important to remember that the tank is only treated as a junction in the initial conditions. During the transient simulation it's still treated as a hydropneumatic tank. Basically, treating it as a junction in the initial conditions is another way of establishing the initial hydraulic grade. The transient simulation will use that hydraulic grade along with the gas volume as the starting conditions. The gas will then expand and contract accordingly during the transient simulation, based on the gas law. If you already know the hydraulic grade that you'd like to use as the initial conditions, you would choose "false" for "treat as junction?" and enter it under the "physical" section of the tank properties. The initial conditions solver will then compute the flow/head in the rest of the system, with the hydropneumatic tank as the boundary condition. In this case, the tank will likely have either a net inflow or outflow, to balance energy across the system. So your transient simulation may not begin at a true "steady" condition. Initial Conditions Attributes The following attributes of the hydropneumatic tank influence the initial conditions calculation (steady state or EPS). You'll notice that they are all within the "Operating Range" or "Physical" section of the hydropneumatic tank properties. Elevation (Base) - The elevation of the base of the tank. It is used as a reference when entering initial hydraulic grade in terms of "Level" (i.e., if the "Elevation (Base)" is set to 20 m and the operating range is set to "Level", a "Level (Initial)" value of 1.0 represents an elevation of 21 m). Operating Range Type - Specify whether the initial hydraulic grade of the tank is based on levels measured from the base elevation or as elevations measured from the global datum (zero). For example, if the base elevation is 20 m, you want the initial hydraulic grade to be 70 m, and you want to use levels, then select "Level" for this field and enter 50 m as the initial level. HGL (Initial) or Level (Initial) - Depending on the operating range type selected, this represents the known boundary hydraulic grade at the tank during steady state. Remember that it includes the water surface elevation plus the pressure head of the compressed air in the hydropneumatic tank. The transient simulation will begin with this head. However, if you've selected "True" for the "Treat as Junction" attribute, the transient simulation will ignore this value and instead use the computed steady state hydraulic grade (seen in the "Results" section of the tank properties). Note that said computed hydraulic grade still represents the water surface PLUS the air pressure head - it is the total head at that point in the system (see further above for more information on the "Treat as Junction" attribute). So, let's say for example you ran a steady state, treating the tank as a junction to find the 'balanced' head in the tank (as if it already responded to the system conditions) but then wanted to change it back to being treated as a tank (for purposes of analyzing the behavior in an EPS simulation or something else), yet still begin the simulation with the same, balanced head. To do this, you would copy the computed hydraulic grade (from the results section of the properties) into memory, set "Treat as Junction?" to "False", then paste that hydraulic grade value into the "HGL (Initial)" field. When re-computing initial conditions, the initial results will then be equivalent to the original case where the tank was treated as a junction. Liquid Volume (Initial) - This represents the volume of liquid in the tank at the start of the initial conditions, corresponding to the initial HGL. This includes the inactive volume below the effective volume, when using the "Constant Area Approximation" tank calculation model. It is mainly used during an EPS, but also to establish the initial gas volume used by the transient simulation, when "treat as junction" is set to "false". In that case, the initial gas volume is the difference between the "Volume (Tank)" and the "Liquid Volume (Initial)". When "treat as junction" is set to "true", the initial liquid volume field is not directly used by the transient simulation. Elevation - The elevation from which to calculate pressure in the hydropneumatic tank. Because of that, the most accurate elevation would typically represent the bottom of the tank. However, if the bottom of the tank is close to the ground surface elevation, that can be used as well. It could also be set to the estimated water surface, since the air pressure (used in the gas law equation) is above that point. However, the bottom elevation and water surface are typically very close, so this likely will not make a noticeable difference. Note : If a modeler is using "Fixed" Elevation Type, the value entered here will always be used for the pressure calculations. If the modeler believes that the water surface elevation will have a significant impact on the pressure calculations, they should set Elevation Type to "Variable Elevation" and enter the tank dimensions. Volume (tank) - This represents the total internal volume of the tank. In an EPS simulation, or when "Treat as junction" is set to "false", this is used to find the initial gas volume so that the gas law equation can be used (difference between this and the "Liquid Volume (initial)"). This is also used when using the bladder option ("Has Bladder?" = "True") to establish the pressure/volume relationship used during the transient simulation. HAMMER assumes the bladder occupies this full tank volume at its "preset pressure," so this full tank volume value is needed by the gas law equation. (see more below). As for the transient simulation itself, the full tank volume attribute is only used indirectly (since it establishes the initial conditions) and as a reference: Since by default the liquid service elevation in a hydropneumatic tank is not tracked and is assumed to be fixed (see "tank type" further below under "Transient Simulation Attributes") the "Volume (tank)" attribute is also used for reference purposes during the transient simulation. The calculated volume of gas is compared to it to determine if the tank becomes empty. Treat as Junction? - Selects whether or not the tank is treated as a junction during the initial conditions. If "False," the "HGL (Initial)" or "Level (Initial)" field is used for the initial head. If "true," the initial conditions solver acts as if the tank is a junction and computes normal/'line pressure. Tank Calculation Model - Specifies whether to use the gas law or a constant area approximation method during EPS initial conditions. The constant area approximation uses a linear relationship; the user must specify minimum/maximum HGL and the corresponding volume between. The gas law model is non-linear and follows the gas law--as gas is compressed, it becomes harder to compress it more. Atmospheric Pressure Head - When using the gas law tank calculation model, this field represents atmospheric pressure at the location being modeled. This is required because the gas law equation works in absolute pressure, as opposed to gauge pressure. Note: The "atmospheric pressure head" field is not used during the transient simulation. The transient calculation engine assumes an atmospheric pressure head of 1 atm or 10.33 m. HGL on/HGL off - Exposed when using the constant area approximation method. The "HGL on" field is the lowest operational hydraulic grade desired, and the "HGL off" is the highest operational hydraulic grade desired. Corresponding controls should be entered to turn the pump on and off during an EPS simulation. Note that typically a transient simulation will use steady state initial conditions, so these fields are not considered; only the steady state HGL and user-entered gas volume are used to define the initial volume and head for the transient simulation. Volume (effective) - Exposed when using the constant area approximation method. Represents the volume between the HGL on and HGL off fields. Gas Law vs. Constant Area Approximation For the initial conditions, the user must select either "gas law" or "constant area approximation" for the "Tank calculation model" attribute of the hydropneumatic tank. The constant area approximation selection exposes the "Volume (effective)," "HGL on," and "HGL off" fields. The gas law selection exposes the "Atmospheric pressure" field. These fields are primarily there to support the WaterCAD and WaterGEMS products, which can directly open a HAMMER model. They are only used to track the change in HGL/volume for EPS simulations, which typically aren't used in HAMMER. A transient analysis typically begins with a steady state simulation, which only considers the "HGL (Initial)" and "volume of gas (initial)". This is because a steady state simulation is a snapshot in time, so the head/volume are not changing. So in most cases, it does not matter which tank calculation method you choose. You will likely want to select "gas law" for simplicity, but additional information on both approaches is provided below. Constant area approximation: This method approximates a hydropneumatic tank by constructing a normal tank based on hydraulic grades. The HGL on and HGL off fields represent the liquid level plus the pressure head, and an approximated diameter is computed based on the effective volume. So, you essentially have a tall, skinny tank whose water surface elevation approximates the HGL in a hydropneumatic tank. Gas Law: This method uses the ideal gas law, PV=nRT, to compute new hydraulic grades as liquid volume changes in the EPS simulation (nRT is assumed to be constant). The initial liquid volume is subtracted from the total tank volume to find the gas volume. The physical "elevation" is subtracted from the initial HGL to find the gauge pressure. The atmospheric pressure is added to the gauge pressure to get absolute pressure, which is used in the ideal gas law equation. Both methods typically yield similar results within the "effective" control range, but the gas law is technically more accurate. Transient Simulation Behavior The following section explains how HAMMER handles hydropneumatic tanks during the transient simulation. There are two distinct tank configurations: with a bladder and without a bladder. Without a Bladder The transient simulation uses the hydraulic grade from the initial conditions, along with the initial gas volume, which is either user-entered (if "treat as junction" = true") or calculated based on the difference between the "Volume (tank)" and "Liquid Volume (Initial)" (if "treat as junction" = false). As pressure in the system drops due to a downsurge, this gas volume expands and water injects into the system. Pressure upsurges cause the gas to compress as water re-enters the tank. This compression and expansion occurs in accordance with the isothermal gas law. A constant number of moles / mass of gas in the tank and constant temperature is assumed, so the 'nRT' term in the gas law equation is replaced by a constant, K. Thus, the equation used is PV k =K, Where P = absolute pressure (feet or meters), V = gas volume (cubic feet or cubic meters) and k is the Gas Law Exponent specified in the tank properties. Thus, the constant K is computed from the initial gas volume raised to the exponent, multiplied by the initial pressure. The pressure P is the initial hydraulic grade minus the tank physical elevation, plus atmospheric pressure (1 atm or 10.33 m). This way, a new air volume can be computed based on pressure changes during the transient simulation. For example, consider a tank who's initial gas volume is 0.8 m 3 , initial hydraulic grade is 150 m, physical elevation is 100 m and gas law exponent is 1.1. From this, HAMMER computes the "K" constant as: (150 - 100 + 10.33)(0.8 1.1 ) = 47.2 . Since K is known now, the change in pressure can be computed based on changes in volume due to inflow/outflow. For example, say that the tank filled such that the gas volume was compressed to 0.5 m 3 . Based on the K constant of 47.2, this means that the corresponding pressure = (47.2) / (0.5 1.1 ) = 101.175 - 10.33 = 90.845 m. (a hydraulic grade of 100 + 90.845 = 190.845 m) Note: In the formula above, the pressure P is measured from the bottom of the tank (the physical elevation). This is because by default, HAMMER does not track the liquid level in the hydropneumatic tank. This assumption should be fine in most cases, because these tanks are usually relatively small and thus the change in liquid level would have a minimal impact. However if you'd like HAMMER to be able to account for the liquid level (water height), check out the section further down in the TechNote called "Tracking the Liquid Level". Note: In HAMMER 08.11.01.32+, the "Volume of gas (Initial)" field only needs to be entered if your hydropneumatic tank is treated as a junction or if you are choosing to specify custom initial conditions (and are not using a bladder). In other cases, the initial gas volume is derived from the total tank volume minus the initial liquid volume. With a Bladder If your hydropneumatic tank has its gas contained within a bladder, then you must enter a gas preset pressure. This is the pressure inside the bladder before the tank is submitted to pipeline pressure; basically the pressure that you "precharge" it to, before installation. The preset pressure is typically a percentage of the pipeline pressure; a possible range is 5% to 80%. Since the tank is not yet installed when the bladder is precharged, it means that the gas takes up the entire tank volume. So, HAMMER can calculate the initial gas volume inside the bladder (when submitted to pipeline pressure) based on the full tank volume, the preset pressure and the pipeline hydraulic grade. First, the constant K in the gas law (PV = K) is computed based on this preset pressure and the full tank volume, "Volume (Tank)." The transient simulation's initial gas volume is then computed based on the K constant and the initial conditions hydraulic grade. The initial conditions hydraulic grade is either the user-entered value in the "HGL (Initial)" field, or the computed steady state hydraulic grade, depending on the "treat as Junction?" selection. For example, consider a tank that has been given a full volume of 500 L and the initial conditions pressure head is 50 m. Assume that the pre-charge pressure is 5% of the steady state pipeline pressure. (this is a number that you would know ahead of time) So, the gas preset pressure is set to 2.5 m (50 m times 5%). In this case, HAMMER computes the 'K' constant as (2.5 m + 10.33 m)(0.5 m 3 ) = 6.415. Since K is known now, the initial gas volume for the transient simulation (after the bladder is submitted to pipeline pressure) is computed as V = K/P = (6.415)/(50 m+10.33 m) = 0.106 m 3 = 106 L. Conversely, let's consider a case where you want the tank's bladder to be compressed to a specific size when submitted to pipeline pressure (rather than assuming a percentage of pipeline pressure such as 5%) and would like to know what you would need to enter for the preset pressure to achieve this. Let's assume the same full tank volume/size of 500 L, and initial conditions pressure head of 50 m. Let's assume you want the bladder to be compressed to an initial gas volume of 200 L. First, we must calculate the K constant based on the gas law when the tank is installed, where the "P" is the initial pipeline pressure (50m) and the "V" is the desired gas volume of 200 L (0.2 m^3) : K = (50m+10.33m)*0.2m^3 = 12.066. Next, take this "K" and calculate the preset pressure that the bladder would need to be charged to before installed, where the bladder occupies the full volume (500L / 0.5 m^3). The gas law equation can be rearranged in this case, to P=K/V : P = (12.066 / 0.5 m^3)-10.33 = 13.8 m. So, you would need to use a preset pressure of 13.8 m to achieve an initial gas volume of 200 L, in a system where the initial pipeline pressure is 50 m and the full tank volume is 500 L. Note: The gas law exponent is assumed to be 1.0 in this particular calculation for finding the initial gas volume of the transient simulation. Once the transient simulation begins, the gas law exponent entered in the tank properties (which defaults to 1.2) is used for calculating changes in gas pressure/volume. Since the gas law works with absolute pressures, atmospheric pressure head must be added in the calculation. HAMMER assumed atmospheric pressure head is 1.0 atm, which is the 10.33 m you see in the above example. If you use the second approach above to calculate preset pressure based on assumed initial gas (bladder) volume, it is possible to end up with a negative preset pressure, if the initial pressure is less than atmospheric pressure. This can be a real situation because a slightly negative gage pressure is still a positive absolute pressure. Practically speaking, it means that your initial pressure is very low and the bladder would actually be slightly deflated in order to achieve the desired initial gas (bladder) volume. Under the assumption that the bladder fills the containing tank before being submitted to pipeline pressure, this deflated bladder would indeed experience a negative gage pressure in order for it to "stretch" to fill the containing tank. However there are still moles of gas inside the bladder, so it can still be compressed and follow the gas law relationship between volume and pressure. In this situation, check if the initial pressure, elevations and assumed initial bladder size are correct, as it would not be typical for a hydropneumatic tank to experience such low initial pressures. To see the initial gas volume in the bladder at the start of a transient simulation, ensure that text reports are enabled in the calculation options and a number is entered for the "Report Period" of the tank, then look at the bottom of Reports > Transient Analysis Reports > Transient Analysis Detailed Report. At the top of the table of results for the tank, note the volume for time zero. This is the initial gas volume - the compressed size of the bladder. Intuitively, as long as the gas preset pressure is lower than the pipeline pressure in steady state, the initial volume of gas in the tank will be less than the total volume. Typically, the preset pressure is relatively small, but that may not always be the case. Below is a comparison of two possible bladder tank configurations (at opposite extremes of the spectrum) for a particular system, with an emergency pump shut down event. Observe the graph of time vs. head at the tank location, summary of min/max gas pressure (in meters) and gas volume (in cubic meters) along with transient profile envelope (blue line is minimum head, red line is maximum head.) In the first case, the pre-charge pressure is 5% of the pipeline pressure, with a 500 L tank. In the second case, the pre-charge pressure is 80% of the pipeline pressure, with a 13,000 L tank. With a low preset pressure, the bladder is initially compressed to a relatively small size. So, it is less likely for the tank to drain completely, and thus a relatively small tank size is used without becoming empty. However, per the gas law, the rate of pressure decrease will be higher for a vessel with a lower preset pressure. So, the graph and profile show minimum and maximum transient pressures that may be too extreme for this system. On the other hand, with the high preset pressure case, the bladder isn't compressed by very much when submitted to pipeline pressure. So, a much larger tank size is required to prevent the entire tank from draining of water. However, in contrast to the low preset pressure case, the minimum and maximum transient pressures are much more reasonable. As you can see, the modeler needs to closely examine what is happening in the results for certain tank configurations. Testing different preset pressure values is something you can easily do in HAMMER to see the effects of either option. The text output logs can show you the gas volumes are pressures during your simulation. Note: Remember that HAMMER assumes that the size of your hydropneumatic tank is large enough so that it does not become completely empty. So, regardless of whether you are using a bladder or not, if the volume of gas exceeds the total tank volume during the transient simulation, a notification will be displayed, but gas volumes above the total tank/bladder volume will still be calculated since HAMMER cannot model an empty tank. A gas volume in excess of tank volume tells you is that the tank you used is not sufficient and you will likely need to consider a different preset pressure, larger tank, different configuration, additional protection, etc. Transient Simulation Attributes The following hydropnematic tank attributes influence the transient simulation calculation: Diameter (Tank Inlet Orifice) - This is the size of the opening between the gas vessel and the main pipe line. It is typically smaller than the main pipe size. It is used to compute the correct velocity through the tank, so the correct headloss is computed based on the minor loss coefficient (the standard head loss equation is used: Hl = K*V 2 /2g.) Minor Loss Coefficient (Outflow) - This is the 'k' coefficient for computing headlosses using the standard headloss equation, H = kV 2 /2g. It represents the headlosses for tank outflow. If you lump other minor losses through the tank assembly (bends, fittings, contractions, etc) into this coefficient, keep in mind that the velocity is calculated using the area of the "diameter (tank inlet orifice)" that you entered. Ratio of Losses - This is the ratio of inflow to outflow headloss. For flows into the tank (inflows), the "minor loss coefficient" is multiplied by this value and the losses are computed using that. For flows out of the tank, HAMMER only uses the "Minor Loss coefficient". So, if you enter a minor loss coefficient of 1.5 and a ratio of losses of 2.5, the headloss coefficient used when the tank is filling would be 1.5 X 2.5 = 3.75. Gas Law Exponent - refers to the exponent to be used in the gas law equation. (the 'k' in PV^k = constant) The usual range is 1.0 to 1.4. The default is 1.2. Note: For dipping tube type hydropneumatic tanks, the gas law exponent value must be greater than 1.0, but other hydropneumatic tank types can use a value of 1.0. A user notification will be generated for cases where a value of 1.0 is used for a dipping tube hydropneumatic tank. Volume of Gas (Initial) - When not using a bladder, the initial volume of gas is an important attribute. This is a required input field, representing the volume of gas inside the tank at the steady state pressure (initial conditions hydraulic grade minus tank physical elevation). During the transient simulation, this gas volume expands or compresses, depending on the transient pressures in the system. For example, consider a 500 L tank with base elevation of 20 m and initial hydraulic grade of 70 m. This means that the air pressure head is ~50 m. So, the user needs to decide how much space (volume) the entrapped gas pocket would take up, at this pressure. Note: In version 08.11.01.XX and greater, if you are not specifying initial conditions and not treating the tank as a junction, then the initial gas volume is not required and the field will not show up. This is because it is either computed from the initial conditions gas volume (which is the full tank volume minus the initial liquid volume for a steady state) or based on the preset pressure (if using the bladder option) Note: In some cases, you may want to analyze a range of different initial conditions, which could potentially change the starting hydraulic grade of your hydropneumatic tank. The gas law can be employed in this case. For example, if you know the initial gas volume is 300 L at a steady state pressure head of 50 m, you can compute the 'K' constant using the gas law, PV k =K: (50 m + 10.33 m)(0.3 m 3 ) = 18.099. (gas law exponent assumed to be 1.0) So, if your new steady state pressure head is 30 m, the new initial gas volume (which you must enter) is computed as V = (18.099)/(30 m+10.33 m) = 0.449 m 3 = 449 L. Note: The transient calculation engine always uses an atmospheric pressure head of 1 atm or 10.33 m when solving the gas law equation. Has Bladder? - Denotes whether the gas is contained within a bladder. If it is set to TRUE, HAMMER automatically assumes that the bladder occupied the full-tank volume at the preset pressure at some time and that the air volume was compressed to a smaller size by the steady-state pressure in the system. The "Volume of gas (initial)" is not used in this case, since it is calculated based on the full tank size, preset pressure and steady state pressure. See "with a bladder" topic for more information. Pressure (Gas-Preset) - This is the pressure (not a hydraulic grade) in the gas bladder before it is exposed to pipeline pressure; the pressure when it fills the entire tank volume. Often called the "pre-charge" pressure; it is only exposed when selecting "true" for "Has bladder?" Report Period - used to report extended results in the Transient Analysis Detailed Report. Represents a time step increment. For example, entering '10' would cause extended results to be reported every 10 time steps. Elevation Type - This allows you to specify the type of approach used in tracking the gas-liquid interface (a new feature as of version 08.11.01.32). By default, the liquid surface elevation is not tracked and is essentially assumed to be fixed, at the tank physical bottom elevation. For more information on how this option is used for tracking the liquid elevation, see "Tracking the Liquid Level" further below. Analyzing Results There are many ways to view the results of your transient simulation. For a hydropneumatic tank, some results are available in the powerful Transient Results Viewer tool and some are found in the text output. Note: Do not confuse initial conditions results with transient results. The result fields in the "Results" section of the hydropneumatic tank properties pertain to the initial conditions calculations only. For example, if you right click the tank, choose "graph" and choose "gas volume (calculated)", this will not show you the gas volume during the transient simulation - it will be for the initial conditions only (specifically EPS initial conditions). Transient Results Viewer The primary tool for viewing results is the Transient Results Viewer. To prepare for its use, first ensure that your transient calculation options are set up correctly (Analysis > Calculation Options). Choose some elements under "Report points", choose the desired report times and select "true" for "generate animation data". Next, create a profile of your pipeline under View > Profiles. Next, compute your model and go to Analysis > Transient Results Viewer. To see the transient envelope, select your profile path and click "plot". To see how the head and vapor volume changes over time throughout your profile, click the "animate" button and use the animation controls. This will give you a good visualization of how the hydropneumatic tank performs. To see graphs of HGL, flow and/or vapor volume over time, select one of your report points under "Time Histories", select the attribute to graph and click plot. For example, you may want to see the flow and head at the hydropneumatic tank location. Note: the "volume" reported in the transient results viewer is only air or gas introduced into the pipeline. It does not show the volume of gas inside the hydropneumatic tank itself. The same applies to the "air volume (maximum, transient)" field shown in the "Results (Transient)" section of the hydropneumatic tank properties. Beginning with HAMMER V8i SELECTseries 5, additional results are available in the Transient Results Viewer. These were previously only available in text reports. For hydropneumatic tanks, these include results for gas volume, gas pressure, water level, and water inflow. To access these, choose the Extended Node Data tab in the Transient Results Viewer. Text Reports HAMMER's text output results also offer important information for hydropneumatic tanks. To prepare for viewing this information, first check your transient calculation options. "Show standard output log" and "Enable Text Reports" should be set to "true". Next, enter a number for the "report period" field of your hydropneumatic tank. This represents how often extended text results will be reported. For example, if your time step is 0.01 seconds and you enter '10' for the report period, it means you'll see extended text results every 10 time steps or every 0.1 seconds. As mentioned above, some of these results are available in the Extended Node Data tab in the Transient Results Viewer. For users with older versions of HAMMER, they will still need to use the steps below to view the results. The first text report of importance is the Transient Analysis Output Log, under Report > Transient Analysis Reports. Scroll down to the section starting with "THE EXTREME PRESSURES AND VOLUMES". This part of the report summarizes the maximum and minimum gas pressure and volume for the transient simulation. Lastly, to see a table of extended hydropneumatic tank results, open the Transient Analysis Detailed Report, under Report > Transient Analysis Reports. Scroll down near the bottom, to the section starting with " ** Gas vessel at node" and you will find a table of gas volume, tank hydraulic grade, pipeline hydraulic grade and tank inflow, over time. The difference between the "head-gas" and "head-pipe" is the headloss induced by the minor loss coefficient at the tank's connecting pipe. Negative values for "inflow" represent tank outflow. Starting in HAMMER V8i SELECTseries 5, this data can now be viewed directly from the Extended Node Data tab in the Transient Results Viewer. If you have an older version of HAMMER, you must manually generate a graph using an external application such as Microsoft Excel. Here are the steps, assuming Microsoft Excel 2007: Highlight the table of extended results, then copy/paste it into a separate .txt file (using Windows Notepad). Open Microsoft Excel and start a new spreadsheet. Click the "Data" tab, choose "From Text", then select your file. Choose "Fixed width", then "next". Set up the field widths so that the columns of data are separated appropriately. Set up a line graph with the appropriate columns (Time, plus whatever attribute you'd like to graph. For example, volume of air) Tracking the Liquid level In previous versions of HAMMER (08.11.00.30 and below), HAMMER did not track the liquid level (elevation of the interface between the liquid and the gas) and essentially assumed that it was fixed. As of HAMMER V8i SELECTseries 1 (08.11.01.32), HAMMER now supports tracking of the liquid/gas interface, via the "Elevation Type" field in the Hydropneumatic tank properties. This field presents 3 options, Fixed, Mean Elevation and Variable Elevation. Fixed This is the default option for the "Elevation Type" field and is consistent with the behavior of previous versions. The liquid elevation is assumed to be at a fixed location during the transient simulation, equal to the bottom of the tank. The gas pressure used in the gas law equation is the pressure above the user-entered "elevation" field, accounting for liquid pressure plus the air pressure. This is acceptable for most cases, mainly because the elevation difference between the range of possible liquid levels is typically quite small. So, it does not account for much of a pressure difference. This can be observed by adjusting the "Elevation" attribute in the tank properties. Mean Elevation Selecting "Mean Elevation" exposes the "Liquid Elevation (Mean)" field, which allows you to specify a custom liquid (water surface) elevation, instead of assuming it is equal to the tank bottom (as is with the "fixed" option). It represents the average elevation of the liquid/gas interface throughout a transient. This is useful in cases where the liquid elevation is significantly higher than the tank bottom, but doesn't move significantly during a transient simulation. So, although no tracking of changes in liquid elevation occurs, it allows you to get a more accurate calculation in some cases. The gas pressure used in the gas law equation during the calculations is the pressure above the mean elevation that you enter. Variable Elevation Selecting "Variable Elevation" exposes the "Variable Elevation Curve" field, which allows you to enter a table of liquid elevation versus equivalent diameter. The variable level hydropneumatic tank type is for users who have detailed information about the tank's geometry and want to perform as accurate a simulation as possible. Typically, this type of representation would be selected in the detailed design stage. It would also be appropriate in the case of low-pressure systems and/or relatively tall tanks with large movements of the interface relative to the HGL of the gas. The initial liquid level is determined from the initial gas volume which is an input parameter. The tank cross-sectional area at any elevation is interpolated from an input table of the vessel's geometry spanning the range from the pipe connection at the bottom to the top of the tank. After computing the transient simulation with a variable elevation hydropneumatic tank, you can view the liquid level over time by looking at the Transient Analysis Detailed Report. This report is found under Report > Transient Analysis Reports and will show this extended, tabular data for the tank when you've entered a value for the "report period" property of that tank (see "Text Reports" further above). Note: You must be using at least version 08.11.02.31 of HAMMER in order to use the variable elevation option with a bladder. Other Types of Hydropneumatic Tanks There are other types of hydropneumatic tanks which can be modeled in HAMMER. Detailed information on how this work can be found in HAMMER's Help documentation. In addition, the hydropneumatic model sample file in HAMMER V8i SELECTseries 5 and later has a scenario that includes dipping tube and vented hydropneumatic tanks. These can be used to get a general idea of how the input is entered for these. Vented Vessels This type of hydropneumatic tank has an air valve that admits air into the system from the atmosphere, when the tank drops below atmospheric pressure. (Walski, 2007). A vented hydropneumatic tank is effectively a sealed tank with the addition of an air valve at the top. This allows air at atmospheric pressure to enter the tank during a downsurge so that the device behaves like a one-way surge tank. During an upsurge, the air valve typically throttles the air outflow so that the gas within the tank is compressed and acts as a 'cushion' against transients (just like a sealed hydropneumatic tank). This device offers several practical benefits - for example since the tank typically has no gas inside, there is no need for compressors or a bladder to ensure a required gas volume is maintained. Dipping Tube Vessel A dipping tube hydropneumatic tank has a dipping (or ventilation) tube inside with an air valve at the top. During normal operation the air valve is closed, the water level is above the bottom of the dipping tube, and gas is compressed in the 'compression chamber'. If the hydraulic grade line drops (e.g. after a pump stop) the dipping tube tank acts like a regular (sealed) hydropneumatic tank until the water surface drops below the bottom of the dipping tube, after which the air valve opens and allows air to enter at atmospheric pressure. At this point the tank is acting like a surge tank that is open to atmosphere. If the hydraulic grade line increases again (e.g. if pumps come on), air will be expelled until the hydraulic grade line rise enough to close the air valve. At this point the water surface will be above the bottom of the dipping tube and the tank will act like a regular sealed hydropneumatic tank once again. HAMMER uses air inflow orifice diameter in venting calculation. For the Dipping tube type hydropneumatic tank, the tank elevation-area curve is used to calculate the tank volume. Before the air in the dipping tube tank is compressed, the air volume is the tank volume above the bottom elevation of the dipping tube. When the air is compressed, gas law equation and Newton iteration method is used to calculate the water level and air volume in the tank. Before the air is compressed, the air pressure is Atmospheric pressure, the air volume is the tank volume above the bottom of the dipping tube. When the air is compressed, the water level is calculated using Newton method. Using the gas law equation, an iterative Newton method is used to calculate the water level in the tank (in the gas law equation calculation, the pressure of the air is: Atmospheric pressure + pressure head - level). The air volume calculated in the dipping tube vessel depends on the Gas Volume. If the Gas Volume includes the air volume in dipping tube, the existing way is correct. If the Gas Volume does not include the air in the dipping tube, we should exclude dipping cross-section area from the tank cross-section area. To calculate the initial air volume, the elevation-area curve is used, along with the initial HGL and the elevation of the bottom of the dipping tube. Depending on the configuration, the compression chamber volume may be derived from the elevation-area table alone, not from the "Volume (compression chamber)". Since the volume of the dipping tube itself was not subtracted, this may cause an the unexpected initial gas volume. In an update to HAMMER V8i SELECTseries 5, the volume of the dipping tube is excluded from the volume of the compression chamber (which again is derived from the elevation-area curve.) Addition information can be found here: https://www.environmental-expert.com/downloads/charlatte-araa-dipping-tube-surge-vessel-for-waste-water-datasheet-360178 Example Model The below model is an example of the use of the Hydropneumatic tank in HAMMER and has several scenarios for different configurations. Note: This example is included in recent versions of HAMMER, in the "Samples" folder within the installation folder The link below is to a version that can be opened in HAMMER V8i build 08.11.01.32 and above. Additional information can be found in the Project Properties You must be signed in to download the file. The link will not work if you are not signed in. This model is for illustrative purposes only Click to Download Reference Advanced Water Distribution Modeling and Management - Walski, 2007. Charlatte reservoirs - http://www.charlattereservoirs.fayat.com/en HAMMER V8i, Transient Analysis and Design training course manual (TRN013190-1/0001) Fluid Transients in Pipeline Systems - Thorley, 2004 See Also Protective Equipment FAQ General HAMMER V8i FAQ Extended Node Data at odds with time history graph for hydropneumatic tanks Hydropneumatic tank gas pressure appears to be different from the pressure at the connection Use of the Gas Law Exponent During Initial Conditions vs. Transient simulation

Applies To Product(s): SewerCAD, StormCAD, SewerGEMS Version(s): V8i (with latest patch) or V8i SELECTseries 2 (08.11.02.35 for StormCAD, and 08.11.02.46 for SewerGEMS and SewerCAD) or later Area: Output and Reporting Original Author: Scott Kampa, Bentley Technical Support Group Overview This TechNote will detail the steps needed to create a user-defined profile settings, including default annotations and annotation properties in the Engineering profile. Background Between the upgrade from Bentley StormCAD and SewerCAD version 5.6 to the current build (V8i), a number of changes were made to the Profile feature within the product. The biggest change was with the layout of the profile. StormCAD V8i and SewerCAD V8i offer two different methods of profiling a system: the standard profile introduced with V8 XM and the engineering profile similar to the profiles available in version 5.6. However, during the conversion to V8 XM, the ability for the user to create custom default annotations was lost. As of a recent release of StormCAD V8i and SewerCAD V8i, this feature is now available in the engineering profile. It is also available in SewerGEMS and SewerGEMS Sanitary. Creating Custom Default Annotation Property Settings Bentley StormCAD V8i and Bentley SewerCAD V8i have a default setting for the link and node annotation property settings in the Engineering Profile. However, it is now possible for a user to create custom annotation property settings. Please note that the default settings that come with the product will be used unless overridden by the steps that follow. To create a custom default annotation property for a node, right-click on the label for a manhole or catch basin and select "Annotation Properties..." This will open the Annotation Properties manager. This is where changes to the justification and rotation of the label, as well as additions of lead lines and arrows, are made. In the lower left of the manager is a checkbox that says "Save as Default." Selecting this will save the settings as the default setting. After checking the box and selecting "Okay," the user will get a prompt that says "Would you like to apply these new default settings to all existing Node Annotations?" Selecting "Yes" will set the default. Note that this step is cannot be undone. Also, changes to the conduits or channels (or links) must be made separately. Right-clicking on the link label in the engineering profile will open the Link Annotation Properties managers. Once the default settings for the profile are set, this will now apply to the current profile as well as any profiles created later. Existing profiles can be easily updated to reflect the new default settings. This is done by right-clicking on the link or node annotation in the profile and selecting "Reset All Link/Node Annotation Properties to Default." Note: this must be done separately for the link and node annotations. Creating Custom Default Definition Settings In addition to changing the default annotation properties, additional functionality has been added so the custom defaults can be applied to all future projects on a given workstation. In doing this the annotation definitions set up in the Task Pane for all elements will then be applied to all future profiles. The annotation definitions for already existing profiles will not be changed. In order to create the custom default definition settings, first set the annotation definitions in the Task Pane for the individual elements. Next, select the Tools icon and select "Save Annotation Definition Settings as Default." These annotation definition settings will then be saved as the default settings. Note: This step cannot be undone. If you wish to move these settings from one machine to another, you will need to copy the XML files that are created during the process. Browse to the following file path: Windows XP: C:\Documents and Settings\(user name)\Local Settings\Application Data\Bentley\StormCAD\8\ Windows 7: C:\Users\(user name)\AppData\Local\Bentley\StormCAD\8 Copy the following files: EngineeringProfileAnnotationDefinitionDefaults.xml, EngineeringProfileLinkAnnotationPropertyDefaults.xml, and EngineeringProfileNodeAnnotationPropertyDefaults.xml Note that the last two listed above are only applicable in you have "Saved as Default" for the link and node elements, respectively. If you only save new defaults for the node element, for instance, only EngineeringProfileNodeAnnotationPropertyDefaults.xml will be created.

Example model illustrating how to model a pump startup transient event in Bentley HAMMER.

Applies To Product(s): HAMMER Version(s): 10.00.xx.xx, 08.11.xx.xx Area: Modeling Original Author: Jesse Dringoli, Bentley Technical Support Group Overview This TechNote describes the process by which a user can model a pump startup transient event in HAMMER CONNECT Edition and HAMMER V8i. It also provides an example model file for demonstration. Background In older version of HAMMER (V8 XM), a lengthy procedure was required to model a pump startup: (See Modeling a Pump start-up transient event in Bentley HAMMER|Modeling a Pump start-up transient event in Bentley HAMMER V8 XM ) The user needed to first obtain the rated operating point of the pump by turning it on, then turn the pump off, copy the initial conditions to the user defined fields and enter the rated head/flow, along with valve initial status. This can be cumbersome in some situations. For this reason, HAMMER V8i introduced a new transient pump type called "Pump Start - variable speed/torque". This allows the user to specify the rated head and flow of the pump without having to specify initial conditions. This can greatly simplify the steps need to model a pump startup event. Setting up the Model for a Pump Start-up Before performing these steps, ensure that the demands, physical properties and other settings in the model describe the condition that you would like to represent. Meaning, if you would like to see the transient effects of the pump turning on during high demands and low tank level, ensure that the demands and tank level are adjusted as such. Ensure that the efficiency and transient rotational speed in your pump definition represent the "nominal" conditions. Meaning, the speed should be the speed at which the pump produces the flow/head seen when the pump in question is on (usually full speed), and the efficiency should be the efficiency at that nominal flow/head. This walk-through also assumes a steady-state analysis for the initial conditions and that you have storage downstream of the pump in question, or other pumps, either of which could supply the demands you have entered when the pump in question is off. 1. First, turn the pump on by selecting "On" as the "Status (Initial)" under the Initial settings section of its properties. 2. Go to Analysis > Compute Initial conditions. This invokes the pressure engine to allow us to see the point where it would operate on its characteristic curve, when it turns on. 3. Double click the pump in question to view the properties. Under the "Results" section, you will see the pump operating point. Write down the values seen for "Flow (Total)" and "Pump Head". We will use these later on. If you have any active valves in the model (TCV, GPV, PRV, PSV, FCV, PBV), in places where the flow is zero or near zero in the initial conditions, you will need to find the correct discharge coefficient during this step. To do so, either check for the computed discharge coefficient in the results section of the properties, or temporarily select "true" for "specify initial conditions?" in the transient calculation options, click the valve, then go to Tools > Copy Initial Conditions, choose "selection", then OK - you will now see the discharge coefficient in the "transient (initial)" section of the properties. Record this value and set the "specify initial conditions?" calculation option back to "false". For any valves that you need to do this, morph them into a TCV, choosing "discharge coefficient" as the type, "Active" as the initial status, then enter the discharge coefficient that you recorded. If you do not do this, then HAMMER may use a discharge coefficient that will be inaccurate for higher flow rates once the pump turns back on. (since it will be based on zero or near-zero flow). 4. Under the "Transient (Operational)" section of the pump properties, select "Pump start - variable speed/torque" as the "Pump type (transient)" and enter the appropriate diameter. If the pump has a built-in check valve, enter "0" for the "Time (for valve to operate)", else enter the time that it takes for the built in valve to open (5 sec, 10 sec, 30 sec, etc...). To simulate a pump with no check valve enter a very small number like 0.1 seconds, so the valve is open immediately. Most likely you will enter zero for this. This is an important consideration - please read this article for more. 5. Enter the pump flow and pump head found in step 3, in the "Flow (nominal)" and "Head (nominal)" fields. 6. Change the pump's Status (Initial) under the initial settings to "off" and re-compute initial conditions. 7. Now we must define when and how fast the pump starts up. Go to Components > Patterns to open the Pattern manager. Right click on "Operational (Transient, pump)" select "new" and enter a name. On the right side of this window, enter zero for the starting multiplier, since the starting speed multiplier should be zero (meaning the pump is off.) In the bottom-right table, define the pattern of time versus speed multiplier. IMPORTANT NOTE : the multipliers you enter here multiply against either the speed or the electrical torque, depending on the selection you make for the pump's "Control Variable". If you choose Speed (the default), the multipliers multiply against the full speed entered in the pump definition, so 1.0 means full speed. This means that you cannot simply "flip the switch" in the pattern and have it go instantly from zero to 1.0 (or within a very small time frame) as it would normally take some time for the pump to "ramp up" to full speed. In the example below, the speed jumps from zero to 1.00 (full speed) between 6 and 7 seconds, and then stays on for the duration of the simulation. If the pump takes longer to "ramp up", then the pattern needs to be adjusted. 8. Close the pattern manager and select the pattern that you just created, from the "Operating Rule" dropdown in the pump properties. At this point, the pump properties should look similar to this: 9. The model is now correctly set up and you can compute the transient simulation. Go to Analysis > Compute. Note: If your pump is a variable speed pump ("Is variable speed pump?" = "True"), then you may encounter a notification stating that the rotational speed must be greater than zero. If you encounter this problem, you will need to re-run the initial conditions with the VSP turned on, note the computed relative speed factor, enter it as the "relative speed factor (initial)", set the initial status back to "off", set "Is variable speed pump?" to "false", re-compute initial conditions, then compute the transient simulation. Viewing the Results The results of this model can be viewed just like any other transient simulation. Go to Analysis > Transient Results Viewer. To view a graph of head and flow for the pump, you may want to select a time history for the pipe end adjacent to the pump: As you can see, when the pump starts up, a transient occurs. After about 40 seconds, the head/flow stabilize to the nominal conditions. Note that in many cases, you may not see flow start to occur through the pump until the speed has increased enough so that the downstream head can be overcome. You can also select a transient profile and click the "animation" button: As you can see, there are some problems with vapor pockets forming upstream of the pump when it starts up. A surge tank may be required in this case. Note that you can also view extended data specific to the pump, by entering a number for the "report period" attribute of its properties. For example, "10" would mean that extended data will be reported every 10 time steps. You can view this report by going to Report > Transient Analysis Reports > Transient Analysis detailed report. At the very bottom of this text report, you will see the table of flow, speed, upstream and downstream head: Why is the Transient Simulation not Settling Exactly on the Nominal Head/Flow I entered? In some cases, once the pumps turn on in the transient simulation, they may not settle exactly on the nominal head/flow that you saw when you ran a steady state with the pumps on. This can be due to many reasons: If you're not ramping the pumps up to full speed but instead a relative speed factor other than 1.00, make sure the initial relative speed you entered is correct. The nominal head/flow are the pump head/flow corresponding to the relative speed value you put for "relative speed (initial)", even if the initial status if off. Their values should be equal to the values seen if that pump were to be turned on (at the same initial relative speed factor). For example, say you want a pump to start in the off position, then ramp up to 50% of full speed. First, set the initial relative speed factor to 0.5, initial status to off and transient pump type to pump startup. The nominal head/flow are set to the values seen in a steady state run at 0.5 relative speed. The transient pump pattern then goes from 0.0 to 1.0 multiplier. With that configuration, HAMMER understands that the nominal head/flow values correspond to a relative speed of 0.5. From the transient pump type, it knows that the pump will be initially off (zero flow/head) and that multipliers in the pattern multiply against the initial relative speed factor. This way, 0.0 represents the pump still being off and 1.0 represents the pump being at the initial relative speed factor, which corresponds to the nominal head/flow values. If you have any valves (GPV, TCV, PBV, FCV, PRV, PSV) that are active in the initial conditions, but in a location where there is zero flow due to the pumps being off, the calculated discharge coefficient (which the transient calculation engine uses) may not be an accurate reflection of that valve, when higher flow occurs. As seen earlier in this TechNote, you may need to compensate for any occurrences of this by finding the discharge coefficient in a steady state run with the pump(s) on, then replacing the valve with a TCV using that same discharge coefficient. Otherwise, the headloss across the valve in the transient simulation when the pump turns on will likely not match the steady state run that you based the nominal head/flow on. The biggest cause of this difference is with HAMMER's handling of friction coefficients. The transient calculation engine needs to use Darcy Weisbach friction factors (f), so a conversion is sometimes done. So, differences can occur if you use another method such as Hazen-Williams. This conversion is always done, even if you're using the Darcy-Weisbach method for the initial conditions, since the coefficient you enter for each pipe is the roughness height (e), not the friction factor (f). In pipes with non-zero initial flow, the Darcy Weisbach coefficient is calculated based on the headloss across the pipe. In pipes that have zero flow in the initial conditions (which may be the case for many of them, since the pump is off), the Darcy Weisbach coefficient will be computed based on the entered Hazen-Williams or Darcy-Weisbach coefficient. However, calculation 'noise' can sometimes occur in the initial conditions, causing the flow in a pipe to be near-zero instead of exactly zero. In your transient calculation options, you will see the tolerance that HAMMER uses to determine pipes that have zero flow, to account for this situation. In some cases, you may need to either make the "accuracy" value smaller in your steady state calculation options, or increase the flow tolerance value in the transient calculation options. Similar to the valve discharge coefficient item, if the flows are near zero but above the flow tolerance, the coefficient that HAMMER computes to use for that pipe may be unreasonable (since it's based on a tiny headloss), especially when higher flows occur when the pumps are on. This situation can happen even if your pipe has a 'real', non-zero flow that is relatively small. To check HAMMER's computed friction coefficients, open the "Output log" under Report > Transient Analysis Reports, and scroll down to the section titled "Pipe Information". Note that even if the zero flow pipes are correctly identified, the Darcy Weisbach friction factor that is computed based on the user entered friction coefficient may still differ from that of the ones based off a positive flow pipe's start and stop head. To check for this difference, run the transient simulation with the pump on and check the aforementioned Output log. If they differ by a lot, you may consider the "Unsteady - Vitkovsky" Transient friction method in the transient calculation options. Another approach to handle this would be to run the initial conditions with the pump on, record the friction factors from the output log, set the "specify initial conditions?" calculation option to "true", run the initial conditions with the pump off, use the "copy initial conditions" tool from the tools menu, then modify the transient initial flows so they are zero (when they should be) and initial friction factor (f) to the values seen in the output log with the pump on. This will force the pipes to use the correct friction factors. Note that version 08.11.01.32 and below of HAMMER have a known issue with the way that the friction factors are computed for zero flow pipes. A patch set is available for this version, which will be incorporated into future versions. Similar to the last item, if you have significant minor loss coefficients on pipes that have zero flow in the initial conditions, you may need to account for them with a different method. The reason is because those pipes will have their friction factor computed based on the entered friction factor only and will not account for the minor loss coefficient. Headloss across the pipe during the transient simulation will be based on the friction factor only. So, the pump may operate at a higher flow and lower head than you would expect, since it doesn't have as much losses to overcome once the pump is on. In this case, you may need to insert a TCV node and enter the headloss coefficient or insert an Orifice Between Pipes element and enter the flow and headloss seen during the initial conditions when the pump was on. If you have any tanks in your model, make sure their hydraulic grade is correct in the steady state run that you retrieved the pump nominal head/flow from. For example, you may want to choose "true" for "treat as junction" for a hydropneumatic tank, so the HGL at that tank in your pump=on steady state will be the value that it would settle on. Then, in the pump=off steady state run that your transient simulation starts with, either keep the tank treated as a junction, with the correct initial gas volume entered, or choose not to treat it as a junction, but enter the hydraulic grade that it would settle on when the pump is off. It is important to understand that HAMMER uses a special four-quadrant pump characteristic curve during the transient simulation, not the pump definition you entered for the initial conditions. These four-quadrant curves are based on your specific speed selection in the transient tab of the your pump definition and allow a pump to operate in all four quadrants (which can sometimes happen in a transient). The values from these curves are relative to your nominal head/flow, so for relative speed factors other than the one used for your nominal head/flow, it can result in slight differences. Since a pump startup case will be settling on the nominal head/flow, this should not make for a significant difference. However, a small difference could occur if the nominal operating point doesn't fall exactly on the four quadrant curve. In the pump properties, check the value for "Time (for valve to operate)". For pumps with zero initial flow, this represents the time to OPEN the valve. So, either enter a small number or enter zero, to represent a check valve. If you accidentally entered a large number here, the pump won't operate at the expected point since it will be working against a closed or partially closed valve. If all else fails, you could consider starting your transient simulation with the pumps on, then use the variable speed transient pump type to have them turn off then turn back on again. You can use the "Report history after" transient calculation option to have the transient reports begin after the pumps have settled in their off position. My pump operating rule is not be followed as expected See below article - this may be due to the "Time (for valve to operate)" Operating Rule not being followed after computing pump shutdown or start up Flow from pump is delayed after pump startup See below article - it typically takes some time for the pump to overcome the discharge hydraulic grade before is can pass flow. Flow from pump is delayed after pump startup Startup appears to occur too quickly / Initial surge too high If the pump appears to start up too quickly and the initial positive pressure spike appears to be higher than expected, it could be related to the Control Variable and the Operating Rule. See below article. Pump Startup occurs too quickly / initial upsurge too severe Error about pressure less than vapor pressure at high points If there are high points in the system, the initial conditions may not reflect the true system conditions with the pump off. See below article: "Initial pressure less than vapor pressure. At the pipe end(s), the elevation(s) or head(s) are incorrect" Example Model The below model is an example of a pump startup in HAMMER. Note: This example is included in recent versions of HAMMER, in the "Samples" folder within the installation folder The link below is to a version that can be opened in HAMMER V8i build 08.11.00.30 and above. Additional information can be found in the Project Properties You must be signed in to download the file. The link will not work if you are not signed in. This model is for illustrative purposes only Click to Download See Also Modeling a pump shut down event in Bentley HAMMER Operating Rule not being followed after computing pump shutdown or start up Product TechNotes and FAQs Haestad Methods Product Tech Notes And FAQs

Example model illustrating the use of the air valve element in Bentley HAMMER.

This example model illustrates the use of the D2A element in Bentley HAMMER.

Applies To Product(s): Bentley HAMMER Version(s): V8i, CONNECT Edition Area: Modeling Original Author: Jesse Dringoli, Bentley Technical Support Group Overview This technote explains how the Discharge to Atmosphere element works and its typical application in HAMMER V8i. It also provides an example model file for demonstration purposes. How it Works The "discharge to Atmosphere" element encompasses a valve to atmosphere, orifice to atmosphere and head vs. flow rating table. It is used to model an opening / orifice that allows flow to leave the pipe network and discharge to the atmosphere. You can model it as a fixed orifice that is always open, or a valve that is either initially open or closed, then opens or closes during the transient simulation. It can be placed in series with the main water line or at a "T" Note: it is important to understand that this element discharges to atmosphere, not between the adjacent pipes. So in the above case of an in-line orientation, flow still passes through the pipeline beneath the valve, regardless of if the valve is opened or closed. In the calculation engine, it is essentially modeled as a demand point located a hydraulically short distance from its node coordinates (based on the wave speeds of the pipes connected to it). The initial pressure and flow (entered by the user) are used to automatically calculate a flow emitter (orifice) coefficient, which will be used during the simulation to calculate transient outflows. This applies to both the initial conditions (steady state) solver as well as the transient solver (they both use the same resulting pressure/flow relationship) Basically HAMMER uses that coefficient to calculate other flows and their corresponding pressure drop: Q = C A (2 g P)^0.5 Q - Discharge (cfs, cms) C - A 'discharge coefficient' (distinct from CV used elsewhere in HAMMER) which will be computed based on the typical flow/pressure A - The cross-sectional area of the opening (ft, m) g - gravitational acceleration P - Pressure head (ft, m) As you can see, once the "C" is calculated from the initial head/flow, HAMMER can solve for other flows, as the pressure head changes during the simulation. Note: if pressure in the system becomes subatmospheric (below zero) during the simulation, the discharge to atmosphere element allows air into the system. When to Use it Common applications of the D2A acting as a valve Opening or closing of a hydrant, blowoff, sprinkler or other discharge - Select "Valve" as the Discharge Element type and specify the initial status. If the valve is initially closed at the start of the transient simulation, it will open and vice versa. Set the time to start operating and the time to be fully open; the valve opening increases linearly. Set the emitter value for the element by specifying the pressure drop at some flow rate. Modeling a main break - The discharge element type is also "valve" in this case, but the "time to Fully Open or Close" would be zero. This is because it is conservative (for a design scenario) to model the rupture occuring quickly and producing a large opening. Essentially the initial conditions describe the normal pipe and appropriately conservative flow conditions just before the break, then the transient simulation instantly opens the 'valve', to initiate transition to a ruptured condition. To represent the opening's size, it is recommended that the user set the "Pressure drop (typical)" to the steady-state pressure (observed prior to the break), and only vary the "flow (typical)" according to the equation further above. A sensitivity analysis wherein the cross sectional area, A is varied would illustrate the consequences of a range of breaks, with an upper limit to A being the diameter of the incoming pipe(s). The analysis should also consider different locations of the break(s). Depending on the pipe network's topology, a sudden break can lead to the formation of vapor pockets with ensuing collapses and pressure spikes. Common applications of the D2A acting as an Orifice Demand/consumption points that can let air in. In HAMMER V8i, any demand at a node (junction or hydrant) is called a consumption node and is treated as an orifice discharging to atmosphere that cannot allow air back into the system during periods of subatmospheric pressure. This is because the majority of water demands entered into hydraulic models are really the sum of several houses or demand points, each located at a significant distance from the point where their aggregate demand is being modeled. HAMMER assumes that any air allowed into the system at the individual demand points cannot reach the aggregate demand location. If this is not the case, you must model the demand using the Discharge To Atmosphere element, set as an orifice. This is because upon subatmospheric pressure, the discharge to atmosphere element allows air into the system. Any free discharge point. For example, the end of a sewer force main that discharges to an unsubmerged manhole, or a free discharge into the top of an un-modeled tank. You would need to decide how to compute the headloss through the pipe outlet, but a decent estimate might be headloss = k*v 2 /2g, where k is set to 1, v is the flow velocity and g is gravity. Alternatively, if the outlet orifice is smaller than the pipe diameter (unlikely) you might want to use the orifice equation, V = C*(2g*headloss) 0.5 . In both cases, the headloss is essentially the pressure drop. These equations are very similar to each other. Basically you would select an approximate flow (and therefore velocity) and use one of the above approaches to solve for the "Pressure drop (typical)". In order to do this, you would need to estimate a value for C. There is some documentation available for reference for such estimates. For instance, Brater and King (1976) lists orifice coefficients for various heads and sizes of circular, square, rectangular, and triangular shapes, and the U.S. Soil Conservation Service (1986) provides a chart of orifice coefficients for orifice plates placed over pipe opening. As an example, assume a case where the flow is 10 cfs through a 12 inch opening. The velocity in this case would be: V = Q/A = 10 / (pi*0.5^2) = 12.73 ft/s. If you assume C = 0.6, the headloss is calculated as: headloss = (V/C)^2 / 2g = (12.73 / 0.6)^2 / (2 * 32.174) = 7 ft. In this example, the "Pressure Drop (Typical)" would be set as 7 ft H2O. Transients initiated by an 'inrush' event. When a pump turns back on in a sewer force main, it may expel some air from the downstream end. The headloss through the discharge opening causes a resistance that can result in a severe upsurge once the water column reaches the opening. For example, with a small orifice size, an upsurge occurs when the flow reaches it, because the water basically can't get out of the pipe fast enough. Modeling this situation can be done by using the Discharge to Atmosphere element, operating as an orifice. The initial conditions must describe the low head condition (zero pressure at the discharge to atmosphere element) and you must enter a volume of air in the "Gas Volume (initial)" field. You would then have the head increase during the transient simulation (pump turning on or periodic head element with head value increasing, for example.) The "Flow (typical)" and "Pressure drop (typical)" would be estimated similar to item 2. Basically the higher the "Pressure Drop (typical)", the smaller the orifice size, and the more resistance to flow, resulting in a higher upsurge after the air pocket is expelled. Note: The "Gas Volume (Initial)" will impact the timing of the release of the air. The value you enter will be up to your engineering judgment, but a good starting point may be the volume of the "empty" pipe. A larger volume of air for the same size orifice will take longer to be expelled from the D2A. This, in turn, will impact the head increase at the source. The most important impact on the system will occur with the air is fully expelled, which is when the transient would occur. So while a large air volume will take longer to expel, the setup and size of the D2A may prove to the be most important part of the transient event. Impulse turbine. The turbine element in HAMMER is not used to represent impulse turbines. Transients caused by impulse turbines can be approximated in HAMMER by using a Throttle Control Valve (TCV) or Discharge to Atmosphere element to represent the turbine nozzle. Note: the "rating curve" discharge element type is used when the discharge out of your orifice does not follow a typical orifice-equation relationship. It allows you to explicitly define the flow released out of the system for certain pressures at the discharge location. Attributes The following attributes are available when the "discharge element type" is set to "Valve": "Valve Initial Status" - This specifies whether the valve is initially open or initially closed. "Time to Start Operating" - The valve starts to operate after this time. (either starts to open or starts to closed, based on the initial status selection) It is measured from the start of the simulation. So a value of 5s means that the valve remains in a fixed position for the first 5 seconds, and then starts to operate. "Time to Fully Open or Close" - This is the time it takes for the valve to either fully open (if the initial status is closed) or fully close (if the initial status is open. It is measured from the "time to start operating". Meaning, if the "time to start operating" is set to 5s and the "time to fully open or close" is set to 10 seconds, then the valve closes linearly between time t=5 and t=15. (the valve is fully closed 10 seconds after it starts operating). "Flow (Typical)" - This is the typical discharge out of the valve when it is open. "Pressure Drop (Typical)" - This is the pressure corresponding to the typical flow through the valve. It is referred to as the "drop" because the pressure beyond the orifice is zero. The pressure and flow computed in the initial conditions will not necessarily be equal to these values, so you only need to enter any known pair. For example, if modeling a hydrant closure, you might enter the typical pressure and flow as the flow and pressure observed in a field test when the hydrant was opened. You are basically defining an orifice size by way of the "typical" flow and pressure drop fields. By supplying one pair of pressure and flow, HAMMER can figure out the relationship based on the orifice equation that gives the pressure drop for any flow value. So, if unsure, you can use the orifice equation along with the size of your opening and an estimate of the "head" (pressure head drop) to solve for the typical flow. Selecting a pressure head drop close to a typical value you might see under normal operating conditions will yield the most accurate pressure/flow relationship during both the initial conditions and transient simulation. See further above under "How it works". Note: a standard 2.5 in. (100 mm) hydrant outlet would have a pressure drop of roughly 10 psi at 500 gpm. When the Discharge Element type is set to "orifice", only the typical pressure drop and typical flow are available. When set to Rating Curve, only a rating curve table is available, where you would enter the table of head versus flow for your discharge. Initial conditions and transient head/flow is computed based on the values in this rating table. Example Model The below model is an example of the use of the D2A element in HAMMER and has several scenarios for different configurations. Note: This example is included in recent versions of HAMMER, in the "Samples" folder within the installation folder The link below is to a version that can be opened in HAMMER V8i build 08.11.00.30 and above. Additional information can be found in the Project Properties You must be signed in to download the file. The link will not work if you are not signed in. This model is for illustrative purposes only Click to Download See Also How do do WaterCAD/WaterGEMS treat the discharge to atmosphere element? Product TechNotes and FAQs Haestad Methods Product Tech Notes And FAQs Protective Equipment FAQ General HAMMER V8i FAQ

Applies To Product(s): Bentley HAMMER Version(s): V8i, CONNECT Edition Area: Modeling Original Author: Jesse Dringoli, Bentley Technical Support Group Overview This TechNote explains how the Air Valve element works and its typical application in HAMMER. How it Works and When to Use it The Air Valve element (sometimes referred to as a combination air valve or CAV) is typically placed at high points in the pipeline and other areas that are susceptible to sub-atmospheric pressure during a transient event. They allow air to enter into the system during periods when the head drops below the pipe elevation and expels air from the system when water columns begin to rejoin. After the air has been expelled and the pressure is positive, the valve becomes closed. If you are analyzing an existing system that has air valves, you should place them at the appropriate location(s). If analyzing a proposed system or system improvements, you will likely want to first compute the transient simulation without the air valves. In the transient results viewer, you would check the pressure envelope to identify critical points where air valves may help prevent vapor pockets. Then, you would place the air valve(s) along your pipeline and compute the transient simulation for a range of air valve types/configurations. Comparing the profile animation or pressure envelope for each trial of air valve configurations (orifice sizes/types, etc) will give you a good idea of the sensitivity/behavior of the air valve(s) in your system. There are essentially two ways in which an active air valve can behave: Pressure below atmospheric - air valve is open and acts to maintain pressure to 0 on the upstream end. Pressure above atmospheric - air valve is closed and acts as any junction node. The presence of air in the line limits sub-atmospheric pressures in the vicinity of the valve and for some distance to either side, as shown on HAMMER profile graphs. Air can also reduce high transient pressures if it is compressed enough to slow the water columns prior to impact. Note: low or sub-atmospheric pressure can still occur further along the pipeline; the air valve element only provides local protection. Typically, the air inlet orifice is large (1-3"), so as to allow free air intake and not throttle due to the sonic limit. If the air inflow orifice is too small, the model may show the hydraulic grade dipping below the physical elevation of the air valve (negative pressure) in an animation of the profile. Limiting air outflow using a small orifice will cause the air to compress inside the pipe and cushion the water column collapse. Without an air valve, sub-atmospheric pressure (such as those caused by an emergency pump shutdown) can cause contaminants to be sucked into the system, thin-walled pipes can collapse and also vapor pockets can form (as the water boils at such low pressures) and subsequently collapse or damage pump impellers. However, you must be careful when using the air valve, since extreme high pressure surges can be caused when the air pocket collapses. Meaning, if the air inside the air valve is expelled too quickly, the water columns in the adjacent pipes can collide at a high velocity and the force will cause a severe transient. This is similar to the surge that occurs when a water column slams against a closed valve, except in this case the momentum of two water columns are hitting each other, without the delay involved with valve closure. However, an air outlet orifice that is too small can also cause a problem, if the air cannot escape quickly enough. So, care must be taken to select an appropriate air valve type and size, so as not to cause worse transients than if no valve had been used. It is common to use a "triple-acting" air valve to help against this problem, as this type of air valve throttles the size of the outflow orifice (typically using a float.) For example, consider the below animations, which illustrate a pump shutdown event with an air valve at the high point. The first depicts a double acting air valve that releases air too quickly (outflow orifice size is likely too large.) Notice the high pressure transient that occurs when the water columns collide. The second animation depicts a triple acting air valve. Large to small outflow orifice transition is configured in such a way that it provides a cushion that helps with the water column collision, but also doesn't raise the pressure too much before that happens. You'll notice that the head starts to increase when the transition to the small outflow orifice occurs, but the flow is not restricted enough to cause this head increase to become too severe. Double-acting with large outflow orifice Triple-Acting Inactive Air Valves In some cases, you may want to analyze the system without the air valve. For example, you may have a "no protection" scenario that describes the system without air valves, or a scenario where an alternative protection approach is taken. In these scenarios, you cannot simply delete the air valve, or even make them inactive by choosing "false" for "is active?". The reason is because every pipe must have a node at each endpoint. You also cannot simply select "true" for the "Treat as junction?" attribute, as this only applies to the initial conditions (Steady State or EPS). This situation should be approached by first using different active topology alternatives, then using one of two methods: 1. Place the air valves at a "tee" to the main pipeline. This way you can simply make the air valve and adjacent pipe inactive in the scenarios where the air valves are not present. This method is easier to manage and will account for headloss in the lateral pipe, which can sometimes be significant. Note that the hydraulics may be slightly different in this "tee" approach when compared to the "in-line" approach (option 2 below), as the air pocket will expand only on one side of the air valve as opposed to both sides with the in-line approach. (Please also refer to the section below, "Tracking of air pockets" regarding limitations of air pocket tracking.) Plus, the extra pipe may change the timing of transient wave interactions because it introduces a three-way junction and because it will typically be short and therefore susceptible to having its length or wave speed significantly adjusted. (see more on that here ) With that said, the real system most likely has a tee pipe connecting between the main and the air valve device. 2. In the scenario(s) where the air valves are not present, make the air valve and both adjacent pipes inactive, then make a new pipe going around the air valve active. Do the opposite in the scenarios where the air valves are present - make the air valve and adjacent pipes active but the other, single pipe inactive. Be careful when using this approach, as friction headloss in the lateral pipe is omitted. You may want to ensure that the bypass pipe and the pipes between the air valve and the adjacent junctions are long enough so as not to cause significant adjustment to the length or wave speed. (see more on that here ) If you're not sure which approach is best, try a sensitivity analysis - try both methods and compare the differences in the transient response for the event you're trying to simulate. If no notable difference is seen in the transient response, then it may be "safe" to use the approach that is easiest for you to manage in your model. What if my air valve is open during the Initial Conditions? If you are pumping over a high point with an air valve that is open under normal operating conditions, with some amount of part-full flow in the downstream pipe (which then resumes to pressure flow), there are some important considerations. As seen in this TechNote, you can choose "false" for the "treat air valve as junction?", and the upstream pump will "see" the high point and know to add enough head to overcome it in the initial conditions (steady state). When an air valve is used in the initial conditions, it is internally treated as a PSV, in order to force an upstream pump to add enough head to keep positive pressure at the high point. Because of this, a head loss occurs through the air valve (PSV) in order to balance energy across the network. So, you may notice a large drop in hydraulic grade downstream of the air valve, without it being reported in the pipe's "head loss" field. In some cases, this may cause the pressure at downstream nodes to be negative. This situation should be interpreted as part-full flow when looking at the initial conditions. More on this is explained in this TechNote. Because of the aforementioned behavior, you will have head losses and pressures that may not be realistic. The problem is that HAMMER requires the initial conditions to be very accurate. The equations behind HAMMER assume full-flow in pipes. Although the negative pressures seen in this case aren’t really negative, HAMMER doesn’t know this. So, if the negative pressure is below the vapor pressure limit set in your calculation options, HAMMER assumes that vapor would actually have formed at those locations. Even if the pressure does not drop to the vapor pressure limit in the part-full sections, you might encounter a friction loss error for the pipe. Because of these complexities, the modeling approach must be modified in these situations in order to do a transient analysis. (assuming of course that part flow is really expected). Meaning, the system should be ended at the point where full flow transitions to part-full flow. It is recommended that this be done with a reservoir, demand or Discharge-to-Atmosphere. (see item 2 in this TechNote, under the section titled Common Applications of the D2A acting as an orifice). This approach is typically acceptable because the transient waves would not propagate past the air gap formed at the air valve. Tracking of Air Pockets HAMMER is able to track the volume of air entering the system at an air valve, but the following assumptions/limitations apply: - The air pocket takes up the entire cross section of the pipe - The air pocket is localized at the point of formation (the air valve node). So, the extent of the air pocket along the pipeline is unknown and the air-liquid interface is assumed to be at the node location. (by default) - The reduction in pressure-wave speed that can result from the presence of finely dispersed air or vapor bubbles in the fluid is accounted for by configuring the Wave Speed Reduction Factor in the calculation options. - Air pockets entering an air valve can only exit the system through the same point. Basically it is assumed that the pocket cannot be swept downstream and expelled elsewhere. In most modeling cases these assumptions are acceptable and should not result in significant error. In each case, the assumptions are made so that HAMMER's results provide conservative predictions of extreme transient pressures. Note that since the air pocket is reported at the air valve location, you will need to include the air valve in your profile in order to see air pockets forming in profile view. If your air valves are on a "Tee" from the main line, you will not see air volume reported in the profile, as the air valve element will not be directly included in the profile path. If you need to track the location of the air-liquid interface of an air pocket entering the system (instead of assuming it's localized at the air valve node), you can use the Extended CAV method. To do this, select "true" for the "Run Extended CAV?" attribute, in the transient calculation options (Analysis > Calculation Options > Transient Solver). When a sufficiently large volume of air enters a pipeline, the flow regime evolves from hydraulic transients to mass oscillations. Thus, at least in the vicinity of the air, the system may be represented by rigid-column theory in lieu of the elastic approach. Using the Extended CAV option activates this rigid (inelastic) approach. Besides improved computational efficiency, the rigid approach allows for the tracking of the air-liquid interface. When using extended CAV, the program will automatically switch between the regular (concentrated/elastic) and Extended (rigid) based on the percentage of the adjacent pipe volume that the air pocket occupies. There are two ways to observe the air/liquid interface tracking when using the Extended CAV option: Open the Transient Analysis Output Log under Report > Transient Analysis Reports and scroll down to the section beginning with: *** SNAPSHOT OF EVERY END POINT AT START OF TIME STEP 2 *** Below this table, you will find information pertaining to element statuses, including Extended CAV air/liquid interface. For example: At time step "4341" at CAV "Air Valve" with neighbor "J-3 ", the elevation, level and volume are: 137.000 135.361 0.966 Open the Transient results viewer and animate a report path including the air valve and adjacent pipes. As the pipeline fills with air, you can observe the change in HGL downstream of the air valve. This is the air/liquid interface: In some cases, the extended CAV model may not be appropriate. For example, if you have a triple acting air valve with transition volume, it may not be appropriate since that is more of an elastic situation. The extended CAV option is typically used when relatively large volumes of air enter the system. Note: the Extended CAV option will only track air volume up to the extents of the adjacent pipe(s). In the event that the air expands greatly so that the interface moves down towards the neighbor node to the verge of draining, HAMMER issues a warning message, freezes the horizontal surface at the elevation of the neighbor node, and continues to track the volume (which could conceivably exceed the branch's volume). Air Flow Rate Calculation To compute the flow rate of air through the air valve element when specify the openings as equivalent diameters, HAMMER uses the following equation: where Po is the density of air at 4°C and 1 atmosphere (=1.293 g/l), S=0.6A, with A being the cross-sectional area of the orifice. The throttling of air flow due to the "sonic velocity" is automatically calculated using the below formulation: where Y is the exponent in the gas law, p is the absolute pressure, the subscript 0 denotes standard conditions, and p/py = constant. For air inflow, (1) is again applicable, except that the ratio within the square brackets is inverted to be p/p0 as p0>p in this instance. the exponent, Y, in the gas law is hard-coded as 1.4, which corresponds to adiabatic compression/expansion appropriate for the typically rapid processes which occur. Note that "Vmax" is not the same thing as the sonic limit. Vmax is the maximum velocity that would be achieved by a fluid when it is accelerated to absolute zero temperature in an imaginary adiabatic expansion process. It is a term used in the calculations for air flow rate, but the sonic limit is ~340 m/s (1115 ft/s) at 60 degrees F. Note : the above is used to calculate the "free air" flow rate, at atmospheric pressure. Currently, the air flow rate reported by HAMMER in the text reports is the flow rate at pipeline pressure, which will be different due to differences in air density. Note: you can enter a rating curve of pressure versus air flow rate, instead of specifying an equivalent orifice. See further below. Air Valve Types and Attributes General The following attributes are available in the air valve properties, regardless of the air valve type: "Treat Air Valve as junction" - This option specifies whether or not to treat the air valve as a junction element during the initial conditions (steady state or EPS). When set to "false", the valve may allow part full flow during the initial conditions, depending on the system conditions. This is mainly used for sewer force mains and is typically not used during a transient analysis. This setting has no effect on the transient simulation itself. Meaning, the air valve will still function as an air valve during the transient simulation, even if this is set to "true". Further details on this feature are beyond the scope of this TechNote. "Elevation" - This field identifies the elevation of the air valve. The elevation is important because it determines the pressure at that node. It should be set to the elevation of the opening of the actual valve. When the hydraulic grade at the air valve location drops below the air valve's elevation, air intake starts to occur, since the pressure at that node would then be below zero. "Report Period" - entering a number in this field will allow HAMMER to report extended results for the air valve. For example, a report period of '10' would cause extended results to be reported every 10 time steps. so, if the calculation time step was 0.01 seconds, that means you will see these results at a 0.1 second interval. To view these extended results after computing the transient simulation, go to Report > Transient Analysis Reports > Transient Analysis Detailed Report. Scroll down almost to the bottom, to the section beginning with " ** Air valve at node Air Valve**". Below this, you will see a table of time, air volume, head, air mass and air outflow rate. Note that the flow rate shown here is the flow rate at pipeline pressure, which will be different than the "free air" flow rate, due to differences in air density. "Air Volume (initial)" - This field is available when using either the Double Acting or Triple Acting air valve type. It is used when modeling an air valve that is initially open. Like the "Treat air valve as junction?" attribute, this is rarely used. Intuitively, the initial conditions pressure must be zero in this case (air valve is open), and the air present inside the air valve is entered in this field. This might occur at a high point that operates under part-full flow in normal conditions (when the pump is on.) "Air valve type" - This is where you specify which type of air valve will be used during the transient simulation. Details on how each type works and their corresponding input parameters are found below. "Air Flow Calculation Method" - This allows you to specify whether the air flow rate calculation is determined by a user-entered rating curve or calculated based on an equivalent orifice diameter. Double Acting With the double acting air valve, both inflow and outflow orifices are available. The diameters of these orifices don't change and there are two different actions: Air inflow through the inflow orifice diameter Air outflow through the outflow orifice diameter "Air Volume (Initial)" - The volume of air inside the air valve at the start of the simulation. If you need to enter a value here, then the pressure from the initial conditions must be zero (i.e., the air valve is open). This would only be used if you wanted to model an air valve that is open during the initial conditions, which is not typical. In most cases involving a pump, it is easier to begin the simulation with the pump on, then have the pump shut down and subsequently restart after an appropriate length of time, using the variable speed transient pump type. "Diameter (Air Inflow Orifice)" - This is the diameter of the orifice for injection of air into the pipeline. This diameter should be large enough to allow the free entry of air into the pipeline. If set to zero, no inflow will occur. "Diameter (Air Outflow Orifice)" - This is the diameter of the orifice that allows discharge of air out of the air valve, upon increase in pipeline pressure. It should be small enough to throttle the air flow and cushion the speed of the air pocket collapse. If set to zero, the air valve will act like a vacuum breaker type, in that no air can be released and the trapped air pocket will be compressed. Triple Acting This air valve type is used to model a triple acting air valve, which has an air inflow orifice at a fixed size and a variable-diameter air outflow orifice. Typically a float is used to decrease the orifice size, just before the air pocket is completely expelled. There are three different actions: Air Inflow Air Outflow through the large orifice Air Outflow through the small orifice When the air valve opens, air inflow comes in through the inflow diameter. When pressure returns, air escapes out of the large diameter outflow orifice. Just before all of the air has escaped, the float is pushed up, which decreases the diameter of the outflow orifice down to the "small" value. This cushions the air pocket collapse and subsequent collision of the water columns. "Diameter (Air Inflow Orifice)" - This is the diameter of the orifice for injection of air into the pipeline. This diameter should be large enough to allow the free entry of air into the pipeline. If set to zero, no inflow will occur. "Diameter (Large Air Outflow Orifice)" - This is the diameter of the outflow orifice when the float is at the lowest position. It is the size of the orifice when the air volume inside the air valve is greater than or equal to the transition volume or when the air pressure is less than or equal to the transition pressure (depending on the method you selected to trigger the switch from large to small outflow orifice). "Diameter (Small Air Outflow Orifice)" - This is the diameter of the outflow orifice when the float is at the highest position. It is the size of the orifice when the air volume inside the valve is less than the transition volume or when the air pressure is greater than the transition pressure. (depending on the selected method) "Trigger to Switch Outflow Orifice Size" - You can choose to have the triple-acting air valve switch from the large to the small outflow orifice size based on a transition pressure or a transition volume. When selecting "Transition Volume", a "Transition Volume" input field is available and when selecting "Transition Pressure", a "Transition Pressure" field becomes available. "Transition Volume" - If you're using the transition volume option, this is the Volume of air between the lowest and highest position of the float. (The amount it can change) Basically it is the volume of air left in the system when the water starts to raise the float to decrease the orifice size. It is usually approximated as the volume of the body of the valve. "Transition Pressure" - If you're using the transition pressure option, this is the pressure at the air valve location (i.e. the HGL minus the elevation) above which the outflow orifice switches from the large to the small size. Note: typically in real life it actually takes a small amount of time to transition from the large to the small orifice diameter, but it is generally pretty quick so we model it as instantaneous. Meaning, the diameter decreases to the "small" value, as soon as the volume of air is less than the "transition volume", or as soon as the pressure is greater than the "transition pressure" (depending on the method you selected.) Not all triple-acting air valves trigger the outflow orifice transition based on a transition volume or pressure. For example, it may be based on velocity. In these cases, you will need to determine the air volume or system pressure at the air valve, at the time when your conditions is met. Start by setting the small outflow orifice diameter equal to the large, then enter a number in the "report period" field. After computing the transient simulation, open the transient analysis detailed report from the Report menu and scroll down to the bottom. You will see a table of air flow rate, air volume, pressure, etc over time, which you can use to determine this. Vacuum Breaker With the vacuum breaker air valve type, only the air inflow orifice diameter needs to be configured. This air valve type lets air into the system during sub-atmospheric pressure, but assumes the outflow diameter is very small (effectively zero) so it doesn't let air out. You will see the air volume change as the air pocket is compressed, but the mass of air in the pipe doesn't reduce. There is probably a very limited number of applications for this type valve. However, it could be used for a draining pipeline. Note: any air pocket left in the system due to a vacuum breaker valve is assumed to be expelled out of the system by some other means. HAMMER currently cannot track the behavior of these trapped air pockets (the underlying assumption is that the air must exit the system where it came in) "Diameter (Air Inflow Orifice)" - This is the diameter of the orifice for injection of air into the pipeline. This diameter should be large enough to allow the free entry of air into the pipeline. Slow Closing Although similar to the other air valve types, the slow-closing air valve only has a single orifice involved; for the expulsion of air and liquid. An air inflow orifice is not required because HAMMER assumes that air will be freely allowed into the system (no throttling) when the head drops below the air valve elevation. The valve starts to close linearly with respect to area only when air begins to exit from the pipeline (after the head begins to rise). It is possible for liquid to be discharged through this valve for a period after the air has been expelled, unlike the other air valve types, which closes when all the air has been evacuated from the pipeline. Typically you will want the valve to be fully closed after all air has been expelled, but before too much water has been expelled. "Diameter (Air Outflow Orifice)" - This is the diameter of the orifice that allows discharge of air out of the air valve, upon increase in pipeline pressure. It should be small enough to throttle the air flow and cushion the speed of the air pocket collapse. Note: there are many other advanced air valves that work differently than the types currently available in HAMMER (some work on flow rate), but they are not yet supported. A conservative approximation using one of the available types should normally suffice in this case. Future versions of HAMMER may allow the user to enter a custom pressure versus air flow rating table. Using a Custom Air Flow Curve Traditionally, the openings for air flow into and out of an air valve are specified in terms of an equivalent diameter. As of V8i SELECTseries 2 (08.11.02.31) you can now specify a pressure vs. air flow rating curve for any of the openings, instead of an equivalent orifice. This is convenient in cases where the manufacturer provides a rating curve instead of orifice sizes Positive flows and pressures should be entered for outflow and negative flows and pressures should be entered for inflow. Air valve rating curves can be stored in a new air flow curve engineering library (some example data is included) Note that the flow rates entered here are the "free air" flow rates, at atmospheric pressure. Currently, the air flow rate reported by HAMMER in the text reports is the flow rate at pipeline pressure, which will be different due to differences in air density. Example Model The below model is an example of the use of the air valve element in HAMMER and has several scenarios for different configurations. Note: This example is included in recent versions of HAMMER, in the "Samples" folder within the installation folder The link below is to a version that can be opened in HAMMER V8i build 08.11.00.30 and above. Additional information can be found in the Project Properties You must be signed in to download the file. The link will not work if you are not signed in. This model is for illustrative purposes only Click to Download See Also How to graph extended transient results such as gas volume for hydropneumatic tanks, pump or turbine speed, air valve extended data, etc. Protective Equipment FAQ General HAMMER V8i FAQ AWWA Book: M51 Air Valves: Air Release, Air/Vacuum, and Combination, Second Edition ARI Air Valves (contains many animations)

Applies To Product(s): Bentley HAMMER Version(s): CONNECT Editioni and V8i Area: Modeling Original Author: Jesse Dringoli, Bentley Technical Support Group Overview This technote explains how to set up an initially partially closed valve that changes positions during the transient simulation. An example model is provided for demonstration, and version 08.11.01.32 of HAMMER is assumed. Background In older versions of HAMMER, all valves (including TCV, GPV, PRV, etc) were assumed to be either fully open or fully closed in the initial conditions. So, the transient operating rule (which describes when and how fast a valve closes during the transient simulation) was required to begin with either 100% (fully closed) or 0% (fully open). However, as of HAMMER V8i SELECTseries 1, you can now model a valve that is initially partially closed. The process by which this can be done is described below. Establish the Initial and Fully-Open Conditions The first thing you will need to do is enter the head loss or discharge coefficient that describes the hydraulics of the valve during the initial conditions. You must also enter the coefficient for the fully-open position of that valve, so that HAMMER can determine the relative discharge coefficient at certain positions of the valve (discussed later on in this technote.) 1. In the properties of the TCV, select "Discharge Coefficient" as the "Coefficient Type", then set the initial status to active. Enter the discharge coefficient representing your valve's initial position. 2. For the "Discharge Coefficient (Fully Open)" field, enter the discharge coefficient representing the valve in its fully open position: How can I Determine the Discharge Coefficient? Most valve manufacturer can provide a table of discharge coefficient for a range of valve positions. The discharge coefficient is sometimes referred to as "Cv" and describes the flow for a unit pressure (such as gpm/psi 0.5 ). So, the discharge coefficient for a certain desired initial closure position can be looked up on the table. For example, consider the below table: In this case, the fully open discharge coefficient would be set to 10.0. If you know the valve is initially 20% closed, the initial discharge coefficient would be set to 5.0. What if I'm not using a TCV? Note: skip this section if you are using a TCV As of version 08.11.01.32 of HAMMER, only the Throttle Control Valve (TCV) supports initial partial closure. If you're using a FCV, PRV, PSV, PBV or GPV, you'll need to convert it to an equivalent TCV first, using the below steps. Note: when computing initial conditions with any valve type, there will be one single specific head loss across the valve for that steady state condition. HAMMER converts this head loss into a discharge coefficient to be used in the transient calculations. 1. First, compute initial conditions to see the head loss through your valve. The below example uses a GPV: This head loss will be based on the type of valve you choose. For example for this GPV, the head loss was based on the GPV head loss curve. In another example, the head loss through a FCV would be the head loss necessary to achieve the desired FCV flow rate. To derive the discharge coefficient, you can use the following formula: Cv = { (39.693 * D 4 ) / [Hl / (V^2 / 2g) ] } 0.5 Where Cv is the discharge coefficient (cfs/(ft H2O)^0.5), D is the diameter (ft), V is the velocity (ft/s) and Hl is the head loss (ft). However, a shortcut can be employed to find the discharge coefficient… 2. Go to Analysis > Calculation Options and open the transient calculation option set associated with the current scenario. In the properties of the calculation options, choose "True" for "specify initial conditions?" 3. Go to Tools > Copy Initial Conditions. Choose the desired timestep (0.000 hours for steady state) and click OK. This will copy the discharge coefficient to a special field in the valve properties, which you can view under the "Transient (Physical)" section: 4. Next, morph the valve into a TCV, by selecting the TCV from the layout toolbar and clicking directly on top of the valve: 5. Now, enter the discharge coefficient found in step 3 as the initial discharge coefficient for the TCV. The fully open discharge coefficient will also still need to be entered. One way to find this would be to compute initial conditions with the original valve (GPV, FCV, PRV, PSV or PBV) set to "inactive". In this case, the initial conditions solver will use the "minor loss coefficient" that you entered, which represents the fully open condition. You would then use steps 2-4 above to find the discharge coefficient, then enter it as the TCV's fully open discharge coefficient. 6. Choose "false" for "specify initial conditions" in the transient calculation options, compute initial conditions, then verify that the computed head loss is the same as it was with your other valve type: What if I only know the head loss coefficient? It is always preferable to describe your valve with a discharge coefficient, since HAMMER always uses discharge coefficients in the transient calculations. As of HAMMER version 08.11.01.32, is it not recommended to use the "headloss coefficient" coefficient type for a TCV, if you need to model it in an initially partially closed position. To determine the equivalent discharge coefficient, either computer initial conditions and look at the calculated discharge coefficient in the Results section of the TCV properties, or use the following formula: Cv = ((39.693 * D 4 ) / H) 0.5 Where D is the diameter (ft), H is the headloss coefficient and Cv is the discharge coefficient (cfs/(ft H2O) Note: the "Minor Loss Coefficient" should be converted to the "Discharge Coefficient (fully open)". What if I Want to Use the Valve Characteristics Curve Coefficient Type? There are three options available for the "coefficient type" for a TCV: Discharge coefficient, headloss coefficient and Valve Characteristics curve. The latter option lets you enter the initial valve setting in terms of relative closure percentage, instead of a head loss or discharge coefficient. For example if you know your valve is 20% open in the initial conditions, you would simply enter 20%. However, some extra work is necessary with this option. Essentially you will need to relate relative closure percentages to discharge coefficients, in order to be able to refer to positions in terms of percent. This is done using the Valve Characteristics selection, described in the next section. For example if you enter 20% as the "Relative Closure (initial)", HAMMER needs to look that percentage up in the valve characteristics curve, to find the corresponding relative discharge coefficient. Then, based on the fully open discharge coefficient, it knows the discharge coefficient corresponding to 20%. Establish the Valve Characteristics The next step in the process of modeling an initially partially closed TCV is to select or define the valve characteristics curve. This is basically a table of relative closure versus relative discharge coefficient, which HAMMER uses to translate a percent open to a discharge coefficient . Basically when you model a valve closure in HAMMER, you are entering a table of time versus relative closure. This is done under Components > Patterns and is selected in the TCV properties under the Transient Operating Rule. In order for HAMMER to understand what these percentages really mean, it needs to translate them into a discharge coefficient. Every valve behaves a bit differently as it closes, so for example a value of 90% closed in your operating rule might not necessarily mean that the valve's open area is 10% of the fully open area. Therefore, the Valve Characteristics table is used to define this relationship. By default, several standard valve types are available, in the "valve type" field (such as butterfly, globe, needle). The table of relative closure versus relative discharge coefficient is not visible to the user for these predefined valves, but is defined based on the following equations: Note: the X axis represents relative closure and the Y axis represented relative discharge coefficient. The two equations on the right side can be used to derive tabular values from which the curves were constructed. For example, let's say you wanted to use the "butterfly" valve characteristics selection, and you want the valve to be initially 25% closed, with a fully open discharge coefficient of 10.0 cfs/ft H2O 0.5 . In this case, we can determine from the above diagram that the 25% relative closure translates to a relative discharge coefficient of 58.7%, which means a discharge coefficient of 0.587 X 10.0 = 5.87 cfs/ft H2O 0.5 . Note: The relative discharge coefficient values are relative to the value entered for "Discharge Coefficient (fully open)". You can also define a user defined table of relative closure versus relative discharge coefficient, by selecting "user defined" as the valve type. This exposes the "Valve Characteristics" attribute, which is where you would enter the table of relative closure versus relative discharge coefficient to define the characteristics of your valve. Note: remember that HAMMER uses relative closure, so 0% means fully open and 100% means fully closed. Other places may use relative opening, where the opposite is true. Establish the Transient Operating Rule The last step needed to model the closure of an initially partially closed valve is to tell HAMMER when the valve closes (or opens) during the transient simulation and how fast it occurs. This is done by establishing a table of time versus relative closure, called the Operating Rule. First, go to Components > Patterns and create a new pattern under "Operational (transient, valve)". Here you can enter the table of relative closure over time. Next, select the name of the pattern you just created in the "Operating Rule" field in the TCV properties. Intuitively, the "Starting relative closure" field in the pattern must match the initial relative closure, which you can see in the "results" section of the properties of the TCV: Putting it All Together To summarize what we've done, let's consider the following example valve: From the Operating Rule, the valve is initially 20% closed. From the Valve Characteristics table, a 20% relative closure translates to a 50% relative discharge coefficient. The "fully open" discharge coefficient is 10.0, so the initial discharge coefficient must be 10.0 X 50% = 5.0. 5.0 is entered as the initial discharge coefficient, so when the initial conditions are calculated, the computed relative closure (in the results section of the properties) is 20%. Let's say you wanted to run another scenario where the valve starts at 90% closed. First, you would modify or create a new operating rule, with the "Starting Multiplier" set to 90%. Next you would need to match up the initial discharge coefficient to the 90% by looking at the characteristics curve. A 90% relative closure translates to a 5% relative discharge coefficient. 5% of the fully open discharge coefficient of 10.0 is 0.5. So, the initial discharge coefficient would be set to 0.5. Troubleshooting What does the following message mean? "The valve's Initial Closure percent does not match the initial closure percent in the valve's referenced Operating Rule. The Operating Rule will be used as specified, but should be modified in order to get the expected results." This means that the Starting Relative Closure in your transient operating rule is not in agreement with the initial conditions of the valve. Check the "Relative Closure (Calculated)" field in the "Results" section of the properties of the TCV, to see what the initial relative closure is (which is calculated based on the initial discharge coefficient, fully open discharge coefficient and valve characteristic curve). You'll need to adjust the initial discharge coefficient so that the initial relative closure matches your pattern, or adjust the starting multiplier in your transient operating rule so that it matches the computed initial relative closure. If you're using a FCV, PRV, PSV, PBV or GPV, you will need to convert it to an equivalent TCV, using the method described further above in this technote. Example Model The below model is an example of an initially partially closed valve in HAMMER. Note: The link below is to a version that can be opened in HAMMER V8i build 08.11.01.32 and above. Additional information can be found in the Project Properties You must be signed in to download the file. The link will not work if you are not signed in. This model is for illustrative purposes only Click to Download See Also Product TechNotes and FAQs Haestad Methods Product Tech Notes And FAQs Protective Equipment FAQ General HAMMER V8i FAQ

Hello Thanasis, Before performing the transient analysis in Hammer, you should perform the hydraulic analysis of the model using either WaterCAD or WaterGEMS. The initial conditions like pump modeling, tank modeming should be done first in WaterCAD/GEMS before performing the transient analysis. The pump combination curve option is available in WaterCAD, WaterGEMS and SewerCAD but not in Hammer. Here is technote including detailed information about Pump combination curve. You can enter the pump curves by going to Components>Pump definitions and pump start stop levels can be configured with the help of the controls. Please see below link to know more about how to set up the controls in model.

Product(s): Bentley WaterGEMS, WaterCAD Version(s): 08.11.XX.XX Area: Help and Documentation Problem What is difference between Colebrook White Coefficient and Darcy Weisbachcoefficient. Convert coefficient, roughness factor, roughness height. Problem ID#: 71119 Solution The Colebrook-White equation is used to iteratively calculate for the Darcy-Weisbach friction factor: Colebrook White Coefficient and Darcy Weisbach coefficient are same in water products. See Also

Product(s): Bentley WaterGEMS, WaterCAD Version(s): 08.11.XX.XX Area: Modeling Problem What is difference between Initial concentration and base concentration, Water Quality, Constituent Problem ID#: 67477 Solution Initial concentration is the concentration at the element at time 0 i.e at the start of the constituent analysis. In many cases one will not know this initial value and will have to run an analysis for sufficiently long a period as to attain a solution where equilibrium has been reached. (If you have some idea about what the initial concentration might be it will be used by the software to reduce the time for the simulation to reach equilibrium. ) Whereas Concentration (Base) is a value associated with the element that is a constituent source, for that you need to select “True” for field “Is Constituent Source? “in the element properties. You can either specify the “Concentration (Base)” value or setup the following 3 booster types: 1. Flow paced booster: Adds a fixed concentration to that resulting from the mixing of all inflow to the node from other points in the network. 2. Concentration: Fixes the concentration of any external flow entering the node such as reservoir flow or negative demand (inflow). You would use this when you know the concentration of a flow source into the system. 3. Set point booster: Fixes the concentration of any flow leaving the node (as long as the concentration resulting from all inflow to the node is below the set point). So, this will adjust concentration up, but not down if it is already higher than the set point. See Also

Product(s): Bentley SewerGEMS, CivilStorm, StormCAD Version(s): 08.11.XX.XX Area: Layout and Data Input Problem Does storm-sewer products have Preloaded Rainfall Distribution Data? Solution Bentley does not offer any rainfall data/storm data of any kind other than the arbitrary example - "Uer defined IDF table Data" included in the engineering library. There are many places to find rainfall and I-D-F data, check with your reviewer to obtain the proper intensity-duration-frequency data for your geographical design area. You can enter I-D-F data into storm-sewer products as user defined IDF table, I-D-F tables equation or IDF curve equation. Some useful links containing rainfall information for the United States are given below: National Weather Service-National Oceanic and Atmospheric Administration United States Geological Survey USGS-Waterdata US Army Corp of Engineers Nati onal Oceanic and Atmospheric Administration National Climatic Data Center Tennessee Valley Authority International Bounda ry and Water Commission Geography Network South Carolina DOT See Also http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/20795.what-is-the-expected-text-file-format-for-idf-import

Product(s): Bentley SewerGEMS, CivilStorm, SewerCAD Version(s): 08.11.XX.XX Area: Modeling Problem What is a virtual pressure pipe? What does it mean when you choose "true" for "Is Virtual?" for a pressure pipe and how virtual pipes are handled by each solver? Problem ID#: 47176 Solution A virtual pipe basically means that the flow that comes into one end instantly goes to the other, with no hydraulic effects. It's essentially a way to connect elements without impacting the hydraulics. For example, you may have a pump station with multiple pumps in parallel; in this case, you can simplify the hydraulics by making the pipes adjacent to those pumps virtual. This will eliminate the complexities involved with the manifold that would otherwise be created just downstream of the pump station. (which the dynamic wave calculation engine can sometimes have trouble with) How each solver of storm-sewer products handle the virtual pipes whether that may be gravity pipe or pressure pipe is mentioned below. Implicit - Virtual Pipes handled as expected. GVF-Convex - Virtual Pipes handled as expected. Explicit - Virtual Pipes must be used as the link on the Upstream end of a Pump. GVF-Rational - Virtual Pipes not supported in GVF-Rational. Virtual Pipes are converted to Small Physical Pipes.

Applies To Product(s): Bentley WaterGEMS Version(s): 08.11.06.58 and later Area: Modeling Original Author: Scott Kampa & Mark Pachlhofer, Bentley Technical Support Group SCADAConnect Simulator for WaterGEMS V8i SELECTseries 6 and CONNECT Edition This TechNote provides details on using the new SCADAConnect Simulator found in WaterGEMS V8i SELECTseries 6 and WaterGEMS CONNECT Edition. Some of the information may overlap with information found in the existing TechNote for SCADAConnect Simulator for WaterGEMS V8i SELECTseries 5 . The SELECTseries 6 release of WaterGEMS included a major upgrade to SCADAConnect Simulator. There has been a complete rewrite of the user interface making it much easier for a non-modeler to create runs for pipe breaks, fire flows, shut downs, unusual demands, or overriding controls. The CONNECT Edition release of WaterGEMS includes additional available features, such as power outages, pipe shutdowns, and the ability to import control overrides. Note: A SCADAConnect Simulator license is only available with WaterGEMS. WaterGEMS includes a free unlimited signal license. If you have WaterCAD, you not have access to this tool. The TechNote will also include a general workflow for using SCADAConnect Simulator. SCADAConnect Simulator provides a way for users to modify and run a model scenario from a very simple user interface without the need to interact with some of the more sophisticated features of WaterGEMS. It will allow you to quickly adjust daily demands and controls and to simulate a pipe break or fire response. It will also allow you to easily scroll through time using the Time Browser, graph elements of interest, view user notifications, create views of specific areas for quick viewing access, and create customized element alerts. These tools can be used for running model input data, historical SCADA data, or live SCADA data. User Interface The user interface has a new easier-to-use layout. A screenshot of SCADAConnect Simulator from the SELECTseries 6 release can be found below: In the Home tab, the upper part of the dialog is split into the SCADA Simulation section and an Emergency Response section. The SCADA Simulation section includes access to the following features: Time browser, to scroll through time in your run User notifications SCADA elements FlexTable for viewing or modifying your SCADA data Graphs tool for creating graphs for visual display of how properties like pressure, hydraulic grade, velocity, and flow occur over time Named views for creating scaled views of specific areas of interest in your model The Emergency Response section includes access to the following features: Create a new pipe break or fire response by using the 'New' button Easy access to the 'Edit' button to make changes to your existing input Highlight button to show elements in your model for the selected run, which allows for easy location of study areas Find button, which allows for quick and efficient location of an element by label or ID for a faster response analysis of a pipe break Delete button Isolate break icon for entering your pipe break information Icon to expand or collapse the tree structure for the daily demand adjustments, control overrides, pipe breaks, and fire responses. Some of these features will be explained in greater detail below. In the Emergency Response tab in the ribbon allows the user access to the Pipe Break, Fire Response, Pipe Shutdown, and Power Outage features. These will be explained in detail below. Pipe Shutdown and Power Outage are not available in WaterGEMS V8i SELECTseries 6. The Configure tab allows the user access the SCADA Signals, which is where you import the SCADA data for use in WaterGEMS. Import Initial Settings and Results Publishing is also available from this tab. The features in the Configure tab, as well as some of the information in SCADA Simulation section of the Home tab were previously available in SCADAConnect Simulator for WaterGEMS V8i SELECTseries 5. The middle section of the main SCADAConnect Simulator dialog gives the user quick access to features available in SCADAConnect. In addition to the features found in the Emergency Response tab, it also includes Daily Demand Adjustments and Control Overrides. The bottom section of the dialog allows the user to select between Historical or Live simulations, define the run time, and compute the simulation. Computing the simulation will come after all SCADA data is imported and the necessary SCADA elements are included in the model. General Features Auto isolate pipe break tool Clicking the “Auto-Isolate” button will automatically select the closest elements (such as isolation valves that are available to close off this pipe from the system and add them to the bottom portion of the window below. You can also choose to select the elements from the drawing using the “Select in Drawing” icon (outlined by the red box). You can also exclude certain elements from those you want isolated, highlight all the elements that are included in the run using the Highlight button, zoom to a selected element in the drawing for easy location, and quickly zoom in or out of the drawing using the drop down menu that allow you to scale your model by current view or a percentage of the current view (25%, 50%, 75%, 100% - 400%). This will allow you to easily identify the area that you are studying while allowing you to examine what happens in other parts of the model while the break scenario is running. Customized SQL Statements for optimal performance This new feature will allow you to accommodate any SQL extensions that your database may support, opening potential support for other data historians such as GE Proficiency. In order to enable customization, click the checkbox for the "Customize SQL Statements,” which will make the statement text boxes editable. If you make a mistake or want to reset the statements to the default you can click the "Reset to default" button that his highlighted by the blue box in the screen show below. To locate this feature, click the SCADA Signals button on the Configure tab to open the SCADA Signals window, then right click on the folder label and choose "Edit Data Source..." Added intermediate time steps for control overrides and fire flow demands While this change cannot be seen visually, it will allow time steps to be inserted by SCADAConnect Simulator for hydraulic calculations when a control override is applied or a flow demand is added or removed. This will improve the accuracy of the calculation results. Network Demand Calculator Right-clicking on “Daily Demand Adjustments” in the tree view allows you to edit the demands or unit demands without changing the input of the main model itself. You can select the scope that you want to edit by selecting a selection set (or leaving the default of “Entire Network”), choose the demand pattern that you want to use (the default is “All Base Demands”), and set the operation (add, divide, multiply, subtract, or set) of the value you define. This allows you to quickly adjust demands that will be used when you compute through SCADAConnect Simulator. In the lower right corner of this dialog you can then use the green compute button to estimate the total daily demand given your adjustments. Signal Value Mapping for translating SCADA signal values and formats SCADA signal values can be mapped to a raw signal value in the Database Source dialog. This takes into consideration that SCADA signal values may have varying formats and provides additional flexibility to transform these values into a form the software can interpret. This new feature can be accessed in SCADAConnect Simulator by going to the Configure and choose SCADA Signals, or my going to the Components pulldown menu from the main interfact and selecting SCADA Signals. Available options for the status types are , Threshold, and Single Value. The Threshold type allows the use of operators =,!=, , >=, and . When the Single Value type is selected, only = and are available. Usually the SCADA system is protected from the Internet or other outside threats by a firewall or other security measures, allowing you to connect with the OPC server directly or export t file with data needed to SCADAConnect . General Workflow Setup In order to run the simulator, it is necessary to have a model with an existing Extended Period Simulation (EPS) scenario. When using a baseline scenario as a starting point for some SCADAConnect Simulator runs, the user may not want to modify an existing scenario on which the later SCADAConnect runs are based. This is because SCADAConnect Simulator runs can modify the calculation options (such as start time, demand adjustments, or control overrides) or initial settings (such as tank levels or pump status). Because of this, it is advisable to create a child scenario of the original scenario and make that the new baseline scenario. This new child scenario should have a different calculation option and a different initial settings alternative. The screenshot below shows a sample of what this might look like. In the screenshot, the starting scenario is "EPS-Normal,” with an initial conditions alternative called “Base-Initial Settings” and a calculation option call “EPS24.” A child scenario was created called “EPS-from SCADA.” This new scenario uses a new child alternative called “Initial Settings-from SCADA” and a new calculation option called “SCADA Calculation Options.” Setting up the SCADA Simulator this way would enable the user to try a wide variety of adjustments without changing the settings for the starting scenario. This setup of a new scenario and alternative is not necessary, though a new calculation option would be generally be used. Once you have a working model, review the SCADA data that you have. You will need to add SCADA elements that will represent the data you will be reviewing. For instance, if you have SCADA data for pump flow and pump status, you will include a SCADA element for each of these. Generally, the SCADA element will be added manually. Select the SCADA element from the Layout toolbar and place it near the element it is associated with. Pumps and tanks are common elements that SCADA elements will be associated with, but they can also be associated with pipes and valves. It is important to have a good understanding of your data so you know where to add SCADA elements. The screenshot below shows SCADA elements associated with two pumps and a pipe in a sample mode, Example5.wtg. This example file can be found at C:\Program Files (x86)\Bentley\WaterGEMS\Samples\Example5.wtg. The SCADA data associated with this example is an Excel worksheet. That worksheet contains data for pipe flow in P-1 and relative speed factor data for the pumps. With that data available, SCADA elements were included for these three elements. (Note: there are also SCADA elements in this sample model associated with a tank, as well as a few other pipes in the system. The focus is on these elements for clarity.) Once the SCADA Elements are added, you will need to associate them with an model element. To do this, double-click the SCADA element to view the properties. Find the attribute Model Element and select “Select Model Element.” This will open a Select toolbar to allow you to choose and element in the drawing pane. When you select the element, it will be connected with a dashed line, as shown in the screenshot above. You will also need to assign the Field attribute. This denotes what element property field the SCADA Element represents. For a pump, this could be Flow or Relative Speed Factor. For a tank, this could be Level. For a pipe, this would be Status or Flow. You can set the Field attribute for the SCADA Element either in the properties grid or by opening the SCADA FlexTable and setting the Field attribute there. The SCADA Element FlexTable can be accessed in SCADAConnect Simulator from the Home tab and choosing SCADA Elements. It can also be reach from the main user interface through View > FlexTables. Below is the property grid for a SCADA element associated with a pump, and representing the pump’s relative speed factor. The next step would be to link the SCADA data to the SCADA Elements in the model. You can do this in SCADAConnect Simulator by going to the Configure tab and select the SCADA Signals button. From the main user interface, you can open this by going to Components > SCADA Signals. Either option will open the dialog shown below. On the left side of the dialog, you will see the SCADA connections available for the model. To create a new connection, click the New button. You will see the available sources that are available in SCADAConnect: Database Source (which include a wide array or source and include Excel or Access files), OPC Historical Source, OPC Real-Time Source, and Citect Source. Data Sources Database Source For Database Source connections, select New > Database Source. This will open Database Source dialog. Note: If you have a 64-bit machine with 32-bit Office, make sure that you are working in the 32-bit version of WaterGEMS if you are using Excel or Access files. You can find the 32-bit version of WaterGEMS here: C:\Program Files (x86)\Bentley\WaterGEMS\WaterGEMS.exe. Click on the "Edit..." button beside the Connection pulldown menu. This will open a Database Connection dialog, as shown below: For Data Source Type, choose the appropriate data source, such as Excel. Next to Data Source, click the ellipsis ("...") button and select data source file. Next, click on Test Connection button and make sure to see "Connection succeeded" message. Then, click OK to close the Database Connection window. This will return you do the Database Source dialog. Then continue to fill in the data. What is entered will depend on the data source and the available data. The data from Example5.wtg can offer some guidance, since this uses an Excel file for the data. Table Name is the data table that contains the SCADA data. Source Format can vary depending on the source. For many database sources, there is one value per row, so that option would often be selected. Signal Name Field is the column in the data source that contains the 'Tag' or 'Signal' name. Value Field is the column that contains the SCADA value. Time Stamp Field contains the FULL date and time. Questionable Field is not supported by all SCADA systems. You can leave this as the default if you are unsure. Lastly, you would choose whether the data is real-time or historical. Database source are typically historical sources. Next, choose the Select SCADA Signals button. You will see the dialog below: The available SCADA elements will be listed on the left side. Add the necessary signals by, double-clicking the label or clicking ">" or ">>" button. The ">>" will add all. Click OK button when finished. The Database Source will now be filled in. SCADA Signals window will now list the signals in the left panel as a tree structure. Clicking on the signal on the left will show the corresponding data. Make sure to click either on Refresh or Auto Refresh to see the data. The screenshot below shows the data from the Excel source file for the SCADA element associated with pipe P-1 in the earlier screenshot. OPC Source The OPC Source type gives WaterGEMS users the ability to connect to the OPC server and allow the user to communicate directly to the same interface that SCADA operator uses. There are two types of OPC connection, Real-time and Historical. If the OPC server is in the same machine as WaterGEMS, click on the drop-down next to OPC Server: and select the server. If OPC server is in another computer (which can be remotely reached at) then put a check on Host and then click "Refresh" button. Once the source is selected, click on the Select SCADA Signals button and add the interested signals towards the right list, in the new window. Citect Source The Citect Source allows the user to bring data from the Citect server/database directly to SCADAConnect Simulator. After selecting Citect Source from the New button, click on Edit button. For the Remote Server, enter the server name if WaterGEMS is on a different machine than the Citect Server. If WaterGEMS and the Citect are on the same machine, this does not need to be provided. For the Authentication, if a user name and password is required, include that here. Once this information in filled in, choose Test Connection and make sure you get the "Connection succeeded" message. Click OK until Citect Source window is active. Next, select SCADA Signals button. Add the signals to right side of the list either by double-clicking or by clicking > sign. The ">>" will add all the signals to the list in the right. Click OK to close the window and back on Citect Source window. Click OK again to close the Citect Source window. Now, the SCADA Signals window will show the list of the SCADA Signals and their value. Assigning Data Now that WaterGEMS knows what model elements are associated with the SCADA signals and where tags in the SCADA file are located, the SCADA elements need to be matched with the tags. This can be done element-by-element in the property grid or more quickly by opening the SCADA Element FlexTable. How you assign the data will depend on what kind of data it is: real-time or historical. If you are using historical data, find the column for “Signal (Historical).” For each row of the FlexTable, pick the SCADA tag associated with that element. When done, the table should look like the screenshot above. (If you are using real-time data, you would use the “Signal (Real-time)” column in the FlexTable.) Computing and Results Now that the data is assigned to the SCADA elements in the model, you are ready to compute. The steps you take will depend on what you are trying to do. Open SCADAConnect Simulator, if you have not already. With the setup complete, an operator can basically do whatever they need to in order to analyze the system and add SCADA data to the model. This includes new features related to pipe breaks and fire response runs. If all you need to do is to run a model with historical or real-time data, you are ready to simply compute. At the bottom of SCADAConnect Simulator, set the Baseline Scenario to the scenario you are computing. In the screenshot above, this is for a scenario using the historical data from an Excel spreadsheet. Click the Compute button and the model will run. SCADA Data and model data for the associated element will now be available in the SCADA Element FlexTable. With Historical SCADA data, this can help with model calibration and to make sure that the model response is accurate. Live SCADA runs can also help with this, but can also be used in real time to make sure that pumps and valves are working correctly and that flow and pressure results are accurate. The latter could be important in finding places where there might be leaks or valves that are partially closed. The Live SCADA data can also use an auto-compute function. If the operator sets the calculation option to use Auto-Compute, the program will compute automatically on a regular basis There may be cases where you want to adjust the demands or change the controls that the model uses. With SCADAConnect Simulator, you can do this without the need to make physical changes to the model files themselves. For demand adjustments, right-clicking on “Daily Demand Adjustments” in the middle of the SCADAConnect Simulator dialog will allow you to edit the demands or unit demands. You select the scope that you want to use, choose the demand pattern that you want to use, set the operation of the value set. In the lower right corner of this dialog you can use the compute button to estimate the total daily demand. When you create one of these, it appears in the tree form list beneath Demand Adjustment. You can also override controls that might be present on elements in the model. For instance, there may be a control on a pump in the system where it turns off at a certain level. However, in your SCADA run, you would like to change that level to something else without changing the control in the baseline model. To do this, right-click on Control Override to open the dialog below. This allows you to create control overrides to quickly creating study situations. To create a control override, right-click on Control Override in the middle of the SCADACOnnect dialog and select the New button at the top of the window. Select the element to be controlled by clicking the ellipsis button in the “Controlled Element” column. Select the attribute of the element to change in the next column, set the value of the element, start date and start time for the control, duration for the control, the priority, if any, and any notes about the control. When you create one of these, it appears in the tree form list beneath Control Override. Starting with WaterGEMS CONNECT Edition, Control Override information can now be imported into SCADAConnect Simulator. In earlier versions of SCADAConnect Simulator, control overrides (cases where you may want to apply different controls than what is currently in the scenario) needed to be applied manually. With WaterGEMS CONNECT Edition, you can now import historical pump information to automatically create the controls in the model and apply the overrides. In SCADAConnect Simulator, select the Configure tab and choose Import Historical Overrides. This will open a new dialog that will allow you to import the controls from an existing source file. The SCADA Signals will already need to be set up the correct source to do this. The SCADA Elements will appear in the box in the lower left. The control override can be filtered for a certain time span. Once you have that selected, click the Import button to import the control overrides. They will then appear in the middle section of the SCADAConnect Simulator dialog. Tools There are four tools available in SCADAConnect Simulator for WaterGEMS CONNECT Edition. Two of these tools are available in WaterGEMS V8i SELECTseries 6. These are Pipe Break, Fire Response, Power Outage, and Pipe Shutdown. The Pipe Break option enables the user to specify a pipe break or a shutdown of a portion of the distribution system. (A shutdown is simply an isolated pipe break with zero leak flow.) You can create a new Pipe Break multiple ways. You can right-click on Pipe Break in the tree form. From the Home tab, you can click the New button and then choose Pipe Break. From the Emergency Response tab, you can choose Pipe Break Response. Any other these options will generate a Select tool bar to allow you to choose a pipe. After selecting the pipe, the following dialog is displayed. You can set the leakage flow rate and choose the start time to isolate the break by checking the isolate break checkbox. Clicking the checkbox allow you to set the date and the time to run the simulation, as well as input an isolation duration. Enabling the checkbox also enables the “Isolate Break” button, which opens the window shown below. Clicking the “Auto-Isolate” button will automatically select the closest isolation valves that are available to close off this pipe from the system and add them to the bottom portion of the window below. See the New Features section above for details on this feature. When a Pipe Break is active, an icon will appear in the drawing page, showing where this will occur. Fire Response enables the user to place a fire demand (or other emergency flows) at a junction for a period of time to determine its impact on pressure and flows and possibly test alternative ways of responding to the fire. Like Pipe Break, you can create a new Fire Response multiple ways. You can right-click on Fire Response in the tree form. From the Home tab, you can click the New button and then choose Fire Response. From the Emergency Response tab, you can choose Fire Response. Any other these options will generate a Select tool bar to allow you to choose a junction or hydrant. After selecting the node, the following dialog is displayed. The new fire response dialog is similar to the pipe break dialog, except in here you define the demand node and demand that you want applied to that node instead of supplying a leakage flow. After running the fire response you can easily use the time browser button at the top of the home tab along with the graphs button to view how your model responds over time. When a Fire Response is active, an icon will appear in the drawing page, showing where this will occur. In the middle part of the Home tab, you will see any demand adjustments, control overrides, fire responses, or pipe breaks that you include in your run. If you do not want to have these applied when you compute, you would simply uncheck the box beside. Similarly, this tree form allows you to have multiple items, such as two fire responses. You may not want to have both apply for a given run and in such a case, you would uncheck on fire response in the tree form and leave the other checked, similar to what is shown below. The tree form also always you to edit existing items by right-clicking on an existing item. When you right-click on an existing item, you also have a Zoom To option, which will highlight the item in the drawing. Power outage events enable the user to mark pumps or variable speed pumps as being affected by a power outage. As part of the SCADAConnect simulator tool, this provides a simple interface for an operator to simulate the impact of such an event. This tool is accessed from the Emergency Response Tab in SCADAConnect Simulator. There are two ways to access this. You can either right-click on the Power Outage selection in the middle of the dialog or you can click the "Quick Add" button at the top of the SCADAConnect Simulator dialog. This opens a Select toolbar that allows you to select pumps that may see or have seen a power outage at some point. Once the pumps have been selected, you can enter the data in the Power Outage table, including the start of the outage and the length of time it runs. This will allow you to account for an outage during an historical simulation or to plan for an outage in real-time simulations. When the run is computed in SCADAConnect Simulator with a Power Outage applied, the solution will include the results when the pump is not available. You can include multiple power outage events in the simulation. If the event does not need to be included, you can uncheck the box in the Enabled column. When the pump is enabled for a power outage, the symbol below will appear over the pump in the drawing pane. See: Wiki: SCADAConnect Simulator for WaterGEMS Help: SCADAConnect Simulator - Power Outages Pipe shutdown events enable the user to shut down a portion of the distribution system and simulate the results of doing so. This allows an operator to simulate the impact of the closure of a pipe, in a simple interface. This tool is accessed from the Emergency Response tab of the SCADAConnect Simulator. There are two ways to access this. You can either right-click on the Pipe Shutdown selection in the middle of the dialog or you can click the "Quick Add" button at the top of the SCADAConnect Simulator dialog. This opens a Select toolbar that allows you to select pipe or pipes that are part of the pipe shutdown. Once the pipes have been selected, you can enter the data in the Active Pipe Shutdowns table, including the start time of the pipe shutdown and the length of time it lasts. Since the pipe shutdown involves closing valves or pipes, the next step is to isolate the pipe. The Auto-Isolate button at the top of the Active Pipe Shutdowns table allows for a simple way to do this. Click the Auto-Isolate button and the program will populate the valves needed to isolate the pipe. If there are no isolation valve or other valves in the model in that part of the system, the user can select pipe elements to close. It is up to the user to ensure that these pipes have sufficient valves to accomplish this isolation. During the time that the shutdown is isolated, the flows in pipes in that area are zero and the demands are zero. The hydraulic grade and pressure in the isolated area will not have valid results. Viewing Results The SCADA data can be used to help calibrate a model by comparing data from the SCADA system with model results. There are several ways to do this. Comparing graphs is one way. In SCADAConnnect Simulator, there is a Graphs button. Clicking this will open the Graphs manager. Choose the New button, then Line-Series Graph. The Select toolbar will open. Choose the SCADA Element you want to graph. The line data will be the model results; the points will be the SCADA values from your data source. To create a graph, you can also go to the drawing in the main user interface, right-click on the SCADA Element, and select Graph. This graph will not automatically be saved to the Graph manager, but you can add it by clicking the “Add to Graph Manager” button. Numerical results can also be viewed from the SCADA Element FlexTable, though this will only be for the current time step. You can use the time browser to step forward in time to see the results change. This can be useful if you want to see the results for all SCADA Elements for a given time step. For viewing results from a a tool like Pipe Break, Fire Response, Power Outage or Pipe Shutdown, there is not going to be a SCADA element to graph. Instead, you would graph the element associated with what you are modeling and/or the elements around it. For instance, assume you have a Fire Response where an additional fire demand is applied to a node for 1 hour. After computing this, you can graph the pressure at that node to see how the additional demand will impact the pressure at that location. You can also graph the pump flow or tank level to see that response. The Named Views option can be useful to quickly zoom to a section of interest in the drawing pane. First, zoom to a section of the model that you are interested in. In SCADAConnect Simulator, choose the Home tab and then Named Views. In the dialog that opens, click New > Named View. This will save this view. If you zoom back out and select the Named View from the dialog, it will zoom right back to the extent of the Named View. SCADA Results Publishing is a feature applicable to the OPC Source. This tool basically defines how things are mapped from the hydraulic model to the OPC. If results from an element are desired to display in an existing OPC then this tools comes into play. In order to push the result, the simulation must be run from SCADAConnect Simulator. The View Log button can be useful during troubleshooting when the feature does not behave as expected. Clicking the highlighted button will open up the log file in a notepad. Troubleshooting The pump status was not displayed after computing the model. This is likely because the status is a text string and needs to be mapped to the On/Of property. This is done by going back into the SCADA Signals dialog (Components > SCADA Signals). Double-click on SCADA Data Source you are using, or right-click and choose “Edit data source.” Select the Signal Value Mappings tab. In the Pump Status Section, pick Single Value from the Type pulldown menu, and set On to “On” and Off to “Off.” I am getting an error message “Citect API dlls are missing...” Please navigate to this page . When doing a Test Connection with Citect, the following message is generated: “Unable to open the Citect connection” Make sure the server name is spelled correctly and can be pinged from the command line. Try with and without the Authentication. When doing a Test Connection with Citect, the following message is generated: “Citect is not available when running as 64-bit” Make sure to run the 32-bit of WaterGEMS/CAD. For more details click here . When using Citect, it will still not connect Try to enable a legacy connection. Step are shown in this page . Also, make sure that the CtAPI dlls version is the same as the Citect version. I can see the graph in SCADA Signal Editor but not in the Graphs, how can fix? If data and graph are visible in SCADA Signal Editor but not in the graphs, then it most likely due to the date. Please make sure the data in the Calculation Options and the date when data were recorded are the same. See Also Free Webinar on SCADAConnect in SewerGEMS SCADAConnect Simulator in WaterCAD and WaterGEMS V8i SELECTseries 5 SCADAConnect in SewerGEMS How can I publish my computed model results to a SCADA HMI?

Applies To Product(s): WaterGEMS, WaterCAD Version(s): 10.00.xx.xx, 08.11.06.xx Area: Modeling Original Author: Sushma Choure, Bentley Technical Support Group Overview This TechNote describes the three basic methods of creating simple controls in WaterCAD or WaterGEMS. Assigning particular controls to a particular scenario is also described later this Technote. Note : This TechNote is applicable WaterGEMS/WaterCAD CONNECT Edition or V8i SELECTseries 6. Here is the technote for older versions of the water products. Background In WaterGEMS, controls can be modeled to introduce a user-defined action to a hydraulic element. When one or more conditions provided by the user are met during the model simulation, the action or actions provided by the user will be introduced in the model operation. In a real system, these types of controls are sometimes referred as Programmable Logical Controls (PLCs). SCADA systems and time-based plant operations are major sources of PLCs that should be included in a water model. Including controls in the model is most essential when performing an Extended Period Simulation (EPS). Controls can be created for a number of element types, including pumps, valves and pipes. The example below shows controls for pump status based on tank level, but a control could also be made for valve status or setting as well as pipe status as the Action. How to Create a Control in WaterCAD or WaterGEMS V8i There are two methods to access main Control dialog box: From WaterGEMS Component menu, select "Controls," or, From the properties of selected element, under Operational category, click the ellipses button (small button with three dots) of Controls attribute. The only difference is that, when accessing the Controls dialog from the element properties, the controls will be filtered to display only those pertaining to the selected element. The images below show the places where the Control dialog box can be obtained. The screen below shows the Control dialog box and describes some of the major icons/tabs. The image also illustrates the ways of creating controls. Depending on your requirements, each way has its own advantages. Method 1: Control Wizard Method Creating controls using the wizard is very simple and can save time, however, this approach is only applicable when creating controls on pumps that operate based on tank level. To use the wizard, click the 'Control Wizard' icon (fifth icon from left) and follow the steps shown in the images below. a. Select the pump to which you want to assign a control, from the drop-down list. b. Select the tank from the drop-down list, whose water level will dictate the pump status. Based on requirements you may pick other options also. c. Provide the logical operator such as greater than '>' or less than ' " in the drop-down will show all controls. c. In the left portion of defining conditions, you have option of creating simple or composite condition using the small drop-down arrow. d. While selecting the element using 'IF' condition, instead of selecting from the drop-down list, you have new option of selecting the condition from the list of conditions created, rather than browsing one by one from the drop-down list for existing conditions, suing small black arrow or small search button. e. Follow the steps in the image below to create a condition. Note that the actual conditions and actions shown will be specific to your own model. f. Follow the steps in the image below to create an Action for your condition. Again, the actions displayed are specific to your model. g. After creating the conditions and actions, the Control dialogue box should look something like below: Method 3: Creating Controls Using the "Conditions" and "Actions" Tabs (Required for Composite Conditions and/or Actions) This method allows you to create conditions and actions separately under the Conditions and Actions tab. It is necessary to use this approach when creating a control with multiple conditions and or/actions (i.e., a composite condition or action) using AND or OR. a. To create a condition in the Conditions tab, follow the steps in the image below. b. Next, create and Action in the Actions tab by following the steps in the image below. c. After creating Conditions and Actions, go to the Controls Tab and select the New button to create a new control. In the lower part of the window, select the Condition and Action(s) you created in the previous steps to build the desired control. Creating a Control Set Control sets allow you to manage and modify controls. The use of multiple control sets enables you to apply different controls to different scenarios. This section describes how to set up control sets themselves. Details on assigning a particular Control in a particular scenario are provided in the next section. To create a control set, select control set icon ( third from left), click the drop-down list and select 'Add / Remove Control Sets', which will open the list of control sets.(see "third option" in image below). The count field lets the user know how many controls are included in a given control set. You need to create a control set in this window before you can begin associating controls to it as shown in the “Control Sets” window above. To include a control in your control set, select second option from the drop down list - Edit Control sets. To make this option active select any control in the controls list (as highlighted in the second image below). This will open the Editable control sets dialogue.Repeat this process until all of the desired controls are in the selected items list, and then click OK. To open the control sets for multiple controls, select multiple controls using Ctrl button or using the shift button, and then select edit controls sets. The below dialogue box contains, the conditions and actions columns of controls and also else option for composite controls. the right hand side editable columns are of the controls sets. By checking the box nex to controls, of particular control set , it makes the control active for that control set. you also have option of global editing the columns, meaning making the controls active or inactive for a particular control set in one go by right clicking on the column of say "Variable Speed Pumping" control set>Global edit. Also you can filter or sort the controls based on the status on/off. Assigning a Control Set to an Alternative for use in a Scenario To make controls scenario specific, it is necessary to add controls to a control set, as previously described, and then assign that control set to the Operational Alternative utilized by the desired Scenario. Open the Alternatives dialog and either edit the existing Operational Alternative or create a new one, if needed. Double-click the alternative to edit it (see "1" below). Click the down arrow ("2"), select the desired control set ("3"), and then click Close to save your changes. c. Finally, if you created a new Operational Alternative, you will need to edit the desired Scenario's Operational Alternative so that it uses the new one. Recognizing Elements with Controls To identify whether an element has an active control, look for the following symbol next to the element. If the symbol is not present, then it's likely the control you created is not assigned to the control set being utilized by the current Operational Alternative. Priorities in Controls You have the ability to add a priority value to a control. To set a priority for the control being created, it needs to be a logical control. To activate the priority drop-down list, click the check box next to Priority. You can set a priority of 1-5, with 5 being the highest priority. If multiple controls meet a certain condition and they have conflicting actions, the control with the highest priority will be used. Note: At calculation time, the priority is used to determine the logical control to apply when multiple controls require that conflicting actions be taken. Logical controls with identical priorities will be prioritized based on the order they appear in the 'Logical Control Set' in the 'Operational Alternative'. A rule without a priority value always has a lower priority than one with a value. For two rules with the same priority value, the rule that appears first is given the higher priority. Duplication of Controls Controls can be duplicated depending upon your requirement, whether you want to duplicate only control or conditions and actions as well. When first option is selected of duplicating full control, along with the control, condition and action of that control will also be duplicated, which you can see in the conditions and actions tab. When second option is selected, then only the control will be duplicated, by reusing the existing condition and action of original control. Import and export of Controls Now you have ability of importing and exporting controls from one project to another using this new feature of import/export. This will save your quality time consumed in recreating the controls for new projects. Once you have created controls, control sets , you can export them to a new file which can be saved as .ctl or .txt or as tab delimated excel file. After exporting save the file to the desired location and then you can import this controls file into a new model or existing model without having to rebuild the controls. Percent Full condition for tanks The tanks element received a new “Percent Full” condition option that will allow you to specify a given action to occur when your tank gets to a certain percent level full. There are also newly added actions for the pump element that will allow you to create a control to have a pump achieve a target pressure and pump target head, which will be useful for VSP pumps. For more on this, see further below under the VSP section. See Also Product TechNotes and FAQs Haestad Methods Product Tech Notes And FAQs Hydraulics and Hydrology Forum