Dear Colleagues, Hello all.I had two quick questions 1.This is about Darwin designer.I am optimizing my network of 46 pipes and 40 junctions for a peak hour +fire timestep at 10th hour but when i export the scenario and run the model,there is some minimum pressure violation in some junctions/nodes at peak hour. Just requesting someones opinion on how i can eliminate this..I tried to tweak a few of the GA options e.g increasing the default penalty factor for instance but no effect. 2.I had old WaterCAD files .WCD and i only have WaterGEMS V8i series 6 installed but no WaterCAD.How can i open these files in WaterGEMS. Thanks and kind regards, Simon

Hi Craig, Had it been occurring only for the biggest diameter pipe in conduit catalog it was ok. But the problem is, it happens for all the pipes . Best Regards Jatin Talwar

Michael, your option #2 might also work in the meantime. You could create a pipe prototype with the properties for your hydrant laterals, then connect a pipe between the imported hydrants and the nearest junction.

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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 V8i. 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 Click to Download Note: the above model is for example purposes only. It can be opened in version 08.11.01.32 and above and you can find additional information under File > Project Properties. 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

Hello Diego, Can you understand English? I am including both an English and Spanish (machine-translated) version of my answer below. Inglés :: The volume of the the dipping tube hydropneumatic tank is determined by the Elevation-Area curve which you must enter. Depending on the configuration, the compression chamber volume may be derived from the elevation-area table alone or from the "Volume (compression chamber)". More information can be found in the "Dipping Tube" section of the below wiki article. Español : El volumen del tanque hidroneumático del tubo de inmersión viene determinado por la curva de área de elevación que debe introducir. Dependiendo de la configuración, el volumen de la cámara de compresión puede derivarse de la tabla de área de elevación sola o del "Volume (compression chamber)". Puede encontrar más información en la sección "Dipping Tube" del siguiente artículo wiki. Modeling Reference - Hydropneumatic Tanks

Please provide the model files using one of the options in the link below. Sharing Hydraulic Model Files on the Haestad Forum

Just to clarify - if you go with option #2, your comment about isolation valves is indeed important. With a flushing study, location of valves (that may be closed off) can be important, so be sure to consider this After reading your original message again, I'm now not quite certain if the lateral pipes are included in the GIS or not. Are you saying that the hydrants are floating on their own with no lateral polyline represented in the GIS, or that the lateral lines are there but just not "snapped" to the main line at a point/junction? For the latter, one possible solution would be to use the GIS-ID feature to import the main pipes (excluding hydrant laterals) first, then do a separate Modelbuilder run to import the lateral pipes. With the option set to create nodes at pipe endpoints if none found, it will create a junction at the end of the lateral, overlapping (but not connected to) the main pipe. You could then run the batch pipe split tool to split the main pipe and attach the junction. With the use of the GIS-ID feature, the same underlying GIS-ID will be used for the two resulting pipes (from the split) that represent the single pipe in the GIS. Here are some related articles that may help on that subject: Building A Model Using ModelBuilder How to populate or update an existing model with GIS-IDs Junctions appear to overlay a pipe instead of connecting to it

Muchas gracias por su respuesta. Si, entiendo ingles pero soy un desastre escribiendo. Le hago una consulta adicional para confirmar bien el tema: En el ejemplo que Usted me da entiendo que el dipping tuve varía entre la cota 1 y 3.31, pero mi consulta es que pasa con el volumen por debajo de 1? Entre 0 y 1, el diámetro equivalente será mayor, porque no llega hasta el fondo el dipping Tube, es volumen neto, sin restar el cilindro interior? para calcular el volumen entre 0 y 1 ingreso otro valor en esa misma tabla con una área mayor? y ese volumen será el que actúa como surge tank cuando el líquido pasa por debajo de la cota 1? En tanques típicos, cual sería la profundidad hasta la que llega el dipping tube, expresada como porcentaje de la altura total del tanque? Nuevamente muchas gracias por su tiempo y su respuesta. Saludos, Diego Capponi

Applies To Product(s): CivilStorm, SewerGEMS Version(s): CONNECT Edition, V8i (SELECTseries 2) or later Area: Modeling Original Author: Scott Kampa, Bentley Technical Support Group Overview The purpose of this TechNote is to discuss the Long Term Continuous Simulation (LTCS) function available in CivilStorm V8i SELECTseries 2 and SewerGEMS V8i SELECTseries 2 and later. Background EPA SWMM has the capability of running long term continuous simulations, but previous builds of CivilStorm and SewerGEMS were mainly designed for computing event-based simulations. CivilStorm and SewerGEMSV8i now include the capability of running such a simulation. The CONNECT Edition releases and any release later than V8i SELECTseries 2 include this feature. Long Term Continuous Simulation will use data such as rainfall, temperature, evaporation, infiltration, snow packs, as well as aquifer and groundwater data. While it is possible to compute with the Implicit engine, it is designed for use with the Explicit (SWMM) engine, which is better at handling the large amounts of data goes into such a simulation. This TechNote will review the data needed to complete the simulation and the steps to successfully run the model. Rain Fall Data Where CivilStorm and SewerGEMS used storm data such as Time-Depth curves or IDF tables to define a storm event, a new item called “Rain File” is included for use of historical data used in LTCS. These files can come in a number of different allowable formats, including DSI-3240 and DSI-3260 (National Weather Service), HLY03, HLY21, and FIF21 (Environment Canada). Besides these predefined file formats, you can also use a SWMM format text file where the data is separated by space, such as what is shown in the screenshot below. To add these files for use in LTCS, go to Components > Storm Events. Select the New icon and choose Rain File. You can rename the rain file item or leave the default name. Once this is created, you will need to select the file being used. Click the ellipsis (“…”) button next to the item “Rain File” on the right and browse to the rain file being used. Change the items “Rain Data File Type” and “Rain Units” as needed. In the table on the right, enter a label, the return event (in years), the Station ID (which is likely in the rain file), and the time increment from the rain file. Click Close to return to the drawing. Next, select Components > Global Storm Event. In the pulldown for the column “Global Storm Event,” choose the storm you just created in the previous step. Climatology Data The previous steps are the same as applying any storm event to a CivilStorm or SewerGEMS model. The power of the Long Term Continuous Simulation is the ability to include other climatological data that can be used to get an accurate representation of the event. These include Temperature, Evaporation, Wind Speed, Snow Melt, and Areal Depletion. To add this data to the model, go to Components > SWMM Extensions > Climatology. These will be touch on briefly in the section below. Temperature Data The temperature data in this section is used to specify the temperature data used for snow melt computations. There are three selections. “No Data” is used when snow melt will not be simulated. “Climate File” is used when the data is in an external climate file. Choose this allows the user the import a DAT file with the data and specify the time that the data starts. “Time Series” refers to temperature variation over time. This selection opens a table in the Climatology dialog that allows the user to enter the time and temperature. Note: The climate files that can be used for the “Climate File” option are DSI-3200 or DSI-3210 files available from the National Climatic Data Center, Canadian climate files available from Environment Canada, and user-prepared climate files where each line contains a recording station name, year, month, day, maximum temperature, and minimum temperature. The file can also optionally include evaporation rates and wind speed. If no data are available for any of these items on a given date, then an asterisk should be entered as its value. When a climate file has days with missing values, CivilStorm and SewerGEMS will use the value from the most recent previous day with a recorded value. User-prepared climate files must use the same units as the project being analyzed. For US units, temperature is in degrees F, evaporation is in inches/day, and wind speed is in miles/hour. For metric units, temperature is in degrees C, evaporation is in mm/day, and wind speed is in km/hour. Evaporation Data This section allows user to enter evaporation rates for the study area. There are a number of selections for this section. “No Evaporation” is used when evaporation will not be simulated. “Climate File” will reference the same DAT file used in the Temperature data tab. This cannot be used unless a climate file for temperature is specified. The user can enter values for the monthly pan coefficients in the table. “Monthly Evaporation” allows the user to enter the average evaporation rate for each month. “Constant Evaporation” means that the evaporation rate will remain the same throughout the simulation, independent of the time of year. “Time Series Evaporation” allows the user to enter the evaporation rate for a given time in the simulation. Wind Speed Data This section allows the user to input wind speeds. It is primarily used to calculate snow melt rates, as snow will melt faster at higher wind speeds. The units for wind speed are miles/hour (US Customary) and kilometers/hour (System International). “Climate File” refers to the wind speed data in the same climate file used for temperature and evaporation data. “Monthly Averages” allows the user to enter the average wind speed for a given month. Snow Melt Data This section allows the user to enter climatic variables for their study area. Default values are included, which can be adjusted for the area. “Dividing Temperature Between Snow and Rain” is simply the temperature where the precipitation from the rain file is assumed to snow instead of rain. “ATI Weight” refers to the Antecedent Temperature Index, which reflects the degree of heat transfer within a snow pack during non-melt periods is affected by prior air temperatures. Small values are used for deeper snow packs, which result in reduced rates of heat transfer. “Negative Melt Ratio” is the ratio of the heat transfer coefficient of the snow pack during non-melt conditions to the coefficient during melting conditions. “Elevation Above MSL” is the elevation of the area above sea level. “Latitude” is the latitude of the study area. “Longitude Correction” is a correction between true solar time and standard clock time. Areal Depletion Data Areal depletion refers to the tendency for a snow pack to melt unevenly over a surface. This tab allows the user to specify points for an areal depletion curve for both pervious and impervious surfaces. Other Factors in LTCS As mentioned above, LTCS can utilize a number of different inputs and parameters to running the simulation. These additional factors include aquifers, snow pack, infiltration, and groundwater. Snow Pack This is accessed by going to Analysis > SWMM Extensions > Snow Pack. These objects contain parameters that characterize the buildup, removal, and melting of snow over the follow sub-areas of a catchment: Plowable, Impervious, and Pervious. Each of these sub-areas have the same parameters, as defined in the Help documentation. This section also defines the Snow Removal parameters in a separate tab. To create a new Snow Pack item, click the New icon. This will make the property fields editable and allow the user to go to the Snow Removal tab. To apply this to a catchment, open the catchment properties. Find the attribute “Has Snow Pack?” and set this to True. The Snow Pack created in this SWMM Extension can then be included. Aquifers This is accessed by going to Analysis > SWMM Extensions > Aquifers. Aquifers are sub-surface groundwater areas used to model vertical movement of water infiltrating from catchments. They also permit infiltration from groundwater into the system or exfiltration of surface water. To create a new Aquifer, click the New icon and enter the required data. Definitions of these can be found in the Help documentation. To include this in the simulation, open the catchment properties and set the item “Apply Groundwater” to True. You will then be able to select the Aquifer created in this SWMM Extension. Groundwater Groundwater data are used to calculate the groundwater exchange between the aquifer and the node in the drainage system. A catchment contains the groundwater data and the user can view or edit the groundwater data in the catchment property grid. After setting the attribute “Apply Groundwater” to True, the groundwater parameters are opened. The groundwater flow formula is described as: The coefficients and exponents in the catchment properties related to groundwater will be applied to this equation to calculate the flow of groundwater in the system. Infiltration Infiltration of rainfall from the pervious area of a catchment into unsaturated upper soil zone can be described using 3 different models: Horton, Green-Ampt, and SCS Curve Number. To successfully run SWMM5 engine, all catchments must use the same infiltration method. This can be assigned in the Calculation Options when using the Explicit (SWMM) engine. You can also assign it in the catchment properties. Calculation Options Once the data is inputted, it is time to compute the model. To make sure that everything runs correctly, you will want to make some adjustments to the calculation options (Analysis > Calculation Options). First, LTCS works best with the SWMM engine. To change this, find Engine Type and change this to “Explicit (SWMM 5)”. Next make sure that the Simulation Start Date and Simulation Start Time match up with the date and time in the rain file used as the storm for the simulation. You will also need to set the end time. The easiest way to assure that this is correct is to change the field Duration Type to “End Date \ End Time” and enter the End Date and End Time that corresponds with the rain file. Other possible calculation options that are used include “Start Sweeping On” and “End Sweeping On” which are included when street sweeping activities are expected to impact the simulation. “Catchment Results Type,” “Nodes Results Type,” and “Links Results Type” specify the degree of results generated for the different element types. This can include all results, no results, or results for a given selection set of elements. It is also possible to save and use Rainfall Files, Runoff Files, and RDII Files. For more information, see the following link: LTCS also supports Hot Start files. Hot start files are binary files created by the SWMM engine that contain hydraulic and water quality variables for the drainage system at the end of a run. The hot start file saved after a run can be used to define the initial conditions for a subsequent run. Hot start files can be used to avoid the initial numerical instabilities that sometimes occur. For this purpose they are typically generated by imposing a constant set of base flows (for a natural channel network) or set of dry weather sanitary flows (for a sewer network) over some startup period of time. The resulting hot start file from this run is then used to initialize a subsequent run where the inflows of real interest are imposed. It is also possible to both use and save a hot start file in a single run, starting off the run with one file and saving the ending results either to the same or to another file. The resulting file can then serve as the initial conditions for a subsequent run if need be. This technique can be used to divide up extremely long continuous simulations into more manageable pieces. When this field is set to True a hot start file will be generated from the end results of the run. More information on this can be found in the Help documentation. Viewing Results After computing the model, you can view results just as you can with any other model file. This includes graphs, profiles, and viewing results in the properties or element FlexTables. Another useful tool is the Statistics dialog (Analysis > Statistics). With this you can select an element and choose the element, the result field to be analyzed, the time period, and the statistic type. You can also set minimum and maximum event thresholds. When you click the Compute button, you get a series of results depending on the statistic type you used. See Also What is the purpose of the Rainfall File, Runoff File, and RDII File in the Calculation Options? Product TechNotes and FAQs Haestad Methods Product Tech Notes And FAQs [[General WaterGEMS V8 FAQ|General WaterGEMS V8 FAQ]] External Links Hydraulics and Hydrology Forum Bentley LEARN Server

Applies To Product(s): Bentley SewerGEMS Version(s): 10.00.xx.xx, 08.11.xx.xx Area: Calculations Original Author: Jesse Dringoli, Bentley Technical Support Group Problem When computing a long term continuous simulation model with a rain file and the Explicit (SWMM) solver, an error message called Error 318 is generated. Problem ID#: 71561 Solution The issue is likely related to inconsistent information in the Rain File, such as an incorrect date or bad formatting. Review the rain file to make sure the formatting is correct and check for incorrect dates, such as February 30th. See Also [[Running a Long Term Continuous Simulation|Running a Long Term Continuous Simulation]]

Applies To Product(s): CivilStorm, SewerGEMS Version(s): CONNECT Edition, V8i (SELECTseries 2) or later Area: Modeling Original Author: Scott Kampa, Bentley Technical Support Group Problem What is the purpose the Rainfall File, Runoff File, and RDII File in the Calculations Options? Why are the files not being created? Solution The Rainfall File, Runoff File, and RDII File are primarily used with the Long Term Continuous Simulation workflow. LTCS allows a user to run a long simulation to see the impact of a system, taking into account a lot of different factors. Information on LTCS can be found in the link in the See Also section below. The Rainfall File, Runoff File, and RDII File are created to aid in the calculation of this type of simulation. In order for these to be created, you must used an external Rain File. This is one of the storm types available in the Storm Data dialog. Rain Files contain gage data that can be applied to a system. These are typically .TXT or .DAT files. These are explained in further detail in the link related to Long Term Continuous Similar below. The Rainfall File and Runoff File will not be created if you are using a different storm data type, like Rainfall Files are binary files that can be saved and reused from one analysis to the next. The rainfall interface file collates a series of separate rain gage files into a single rainfall data file. Normally a temporary file of this type is created for every SWMM analysis that uses external rainfall data files and is then deleted after the analysis is completed. However, if the same rainfall data are being used with many different analyses, requesting SWMM to save the rainfall interface file after the first run and then reusing this file in subsequent runs can save computation time. To create and save a Rainfall File, open the properties for the Calculation Options and set the value for Rainfall File Mode to "Save". Click the dropdown menu for the the property Rainfall File and clicked the ellipsis (...) button. Give the file a name or select an existing file. When you compute the model, a Rainfall File will be created or saved. When you want to use this file, set Rainfall File Mode to "Use". The following file modes are available: None -When this option is selected, no Rainfall File will be used or saved. Use -When this option is selected, the Rainfall File field will become available, allowing you to select the rainfall file to use. Save -When this option is selected, the Rainfall File field will become available, allowing you to specify the name and location for the rainfall file to be saved. Runoff Files can be used to save the runoff results generated from a simulation run. If runoff is not affected in future runs, the user can request that SWMM use this interface file to supply runoff results without having to repeat the runoff calculations again. Note that the Runoff File will only be created if you are using the EPA-SWMM runoff method in the model's catchments. The steps to create, save, or use this file are as found in the steps for the Rainfall Files above. RDII Files are a text file that contains a time series of rainfall-dependent infiltration/inflow flows for a specified set of drainage system nodes. This file can be generated from a previous SWMM run when Unit Hydrographs and nodal RDII inflow data have been defined for the project, or it can be created outside of SWMM using some other source of RDII data (e.g., through measurements or output from a different computer program). The manholes in the model need to be have the properties setup like the screenshot below: The steps to create, save, or use this file are as found in the steps for the Rainfall Files above. See Also Running a Long Term Continuous Simulation Error 318 appears when computing model using the SWMM solver

Diego, The variable elevation curve represents the entire tank - from bottom / base to the top. So, the 1.00 m value for Liquid Elevation represents the bottom of the tank and the 3.31 m represents the top of the tank. You will notice in the screenshot, the "Elevation (Bottom of dipping tube)" is between the two, at 2.529 m. These are all in elevations (with sea level as the datum), not levels. So, between an elevation of 1.00 and 2.529 m, the tank acts as a regular surge tank and above an elevation of 2.529 m, it acts as a hydropneumatic tank as the gas in the compression chamber compresses. If your particular tank had an elevation of zero at the bottom, with a different diameter, then you would indeed have another entry in the variable elevation curve with 0.00 m liquid elevation and an equivalent diameter less than 1.19 m. I do not know what a typical depth would be, between the bottom of the dipping tube and the bottom of the tank. I would suggest looking at some tank manufacturer data. Español: La curva de elevación variable representa el tanque entero - desde el fondo / base hasta la parte superior. Por lo tanto, el valor de 1,00 m para la elevación del líquido representa el fondo del tanque y el 3,31 m representa la parte superior del tanque. Te darás cuenta en la captura de pantalla, la "elevación (parte inferior del tubo de inmersión)" está entre los dos, a 2.529 m. Estos son todos en elevaciones (con el nivel del mar como el dato), no los niveles. Por lo tanto, entre una elevación de 1,00 y 2,529 m, el tanque actúa como un tanque de sobretensión regular y por encima de una elevación de 2,529 m, actúa como un tanque hidroneumático como el gas en la compresión se comprime compresión. Si su tanque particular tenía una elevación de cero en la parte inferior, con un diámetro diferente, entonces realmente tendría otra entrada en la curva de elevación variable con 0,00 m de elevación de líquido y un diámetro equivalente menor de 1,19 m. No sé lo que sería una profundidad típica, entre el fondo del tubo de inmersión y el fondo del tanque. Sugeriría mirar algunos datos del fabricante del tanque.

Product(s): WaterGEMS, WaterCAD Version(s): 08.11.XX.XX Area: Output and Reporting Problem Why is the Pressure (calculated residual) field value show N/A for a steady state or EPS? Solution The residual pressure field is available for fire flow analysis, but is shown as N/A for the hydraulic analysis, flushing, water quality analysis etc. Residual pressure is nothing but the calculated pressure at any node during a fire event. The Pressure (calculated residual) field is available only with an automated fire flow analysis, to understand how much residual pressure there is at that junction or hydrant. Apart from fire flow analysis Pressure (calculated residual) field will always show as N/A for all other types of calculations. During automated fire flow, a value of "N/A" will also be shown for nodes that are not part of the fire flow nodes selection set, specified in the fire flow alternative. See Also

Product(s): SewerGEMS, CivilStorm, StormCAD Version(s): 08.11.XX.XX and 10.00.XX.XX Area: Modeling Problem Using the GVF-Rational (StormCAD) solver, what are the different types of inflows that a user can apply at a catch basin and where specifically does the flow enter? (subsurface or inlet approach) Solution Catchment Rational Flow: Rational flows that approach the inlet at the surface. External CA/Tc Flow: Rational flow that enters subsurface. Additional Subsurface Flow: Additional flow entering subsurface. Additional Carryover Flow: Additional flow entering above the inlet (can be bypass). Known Flow: Supersedes all upstream flows at this point in the system and enters subsurface. See Also Understanding Known Flows Understanding Flow (Additional Subsurface) and Flow (Additional Carryover) Entering catchment data directly to a catch basin

Product(s): SewerGEMS, StormCAD, CivilStorm, PondPack Version(s): 08.11.XX.XX 10.00.XX.XX Area: Layout and Data Input Problem What happened to the E, B, D coefficient IDF curve type? IDF curve equation coefficients E, B, and D are now labeled A, B, and N. [Problem ID#: 39295] Solution The naming of the coefficients in the IDF curve equation format has changed in V8i. Mapping for the new naming convention is as follows: e -> n b -> a d -> b [Solution ID#: 500000065903] See Also Import IDF Equation Storm Data

Excelente!!! Muchas Gracias, ahora si me quedó claro que datos y como ingresarlos.

Applies To Product(s): Haestad Products Version(s): V8i XM, V8i Environment: N/A Area: N/A Subarea: N/A Original Author: Bentley Technical Support Group Deleted - replaced with video content here: http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/25234.setting-the-correct-feature-level-in-the-municipal-license-administrator Overview This video demonstrates how to configure the license management tools for Bentley products that use SELECTserver (XM) licensing. Support Video Clip (Recorded in 1024 x 768 resolution. Right-click for playback options.) (Please visit the site to view this video) See Also Hydraulics and Hydrology Product Licensing (Activation) FAQs and Troubleshooting [TN] Product TechNotes and FAQs Haestad Methods Product Tech Notes And FAQs

Simon, 2. The .WCD file will have to be converted to a .WCD.MDB file using WaterCAD 7. If there is already a .WCD.MDB file all you need to do is open the file in WaterGEMS by going to File > Import > WaterGEMS/HAMMER database.

Product(s): PondPack Version(s): 08.11.01.56 Area: Output and Reporting Problem Why is the flow reported at an outfall node higher than expected? [Problem ID#: 39297] Solution This is because the outfall nodes themselves in this case are not loaded into the calculation engine, so the flow reported at the outfall node is actually the total pond inflow. If multiple outfalls discharge into the same pond, or if catchments discharge directly into the pond in addition to the outfall in question, the flow reported at the outfall will be greater than you might expect. to See the flow contributing from that outfall only, look at the flow in the upstream link element (pond outlet or conduit). [Solution ID: 500000065905] See Also How do you direct flow from a channel or conduit into a pond? Can an outfall discharge to a downstream element?