Document Information

Document Type: TechNote 

Product(s):Bentley HAMMER

Version(s):V8i or V8 XM

Original Author:Scott Kampa, Bentley Technical Support Group

Overview

The purpose of this TechNote is to discuss the how to model turbines in Bentley HAMMER. Additional information can be found in the Help documentation for the product. 

Background

Turbines are used in hydropower generation plants. Given the importance of turbines in these systems, it is essential for a modeler to predict the transient pressures that might occur and to implement an adequate surge control strategy to ensure the safety and reliability of the turbine.

Bentley HAMMER can be used to model transient simulations where turbines are involved and analyze potential protective measures that can be used to mitigate the effects of transient events.

Turbines in HAMMER 

Hydropower turbines are located at the downstream end of a conduit, or penstock, to absorb the moving water's energy and convert it to electrical current. Conceptually, a turbine is the inverse of a pump, but very few pumps or turbines can operate in both directions without damage. If the electrical load generated by a turbine is rejected, a wicket gate must rapidly stop flow, resulting in a large increase in pressure, which propagates upstream (in the penstock).

As mentioned above, the primary purpose of transient simulations with turbines is to look at ways to protect the system against rapid changes in the electrical and/or hydraulic components of the hydroelectric system. In each case, hydraulic transients result from changes in the variables controlled by the governor.

Electrical Load or Torque on the turbine-generator system varies with the electrical load in the distribution grid. In steady-state operation, the electrical torque and the hydraulic torque are in dynamic equilibrium. From a hydraulic perspective, electrical torque is an external load on the turbine.

The moment of inertia comes into play here as it can ifluences the rate at which a turbine speeds up or slows down. Moment of inertia is HAMMER is defined by the equation WR^2, where W is the weight on the turbine and R is the radius of gyration.

Moment of inertia is related by torque by way of the following equation:

I*d/dt = M

where:

I is the moment of inertia, which is a constant
 is the rate at which the turbine is spinning (measured in radians per second)
d/dt is the rate of change in (omega) over time (radians per second per second)
M is the net torque applied to the turbine (i.e., the difference between the torque from the water that is spinning the turbine and the torque from the generator that the turbine is attached to).

So if M = 0, then the hydraulic and electrical torque is balanced, and the turbine speed doesn't change (d/dt = 0)

But if the electrical torque drops to zero, such as in a load rejection operating case, then M becomes greater than zero and the turbine starts to speed up. It will speed up quickly if it has a small moment of inertia, and it will speed up less quickly if it has a large moment of inertia.

Speed is another possible control variable for numerical simulations. For turbines, however, the governor strives to keep the turbine at synchronous speed by varying the wicket gate position during load variation and acceptance (assuming a 'perfect' governor). If field data were available, the speed could be used to determine whether the model simulates the correct flow and pressures.

Once the time-varying electrical torque and wicket gate positions are known, HAMMER solves flow, Q, and rotational speed, N, in conjunction with the characteristic curves for the turbine. This yields the transient pressures for the load rejection, load acceptance, emergency shutdown, operator error or equipment failure. The possible emergency or transient conditions are discussed separately in the sections that follow.

Note: 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.

Turbine Properties

Time (Delay until Valve Operates):  The period of time that must elapse before the spherical valve of the turbine activates. This should be set to a large value if it will not impact the operation of the turbine.

Time for Valve to Operate: The time required to operate the spherical valve. By default, it is set equal to one time step. This should be set to a large value if it will not impact the operation of the turbine.

Pattern (Gate Opening): The percentage of wicket gate opening with time. This is set up in the Patterns dialog, found in the Components pulldown.

Operating Case: Allows you to choose among the four possible cases: Instantaneous Load Rejection, Load Rejection (requires torque/load vs. time table), Load Acceptance, and Load Variation.

Diameter (Spherical Valve): The diameter of the spherical valve.

Efficiency: The efficiency of the turbine as a percentage. This is typically shown in the curves provided by the manufacturer. A typical range is 85% to 95%, but values outside this range are possible.

Moment of Inertia: This value will account for the turbine, generator, and entrained water. This is also typically provided by the manufacturer. As mentioned in the previous section, Moment of inertia is HAMMER is defined by the equation WR^2, where W is the weight on the turbine and R is the radius of gyration.

Speed (Rotational): The rotation of the turbine blades per unit time, typically as rotations per minute or rpm. The power generated by the turbine depends on this value.

Specific Speed: Enables you to select from four-quadrant characteristic curves to represent typical turbines for three common types: 30, 45, or 60 (U.S. customary units) and 115, 170, or 230 (SI metric units). You can enter your own four-quadrant data in the XML library. See the Help documentation for more information.

Turbine Curve: This curve is used to define the flow and head for the turbine in the initial conditions computation. For a transient run, HAMMER uses a four-quadrant curve based on Specific Speed, Rated Head, and Rated Flow.

Flow (Rated): Denotes the flow under normal operating conditions. Only applies to the Load Acceptance operating case.

Head (Rated): Denotes the headloss through the turbine under normal operating conditions, corresponding to the rated flow. Only applies to the Load Acceptance operating case.

Electrical Torque Curve: defines the time vs. applied (electrical) torque response for the turbine. Only applies to the Load Rejection operating case.

Setting up the Turbine properties

This section gives a brief overview of the general setup for a turbine. The exact information entered will vary based on the turbine and the modeling case that is being used.

The properties fields “Operating Case” and “Pattern (Gate Opening)” go hand-in-hand, and are the primary modeling usage for a turbine. More details can be found in the next section. There are four operating cases to choose from: Load Rejection, Instant Load Rejection, Load Acceptance, and Load Variation. The pattern is created in the section “Operational (Transient, Turbine). It used in conjunction with this will represent the relative wicket gate opening at the time from the start of the simulation.

The property field “Turbine Curve” is used to determine the relation between flow and head during the steady state analysis used for the initial conditions. If you are modeling a Load Acceptance operating case, you will also need to enter a rated flow and rated head. This is so that the program has a starting point for the development of the four-quadrant curve. In the other modeling cases, the flow and head used are derived from the turbine curve in the initial conditions. Load Acceptance assumes that the initial status of the turbine is closed, meaning there is no rated flow and head results. Instead, the program will use the rated flow and head entered in the properties.

The flow and head relationship defined in the Turbine Curve is not used in the transient analysis. The transient analysis will use a four-quadrant curve derived from the rated flow and head, as well as the moment of inertia, rotational speed, and specific speed.

This information should be available from the turbine manufacturer. The specific speed can be estimated with the following equation:

In US units n is in rpm, P is in hp, and H is in ft.
In SI units n is in rpm, P is in kW, and H is in m.

There are three different specific speeds available to choose from: “SI=115, US=30,” “SI=170, US=45,” and “SI=230, US=60.”

Note: In a case where you need to have a specific four-quadrant curve not represented by the choices above, it is possible to create a custom four-quadrant curve. Please see the Help topic “Pump and Turbine Characteristics in Bentley HAMMER” for details.

Lastly, the property field “Report Period (Transient)” will allow the user to see the turbine results in the Transient Analysis Detailed Report. These results will include the time, the gate opening percentage, flow, speed, and head.

Note: While the four-quadrant curves for turbines have information for different gate openings, a result of 20% gate opening is as low as the report will go. That means it is not possible to compute or interpolate the turbine operating point when the wicket gates are less than 20% open, so what HAMMER does is linearly interpolate from the flow at 20% open down to zero flow (at the time when the operating rule says the wicket gates are 0% open). Without any four-quadrant turbine characteristic curves available for these gate openings, there is no way to compute the turbine behavior.

Modeling cases with Turbines

Like pumps, there are specific operating rules that can be assigned to a turbine in HAMMER. Below is a brief description of each case. There is a sample model which uses each case below. The sample model can be found at C:\Program Files (x86)\Bentley\HAMMER8\Samples\Turbine_Example.wtg.

Load Rejection

Load rejection occurs when the distribution grid fails to accept electrical load from the turbine-generator system. After the load is rejected by the grid, there is no external load on the turbine-generator unit and the speed of the runner increases rapidly. This can be catastrophic if immediate steps are not taken to slow and stop the system. To keep the speed rise within an acceptable limit, the wicket gates must close quickly and this may result in high (followed by low) hydraulic transient pressures in the penstock. Since load rejection usually results in the most severe transient pressures, it typically governs the design of surge control equipment.

During load rejection, the generation of electrical power by the turbine-generator unit should decrease to zero as quickly as possible to limit the speed rise of the unit. To accomplish this, the wicket gates close gradually in order to reduce flow. In a real turbine a governor would control the wicket gate closure rate, however the turbine governor is not modeled explicitly in HAMMER and the user controls the rate of wicket gate closure.

If the power generated by the water flowing through the turbine is greater than the electrical load, then the turbine will speed up; if the electrical load is greater, the turbine will slow down.

Note: Load and gate position are entered in different parameter tables in HAMMER because they may not use the same time interval. HAMMER interpolates automatically as required.

Instant Load Rejection

Instant Load Rejection is similar to the Load Rejection case, except the electrical load on the turbine drops instantaneously to zero (i.e. the turbine is disconnected from the generator).

During instant load rejection, the generation of electrical power by the turbine-generator unit should decrease to zero as quickly as possible to limit the speed rise of the unit. To accomplish this, the wicket gates close gradually in order to reduce flow. In a real turbine a governor would control the wicket gate closure rate, however the turbine governor is not modeled explicitly in HAMMER and the user controls the rate of wicket gate closure.

Load Acceptance

Full load acceptance occurs when the turbine-generator unit is connected to the electrical grid. Transient pressures generated during full load acceptance can be significant but they are usually less severe than those resulting from full load rejection.

HAMMER assumes the turbine initially operates at no-load speed (NLS), and the turbine generates no electrical power. When the transient simulation begins, HAMMER assumes the electrical grid is connected to the output terminal of the generator and wicket gates have to be open as quickly as possible to meet the power demand, all without causing excessive pressure in the penstock.

Note that in this case, HAMMER assumes the turbine governor is ‘perfect.’ In other words the power produced by the turbine always equals the electrical load. Therefore the user doesn't need to enter an electrical load, just a curve of wicket gate position versus time, and the turbine's rated flow and head. Under the Load Acceptance case the turbine will always operate at its rated (or synchronous) speed.

When using Load Acceptance, you must enter the Flow (Rated) and Head (Rated) for the turbine. The transient solver needs these values into order to use the four-quadrant curve. If the turbine was open, these values would be obtained by simply computing the initial conditions. Obviously, when the turbine is closed, the computed values will for the rated flow and rated head will be zero, which will not identify the appropriate four-quadrant curve.

To find the Flow (Rated) and Head (Rated), it is recommended to first set the status of the turbine to Open and compute the initial conditions. Note the Flow and Head results for the turbine and enter this for Flow (Rated) and Head (Rated). Set the turbine to Closed again and compute initial conditions and the transient analysis. The correct four-quadrant curve should now be used.

Load Variation

Load variation on the turbine-generator unit can occur due to the diurnal changes in electricity demand in the distribution grid. During load variation, the governor controls the wicket gate opening to adjust flow through the turbine so that the unit can match the electrical demand. The water column in the penstock and conduit system accelerates or decelerates, resulting in pressure fluctuations.

The transient pressures that occur during general load variation may not be significant from a hydraulic design perspective since they are often lower than the pressure generated during a full load rejection or emergency shutdown.

At steady-state, the turbine-generator system usually runs at full load with the wicket gates 100% open. The amount of electricity produced by the system depends on the flow through the wicket gates. A decrease in electrical load requires a reduction in the wicket gate opening to adjust the flow.

Note that in this case, like in the case of the Load Acceptance operating case, HAMMER assumes the turbine governor is ‘perfect.’ Under the Load Variation case the turbine will always operates at its rated (or synchronous) speed.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

Protective Equipment FAQ

General HAMMER V8i FAQ

External Links

Water and Wastewater Forum

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

thanks Akshaya,

it's ok

giancarlo

Document Information

Document Type: TechNote 

Product(s):Bentley HAMMER

Version(s):V8i

Original Author:Jesse Dringoli, Bentley Technical Support Group

Overview

This technote explains how the Air Valve element works and its typical application in HAMMER V8i. It also provides an example model file for demonstration purposes. 

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 subatmospheric 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:  

1. Pressure below atmospheric - air valve is open and acts to maintain pressure to 0 on the upstream end.
2. Pressure above atmospheric - air valve is closed and acts as any junction node.

The presence of air in the line limits subatmospheric 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 subatmospheric 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, subatmospheric 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 depecits 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. 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 is the recommended method, as it is easier to manage and will account for headloss in the lateral pipe, which can sometimes be significant.

1. 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.

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 propogate 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: 

1. 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 neighbour "J-3 ", the elevation, level and volume are: 137.000 135.361 0.966

1. 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 ~340m/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 forcemains 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 timesteps. so, if the calculation timestep was 0.01 seconds, that means you will see these results at a 0.1second 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 currently the "free air" flow rate, meaning the volumetric rate of air flow at atmospheric pressure conditions. The air flow inside the pipeline will be different 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 partfull 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:  

1. Air inflow through the inflow orifice diameter
2. 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 (ie 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:  

1. Air Inflow
2. Air Outflow through the large orifice 
3. 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 subatmospheric 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.

Example Model

Click to Download

Note: the above model is for example purposes only. It can be opened in version 08.11.00.30 and above and you can find additional information under File > Project Properties.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

Protective Equipment FAQ

General HAMMER V8i FAQ

External Links

Water and Wastewater Forum

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

ARI Air Valves (contains many animations)

Thank you, Terry, Mark, and Bentley, for helping me to re-obtain the model- You saved my day!

(Thank you, Akshaya, for trying to recover the model.)

Thank you all for helping me in timely manner.

I'm looking forward to hearing from you, Mark.

Thanks again.

Yoko

The nominal head and flow represent the normal operating point for the pump. In this case, it sounds like that would be having both pumps on. So, I would run the initial conditions with both pumps on and base the nominal head and flow from that (89 lps @ 52 m each, assuming same pump curve, same losses)

Behind the scenes, they are used in conjunction with the shape of the four-quadrant characteristic curves (selected by way of the Specific Speed) to construct the characteristic curve used for the pump during the transient simulation. It is expected that the nominal operating point is at or near the best efficiency point, otherwise the results may be skewed.

In a case where a pump is turned on in the initial conditions, it uses the initial conditions operating point for the nominal head and flow. When the pump is off, it is unknown, so the user must enter it.

Thanks Wayne, similarly I hope they aren't working you too hard mate!   Early days with the SS4 release, but a big thumbs up to the devs on both the SQLite and new Alternative Management schema.........much bigger and more versatile models now possible with very little overhead penalties! ;-)

Yes, similarly by late yesterday I had reached that conclusion that it must be that the Hydrant curve is a hybrid of calculated/inferred results.  You're right, I eventually eliminated specific modelling elements as being the cause and started concentrating on playing with the general calc engine options, EPS and making different elements active/inactive to see what would change the convergence "path" that the Gradient algorithm/solver followed to settle on the "calculated" points in the curve and seeing that it did, in fact, change the results to give varying degrees of accuracy.

Thanks for giving the run down on how the Hydrant Curves derive, knowing that now we should be able to modify our models/procedures to work around it (I hope). My counter-points to think about would be:

1.  In this particular model, at 5 L/s, Hydrant Curve 1 has a 3 metre calculated pressure error.   That's a lot.   A general purpose modeller would probably expect the Hydrant Curve conformance to a manual run to be quite a bit tighter than that.

2.  Our group uses Hydrant Curve results as direct output to our Hydraulic Modelling Advice service to external hydraulic consultants.  This particular Model/Junction and Hydrant Curve is the basis for a hydraulic report issued to a hydraulic consultant designing a new 5-20 L/s building fire system fed from this water main.   Obviously it's important that we try to get as accurate and consistent modelling results as possible.

3.  The current version of the WaterGems manual infers the Hydrant Curve engine will actually calculate the pressure at each flow point on the curve.  It also recommends users use a high nominal flow, and as large as possible flow step intervals.   However, doing the opposite (use a low nominal flow rate and/or finer flow steps) seems like it will generally yield more accurate results in getting the Hydrant Curve engine to do more actual calculations.

4.  Having the junction demands overridden in the Hydrant Curve instead of being additive can lead to some traps for GP modellers.   In the vast majority of cases, not such an issue as the distributed load from properties across the junctions usually means little reduction in the base load from doing a hydrant curve on one junction with demands.  However, there are a minority of junctions that..........through coincidence.........were selected as the most representative demand point for eg. A major industrial complex, or shopping centre etc. with a point load that significantly contributes the the zone's background demands.   If in creating a hydraulic fire flow/pressure report for someone, if the modellor inadvertantly selects the same junction for a Hydrant Curve as being representative as the connection point for another property's fire service, then he/she will accidentally remove a significant portion of the background demand and not get a true result of available fire flow/pressure.

5.  Ironically, I strongly discourage our team from using Hydrant Curves in EPS runs (even though the software can do it) and only in Steady State.  In general engineering practice the use of the tool is to predict the minimum available fire flows/pressures that can occur.   In a "real-world" system, it is very difficult to make EPS runs give you a "true" potential minimum system design pressure as the EPS simulation is controlling the boundary conditions (tank levels, pump/valve status etc.).  Instead we get our team to directly specify the boundary conditions in Steady State for fire-flow analysis, what the assumed tank levels should be, pump status(es), valve settings etc. that will be the operational condition with the lowest system pressures.

Have a good one mate and thanks again your usual detailed insight!

Dear Mal;

thanks a lot for your response.

Sayed Ali

Loy,

AQUIS is one software with certain data structure and WaterGEMS is another with a different data structure hence there is no direct way to import or export data either way.

To my understanding AQUIS supports exporting to EPANET file format. I would say this is the best, fastest, easiest way to go. Export out to EPANET file format, open the file in EPANET, Save As to a different name and then import to WaterGEMS from File > Import > EPANET. (Opening in EPANET and saving helps to clear a few things so it's good to do)

If AQUIS does not support exporting to EPANET (for whatever reason) and if you have access to AQUIS software then I assume, you can export your features (elements, it's data) to shapefiles. Export or copy/paste the tabular data like pump curve, demand pattern to spreadsheet software like MS Excel. Once you have data in shapefile, dxf, Excel etc, you can use ModelBuilder (Tools > ModelBuilder) to Import your data to a Blank model (or an existing model). These link help you understand how ModelBuilder works.
http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/2821.aspx
http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/3070.aspx 
http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/updating-a-model-using-model-builder-tn.aspx

Now for any reason you don't have access to the AQUIS software then it really depends on file itself. If the AQUIS file is not a binary file then try to open it with some suitable application and may be you can export/copy data to files like shapefile, xls etc so that later you can use ModelBuilder.

HTH

Document Information

Document Type: TechNote 

Product(s):Bentley HAMMER

Version(s):V8i

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

1. 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. 
2. 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

1. 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.
2. 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*v²/2g, 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. Of course 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)".
3. Transients initiated by an 'inrush' event. When a pump turns back on in a sewer force main, it may expell 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.
4. 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

Click to Download

Note: the above model is for example purposes only. It can be opened in version 08.11.00.30 and above and you can find additional information under File > Project Properties.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

Protective Equipment FAQ

General HAMMER V8i FAQ

External Links

Water and Wastewater Forum

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

I added a few sentences to the referenced D2A technote to help clarify for future users.

As Mal mentioned, the pressure/flow relationship that you establish is used in both the initial conditions as well as the transient simulation. It is certainly possible for it to have a more significant impact on the transient response compared the steady state response. For instance when your pump is on during the initial conditions, adjusting the typical flow and pressure drop fields may not have a large impact (though, it depends on the network configuration, scale and values that you enter). If you then simulate an emergency shut down of that pump during the transient simulation, the D2A might be 'exercised' in more unstable ways (interaction with wave reflection, pressure becoming subatmospheric and air pocket forming, etc) in which case adjusting those values could have a larger impact on the resulting pressure envelope.

Thanks,  I actually figured it out about 15 min ago but it wouldn't let me delete the thread or reply to my own post.  I had created a custom query Physical_PipeMaterial = 'Ductile Iron' AND HMIActiveTopologyIsActive = True.

Overview

This TechNote describes the three basic methods of creating simple controls in your WaterCAD or WaterGEMS model. Assigning particular controls to a particular scenario is also described in the later part of the Technote. The first two methods apply only to WaterCAD V8i or WaterGEMS V8i, but the third method is similar in the V8 XM versions.

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).

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 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 button from left) and follow the steps shown in the images below.

1. Select the pump to which you want to assign a control.

1. Select the tank whose water level will dictate the pump status. Based on requirements you may pick other options also.

1. Provide the logical operator such as greater than '>' or less than '<' under "On Operator," as well as the ON HGL (Hydraulic Grade Line) of the tank. In the same fashion, provide the OFF conditions.

1. Click the Create button to create the necessary conditions /actions and the control in the Control dialog box. Please scroll to Control Set for further information.

Method 2: Create Conditions and Actions from Controls Tab 

This method allows you to create both conditions and actions in one place. 

1. Click the 'New' button.

1. Review the bottom part of the Controls tab, which now shows various buttons and dropdowns. The left portion is for defining Conditions, the middle portion is for defining Actions, and the right portion is for defining optional ELSE Actions. The Conditions and Actions available in the list boxes in this area are filtered based on the elements you selected in the dropdowns. Selecting "<All>" in the dropdown will show all controls.

1. 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.

1. Follow the steps in the image below to create an Action for your condition. Again, the actions displayed are specific to your model.

1. After creating the conditions and actions, the Control dialog 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.

1. To create a condition in the Conditions tab, follow the steps in the image below.

1. Next, create and Action in the Actions tab by following the steps in the image below.

1. 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.

1. To create a control set, on the Control Sets tab, click the New button (see "1" in image below). A dialog will appear.
2. To include a control in your control set, select the control from the list of available items on the left, and use the right arrow button ("2" in the image below) to add it to the list of selected items on the right. Repeat this process until all of the desired controls are in the selected items list, and then click OK.

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.

1. 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).
2. Click the down arrow ("2"), select the desired control set ("3"), and then click Close ("4") to save your changes.

1. 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 most probably the control you created is not assigned to the control set being utilized by the current Operational Alternative.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs 

Water and Wastewater Forum

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Overview

The purpose of this technote is to briefly review the methodology for setting up a formula-based User Data Extension. Additional information can be found in the Help section for the program.

Background

User Data Extensions (UDX) have been a feature available in the water and waterwater products for some time. With the release of SELECTseries 2 builds of the software, a new Formula field was added to give extra flexibility to the user. This feature will allow the user to calculate results that the programs might not otherwise generate and display these results in the element properties or FlexTables.

General Information on User Data Extensions

User Data Extensions allow the user to create new fields for use in reporting, graphing, or data analysis. For example, you can add a field for keeping track of the date of installation for an element or the type of area serviced by a particular element.

The UDX dialog can be accessed directly by going to Tools > User Data Extensions or by selecting the UDX icon from the toolbar.

Selecting either of these will open the User Data Extension dialog.

There are a number of data types available. These include integers, real (or any fraction decimal number), text, date/time, boolean (true or false), and formula.

There is a label field to allow the user to give the UDX a unique name so that it can be easily viewed in the element properties or FlexTables. With real and formula UDX fields, the user must also enter Dimension, Storage Unit, and Numeric Formatter.

To create a UDX, highlight the element and select the New icon. The section on the right will fill in with default data. As this technote is related to formula-based User Data Extensions, change the Data Type to “Real (Formula)”. When this is completed, the Units section will appear. Enter the appropriate Dimension, Storage Unit, and Numeric Formatter for analysis you will be conducting. You should also change the label to something recognizable for the analysis. Once you have done, select Okay.

Note: Once you select Okay, some fields, such as Data Type, Dimension, and Storage Unit, cannot be changed or edited. The formula itself can still be edited though.

Formula-based User Data Extensions

The water and wastewater programs give a wide range of results that are generated after the computing a model. In most cases, these results are sufficient for analyzing and reporting on a system. However, there are times when a user may want to see a set of results that are not available in the program. It was for cases like this that the formula-based User Data Extension was developed.

Note: You cannot create a formula that uses properties from more than one element type.

The formula-based UDX allow the user to generate new results based on the data already calculated after computing the model. The basic steps below are universal, with only the element types and available properties differing depending on the product. The example below will be using WaterGEMS.

Let us say that you want to display the percentage of pressure head compared with the calculated hydraulic grade for the junctions in a WaterGEMS model. To begin, open the User Data Extension dialog. Create a new UDX by selecting the New icon at the top of the dialog. Change the label to something recognizable to these results and change the Data Type to “Real (Formula)”. Since the result will be a percentage, change the Dimension field to “Percent”, the Storage Unit to “%”, and Numeric Formatter to “Percent”.

Next, click in the Formula cell. An ellipsis (...) will appear.

Click this to open the Formula dialog.

In the upper left is a list of all available properties for the junctions. The list is in alphabetical order. The same properties are accessible through the “>” icon above the list. In the upper right are all of the mathematical functions available. The empty window in the lower part for the dialog is where the formula is built.

To move a property to the lower window, simply doubleclick the name. It will then appear in the window. Note that the appearance is not the same as the property list; the window shows the Access database table name for that property. To include a simple math function, like multiplication or subtraction, click the corresponding button. For the geometric or trigonometric math functions, doubleclick the name to include in the formula.

In the example where we want the percentage of the pressure head compared with the calculated hydraulic grade, first select the “(“ icon. Next, find “Pressure Head (ft)” in the properties list and doubleclick. Next choose the divide icon, then the “Hydraulic Grade (ft)” property, and then the “)” icon. Since we want this as a percent multiply this by 100.

Once completed, select Okay to return to the User Data Extension dialog. Click Okay again to save the UDX.

Remember: many features, including the Data Type, Dimension, and Storage Unit, cannot be changed or edited after selecting okay.

Viewing Results

Since the results are saved as user data extensions, you can view the results in either the element properties or the FlexTables.

After computing the model, doubleclick on a junction to open the Properties dialog. Find the section “User Defined”. This is where the formula UDX will be located. Since the model was computed, you should see the results.

To see the results in the FlexTables, open the element FlexTable (through View > FlexTables, for instance). With the FlexTable open, select the Edit icon. Scroll through the list on the left to find the UDX field. The list is in alphabetical order. Select the Add button and it now appear in the list on the right. Click Okay to return to the FlexTable. The statistical analysis results should now be available.

This data is also available for results presentation in graphs and data tables.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

External Links

Water and Wastewater Forum

Bentley Technical Support KnowledgeBase

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Overview

The purpose of this technote is to address the engine compatibility modes and new calculation options that have been added to Bentley WaterCAD/WaterGEMS/Hammer V8i Select Series 2 (SS2). Additional information may be found in the Help menu of each program.

Background

The change in the Bentley products to include the upgraded EPANET engine was designed so that the user can turn it off and is even disabled (by default) for existing models. Only new models will have the new behavior turned on (by default). All changes to the user interface are fairly minor and are purely controlled at the calculation options level.

The new user interface includes 4 new calculation options added under the ‘Hydraulics’ section of the Calculation Options dialog. Each option will be covered in detail below.

Engine Compatibility Modes

The ‘Engine Compatibility’ Calculation option in V8i SS2 replaces the ‘Use EPANET Compatible Results?’ option, as seen in V8i SS1. In previous versions of WaterCAD/GEMS/Hammer (prior to V8i SS2), there was a ‘Use EPANET Compatible Results?’ option. When set to true, you were using EPANET 2.00.10. The software has been extended to include compatibility modes, which now includes the old behavior based on EPANET 2.00.10, as well as the revised engine changes in EPANET 2.00.12.

There are now 4 engine compatibility modes.  

WaterGEMS 2.00.12 – this engine is based on the EPANET 2.00.12 engine, including Bentley modifications. Choose this option to get all the latest engine improvements and fixes made by Bentley and an engine mode that is based upon EPANET 2.00.12.This is the default for new models. Meaning any new model created in WaterGEMS V8i SS2 will default to the ‘WaterGEMS 2.00.12’ engine compatibility option.

WaterGEMS 2.00.10 – this engine is based on the EPANET 2.00.10 engine, including Bentley modifications. Choose this option to maintain compatibility with previous versions of WaterGEMS (meaning V8i SS1 and earlier) where the computational engine is based upon EPANET 2.00.10. This is the default for upgraded (existing) models. Note: the ‘Use Linear Interpolation for Multi Point Pumps?’ option is FALSE by default in existing models as well. These default options are designed to make the transition smoother for users.

IF an existing model has ‘Enable EPANET Calculation Results?’ set to TRUE, then the ‘Use Linear Interpolation for Multi Point Pumps?’ option is hidden (as it will not apply).

EPANET 2.00.12 – models run using this engine have results that are compatible with EPANET 2.00.12. If choosing a version of the EPANET engine, any enhancements, calculation corrections, bug fixes, etc. made by Bentley will be disabled to match the specific EPANET version results. Imported EPANET models will default to the appropriate EPANET version.

EPANET 2.00.10 – models run using this engine have results that are compatible with EPANET 2.00.10.

Note: The following engine compatibility matrix is included in the WaterGEMS/WaterCAD/Hammer V8i Select Series 2 Help file (Modeling Capabilities>Calculation Options>Engine Compatibility Calculation Option).

Additional Calculation Options

If the user has selected either the WaterGEMS 2.00.12 or EPANET 2.00.12 versions, there are three additional calculation options now available. These options are the same for both the EPANET and WaterGEMS 2.00.12 engines.

Convergence Check Frequency – The Convergence Check Frequency option sets the number of solution trials that pass during the hydraulic balancing before the status of pumps, check valves, flow control valves (FCV) and pipes connected to tanks are once again updated. The default value is 2 (meaning that status checks are made every other trial). A value equal to the maximum number of trials would mean that status checks are made only after a system has converged. The frequency of status checks on pressure reducing (PRV) and pressure sustaining valves (PSV) is determined by the Damping Factor option.

Convergence Check Cutoff – The Convergence Check Cutoff option is the number of solution trials after which periodic status checks on pumps, check valves, flow control valves (FCV) and pipes connected to tanks are discontinued. Instead, a status check is made only after convergence is achieved. The default value is 10 (after 10 trials, instead of checking status every “convergence Check Frequency” trials, the status is only checked after convergence is achieved).

Damping Limit – The Damping Limit is the accuracy value at which solution damping and status checks on PRVs and PSVs should begin. Damping limits all flow changes to 60% of what they would otherwise be as future trials unfold. The default value is 0 (zero), which indicates that no damping should be used and that status checks on control valves are made at every iteration. Damping might be needed on networks that have trouble converging. A limit of 0.01 is suggested (relative to the default calculation hydraulic accuracy of 0.001).

Additional Post Calculation Warnings

Post Calculation warnings have been added to advise a user if they are using any features that are NOT supported by EPANET when they are running with one of the two EPANET compatibility settings. These are POST calculation and will not be displayed when validating a model (i.e. these calculation warnings are only displayed when computing a model.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

[[General WaterGEMS V8 FAQ|General WaterGEMS V8 FAQ]]  

External Links

Water and Wastewater Forums

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

How do I fix "input error: 299hm" error?

First, close your software. Then, Browse to your program's folder (for example, C:\program files\haestad\wtrc\ or  C:\program files\Bentley\WaterGEMS) and find license.ini (you may need to go to tools>folder options>view and uncheck "hide extensions for known file types" so you can see the .ini extension). You may also need to go to view>details and click the "name" column heading to sort in alphabetical order by name, then scroll down to find license.ini. Once you have located the file, make a copy of it by rightclicking and going to "copy". Now, browse to the root of your hard drive (C:\ in most cases) and paste the copy of license.ini there. Make sure you click on a blank space, rightclick, then go to "paste".

How do I integrate WaterGEMS 3.0 with ArcGIS 9.2?

ArcGIS 9.2 is not supported by WaterGEMS 3.0 and may cause Arcmap to crash. In order to properly integrate, you will need to upgrade to WaterGEMS V8 XM.
If you would like to stay with WaterGEMS 3.0, then to fix your arcmap, you must unregister some WaterGEMS components. Please follow these steps:
Save the following file to your WaterGEMS install folder (the default is C:\Program Files\Bentley\Wtrg\) and run it from there.
ftp://ftp.bentley.com/pub/knowledgebase/attachments/WtrgUnReg1.bat
Save the following file to your WaterGEMS extensions folder (the default is C:\Program Files\Bentley\Wtrg\extensions\) and run it from there.
ftp://ftp.bentley.com/pub/knowledgebase/attachments/WtrgUnReg2.bat
These 2 batch files will unregister the WaterGEMS COM components related to ArcGIS.

How to import WaterGEM 3.0 or WaterCAD 7.0 files to WaterCAD V8 XM or V8i standalone while preserving the old presentation settings?

 There are several ways of converting old WaterGEMS/WaterCAD files to WaterCAD v8 XM. If you need to also export the presentation setting for the older file please follow the instructions below:

Prerequisites:

 A) You have to have version 7 and 8 both installed on the same machine.

b)  Version 7 must be installed prior to version 8 in order to have this functionality active.  

Instructions:

1.  Open WaterCAD/WaterGEMS file in version 7 or Version 3.0.  Go to File > Export > presentation settings and save the file.  

2.  Then open up WaterCAD/WaterGEMS v8 XM or V8i and then go to File > Import > GEMS database.

3. Browse to and open the .MDB file that you saved from the old version. This should bring all the color codings and annotations from the old version to this new version.

If there is no old version available, you can always take the second step above and recreate all the color codings and annotations. 

How do I import Cybernet project in WaterGEMS 3.0/WaterCAD 7? 

In order to open Cybernet project in WaterGEMS/WaterCAD, you must have .inp file type.  

Go to File > Import > Network and select cybernet 2.0 and browse to cybernet file and open it.  Once you open this file in version 3.0 or version 7 of WaterCAD, you just need to save it to see real conversion.  After saving it in WaterGEMS/WaterCAD go back to the project directory, you should now see a .wcd and .mdb files converted from Cybernet. 

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

What is the difference between WaterCAD and WaterGEMS?

WaterGEMS allows you work inside of ArcGIS and includes Darwin Calibrator, Darwin Designer and Skelebrator. WaterCAD cannot be integrated with ArcGIS and the Calibrator, Designer and Skelebrator features are optional, at an extra cost. Beyond this, equal versions (ie WaterCAD 08.11.00.30 and WaterGEMS 08.11.00.30) are identical.

How can I find my registration / license information and version / build number?  

Inside the program, this is found under Help > About WaterGEMS (or Help > About WaterCAD) 

Where do I go to change the analysis type, timestep, duration, etc?

In previous versions (7.0 and below), this was done in the "GO" window. In V8, this is done in the calculation options.

o access the calculation options, click the Analysis menu and choose "calculation options". Then, double click your calculation option set to see the properties.

 To choose the analysis type, such as steady state, EPS, water age, select the appropriate choice for the "analysis type" field. For steady state and EPS, select "hydraulics only" and then select the appropriate choice for the "time analysis type". Once EPS, Age, Trace or constituent is selected, you can then choose the duration, timestep, etc.

After you configure the calcuation options, make sure your calculation option set is selected for the appropriate scenario. To do this, go to Analysis > Scenarios, double click the scenario in question and make sure the correct calculation option set is seleced. Multiple scenarios can use/reference the same calculation option set and multiple calculation option sets can be created. For example, you can duplicate an EPS calculation option set in the calculation options manager, select a different duration and use that in a child scenario to analyze a longer period, while keeping the old scenario intact.

How can I reset or change the numbering of the element labels?  

 Go to Tools > Options > Labeling. For the element type in question, you can change the number of the label of the next element that will be layed out. You can also change the prefix, digits, suffix and increment. Click the "Reset" button to reset the "next" number based on how many of that element exist in the model.

When I lay out a pipe, it always initially comes in as 6". Can I change the default values of the properties of new elements? 

Yes, go to View > Prototypes. Create a new prototype, double click it and change the properties to what you desire. The prototype marked as current will designate the properties of newly laid out elements. 

My annotation/symbols are huge or take up the entire drawing area, as one big blob. What's going on? 

Your drawing style may be set to GIS. GIS drawing style is zoom independent, so the annotations/symbol sizes will stay the same size no matter how far in or out you zoom. To change to CAD drawing style (scaled), click the drawing style button at the top of the Element Symbology manager (Tools > Element Symbology) and choose "CAD". You can also adjust the text and symbol sizes under Tools > Options > Drawing. 

What is the difference between the junction and hydrant elements? 

The hydrant element is the same as the junction; you can enter the elevation and demand and connect pipes to it. However, the hydrant allows you to model the lateral pipe without actually drawing it. So, you could place the hydrant on the main water line, choose "true" for "include lateral loss" and enter the length/diameter. Otherwise, with a junction, you would have to draw an extra pipe out from the main line to model the lateral, which counts toward your license's pipe limit and can clutter your pipe report.

You can also easily open/close fire hydrants with the hydrant element. You can choose "open" or "closed" as the hydrant status to control whether or not the entered emitter coefficient is applied (which in turn would be used to compute a demand.) Otherwise, with a junction, when you enter an emitter coefficient, the program will always use it.

Lastly, the hydrant symbol appears as a hydrant and you can organize your hydrants better, instead of having them all look the same and all appear in the same report. 

How do I global edit demands? 

This is done in the Demand Control Center. Go to Tools > Demand Control Center. You can right click on the "base flow" field and choose to global edit. Changes made in the demand control center apply to the demand alternative assigned to the current/active scenario. Alternatively, you can multiply your base demands without altering them by using the "demand adjustments" option in you calculation options.

Which demands are used for a steady state simulation?  

By default, a steady state simulation uses the base demands entered at node elements. Demand patterns are not considered. 

How can I filter a FlexTable based on a selection set (to only show elements in that set)?

Double click your selection set to select the elements, then right click anywhere in the drawing and choose "edit group". Double click the desired flextable and it will filter to only show elements contained in that selection set. You can also right click on a table in the flextables manager and choose "open on selection", after double clicking the selection set. 

Why do I sometimes see a negative flow through a pipe?  

A negative flow value indicates orientation of the flow with regard to the orientation of the pipe itself. The flow arrow symbol on the pipe in the plan view always indicates the direction of flow, and the orientation of the pipe itself is indicated by the "start node" and "Stop node" fields in the pipe properties.

If water is flowing from the "start node" to the "stop node", the flow arrow will point that way and the flow result value will be positive. If water is flowing from the "stop node" to the "Start node", the flow arrow will point that way and the flow result value will be negative. Basically the absolute value of the flow result field is always indicative of the flow rate through that pipe, but a negative sign will be added to indicate direction.

The reason why this behavior occurs is because in some systems, flow can often reverse direction over the course of a day. Showing the negative sign in front of the calculated flow value is one way for the user to distinguish the current direction of flow. In general, it is recommended that you lay out pipes in the direction that water will generally/usually be flowing, so that the calculated flows will be positive for most pipes. If you need to reverse the orientation of the pipe, you can do so by using the "node reversal" field at the top of the pipe properties.

Note that you can see the absolute value of flow through the pipe by looking at the "flow (absolute)" field in your pipe flextable. As you might expect, this basically removes the negative sign from the value seen in the "flow" result field.

How can I remove/disable pipe flow arrows? 

Double click "pipe" in the element symbology manager (View > Element Symbology) and the properties window will populate with some options, including "show flow arrows?" Select "False" for this option to turn them off. In some cases, you may need to refresh the drawing by pressing F5. 

Why do I keep getting prompted to compact the database when I open my model? What does this mean? 

When you delete an item in your model, it isn't fully removed from the database (mainly due to the undo feature.) The "compact database" function will remove these old entries and save on disk space. Under Tools > Options > Global, you can choose to have the program automatically compact the database after open the model a certain number of times. This is why you encounter that prompt. 

Why do I see residual mouse trails (visual artifacts) left behind when moving things in the drawing pane?  

Sometimes you may see leftover "ghost" trails remaining in the drawing pane when zooming, drawing a box around elements or connecting a pipe. This is a common issue with certain video cards / graphics hardware.

If you are using Windows XP or Windows 2000, try the following:
- Turn down video acceleration by going to start > control panel > display > settings > advanced > troubleshooting
- Switch the buffering and veritical synchronization settings in your video card`s advanced options
- Update your video card drivers from the manufacturer`s website

If you are using Windows Vista, please try editing your video card`s setting and enable Anti-aliasing (e.g. 2x, 4x, etc as
opposed to None or Application Controlled).

If this does not help and you have the V8 XM generation version of the software (example: StormCAD V8 XM, WaterGEMS V8 XM), then
try these steps:
1) Make sure the program is closed and then open up windows explorer
2) Browse to C:\Documents and Settings\\Application Data\Bentley\\8\ (where "" is the name of
the user that you are logged in as and "" is the program you are experiencing this problem in.

NOTE: If you have Windows Vista, this file is located under: C:\Users\<username>\AppData\Roaming\Bentley\<software>\8\

3) Right click on Haestad.Framework.Application.GlobalUserOptions.xml and choose to edit. It should open in Notepad.
4) Locate the entry near the bottom called "AllowPartialRedraw="true"". Change "true" to "false", save and close the file.
5) Reopen the program and try the zoom tool

Note that you may need to have the latest build of the V8 XM generation for this option to be available.
Also note that if you have a V8i edition product (08.11.XX.XX) then you should have this option under Tools > Options >
Global - "use accelerated redraw". Simply toggle this to resolve the issue.

My properties window doesn't appear when I try to open it. Where did it go? 

This issue can also happen to other windows/tools, such as FlexTables. Sometimes a window may have been docked/moved in such a way that it is now hidden from view, or outside the bounds of your desktop. If you are unable to locate the window, you can reset the default window locations using View > Reset Workspace. 

How can I open a model created in an older version (7.0 and below) and retain its presentation settings?

To open the model, you must select "database files" from the "files of type" dropdown when opening a model, and browse to the .mdb file associated with the older model. Since the presentation settings (color coding, annotation, etc) are stored in the .wcd file, they will not be imported by default. In most cases, this is fine, and you can skip the prompt for presentation settings, since V8 XM includes more robust options for color coding and annotation. 

If you would like to retain the presentation settings, you must export them from version 7 first, by open the model in version 7 and going to File > Export > V8 XM Presentation Settings. Note however that this menu item will not be present unless the exact build of version 7 is 07.00.061.00 and WaterGEMS/CAD V8 XM must have been installed second, since the installation of V8 XM is what places that menu item in V7.

For very old models, created in Version 5 or below, you will only have a .wcd. So, you'll need to first open the model in V7 (which can open .wcd files) and save it, in order to create the .mdb file that you can import into V8.

A user with an older version is not able to open a project I sent them. Can a model be 'saved down' to an earlier version? 

A model cannot be saved 'down' and most versions are not forwards compatible. For example, if you've created and saved a model in WaterGEMS V8 XM, a user with WaterGEMS V7.0 will not be able to open it. V8 XM has introduced many new element types and features, which cannot be interpreted by the older version.

Also, there have been numerous service packs of V8, many of which are also not forward compatible. For example, build 08.09.165.00 can open models saved in 08.09.165.12, but cannot open models saved in 08.09.400.34+. The reason is because the structure of the database files used to store model data (the 'schema') was changed to accomodate improvements and new features. The older versions cannot interpret the new database format.

If the user is not able to upgrade to your version, the best workaround would be to export the model to the standard EPANET 2.0 format (File > Export > EPANET). This format can be opened in most older version. For example in V7.0, you can import EPANET via File > Import > Network. Another workaround would be to export the model to shapefiles and then import those shapefiles with the older version.

Can I restore a backup of my projects? 

Yes. Every time you save your model, the program automatically saves backup copies of the last model revision. To restore a backup copy, close the program and open the folder that the model is saved to. In this folder, you will see many files. Every WaterGEMS/CAD model file is comprised of 3 main files, with extensions of .wtg, .wtg.mdb and .wtg.dwh. The backups of these files have extensions of .wtg.##.bak, .wtg.mdb.##.bak and .wtg.dwh.##.bak. (where "##" is a number, corresponding to the backup level). For example, if you saved your model as Model1.wtg, the backup files will be Model1.wtg.01.bak, Model1.wtg.mdb.01.bak and Model1.wtg.dwh.01.bak. Sinmply copy these 3 files to another folder and remove the ".01.bak" extensions, leaving the extensions as .wtg., .wtg.mdb and .wtg.dwh.

To configure the number of backup revisions, go to Tools > Options. In the "Global" tab, you can choose how many backup "levels". For example, if you set this to '2', then backups for the last two saved model revisions will be retained. Otherwise, if you keep this at the default of '1', the previous backup will be overwritten when you save the model.

Why are there so many extra element types, such as surge tank, rupture disk, Periodic head-flow?

These elements were added in version 08.09.400.34 to support the new version of our transient simulation product, HAMMER. Models developed in WaterGEMS or WaterCAD can be directly opened in HAMMER. So, the user can lay out their transient related elements in their WaterGEMS/CAD hydraulic model, open the model in HAMMER and be ready to perform a transient simulation. The user can then re-open that model back in WaterGEMS if they'd like, without losing information on the transient elements. The following is a list of transient elements and how they are handled during a WaterGEMS/CAD steady state or EPS simulation:

• Periodic Head/Flow Element using Head: A reservoir with the HGL determined from the sinusoidal wave properties, or from the head pattern. Only the initial (time zero) HGL is applied so that the steady state analysis will correspond to the transient initial conditions.

• Periodic Head/Flow Element using Flow: A junction with demand determined from the sinusoidal wave properties, or from the flow pattern. Only the initial (time zero) flow is applied so that the steady state analysis will correspond to the transient initial conditions.

• Air Valve: If the "Treat Air Valve as Junction" property is set to True the Air Valve is loaded as a junction with no demand. If the "Treat Air Valve as Junction" property is set to False, the air valve is loaded such that it opens the system to atmosphere. This is most commonly used to simulate high points in pumped sewer systems, so the default behavior is to treat the air valve as a junction.

• Hydropneumatic Tank: A hydropneumatic tank is loaded as a normal tank with the properties of the tank being dictated by the tank calculation model that is used.

• Surge Valve: Junction with no Demand.

• Check Valve: Short Pipe with a Check Valve in line with the direction of flow.

• Rupture Disk: Junction with no demand.

• Discharge to Atmosphere: For the Orifice and Valve types this element is loaded as a junction with emitter coefficient determined by the flow and pressure drop properties. If either of these properties are invalid (<= 0) then no emitter coefficient is loaded. Furthermore, for the valve type if the valve is initially closed, no emitter coefficient is loaded. For the rating curve type this element is loaded as a reservoir connected to a GPV with rating curve used as the GPV headloss curve.

• Valve with linear area change: GPV with a headloss curve based on the valve's discharge coefficient.

• Turbine: GPV using the turbine's headloss curve.

• Orifice between pipes: GPV with a headloss curve calculated from the nominal head/flow loss using the orifice equation.

• Surge Tank: Without a check valve, this element is loaded as a tank. With a check valve this element is loaded as a Junction.

What does it mean when an element is "hydraulically disconnected"? 

This means that there is no open path for water to reach that element. It could be due to a closed pipe or mistake in the data input. 

What is the meaning of the notification "Valve cannot deliver flow", with regards to a Flow Control Valve (FCV)? 

This simply means that the flow through the valve is less than the setting that you entered, so it is inactive. Note that a FCV does not set the flow; it limits it.

If the flow through it is showing up as greater than the setting, then this could mean that the orientation of the valve is incorrect. Check the "downstream pipe" property of the FCV. This is due to the flow reported at the valve having a negative sign in front of it - an FCV will not limit negative flow, even though this just refers to the direction of flow.

What does the notification "pump cannot deliver desired head" mean? 

This means that the pump would have to add more head to the system than is specified in the shutoff head, in order to push the water up to the downstream junction. Basically, the pump cannot add enough head to be able to overcome the elevation. 

What does it mean when you encounter the message "network unbalanced"? 

This means that for a particular timestep, the program could not converge on a balanced solution within the maximum number of trials. Between calculation iterations, the program checks the relative change in flow, whose default value is 0.001. If it's below the "accuracy" value designated in the calculation options, the timestep is balanced or is said to have converged, else it tries another iteration. You can try increasing the "max trials" and/or "accuracy" value in the calculation options, but you should also closely check your data for mistakes. If this is an EPS simulation, you may get some clues as to what is happening by checking the status of your elements in the timestep before the unbalanced one. You can also open the .RPC file associated with your model using a text editor, such as NotePad, then check what status changes are occuring between trials. The .RPC file is an output file that's created upon computing your model and is found in the same location where you saved your model files. Typically, an unbalanced model is caused by problems with logical controls, valve settings (PRV, PSV, FCV setting and status), empty/full tanks or near-zero flows. First check if your data input is correct, then consider simplifying cases where the constraints are too "tight". Meaning, any time you have a control or dynamic element, (which can change status) the change it makes could in turn cause the hydraulics to be in a situation that causes another element to change status. That change could then in turn cause the opposite change to occur in another element, and so forth. Checking the element status changes during trials in the .RPC file will help you understand which elements may be running into this condition. Basically, you should make that sure your model is not too tightly controlled/constrained.

How can I find out what version a model was created in? 

The exact version of WaterGEMS/CAD that a model was last saved in is stored in the .wtg file. These are simply .xml files, so you can open them in a text editor such as Notepad. On the third line of text, the build number will be shown after "ProductVersionLastModified=". 

How do I import a CAD drawing? (DXF, DWG, DGN) 

This is done through the Modelbuilder tool, under the Tools menu. First, save it as a DXF. Select "CAD files" as the source in Modelbuilder and make sure to choose the "establish connectivity using spatial data" option as well as the "" key/label field. For more detailed steps see Importing A CAD Drawing In Bentley WaterGEMS 

How can I export my model to shapefiles? 

This is done using the export button in each element type's flextable. For example, to export your pipes to a polyline shapefile, go to View > Flextables > Pipe Table. Use the yellow edit button to add/remove/arrange the fields you'd like included in the shapefile, filter as needed and click the Export button at the top left corner. Select a location for your shapefile, click OK, specify labels for each column and click OK. If you'd like to export node elements to point shapefiles, open their respective flextable and do the same thing. 

When importing a DXF as a background, it does not show up in the model, even when pressing zoom extents. 

Since all layers will be displayed, this could be due to some extra elements being located far way from the main drawing. So, when you click the zoom extents button, the model will zoom very far out in order to display everything. It could also occur if your model is located in a different place (based on the X/Y.) Try going to View > Zoom > Zoom Center and zooming to a coordinate that you know is within the drawing. Also try saving and reopening the model.

When using the AutoCAD platform, should I use layers to change pipe color/thickness?

The preferred method would be to use the element symbology manager. For example, go to the WaterCAD/WaterGEMS menu, select "View" and then "element symbology..". You can use this tool to establish color coding for each individual element type and even for certain selection sets of elements. You can also change the pipe thickness in the properties window after double clicking the "Pipe" entry at the top of the Element Symbology manager. Since element symbology is so robust, there should be no need to use AutoCAD layers to handle your symbology.

When printing the model plan view, why do I see extra blank/white space? 

When printing the plan view, the program will fit the entire drawing pane to the paper size. So, if there is extra white space in the drawing pane, this will be included. If your model has an elongated shape, you will need to dock toolbars to the sides of the drawing pane and stretch the separators to manipulate the shape of the drawing pane, so that extra white space is not included. 

Note however that the aspect ratio will be retained, meaning it will not stretch the model. So, if you are trying to print a wide model on a 8.5X11 sheet of paper, extra white space will remain below the model, since the program will not stretch the model vertically. 

My controls aren't being followed. What's going on?

First, check if this is an EPS (extended period simulation) or steady state. If steady state, note that logical controls cannot be used and will be ignored. A control is designated as logical by the "evaluate as simple control?" check box, in the controls tab of the Controls editor window.

If the model is EPS or if simple controls are used, then you should check your control sets. In the Controls editor window, click the control sets tab and ensure that the control(s) in question are included in your control set. Also, go to Analysis > Alternatives, expand the Operational alternatives, double click the one used in the current scenario (designated by the red check mark) and ensure that the correct control set is being used.

What does the "evaluate as simple control" checkbox mean? What is the difference between simple and logical controls? 

Simple controls are used in both steady state and EPS and support only basic "IF A THEN B" conditions/actions. Logical controls are only used in EPS (not supported in steady state) and support more complex statements, such as "IF A THEN C AND D ELSE E". There are also slight differences in the way the controls are checked and applied. 

How can I import demand information from a spreadsheet? 

As long as your spreadsheet contains a label field, with labels that match your model elements, you can do this with Modelbuilder. Choose "Excel 8.0" as the source type and make sure to use the "Junction - demand collection" table type. For more information, see this Technote.

When importing a submodel, why do my new elements turn inactive and old elements change their attributes to the defaults in the new scenarios? 

This will occur if your current scenario is one that did not exist in the model that the submodel was created from. Basically there is no way for the program to know which physical/topology information should be used for the new elements, in a scenario that was not present in the submodel. So, the default values are used for those new elements in those existing scenarios (the default value for "is active? is "false"). If you switch your active scenario to one from the submodel's original model, the submodel elements will become active, but then the elements from the original model will become inactive, for the same reason.

When importing a submodel, you should first make sure the structure (parent/child relationship/hierarchy) and labels for both the alternatives and scenarios match, between the source and destination model. Otherwise, the above difficulties will occur, due to the program creating new alternatives/scenarios. If all the scenario/alternative labels/structures match, then the program will know where to place all of the data (which is stored in the alternatives) from the submodel, so the physical/topology information will be present in your scenarios.

What is criticality? What is the purpose of the "criticality" and "outage segment" subsections? 

Criticality is a unique and flexible tool to evaluate a water distribution system and identify the most critical elements. The user is allowed to shut down individual segments of the system and the results on system performance are determined. Rather than having to do this through the scenario manager, the user will be able to simulate a set of outages in a single run. This set can vary from a single element to each possible segment in a large system.

First, note that the program automatically figures out the segments in your model based on valves, and lists them with the elements that are included.

Outage segments - when you click on each segment listed in there, it highlights that segment in blue (in the drawing pane) and any downstream, disconnected segments in red. So if a particular segment that you click on would cause a downstream segment to be disconnected from a source when all it's bounding valves are closed, that disconnected segment shows up as red.

Criticality - when you click each segment in there, it will show you information on the demands that are not met when that segment's bounding valves are closed. For example, if the closure of a particular segment would cause half of the demands in the model to be disconnected, then when you click on that segment in the list, it will show you 50% as the shortfall. Note that the option "run hydraulic engine" exposes some additional constraints. For example, if you enter a pressure constraint of 20psi, then if there are any demand nodes whose pressure falls below 20psi when that segment is closed, then those demands are considered to be not satisfied, and the "shortfall" will be effected accordingly.

Why do I get a user notification about negative pressure at a pump?

This commonly occurs in cases where the user models the pump station (or connection to an existing system) using a reservoir and pump, with short pipe between them. Typically the same elevation is used for both the pump and reservoir nodes. Since the reservoir elevation defines the boundary hydraulic grade and since there will always be some amount of headloss through a pipe, this means that the hydraulic grade at the pump node location will be slightly below the physical elevation. The suction pressure of the pump is derived from the difference between the hydraulic grade and the physical elevation, so that is why the pressure ends up being negative.

You can simply ignore this informational message, but if you'd like to remove it, the solution is to simply raise the elevation of the reservoir by a small amount. Make sure the pipe has a very large diameter and smooth roughness coefficient, too (to minimize headlosses.)

If the upstream hydraulic grade or reservoir elevation is correct, then this negative pressure message is accurate. To better understand what is happening, create a profile of the hydraulic grade and physical elevation for this segment of piping - you will see that the hydraulic grade is below the pump elevation. If this is an existing system, you may need to check your NPSH to ensure that cavitation will not occur at the pump. You can also investigate ways to increase the hydraulic grade upstream of the pump.

When laying out new elements in WaterCAD/GEMS for AutoCAD, why do elements automatically go to certain layers instead of going to the current layer?

In version 7, there was a tool called "Element Properties" which could be uses to control which layer certain WaterCAD elements were automatically sent to. But this tool is no longer available in V8/V8i. If the model was created in version 7 and then opened in V8, the element properties designations may be retained.

To resolve this, you can start a new drawing, import WaterCAD model, re-set all the layers and other AutoCAD tools. It is recommended to lay out all the WaterCAD elements in layer 0.

Why are there 2 entries for the same alternative in the dropdown menu in the properties of a scenario? One with an "i" and one without it.

When you create a child scenario, by default it inherits the selection/configuration of alternatives of the parent scenario. In which case, you will see the "I" next to the name of the alternative. If you pick the alternative without the "I" in the child scenario, then it will no longer inherit any change to the alternative selection made in the parent scenario. For example, Base Scenario is the parent, and it has Base Trace selected as the Trace alternative. Now, if you go to the Child scenario, "< I > Base Trace" will automatically be selected. If you change the alternative selection in the Base Scenario to "Trace 1" for instance, the Child scenario will inherit the same alternative selection ("Trace 1"). However, if in the Child scenario you select "Base Trace" (without the "I"), then changing to the alternative in the Base scenario to "Trace 1" will not change the alternative selection in the child scenario. (the selection is kept "local")

What is the asterisk column in the Alternative Editor Dialog Box used for?

The first column (with the asterisk) contains check boxes, which indicate the records that have been changed in this alternative. If the check box is selected, the record on that line has been modified and the data is local, or specific, to this alternative. If the check box is cleared, it means that the record on that line is inherited from its higher-level parent alternative. Inherited records are dynamic. If the record is changed in the parent, the change is reflected in the child.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

WaterGEMS V8 Modeling FAQ 

[[WaterGEMS for ArcGIS FAQ|General WaterGEMS for ArcGIS FAQ]] 

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Overview

This Technote describes the process by which a user can import demand information from a spreadsheet using Modelbuilder. It assume Bentley WaterCAD or WaterGEMS V8i (08.11.XX.XX). The process is slightly different in V8 XM (08.09.XX.XX).

Background

In WaterCAD and WaterGEMS, demands can be entered as a base flow plus a pattern, or as a unit demand type and count. Also, multiple demands can be entered for each node (junction, hydrant, etc.)

If your demand data is contained within an Excel Spreadsheet and you have a field that contains labels that match your model's node labels, you can use the Modelbuilder feature to import them. For example:

Note: If your demands are in shapefile form, you should use the Loadbuilder tool, which can utilize the spatial information contained in the shapefile to assign demands, using many different methods. 

If you attempt to import this information using Modelbuilder, you may end up with the following unexpected results: 

This is due to the user selecting "junction" as the table type, which only provides read-only "demand" attributes to link your data to.  

Preparation

1. First, you should of course ensure that all your junctions and other elements are present in the model. When we import the demands from the spreadsheet, they will automatically update these existing elements.
2. Next, if you have not done so already, you'll need to set up any demand patterns that you'll be using. These are typically diurnal curves that adjust the base demand over the course of the EPS simulation. Go to Components > Patterns. Create a new hydraulic pattern and enter the starting multiplier along with the table of time/multiplier:

1. Open your source spreadsheet and ensure that it is formatted properly. Ensure that you have columns for the junction label, base demand and pattern, with a header at the top (see first illustration further above.) Ensure that the labels for your patterns match the ones in the source file that contains the loading data. If you would like to use a fixed pattern, simply enter "Fixed" under the pattern column for those junctions. (or, omit the pattern column altogether, if all junctions will have fixed demands.) 

Properly Importing your Demands in Modelbuilder 

Note that when you import demands using this process, they will override any previous demands assigned to those nodes included in the spreadsheet. So, this process cannot be used to 'update' an individual demand for nodes that have multiple items in the demand collection. All of the demands that should be present for a particular manhole should be included in the spreadsheet when using this process. 

Note: if you have WaterCAD or WaterGEMS V8 XM Edition (08.09.XX.XX) then the following Modelbuilder steps will be slightly different, as that version is older. The basic process is the same though.

1. Start a new modelbuilder run by going to Tools > Modelbuilder and clicking the white paper button. Select your data source type and then the file itself. Click the checbox next to the layer/worksheet that contains the data. You can click "show preview" to check the data in the later selected:

1. Click Next and uncheck the "create nodes if none found at pipe endpoint" check box:

1. Click Next and uncheck everything except for "update existing objects in destination if present in source". This is because we are updating elements, not creating or deleting them.

1. Click Next and accept the default "Current Scenario" and "Label". This is because we will be updating our current scenario and using the WaterCAD/GEMS label field.

1. Click Next to display the field mappings. This is an important step. First, click the layer on the left side (representing the worksheet containing your demands) and select "Junction - Demand collection" as the "Table Type". This is because the data that we are updating is not directly within the junction itself, but within the junctions' demand collection. A collection means that there are multiple items for each individual junction (composite demands are possible.) For example, you may have noticed that there are two individual demands for J-1 in the source spreadsheet shown in the first illustration. This is a composite demand.

For the "Key fields", select the column header that you used for the labels (most likely "Label".) This is used to link the demand entries with the junctions in your model.

In the bottom right corner, you must map fields in your spreadsheet to fields in WaterCAD/GEMS. This is because WaterCAD/GEMS cannot interpret your labels. For example, if you had a column called "Base_flow", there is no way for it to know that this means the Base Demand.

'Demand (Base)' - this should be mapped to your base demand column. Ensure that the correct units are selected.

'Pattern (Demand) (Label)' - this should be mapped to your pattern column

1. Click "next" and choose "yes" when prompted to build the model. You can uncheck the options concerning selection set creation. 

In the Modelbuilder Summary, you should receive a message stating that a certain number of your junctions were updated.

1. Close Modelbuilder and examine your demands. You can use the Demand Control Center (under the Tools menu) to easily view all demands:

What if I have unit demands?

If you have unit demands (unit demand label + count), you'll need to do a separate Modelbuilder run using a slightly different process. The unit demand information will need to be in a different worksheet in your spreadsheet (or a different spreadsheet altogether) with columns for the junction label, Unit demand, unit demand count and Pattern:

Instead of defining patterns in your model, you'll need to first import the Unit Demand types, under Components > Unit Demands. Either click the "new" button and define them, or import some commonly used ones from the engineering libraries (purple book icon)

In the last Modelbuilder step, you would select "Junction - unit demand collection" as the table type, instead of "Junction - demand collection". You would map the following fields:

'Unit Demand (Label)' - this should be mapped to the column that represents the type of unit demand.

'Number of Unit Demands' - this should be mapped to the column that represents the 'count' of units. For example, if the unit demand is "Residential" with it's demand representing 1 house, then a 'count' of '10' would represent 10 houses. The program will multiply the unit demand by the count to acheive the total unit load.

'Pattern (Demand) (Label)' - this should be mapped to the column that represents the pattern associated with each unit demand.

After Modelbuilder imports the data, you can view your unit loads in the Unit Demand Control Center, under the Tools menu. This tool will also show you the computed demand based on the unit demand and the "number of unit demands" (the count.)

What if I want to place demands on hydrants?

To import demands into hydrants instead of junctions, you would select "Hydrant - Demand collection" as the table type, instead of "Junction - Demand collection". Or, "Hydrant - Unit demand collection" if using unit loads. However, hydrants usually represent demands that would only occur during a fire (using the automated fireflow routine or emitter coefficient). So, demands are typically not assigned directly to them.

See Also

Product TechNotes and FAQs

Water and Wastewater Forum

Haestad Methods Product Tech Notes And FAQs

External Links

Bentley homepage

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Overview

This Technote describes the process of importing patterns from an Excel spreadsheet into a model using ModelBuilder. 

Create a Spreadsheet

The first thing you would need to do if this isn't already done is create a spreadsheet.  This spreadsheet will have two sheets.  On the first sheet, the pattern names will be listed along with the start time, the starting multiplier and the pattern format.

On the second sheet, will be the pattern curves.

Using ModelBuilder to Import the Patterns

1.  Go to Tools > ModelBuilder.

2.  Select a Data Source type:  (This would be the Excel spreadsheet that you have created.) 
Make sure that both sheets are checked on the bottom left of the dialogue box.  Click on Next.

3.  The next screen will have the spatial and connectivity options.  Specify whether the coordinate unit in your data       source is in feet or meters. Uncheck the box next to "Create nodes if none found at pipe endpoint".  Click on Next.

4.  Check boxes as shown below.  Click Next.

5.  Check boxes as shown below.  Click Next.

6.  For the first sheet, click on the > Components > Pattern.  For the key field select Pattern.

On the bottom part, click on the > for Property and select Pattern Summary to map the fields.

For the second sheet, click on the > Collections > Pattern Curve.  For the key field, select Pattern.  Map the fields.

Click on Next.

7.  On the screen for creating a model, select Yes for "Would you like to build a model now?".  Click on Finish.

The patterns can be checked by going to Components > Patterns.  The patterns you create will not look exactly as the screen shots below, however this is an example of the results of the import.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

[[General WaterGEMS V8 FAQ|General WaterGEMS V8 FAQ]]  

External Links

Water and Wastewater Forums

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Overview

Time Series Field Data can be imported into WaterCAD and WaterGEMS V8 XM and V8i using ModelBuilder. This technote explains how to do it.

Background

All tabular data entry grids in WaterGEMS allow you to easily paste in data from Excel. Simply copy the data from Excel, and click [Ctrl]+[V] to paste it into WaterGEMS. If that is not an option in the case where you need to bring in a lot of data, ModelBuilder can be used to import this data.

WaterGEMS Time Series Field Data

Here is the "Components" > "Time Series Field Data" editor in WaterGEMS:

The data in here maps onto the following *two* table types in ModelBuilder: Time Series, and Time Series Collection. The "Time Series" mapping represents entries in the TreeView along the left of the form (including the simple "Start Date Time", "Element", and "Notes" values shown on the right). The "Time Series Collection" mapping represents the tabular data shown in the table at the bottom right of the form.

Export Sample Time Series data

To automatically determine the appropriate values for handling Pipe Flow time series data, we're going to first export a sample from WaterGEMS to Excel.

First, create a sample Pipe Flow time series in WaterGEMS as shown above.

Next, create a new Excel .xls file. You will need two "sheets" to receive the data (the default "Sheet1" and "Sheet2" will do).

Note: We recommend choosing MSAccess over MSExcel if possible; there is no explicit way to specify the data-type of a column in Excel, which can result in some problems.

Time Series: This is the more involved of the two Excel sheets we need to set up. To determine the columns to define in Excel, create a temporary ModelBuilder connection and get to the "Specify Field Mappings" step (you won't be saving this connection, so to get past Step 1 of the Wizard, just pick any data source). Navigate to this step, choose the Time Series table type, and click on the "Property" drop-down field.

Click on the Sheet1 tab in Excel to define the necessary columns for the "Time Series" table (You don't need all of these columns for Flow Data, but go ahead and define them all to be sure we don't miss any that are required for your use-case). It should look something like this:

Time Series Collection

Again, get to the "Specify Field Mappings" step in ModelBuilder, choose the "Time Series Collection" table type, and click on the "Property" drop-down field to determine the columns to define.

Click on the Sheet2 tab in Excel and define the necessary columns for the "Time Series Collection" table. It should look something like this:

Save and close your spreadsheet.

Define the ModelBuilder Connection

Now we're ready to create the ModelBuilder connection to this spreadsheet.

Open ModelBuilder and create a new Connection.  In step 1 of the Wizard, choose "Excel" as the data source type, browse to the Excel spreadsheet that you created to select it. You should see Sheet1 and Sheet2 in the list of available tables, select those (and unselect any others that appear).

Navigate through the next few steps, just use the defaults there.  When you reach the Mapping Step, set things up for Sheet1 and Sheet2 as shown below:

Navigate to the end of the Wizard. On the last step, click "No" for the "Would you like to build a model now?" prompt and click [Finish].

Synchronize Out from ModelBuilder

Choose the connection you just defined (be sure to close the Excel spreadsheet you just defined), and click the Sync Out toolbar button.

The sample time series data from WaterGEMS will now be available in the Excel spreadsheet you created.
Using that as a go-by, you should be able to enter the data in the appropriate format to import in to WaterGEMS.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

[[General WaterGEMS V8 FAQ|General WaterGEMS V8 FAQ]]  

External Links

Water and Wastewater Forums

Bentley Technical Support KnowledgeBase

Bentley LEARN Server