Applies To 
   
  Product(s): Bentley HAMMER
  Version(s): V8 XM
  Environment:  N/A
  Area:  N/A
  Subarea:  N/A
  Original Author: Jesse Dringoli, Bentley Technical Support Group
   

 

 

 

 

 

 

 

 

Can I open WaterGEMS/CAD V8 XM models?

Yes. HAMMER V8 XM uses the same file format as WaterGEMS and WaterCAD V8 XM, so you can directly open the files. All three programs conveniently use a .wtg and .wtg.mdb file to store the model data.

 

What is HAMMER's calculation engine based upon? 

HAMMER uses the Method Of Characteristics.

 

What kind of demands should be used as the initial conditions of a transient simulation? 

Typically, you should run a transient simulation for the maximum and minimum demand hours for each of the development conditions (network and demand points) under consideration. 

 

Are pipe bends (vertexes) used in the force calculations? 

No, currently they are not considered. If you need to study the effects of transient forces (X/Y/Z) on a pipe with vertexes, you should consider replacing the bends (vertexes) with junctions.

 

When I create a graph under View > Graphs, this seems to only show the initial conditions. Where can I view detailed graphical results of the transient simulation?

The transient results are viewed in the Transient Results Viewer, located under the Analysis menu. The amount of results included in here is determined by the report period, report points, and "Generate Animation Data" settings, under Analysis > Calculation Options > Transient Calculation Option

 

How do you define the starting conditions of the transient simulation?

The starting conditions of the model before a transient occurs are defined in one of two ways. First, you can invoke the WaterGEMS steady state solver (Analysis > Compute Initial Conditions) to calculate them for you, based on the demands, boundary conditions, and other element attributes. This is the same solver that Bentley WaterCAD and WaterGEMS use. The transient solver then uses the computed flows and hydraulic grades as the starting conditions. 

Alternatively, you can define your own starting conditions (flow and head) by choosing "True" for the attribute called "Specify Initial Conditions?" in theTtransient Calculation Options (Analysis > Calculation Options.) When doing this, the transient solver will no longer use the head/flow computed by the "Compute Initial Conditions", but instead will use the head and flow values that you must enter in the "Transient (Initial)" section of each element's properties. Note that if you want to slightly modify some computed initial conditions, you can copy them over to the user-defined initial conditions fields first by using the "Copy Initial Conditions" tool (under the Tools menu) and then alter them as you see fit.

 

How can I view extended transient results, such as pump speed, air flow of a CAV, gas volume of a hydropneumatic tank, etc., for each timestep?

First, enter a number for the "Report Period" attribute of an element. This represents how often the results will be saved for. For example, a report period of '10' means that results will be shown at every ten timesteps. Make sure text reports are enabled in the Transient Calculation Options. Now, when you compute initial conditions, extended results will be displayed, under Report > Transient Analysis Reports > Transient Analysis Detailed Report. Scroll down to the bottom to see a table of data for the element(s) with a report period.

 

How can I generate a graph of the various extended results seen in the Detailed Report when using a report period for certain elements? (such as hydropneumatic tank, air valve, pump)

Follow the steps below. Note that this assume you are using Microsoft Office 2007 edition. The process may be different for other versions.

1) Copy/paste the text from the .rpt file pertaining to your particular graph into a separate .txt file in Notepad. This is the table of extended transient results seen at the bottom of the transient analysis detailed report.

2) Open Microsoft Excel and start a new spreadsheet (the process is likely different with older versions of Excel).

3) Click the "Data" tab, choose "From Text" and select your file.

4) Choose "Fixed Width", then "Next."

5) Set up the field widths so that the columns of data are separated appropriately.

6) Set up a line graph with the appropriate columns (Time, plus whatever attribute you'd like to graph. For example, volume of air for a hydropneumatic tank).

 

I am using FCV, PRV and PSV valves in my model, but they do not seem to be working during the transient simulation, per the setting I have entered. Why?

The pressure reducing / pressure sustaining / flow control properties of these valves are only used during the initial conditions calculation. This is because HAMMER assumes that during the transient event, these valves cannot react quickly enough to the changes in flow/pressure. If you are running a long transient simulation and need to model the effects of these valves, you'll need to use an operating rule on the valve to close them.

 

Can you use simple or logical controls during the transient simulation?

No, the controls that you enter under Components > Controls only apply to the initial conditions calculation. To control elements during the transient simulation, you'll need to set configurations in the individual element (such as closure time for the check valve node) or operating rules (such as the pattern of time vs. relative closure for a valve). For example, an operating rule for the actions of a TCV  or the time delay until shutdown for a pump.

 

What does the following user notification mean, and what is the deviation based on? - "WARNING: The wavespeed or length approximations deviate excessively from the entered values. Lengthen short pipes and/or subdivide longer pipes." 

The deviation mentioned here is based on a percent adjustment found under Analysis > Transient Time Step Options.

HAMMER tries to have a wave travel from one end of the pipe to the other end in even multiples of the time step. Therefore, HAMMER will try to adjust the length of the pipe to allow this to happen. By default, if it has to adjust the length more than + or - 50% (the default option at the bottom right of the Transient Time Step Options dialog), then you get the warning above.

The best scenario is to have all your pipe lengths the same. However, that is not always feasible, so it is recommended that you set them as closely as possible so that the adjustment is not too large.

There other steps that you can try as well. First, you can adjust the time step to a smaller value by selecting "Use Custom Time Step." You can also set this in the Transient Calculation Options by setting the attribute "Has User Defined Time Step?" to "True." Second, if you the setting for "Run Duration Type" in the Transient Calculation Options is to set "Time Steps," you can enter another value, then return to the Transient Time Step Options dialog and click the Update button to see the new maximum and mean adjustment. Third, you can toggle between adjusting the wave speed or length in the Transient Time Step Options dialog, again click Update to see the new results. Finally, you can simply ignore the warning if the results make sense and look correct to you - it's up to your engineering judgment. If you do make adjustments, the typical trade-off is between accuracy and run time. The smaller you make the time step, the accuracy will be better (i.e., less adjustment will need to be required), but the longer the transient run will take to complete.

For more information, see Bentley Technical Support KnowledgeBase.

 

How can I find Water Deceleration in a Pipeline with a check valve? 

First, run the Initial Condition analysis and record the velocity in the pipe downstream of the check valve. Let's assume it is 4 ft/second.

Next, run the transient simulation and open the Transient Results Viewer. Plot a time history graph of flow in the pipe downstream of the check valve and measure the time from when the pump turns off until the flow curve crosses the x-axis (i.e. when flow reaches zero). Let's assume it is 2 seconds.

So the deceleration of the water column is 4 ft/second / 2 seconds = 2 ft/s^2.

This is an average deceleration rate, which is typically what valve manufacturers provide.

 

How does the Transient Results Viewer work and how can I use it to view my results?

The Transient Results Viewer displays transient results in graph form. It can also animate hydraulic grade in a profile.

The "Paths (Profiles)" pulldown at the top allows you to select a profile (defined in the main user interface under View > Profiles) and then either plot or animate it. The "Plot" will provide the minimum and maximum transient envelope. The "Animate" button will allow you to see the hydraulic grade profile as it changes over time. This is useful in understanding how certain transient inducing events affect the system as a whole. If the Animate button is grayed out, make sure "Generate Animate Data" is set to "True" in your Transient Calculation Options. To reduce the amount of profiles available, go to View > Profiles, right-click on the ones you would like to omit from the Transient Results Viewer and deselect "Transient Report Path".

The "Time Histories" pulldown at the bottom of the Transient Results Viewer displays end points that are available to graph. The number of endpoints listed are determined by the "Report Points" option in the Transient Calculation Options. Note that transient simulation results are available at the ends of the pipes where they meet a node element. For example, the upstream side of a pipe or the downstream side of a pump. For time histories, you can plot the head, pressure, flow, air/vapor volume, and force (if you've chosen to compute transient force.)

 

What do the different colored lines in a Transient Results Viewer profile represent?

In general, you can right-click on the frame/axis of the plotted profile, select "Format Data" and see the names of the various plotted lines in the dropdown.


For an animated profile, check the below diagram:

 

For a plotted head envelope:

Solid black line - Physical elevations
Dashed black line (or solid orange line if a pressure plot) - Initial conditions head
Solid red line - Maximum transient head
Dashed blue line - Minimum transient head
Red line at top - Max vapor/air volume
Dashed yellow line - Vapor pressure (as a reference)

 

How can I add a new material such as HDPE to the material library?

  1. Go to Components > Engineering Libraries and click the plus sign next to "Material Libraries"
  2. Right-click MaterialLibrary.xml and choose "Add Item." A new material entry will appear at the bottom of the list.
  3. Right-click this new material entry, choose Rename and enter the name (such as 'HDPE').
  4. On the right side, enter the friction coefficients, Young's Modulus, and Poisson's Ratio for your new material, and then click Close.

Note: The Young's Modulus and Poisson's Ratio are only necessary if you need to use the automatic wave speed calculator tool, under Tools > Wave Speed Calculator.

If you would like to create a new engineering library (.xml file) instead of altering the default MaterialLibrary.xml, simply right-click on "Material Libraries", choose "Create Library", choose a location to save the file, then repeat steps 2-4 above, replacing 'MaterialLibrary.xml' with the name of your library.

 

What is the difference between the "Elevation" and "Elevation (Inlet/Outlet Invert)" fields in the properties of a reservoir?

The "Elevation" represents the water surface elevation and the "Elevation (Inlet/Outlet Invert)" represents the invert of the pipe that attaches the reservoir to the system. Pressure at the reservoir location is determined by the difference between these values.

 

How can I model a "Shut Down After Time Delay" pump that has neither a check valve or control valve? 

When using "Shut Down After Time Delay" transient pump type, you must select either "Control Valve" or "Check Valve" as the Pump Valve Type. If you do not want a check valve or control valve, select "Control Valve" as the Pump Valve Type and enter a large number, such as 9999999 seconds for the field "Time (For Valve to Close)". 

 

How can I plot multiple time histories in the same graph or multiple profile plots on the same profile?

Natively there is no direct way to do this with the Transient Results Viewer. However, you can do it using the process below. This is useful in cases where you would like to compare transient profile/time series results between scenarios.

1) Open the first time history graph (or profile plot). 
2) Right-click in the middle of the graph and choose Save As > HAMMER graph. Save the .grp file.
3) Close the first graph (or profile plot), then go to File > Open and reopen it
4) Right-click on the frame of the graph and choose "Copy Data"
5) Open the second graph (or profile plot), right-click on the frame, and choose "Paste Data (+)".

Note: you may have to adjust the Y axis scale if the pasted data doesn't fit in second graph.

 

See Also

Product TechNotes and FAQs

Licensing TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

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