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Prepare a model for analysis in Bentley HAMMER
The purpose of this is to minimize the number of links in the model to the main trunk line and as few branches as possible to still observe the transient accurately. This is done in order to have a shorter run duration, makes the models easier to troubleshoot, and makes them easier to analyze the results.
HAMMER uses the same file type as WaterGEMS and WaterCAD, and for that reason, a user can directly open a model created in WaterGEMS or WaterCAD in Bentley HAMMER. This makes for a convenient analysis of a system.
It is generally recommended that the HAMMER model is a well-calibrated system. HAMMER will run on a model that has not been calibrated, but the results may not be as accurate since the initial conditions calculation will not be as accurate.
The initial conditions calculation should have the expected results for a given time step. For instance, the pressure and flow results should be reflective of the system. Element elevations should be entered and accurate as well. Since elevation and pressure are related, accurate input is required for good analysis. Information on elevations in HAMMER can be found at the following link: What does node elevation represent?
If there are any unexpected user notifications, these should be resolved. If you receive a red user notification, such as a "Network Unbalanced" message, this will need to be resolved before you compute the transient run to assure the most accurate results possible. You can find that many of the notifications that you could receive are addressed in a wiki or forum post, which will allow you to locate the content you're looking for. This wiki article will explain how you can search our Communities site for that information.
If you have a large system, you may want to consider simplifying or skeletonizing it. HAMMER will compute large models, however the run time will be quite long. Transients are less likely be impactful with smaller pipes leading to individual customers compared to the results in a larger main after a pump station. The Skelebrator tool can help with simplifying a model. You can find information on using Skelebrator in the Help documentation.
Note: in recent versions of HAMMER, Skelebrator is included. For older versions, you may need to use Skelebrator in WaterGEMS.
You could also select a key series of pipes and nodes in the model and export these as a submodel. You could then import the submodel into a new model. Note that some adjustment may be needed in order to assure that the imported submodel computes and gives the correct initial conditions results. Finally, you can use active topology selection to make only the elements you are interested in active in the model. As with the submodel method, some adjustment may be needed to assure the model computes correctly.
Other steps that can be taken to simplify a model for HAMMER analysis are outlined below:
1) Use Network Navigator and choose the ‘Network Trace’ option from the pull down menu. From there choose the “Path to the Nearest Downstream Element of Specified Type…” or the “Path to the Nearest Upstream Element of Specified Type” depending on which end you choose to start from. This will locate the most direct path to those elements.
2) Choose the Start Element in the query parameters dialog box by clicking on the drop down arrow next to <None> and choosing the “Select…” option to select the element from the drawing pane. Once it’s selected choose the ‘Element Type’ from the drop down list below that. Finally, click the compute button in the upper right corner of the window to execute the query.
3) Click the selection arrow icon to the immediate left of the pencil icon that looks like an arrow with dots in the upper left to select the elements in the drawing. Once the elements are selected right click on one of the selected pipes in the drawing pane and choose “Create Selection Set”. Label the selection set appropriately.
4) With the selection set highlighted (red by default) click Edit > Invert Selection. This will choose all the other elements in your model. Hold down the control button and left click on the branches that you’d like to remain in the model. This will remove them from the selection set you’re going to create. Right click on one of the pipes that’s still highlighted and choose “Create Selection Set” then name it appropriately.
5) Go to Tools > Active Topology Selection and click the drop down arrow next to the third icon to the left and choose the selection set you created in step 4. This will highlight those pipes. Click the green check mark icon to inactivate those pipes.
Can Water Hammer do transient analysis for one zone in the model?
General HAMMER V8i FAQ