What should the run duration of a HAMMER model be set to?

  Applies To 
  Product(s): HAMMER
  Version(s): V8i, CONNECT Edition
  Area:  Modeling
  Original Author: Scott Kampa, Bentley Technical Support Group

Problem

What should the run duration of a HAMMER model be set to?

Solution

Generally, you would want to run a model for as long as it takes to reach equilibrium (for pressure waves to reach or approach a final steady state). Usually that will be on the order of several times the time it takes for the transient to travel from its source to the far end of the system and back (the characteristic time). You can try a couple of different times, keeping in mind that a longer run duration will take longer to compute. 

Note that in some situations the model may never achieve the final steady state - you may see waves bounce back and forth without dissipation. This can happen in the absence of friction - an example is seen here. In this case you may simply need to run the transient simulation long enough to see the initial impact of the transient event, or you may need to consider using a different transient friction method with a very long duration.

Also, if you are modeling a pump shutdown event and there is no other water source available to maintain a positive pressure in your system, air or vapor pockets may form and never collapse unless you simulate the restart of that pump. In such a case, consider modeling a pump shutdown followed by restart within the same simulation in order to assess the impact of vapor or air pocket collapse. In this case the duration would be set long enough for the system to settle back on it's final steady state with the pump back on. See: Modeling a pump startup and shutdown transient event in the same simulation

See Also

How to set the initial start time for a transient run in HAMMER

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