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

  Applies To 
  Product(s):
HAMMER
  Version(s): V8i, CONNECT Edition
  Area:  Layout and Data Input
  Original Author: Mark Pachlhofer, Bentley Technical Support Group

Problem

How do you define the starting conditions (starting steady state) of a transient simulation?

Solution

A transient is a transition from one steady state to another. In HAMMER you must establish the starting steady state, along with the trigger of the transition (such as a pump shutting down).

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 those 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 the transient calculation options (Analysis > Calculation options > Transient.) This is rarely needed and primarily a legacy feature carried over from older versions of HAMMER. However 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.


See Also

"Specify initial conditions" calculation option and "Transient (Initial)" element properties

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