| Product(s): |
HAMMER |
| Version(s): |
V8i, CONNECT Edition |
| Area: |
Modeling |
Problem
Can simple or logical controls be used during a transient simulation?
Background
During a transient simulation in HAMMER, logical/simple controls do not apply. The controls that you enter under Components > Controls only apply to the initial conditions calculation (steady state or EPS), and do not apply to the transient simulation. This is primarily because of the small timescale. When a simulation duration is on the order of seconds or minutes, and the timestep is hundredths of a second, the reaction time becomes a factor, and the user will tend to want to focus on the immediate impact of the transient event.
To control elements during the transient simulation, you'll need to use configuration in the individual equipment (such as closure time for the check valve node) or operating rules (such as the pattern of time vs. relative closure for a valve).
The steps below are designed using an example of having a bypass pipe going from the discharge side of a pump to the suction side to recycle water. On the bypass pipe there is a TCV and that needs to open when the pressure in a given downstream pipe reaches a given pressure.
Solution
Run the model, observe the results, create a pattern, rerun the model
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Make sure the model is set up correctly and run the initial conditions. The initial conditions should have the TCV being in a closed state with the Transient (Operational) Operating Rule set to fixed.
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Run the transient simulation
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Observe the results of this situation so that a pattern can be created to assign to the TCV and pump. You're looking for the time the pressure in your downstream pipe hits that critical pressure. The pattern is going to be designed based on this time.
- Go to Components > Patterns > Create a new Operational(Transient, Valve) pattern. This is a pattern based on the time from start (sec) vs. the relative closure (%). Note that a relative closure of 0% means the valve is 0% closed, or 100% open. Conversely, a relative closure of 100% means the valve is 100% closed, or 0% open. If the valve is supposed to open at 5 seconds the pattern might look as follows.
Time from Start (sec) = 1 , Relative Closure(%) =100
Time from Start (sec) = 5 , Relative Closure(%) = 0
Time from Start (sec) = 400 , Relative Closure(%) = 0
This pattern assumes the valve open immediately and fully at 10 seconds. You can adjust you pattern to suit your needs if you valve fully opens over a period of time.
Once this is done assign the pattern to your TCV valve.
5. You will need to do the same thing for you pump if you intend to shut it down too. Go to Components > Patterns > Create a new Operational(Transient, Pump) pattern. This is a pattern of Time vs. a Multiplier where the multiplier is 0 for off and 1 for on.
6. Rerun your model and observe the results.
See Also
OpenFlows Product TechNotes And FAQs