I'm using Water Hammer to perform a transient analysis for a new pipe line. The model is a large one (over 150,000 pipes) with many different water zones. Is it possible that I use the entire model to get the initial conditions but only do transient analysis for a particular zone? I can export that zone as a submodel and apply the initial boundary conditions to the submodel to reduce the pipe numbers, though I wonder if there is a way to do this using the full model, i.e. only run transient analysis for that zone with the full model file.
MISSING RESOURCE: VerifiedBy Sushma Choure
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Please see imbedded comments below:
After I set "Specify Initial Conditions" to "true", computed initial conditions, and then copied the initial conditions for a certain time step (for example at Time 4 hrs), consequently I got the notice of how many elements were affected. Does that mean the initial conditions at Time 4 hrs were assigned to the current scenario automatically? I did see some additional properties exposed under Transient (Initial).
[Jesse] When you use the copy initial conditions tools, it takes all the hydraulic results from the initial conditions at the selected time (see dropdown at the top of the tool) and populates those extra data entry fields you noticed. Setting the "specify initial conditions" option to "true" then tells HAMMER to use those results (the ones in the new fields) as the initial conditions, not the calculated values.
Is there a way that I can copy the initial conditions of this scenario (i.e. full model) to another scenario (i.e. with different active topology)?
[Jesse] the custom initial conditions are stored in the Transient alternative so yes, as long as your new scenario uses the same transient alternative (or a child of one) then it should use those same settings.
Do I still need to change "Initialize Transient at Time (hours)" to "4" before compute initial conditions? Probably yes if I need to use demands at that time step, right?
[Jesse] No. See above - when the "specify initial conditions" option is set to true, it always uses the custom initial conditions fields (the new fields that you see in the properties) as the basis for the initial conditions of the transient run. If you set the time to 4 hours in the copy initial conditions tool, those custom initial conditions will be set to the initial conditions from hour 4.
What I did for the submodel is to still keep the PRV active and add a reservoir upstream of the PRV, then set the elevation equal to the average hydraulic grade (over 24hrs) obtained from initial condition calculation. Then I set "Initialize Transient at Time (hours)" to "4" to use the demand at that time step. Any comments on this?
[Jesse] that sounds reasonable to me, as long as you're OK with how the transient waves will reflect off the reservoir. It won't be quite the same as it would be in the real system since the waves would travel further upstream.
Here's a related discussion I found (try searching, you may find more):