Dear Bentley team,
I have a following queries on Hammer/WaterGEMS,
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Jayakanthan said:I have a pumping system with main control valve on discharge line & one more control valve on minimum re-circulation line. I wanted to know that whether I can do simulation when control valve on main discharge line is closing at the same time I need to open control valve on minimum re-circulation line, I can say both valves should operate with a time delay. Is it possible to do this case using Hammer.
Yes, you can specify different Operating Rules (closure patterns) on valves for a transient simulation in HAMMER. Use the TCV element and read more in this article: Modeling Reference - Valve Closure
Jayakanthan said:I need to mention pressure as a input on destination point, where can I mention pressure as a input as fluid vapour pressure is higher than the atmospheric pressure , hence I cannot use either reservoir option or a junction option to allocate the demand. If allocate demand for the junction since initially control valve is in closed condition hence simulation is showing error as initial pressure is less than the vapour pressure.
If you need to model a valve that is initially closed but when it opens, water leaves a junction (as a demand), try modeling it as a Discharge To Atmosphere. This is essentially a pressure dependent demand so the outflow will be zero if the pressure is zero, and the outflow will be positive as the pressure rises. If you simply want to assume a constant pressure at the downstream end of the system, convert the pressure to HGL and enter that as the elevation of a reservoir element (and enter the "inlet/outlet invert" elevation as the actual elevation of the discharge point. If this does not help, please explain in a bit more detail what the discharge point represents and what you need to model.
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Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.
Thank you for your reply.
As fluid vapour pressure is above the atmospheric pressure. Hammer is showing following error "Initial pressure less than vapour pressure. At the pipe end(s), the elevation(s) or head(s) are incorrect." I have attached Hammer file for your review please.
I am unable to resolve it, could you please help me.
Thank youSimulation files.rar
The file you attached only contained the .WTG file. In order to open the model, we will also need the .WTG.SQLITE file. Alternatively if you're using a recent version, you can go to File > Save to Package and send the resulting ZIP file. See: Sharing Hydraulic Model Files on the OpenFlows Forum
Are you saying that you have set the vapor pressure limit calculation option to be above zero? That calculation option represents the pressure below which water turns into vapor. What type of fluid are you trying to model?
Or, are you saying that the default vapor pressure calculation option is using used (-14 psi) but that you're encountering an error stating that the initial pressure is less than vapor pressure? If so, you would need to check the node in question and fix the initial conditions to prevent the negative pressure from occurring, as this would mean the system is not in steady state (because if the pressure really were below the vapor pressure limit, there would be a vapor pocket).
We have used Propane in this simulation.
I have again attached simulation file for your review. (Size of the file is big if i create file from File > Save to Package & unable to upload)
6253.Simulation file.rarThank you
In the model provided, if you compute just the initial conditions calculation, there is a disconnected demand node. This is occurring because TCV "SPILLBACK VALVE-1" is closed. The results in the initial conditions is not valid, which is the reason that you are seeing the issue. If you set the TCV status to active and then compute the model, the error no longer occurs.
Based on the operating rule on the TCV, it appears that this valve is closed by design. You may need to adjust the operating rule and the initial status of the valve. Instead of starting out closed, set the intitial status to either Inactive or Active. Compute the initial conditions and note the percent closure of the valve. Adjust the operating rule to the start multiplier is at the percent closure at the start of the simulation, then use the operating rule to close the valve. Leave it closed for a certain amount of time, then have it open again. The amount of time the valve will be closed may take some trial and error. You want it closed long enough to reach a new equilibrium. The workflow above is similar to this link related to pumps.
In addition, note that HAMMER was designed with water in mind. The following link includes information related to this: Modeling other fluis or fluid temperatures.
Sorry for the delay reply due holidays here.
Control valve on spill-back line is closed position only on initial conditions and flow is going to main discharge line. In this case i cannot use Inactive option during initial conditions as control valve is in closed position.
Our question are:
"when control valve on main discharge line is closing, then after some time delay I need to open control valve on spill-back line (which is initially closed position actually), Is it possible to do this case using Hammer.
we cannot use the element "discharge to atmosphere" for this application as well as reservoir as the vapor pressure of the fluid is higher than the atmospheric pressure. Hence in the simulation providing a notification "error, initial pressure less than vapor pressure of the fluid". could you tell us how to resolve this issue.
The best option may then be to start with the TCV initially open. You can set up your operating rule to close the valve, leave it closed long enough to come to a new equilibrium, then reopen the valve. The workflow is similar to the steps in this link.
Above mentioned method/option is good & we can do simulation with this option.
Thank you for providing best solution.