Hello,
I have a working 36hr EPS hydraulic scenario and would like to setup a transient scenario for a pump trip. My attempt in doing so has not been successful and I was seeing my zone draining and my pump station (that feeds the zone) dead heading, with flow reversing through the pump towards the boundary conditions.
Regards,
Youssef
Hello Youssef,
1. Using the "Initialize transient runs at time" property is the way to choose the time that the transient run will begin for an EPS initial conditions calculation. You will want to make sure that the initial conditions calculation runs without any red user notifications and that the model is calibrated. If the initial conditions input is inaccurate, the transient results will be too.
If the initial conditions calculation computes without an error and if the results at a given time step are accurate, there would be no need to change the settings at the boundaries. However, you could also simply run a steady state initial conditions with the boundary elements set as they should be as an alternative to using the EPS run as the starting point.
If you are seeing strange transient results or initial surges, that may indicate an issue with the initial conditions calculation. Given the error you mention in your next question, that may actually be the case.
2. In the screenshot you sent, it appears that there are two pipes downstream of the pump and one of these is inactive. If that is the case, the error about the pump not being connected to a downstream pipe may be occurring because the pump is actually connected to the inactive pipe. Open the pump properties and look for the Downstream Pipe attribute near the top of the dialog. Click in the cell and make sure that the pump has the correct downstream pipe. See this link for details.
As mentioned above, you will want to make sure that the initial conditions calculation is accurate and running without errors. If there are any red user notifications, that is an indication of something that will need to be fixed. Other warning-level notifications may need to be reviewed as well.
If this doesn't help, we will likely need to see a copy of the model files.
Scott
Hi Scott,
That was helpful, thank you. Now I am stuck with a dilemma. I tried skelebrating one zone in my model to decrease computation time of the transient model, however, once I do that and try to initialize initial conditions, I get a lot of errors with negative pressures at junctions. This error was never present before skelebration. But if I do not skelebrate it, the computation fails due to the model being too large. Any thoughts on this?
Regards,Youssef
A lot depends on which method you used to skeletonize the system. if you used anything but Smart Pipe Removal, you should have virtually the same results for the full and skeletonized model because the methods preserve capacity. Smart Pipe Removal doesn't do that.
You apparently removed some important capacity.Try running some standard WaterGEMS runs with the full and skeletonized model and see where the differences occur.
Hi Tom,
I thought I replied but I am not able to see my response. Anyway, thank you so much for your help. It ended up being the "smart pipe removal" skeletonization method that was messing up my output as I was not aware that it compromised the system hydraulic capacity. Speaking of which, does Bentley offer any "rigorous" courses for us to truly grasp the software and its computational methods?
Another thing Scott Kampa, following the computation of the Hammer model, the transient results viewer is showing me results every approximately 3.4 seconds in the "dynamic" graph. Even though my report times are set to all and time step interval is set to 0.01 seconds. Any thoughts? Also, the model takes approximately 30 minutes to compute even though I selected the "critical" report points (approximately 1,000 pipes and junctions versus the approximately 3,000 in the skelebrated model). Any thoughts on that as well?
Bentley offers training for all products, including HAMMER. We post upcoming instructor-led classes on our calendar. You can also find HAMMER training material on our Youtube channel and Learnserver.
For the results reporting, you likely have a user notification that says "The period between path histories has been increased by a factor of X to limit the number of path records to Y." This occurs because there is a limit to the size of the report file HAMMER will generate. To account for this, HAMMER will increase the reporting time step by some factor. You can reduce this in a number of ways, such as running the model for a shorter time or decreasing the number of report points. This link has more information on that.
Answer Verified By: Larry Abla
Thanks, Scott. I will be on the lookout for upcoming training sessions on your calendar. I have been referring to the Youtube videos, which have been helpful.
Got it, that explains it. Thanks again.