I am having an issue with my model, where I have to calculate the transient forces on a pipe that is subjected to surge dew to a sudden stop of a pump.
The problem is that even though the wave is passing from the junction, the forces seem to be the same, as you can see the attached picture.
Shouldn't I see the forces constantly changing in sync with the pressure wave travelling back and forth?
Note that all junctions have the precise X, Y and Z coordinates and distances between. I have tried to run the model with either user length or scaled and the results are the same.
Any pointers on something I might be missing?
Hello Anthimos,
I would recommend looking at an animation of a profile through this area as well, as that might give you an idea of what is happening at the time the the force results change. You can have the profile and time history graph open at the same time. When you run the profile animation, you can see what occurs near this part of the model and see if the results make sense.
I would also recommend reviewing this link and the HAMMER Help topic "Transient Forces." This Help topic includes information about how the forces are calculated and the equations used.
If that doesn't help, a copy of the model will be useful. This link has the steps on how to send the files to us.
Regards,
Scott
Hello Scott,
from my point of view the transient forces are (for some reason that I can't identify) wrong. I have 8 junctions selected for the review of the forces, and on all of them the results seem wrong.
If you check the attached model, you will see that, for example, at Nodes 2A145 to 2A147 the forces are 0 at the beginning of the simulation and suddenly jump to some values and stay there for the duration of the simulation with some very minor fluctuations, while at Nodes 2A1 and 2A63 even though the results are different, they still seem wrong. Also the HPT doesn't seem to affect the transient forces (well, maybe a little, but not the general behaviour)
I can't explain the above and I can't figure out the problem.
You can find the model on the attached zip file.
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Hello Anthimos, we are looking into this and will get back to you shortly. Thank you for providing the model files. It appears to be related to the Extended CAV calculation option.
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: Anthimos Spyridis
As Jesse mentioned above, this issue appears to be related to the use of the Extended CAV calculation option. If you open the Transient Calculation Options and set "Use Extended CAV" to False, the force results are much improved.
I have asked our development team to look into this to be fixed in a future release of HAMMER. The reference number for this is 982273. I have also opened service request 7000857992 on your behalf. Once this issue is fixed, you should receive a notification by email.
Scott Kampa
To add to Scott's answer - if you're not sure what the "Extended CAV" option does, you can read more about it here: Modeling Reference - Air Valves
It basically enables extended tracking of the air-liquid interface at air valves, and it looks like the transient Force calculations do not work well in pipes that are partially full of air with this method.