I'm doing a simple water system pipe pressure problem with WaterGEMS. I've entered all pipes, etc and I've computed the model and I'm analyzing the pressure at a junction by looking at it's properties I now want to change the roughness factor of all pipes uniformly to reduce the pressure at this junction so I've changed the Darcy-Weisbach roughness "e" in the pipe table for all pipes. I've computed the model and have noticed a different pressure at the junction. When I change the roughness values a second time and compute the model, the pressure doesn't change at the junction.. Overall, I'm analyzing the pressure at the junction by changing the pipe roughness. Am I following the correct steps in doing a simple analysis of the junction? It seems like this is the straight forward process but I'm not sure why the pressures don't change on my second iteration of changing the pipe roughness. Any help is appreciated...thanks...J
Hi John,
If you replied by email, the information below your response is lost in the reply that was posted on the forum. Can you please post another reply with the red responses you mentioned? The screenshots do not indicate what your friction method is set to, the pipe flow or the two friction factors you're comparing.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
John - here are a few other thoughts:
I’m globally editing/changing all pipes in the pipe table in the D-W e (m) column.
2) What method are you using to change them?
See answer 1
3) What is the exact change you are making? Meaning what is the original roughness height, the second roughness height and the third roughness height value? As Sushma mentioned, perhaps the change is so small for the flow through the pipes, that the pressure does not change with your current display precision. Perhaps you can provide an example pipe with the data input (roughness height, diameter, length, etc) and the flow value seen with both roughness values.
The initial D-W value I believe is from the Ductile Iron Material Section. The original value based upon the Ductile Iron Material is 0.0003 as shown in the pipe table. When I change that value to 0.09 and compute the model, the pressure as shown in the properties dialog for J5 under Results changes from the original 296 kPa to 387 kPa which further exceeds the field value. So, I arbitrarily choose a second iteration of the roughness value of 0.60 (global edit as discuss in #1 above). When I compute the model, the pressure shown in the J5 properties dialog box REMAINS at 387 kPa and will remain at this number regardless of any value I What am I missing? What is the correct procedure?
4) In the calculation option set that is active for your current scenario, is the friction method set to Darcy-Weisbach? 5) What is the general layout of the system where you are changing the roughness? For example a pump between a reservoir and a tank, a pump from a reservoir to a closed system with demands, something else? 6) Are you seeing any red user notifications indicating that the second run failed or was unbalanced?
Have you tried to open and close the pipe flextable to see if the values change?
Mark
Hello John,
I ran a test with a 10 l/s demand at the end of a 200 m long, 200 mm diameter pipe with a D-W e of 0.0003 m and the friction loss across the pipe was 0.129 m.
Next, I changed the value to 0.09 m, re-computed the model and the friction loss was 1.545 m.
Lastly I changed it to 0.6 m and the headloss was 156 m. Assuming that the 0.6 was a typo in your message, I changed it to 0.06 m and the friction loss was 1.087 m.
Can you provide an example pipe's length, diameter and flow? Or, can you provide a copy of the model files (.WTG and .WTG.SQLITE files, zipped), per the below instructions?
Sharing Hydraulic Model Files on the Haestad Forum