open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,

I am facing an issue when using Telemac3D in MPI mode. I have a flume test with a weir overtopping, on upstream side when the flow is sub-critical, everything is fine, however on downstream side when the flow accelerating and become supercritical, I have notice the wiggles at the border of two partitioned segments and the attached image shows the free surface flow and wiggles at each segment edge.


Any idea to resolve this issue greatly appreciated!

Amanj

Hello Amanj,

Which release of TELEMAC-3D do you use?
Do you have the same behaviour when changing the number of processors and also between subdomains?
I assume you tried in serial mode and do not see this kind of wiggles, do you?
On the figure you sent, there are also 2 other wiggles on the right, are they also located between 2 partitioned domains?

Can you upload the steering file? Did you add any FORTRAN FILE?

Chi-Tuan

Hello Chi-Tuan,

Thank you for your response to my post, the version is V8P1R1. I tried with 40 processors and now I am trying with 20 instead and seems the wiggles are went away. Its coupled with Sisyphe and the wiggles appeared on steep slope only. The fortran file is just for defining the rigid bed ( nonerode).

Thank you,
Amanj

How many elements are there in your mesh?
You should not have a too small number of elements for each subdomain otherwise you may have issues. I would not advise to have 2,000 elements or less per subdomain after partitioning.

Chi-Tuan

total elements are 16864 and when using 40 cores, means each sub domain is approximately 420 elements.

Is there any logic behind this?

amanj

There is a balance to find between the time of computation on every subdomain and the time of communications between every subdomain. If the number of elements per subdomain is too low, you will spend more time to communicate rather than to compute. And it also may lead to errors.

Moreover, I am not sure that for your computation, using 40 or 20 processors leads to faster CPU times than less than 10 (I would try first with 1, 2 and 4 processors).

Chi-Tuan

I agree, I should try with a smaller cores number first and then gradually increase.

Thank you Chi-Tuan,

Amanj