[Varada]

Hello Reef3d Team,

I'm seeking some clarification regarding the usage of symmetry boundary conditions in my CFD simulation. I have a wave tank with dimensions of 25m in length, 18m in width, and 1m in height. The main questions I have are related to placing a solid body which is symmetric along the x-axis or the length axis of the tank.

Firstly, if I set one side of the flume as a wall boundary and the other side as a symmetric boundary with the dimensions of the flume being 25m x 9m x 1m, should I place the entire solid object inside the domain, or only half of it?

Additionally, I encountered an issue where, when using a symmetric boundary on one side of the domain (making it half as the original), I couldn't obtain wave elevation measurements right at the symmetric boundary. If I wish to measure the elevation precisely at the center of the tank using the symmetric boundary, where should I position the probes?

Another concern I have is related to exporting visualization files in ParaView. Currently, I can only visualize half of the domain. Is there a method to view the entire domain in ParaView even after implementing a symmetric boundary?

Thank you in advance for your assistance.

[Felix_Sp]

Hello

(I am not from the REEF3D-Team but anyway)

1. You can place the whole object or the halved. It should not matter too much as REEF3D does use the IBM. I am always using the whole object, because I am used to having problems with meshing in OpenFOAM.

2. I am not sure what you are doing wrong. I am getting measurements if I put a probe (P 51) directly on a symmetry boundary. Maybe share your input files?

3. You can use "Filters->Alphabetical->Reflect" to do this.

Cheers

[Varada]

Thank you for your reply. I followed your advice and ran the code with the attached files. Please take a look at the results. As we discussed earlier, there are some differences in the wave elevation measurements on the symmetry face, which you can see in the output files I've attached.

[Felix_Sp]

Hello,

This is really weird, seems to be a bug in the print_wsf.cpp. The flag[n] in line 156 is always at zero for your case. If one forces the flag[n] to be 1 by:
for(n=0;n<gauge_num;++n)
flag[n]=1
then I get measurements at your boundary. I guess there is a rounding problem in the position_ijk_center.cpp leading to an index in the boundarycheck.cpp that sets the check to 0, but am unsure. I always investigated a symmetry boundary on the opposite face (C 13 3). That actually works. So I guess part of the problem is also the staggered grid?

An easy fix would be to set the y value of your probes to 8.9999999999 or sth. like this. Should be identical with your boundary. Otherwise, you have to fix the bug or wait for a patch. You could also force the flag to be always 1, but this might be problematic if you use your code in the future.

Cheers