[Swempa]

Hello,

Is there a way to prevent bridging in OpenFOAM when meshing a thin/detailed volume, without decreasing the element size in the mesh.

There is a function in Star CCM+ for the "wrapper", which is called "contact prevention" and where one can define multiple patches which should not be in contact with each other. With this function activated the meshing will always inflate the volume and no bridging will appear.

Is there a similar way to prevent this problem in OpenFOAM?

Thanks and Cheers

[piu58]

From my experience you should make the mesh 3 times finer than the width of the structure. If you go much below this point, the structure is numerical "widened" which may give far unreal results. Of course, a no slip b.c. helps but that cannot be used in all model cases.

In some FEM solvers 3d and 2d or even 1d elements may be combined. OF however, is always 3d.

[Swempa]

Originally Posted by piu58

From my experience you should make the mesh 3 times finer than the width of the structure. If you go much below this point, the structure is numerical "widened" which may give far unreal results. Of course, a no slip b.c. helps but that cannot be used in all model cases.

In some FEM solvers 3d and 2d or even 1d elements may be combined. OF however, is always 3d.

Servus Uwe,

Thanks for the quick reply.

Changing the b.c. is not a solution and the goal is to only adjust the mesh.

For sure refining the specific area is a well known solution but in my opinion it has two main disadvantages:
• One need to do this manually, means one needs first to create a mesh, have to have a look where bridging is appearing and then one have to adapt these patches. In worse case one have to do this a few times to get rid of the bridging.
• The solution can also be “wasting” a lot of cells because of to big refinement regions.

My understanding about the contact prevention in Star-CCM+ is that it is working in this way that its looking for bridging in a defined areas, and when it is risk of bridging will the algorithm automatically refine only this zone. End-effect is that one is not wasting cells and its more or less an automatic process.

Is there something similar in OpenFOAM and SnappyHexMesh?

Thanks and Cheers

[akidess]

On surfaces that should not bridge, you can locally increase the refinement level. Apart from that, shm has a gapRefine setting you can use. With both you need to be careful not to obtain gaps where you actually want the mesh to be bridged.