Coreform Cubit Version:2022.4)
Platform: win11
Issue
Dear all,
I want unmerge the surface in volume, but always get no entities, how can I mesh all and unmerge the surface inside of volume?
Thank you very much!
shineusn.cub (8.0 MB)
Hi,
Welcome to the forum. Merging and unmerging have very specific meanings in Cubit. Surface 17 is embedded in Sheet Body 3, and it is not currently merged in the model. Merging is done on coincident surfaces, curves, and vertices. You cannot merge or unmerge (in the Cubit sense of the words) the two bodies in your model.
The easiest thing to do in this case is to do a Boolean operation between the two parts.
subtract body 3 from volume 1
vol 4 scheme tetmesh
Surface 18 size 1500 # make the fault mesh denser so we can see it in the tetmesh
mesh vol 4
draw tet all
# turn on the clipping plane
If you have more complex faults, especially some that intersect both top and the bottom of the surrounding volume, you may have to mesh the faults first and then use the tetmesh respect option.
surface 17 scheme trimesh
surface 17 size 1500
mesh surf 17
vol 1 scheme tetmesh
vol 1 tetmesh respect tri in surf 17
mesh vol 1
The results will be slightly different but both methods will give a valid tet mesh in this case.
Karl
Dear Karl,
Thanks a lot, I tried to mesh and successfully, if I want to unmerge the inner faces? How should it be modified?Or how to divide the inner surface into two layers (may be a little different vertex) ?
Thank you!
Hi @shineusn,
I have created a video showing how to create a double-sided surface with Cubit. This will create a slip plane. Depending on your analysis code, you might also have to create a contact boundary condition between the nodes on the two surfaces. The process is a little involved because we are asking the tet-meshing algorithm to ignore some of the built-in optimizations that it would normally use.
The basic steps to create a mesh that allows for slippage are as follows.
- Copy the fault plane surface.
- Merge the curves on the duplicated surfaces.
- Set meshing parameters on the duplicated surfaces
- Mesh the surfaces individually
- On one surface swap edges to make sure you don’t have duplicate triangles at the surface corners.
- Offset the interior nodes on one of the surfaces.
- Use the tetmesh respect option to include the triangles in the fault planes as part of the tet-mesh.
- Mesh the volume
- Return the offset nodes to their original location.
As this is quite involved, I created a 5-minute video that shows the techniques required to create disconnected tetrahedra on the fault plane.
Thanks,
Karl
2 Likes
Dear Karl,
I tried this method and it works now, really huge help.
thank you very much！
Hi Karl,
This is very nice way to generate tetrahedral elements. Is there any way to do hexahedral elements for double sided fault surface? I’m trying sculpt, but it does not work well so far.
Thanks in advance.
Best,
Qingjun
Hi Qingjun,
I have never tried doing double sided surfaces in sculpt. I will have to see if that is even supported. In a typical hex mesh, you can’t just insert a surface and hex mesh around it. You will have to modify the topology so that the surface is part of a volume that can be hex meshed.
In the example below, I swept the surface surface through the other geometry to create two volumes. The inner volume can be represented with a mapped mesh and the outer volume is a one-to-many swept mesh. I did the imprint and merge steps to create a conformal mesh. Then I unmerged the surface. Note that this unmerge kept the boundary nodes merged and just unmerged the interior nodes.
As an example,
reset
brick x 150 y 150 z 50
create surf rectangle x 20 y 20 z 20
create surf rectangle width 50 height 20
webcut volume 1 sweep surface 7 perpendicular outward through_all
delete vol 2
volume 3 size 3
volume 1 size 10
imprint all
merge all
unmerge surf 12
Surface 13 scheme pave
mesh vol all
topology check coincident node node all tolerance 1e-06 draw brief result group
draw coincident_nodes
draw surf 12 add
Thanks,
Karl