Remeshing the Fluid Region in FSI

FSI simulations with large displacements of the solid structure can result in large deformations of the fluid mesh. When these distortions affect the quality of the fluid mesh, you can create a new fluid mesh based on the deformed solid structure. A typical application is the simulation of valves with large displacements. As the strains and stresses on the solid are directly related to the mesh deformations (due to the Lagrangian formulation), you only remesh the fluid region while keeping the original solid mesh. Remeshing the solid structure would reset all stresses and strains to zero.

The following workflow assumes that the geometry part for the fluid is extracted from the solid geometry using part operations. See Extract Volume.

To remesh the fluid region, you extract the deformed solid surface and export it to a file. You then replace the geometry part representing the solid with the deformed solid surface and regenerate the fluid mesh using the target part of the replace part operation. For the Replace Part operation to be successful, the target part for the operation must be a mesh part without CAD association. To extract the deformed solid surface:

  1. If the simulation is still running, stop the simulation.
  2. Right-click the Representations > Volume Mesh node and select Extract Boundary Surface...
  3. In the Extract Boundary Surface dialog, select the solid region and click OK.
  4. Right-click the Representations > Extracted Surface > Regions > Solid Region node and select Export Region...
  5. Using the Save dialog, save the exported surface as a .dbs file.
  6. Expand the Geometry > Operations node.
  7. Replace the part representing the solid with the extracted solid surface using a Replace Part operation. For instructions, see Replacing a Part in a Parts-Based Volume Mesh.
    As the .dbs file is a tessellated part, make sure that the target part that you select for the Replace Part operation is also a tessellated geometry. To do this, set the target part to a mesh part without CAD association.
  8. Create weak in-place contacts between the surfaces of the new solid part and the surfaces of the original solid part. For instructions, see Creating Weak In-Place Contacts.
  9. Regenerate the fluid mesh using the target part of the replace part operation. Make sure that you keep the original solid mesh.

    After remeshing, the fluid mesh is based on the new solid part, which represents the deformed structure, whereas the solid mesh is based on the undeformed part. As the deformation of the solid structure is a result of the fluid loads, the new fluid mesh is directly linked to the solution state in the structure at the time of remeshing. Simcenter STAR-CCM+ stores the solid mesh configuration at the time of remeshing and uses it for all subsequent mapping of data between the fluid and the solid mesh.

  10. Continue running the simulation as required.

    If you clear the solution, deactivate Reset Mesh. Activating this setting would result in a mismatch of the boundaries at the FSI interface. When this setting is deactivated, the solid and fluid meshes remain in a consistent configuration.