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Export a design candidate from the Post Processing.
Make sure the intersected geometry is used. Otherwise a manual intersection needs to take place in MSC Apex Generative Design or MSC Apex.
Import the intersected STL-file into MSC Apex as a mesh.
Use the Geometry-from-Mesh tool to create a faceted body.
Delete the imported surface mesh.
Remesh the geometry with a solid mesh (Tet-elements).
Apply the boundary conditions:
Make sure that the applied boundary conditions are the same as in the optimisation (Loads are applied similar as RBE3 elements and fixations as RBE2 elements)
You can find a step by step tutorial here.