We use Rhinoceros to create ships models and export them to COMSOL for FEA. We use mainly STEP as intermediate format between Rhino and COMSOL. We get a lot of errors when we import the STEP file into COMSOL. We have to merge surfaces or to correct trimmed surfaces. Are there some important guide lines for creating the model in Rhino, that eventually will be imported in COMSOL for FEA ?