[ LS-Dyna ] Rigid Body with *ELEMENT_MASS_MATRIX

LS-Dyna ignores *ELEMENT_MASS_MATRIX for rigid nodes (*MAT_20, *CONSTRAINED_NODAL_RIGID_BODY, *DEFORMABLE_TO_RIGID)

This is a result of rigid bodies being implemented differently than deformable bodies. For rigid bodies, one single unique mass is associated for each body at the center of mass. The implementation is such that a full mass matrix is not used. Changing to a deformable material or using *PART_INERTIA are better alternatives.

Personally, I have found that attaching the mass matrix element to a line body with *MAT_GENERAL_JOINT_DISCRETE_BEAM can work for such an application.

Note: in the future, this lack of compatibility will be noted in the manual.