ASSIGN MASS

ASSIGN MASS

The assign mass panel allows you to add mass and change the centre of gravity of a group, part-set or assembly. This is done by adding lumped masses on the nodes in the group (or a subset of the group if you use the subgroup option) or by creating/modifiying *ELEMENT_MASS_PART(ADD) definitions. Movement of CofG is more restricted if using the EMP method but the principles of mass distribution are the same.

A new assign mass may be created using either method, and an existing one may be swapped from one to the other.

It is impossible to assign mass to nodes of a part which is defined with a *PART_INERTIA card as the lumped masses will be ignored by Ansys LS-DYNA. However, this does not mean that part inertias cannot be present in a massing up operation. They can be, but must be wholly contained in the group to be valid and included in the mass calculation. See the part inertias section in the problems below for more details.

Similarly in part mode, PRIMER will expect any *ELEMENT_MASS_PART_SET(ADD) definitions to be fully contained within the group,etc. *ELEMENT_MASS_PART_FINMASS definitions are analogous to *ELEMENT_MASS_NODE_SET in the node method and will be locked against change of mass.