Mass Properties

A node with a mass property concentrates mass and inertia at a single point. In a static analysis (linear or non-linear), the only effect of a mass is to give a loading based on m × g when gravity loads are applied to the structure. In a dynamic analysis both mass and inertia are used in the construction of the mass matrix

Definition

Name

The name is only used as a convenient way of identifying a mass property.

Mass, Inertia

This defines the mass and a (symmetric) inertia tensor. The terms that make up the inertia tensor are described more fully in the theory section.

Care should be taken in defining the off-diagonal terms to ensure a positive definite matrix so that the resulting principal inertias are positive.

Mass Modifiers

The mass modifiers allow the mass to be varied in the different directions. These can be specified as a mass value or as proportion of the actual mass. This only applies to mass and in dynamic analysis. Typically this is used to add mass in some directions when a structure is in contact with a fluid.

Note about the property axis

Mass property is only used to by nodes,  the nodal constraint axis of the node will be used as the mass property axis.