24.1.1 Point masses

**Products: **ABAQUS/Standard ABAQUS/Explicit ABAQUS/CAE

Mass elements:

allow the introduction of concentrated mass at a point; and

are associated with the three translational degrees of freedom at a node.

In addition to point masses, ABAQUS provides a convenient nonstructural mass definition that can be used to smear mass from features that have negligible structural stiffness over a region that is typically adjacent to the nonstructural feature. The nonstructural mass can be specified in the form of a total mass value, a mass per unit volume, a mass per unit area, or a mass per unit length (see “Nonstructural mass definition,” Section 2.6.1).

Defining the mass value

You specify a mass magnitude, which is associated with the three translational degrees of freedom at the node of the element. Specify mass, not weight. You must associate this mass with a region of your model.

Input File Usage: | *MASS, ELSET= |

where the ELSET parameter refers to a set of MASS elements. |

ABAQUS/CAE Usage: | Property or Interaction module: Point mass/inertia: select point: Magnitude: Mass: mass magnitude |

You can define a general mass matrix explicitly in ABAQUS/Standard if the introduction of individual terms on and off the diagonal of the mass matrix is desired. See “User-defined elements,” Section 26.15.1, for details.

Input File Usage: | Use both of the following options: |

*USER ELEMENT *MATRIX |

ABAQUS/CAE Usage: | Defining the mass matrix explicitly is not supported in ABAQUS/CAE. |

Defining damping for MASS elements

In ABAQUS/Standard you can define mass proportional damping for direct-integration dynamic analysis or composite damping for modal dynamic analysis. Although both damping definitions can be specified for a set of MASS elements, only the damping that is relevant to the particular dynamic analysis procedure will be used.

In ABAQUS/Explicit damping cannot be defined for MASS elements.

You can define inertia proportional damping for MASS elements in direct-integration dynamic analysis. See “Material damping,” Section 20.1.1, for details.

Input File Usage: | *MASS, ALPHA= |

ABAQUS/CAE Usage: | Property or Interaction module: Point mass/inertia: select point: Damping: Alpha: |

You can define the fraction of critical damping to be used with the MASS elements when calculating composite damping factors for the modes when used in modal dynamic analysis. See “Material damping,” Section 20.1.1, for details.

Input File Usage: | *MASS, COMPOSITE= |

ABAQUS/CAE Usage: | Property or Interaction module: Point mass/inertia: select point: Damping: Composite: |