24.1.1 Point masses

Products: ABAQUS/Standard ABAQUS/Explicit ABAQUS/CAE

References

Overview

Mass elements:

allow the introduction of concentrated mass at a point; and
are associated with the three translational degrees of freedom at a node.

If rotary inertia is also required (for example, to represent a rigid body), use element type ROTARYI (“Rotary inertia,” Section 24.2.1).

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=name* mass magnitude
	where the ELSET parameter refers to a set of MASS elements.

ABAQUS/CAE Usage:

Property or Interaction module: SpecialInertiaCreate: Point mass/inertia: select point: Magnitude: Mass: mass magnitude

Defining the mass matrix explicitly in ABAQUS/Standard

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.

Direct-integration dynamics

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: SpecialInertiaCreate: Point mass/inertia: select point: Damping: Alpha:

Modal dynamics

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: SpecialInertiaCreate: Point mass/inertia: select point: Damping: Composite: