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*BASE MOTION
Define the base motion for linear, eigenmode-based, dynamic procedures.

This option is relevant only during linear dynamics procedures that use the natural modes of the system (*STEADY STATE DYNAMICS without the DIRECT parameter, *MODAL DYNAMIC, and *RANDOM RESPONSE).

Products: Abaqus/Standard  

Type: History data

Level: Step

References:

Required parameter:

DOF

Set this parameter equal to the direction (1–6, including rotations) for which the base motion is being defined. This direction is always a global direction.

Set this parameter equal to 8 for the acoustic degree of freedom, which is for use for secondary base motions only in the SIM-based architecture.

Required parameter for *MODAL DYNAMIC and *STEADY STATE DYNAMICS analyses: 

AMPLITUDE

Set this parameter equal to the name of the *AMPLITUDE option that defines the time history (*MODAL DYNAMIC) or frequency spectrum (*STEADY STATE DYNAMICS) of the motion. This parameter is irrelevant for the *RANDOM RESPONSE procedure. The parameter DEFINITION=SOLUTION DEPENDENT cannot be used in an *AMPLITUDE referenced by this option.

Optional parameters:

BASE NAME

Set this parameter equal to the name of the base if this base motion is to be applied to a secondary base. The base name is defined with the BASE NAME parameter on the *BOUNDARY option in the *FREQUENCY step.

LOAD CASE

Set this parameter equal to the load case number. This parameter is used in *RANDOM RESPONSE analysis, where it is the cross-reference for the load case on the *CORRELATION option.

SCALE

Set this parameter equal to the scale factor for the amplitude curve. The default is SCALE=1.0. This parameter applies during *MODAL DYNAMIC and *STEADY STATE DYNAMICS procedures.

TYPE

Set TYPE=ACCELERATION (default), VELOCITY, or DISPLACEMENT.

Optional, mutually exclusive parameters for steady-state dynamics analysis: 

IMAGINARY

Include this parameter to define the imaginary (out-of-phase) part of the base motion record given by the amplitude definition.

REAL

Include this parameter (default) to define the real (in-phase) part of the base motion record given by the amplitude definition.

There are no data lines associated with this option unless a primary base motion defines rotation about a point that is not the origin of the coordinate system. 

Data line to define the center of rotation for a prescribed rotation: 

First (and only) line:

  1. X-coordinate of the point about which the rotation is applied.

  2. Y-coordinate of the point about which the rotation is applied.

  3. Z-coordinate of the point about which the rotation is applied.

This data line is relevant only for a primary base motion defined in the *MODAL DYNAMIC and *STEADY STATE DYNAMICS procedures.