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##

*BASE MOTION

Keyword type: step

This option is used to prescribe nonzero displacements and/or accelerations in
*MODAL DYNAMIC and *STEADY STATE
DYNAMICS calculations. The parameters DOF and
AMPLITUDE are required, the parameter TYPE is optional.

The prescribed boundary condition applies to the degree of freedom DOF in all
nodes in which a homogeneous *BOUNDARY condition has been defined for this
degree of freedom. If using *BASE MOTION it is good practice to define these
*BOUNDARY conditions BEFORE the step in which *BASE MOTION is used, else the
effect may be unpredictable. The parameter DOF can only take the values in the
range from 1 to 3. With the parameter AMPLITUDE the user specifies the
amplitude defining the value
of the boundary condition. This amplitude must have been defined using the
*AMPLITUDE card.

The TYPE parameter can take the string DISPLACEMENT or ACCELERATION. Default
is ACCELERATION. Acceleration boundary conditions can only be used for
harmonic steady state dynamics calculations, displacements can be used for any
modal dynamic or steady state dynamic calculation. Since only three degrees of
freedom are at the user's disposal, defining more than three *base motion
cards does not make sense.

The *BASE MOTION card is more restrictive than the *BOUNDARY card in the sense
that the same amplitude applies to a specific degree of freedom in all nodes
in which a homogeneous boundary condition for exactly this degree of freedom has been defined. It is, however,
less restrictive in the sense that for steady state dynamics calculations also
accelerations can be applied.

First line and only line:

- *BASE MOTION
- Enter any needed parameters and their value.

Example:
*BASE MOTION,DOF=2,AMPLITUDE=A1

specifies a base motion with amplitude A1 for the second degree of freedom for
all nodes in which a homogeneous boundary condition was defined for precisely
this degree of freedom.

Example files: beamdy10bm.

** Next:** *BEAM SECTION
** Up:** Input deck format
** Previous:** *AMPLITUDE
** Contents**
guido dhondt
2018-12-15