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STEADY STATE DYNAMICS
Set SUBSPACE PROJECTION=EIGENFREQ UENCY if the projections onto the modal
subspace of the dynamic equations are to be performed at each eigenfrequency within the
requested ranges and at the eigenfrequencies imm ediately outside these ranges. The projections
are then interpolated at each frequency requested on the data lines. The interpolation is done on a
logarithmic or linear scale depending on the value of the FREQUENCY SCALE parameter. This
value cannot be used for coupled acoustic-structural analysis.
Set SUBSPACE PROJECTION=PROPERTY CHANGE to select how often subspace
projections onto the modal subspace are performed based on material property changes as a
function of frequency. The interpolation is done on a logarithmic or linear scale depending
on the value of the FREQUENCY SCALE parameter. This value cannot be used for coupled
acoustic-structural analysis.
Optional parameters:
FREQUENCY SCALE
Set this parameter equal to LOGARITHMIC (default) or LINEAR to determine whether a
logarithmic or linear scale is used for output. If the SUBSPACE PROJECTION parameter is
included and is set equal to either EIGENFREQUENCY or PROPERTY CHANGE, the same scale
will be used for the interpolation of the subspace projections.
INTERVAL
Set INTERVAL=EIGENFREQUENCY if the frequency ranges specified on each data line are to be
subdivided using the system’s eigenfrequencies. This option requires a preceding
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FREQUENCY
step and is the default if the DIRECT parameter is omitted.
Set INTERVAL=RANGE if the frequency range specified on each data line is to be used
directly. This option is the default if the DIRECT parameter is included.
REAL ONLY
This param eter is relevant only if the DIRECT or the SUBSPACE PRO JECTION parameter is
included. Include this parameter if damping terms are to be ignored so that a rea l, rather than a
complex, system matrix is factored. This option can reduce computational tim e significantly for the
DIRECT procedure and, to a lesser exte nt, for the SUBSPACE PROJECTION procedure.
Optional parameters for SUBSPACE PROJECTION=PROPERTY CHANGE:
DAMPING CHANGE
Set this param eter equal to the maximum relative change in damping material properties before a
new projection is to be performed. The default value is 0.1.
STIFFNESS CHANGE
Set this parameter equal to the maximum relative change in stiffness material properties before a
new projection is to be performed. The default value is 0.1.
18.34–2
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