This option is used to perform eigenvalue extraction to calculate the natural frequencies and corresponding mode shapes of a system.
Product: ABAQUS/Standard
Type: History data
Level: Step
Set EIGENSOLVER=LANCZOS (default) to invoke the Lanczos eigensolver.
Set EIGENSOLVER=SUBSPACE to invoke the subspace iteration eigensolver.
Set NORMALIZATION=DISPLACEMENT (default) to normalize the eigenvectors so that the largest displacement, rotation, or acoustic pressure (in coupled acoustic-structural extractions) entry in each vector is unity.
Set NORMALIZATION=MASS to normalize the eigenvectors with respect to the structure's mass matrix (the eigenvectors are scaled so that the generalized mass for each vector is unity).
Set this parameter equal to the frequency at which to evaluate frequency-dependent properties for viscoelasticity, springs, and dashpots during the eigenvalue extraction. If this parameter is omitted, ABAQUS/Standard will evaluate the stiffness associated with frequency-dependent springs and dashpots at zero frequency and will not consider the stiffness contributions from frequency-domain viscoelasticity in the *FREQUENCY step.
Set ACOUSTIC COUPLING=ON (default) to include the effect of acoustic-structural coupling during the natural frequency extraction procedure in models with acoustic and structural elements coupled using the *TIE option or in models with ASI-type elements.
Set ACOUSTIC COUPLING=OFF to ignore the effect of acoustic-structural coupling during natural frequency extraction in models with acoustic and structural elements coupled using the *TIE option or in models with ASI-type elements.
Set this parameter equal to the biasing parameter to be used to distribute the frequency intervals for the parallel Lanczos solver. If this parameter is omitted, equal size intervals will be used (unless USER BOUNDARIES are set).
The BIAS and USER BOUNDARIES parameters are mutually exclusive.
Set this parameter equal to the number of frequency intervals for the parallel Lanczos solver. If this parameter is omitted, ABAQUS/Standard will use a single frequency interval. If the specified value is larger than the number of CPUs requested for the analysis, the value will be reset to the number of CPUs.
Include this parameter to indicate that residual modes are to be computed based on the loads specified in the immediately preceding static perturbation step.
Include this parameter to indicate that the frequency interval boundaries for the parallel Lanczos solver will be specified on the data line.
The BIAS and USER BOUNDARIES parameters are mutually exclusive.
First line:
Number of eigenvalues to be calculated. This field can be left blank if the maximum frequency of interest is provided and the evaluation of all the eigenvalues in the given range is desired. The number of requested eigenmodes must be provided in a cyclic symmetry analysis or if the analysis includes more than one natural frequency extraction step.
Minimum frequency of interest, in cycles/time. If this field is left blank, no minimum is set. This value is required if NUMBER INTERVAL is greater than one.
Maximum frequency of interest, in cycles/time. If this field is left blank, no maximum is set. This value is required if NUMBER INTERVAL is greater than one or if the first field was left blank.
Shift point, in squared cycles per time (positive or negative). The eigenvalues closest to this point will be extracted.
Block size. If this entry is omitted, a default value, which is usually appropriate, is created.
Maximum number of block Lanczos steps within each Lanczos run. If this entry is omitted, a default value, which is usually appropriate, is created.
Subsequent lines (only if USER BOUNDARIES has been requested):
Give the desired frequency interval boundaries, eight per data line (there must be exactly NUMBER INTERVAL – 1 values given).
Repeat this line as often as necessary to define all frequency interval boundaries.
First (and only) line:
Number of eigenvalues to be calculated.
Maximum frequency of interest, in cycles/time. This user-specified maximum frequency is increased automatically by 12.5% to help capture closely-spaced modes. ABAQUS/Standard will also report all eigenvalues that converge in the same iteration as those in the specified range, even if their frequencies are more than 12.5% above the maximum frequency specified by the user. If this field is left blank, no maximum is set.
ABAQUS/Standard will extract frequencies until either of the above limits is reached.
Shift point, in squared cycles per time (positive or negative). The eigenvalues closest to this point will be extracted.
Number of vectors used in the iteration. If this entry is omitted, a default value, which is usually appropriate, is created. The default number of vectors used is the minimum of (n+ 8, 2n), where n is the number of eigenvalues requested (the first data item on this data line). In general, the convergence is more rapid with more vectors, but the memory requirement is also larger. Thus, if the user knows that a particular type of eigenproblem converges slowly, providing more vectors by using this option might reduce the analysis cost.
Maximum number of iterations. The default is 30.