Defines data needed to perform real eigenvalue analysis.
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Figure 19 – Modes Analysis Section |
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Method of eigenvalue extraction:
Sets which method will be used to find eigenvalues. See the following table:
INV |
Inverse power method, symmetric matrix operations. |
DET |
Determinant method, symmetric matrix operations. |
GIV |
Givens method of tridiagonalization. |
MGIV |
Modified Givens method (see Remark 2). |
FEER |
Tridiagonal reduction method, symmetric matrix operations. |
FEER-Q |
See Remark 1. |
FEER-X |
See Remark 1. |
UINV |
Inverse power method, un-symmetric matrix operations. |
UDET |
Determinant method, un-symmetric matrix operations. |
Remarks
- The rigid body frequencies are set to zero, unless FEER-X is requested. If FEER-Q is requested, certain key areas in FEER computations are done in quad precision (Real*16) for 32-bit word machines and in double precision for 60- and 64-bit word machines. The FEER-Q request would yield much better rigid body eigenvalues, but it may take two to three times longer to compute than FEER or FEER-X.
- Givens method requires the mass matrix not to be singular. The MGIV method allows a singular mass matrix. The bigger dynamic matrix will require more CPU time and more memory.
-Frequency range of interest
:
(Required for METHOD = DET, INV, UDET, or UINV) (Real <=0.0; F1<= F2). If METHOD = GIV, frequency range acts over desired eigenvectors. The frequency range is ignored if ND > 0. In this case the ND number of first eigenvectors associated to positive roots is found. (Real, F1<=F2).
If METHOD = FEER, F1 is the center of range of interest (Default is F1 = 0.0) (Real > 0.0), and F2 is an acceptable relative error of tolerance expressed as percentage on frequency-squared (Default percentage is 0.1/n, where n is the order of the stiffness matrix) (Real > 0.0).
-Estimate number of roots
in range (Required for METHOD = DET, INV, UDET, or UINV. Ignored for METHOD = FEER) (Integer > 0).
-Desired number
The value of this field always has to be a positive integer.
This field has the following functions:
- For methods DET, INV, UDET, or UNIV: represents desired number of roots. If left blank, the default of '3 * Estimated number' is taken.
- For method GIV: represents desired number of eigenvectors.
- For method FEER: represents desired number of roots and desired number of eigenvectors. If left blank, an automatic numbers are calculated to extract at least one accurate mode.
-Mass orthogonality test:
Method for normalizing eigenvectors.
The following are the available methods:
MASS |
Normalizes eigenvectors to unit value of the generalized mass. |
MAX |
Normalizes eigenvectors to unit value of the largest component in the analysis set. |
POINT |
Normalizes eigenvectors to unit value of the component defined in fields NodeID and DOF. If the defined component is set to zero, the method is changed to MAX by default. |
-NodeID:
Node or scalar point identification number (Required if and only if Mass orthogonality test is set to POINT). The value of this field always has to be a positive integer.