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This command is used to perform a generalized eigenvalue problem to determine a specified number of eigenvalues and eigenvectors.
eigen <$type> $numEigenvalues
$type |
eigen-value analysis type: |
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frequency |
solve: K- l M |
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generalized |
solve: K- l M (default) |
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standard |
solve: K- l I |
$numEigenvalues |
number of first eigenvalues (l) to be determined |
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The eigenvectors are stored at the nodes and can be printed out using Node Recorder or the Print command.
NOTE: The current eigensolver is able to solve only for N-1 eigenvalues, where N is the number of interial DOFs. When running into this limitation, the user should add negligible masses to additional unrestrained degrees of freedom.
For example, for a 3-dof/node problem, instead of:
mass 1 100 0 0
the user should input:
mass 1 100 1e-9 0
where dof-2 at node 1 is unrestrained.
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