Eigenvalue Parameters

The eigenvalue analysis provides the eigenfrequencies and mode shapes that are used as the basis for the VIV response calculation.

1. Free vibration options

  • Number of eigenvalues : Number of eigenvalues to be calculated

The number of eigenvalues to be calculated is the total number of frequencies. Once these have been found, the program selects the cross-flow or in-line frequencies as relevant. Approximately 50% of the calculated frequencies are in-line and 50% are cross-flow.

In order to study VIV response up to frequency no. 30, at least 60 eigenvalues must be specified.

2. Computation parameters

The parameters correspond to Lanczos' method for solution of eigenvalue problems.

  • Max relative error : Maximum acceptable relative error in the computed eigenvalues

  • Number of Lanczo steps : Maximum number of Lanczos steps (vectors) to be used

Both parameters are set to default unless the values are made editable and specified by the user.

3. Debug print

  • Number of eigenvectors : Number of eigenvectors to be printed

If zero, all eigenvectors are printed.

For details, see VIV frequency analysis - input reference.