Using the subspace iteration eigensolver for a frequency extraction procedure

1. In the Edit Step dialog box, display the Basic tabbed page.

2. In the Description field, enter a short description of the analysis step. Abaqus stores the text that you enter in the output database, and the text is displayed in the state block by the Visualization module.

3. From the list of Eigensolver options, choose Subspace.

4. In the Number of eigenvalues requested field, enter the number of eigenvalues that you want Abaqus/Standard to calculate.

5. Toggle on Frequency shift (cycles/time)**2 to specify a positive or negative shifted squared frequency, S. If you toggle this option on, enter a value for the frequency shift in the field provided. For more information, see Frequency shift.

6. Toggle on Maximum frequency of interest (cycles/time) to specify an upper limit to the frequency range within which Abaqus/Standard will calculate eigenvalues. If you toggle on this option, enter a value for the maximum frequency in the field provided.

   Abaqus/Standard will extract eigenvalues until either the requested number of eigenvalues has been extracted or the last frequency extracted exceeds the maximum frequency of interest.

7. Enter a value for the number of Vectors used per iteration. In general, the convergence is more rapid with more vectors, but the memory requirement is also larger. Thus, if you know that a particular type of eigenproblem converges slowly, providing more vectors by using this option might reduce the analysis cost.

8. Enter a value for the Maximum number of iterations. The default is 30.

1. In the Edit Step dialog box, display the Other tabbed page.

2. Accept the default Matrix storage setting. Since Abaqus/Standard provides eigenvalue extraction only for symmetric matrices, steps with eigenfrequency extraction or eigenvalue buckling prediction procedures always use the symmetric matrix storage and solution scheme. You cannot change this setting. In such steps Abaqus/Standard will symmetrize all contributions to the stiffness matrix.

3. Choose an option for normalizing eigenvectors:

   • Choose Displacement to normalize the eigenvectors so that the largest displacement, rotation, or acoustic pressure entry in each vector is unity.

   • Choose 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).

   For more information, see Normalization.

4. Toggle on Evaluate dependent properties at frequency to evaluate frequency-dependent properties for viscoelasticity, springs, and dashpots during the eigenvalue extraction. If you toggle on this option, enter the desired evaluation frequency in the field provided. For more information, see Evaluating frequency-dependent material properties.

When you have finished configuring settings for the frequency step, click OK to close the Edit Step dialog box.