Configuring a complex frequency procedure

A complex frequency procedure performs eigenvalue extraction to calculate the complex eigenvalues and the corresponding complex mode shapes of a system. It is a linear perturbation procedure and requires that you perform an eigenfrequency extraction procedure (described in Configuring a frequency procedure”) prior to the complex eigenvalue extraction. For more information, see Complex Eigenvalue Extraction.

This task shows you how to:

Create or edit a complex frequency procedure

  1. Display the Edit Step dialog box following the procedure outlined in Creating a step (Procedure type: Linear perturbation; Complex frequency), or Editing a step.
  2. On the Basic and Other tabbed pages, configure settings such as the number of eigenvalues requested and matrix solver preferences as described in the following procedures.

Configure settings on the Basic tabbed page

  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. Choose an option for specifying the Number of eigenvalues requested:

    • Choose All if you want Abaqus/Standard to report all the eigenmodes available in the projected subspace, formulated on the basis of all eigenmodes computed in the preceding frequency step.

    • Choose Value to enter a specific number of eigenmodes that you want Abaqus/Standard to report.

  4. Toggle on Frequency shift (cycles/time) to specify a shift point, S, for the complex eigenvalue extraction procedure (S ≥ 0). Abaqus/Standard reports the complex eigenmodes, μn, in order of increasing |I⁢m⁢(μn)-S| so that the modes with the imaginary part closest to a given shift point are reported first. This feature is useful when a particular frequency range is of concern. The default is no shift.
  5. Toggle on Minimum frequency of interest (cycles/time) to specify a lower limit to the frequency range within which Abaqus/Standard reports eigenmodes.
  6. Toggle on Maximum frequency of interest (cycles/time) to specify an upper limit to the frequency range within which Abaqus/Standard reports eigenmodes.
  7. Toggle on Include friction-induced damping effects to include friction-induced contributions to the damping matrix. For more information, see Contact Conditions with Sliding Friction.

Configure settings on the Other tabbed page

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

    (For information on displaying the Edit Step dialog box, see Creating a step, or Editing a step.)

  2. Choose a Matrix solver option:

    • Choose Use solver default to allow Abaqus/Standard to decide whether a symmetric or unsymmetric matrix storage and solution scheme is needed.

    • Choose Unsymmetric to restrict Abaqus/Standard to the unsymmetric storage and solution scheme.

    • Choose Symmetric to restrict Abaqus/Standard to the symmetric storage and solution scheme.

    For more information on matrix storage, see Matrix Storage and Solution Scheme in Abaqus/Standard.

  3. Toggle on Evaluate dependent properties at frequency to enter a frequency at which Abaqus/Standard will evaluate frequency-dependent material properties. For more information, see Evaluating Frequency-Dependent Material Properties.

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