Configuring a buckling procedure

An eigenvalue buckling analysis is generally used to estimate the critical buckling loads of stiff structures (classical eigenvalue buckling). This type of analysis is a linear perturbation procedure, and buckling loads are calculated relative to the base state of the structure. For more information, see Eigenvalue buckling prediction.

This task shows you how to:

Create or edit a buckling procedure

  1. Display the Edit Step dialog box following the procedure outlined in Creating a step (Procedure type: Linear perturbation; Buckle), or Editing a step.

  2. On the Basic tabbed page, configure settings such as eigensolver extraction method and maximum number of iterations as described in the following procedures.

    The Other tabbed page displays the default matrix storage option. You cannot change this setting because Abaqus/Standard provides eigenvalue extraction for only symmetric matrices. In eigenvalue buckling prediction procedures Abaqus/Standard symmetrizes all contributions to the stiffness matrix.

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 either the Lanczos eigensolver or the Subspace iteration eigensolver.

    The Lanczos method is generally faster when a large number of eigenmodes is required for a system with many degrees of freedom. However, this method does have some limitations (see the warning at the bottom of the Basic tabbed page). The subspace iteration method may be faster when only a few (less than 20) eigenmodes are needed. For more information, see Selecting the eigenvalue extraction method.

  4. In the Number of eigenvalues requested field, enter the number of eigenvalues that you want to be estimated. Significant overestimation of the actual number of eigenvalues can create very large files. If you underestimate the actual number of eigenvalues, Abaqus/Standard will issue a corresponding warning message.

  5. If you selected the Lanczos eigensolver, do the following:

    1. Toggle on Minimum eigenvalue of interest to enter a lower limit to the range of eigenvalues Abaqus/Standard will extract. If you toggle on this option, enter the value in the field provided.
    2. Toggle on Maximum eigenvalue of interest to enter an upper limit to the range of eigenvalues Abaqus/Standard will extract. If you toggle on this option, enter the value in the field provided.

      If you specify a range of eigenvalues, Abaqus/Standard will extract eigenvalues until either the requested number of eigenvalues has been extracted in the given range or all the eigenvalues in the given range have been extracted.

    3. Choose a Block size option:

      • Choose Default to use the default block size of 7, which is usually appropriate.

      • Choose Value to enter a particular block size in the field provided. In general, the block size for the Lanczos method should be as large as the largest expected multiplicity of eigenvalues.

      For more information, see Selecting the eigenvalue extraction method.

    4. Specify your preference for the Maximum number of block Lanczos steps:

      • Choose Default to allow Abaqus/Standard to determine the number of block Lanczos steps within each Lanczos run. The default value is usually appropriate.

      • Choose Value to enter a limit to the number of Lanczos steps within each Lanczos run. In general, if a particular type of eigenproblem converges slowly, providing more block Lanczos steps will reduce the analysis cost. On the other hand, if you know that a particular type of problem converges quickly, providing fewer block Lanczos steps will reduce the amount of in-core memory used.

  6. If you selected the Subspace eigensolver, do the following:

    1. Toggle on Maximum eigenvalue of interest to enter an upper limit to the range of eigenvalues Abaqus/Standard will extract. If you toggle on this option, enter the value in the field provided.

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

    2. 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.
    3. Enter a value for the Maximum number of iterations. The default is 30.

  7. Click OK to save the step and to close the Edit Step dialog box.