Configuring a subspace-based steady-state dynamic analysis

You can configure a subspace-based steady-state dynamic analysis to calculate the steady-state dynamic linearized response of a system to harmonic excitation. This type of procedure is based on direct solution of the steady-state dynamic equations projected onto a subspace of modes. You must first extract the modes using the eigenfrequency extraction procedure (described in Configuring a frequency procedure”). For more information, see Subspace-Based Steady-State Dynamic Analysis.

This task shows you how to:

Create or edit a subspace-based steady-state dynamic procedure

  1. Display the Edit Step dialog box following the procedure outlined in Creating a step (Procedure type: Linear perturbation; Steady-state dynamics, Subspace), or Editing a step.
  2. On the Basic and Other tabbed pages, configure settings such as frequency range 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.

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

  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 one of the following options:

    • Choose Compute real response only if you want Abaqus/Standard to ignore damping terms. This option can reduce computational time.

    • Choose Compute complex response if you want to include damping terms and allow a complex system matrix to be factored.

  4. Choose a Scale option to indicate whether you want the frequency range(s) of interest to be divided using a Logarithmic or Linear scale.
  5. 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.
  6. Toggle on Use eigenfrequencies to subdivide each frequency range if you want the frequency range(s) of interest to be subdivided using the system's eigenfrequencies. For more information, see Selecting the Type of Frequency Interval for Which Output Is Requested.
  7. Click the arrow to the right of the Projection field, and select an option for controlling the frequency of the subspace projections:

    • Select Evaluate at each frequency to project the dynamic equations onto the subspace at each frequency you specify. This method is the most computationally expensive.

    • Select Constant to perform only one projection using model properties evaluated at the center frequency of all ranges and individual frequency points that you specify. This method is the least expensive. However, you should choose this method only when the material properties do not depend strongly on frequency.

    • Select Interpolate at eigenfrequencies to perform the projections at each extracted eigenfrequency in the requested frequency range and at eigenfrequencies immediately outside the range. The projected mass, stiffness, and damping matrices are then interpolated at each frequency point requested.

    • Select As a function of property changes to select how often subspace projections onto the modal subspace are performed based on material property changes as a function of frequency. If you select this option, do the following:

      1. In the Max. damping change field, enter the maximum relative change in damping material properties before a new projection is to be performed.

      2. In the Max. stiffness change field, enter the maximum relative change in stiffness material properties before a new projection is to be performed.

    • Select Interpolate at lower and upper frequency limits to perform projections at the lower and upper limits of the last frequency range. This method can be used only with the SIM architecture.

  8. Enter the following data in the Data table:

    Lower Frequency

    The lower limit of the frequency range or a single frequency, in cycles/time.

    Upper Frequency

    The upper limit of the frequency range, in cycles/time. If you enter zero, Abaqus/Standard assumes that results are required only at the frequency specified in the Lower Frequency column.

    Number of Points

    The number of points in the frequency range at which results should be given.

    If you toggled on Use eigenfrequencies to subdivide each frequency range, this is the number of points at which results should be given, including the end points, from the lower limit of the frequency range to the first eigenfrequency in the range; in each interval from eigenfrequency to eigenfrequency; and from the highest eigenfrequency in the range to the high limit of the frequency range.

    If you toggled off Use eigenfrequencies to subdivide each frequency range, this is the total number of points in the frequency range, including the end points.

    Bias

    The bias parameter. This parameter is useful only if you request results at 4 or more frequency points. It is used to bias the results points toward the ends of the intervals so that better resolution is obtained there. This option is recommended if you have toggled on Use eigenfrequencies to subdivide each frequency range, since the ends of each interval are the eigenfrequencies where the response amplitudes vary most rapidly.

    For more information, see The Bias Parameter.

    For detailed information on how to enter data, see Entering tabular data.

Configure settings on the Other tabbed page

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