Creating Mass Scaling

In an Explicit Dynamics step Abaqus for CATIA V5 marches the solution of a dynamic event forward through a series of small time increments until it reaches the specified time span for the step. A stable time increment based on the current dilatational wave speed in the model determines the size of each time increment in the analysis step (for details, see Explicit dynamic analysis in the Abaqus Analysis Guide). If the stable time increment is small, more increments are required to complete the step, and the analysis can become lengthy and computationally expensive.

Increasing the mass of a model effectively decreases the associated dilatational wave speed, which lengthens the stable time increment and leads to more efficient solutions. Abaqus for CATIA V5 offers an option when creating an explicit dynamics step that artificially scales the mass of a model to achieve a more desirable stable time increment. You can scale the mass of an entire model, scale only a particular region of a model, or apply different scale factors to different areas of a model. The scaling factor can be specified directly or calculated by Abaqus to achieve a specific stable time increment. Abaqus can also change the scaling factor over the course of a step to account for changes in element size due to deformation. For further discussion of mass scaling techniques, see Mass scaling in the Abaqus Analysis Guide.

Mass scaling in Abaqus for CATIA V5 is applied to the model in the Initialization step and remains in effect for all subsequent steps in an analysis. You cannot alter mass scaling definitions between steps. Artificial mass scaling does not affect the behavior of the following model entities:

Mass scaling will have no effect if you directly specify a time increment as part of a fixed incrementation scheme for an explicit dynamics step (see Inserting a New Explicit Dynamics Step).

This task shows you how to add mass scaling to a model in an Explicit Dynamics case.

  1. Click the Mass Scaling icon .

    The Edit mass scaling dialog box appears, and a Mass Scaling object appears in the specification tree under the Mass Scaling Assignments set for the Initialization step (the Mass Scaling Assignments set does not appear in the specification tree until you create a Mass Scaling object).

  2. You can change the identifier of the mass scaling object by editing the Name field.

  3. Select the Region in which the mass will be scaled:

    • To scale the mass for the entire model, select Whole model.

    • To scale the mass for a particular body within the model, select Set and select a body or body group from the window or specification tree.

  4. Select whether the scaling factor is fixed at the beginning of the step or is variable throughout the analysis.

  5. If you chose to fix the scaling factor at the beginning of the step, select at least one of the following options:

    • To directly specify a scaling factor, toggle on Scale by factor and enter the scaling factor in the field provided.

    • To let Abaqus automatically calculate a scaling factor based on a target stable time increment, toggle on Scale to target time increment and enter the increment in the field provided; then specify how Abaqus should apply the scaling factor:

      • If you select Uniformly to satisfy target, Abaqus determines the default stable time increment for the entire region, then applies a uniform scaling factor to the region until the stable time increment reaches the target.

      • If you select If below minimum target, Abaqus determines the default stable time increment for each element in the region, then applies a scaling factor to only those elements with a stable time increment below the target.

      • If you select Nonuniformly to equal target, Abaqus determines the default stable time increment for each element in the region, then applies a unique scaling factor to each element so that its stable time increment is equal to the target. The scaling factor may be less than one for some elements.

    If you directly specify both a scaling factor and a target stable time increment, Abaqus first scales the region's mass uniformly, then applies any additional scaling in accordance with the target time increment parameters.

  6. If you chose to vary the scaling factor throughout the analysis, specify the following options:

    1. Enter a target stable time increment in the Scale to target time increment field.

    2. Specify how Abaqus should apply the scaling factor:

      • If you select Uniformly to satisfy target, Abaqus determines the default stable time increment for the entire region, then applies a uniform scaling factor to the region until the stable time increment reaches the target.

      • If you select If below minimum target, Abaqus determines the default stable time increment for each element in the region, then applies a scaling factor to only those elements with a stable time increment below the target.

      • If you select Nonuniformly to equal target, Abaqus determines the default stable time increment for each element in the region, then applies a unique scaling factor to each element so that its stable time increment is equal to the target. The scaling factor may be less than one for some elements.

    3. Specify how frequently Abaqus should recalculate the scaling factor:

      • To recalculate the scaling factor after a fixed number of analysis increments, select Every and enter the number of increments in the field provided.

      • To recalculate the scaling factor at regular time intervals within a step, select At and enter the number of intervals within the overall step time.

  7. Click OK in the Edit mass scaling dialog box.