Autodesk Nastran Solvers and Related Options

Autodesk Nastran Solvers

In the Autodesk Simulation Mechanical 2015 Product Enhancements release, you can now choose to run certain simulations using Autodesk Nastran solvers. These Nastran solvers are available for the following four analysis types, as an alternative to the native Simulation Mechanical solvers:

When you run a simulation using an Autodesk Nastran solver, you can view the summary and log files within the Output Bar, just as you can for all of the Simulation Mechanical solvers.

How to Choose which Solver to Use

There are three places where you can choose which solver to use. The Nastran option and command will only be available for the four previously listed analysis types:

  1. Specify the preferred solvers using the new Processors tab of the Options dialog box (Tools Options Application Options Processors). Only Nastran-supported analysis types are listed in this dialog box tab. All other analysis types use the native Simulation Mechanical solvers. Use the drop-down box in the Default Processor column to choose from the following two options:
    • SimMech: Use the native Simulation Mechanical solver by default.
    • Nastran: Use the alternative Autodesk Nastran solver by default.

    When you click the Analysis Analysis Run Simulation command, the default processor will initially be used. Note that this command is also available from the context menu that appears when you right-click a Design Scenario heading in the browser.

  2. Choose from the following two commands in the Analysis panel of the Analysis ribbon tab. These ribbon commands override the default solver specified in the Application Options (see item 1 above).
    • Run Simulation Run with SimMech: Use the native Simulation Mechanical solver.
    • Run Simulation Run with Nastran: Use the alternative Autodesk Nastran solver.

    These commands are also available from the context menu that appears when you right-click a Design Scenario heading in the browser.

    Note: Once you have overridden the default processor, the Analysis Analysis Run Simulation command will call the same solver if you re-analyze the same design scenario. However, the default processor is not changed. The initial action of the Run Simulation command continues to follow the Default Processor settings for other design scenarios and future models.
  3. Choose which solver to use for each design scenario using the drop-down box in the Processor column of the Solver Manager. The available choices are:
    • SimMech: Use the native Simulation Mechanical solver.
    • Nastran: Use the alternative Autodesk Nastran solver.
      Note: The initially displayed processor is dependent upon the default solver specified in the Processor tab of the Application Options (see item 1 above).

Nastran Error Handling Options

The Nastran error handling preference is specified within the Processors tab of the Options dialog box (Tools Options Application Options Processors). Here, you specify what the program will do when an Autodesk Nastran solver returns an error message due to an incompatibility in the model. Examples of incompatibility errors are unsupported loads, material models, or element types.

There are two options listed in the Error Handling section of the Processors tab. The choices (selected by radio button) are:

Note: For errors other than those due to incompatibilities, the analysis will be canceled. In this case, if you want to try rerunning the analysis using the Simulation Mechanical solver, you must do so manually.

Nastran Stress and Strain Output Options

Currently implemented Autodesk Nastran solvers do not permit the output of both stress and strain results in a single case. To handle this limitation, options have been added for the linear analyses that produce actual or normalized stress and strain outputs and that are supported by Autodesk Nastran.

For Static Stress with Linear Material Models, two columns have been added to the Load Case Multipliers table within the Multipliers tab of the Analysis Parameters dialog box. Therefore, you can set the output option for each individual load case:

For Natural Frequency (Modal) analyses, the stress/strain output options are located within the Output tab of the Analysis Parameters dialog box. The following two options (selected by radio button) appear in the Nastran Stress/Strain section of the Output tab:

Note: These stress/strain output options have no effect when using the native Simulation Mechanical solvers. If the Autodesk Nastran solver is used, only the requested type of output is generated. If the unsolved model is exported to a Nastran file, then the stress/strain option controls the requested output type in the Case Control section of the Nastran deck.

Nastran-Specific Solid Mesh Characteristics (Splitting Pyramid Elements)

The default solid mesh type in Simulation Mechanical is a hex-dominant hybrid mesh consisting of 8-node bricks, 6-node wedges, 5-node pyramids, and 4-node tetrahedra. Nastran solvers typically do not directly support pyramid elements. Depending upon the particular Nastran version, each pyramid must either be represented as a degenerate CHEXA brick element or must be split into two tetrahedral elements.

A new feature of the Simulation Mechanical 2015 Product Enhancements release is the following: When you run a simulation using the Autodesk Nastran solver, all pyramid elements within the solid mesh are automatically split into tetrahedra before the solver is called. This is true whether the Default Processor is set to Nastran or you use the Run with Nastran ribbon command.

Note: This pyramid-splitting operation is only performed for Autodesk Nastran solutions within Simulation Mechanical. If you export an unsolved model to a Nastran file, the pyramids are represented as degenerate CHEXA elements in the resulting Nastran deck.
Parent topic: Simulation Mechanical 2015 Product Enhancements Release (June 2014)