Translating an Abaqus substructure to an MSC.Adams flexible body

The following procedure summarizes the typical usage of the abaqus adams translator:

1. Create an Abaqus substructure. (General guidelines for building Abaqus models with substructures are described in Using substructures.)

   The substructure generation step must write at least the mass and stiffness matrices. It can also write the recovery and viscous damping matrices. The FLEXIBLE BODY option must be used. For example,

   *SUBSTRUCTURE GENERATE, MASS MATRIX=YES, RECOVERY=YES, VISCOUS DAMPING=YES
   *FLEXIBLE BODY, TYPE=ADAMS

   • If TYPE=ADAMS, a flexible body including all high-order inertia invariants is created.

   • If TYPE=ADAMS, REDUCED FORMULATION, a simplified flexible body (without high-order inertia invariants I5 and I9) is created.

   In addition, you can add the following data to translate stress and/or strain:

   *ELEMENT RECOVERY MATRIX, POSITION=AVERAGED AT NODES
   S,
   E,

   You can recover results on a subset of the model using the ELSET parameter for the substructure generation and element recovery matrix options shown above. When running the translator, you must use the mnf_elset command line option to define this element set.

   If the Abaqus analysis did not use SI units (meters, kilograms, Newtons, and seconds), you must define units when you run the translator using the length, mass, force, and time command line options. If the Abaqus analysis uses American or English units (inches, pounds force, and seconds), the mass unit is slinch.

2. Run the Abaqus analysis.

3. Run the abaqus adams translator to read the substructure SIM database produced by the analysis and to create the modal neutral file.

Typically, for a non-prestressed, unrestrained substructure in three dimensions, you expect to find six rigid body modes with associated zero eigenvalues. The situation is, in general, different for prestressed substructures, which may have fewer than six modes with zero eigenvalues. Prestressing may change some expected zeroes into values that are significantly positive or negative, depending on the sign of the prestress.

By default, the translator deletes modes with negative eigenvalues and reorthogonalizes the reduced basis. If you want to retain modes with negative eigenvalues, define the environment variable MDI_MNFWRITE_OPTIONS.

• On Linux platforms type the following command:

  setenv MDI_MNFWRITE_OPTIONS negative_roots_OK

• On Windows platforms type the following command:

  set MDI_MNFWRITE_OPTIONS=negative_roots_OK

In this case the translator will treat modes with negative eigenvalues in the same manner as all other modes.