OptiStruct Enhancements Pertinent to Multibody Simulations

This section documents other important enhancements that have been made to OptiStruct that you should be aware of.

After a MotionSolve run, it is possible to recover displacements, velocities, accelerations, stresses, and strains for the flex-body in OptiStruct in order to create .op2 and .h3d results files for fatigue analysis. The procedure is explained as follows:

•	First, you perform a MotionSolve simulation with a model that contains flexible bodies. MotionSolve creates a results file (*.mrf) that contains the modal participation factors at each time step for the Flex Body.

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Next, in OptiStruct, perform a residual run to recover displacement, velocity, acceleration, stress, and strain results for interior girds and elements in the Flex Body based on the modal participation results from MotionSolve. In the residual run, the Flex Body filename_recov.h3d file and the .mrf results file are specified using the ASSIGN data:

-	ASSIGN, H3DMBD, 30101, ’pfbody_1_recov.h3d’

-	ASSIGN, H3DMBD, 30102, ’pfbody_2_recov.h3d’

-	ASSIGN, MBDINP, 10, ’pfbody.mrf’

The 10 in the ASSIGN, MBDINP data corresponds to the SUBCASE for which the MotionSolve results will be used. In SUBCASE 10, instead of performing a transient analysis, OptiStruct will just use the results from MotionSolve.

The 30101 and 30102 in the ASSIGN, H3DMBD data refer to the Flex Body ID’s in the .mrf file3.

•	PARAM, MBDREC: The parameter MBDREC can be used to create solver and recovery .h3d files during Component Mode Synthesis (CMS)

•	PARAM, CMSDIRM: The parameter CMSDIRM can be used to allow or disallow flexible body generation when directional masses are defined in the input file

•	ASSIGN, H3DMBD: Identifies an external nodal flexh3d file that contains the analysis recovery information for displacements, velocities, accelerations, stresses and strains.

•	ASSIGN, MBDINP: Identifies an external file from which to read the modal participation factors calculated by MotionSolve for transient analysis

•	CMSMETH, 1, CBG, , 15: CBG is the keyword that instructs OptiStruct to create the CMS flexible body with additional geometric stiffness data using the Craig-Bampton CMS method

Two H3D files are generated when the PARAM, MBDREC option is used.

•	A PLOTEL based FlexH3D file that contains a minimum set of graphics and all the necessary information required by MotionView and MotionSolve to perform a multibody simulation with CMS flexible bodies.

•	A “Recover FlexH3D” file that contains all the information need by OptiStruct to recover the full set of stress and strains from a MotionSolve simulation.

The overall process for using this is illustrated below.

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•	A small file *.h3d contains the minimum amount of information needed for MBD simulation in MotionSolve. FlexH3D files are significantly smaller (sometimes by 100x), and file management becomes much simpler.

A larger file *_recov.h3d will also be generated that contains the information from the small file as well as recovery information for displacement, velocity, acceleration, stress, and strain.