Recover MBD Analysis Results

After MotionSolve is run, it is possible to recover displacements, velocities, accelerations, stresses, and strains for the flexbody in OptiStruct in order to create .op2 and .h3d results files for fatigue analysis.

The procedure is explained below.

After running MotionSolve, a residual run can be made to recover displacement, velocity, acceleration, stress, and strain results for interior grids and elements in the Flex Body based on the modal participation results from MotionSolve. After running MotionSolve, a resulting <filename>.mrf file is created that contains MotionSolve results including the modal participation factors at each time step for the Flex Body for transient analysis. 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'

Where, the 10 in the ASSIGN,MBDINP data references 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 file.

For transient analysis, the number of time steps in the transient analysis run must match the number of time steps used in the MotionSolve analysis. While the transient analysis data is ignored, there must still be some dummy loading data (TLOAD, DAREA, and TABLED data). A sample of input data for a transient analysis run is:
OUTPUT OP2
OUTPUT H3D
ASSIGN,H3DMBD,30103,MBD_pfbody_BODY_2_PROP_6_recov.h3d
ASSIGN,H3DMBD,30102,MBD_pfbody_BODY_1_PROP_9_recov.h3d
ASSIGN,H3DMBD,30104,MBD_pfbody_BODY_3_PROP_10_recov.h3d
ASSIGN,MBDINP,1,MBD_pfbody_mbd.mrf
SUBCASE       1                            
  TSTEP(TIME) =        4
  DLOAD =        3
  DISPLACEMENT = ALL
  STRESS = ALL
  SPC = 1
$
BEGIN BULK
GRID    9999999   $ Dummy GRID since at least one GRID is required
$------+-------+-------+-------+-------+-------+-------+-------+-------
TSTEP          4 300    .0003333   1  
TLOAD1         3       3            DISP       2
TABLED1        2  LINEAR  LINEAR
+            0.0     1.0    10.0     1.0ENDT   
$
$ Dummy load on the dummy grid
SPC            1 9999999       1
SPCD           3 9999999       1  -200.0  
ENDDATA

A dummy grid and a dummy load has been added for the OptiStruct analysis run.