Two Step Modeling

1. Analysis of the global model
   • In this stage, the global model is analyzed, and the results are stored in along with model information (nodal coordinates).
2. Analysis of the local model
   • The results from the global model are imported from .h3d file using ASSIGN,H3DRES.
   • The specific subcase in the global model, from which results are to be imported, is specified using IMPORT,SUB.
   • A grid set is defined for the nodes in the interface/transfer zone (local side).
   • SPCD is defined on these grid sets with a value = M to signify the mapping.
     Note: The mapping displacement enforcement can also be directly through SPC instead of SPC/SPCD combination.
   • The mapped enforced displacements on this grid set is calculated and applied internally by OptiStruct through point cloud interpolation.

SUBCASE 1001 
	ANALYSIS STATICS	
	LABEL Global
	SPC = 10
	LOAD =20
	DISP (ROTA, H3D) = SET_ID
BEGIN BULK
..
Bulk data of the Global Model
..
ENDDATA

ASSIGN, H3DRES, 100, global_model.h3d
SUBCASE 2001  
	LABEL Local
	ANALYSIS STATICS
	SPC = 200
	LOAD = 400
 
IMPORT (SUB = 1001) = 100
BEGIN BULK
.
.
SPC, 200, 1000, 123456, 0.0
+, GSET

SPCD, 400, 1000, 123456, M
+, GSET
SET, 1000, GRID, LIST
+, 61040, 61041, 61042, 61043, 61044, 61045, 61046, 61047,
+, 61048, 61049, 61050, 61051, 61052
ENDDATA

1. Currently, only displacement results can be mapped in the two step submodeling process and only .h3d file format is supported.
2. By default, only translational displacements are mapped and if rotational displacements are desired, then they must be additionally requested.
3. Supported analysis types for two-step submodeling process include linear and nonlinear (SMDISP/LGDISP) static analyses and direct and modal transient analyses. For direct and modal transient analysis, the typical application is to use modal transient for the global model and direct transient for the local model. However, all combinations of global and local models are supported. For transient analysis in the local model, the SPCD used for displacement mapping definition should be referenced via a TLOAD1 entry and referenced along with any other applied loading.
4. Global-local analysis (submodeling) supports random response analysis, wherein the results of frequency response subcases are mapped using ASSIGN from a global H3D file to the local model. The IMPORT entry is used along with the SPCD M option in the local model to map at the interface. This is also applicable for acoustic analysis involving fluid cavity and coupling surfaces.
5. For frequency analysis, the IMPORT entry with SPCD(M) option allows displacement/velocity/acceleration results from .h3d files to be mapped as SPCD loads; subsequently, the random response analysis can be performed in the local model.
   An example of the setup for the IMPORT function with SPCD(M) is shown below:

   ASSIGN ,H3DRES,1000,'glb.h3d’
   
   SUBCASE 11
   ANALYSIS MFREQ
     IMPORT(SUB=11)=1000    
     DLOAD = 6
     FREQ = 1
     SPC = 137
   METHOD=10  
   
   SUBCASE 12
   ANALYSIS RANDOM
   RANDOM=20
   DISPLACEMENT(PSDFC) = ALL
   STRESS(RMS) = ALL
   
   BEGIN BULK
   EIGRA,10,0.0,500.0
   RANDPS,20,11,11,1.0,0.0,5 
   TABRND1,5
   +,1.0,0.01,100.0,0.05
   SET,1849,GRID,LIST,
   +,101,102
   SPC,137,1849,123456,0.0D0,
   +,GSET,
   SPCD,6,1849,123456,M,
   +,GSET,
   RLOAD1,6,6,,,1.0,0,DISP