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2.Perform the generation pass using SEOPT and any other /SOLU commands to define any necessary options for the substructuring analysis.

3.Use SEGEN to define the options for the automatic superelement generation process. If stopStage

= PREVIEW is selected, then the model is only broken into domains (superelements). No reduced matrices are created and the superelements (.SUB files) are not actually created. You can then graphically (visually) preview each domain by using /PNUM,DOMAIN. By default, master DOFs are automatically defined at each of the following locations: all DOFs on the interfaces between each superelement, all DOFs associated with contact elements (TARGE169 to CONTA177), and at all DOFs associated with nodes having a point load defined. The option to manually define the master DOF only makes sense AFTER a 'preview pass' has been made, as the exact number of superelements and the superelement boundaries for each superelement cannot be known until the process is completed at least once.

Note

Due to the heuristics in the automatic domain decomposer, which is used to create the domains that will become superelements, the number of defined superelements may exceed the number of requested superelements.

After completing a preview pass, you can then add master DOFs or remove master DOFs that were automatically defined during the preview pass. At least one master DOF must be defined for each superelement. Then set stopStage = GEN, and if any master DOFs were added or removed, set mDof = YES, and solve the model.

4.Use SOLVE to either preview or generate the automatically created superelements. Note that multiple load steps are not supported with automatic superelement generation.

10.6. Nested Superelements

A powerful substructuring feature is the ability to use nested superelements (one superelement containing another). When you generate a superelement, one of the elements in the generation pass may be a previously generated superelement.

For example, suppose that you have a superelement named PISTON. You can generate another superelement named CYLINDER which contains the superelement PISTON. Now, for a complete analysis of the cylinder and its piston, you will need to perform one use pass and two expansion passes. The use pass calculates the reduced solution for the master DOF in the superelement CYLINDER. The first expansion pass calculates the complete solution for CYLINDER and the reduced solution for PISTON. The second expansion pass then gives you the complete solution for PISTON.

You can also generate transformed nested superelements (using SETRAN or SESYMM commands). It

is important in this case to perform the expansion pass in the exact reverse order used for the generation pass.

10.7. Prestressed Substructures

In modeling a system's behavior properly, it may be important to consider its stress state. That stress state will influence the values of the stiffness matrix terms. The stress state from a previous structural solution may be included when the stiffness matrix is formed in a superelement generation pass. Stress stiffening can provide strength in a structure which would normally not have any resistance to certain loadings. For example, a stretched cable can resist a normal loading while a slack cable cannot. Stress

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