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11. Postprocess results in the superelement using standard techniques.

Note

An expansion pass is not valid if the use pass was a PSD analysis.

10.3. Sample Analysis Input

A sample command input listing for a substructuring analysis is shown below. This example assumes a single superelement which is possibly combined with nonsuperelements.

!GENERATION PASS

!Build the model (superelement portion)

FINISH

! Apply loads and create the superelement matrices

278

! reduced solution for superelements (USE.DSUB)

FINISH

!... Review results in nonsuperelements

!EXPANSION PASS

! ... Review results in superelements

For more information, see the ANTYPE, SEOPT, M, ET, SETRAN, SE, CPINTF, EXPASS, and SEEXP command descriptions.

10.4. Top-Down Substructuring

The substructuring procedure described in the previous section is called bottom-up substructuring, meaning that each superelement is separately generated in an individual generation pass, and all superelements are assembled together in the use pass. This method is suitable for very large models which are divided into smaller superelements so that they can "fit" on the computer.

For substructuring of smaller models or of systems with global project geometry controls, and for isolated component analysis, you can use a slightly different technique known as top-down substructuring. This method is suitable, for instance, for substructuring of the linear portion of nonlinear models that are small enough to fit on the computer. An advantage of this method is that the results for multiple superelements can be assembled in postprocessing. The procedure for top-down substructuring is briefly explained below, and is followed by a sample input.

1.First build the entire model, including both the superelement and nonsuperelement portions. Save this model on a named database file (for example, FULL.DB). The full model database is later required for the expansion pass. It will also be required for the use pass if the model consists of nonsuperelements.

2.Perform the generation pass on a selected subset of the entire model. Because the full model has already been built, all you need to do is to select the elements for the superelement portion, apply the desired loads (for the load vector), and create the superelement with the SOLVE command (Main Menu> Solution> Solve> Current LS).

The use of components may be helpful for this. To group items into a component, use the CM command (Utility Menu> Select> Comp/Assembly> Create Component).

If multiple superelements are to be generated, you will need to exit and re-enter SOLUTION each time and repeat the select-load-solve steps. Be sure to use a different jobname for each superelement.

3.Perform the use pass. Enter PREP7 and start by restoring the full model database and then selecting only the nonsuperelement portion of the model. Next, define the superelement type [ET, TYPE] and read in the appropriate superelement matrices. In most cases, you don't need to worry about the

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connecting nodes between the superelements, because they were all generated from a single model.

Enter SOLUTION and define the analysis type and analysis options. Apply loads on the nonsuperelements, read in load vectors (if any), specify load step options, and initiate the use pass solution.

4.Perform the expansion pass. Start by restoring the full model database, with all elements and nodes active. Then expand each superelement separately, using the appropriate jobnames and exiting and re-entering SOLUTION each time. You can then review the results in each superelement using normal postprocessing procedures. Use of the full database, FULL.DB, allows the reading in of multiple superelement results:

RESUME,FULL,DB

/POST1

FILE,GEN1

SET,...

FILE,GEN2

SET,...!Will not clear previous superelement results

A sample input for top-down substructuring follows. This example assumes a model with one superelement and other nonsuperelements.

!Sample input for top-down substructuring

!BUILD THE FULL MODEL

Please see the ANTYPE, SEOPT, M, ET, SE, EXPASS, and SEEXP command descriptions for more information.

10.5. Automatically Generating Superelements

When creating multiple superelements, the two methods described in the previous sections (bottomup substructuring and top-down substructuring) both require repeating a set of /SOLU commands for each superelement you want to create. These methods also require a master DOF to be defined for each superelement. If any superelements connect to each other, then the master DOF must be chosen carefully on the interface(s) between each connecting superelement.

When creating multiple superelements, use the following automatic superelement generation process to quickly create superelements (.SUB files), as well as the master DOF necessary on the interfaces between each superelement. This simplifies the creation of the superelements and it efficiently breaks a larger model into smaller models, for example, to be used in a nonlinear analysis.

To automatically generate superelements:

1.If using the bottom-up substructuring method first create the part of the model that will become superelements. If using the top-down substructuring method, first create whole model, then select the part

of the model that will become superelements.