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Chapter 10: Substructuring

Substructuring is a procedure that condenses a group of finite elements into one element represented as a matrix. The single-matrix element is called a superelement. You can use a superelement in an analysis as you would any other element type. The only difference is that you first create the superelement by performing a substructure generation analysis.

Substructuring is available in the ANSYS Multiphysics, the ANSYS Mechanical, and the ANSYS Structural products.

The following substructuring topics are available:

10.1.Benefits of Substructuring

10.2.Using Substructuring

10.3.Sample Analysis Input

10.4.Top-Down Substructuring

10.5.Automatically Generating Superelements

10.6.Nested Superelements

10.7.Prestressed Substructures

10.8.Where to Find Examples

10.1. Benefits of Substructuring

Substructuring reduces computer time and allows solution of very large problems with limited computer resources. Nonlinear analyses and analyses of structures containing repeated geometrical patterns are typical candidates for substructuring. In a nonlinear analysis, you can substructure the linear portion of the model so that the element matrices for that portion need not be recalculated at every equilibrium iteration. In a structure with repeated patterns (such as the four legs of a table), you can generate one superelement to represent the pattern and simply make copies of it at different locations, thereby saving a significant amount of computer time.

You can also use substructuring on models with large rotations. For these models, the program assumes each substructure to rotate about its mass center. In 3-D cases, the substructures contain three rigid body rotations and three translational motions. With a large rotation model, you do not constrain the substructure until the use pass because each substructure is treated as a single finite element that should allow rigid body motions.

An example is an analysis that is too large for the computer in terms of model size or disk space requirements. In such a situation, you can analyze the model in pieces, where each piece is a superelement small enough to fit on the computer.

10.2. Using Substructuring

A substructure analysis involves three distinct steps, called passes:

10.2.1.Step 1: Generation Pass (Creating the Superelement)

10.2.2.Step 2: Use Pass (Using the Superelement)

10.2.3.Step 3: Expansion Pass (Expanding Results Within the Superelement)

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