Superelement analysis

In Pre/Post, you can perform superelement reductions on FE components. The software implements these solutions by writing the EXTSEOUT case control command to the solver input file. After solving, you can use the reduced matrices to represent the components in a system model. For more information, see Using superelements in an assembly FEM.

The following Simcenter Nastran solution types can perform these reductions.

• SOL 101 Superelement

• SOL 103 Superelement

• SOL 414,103 Eigenvalues and Superelement Reduction in a rotor dynamics analysisFor more information, see Rotor dynamic analysis with superelements (SOL 414,103).

For SOLs 101, 103, and 114,103, you use sets to define degrees of freedom for the boundary where the component is connected to other components in the structure.

• Analysis (ASET): This set contains all boundary degrees of freedom of the superelement. It is considered fixed by default.

• Fixed Boundary (BSET): This subset of the ASET contains all fixed boundary degrees of freedom.

• Free Boundary (CSET): This subset of the ASET contains all free boundary degrees of freedom.

Note:

You can use DOF Sets to define ASET, BSET, and CSET explicitly. Reference the defined DOF Sets in the DOF Sets group on the Bulk Data tab in the Edit Solution dialog box. However, you can also define the sets using the Fixed Boundary Degrees of Freedom and Free Boundary Degrees of Freedom constraints, as described below.

SOL 101 Superelement

With this static condensation reduction, all stiffness, mass, and damping is reduced to the superelement boundary (that is, to the ASET). All boundary degrees of freedom are fixed.

Define the fixed degrees of freedom for the boundary using the Fixed Boundary Degrees of Freedom constraint.

SOL 103 Superelement

This solution generates a Component Mode Synthesis reduction to represent the component's dynamic behavior. The boundary degrees of freedom can be fixed or free.

• Define the fixed boundary degrees of freedom using the Fixed Boundary Degrees of Freedom constraint.

• Define the free boundary degrees of freedom using the Free Boundary Degrees of Freedom constraint.

In an SOL 103 Superelement solution, you must also create SPOINTs to store the reduced modes in the QSET. To do this, define a value in the Number of Generalized DOF box in the Case Control tab of the Edit Solution dialog box. The software writes this value to the Nastran input file as follows:

QSET1, 0, N1, THRU, N2

SPOINT, N1, THRU, N2

where

• N1 = round up to nearest 100000 integer from the highest node number in the model + 1

• N2 = N1 + Number of Generalized DOF – 1

For example, if the highest node number in the model is 121366, and Number of Generalized DOF is 300, the bulk data is written as

QSET1, 0, 200001, THRU, 200300

SPOINT, 200001, THRU, 200300

The total number of SPOINTs must be more than the number of requested modes plus all of the fixed boundary degrees of freedom.

Note:

For more information, see the Simcenter Nastran Superelement User's Guide.

How do I

Replace Base FEM components with superelements

Load and display superelement results

Update a system model

Learn more

Using superelements in an assembly FEM

System modeling workflow

Generating external superelements for Pre/Post system models

Replacing a component FEM with a superelement

Superelement mapping considerations

Connecting superelement boundary nodes to the residual

Superelement displays

Controlling the display of base FEM approximations

Solving the system model

Example: Assigning external superelements in the bulk data file

Example: Defining superelement connections and orientation

Post-processing system models

Creating a Simcenter Samcef superelement for Pre/Post system models

Supported system model solutions for Simcenter Samcef superelements

DOF sets

Look up more details

Supported system model solutions

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area

Superelement analysis, Simcenter 3D 2021.1 Series

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