OS-HWX-T: 7000 Dynamic Condensation and Residual Analysis using Component Mode Synthesis (CMS) Method

This tutorial demonstrates analysis of reduced structure by the implementation of superelements using Component Mode Synthesis (CMS) method of an airframe section in OptiStruct.

Before you begin, copy the file(s) used in this tutorial to your working directory.
The Component Mode Synthesis (CMS) method is used to reduce a finite element model of an elastic body to the interface degrees of freedom and a set of normal modes. The result can either be used as a flexible body in a multi-body dynamics analysis, or as external matrices representing a superelement assembly in a finite element analysis. As it captures the mass matrix correctly, it is the preferred method for dynamic analysis. Load vectors are not reduced during CMS Super Element creation.

Figure 1. Model Description

A superelement is a reduced representation of the behavior and performance of a structure or a part of a structure. System equations using these matrices are solved to simulate the structure's behavior. This is referred to as Direct Matrix Input or Superelements. The part of the full model that remains after the superelement has been created is the Residual structure. The reduced loading, mass, stiffness, and damping matrices can be generated using multiple methods. The full model is carefully examined to determine the sections or parts that can be reduced out as superelements. The boundaries between the superelements and the residual structure are identified using connection/interface points. After the identification of interface points, the rest of the structure (residual) is now deleted from the full model. Depending on the superelement creation method selected, the corresponding entries are added (CMSMETH).

The following exercises are included:
  • Superelement Generation
    • Create ASET boundary constraints
    • Delete residual structure
    • Request DMIG output
  • Residual (Dynamic Condensation)
    • Delete superelement
    • Create cards to reference DMIG matrices