Formulation of a Craig-Bampton Experimental Substructure Using a Transmission Simulator

Abstract

Recently, a new experimental based substructure formulation was introduced, called Modal Constraint for Fixture and Subsystem (MCFS). This method reduces ill-conditioning by imposing constraints on substructure modal coordinates instead of the physical interface coordinates. The experimental substructure is tested in a free-free configuration, and the interface is exercised by attaching a flexible transmission simulator. An analytical representation of the fixture is then used to subtract its effects from the experimental substructure. The resulting experimental component is entirely modal based, and can be attached in an indirect manner to other substructures using MCFS. In contrast, this work presents a formulation in which the analytical representation of the transmission simulator is in the form of a Craig-Bampton (CB) substructure including fixed-interface modal coordinates and physical interface coordinates. The negative of the analytical representation of the transmission simulator is constrained to the experimental modal model using MCFS by eliminating the fixed-interface modal coordinates. The resulting experimental substructure contains a hybrid set of coordinates, including modal coordinates and the physical interface degrees of freedom, analogous to a CB representation. This new formulation offers the improved conditioning of the MCFS approach, but can be directly connected through the physical interface coordinates to other finite element based substructures.

Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.