Experimental Based Substructuring Using a Craig-Bampton Transmission Simulator Model

Abstract

Recently, a new experimental based substructure formulation was introduced which reduces ill-conditioning due to experimental measurement noise by imposing the connection 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 by constraining the modal degrees of freedom of the transmission simulator to those substructures. This work explores a different alternative in which the transmission simulator is modeled with a Craig-Bampton model, a model that may be more appropriate when the interfaces are connected rigidly. The new method is compared to the authors’ previous approaches to evaluate the errors due to modal truncation using finite element models of several beam systems including one in which the transmission simulator is connected to the component of interest at two points, potentially producing an ill-conditioned inverse problem.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy National Nuclear Security Administration under Contract DE-AC04-94AL85000.