Damage Detection in Dynamic Systems with Nonlinearities

OF THE THESIS Damage Detection in Dynamic Systems with Nonlinearities by William Bruce Dunbar Master of Science in Engineering Sciences (Applied Mechanics) University of California, San Diego, 1999 Professor John B. Kosmatka, Chair In general, damage detection can be described by the process of monitoring a physical dynamic (moving) system accompanied by con rmation and assessment of any degradation of system performance. This study is concerned with systems that contain nonlinearities in the dynamics that either pre-exist and/or result from some form of damage. Commonly, these systems are mathematically modeled and terms that are representative of a speci c fault are identi ed and monitored in a computer for detection. Health monitoring of dynamic systems for the detection of damage is an important practice in assessing performance of those systems and has a wide application range varying from structural and electro-mechanical systems to bio-medical systems. Although health monitoring of structural and bio-medical systems with nonlinearities has been largely untouched, there exist successful tools for monitoring nonlinear electro-mechanical systems, most of which come from system identi cation (SI) techniques. SI is concerned with deriving dynamic models of systems from experimentally obtained data. This thesis focuses on the application of SI techniques to a structural and an electro-mechanical system that contain nonlinearities. A numerical analysis of identifying linear terms and nonlinear terms (resulting from damage) in a structural system is investigated by applying a SI parameter estimation technique called quasilinearization. Also, an experimental analysis is performed to isolate and detect a dry friction fault in a high precision positioning mechanism. The designed fault detection and isolation scheme involves model tting, dynamic ltering and recursive parameter estimation SI tools. The high precision positioning mechanism is a servo pneumatic cylinder that drives a translational air bearing apparatus, designed to permit the addition of friction on-line. In the last several years, pneumatic cylinders have found wide application in electro-mechanical systems with precision positioning objectives. xvi Chapter