Active Control of Buckling: Centralized and Decentralized Approaches

This thesis examines two different approaches to active buckling control of a compressively-loaded structural element. The phenomenon of buckling is the single most important factor limiting the load-bearing strength of a structure. Active control of buckling allows us to increase the load-bearing capabilities of compressive members, leading to structures that are both stronger and lighter than the passive structures built today. Traditionally, active structural control has been performed by centralized controllers, which assume both the existence of a global model for the system to be controlled, and the availability of global state information. These assumptions fail, however, in the case of large, complex structures which require many sensing sites and are characterized by interactions between members that are difficult to model accurately on a global scale. In recent years, an effort has been underway, notably in the area of vibration control, to develop decentralized control techniques which distribute the control effort throughout the structure, thereby localizing the controller's knowledge and influence. The challenge for the decentralized controller design is to retain global control authority necessary to control the structure as a whole, in spite of the lack of reliance on the global models and the global state information. In this thesis, we investigate the viability of decentralized control as an alternative to centralized control, as applied to active buckling control of a structural member. In order to compare the performance of the two types of controllers, we conduct qualitative analysis, simulation, and experimentation on a prototype beam. The results indicate that even a very simple, unsophisticated decentralized controller is capable of increasing the load-bearing strength of the beam to the levels comparable to those achieved through the use of centralized control. Thesis Supervisor: Gerald J. Sussman Title: Matsushita Professor of Electrical Engineering