Active Control of Vibration

Abstract

vibrations of flexible structures. The great majority of the work has been concerned with feedback control of large flexible systems at relatively low frequencies. The general topic of active vibration control in this context has been admirably treated in recent texts by Professors Meirovitch (1990) and Inman (1989). The subject matter of their texts has largely been devoted to modem control systems with an emphasis on multi-channel feedback control. More recently, as a result of a perceived need in the noise control community, advances have emerged in the active control of vibrations at audio frequencies and for steady state excitation. These advances have been largely due to the recent development of fast digital signal processors together with fast multichannel analogue-to-digital and digital-to-analogue converters. In addition, there have been significant advances in the development and use of control transducers which have enabled the realistic implementation of many active vibration control techniques. The overall aim of the book is to summarise these new advances in active vibration control with an emphasis on the fundamental scientific principles that form the basis of these techniques. In writing this book we have chosen to provide both a basic understanding of the subject and a research reference text. The book is thus aimed towards graduate students, researchers and engineers who have some knowledge of the theory of vibrations, mechanics and control. The book is written as a companion to the text by Nelson and Elliott (1992) which covers, in detail, the related area of active control of sound. In the interest of brevity, much of the material which is common to both fields has not been included in this text and references to Nelson and Elliott (1992) are provided where pertinent. However, when the material is essential to the understanding and continuity of the text, it is included in this book. In a similar way to the companion text, the book attempts to combine in a unified manner, material from mechanical vibrations, acoustics, signal processing, mechanics and control theory. Key new areas discussed in the text are the use of feedforward control, the modelling and use of distributed strain actuators and sensors, the control of waves in structures, the theory and implementation of active isolation of vibration and the active control of structurally radiated sound. Throughout the text considerable effort is directed towards highlighting and clarifying the dual nature of the 'wave' and 'mode' descriptions of the vibrations of structures. It is demonstrated that either form of description has its advantages, depending upon the type o