Mechanics: Dynamical Systems – serie

The purpose of this book is to provide students, practicing engineers and scientists with a treatment of nonlinear phenomena occurring in physical systems. Although only mechanical models are used, the theory applies to all physical systems governed by the same equations, so that the book can be used to study nonlinear phenomena in other branches of engineering, such as electrical engineering and aerospace engineering, as well as in physics. The book consists of two volumes. Volume I is concerned with single­ degree-of-freedom systems and it presents the fundamental concepts of nonlinear analysis. Both analytical methods and computer simulations are included. The material is presented in such a manner that the book can be used as a graduate as well as an undergraduate textbook. Volume II deals with multi-degree-of-freedom systems. Following an introduc­ tion to linear systems, the volume presents fundamental concepts of geometric theory and stability of motion of general nonlinear systems, as well as a concise discussion of basic approximate methods for the response of such systems. The material represents a generalization of a series of papers on the vibration of nonlinear multi-degree-of-freedom systems, some of which were published by me and my associates during the period 1965 - 1983 and some are not yet published.

Nowadays, the engineering practice raises far more vibration problems than can be theoretically explained or modelled. Because Df this, measurements are used in almost all fields of industry, transportation and civil engineering in studies of mechanical and structural vibration. They are an invaluable tool for designing products and machines with high reliability and low noise level, vehicles and buildings with improved comfort and resistance to dynamic loads, as well as for obtaining increased safety of opera­ tion and optimum running parameters. In order to cope with the increasing demand for experimental measurement of vibration characteristics, young engineers and designers need an introductory book with emphasis on "what has to be measured" and "by what means" before learning "how measurements are done". The expertise to perform vibration measurements must be gained in time, with every new investi­ gation and studied problem . .A detailed presentation of instrumentation and measuring techniques is beyond the aim of this book. Such information can be found in product data sheets, application manuals and hand­ books supplied by equipment manufacturers. Only general princi­ ples and widely used methods are presented herein, in order to provide the reader with an overview of the instrumentation and techniques encountered in vibration measurement.

This book is based on a number of lectures presented at CISM* -Course on "Stochastic Methods in Structural Mechanics", August 28 -30,1985 in Udine, Italy. The chapters presented here are either expanded and/or updated versions of these lectures. The purpose is to introduce readers to basic principles of stochastic methods of structural mechanics, particularly to those of dynamics. For those readers who wish to pursue the study further, the references provided in each chapter will serve as a useful source of information. Nevertheless the readers find some of the advanced topics presented by the authors immediately useful for their own application. The first section of Chapter 1 introduces the reader to the basic principles of probability theory followed by the discussion of methods to calculate time invariant structural reliability estimates, where the exact methods are particularly emphasized. The Chapter continues with a first introduction to the theory of stochastic processes. The properties of Gaussian and other type of processes are discussed. In dealing with observed data, tests of stationarity, as well as methods to estimate power spectra are described in some detail. The Chapter closes with a first treatice of excursions of stochastic processes in terms of number and duration of excursions, extremes, envelopes and time to first excursions. In Chapter 2 linear structures under stochastic loading are analyzed by applying the concepts as outlined in Chapter 1. The analyses are carried out in the time and frequency range respectively.

Nowadays, the engineering practice raises far more vibration problems than can be theoretically explained or modelled. Because Df this, measurements are used in almost all fields of industry, transportation and civil engineering in studies of mechanical and structural vibration. They are an invaluable tool for designing products and machines with high reliability and low noise level, vehicles and buildings with improved comfort and resistance to dynamic loads, as well as for obtaining increased safety of opera­ tion and optimum running parameters. In order to cope with the increasing demand for experimental measurement of vibration characteristics, young engineers and designers need an introductory book with emphasis on "what has to be measured" and "by what means" before learning "how measurements are done". The expertise to perform vibration measurements must be gained in time, with every new investi­ gation and studied problem . .A detailed presentation of instrumentation and measuring techniques is beyond the aim of this book. Such information can be found in product data sheets, application manuals and hand­ books supplied by equipment manufacturers. Only general princi­ ples and widely used methods are presented herein, in order to provide the reader with an overview of the instrumentation and techniques encountered in vibration measurement.

This text 1s designed to introduce the fundamentals of esti­ mation to engineers, scientists, and applied mathematicians. The level of the presentation should be accessible to senior under­ graduates and should prove especially well-suited as a self study guide for practicing professionals. My primary motivation for writing this book 1s to make a significant contribution toward minimizing the painful process most newcomers must go through in digesting and applying the theory. Thus the treatment 1s intro­ ductory and essence-oriented rather than comprehensive. While some original material 1s included, the justification for this text lies not in the contribution of dramatic new theoretical re­ sults, but rather in the degree of success I believe that I have achieved in providing a source from which this material may be learned more efficiently than through study of an existing text or the rather diffuse literature. This work is the outgrowth of the author's mid-1960's en­ counter with the subject while motivated by practical problems aSSociated with space vehicle orbit determination and estimation of powered rocket trajectories. The text has evolved as lecture notes for short courses and seminars given to professionals at Pr>efaae various private laboratories and government agencies, and during the past six years, in conjunction with engineering courses taught at the University of Virginia. To motivate the reader's thinking, the structure of a typical estimation problem often assumes the following form: • Given a dynamical system, a mathematical model is hypothesized based upon the experience of the investigator.

The purpose of this book is to provide students, practicing engineers and scientists with a treatment of nonlinear phenomena occurring in physical systems. Although only mechanical models are used, the theory applies to all physical systems governed by the same equations, so that the book can be used to study nonlinear phenomena in other branches of engineering, such as electrical engineering and aerospace engineering, as well as in physics. The book consists of two volumes. Volume I is concerned with single­ degree-of-freedom systems and it presents the fundamental concepts of nonlinear analysis. Both analytical methods and computer simulations are included. The material is presented in such a manner that the book can be used as a graduate as well as an undergraduate textbook. Volume II deals with multi-degree-of-freedom systems. Following an introduc­ tion to linear systems, the volume presents fundamental concepts of geometric theory and stability of motion of general nonlinear systems, as well as a concise discussion of basic approximate methods for the response of such systems. The material represents a generalization of a series of papers on the vibration of nonlinear multi-degree-of-freedom systems, some of which were published by me and my associates during the period 1965 - 1983 and some are not yet published.

This book is based on a number of lectures presented at CISM* -Course on "Stochastic Methods in Structural Mechanics", August 28 -30,1985 in Udine, Italy. The chapters presented here are either expanded and/or updated versions of these lectures. The purpose is to introduce readers to basic principles of stochastic methods of structural mechanics, particularly to those of dynamics. For those readers who wish to pursue the study further, the references provided in each chapter will serve as a useful source of information. Nevertheless the readers find some of the advanced topics presented by the authors immediately useful for their own application. The first section of Chapter 1 introduces the reader to the basic principles of probability theory followed by the discussion of methods to calculate time invariant structural reliability estimates, where the exact methods are particularly emphasized. The Chapter continues with a first introduction to the theory of stochastic processes. The properties of Gaussian and other type of processes are discussed. In dealing with observed data, tests of stationarity, as well as methods to estimate power spectra are described in some detail. The Chapter closes with a first treatice of excursions of stochastic processes in terms of number and duration of excursions, extremes, envelopes and time to first excursions. In Chapter 2 linear structures under stochastic loading are analyzed by applying the concepts as outlined in Chapter 1. The analyses are carried out in the time and frequency range respectively.

In the last decade the development in vibration analysis was char­ acterized by increasing demands on precision and by the growing use of electronic computers. At present, improvements in precision are obtained by a more accurate modelling of technical systems. Thus, for instance, a system with one degree of freedom is often not accepted, as it used to be, as a model for vibration analysis in mechanical engineering. As a rule, vehicles and machines have to be modelled as systems with many degrees of freedom such as multibody systems, finite element systems or con­ tinua. The mathematical description of multi-degree-of-freedom systems leads to matrix representations of the corresponding equations. These are then conveniently analyzed by means of electronic computers, that is, by the analog computer and especially by the digital machine. Hence there exists a mutually stimulating interaction between the growing require­ ments and the increasing computational facilities. The present book deals with linear vibration analysis of technical systems with many degrees of freedom in a form allowing the use of computers for finding solutions. Part I begins with the classification of vibrating systems. The main characteristics here are the kind of differential equation, the time depen­ dence of the coefficients and the attributes of the exciting process. Next it is shown by giving examples involving mechanical vibrating systems how to set up equations of motion and how to transform these into state equations.