Fundamentals of Structural Dynamics - Roy R. Craig - ebook

Fundamentals of Structural Dynamics ebook

Roy R. Craig

0,0
599,99 zł

Opis

From theory and fundamentals to the latest advances incomputational and experimental modal analysis, this is thedefinitive, updated reference on structural dynamics. This edition updates Professor Craig's classic introduction tostructural dynamics, which has been an invaluable resource forpracticing engineers and a textbook for undergraduate and graduatecourses in vibrations and/or structural dynamics. Along withcomprehensive coverage of structural dynamics fundamentals,finite-element-based computational methods, and dynamic testingmethods, this Second Edition includes new and expanded coverage ofcomputational methods, as well as introductions to more advancedtopics, including experimental modal analysis and "activestructures." With a systematic approach, it presents solutiontechniques that apply to various engineering disciplines. Itdiscusses single degree-of-freedom (SDOF) systems, multipledegrees-of-freedom (MDOF) systems, and continuous systems in depth;and includes numeric evaluation of modes and frequency of MDOFsystems; direct integration methods for dynamic response of SDOFsystems and MDOF systems; and component mode synthesis. Numerous illustrative examples help engineers apply the techniquesand methods to challenges they face in the real world. MATLAB(r) isextensively used throughout the book, and many of the .m-files aremade available on the book's Web site. Fundamentals of StructuralDynamics, Second Edition is an indispensable reference and"refresher course" for engineering professionals; and a textbookfor seniors or graduate students in mechanical engineering, civilengineering, engineering mechanics, or aerospace engineering.

Ebooka przeczytasz w aplikacjach Legimi na:

Androidzie
iOS
czytnikach certyfikowanych
przez Legimi
Windows
10
Windows
Phone

Liczba stron: 990




Table of Contents

Preface to Structural Dynamics—An Introduction to Computer Methods

Preface to Fundamentals of Structural Dynamics

About the Authors

Chapter 1: The Science and Art of Structural Dynamics

1.1 INTRODUCTION TO STRUCTURAL DYNAMICS

1.2 MODELING OF STRUCTURAL COMPONENTS AND SYSTEMS

1.3 PROTOTYPE SPRING–MASS MODEL

1.4 VIBRATION TESTING OF STRUCTURES

1.5 SCOPE OF THE BOOK

1.6 COMPUTER SIMULATIONS; SUPPLEMENTARY MATERIAL ON THE WEBSITE

Part I Single-Degree-of-Freedom Systems

Chapter 2: Mathematical Models of SDOF Systems

2.1 BRIEF REVIEW OF THE DYNAMICS OF PARTICLES AND RIGID BODIES

2.2 ELEMENTS OF LUMPED-PARAMETER MODELS

2.3 APPLICATION OF NEWTON'S LAWS TO LUMPED-PARAMETER MODELS

2.4 APPLICATION OF THE PRINCIPLE OF VIRTUAL DISPLACEMENTS TO LUMPED-PARAMETER MODELS

2.5 APPLICATION OF THE PRINCIPLE OF VIRTUAL DISPLACEMENTS TO CONTINUOUS MODELS: ASSUMED-MODES METHOD

Chapter 3: Free Vibration of SDOF Systems

3.1 FREE VIBRATION OF UNDAMPED SDOF SYSTEMS

3.2 FREE VIBRATION OF VISCOUS-DAMPED SDOF SYSTEMS

3.3 STABILITY OF MOTION

3.4 FREE VIBRATION OF AN SDOF SYSTEM WITH COULOMB DAMPING

3.5 EXPERIMENTAL DETERMINATION OF THE NATURAL FREQUENCY AND DAMPING FACTOR OF AN SDOF SYSTEM

Chapter 4: Response of SDOF Systems to Harmonic Excitation

4.1 RESPONSE OF UNDAMPED SDOF SYSTEMS TO HARMONIC EXCITATION

4.2 RESPONSE OF VISCOUS-DAMPED SDOF SYSTEMS TO HARMONIC EXCITATION: FREQUENCY-RESPONSE FUNCTIONS

4.3 COMPLEX FREQUENCY RESPONSE

4.4 VIBRATION ISOLATION: FORCE TRANSMISSIBILITY AND BASE MOTION

4.5 VIBRATION MEASURING INSTRUMENTS: ACCELEROMETERS AND VIBROMETERS

4.6 USE OF FREQUENCY-RESPONSE DATA TO DETERMINE THE NATURAL FREQUENCY AND DAMPING FACTOR OF A LIGHTLY DAMPED SDOF SYSTEM

4.7 EQUIVALENT VISCOUS DAMPING

4.8 STRUCTURAL DAMPING

Chapter 5: Response of SDOF Systems to Nonperiodic Excitation

5.1 RESPONSE OF A VISCOUS-DAMPED SDOF SYSTEM TO AN IDEAL STEP INPUT

5.2 RESPONSE OF UNDAMPED SDOF SYSTEMS TO RECTANGULAR PULSE AND RAMP LOADINGS

5.3 RESPONSE OF UNDAMPED SDOF SYSTEMS TO A SHORT-DURATION IMPULSE: UNIT IMPULSE RESPONSE

5.4 RESPONSE OF SDOF SYSTEMS TO GENERAL DYNAMIC EXCITATION: CONVOLUTION INTEGRAL METHOD

5.5 RESPONSE SPECTRA

5.6 SYSTEM RESPONSE BY THE LAPLACE TRANSFORM METHOD: SYSTEM TRANSFER FUNCTION

Chapter 6 Numerical Evaluation of the Dynamic Response of SDOF Systems

6.1 INTEGRATION OF SECOND-ORDER ORDINARY DIFFERENTIAL EQUATIONS

6.2 INTEGRATION OF FIRST-ORDER ORDINARY DIFFERENTIAL EQUATION

6.3 NONLINEAR SDOF SYSTEMS

Chapter 7: Response of SDOF Systems to Periodic Excitation: Frequency-Domain Analysis

7.1 RESPONSE TO PERIODIC EXCITATION: REAL FOURIER SERIES

7.2 RESPONSE TO PERIODIC EXCITATION: COMPLEX FOURIER SERIES

7.3 RESPONSE TO NONPERIODIC EXCITATION: FOURIER INTEGRAL

7.4 RELATIONSHIP BETWEEN COMPLEX FREQUENCY RESPONSE AND UNIT IMPULSE RESPONSE

7.5 DISCRETE FOURIER TRANSFORM AND FAST FOURIER TRANSFORM

Part II Multiple-Degree-of-Freedom Systems—Basic Topics

Chapter 8: Mathematical Models of MDOF Systems

8.1 APPLICATION OF NEWTON'S LAWS TO LUMPED-PARAMETER MODELS

8.2 INTRODUCTION TO ANALYTICAL DYNAMICS: HAMILTON'S PRINCIPLE AND LAGRANGE'S EQUATIONS

8.3 APPLICATION OF LAGRANGE'S EQUATIONS TO LUMPED-PARAMETER MODELS

8.4 APPLICATION OF LAGRANGE'S EQUATIONS TO CONTINUOUS MODELS: ASSUMED-MODES METHOD

8.5 CONSTRAINED COORDINATES AND LAGRANGE MULTIPLIERS

Chapter 9 Vibration of Undamped 2-DOF Systems

9.1 FREE VIBRATION OF 2-DOF SYSTEMS: NATURAL FREQUENCIES AND MODE SHAPES

9.2 BEAT PHENOMENON

9.3 ADDITIONAL EXAMPLES OF MODES AND FREQUENCIES OF 2-DOF SYSTEMS: ASSUMED-MODES MODELS

9.4 FREE VIBRATION OF SYSTEMS WITH RIGID-BODY MODES

9.5 INTRODUCTION TO MODE SUPERPOSITION: FREQUENCY RESPONSE OF AN UNDAMPED 2-DOF SYSTEM

9.6 UNDAMPED VIBRATION ABSORBER

Chapter 10: Vibration Properties of MDOF Systems: Modes, Frequencies, and Damping

10.1 SOME PROPERTIES OF NATURAL FREQUENCIES AND NATURAL MODES OF UNDAMPED MDOF SYSTEMS

10.2 MODEL REDUCTION: RAYLEIGH, RAYLEIGH–RITZ, AND ASSUMED-MODES METHODS

10.3 UNCOUPLED DAMPING IN MDOF SYSTEMS

10.4 STRUCTURES WITH ARBITRARY VISCOUS DAMPING: COMPLEX MODES

10.5 NATURAL FREQUENCIES AND MODE SHAPES OF DAMPED STRUCTURES WITH RIGID-BODY MODES

Chapter 11: Dynamic Response of MDOF Systems: Mode-Superposition Method

11.1 MODE-SUPERPOSITION METHOD: PRINCIPAL COORDINATES

11.2 MODE-SUPERPOSITION SOLUTIONS FOR MDOF SYSTEMS WITH MODAL DAMPING: FREQUENCY-RESPONSE ANALYSIS

11.3 MODE-DISPLACEMENT SOLUTION FOR THE RESPONSE OF MDOF SYSTEMS

11.4 MODE-ACCELERATION SOLUTION FOR THE RESPONSE OF UNDAMPED MDOF SYSTEMS

11.5 DYNAMIC STRESSES BY MODE SUPERPOSITION

11.6 MODE SUPERPOSITION FOR UNDAMPED SYSTEMS WITH RIGID-BODY MODES

Part III Continuous Systems

Chapter 12: Mathematical Models of Continuous Systems

12.1 APPLICATIONS OF NEWTON'S LAWS: AXIAL DEFORMATION AND TORSION

12.2 APPLICATION OF NEWTON'S LAWS: TRANSVERSE VIBRATION OF LINEARLY ELASTIC BEAMS (BERNOULLI–EULER BEAM THEORY)

12.3 APPLICATION OF HAMILTON'S PRINCIPLE: TORSION OF A ROD WITH CIRCULAR CROSS SECTION

12.4 APPLICATION OF THE EXTENDED HAMILTON'S PRINCIPLE: BEAM FLEXURE INCLUDING SHEAR DEFORMATION AND ROTATORY INERTIA (TIMOSHENKO BEAM THEORY)

Chapter 13: Free Vibration of Continuous Systems

13.1 FREE AXIAL AND TORSIONAL VIBRATION

13.2 FREE TRANSVERSE VIBRATION OF BERNOULLI–EULER BEAMS

13.3 RAYLEIGH'S METHOD FOR APPROXIMATING THE FUNDAMENTAL FREQUENCY OF A CONTINUOUS SYSTEM

13.4 FREE TRANSVERSE VIBRATION OF BEAMS INCLUDING SHEAR DEFORMATION AND ROTATORY INERTIA

13.5 SOME PROPERTIES OF NATURAL MODES OF CONTINUOUS SYSTEMS

13.6 FREE VIBRATION OF THIN FLAT PLATES

PART IV Computational Methods in Structural Dynamics

Chapter 14: Introduction to Finite Element Modeling of Structures

14.1 INTRODUCTION TO THE FINITE ELEMENT METHOD

14.2 ELEMENT STIFFNESS AND MASS MATRICES AND ELEMENT FORCE VECTOR

14.3 TRANSFORMATION OF ELEMENT MATRICES

14.4 ASSEMBLY OF SYSTEM MATRICES: DIRECT STIFFNESS METHOD

14.5 BOUNDARY CONDITIONS

14.6 CONSTRAINTS: REDUCTION OF DEGREES OF FREEDOM

14.7 SYSTEMS WITH RIGID-BODY MODES

14.8 FINITE ELEMENT SOLUTIONS FOR NATURAL FREQUENCIES AND MODE SHAPES

Chapter 15: Numerical Evaluation of Modes and Frequencies of MDOF Systems

15.1 INTRODUCTION TO METHODS FOR SOLVING ALGEBRAIC EIGENPROBLEMS

15.2 VECTOR ITERATION METHODS

15.3 SUBSPACE ITERATION

15.4 QR METHOD FOR SYMMETRIC EIGENPROBLEMS

15.5 LANCZOS EIGENSOLVER

15.6 NUMERICAL CASE STUDY

Chapter 16: Direct Integration Methods for Dynamic Response of MDOF Systems

16.1 DAMPING IN MDOF SYSTEMS

16.2 NUMERICAL INTEGRATION: MATHEMATICAL FRAMEWORK

16.3 INTEGRATION OF SECOND-ORDER MDOF SYSTEMS

16.4 SINGLE-STEP METHODS AND SPECTRAL STABILITY

16.5 NUMERICAL CASE STUDY

Chapter 17: Component-Mode Synthesis

17.1 INTRODUCTION TO COMPONENT-MODE SYNTHESIS

17.2 COMPONENT MODES: NORMAL, CONSTRAINT, AND RIGID-BODY MODES

17.3 COMPONENT MODES: ATTACHMENT AND INERTIA-RELIEF ATTACHMENT MODES

17.4 FLEXIBILITY MATRICES AND RESIDUAL FLEXIBILITY

17.5 SUBSTRUCTURE COUPLING PROCEDURES

17.6 COMPONENT-MODE SYNTHESIS METHODS: FIXED-INTERFACE METHODS

17.7 COMPONENT-MODE SYNTHESIS METHODS: FREE-INTERFACE METHODS

17.8 BRIEF INTRODUCTION TO MULTILEVEL SUBSTRUCTURING

PART V Advanced Topics in Structural Dynamics

Chapter 18: Introduction to Experimental Modal Analysis

18.1 INTRODUCTION

18.2 FREQUENCY-RESPONSE FUNCTION REPRESENTATIONS

18.3 VIBRATION TEST HARDWARE

18.4 FOURIER TRANSFORMS, DIGITAL SIGNAL PROCESSING, AND ESTIMATION OF FRFs

18.5 MODAL PARAMETER ESTIMATION

18.6 MODE SHAPE ESTIMATION AND MODEL VERIFICATION

Chapter 19: Introduction to Active Structures

19.1 INTRODUCTION TO PIEZOELECTRIC MATERIALS

19.2 CONSTITUTIVE LAWS OF LINEAR PIEZOELECTRICITY

19.3 APPLICATION OF NEWTON'S LAWS TO PIEZOSTRUCTURAL SYSTEMS

19.4 APPLICATION OF EXTENDED HAMILTON'S PRINCIPLE TO PIEZOELECTRICITY

19.5 ACTIVE TRUSS MODELS

19.6 ACTIVE BEAM MODELS

19.7 ACTIVE COMPOSITE LAMINATES

Chapter 20: Introduction to Earthquake Response of Structures

20.1 INTRODUCTION

20.2 RESPONSE OF A SDOF SYSTEM TO EARTHQUAKE EXCITATION: RESPONSE SPECTRA

20.3 RESPONSE OF MDOF SYSTEMS TO EARTHQUAKE EXCITATION

20.4 FURTHER CONSIDERATIONS

Appendix A: Units

Appendix B: Complex Numbers

Appendix C: Elements of Laplace Transforms

Appendix D: Fundamentals of Linear Algebra

Appendix E: Introduction to the Use of Matlab

Index

Copyright © 2006 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400, fax 978-646-8600, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008.

Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

For general information on our other products and services please contact our Customer Care Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993 or fax 317-572-4002.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic format.

Library of Congress Cataloging-in-Publication Data:

Craig, Roy R., 1934-

Fundamentals of structural dynamics / by Roy R. Craig, Jr. and Andrew J. Kurdila.—2nd ed. p. cm.

Rev. ed. of: Structural dynamics, c1981. Includes bibliographical references and index. ISBN 13: 978-0-471-43044-5 ISBN 10: 0-471-43044-7 (cloth)

1. Structural dynamics—Data processing. 2. Structural dynamics—Mathematical models. I. Kurdila, Andrew. II. Craig, Roy R., 1934-. Structural dynamics. III. Title.

TA654.C72 2006

624.1' 71—dc22

2005043679

The first author dedicates his work on this edition to his grandchildren:

Talia, Kyle,and Hart Barron,and Alex, Brandon,and Chase Lemens.The second author dedicates his work to his wife, Jeannie, and to his children:

Patrick, Hannah, and Justin.

Preface to Structural Dynamics—An Introduction to Computer Methodsa

The topic of structural dynamics has undergone profound changes over the past two decades. The reason is the availability of digital computers to carry out numerical aspects of structural dynamics problem solving. Recently, the extensive use of the fast Fourier transform has brought about even more extensive changes in structural dynamics analysis, and has begun to make feasible the correlation of analysis with structural dynamics testing. Although this book contains much of the material that characterizes standard textbooks on mechanical vibrations, or structural dynamics, its goal is to present the background needed by an engineer who will be using structural dynamics computer programs or doing structural dynamics testing, or who will be taking advanced courses in finite element analysis or structural dynamics.

Although the applications of structural dynamics in aerospace engineering, civil engineering, engineering mechanics, and mechanical engineering are different, the principles and solution techniques are basically the same. Therefore, this book places emphasis on these principles and solution techniques, and illustrates them with numerous examples and homework exercises from the various engineering disciplines.

Special features of this book include: an emphasis on mathematical modeling of structures and experimental verification of mathematical models; an extensive introduction to numerical techniques for computing natural frequencies and mode shapes and for computing transient response; a systematic introduction to the use of finite elements in structural dynamics analysis; an application of complex frequency-response representations for the response of single- and multiple-degree-of-freedom systems; a thorough exposition of both the mode-displacement and mode-acceleration versions of mode superposition for computing dynamic response; an introduction to practical methods of component-mode synthesis for dynamic analysis; and the introduction of an instructional matrix algebra and finite element computer code, ISMIS (Interactive Structures and Matrix Interpretive System), for solving structural dynamics problems.

Although the emphasis of this book is on linear problems in structural dynamics, techniques for solving a limited class of nonlinear structural dynamics problems are also introduced. On the other hand, the topic of random vibrations is not discussed, since a thorough treatment of the subject is definitely beyond the scope of the book, and a cursory introduction would merely dilute the emphasis on numerical techniques for structural dynamics analysis. However, instructors wishing to supplement the text with material on random vibrations will find the information on complex frequency response to be valuable as background for the study of random vibrations.

A primary aim of the book is to give students a thorough introduction to the numerical techniques underlying finite element computer codes. This is done primarily through "hand" solutions and the coding of several subroutines in FORTRAN (or BASIC). Use of the ISMIS computer program extends the problem-solving capability of the student while avoiding the "black box" nature of production-type finite element codes. Although the ISMIS computer program is employed in Chapters 14 and 17, its use is by no means mandatory. The FORTRAN source code and a complete User's Manual for ISMIS are available for a very nominal fee and can be obtained by contacting the author directly at The University of Texas at Austin (Austin, TX 78712).

Computer graphics is beginning to play an important role in structural dynamics, for example, in computer simulations of vehicle collisions and animated displays of structural mode shapes. One feature of this book is that all figures that portray functional representations are direct computer-generated plots.

The text of this book has been used for a one-semester senior-level course in structural dynamics and a one-semester graduate-level course in computational methods in structural dynamics. The undergraduate course typically covers the following material: Chapters 1 through 6, Sections 9.1, 9.2, 10.1, 10.2, 11.1 through 11.4, and Chapter 12. The graduate course reviews the topics above (i.e., it assumes that students have had a prior course in mechanical vibrations or structural dynamics) and then covers the remaining topics in the book as time permits. Both undergraduate and graduate courses make use of the ISMIS computer program, while the graduate course also includes several FORTRAN coding exercises.

Portions of this text have been used in a self-paced undergraduate course in structural dynamics. This led to the statements of objectives at the beginning of each chapter and to the extensive use of example problems. Thus, the text should be especially valuable to engineers pursuing a study of structural dynamics on a self-study basis.

I express appreciation to my students who used the notes that led to the present text. Special thanks are due to Arne Berg, Mike Himes, and Rick McKenzie, who generated most of the computer plots, and to Butch Miller and Rodney Rocha, who served as proctors for the self-paced classes. Much of the content and "flavor" of the book is a result of my industrial experience at the Boeing Company's Commercial Airplane Division, at Lockheed Palo Alto Research Laboratory, and at NASA Johnson Space Center. I am indebted to the colleagues with whom I worked at these places.

I am grateful to Dr. Pol D. Spanos for reading Chapter 20 and making helpful comments. Dean Richard Gallagher reviewed the manuscript and offered many suggestions for changes, which have been incorporated into the text. This valuable service is greatly appreciated.

This book might never have been completed had it not been for the patience and accuracy of its typist, Mrs. Bettye Lofton, and to her I am most deeply indebted.

Finally, many of the hours spent in the writing of this book were hours that would otherwise have been spent with Jane, Carole, and Karen, my family. My gratitude for their sacrifices cannot be measured.

Roy R. Craig, Jr., Austin, TX

a Copyright 1981, John Wiley & Sons, Inc.

Preface to Fundamentals of Structural Dynamics

Although there has been a title change to Fundamentals of Structural Dynamics,this book is essentially the 2nd edition of Structural Dynamics—An Introduction to Computer Methods, published in 1981 by the senior author. As a textbook and as a resource book for practicing engineers, that edition had a phenomenal run of a quarter century. Although this edition retains the emphasis placed in the first edition on the topics of mathematical modeling, computer solution of structural dynamics problems, and the relationship of finite element analysis and experimental structural dynamics, it takes full advantage of the current state of the art in each of those topics. For example, whereas the first edition employed ISMIS, a FORTRAN-based introductory matrix algebra and finite element computer code, the present edition employs a Matlab-based version of ISMIS and provides many additional structural dynamics solutions directly in Matlab.

The new features of this edition are:

1. A coauthor, Dr. Andrew Kurdila, who has been responsible for Chapters 6, 15, 16, and 19 and Appendices D and E in this edition.

2. A greater emphasis on computer solutions, especially Matlab-based plots; numerical algorithms in Chapters 6, 15, and 16; and digital signal-processing techniques in Chapter 18.

3. A new section (Section 5.6) on system response by the Laplace transform method, and a new appendix, Appendix C, on Laplace transforms.

4. An introduction, in Sections 10.4 and 10.5, to state-space solutions for complex modes of damped systems.

5. Greatly expanded chapters on eigensolvers (Chapter 15), numerical algorithms for calculating dynamic response (Chapters 6 and 16), and component-mode synthesis (Chapter 17).

6. New chapters on experimental modal analysis (Chapter 18) and on smart structures (Chapter 19).

7. A revised grouping of topics that places vibration of continuous systems after basic multiple-DOF topics, but before the major sections on computational methods and the advanced-topics chapters.

8. Many new or revised homework problems, including many to be solved on the computer.

9. A supplement that contains many sample Matlab .m-files, the matlab-based ISMIS matrix structural analysis computer program, notes for an extensive short course on finite element analysis and experimental modal analysis, and other study aids. This supplement, referred to throughout the book as the “book's website,” is available online from the Wiley Web site www.wiley.com/college/craig.

The senior author would like to acknowledge the outstanding wealth of knowledge that has been shared with him by authors of papers presented at the many International Modal Analysis Conferences (IMACs) that he has attended over the past quarter century. Special appreciation is due to Prof. David L. Brown and his colleagues from the University of Cincinnati; to numerous engineers from Structural Dynamics Research Corporation, ATA Engineering, Inc., and Leuven Measurement Systems; and to the late Dominick J. (Dick) DeMichele, the founder of IMAC. Professor Eric Becker, a colleague of the senior author at The University of Texas at Austin, was responsible for many features of the original ISMIS (Interactive Structures and Matrix Interpretive System) FORTRAN code.

The authors would like to express appreciation to the following persons for their major contributions to this edition:

Prof. Peter Avitabile: for permission to include on the book's website his extensive short course notes on finite element analysis and experimental modal analysis.

Mr. Charlie Pickrel: for providing Boeing GVT photos (Fig. 1.9a,b) and his journal article on experimental modal analysis, the latter for inclusion on the book's website.

Dr. Matthew F. Kaplan: for permission to use substantial text and figures from his Ph.D. dissertation as the basis for the new Section 17.8 on multilevel substruc-turing.

Dr. Eric Blades: for conversion of the ISMIS FORTRAN code to form the Matlab toolchest that is included on the book's website. Mr. Sean Regisford: for assistance with the finite element case studies in

Sections 15.6 and 16.5. Mr. Garrett Moran: for assistance with solutions to new homework problems and for generating Matlab plots duplicating the figures in the original Structural Dynamics book.

Their respective chapters of this edition were typeset in LTEX by the authors.

Roy R. Craig, Jr., Austin, TXAndrew J. Kurdila, Blacksburg, VA

About the Authors

Roy R. Craig, Jr. is the John J. McKetta Energy Professor Emeritus in Engineering in the Department of Aerospace Engineering and Engineering Mechanics at The University of Texas at Austin. He received his B.S. degree in civil engineering from the University of Oklahoma, and M.S. and Ph.D. degrees in theoretical and applied mechanics from the University of Illinois at Urbana-Champaign. Dr. Craig's research and publications have been principally in the areas of structural dynamics analysis and testing, structural optimization, control of flexible structures, and the use of computers in engineering education. He is the developer of the Craig-Bampton Method of component-mode synthesis, which has been used extensively throughout the world for analyzing the dynamic response of complex structures, and he is the author of many technical papers and reports and of one other textbook, Mechanics of Materials. His industrial experience has been with the U.S. Naval Civil Engineering Laboratory, the Boeing Company, Lockheed Palo Alto Research Laboratory, Exxon Production Research Corporation, NASA, and IBM.

Dr. Craig has received numerous teaching awards and faculty leadership awards, including the General Dynamics Teaching Excellence Award in the College of Engineering, the John Leland Atwood Award presented jointly by the Aerospace Division of the American Society for Engineering Education and by the American Institute of Aeronautics and Astronautics "for sustained outstanding leadership and contributions in structural dynamics and experimental methods," and the D. J. DeMichele Award of the Society for Experimental Mechanics "for exemplary service and support in promoting the science and educational aspects of modal analysis technology." He is a member of the Society for Experimental Mechanics and a Fellow of the American Institute of Aeronautics and Astronautics.

Andrew J. Kurdila is the W. Martin Johnson Professor of Mechanical Engineering at the Virginia Polytechnic Institute and State University. He received his B.S. degree in applied mechanics in 1983 from the University of Cincinnati in the Department of Aerospace Engineering and Applied Mechanics. He subsequently entered The University of Texas at Austin and was awarded the M.S. degree in engineering mechanics the following year. He entered the Department of Engineering Science and Mechanics at the Georgia Institute of Technology as a Presidential Fellow and earned his Ph.D. in 1989.

Dr. Kurdila joined the faculty of the Aerospace Engineering Department at Texas A&M University in 1990 as an assistant professor. He was tenured and promoted to associate professor in 1993. He joined the faculty of the University of Florida in 1997 and was promoted to full professor in 1998. In 2005 he joined the faculty of the Virginia Polytechnic Institute and State University. He was recognized as a Select Faculty Fellow at Texas A&M University in 1994 and as a Faculty Fellow in 1996 and was awarded the Raymond L. Bisplinghoff Award at the University of Florida in 1999 for Excellence in Teaching.

Dr. Kurdila is the author of over 50 archival journal publications, 100 conference presentations and publications, four book chapters, two edited volumes, and two books. He has served as an associate editor of the Journal of Vibration and Control and of the Journal of Guidance, Control and Dynamics. He was named an Associate Fellow of the AIAA in 2001. His current research is in the areas of dynamical systems theory, control theory, and computational mechanics. His research has been funded by the Army Research Office, the Office of Naval Research, the Air Force Office of Scientific Research, the Air Force Research Laboratory, the National Science Foundation, the Department of Energy, the Army Research and Development Command, and the State of Texas.

Chapter 1

The Science and Art of Structural Dynamics

What do a sport-utility vehicle traveling off-road, an airplane flying near a thunderstorm, an offshore oil platform in rough seas, and an office tower during an earthquake all have in common? One answer is that all of these are structures that are subjected to dynamic loading, that is, to time-varying loading. The emphasis placed on the safety, performance, and reliability of mechanical and civil structures such as these has led to the need for extensive analysis and testing to determine their response to dynamic loading. The structural dynamics techniques that are discussed in this book have even been employed to study the dynamics of snow skis and violins.

Although the topic of this book, as indicated by its title, is structural dynamics, some books with the word vibrations in their title discuss essentially the same subject matter. Powerful computer programs are invariably used to implement the modeling, analysis, and testing tasks that are discussed in this book, whether the application is one in aerospace engineering, civil engineering, mechanical engineering, electrical engineering, or even in sports or music.

1.1 INTRODUCTION TO STRUCTURAL DYNAMICS

This introductory chapter is entitled “The Science and Art of Structural Dynamics” to emphasize at the outset that by studying the principles and mathematical formulas discussed in this book you will begin to understand the science of structural dynamics analysis. However, structural dynamicists must also master the art of creating mathematical models of structures, and in many cases they must also perform dynamic tests. The cover photo depicts an automobile that is undergoing such dynamic testing. Modeling, analysis, and testing tasks all demand that skill and judgment be exercised in order that useful results will be obtained; and all three of these tasks are discussed in this book.

A dynamic load is one whose magnitude, direction, or point of application varies with time. The resulting time-varying displacements and stresses constitute the dynamic response. If the loading is a known function of time, the loading is said to be prescribed loading, and the analysis of a given structural system to a prescribed loading is called a deterministic analysis. If the time history of the loading is not known completely but only in a statistical sense, the loading is said to be random. In this book we treat only prescribed dynamic loading.

A structural dynamics problem differs from the corresponding static problem in two important respects. The first has been noted above: namely, the time-varying nature of the excitation. Of equal importance in a structural dynamics problem, however, is the role played by acceleration. Figure 1.1a shows a cantilever beam under static loading. The deflection and internal stresses depend directly on the static load P. On the other hand, Fig. 1.1b shows a similar cantilever beam subjected to a time-varying load P(t). The acceleration of the beam gives rise to a distributed inertia force, as indicated in the figure. If the inertia force contributes significantly to the deflection of the structure and the internal stresses in the structure, a dynamical investigation is required.

Figure 1.1 Cantilever beam under (a) static loading and (b) dynamic loading.

Figure 1.2 shows the typical steps in a complete dynamical investigation. The three major steps, which are outlined by dashed-line boxes, are: design, analysis, and testing. The engineer is generally required to perform only one, or possibly two, of these steps. For example, a civil engineer might be asked to perform a dynamical analysis of an existing building and to confirm the analysis by performing specific dynamic testing of the building. The results of the analysis and testing might lead to criteria for retrofitting the building with additional bracing or damping to ensure safety against failure due to specified earthquake excitation.[1.1,1.2] Automotive engineers perform extensive analysis and vibration testing to determine the dynamical behavior of new car designs.[1.3,1.4] Results of this analysis and testing frequently lead to design changes that will improve the ride quality, economy, or safety of the vehicle.

Figure 1-2 Steps in a dynamical investigation.

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!