Mathematics of Wave Propagation

Mathematics of Wave Propagation

by Julian L. Davis
Mathematics of Wave Propagation

Mathematics of Wave Propagation

by Julian L. Davis

eBook

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Overview

Earthquakes, a plucked string, ocean waves crashing on the beach, the sound waves that allow us to recognize known voices. Waves are everywhere, and the propagation and classical properties of these apparently disparate phenomena can be described by the same mathematical methods: variational calculus, characteristics theory, and caustics. Taking a medium-by-medium approach, Julian Davis explains the mathematics needed to understand wave propagation in inviscid and viscous fluids, elastic solids, viscoelastic solids, and thermoelastic media, including hyperbolic partial differential equations and characteristics theory, which makes possible geometric solutions to nonlinear wave problems. The result is a clear and unified treatment of wave propagation that makes a diverse body of mathematics accessible to engineers, physicists, and applied mathematicians engaged in research on elasticity, aerodynamics, and fluid mechanics.


This book will particularly appeal to those working across specializations and those who seek the truly interdisciplinary understanding necessary to fully grasp waves and their behavior. By proceeding from concrete phenomena (e.g., the Doppler effect, the motion of sinusoidal waves, energy dissipation in viscous fluids, thermal stress) rather than abstract mathematical principles, Davis also creates a one-stop reference that will be prized by students of continuum mechanics and by mathematicians needing information on the physics of waves.


Product Details

ISBN-13: 9780691223377
Publisher: Princeton University Press
Publication date: 01/12/2021
Sold by: Barnes & Noble
Format: eBook
Pages: 411
File size: 19 MB
Note: This product may take a few minutes to download.

About the Author

Julian L. Davis is the author of Wave Propagation in Solids and Fluids and Wave Propagation in Electromagnetic Media, in addition to two texts on the dynamics of continuous media. Following many years as a research scientist at the Army Armament Research Laboratory and the Army's Ballistic Research Laboratory, he works as a consultant in the engineering sciences. He has also served as an aerodynamicist in the commercial aircraft industry and taught applied mathematics at the Stevens Institute of Technology.

Table of Contents

Preface xiii

CHAPTER ONE Physics of Propagating Waves 3

Introduction 3

Discrete Wave-Propagating Systems 3

Approximation of Stress Wave Propagation in a Bar by a Finite System of Mass-Spring Models 4

Limiting Form of a Continuous Bar 5

Wave Equation for a Bar 5

Transverse Oscillations of a String 9

Speed of a Transverse Wave in a Siting 10

Traveling Waves in General 11

Sound Wave Propagation in a Tube 16

Superposition Principle 19

Sinusoidal Waves 19

Interference Phenomena 21

Reflection of Light Waves 25

Reflection of Waves in a String 27

Sound Waves 29

Doppler Effect 33

Dispersion and Group Velocity 36

Problems 37



CHAPTER TWO Partial Differential Equations of Wave Propagation 41

Introduction 41

Types of Partial Differential Equations 41

Geometric Nature of the PDEs of Wave Phenomena 42

Directional Derivatives 42

Cauchy Initial Value Problem 44

Parametric Representation 49

Wave Equation Equivalent to Two First-Order PDEs 51

Characteristic Equations for First-Order PDEs 55

General Treatment of Linear PDEs by Characteristic Theory 57

Another Method of Characteristics for Second-Order PDEs 61

Geometric Interpretation of Quasilinear PDEs 63

Integral Surfaces 65

Nonlinear Case 67

Canonical Form of a Second-Order PDE 70

Riemann's Method of Integration 73

Problems 82



CHAPTER THREE The Wave Equation 85



PART I ONE-DIMENSIONAL WAVE EQUATION 85

Factorization of the Wave Equation and Characteristic Curves 85

Vibrating String as a Combined IV and B V Problem 90

D'Alembert's Solution to the IV Problem 97

Domain of Dependence and Range of Influence 101

Cauchy IV Problem Revisited 102

Solution of Wave Propagation Problems by Laplace Transforms 105

Laplace Transforms 108

Applications to the Wave Equation 111

Nonhomogeneous Wave Equation 116

Wave Propagation through Media with Different Velocities 120

Electrical Transmission Line 122



PART II THE WAVE EQUATION IN TWO AND THREE DIMENSIONS 125

Two-Dimensional Wave Equation 125

Reduced Wave Equation in Two Dimensions 126

The Eigenvalues Must Be Negative 127

Rectangular Membrane 127

Circular Membrane 131

Three-Dimensional Wave Equation 135

Problems 140



CHAPTER FOUR Wave Propagation in Fluids 145



PART I INVISCID FLUIDS 145

Lagrangian Representation of One-Dimensional Compressible Gas Flow 146

Eulerian Representation of a One-Dimensional Gas 149

Solution by the Method of Characteristics: One-Dimensional Compressible Gas 151

Two-Dimensional Steady Flow 157

Bernoulli's Law 159

Method of Characteristics Applied to Two-Dimensional Steady Flow 161

Supersonic Velocity Potential 163

Hodograph Transformation 163

Shock Wave Phenomena 169



PART II VISCOUS FLUIDS 183

Elementary Discussion of Viscosity 183

Conservation Laws 185

Boundary Conditions and Boundary Layer 190

Energy Dissipation in a Viscous Fluid 191

Wave Propagation in a Viscous Fluid 193

Oscillating Body of Arbitrary Shape 196

Similarity Considerations and Dimensionless Parameters; Reynolds' Law 197

Poiseuille Flow 199

Stokes' Flow 201

Oseen Approximation 208

Problems 210



CHAPTER FIVE Stress Waves in Elastic Solids 213

Introduction 213

Fundamentals of Elasticity 214

Equations of Motion for the Stress 223

Navier Equations of Motion for the Displacement 224

Propagation of Plane Elastic Waves 227

General Decomposition of Elastic Waves 228

Characteristic Surfaces for Planar Waves 229

Time-Harmonic Solutions and Reduced Wave Equations 230

Spherically Symmetric Waves 232

Longitudinal Waves in a Bar 234

Curvilinear Orthogonal Coordinates 237

The Navier Equations in Cylindrical Coordinates 239

Radially Symmetric Waves 240

Waves Propagated Over the Surface of an Elastic Body 243

Problems 247



CHAPTER SIX Stress Waves in Viscoelastic Solids 250

Introduction 250

Internal Friction 251

Discrete Viscoelastic Models 252

Continuous Marwell Model 260

Continuous Voigt Model 263

Three-Dimensional VE Constitutive Equations 264

Equations of Motion for a VE Material 265

One-Dimensional Wave Propagation in VE Media 266

Radially Symmetric Waves for a VE Bar 270

Electromechanical Analogy 271

Problems 280



CHAPTER SEVEN Wave Propagation in Thermoelastic Media 282

Introduction 282

Duhamel-Neumann Law 282

Equations of Motion 285

Plane Harmonic Waves 287

Three-Dimensional Thermal Waves; Generalized Navier Equation 293



CHAPTER EIGHT Water Waves 297

Introduction 297

Irrotational, Incompressible, Inviscid Flow; Velocity Potential and Equipotential Surfaces 297

Euler's Equations 299

Two-Dimensional Fluid Flow 300

Complec Variable Treatment 302

Vortex Motion 309

Small-Amplitude Gravity Waves 311

Water Waves in a Straight Canal 311

Kinematics of the Free Surface 316

Vertical Acceleration 317

Standing Waves 319

Two-Dimensional Waves of Finite Depth 321

Boundary Conditions 322

Formulation of a Typical Surface Wave Problem 324

Example of Instability 325

Approximation Aeories 327

Tidal Waves 337

Problems 342



CHAPTER NINE Variational Methods in Wave Propagation 344

Introduction; Fermat's Principle 344

Calculus of Variations; Euler's Equation 345

Configuration Space 349

Kinetic and Potential Energies 350

Hamilton's Variational Principle 350

Principle of Virtual Work 352

Transformation to Generalized Coordinates 354

Rayleigh's Dissipation Function 357

Hamilton's Equations of Motion 359

Cyclic Coordinates 362

Hamilton-Jacobi Theory 364

Extension of W to 2n Degrees of Freedom 370

H-J Theory and Wave Propagation 372

Quantum Mechanics 376

An Analogy between Geometric Optics and Classical Mechanics 377

Asymptotic Theory of Wave Propagation 380

Appendix: The Principle of Least Action 384

Problems 387



Bibliography 389

Index 391

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"The subject matter is important to applied mathematics and engineering students, and there does not exist a book with such a breadth on the subject."—Yu Chen, Rutgers University

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The subject matter is important to applied mathematics and engineering students, and there does not exist a book with such a breadth on the subject.
Yu Chen, Rutgers University

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"The subject matter is important to applied mathematics and engineering students, and there does not exist a book with such a breadth on the subject."—Yu Chen, Rutgers University

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