Acoustics of Moving Inhomogeneities

Andrey (Andrew) Grigorievitch Semenov
Academician N.N., Andreev’s Acoustics Institute of RAS, Moscow, Russia

Series: Physics Research and Technology
BISAC: TEC001000

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A new approach to the theory of sound scattering, diffraction and propagation in slightly compressible media containing moving inhomogeneities is presented. The main concept of this approach lies in enriching the acoustic properties of the media by the consideration of the inhomogeneities’ motion together with the contribution of media flow generated by them. Both factors are conventionally ignored in classic wave scattering theory. Inhomogeneous media are usually presented as continuous with supposed local statistical properties distribution while structural specifics and motion of medium components are ignored being ‘excused’ by their extremely small Mach numbers. However, this approximation is valid for electromagnetic wave scattering only. The analogy between sound and electromagnetic wave propagation in inhomogeneous moving media fails in acoustics of media with moving inhomogeneities. The presented conclusions are based on analytical solutions of sound scattering problems for the Lighthill equation related to a body moving in ideal or viscous media with an arbitrary relationship between sound wavelength and body dimension. The contribution of the ambient flow around moving scatterer to total sound scattering is shown to be at least comparable to the scatterer body motion contribution. Under certain conditions, such as for small moving particles in viscous media, the particle body contribution to scattering as a whole could be safely ignored with respect to the ambient flow contribution. As a result the classic Rayleigh law is to be modified and a few fundamental relationships substituting it are derived. The obtained results are important for a wide range of acoustic problems arising in moving inhomogeneous media, from sound scattering in atmosphere or ocean to sound decay in colloid particle solutions. The consideration of the contribution of the ambient flow to the sound diffraction by a large moving body is shown to be necessary as well. This is why a lot of known diffraction problems, for example such that are used for underwater acoustic system efficiency evaluation should be revised. A few examples of our results are: sound decay predictions in atmospheric precipitation, in turbulent media and in colloid solution of suspended particles involved in Brownian motion. Moreover, some experimental data that were unexplained up to this point are now clarified in light of this new theory. At the same time, we show the necessity of performing additional experiments based on theory predictions. (Imprint: Nova)

Preface

Nomenclature

Introduction

Chapter 1. Acoustics in an Ideal Medium

Chapter 2. Sound Scattering in a Viscous Medium

Chapter 3. Applications of Scattering Theory

Chapter 4. Addenda to Moving Media Acoustics

Conclusion

References

Index

“Dr. Semenov is amongst few scientists who have provided theoretical background to the challenges associated with scattering, propagation and diffraction of sound in the vicinity of moving bodies and particles showing substantial yield of ambient media motion in observed field. Lighthill equation rather than conventional Helmholtz equation is used to describe sound propagation there. In fact this book provides valuable contribution to classical scattering theory and acoustics of moving inhomogeneous media. Disclosed laws and relationships are to be used in practical underwater and atmospheric acoustics. The text is rich in physical details and approximations explaining limits of known laws, such as Rayleigh law, as well as endorsing validity and reality of achieved results. The book is essential for any scientist or engineer taking a serious interest in accurate prediction of experiment data observed in media comprising moving inhomogeneities.” - Prof. Sergey N. Kulichkov, Deputy Director, Institute of Atmospheric Physics, Russian Academy of Sciences, Laureate of Russian Government prize in the field of physical sciences

“This book is written by experienced specialist in acoustics of moving media Dr. Andrew (Andrey) Semenov from Acoustics Institute in Moscow, Russia. It shows insufficiency of current state-of-the art in moving media acoustics. Main chapters of the book are related to the detailed description of sound scattering by moving bodies taking into account specifics of ambient flow and wake arguing their decisive contribution to observed sound signals, say, for ships in ocean or turbulence in atmosphere. This approach developed by the author since the very beginning of 1990s published mainly in ”Acoustical Physics” and realized in new laws and relationships predicting decay rate of sound propagation in moving turbulent inhomogeneous media. Another impressive and informative chapter of the book is related to new partitions of conventional moving media acoustics and especially to the nature of nonlinear losses in vortical superfluid. In general, book will be useful for acousticians and engineers developing acoustic systems for underwater or atmosphere observations, and also for technologists using intensive sound fields for micro and nano items development based on applications of acoustic treatment in solution of moving particles.” - Prof. Igor B. Esipov, Full Professor of Physics Department in I.M. Gubkin’s Oil and Gas University, Moscow, Russia, Vice Editor-in-Chief of “Acoustical Physics” journal, Russian Acoustical Society Executive Board member, Acoustical Society of America member

The book is addressed to physicists and engineers evaluating underwater system potential or developing novel hydroacoustics detection utilities. It could be of interest to specialists involved in atmosphere and ocean ecology acoustics inspection. Book would be helpful to technologists developing procedures based on acoustic treatment of solutions comprising moving particles. With aid of this book specialists could found the origin, development and modification of actual sound field intensity distribution in their problems. Book will be useful as well to undergraduate and graduate students of these specialties.

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