Engineering Vibroacoustic Analysis—Methods and Applications

Engineering Vibroacoustic Analysis—Methods and Applications
Stephen A. Hambric, Shung H. Sung, & Donald J. Nefske
Wiley, UK (2016)

Fellow bibliophiles of senior editor and Auburn University Professor Malcolm J. Crocker’s acoustics handbooks (including the Encyclopedia of Acoustics, the Handbook of Acoustics, and the Handbook of Noise and Vibration Control) will be happy to learn of his latest project for John Wiley & Sons: the Acoustic, Noise, and Vibration Series. Compared with the relative brevity of those older texts, this series promises to give its chapter authors much more space with which to develop acoustic topics in depth. Engineering Vibroacoustic Analysis—Methods and Applications is the second publication in the series, with three titles currently available. Contributing editors for this text are Pennsylvania State University Professor Stephen A. Hambric, and independent research professionals Shung H. (Sue) Sung and Donald J. Nefske. There are an additional fourteen contributing authors.

It is not surprising that the book has an automotive focus since this level of engineering vibroacoustic analysis is typically reserved for the automotive and aerospace industries, and also because the book’s contributors are drawn from researchers with automotive analysis experience.

There are few things more enjoyable than learning a subject from someone who has a firm grasp of the math, science, and practice—and who obviously enjoys sharing that knowledge, helping others to explore it further. Stephen Hambric’s teaching style clearly shows these qualities—he writes in first person, as if you are in the room with him, and often interrupts his detailed explanations of the math and science, breaking the fourth wall to give the reader some bit of practical advice from the experienced practitioner. Of course, the book has seventeen authors, but Professor Hambric’s style is easy to spot where it appears throughout the book.

Chapter 1 is a nice overview of the book, outlining the state of the art and describing how the book is arranged to bring the reader up to speed. It is very useful as a map of where you are, why you’re there, and where you’re headed—which is especially useful when your mind is deep in the details of each chapter.

The next three chapters are a basic-level review of structural vibrations, interior and exterior sound, and the interaction between vibrating structures and sound fields. In Chapter 2, Dr. Hambric develops the vibration theories for beams, plates, and shells; shows how these develop into vibration modes of a structure; and then explores the energy flow and exchange in simple structures using harmonic oscillator theory. We also get a peek at Chapter 11’s technique of Statistical Energy Analysis, albeit applied to a very simple 2 degree of freedom system.

Drs. Sung and Nefske cover the subject of sound in Chapter 3, including formulations for predicting sound within enclosures as well as those methods better suited for predicting sound radiated to the surrounding atmosphere. The derivations are thorough with many references in which to get lost; however, the authors include several well-developed examples.

Chapter 4 is a relatively quick introduction to the problems associated with coupling the structural vibration analysis to the acoustic analysis to obtain an accurate model. Even so, the chapter includes tricks of the trade and an interesting account of how flexural waves in a structure may or may not radiate sound, a discussion of solution practicality, a few thought experiments, and a short historical account of the development of structure–acoustic coupling theory. As is common in all chapters, each new subject builds upon the previous one, step-by-step, and future topics are introduced to maintain the reader’s motivation.

Chapter 5 develops a relatively simple method of coupling the structural model of an automobile interior with an acoustic cavity model of the sound within that interior. There is an interesting discussion of the exchange of energy between car interior and interior panels—panel absorber versus Helmholtz cavity absorber. As this method is generally suited for low frequencies, the examples given in the chapter are simple two degree of freedom systems.

Chapter 6 reviews finite element analysis (FEA) techniques used to model structural–acoustic coupling within finite interiors. Examples give just enough detail to follow the logic along with the appropriate references for more in-depth study. Several derivations and illustrations from this and other chapters are direct copies from Ver and Beranek’s Noise and Vibration Control Engineering (Wiley & Sons, 2006), making it a good idea for the serious student to add that text to their library.

Chapter 7 reviews boundary element analysis (BEA), which is primarily used when modeling structural–acoustic coupling for sound radiated from an immersed vibrating structure to an unbounded fluid. Again, thorough examples are given to demonstrate each concept along with a warning to choose your basis functions wisely.

Chapter 8 shows various ways to set up a problem for a computer model to introduce “sound packages” such as constrained layer damped (CLD) panels into the analysis. It also reviews several physical test methods of obtaining material properties to use as input.

Chapter 9 starts to get deep into the woods, with a discussion of the goals of using structural–acoustic models to optimize a design, and a technical review of the various papers exploring several approaches and simplifications to the problem. Attempted solutions in published papers are reviewed and their limitations are noted. The chapter concludes with a worked-out example of the optimization of a radiating finite beam.

Chapter 10 offers methods to account for variations from calculated operating conditions due to manufacturing variances in dimensions, material properties, and other physical uncertainties.

Chapter 11 introduces statistical energy analysis (SEA), which is used to simplify the analysis of relatively larger structures and/or at relatively higher frequencies by subdividing the problem into smaller regions, calculating averages, and tracking the flow of energy between interconnected modes.

Chapters 12 through 15 explore the work being done on emerging methods, all having the common goal of providing solutions to the structural–acoustic problem at the difficult mid-band frequency range (i.e., structures with characteristic dimensions of 5 to 20 wavelengths).

Engineering Vibroacoustic Analysis is a solid addition to Professor Crocker’s new Acoustics, Vibration, and Noise series. I congratulate Hambric, Sung, and Nefske on an outstanding job producing a text that quickly takes the reader to the research and development level of understanding the subject, and recommend it both as a graduate text and for those within the structural–acoustics R&D fields.

Jon W. Mooney, PE
Acoustics by JW Mooney LLC