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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
VIBROACOUSTIC SIMULATION Learn to master the full range of vibroacoustic simulation using both SEA and hybrid FEM/SEA methods Vibroacoustic simulation is the discipline of modelling and predicting the acoustic waves and vibration of particular objects, systems, or structures. This is done through finite element methods (FEM) or statistical energy analysis (SEA) to cover the full frequency range. In the mid-frequency range, both methods must be combined into a hybrid FEM/SEA approach. By doing so, engineers can model full frequency vibroacoustic simulations in complex technical systems used in aircraft, trains, cars, ships, and satellites. Indeed, hybrid approaches are increasingly used in the automotive, aerospace, and rail industries. Previously covered primarily in scientific journals, Vibroacoustic Simulation provides a practical approach that helps readers master the full frequency range of vibroacoustic simulation. Through a systematic approach, the book illustrates why both FEM and SEA are necessary in acoustic engineering and how both can be used in combination through hybrid methodologies. Striking a crucial balance between complex theories and practical applications, the text provides real-world examples of vibroacoustic simulation, such as fuselage simulation, interior-noise prediction for electric and combustion vehicles, train profiles, and more, to help elucidate the concepts described within. Vibroacoustic Simulation also features: * A balance of complex theories with the nuts and bolts of real-world applications * Detailed worked examples of junction equations * Case studies from companies like Audi and Airbus that illustrate how the methods discussed have been applied in real-world projects * A companion website that provides corresponding Python codes for all examples, allowing readers to work through the examples on their own Vibroacoustic Simulation is a useful reference for acoustic and mechanical engineers working in the automotive, aerospace, defense, or rail industries, as well as researchers and graduate students studying acoustics.
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Vibroacoustic Simulation
An Introduction to Statistical Energy Analysis and Hybrid Methods
Alexander Peiffer
This edition first published 2022
© 2022 by John Wiley & Sons, Inc.
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A catalogue record for this book is available from the Library of Congress
Hardback ISBN: 9781119849841; ePub ISBN: 9781119849865; ePDF ISBN: 9781119849858; Obook ISBN: 9781119849872
Cover image: © visibleimpression/Shutterstock; Courtesy of Alexander Peiffer
Cover design by Wiley
Set in 10/12.5pt STIXTwoText by Integra Software Services Pvt. Ltd, Pondicherry, India
To my parents and Ivonne my love who always supported me
List of Illustrations
Chapter 2
Figure 2.1 Histogram for the height...
Figure 2.2 Histogram of triglycerides in...
Figure 2.3 Bar chart of blood...
Figure 2.4 Comparison of three “...
Figure 2.5 Illustration of the statistical table.
Figure 2.6 Bar chart of the...
Figure 2.7 Percentage bar chart of...
Figure 2.8 Pie chart of the...
Figure 2.9 Stem-and-leaf plot...
Figure 2.10 Boxplot of the iodine...
Figure 2.11 Scatterplot of the correlation...
Figure 2.12 Line graph of the...
Figure 2.13 Semi-logarithmic line graph...
Figure 2.14 Histograms of BMI and...
Chapter 3
Figure 3.1 Venn diagram showing the...
Figure 3.2 Venn diagrams showing the...
Figure 3.3 Venn diagram showing the...
Figure 3.4 Venn diagram showing event...
Figure 3.5 Venn diagrams showing the...
Figure 3.6 Venn diagram showing mutually...
Chapter 4
Figure 4.1 Cumulative distribution function of...
Figure 4.2 Graphical characteristics of the...
Figure 4.3 Graphical characteristics of the...
Chapter 5
Figure 5.1 Simulated height distribution of...
Figure 5.2 Illustration of the cdf...
Figure 5.3 Illustration of the pdf...
Figure 5.4 Illustration of the empirical...
Figure 5.5 Illustration of the standardization...
Figure 5.6 Normal probability plot of...
Figure 5.7 Diagram of the normal...
Figure 5.8 Normal approximation...
Figure 5.9 Normal approximation...
Chapter 6
Figure 6.1 Sampling distribution of...
Figure 6.2 Sampling distribution of...
Figure 6.3 Comparison of the t...
Figure 6.4
X
2
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Figure 6.5 Frequency distribution of...
Figure 6.6 Frequency distribution of the...
Figure 6.7 Illustration of critical values...
Figure 6.8 Illustration of critical values...
Figure 6.9
F
distribution...
Figure 6.10 Illustration of critical values...
Chapter 7
Figure 7.1 Illustration of the rejection...
Figure 7.2 Illustration of the...
Figure 7.3 Illustration of the two...
Figure 7.4 Illustration of the rejection...
Figure 7.5 Illustration of power for...
Figure 7.6 Illustration of power for...
Figure 7.7 Illustration of rejection and...
Chapter 8
Figure 8.1 Illustration of the rejection...
Figure 8.2 Illustration of the...
Figure 8.3 Illustration of the rejection...
Figure 8.4 Illustration of the...
Chapter 9
Figure 9.1 Paw-licking durations (s...
Figure 9.2 Illustration of rejection and...
Figure 9.3 Illustration of p...
Figure 9.4 Illustration of rejection and non-rejection regions for LSD-
t
Figure 9.5
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—...
Chapter 10
Figure 10.1 Illustration of main effect...
Figure 10.2 Testing guidelines for a...
Figure 10.3 Trend of changes in...
Figure 10.4 Illustration of 2×...
Chapter 11
Figure 11.1 Illustration of rejection and...
Figure 11.2 Possible four-fold tables...
Chapter 13
Figure 13.1 Scatterplot of the weight...
Figure 13.2 Variation decomposition of dependent...
List of Tables
Chapter 2
Table 2.1 Raw data on the height (cm) of 153 10-year-old girls.
Table 2.2 Frequency distribution for...
Table 2.3 Frequency distribution of...
Chapter 3
Table 3.1 Meaning of symbols in set theory and probability theory.
Chapter 6
Table 6.1 Means and variances...
Table 6.2 Frequency distribution of...
Chapter 7
Table 7.1 FEM and SEA system description
Chapter 10
Table 10.1 Weight gain (g...
Guide
Cover
Title page
Copyright
Table of Contents
Preface
Acknowledgments
About the Companion Website
Acronyms
Begin Reading
A Basic Mathematics
B Specific Solutions
C Symbols
Index
End User License Agreement
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Preface
The reason and stimulation for this book was an application for a lecturer position several years ago. I slightly panicked due to the fact that in case of success, I would be totally unprepared in terms of lecturing material. So, I decided to write a script in order to have at least something prepared. But, the more I got into the text and the more I tried to collect content for a script on vibroacoustics, I came to the conclusion that there is a need for a modern text book on the subject of vibroacoustic simulation focussing on statistical energy analyses and hybrid methods.
There are many excellent books on acoustics and vibration, but what is missing to my opinion is an overall treatment of vibroacoustic simulation methods. Especially when we are talking about statistical energy analysis (SEA) and the combination of finite element methods (FEM) and SEA, the hybrid FEM/SEA method. In addition, the hybrid FEM/SEA method allows a much clearer and more systematic approach to SEA compared to the original literature and might help to impart the knowledge to students and professionals. It is my persuasion, that every acoustic simulation engineer shall master these simulation techniques to be prepared for vibroacoustic prediction of the full audible frequency range.
What is so special about vibroacoustics that so many methods are required? One answer is that the dynamic properties of structure and fluid systems are so different. This leads to distinct dynamic behavior. There may fit a lot of wavelengths of acoustic waves into a chamber of a machine or a passenger compartment filled with air, whereas the surrounding structure is often stiff and robust, and only a few wavelengths of the structural bending waves fit into the area of the surrounding walls. This strongly influences how energy is transmitted via the walls into the cavity and how small uncertainties affect the system response.
Additionally, there is often a great variety of materials, like foams, fibers, rubbers, etc. in the structure or applied as noise and vibration control, all having different orders of magnitude in wavelengths or even completely different modes of wave propagation.
As a consequence, vibroacoustics is a complex engineering discipline or science because the engineer has to master all those modes of wave propagation in the different systems and media as far as the coupling between those waves for connected subsystems. A thorough treatment of all wave types, couplings, and properties is not possible in a typical lecture or textbook, but it is possible to explain the main idea of how to deal with vibroacoustic phenomena and which means are required to solve the engineering problem. This book tries to extract the basic concepts, so that candidates are in a position to determine, investigate and categorize vibroacoustic systems and make the right decision on how to simulate them.
The frequency range of interest is covering four orders of magnitude from 20 to 20 000 Hz. That is one further reason why various methods for the description of these phenomena are required. At low frequencies it makes sense to investigate the modal behavior of a structure like the first modes of a string. In contrast to this, calculating all standing waves at high frequencies for a large room is not reasonable, as small changes at the boundaries or even temperature will lead to totally different wave forms in the room. Both regimes are addressed by different approaches categorized as (i) deterministic or (ii) statistic methods. The first occurs normally at lower frequencies, whereas the latter is valid at high frequencies. Because of the different wavelengths, it often appears that both cases occur in one vibroacoustic system, and both approaches are necessary. The combination of the two methods is called hybrid FEM/SEA method.
As there are many books on the subjects of deterministic acoustics and vibration available, this book focuses on SEA and hybrid methods. However, as FEM systems of equations are involved in the hybrid method, a minimum understanding of deterministic systems is required.
How is the book organized? It starts with a simple but excellent example for a vibrating system: the harmonic oscillator. In chapter 1 phenomena such as resonances, off resonance dynamics, and numerous damping mechanisms are explained based on this test case. A first step towards complex and FEM systems is made by introducing multiple coupled oscillators as an example for multiple degree of freedom systems. Real excitations often are of random nature. Hence, this chapter ends with tools and methods to describe random signals and processes as far as the response of linear systems to such signals.
Chapters 2 and 3 deal with wave motion in fluids and structures, respectively. Both chapters bring into focus the physics of sources, because the source mechanisms reveal how energy is introduced into the wavefields and how the feedback to the excitation can be characterized. Furthermore, the source dynamics are required when systems are coupled. The dynamics of acoustic and structure systems are shown in chapters 4 and 5. This includes the natural resonances of such systems that will become important for the classification of random systems. Based on analytical models, the low and high frequency behavior of such systems is presented. One aim of the various examples is to illustrate that when sources are exciting those systems, the high frequency dynamics become similar to the free field results from chapters 2 and 3. Chapter 6 deals with the random description of systems. The concept of ensemble average and diffuse fields is applied to typical example systems by using Monte Carlo simulations. Based on such randomized systems and averaged values, it is shown that we get similar results to those you would get from deterministic methods when the uncertainty of dynamically complex systems is considered. This opens the door to the statistical energy analysis (SEA). Some typical one-, two-, and three-dimensional systems are presented in the very detail, so that the reader gets a feeling when and under which conditions the SEA assumptions are valid. The idea is to provide comprehensive examples for the rules of thumb usually used to determine if random methods are valid or not.
In chapter 7 methods for coupling deterministic (FEM) and random (SEA) systems are presented, and the hybrid FEM/SEA method is introduced by describing the coupling between FEM and SEA systems. Based on this, the effect of random on deterministic systems as far as the impact of deterministic on random subsystems is presented. The chapter closes with the global procedure of hybrid FEM/SEA modelling that calculates the joint response of both types of systems.
Chapter 8 applies these coupling formulas to several options of connections. Especially the coupling sections are often missing in text books on SEA for a certain reason: the calculation of coupling loss factors is not easy. However, as it is important to understand the assumptions and limits, the coupling loss factors of point, area, and line junctions are systematically derived. Since junctions are nothing else than noise paths, this chapter is also useful for practical applications, for example the acoustic transmission loss of plates that is an important quantity for airborne acoustic isolation.
The following chapters apply the theory to pure deterministic (chapter 9), pure random (chapter 10), and hybrid FEM/SEA examples (chapter 11). All examples are worked out in detail and show real engineering systems such as mufflers. In chapter 9 the transfer matrix method is introduced as an example of deterministic methods. This allows the simulation of complex lay-ups of noise control treatments applied in chapters 10 and 11.
The presented theory and the examples are calculated using Python scripts. The scripts and the related toolbox are made available as open source code. The author hopes that this toolbox helps to understand and to apply the presented topics. Further contributions to the code of the toolbox are very welcome. The documentation of the toolbox and the GIT repository can be found on the authors website www.docpeiffer.com.
As an acoustic engineer, I am in the somehow unique situation that I had the chance to work on several means of transportation: trains, aircraft, helicopters, launchers, satellites, and finally cars (mainly electric). Because of this experience I am convinced that a deep knowledge of vibroacoustic simulation methods is mandatory to create excellent and low-noise products. This know-how puts the acoustic engineer in the position to apply the right method in the right situation and frequency range. To underline this fact, chapter 12 presents models, basic ideas, pitfalls, and results of some industrial examples from aerospace, automotive, and train industries. Special thanks goes to my former colleague Ulf Orrenius who wrote the train and motivation section of chapter 12. His great experience and knowledge strongly enriched the content of this chapter.
This book is about simulation, but simulation is nothing without validation based on tests. In my view both – simulation and tests – are required to perform a good acoustic design and noise control engineering. Thus, chapter 13 briefly summarizes test and correlation methods together with an outlook to further topics of simulation and ongoing research in the field of acoustic simulation.
In most cases the life of an acoustic engineer means solving the target conflict between the acoustic performance and costs, weight, and space requirements. This is the reason why design engineers are not always the best friends of acousticians during the design phase. The more important it is that you are able to calculate the effect of your decisions for efficient application of the sometimes rare acoustic resources. I hope that this book provides some support for this demanding task.
Coming back to my initial motivation: If I would have to hold a lecture on vibroacoustic simulation now, I would sleep much better.
Alexander Peiffer
Planegg, Germany15 October 2021
Acknowledgments
Special thanks goes to my former colleague Ulf Orrenius who wrote the train- and motivation section of chapter 12. His great experience and knowledge strongly enriched the content of this chapter.
I would also like to thank the Audi AG who provided the models to present the simulation strategy of automotive systems.
Acronyms
2DOF
Two degrees of freedom
ms
Mean square
rms
Root mean square
CFD
Computational fluid dynamics
CFRP
Carbon fiber reinforced plastic
DFT
Discrete Fourier transform
DVA
Dynamic vibration absorber
DOF
Degree of freedom
EMA
Experimental modal analysis
FEM
Finite element method
FFT
Fast Fourier transform
FT
Fourier transform
GFRP
Glass fiber reinforced plastic
HVAC
Heating, ventilation, and air conditioning
MAC
Modal assurance criterion
MDOF
Multiple degrees of freedom
MIMO
Multiple input multiple output
NVH
Noise, vibration, and harshnes
PAX
Passenger
SDOF
Single degree of freedom
SEA
Statistical Energy Analysis
SISO
Single input single output
TBL
Turbulent boundary layer
TPA
Transfer path analysis
TVA
Tuned vibration absorber
