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Periodic Acoustic Black Holes to Mitigate Sound Radiation from Cylindrical Structures

Periodic Acoustic Black Holes to Mitigate Sound Radiation from Cylindrical Structures PDF Author: Jie Deng
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 0

Book Description
Acoustic black holes (ABHs) achieved by progressively diminishing structural thickness have been proved a very efficient approach for wideband vibration reduction, sound suppression, energy harvesting, and wave manipulation. In this chapter, the focus is placed on mitigating the sound emitted from cylindrical shells with embedded ABHs. In the applications of aeronautics, astronautics, and underwater vehicles, cylindrical shells are very common yet the vibroacoustic problems in such structures are very challenging. Even the researches on ABHs for straight beams and flat plates are boosting in recent years, the ABH effect is unclear for curved structures thus it deserves further investigations to push forward their applications. Since cylindrical shells are usually long in, for example, airplanes and rockets, periodic ABHs are designed to alleviate the acoustic emission from them. The Gaussian expansion method (GEM) is employed to recover the vibration field on the cylinder and, based on that, the sound radiation model is developed to determine the emitted sound power level (SWL). The band gaps (BGs) are shown for infinite periodic ABH shells, followed by the vibroacoustic level for a finite periodic shell. Particularly, axial stiffeners are introduced and the influences of their quantity and width are carried out.

Periodic Acoustic Black Holes to Mitigate Sound Radiation from Cylindrical Structures

Periodic Acoustic Black Holes to Mitigate Sound Radiation from Cylindrical Structures PDF Author: Jie Deng
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 0

Book Description
Acoustic black holes (ABHs) achieved by progressively diminishing structural thickness have been proved a very efficient approach for wideband vibration reduction, sound suppression, energy harvesting, and wave manipulation. In this chapter, the focus is placed on mitigating the sound emitted from cylindrical shells with embedded ABHs. In the applications of aeronautics, astronautics, and underwater vehicles, cylindrical shells are very common yet the vibroacoustic problems in such structures are very challenging. Even the researches on ABHs for straight beams and flat plates are boosting in recent years, the ABH effect is unclear for curved structures thus it deserves further investigations to push forward their applications. Since cylindrical shells are usually long in, for example, airplanes and rockets, periodic ABHs are designed to alleviate the acoustic emission from them. The Gaussian expansion method (GEM) is employed to recover the vibration field on the cylinder and, based on that, the sound radiation model is developed to determine the emitted sound power level (SWL). The band gaps (BGs) are shown for infinite periodic ABH shells, followed by the vibroacoustic level for a finite periodic shell. Particularly, axial stiffeners are introduced and the influences of their quantity and width are carried out.

Acoustic Emission

Acoustic Emission PDF Author: Mahmut Reyhanoglu
Publisher: BoD – Books on Demand
ISBN: 1803551054
Category : Technology & Engineering
Languages : en
Pages : 110

Book Description
Structural testing and assessment, process monitoring, and material characterization are three broad application areas of acoustic emission (AE) techniques. Quantitative and qualitative characteristics of AE waves have been studied widely in the literature. This book reviews major research developments in the application of AE in numerous engineering fields. It brings together important contributions from renowned international researchers to provide an excellent survey of new perspectives and paradigms of AE. In particular, this book presents applications of AE in cracking and damage assessment in metal beams, asphalt pavements, and composite materials as well as studying noise mitigation in wind turbines and cylindrical shells.

Application of Acoustic Black Holes To Rotorcraft Structures for Vibration and Noise Control

Application of Acoustic Black Holes To Rotorcraft Structures for Vibration and Noise Control PDF Author: Robert Veltre
Publisher:
ISBN:
Category :
Languages : en
Pages :

Book Description
In recent years, acoustic black holes have proven to be effective vibration damping and transmission loss mechanisms. By tapering the local thickness of the structure, the black holes are able to reduce the bending wave speed thereby focusing strain energy into localized viscoelastic damping. This improves the efficiency of the applied damping layers. Due to their promising potential to both reduce weight and enhance damping, acoustic black holes have a multitude of vehicle born applications. Interior noise reduction in rotorcraft is a prominent application due to the presence of gear meshing noise. In this work, the application of acoustic black hole treatments applied to plates and sandwich panel structures is evaluated computationally using the finite element method. These notional structures were evaluated over the frequency range of sound commonly transmitted by rotorcraft transmission systems. These results are then compared with results given by uniform plates and sandwich panels of similar dimensions. The results indicate that acoustic black holes reduce vibration in the aluminum sandwich panels by 10 dB compared to traditional damping approaches, while reducing weight.

Quiet Structure Design Using Acoustic Black Holes

Quiet Structure Design Using Acoustic Black Holes PDF Author: Philip Feurtado
Publisher:
ISBN:
Category :
Languages : en
Pages :

Book Description
In recent years Acoustic Black Holes (ABHs) have been developed and demonstrated as effective, passive, lightweight vibration absorbers of flexural bending waves in beam and plate like structures. ABHs employ a local power-law thickness profile into a beam or plate, typically resulting in a one dimensional wedge or a two dimensional indentation in the structure. By reducing the thickness of the structure the ABH effect decreases the bending wave speed and increases the transverse vibration amplitude. In the limit where the thickness goes to zero the wave speed goes to zero and the bending waves never reach the thin edge, thus they are `absorbed.' Real, machined ABHs necessarily have some finite truncation thickness. This results in local strain concentrations that effectively dissipate energy when coupled with a high loss material such as a traditional applied damping layer. While the effectiveness of ABHs has been established and demonstrated, there is still a need to develop new insights that can help designers tailor the performance of ABHs for practical, realizable, noise and vibration control applications. This research aimed to expand the existing understanding of ABHs in ways that will be useful and instructive for designing ABH systems for practical noise and vibration control problems. One of the ultimate goals of this branch of ABH research is to be able to prescribe a specific ABH design to suit a given noise and vibration control problem. The results and methods developed here represent a significant and useful step towards that goal. The first step involved investigating the limitations and implications of analytic ABH theory, the frequency dependent performance of ABH systems, and the structural acoustic coupling of embedded ABH systems with both response to distributed pressure excitations and radiation to the fluid surrounding the structure. Analytic ABH theory provides predictions for the vibration reduction from a one dimensional ABH wedge, but the predictions conflict with key underlying assumptions such that better vibration absorption is predicted from more significant violations of the fundamental theory assumptions. It was demonstrated that these effects can be significant for practical ABH designs and contribute to the effectiveness of ABHs, particularly at low frequencies. A new design parameter was developed based on the theoretical assumptions to aid the design, assessment, and optimization of ABHs.The low frequency performance, extension, and optimization of ABHs is also of particular interest because ABHs display a `cut on frequency' above which they become effective vibration absorbers. Experimental investigations were conducted on plates with embedded arrays of ABHs as well as an individual ABH at low, mid, and high frequency in order to gain insight into the frequency dependent behavior of ABHs. The results showed that the low frequency behavior of ABH systems is dictated by the activation of low order local ABH modes within the ABH taper. Analyzing the vibration of the ABH plates in the wavenumber domain also revealed that ABH plates significantly affect the wavenumber characteristics of the structure, reducing the speed of supersonic bending waves to subsonic speeds and reducing the coupling between the structure and the surrounding fluid. Additional transmission loss measurements and computational investigations demonstrated that the wavenumber sweep from the ABH effect also can significantly affect the power injection and response of embedded ABH plates to distributed pressure excitations. Simulation results illustrated conditions for both positive and negative effects for ABH system noise control effectiveness.

Sound and Structural Vibration

Sound and Structural Vibration PDF Author: Frank J. Fahy
Publisher: Elsevier
ISBN: 0080471102
Category : Technology & Engineering
Languages : en
Pages : 666

Book Description
The first edition of Sound and Structural Vibration was written in the early 1980s. Since then, two major developments have taken place in the field of vibroacoustics. Powerful computational methods and procedures for the numerical analysis of structural vibration, acoustical fields and acoustical interactions between fluids and structures have been developed and these are now universally employed by researchers, consultants and industrial organisations. Advances in signal processing systems and algorithms, in transducers, and in structural materials and forms of construction, have facilitated the development of practical means of applying active and adaptive control systems to structures for the purposes of reducing or modifying structural vibration and the associated sound radiation and transmission. In this greatly expanded and extensively revised edition, the authors have retained most of the analytically based material that forms the pedagogical content of the first edition, and have expanded it to present the theoretical foundations of modern numerical analysis. Application of the latter is illustrated by examples that have been chosen to complement the analytical approaches to solving fairly simple problems of sound radiation, transmission and fluid-structural coupling that are presented in the first edition. The number of examples of experimental data that relate to the theoretical content, and illustrate important features of vibroacoustic interaction, has been augmented by the inclusion of a selection from the vast amount of material published during the past twenty five years. The final chapter on the active control of sound and vibration has no precursor in the first edition. * Covers theoretical approaches to modeling and analysis* Highly applicable to challenges in industry and academia* For engineering students to use throughout their career

Acoustic Metamaterials and Phononic Crystals

Acoustic Metamaterials and Phononic Crystals PDF Author: Pierre A. Deymier
Publisher: Springer Science & Business Media
ISBN: 3642312322
Category : Technology & Engineering
Languages : en
Pages : 388

Book Description
This comprehensive book presents all aspects of acoustic metamaterials and phononic crystals. The emphasis is on acoustic wave propagation phenomena at interfaces such as refraction, especially unusual refractive properties and negative refraction. A thorough discussion of the mechanisms leading to such refractive phenomena includes local resonances in metamaterials and scattering in phononic crystals.

Structure-Borne Sound

Structure-Borne Sound PDF Author: L. Cremer
Publisher: Springer Science & Business Media
ISBN: 3662101211
Category : Science
Languages : en
Pages : 591

Book Description
Since structure-borne sound plays an important role in noise control, material testing and machine diagnosis, the relevant properties of the most important elements of a construction (plates, beams and shells) are investigated. Measurement techniques, equations of motion, formulas for wave speeds, resonance frequencies, impedances, transmission coefficients etc. are given. The different damping mechanisms and the radiation properties are treated. The statistical energy analysis (SEA) is also presented. This new edition has been enlarged to include also waves on orthotropic plates, and the vibration and radiation of cylindrical shells.

Computational Acoustics of Noise Propagation in Fluids - Finite and Boundary Element Methods

Computational Acoustics of Noise Propagation in Fluids - Finite and Boundary Element Methods PDF Author: Steffen Marburg
Publisher: Springer Science & Business Media
ISBN: 3540774483
Category : Science
Languages : en
Pages : 584

Book Description
The book provides a survey of numerical methods for acoustics, namely the finite element method (FEM) and the boundary element method (BEM). It is the first book summarizing FEM and BEM (and optimization) for acoustics. The book shows that both methods can be effectively used for many other cases, FEM even for open domains and BEM for closed ones. Emphasis of the book is put on numerical aspects and on treatment of the exterior problem in acoustics, i.e. noise radiation.

Phononic Crystals

Phononic Crystals PDF Author: Abdelkrim Khelif
Publisher: Springer
ISBN: 1461493935
Category : Technology & Engineering
Languages : en
Pages : 247

Book Description
This book provides an in-depth analysis as well as an overview of phononic crystals. This book discusses numerous techniques for the analysis of phononic crystals and covers, among other material, sonic and ultrasonic structures, hypersonic planar structures and their characterization, and novel applications of phononic crystals. This is an ideal book for those working with micro and nanotechnology, MEMS (microelectromechanical systems), and acoustic devices. This book also: Presents an introduction to the fundamentals and properties of phononic crystals Covers simulation techniques for the analysis of phononic crystals Discusses sonic and ultrasonic, hypersonic and planar, and three-dimensional phononic crystal structures Illustrates how phononic crystal structures are being deployed in communication systems and sensing systems

Understanding Acoustics

Understanding Acoustics PDF Author: Steven L. Garrett
Publisher: Springer
ISBN: 3319499785
Category : Science
Languages : en
Pages : 913

Book Description
This textbook provides a unified approach to acoustics and vibration suitable for use in advanced undergraduate and first-year graduate courses on vibration and fluids. The book includes thorough treatment of vibration of harmonic oscillators, coupled oscillators, isotropic elasticity, and waves in solids including the use of resonance techniques for determination of elastic moduli. Drawing on 35 years of experience teaching introductory graduate acoustics at the Naval Postgraduate School and Penn State, the author presents a hydrodynamic approach to the acoustics of sound in fluids that provides a uniform methodology for analysis of lumped-element systems and wave propagation that can incorporate attenuation mechanisms and complex media. This view provides a consistent and reliable approach that can be extended with confidence to more complex fluids and future applications. Understanding Acoustics opens with a mathematical introduction that includes graphing and statistical uncertainty, followed by five chapters on vibration and elastic waves that provide important results and highlight modern applications while introducing analytical techniques that are revisited in the study of waves in fluids covered in Part II. A unified approach to waves in fluids (i.e., liquids and gases) is based on a mastery of the hydrodynamic equations. Part III demonstrates extensions of this view to nonlinear acoustics. Engaging and practical, this book is a must-read for graduate students in acoustics and vibration as well as active researchers interested in a novel approach to the material.