Download or read book Vibration Damping of Aluminum Plates Using Acoustic Black Holes for Application in Aerospace Structures written by Angelina Conti and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years, scientists have investigated the acoustic black hole (ABH) effect as a low-weight high-performance vibration control device for application in aerospace structures. The ABH effect uses a specific power-law skin thickness taper to decrease the velocity of an incident bending wave to nearly zero. Once the velocity has decreased, the wave is unable to reflect back at the far edge, thus trapping it in the ABH. Applying a small amount of viscoelastic damping material to the surface of the ABH dissipates most of the vibration while adding very little weight and cost to the overall structure. Experimental tests prove that the ABH is an effective way to trap and damp vibration energy. The ABH effect is quantified through experimental broadband vibration response comparisons between three aluminum plates of varying degree of vibration control and damping. In general, the low-frequency responses were very similar among all three plates since global modes dominate the response. After the cut-on frequency of the ABH was reached, the ABH effect induced a large variation in the surface averaged mobility, explained by the focusing of energy in the ABH cells. The application of damping material decreased the surface averaged mobility and its variation. Increasing the frequency also decreased the surface averaged mobility variation. These experiments proved that the ABH effect successfully focuses vibration energy from the plate to the center of the two-dimensional ABH and that the added layer of damping material effectively reduces the vibration energy of the structure, while adding very little weight. The ABH could potentially replace traditional heavy and inefficient acoustic treatments, increasing the fuel efficiency by decreasing the weight devoted to acoustic treatment. Future work will include testing an "add-on" ABH device for application in existing airframes.

Download or read book Experimental Investigation of Damping Structural Vibrations Using the Acoustic Black Hole Effect written by E. P. Bowyer and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the results of the experimental investigations into some new geometrical configurations in plate-like structures materialising one-dimensional (1D) acoustic black holes for flexural waves (wedges of power-law profile) and two-dimensional (2D) acoustic black holes for flexural waves (circular indentations of power-law profile). Such acoustic black holes allow the user to reduce the amplitudes of the vibration responses of plate-like structures to a maximum effect, while not increasing the mass of the structures. This thesis also suggests some new real world practical applications for this damping technique. Initially, the effects of geometrical and material imperfections on damping flexural vibrations in plates with attached wedges of power-law profile (1D black holes) were investigated, demonstrating that this method of damping is robust enough for practical applications. Then, damping of flexural vibrations in turbofan blades with trailing edges tapered according to a power-law profile has been investigated. In addition, experimental investigations into power-law profiled slots within plates have been also conducted. Another important configuration under investigation was that of circular indentations (pits) of power-law profile within the plate. In the case of quadratic or higher-order profiles, such indentations materialise 2D acoustic black holes for flexural waves. To increase the damping efficiency of power-law profiled indentations, the absorption area has been enlarged by increasing the size of the central hole in the pit, while keeping the edges sharp. The next step of investigation in this thesis was using multiple indentations of power-law profile (arrays of 2D black holes). It was shown that not only do multiple indentations of power-law profile provide substantial reduction in the damping of flexural vibrations, but also a substantial reduction in radiated sound power. The experimental results have been obtained also for a cylindrical plate incorporating a central hole of quadratic profile. They are compared to the results of numerical predictions, thus validating the results and the experimental technique. Investigations into the effects of indentations of power-law profile made in composite plates and panels and their subsequent inclusion into composite honeycomb sandwich panels are also reported. These indentations again act as 2D acoustic black holes for flexural waves and they effectively damp flexural vibrations within the panels. It was also demonstrated that these indentations can be enclosed in smooth surfaced panels and that no additional damping layer is required to induce the acoustic black hole effect in composite structures. In conclusion, it has been confirmed in this thesis that one and two-dimensional acoustic black holes represent an effective method of damping flexural vibrations and reducing the associated structure-borne sound. Furthermore, this thesis has shown that acoustic black holes can be efficiently employed in practical applications, such as trailing edges of jet engine fan blades, composite panels, and composite honeycomb sandwich structures.

Download or read book Optimization of Acoustic Black Holes for Vibration Reduction written by Cameron McCormick and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A problem that frequently arises in noise control engineering is the need for lightweight structures that are also quiet. In many practical instances of transportation and aerospace design, stiff, lightweight panels are used to reduce overall weight. However, these stiff, lightweight panels are also highly receptive to vibration and can become efficient radiators of sound. Although traditional methods of passive damping can effectively combat this behavior, they usually lead to an increase in overall weight. By modifying the plate thickness according to a specific power law profile, so-called `acoustic black holes' (ABHs) offer a compelling solution to the need for both broadband vibration reduction and reduced weight. ABH vibration absorbers have been shown to be effective at reducing structural vibration, often with a net reduction in overall weight. However, a comprehensive understanding of what constitutes optimal ABH design in finite structures has been historically lacking. This dissertation systematically investigates the many considerations of ABH design for vibration reduction. An optimization framework is developed that combines the modelling of structural dynamics with multi-objective evolutionary optimization, and this framework is used to determine the optimal designs for various ABH applications. By analyzing trends in the optimization results, the tradeoffs inherent in ABH design are illuminated in a more holistic manner than has been undertaken to date.

Download or read book Vibroacoustics of Lightweight Structures with Embedded Acoustic Black Holes written by Yu Xiong and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Interest in lightweight and quiet structures is growing in the aeronautical, automotive, and marine industries. However, lightweight structures can easily result in mechanical vibration and noise issues from an acoustician's view. Therefore, a demand for a novel structure that can be lightweight and quiet is imperative. An acoustic Black Hole (ABH) effect is one of the possible methods to resolve this conflict. The ABH is a practical, lightweight, passive vibration control technique and has been well developed in recent years. In an effort to begin using the ABH effect to design an ABH structure for real applications in the industry, in chapter three of this thesis, a hybrid vibroacoustic analytical model is developed. It allows the engineers to understand the sensitivity of the acoustical responses of the ABH structure with respect to the design variables of material properties and structure dimensions in an analytical form. The hybrid analytical model is then used for optimizing the vibroacoustic responses of an ABH beam structure to provide design guidelines for minimizing the noise radiated by the ABH beam structure through the selection of optimal material properties and structure dimensions. Improving low frequency performance is essential for real applications of ABH structures. In chapter four, by establishing the correlation between local ABH modes and radiation efficiency, the results show the low frequency performance of ABH plates essentially depends on the first low order ABH modes. Following the design guidelines obtained from the hybrid vibroacoustic analytical model, several plates with embedded multiple ABH cells are studied using a structural-acoustics simulation to evaluate and tailor the vibration response and resulting structural-acoustic radiation by attaching discrete tuning masses at the center position of each ABH cell. An appropriate amount of tuning mass (4.7 g) adjusted the reduction dip of radiation efficiency at the critical frequency (2700Hz), showing that a potential improvement could be achieved to mitigate the coincidence dip in sound transmission problems. Non-uniformly distributed tuning masses enhanced the reduction of the plate sound radiation coupling. An additional 4 dB reduction in one-third octave band radiated sound power was achieved, and a total 8 dB reduction was obtained compared to the uniform plate case. The first local ABH modes were tuned to lower frequencies in order to improve the low frequency vibroacoustic performance of the plate structures. Many noise and control applications demand panel structures with high Transmission loss (TL) and low weight. The ABH plates have the potential to act as promising candidates for TL applications. In chapter five, a new multi-scale ABH plate design with two different ABH sizes is proposed. The multi-scale ABH plate results are compared with the results from a single-scale ABH plate, all with and without damping materials and an undamped uniform plate. The measured TL results showed the damped single-scale ABH plate achieved improved TL performance compared with a uniform plate by increasing the TL 5-7 dB at and above the coincidence dip. The new proposed multi-scale ABH plate flattens the TL curve, nearly eliminating the coincidence dip band without adding a net mass compared to the uniform plate. The multi-scale design increased the TL 3 dB relative to the single-scale design, and a total 10 dB TL increase to the undamped uniform plate. Various weights of tuning masses are attached at the center of the ABH cells to manipulate the ABH cut-on at the desired frequency. The results show that adding a tuning mass of 20 g to each large ABH cell, of the damped multi-scale ABH plate, improved the TL 2 dB in the low-frequency bands. The added tuning mass created a series of local resonant and high loss modes in the low-frequency region. The ABH plates not only perform better on TL, but also have less total mass. The damped multi-scale ABH plate is 7\% lighter than the uniform plate. Although the damping materials and tuning masses were applied, the overall weight advantage is still attained. This is the first insight into embedding two different size ABH cells and applying tuning masses to improve the plate TL characteristics.

Download or read book Quiet Structure Design Using Acoustic Black Holes written by Philip Feurtado and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Periodic Acoustic Black Holes to Mitigate Sound Radiation from Cylindrical Structures written by Jie Deng and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on with total page 1050 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Controlling Flexural Waves Using Subwavelength Perfect Absorbers written by Julien Leng and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The vibration control adapted to light structures is a scientific and technological challenge due toincreasingly stringent economic and ecological standards. Meanwhile, recent studies in audible acoustics havefocused on broadband wave absorption at low frequencies by means of subwavelength perfect absorbers. Suchmetamaterials can totally absorb the energy of an incident wave. The generalisation of this method for applicationsin elastodynamics could be of great interest for the vibration control of light structures.This thesis aims at adapting the perfect absorption problem for flexural waves in 1D and 2D systems with localresonators using the critical coupling condition. A study of 1D systems with simple geometries is first proposed. Thisprovides methods to design simple resonators for an effective absorption of flexural waves. The 1D systems thenbecome more complex by studying the critical coupling of 1D Acoustic Black Holes (ABH). The ABH effect is theninterpreted using the concept of critical coupling, and key features for future optimisation procedures of ABHs arepresented. The critical coupling condition is then extended to 2D systems. The perfect absorption by the firstaxisymmetric mode of a circular resonator inserted in a thin plate is analysed. Multiple scattering by an array ofcircular resonators inserted in an infinite or semi-infinite 2D thin plate, called metaplate, is also considered to getclose to practical applications. Through this thesis, analytical models, numerical simulations and experiments areshown to validate the physical behaviour of the systems presented.

Download or read book Wave Models for the Flexural Vibrations of Thin Plates written by Jacques Cuenca and published by . This book was released on 2009 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flexural vibrations of thin structures are strongly related to sound radiation and structural damage, for which they deserve careful attention in many domains of science and engineering. Two aspects of crucial importance are the development of accurate tools for the prediction and analysis of vibrations and efficient vibration damping. In the first part of the thesis, a model of the flexural vibrations of thin convex polygonal plates based on the image source method is presented. The developed approach allows to predict the vibrations of individual plates and plate assemblies of arbitrary convex polygonal geometry and having arbitrary boundary conditions. The method is particularly suitable for mid- and high-frequency dynamics, in that its accuracy is improved with an increase in frequency or structural damping. A tool for estimating the Young's modulus and structural damping ratio of highly damped flat panels is also proposed. The second part of the thesis concerns vibration damping using the acoustic black hole effect. It is weel-known that a flexural wave travelling in a thin plate or beam slows down in a zone of decreasing thickness. Thus, if the thickness decreases sufficiently smoothly to zero, the wave stops travelling, without being reflected back. Such is the principle of the so-called acoustic black hole effect. A model of the flexural vibrations of such profile is proposed, allowing to determine optimal geometrical and material properties in order to maximise vibration damping. Simulated and measured responses show a reduction of vibration level up to 20 decibels.

Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 1020 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Engineering Vibroacoustic Analysis written by Stephen A. Hambric and published by John Wiley & Sons. This book was released on 2016-05-02 with total page 540 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book describes analytical methods (based primarily on classical modal synthesis), the Finite Element Method (FEM), Boundary Element Method (BEM), Statistical Energy Analysis (SEA), Energy Finite Element Analysis (EFEA), Hybrid Methods (FEM-SEA and Transfer Path Analysis), and Wave-Based Methods. The book also includes procedures for designing noise and vibration control treatments, optimizing structures for reduced vibration and noise, and estimating the uncertainties in analysis results. Written by several well-known authors, each chapter includes theoretical formulations, along with practical applications to actual structural-acoustic systems. Readers will learn how to use vibroacoustic analysis methods in product design and development; how to perform transient, frequency (deterministic and random), and statistical vibroacoustic analyses; and how to choose appropriate structural and acoustic computational methods for their applications. The book can be used as a general reference for practicing engineers, or as a text for a technical short course or graduate course.

Download or read book Structural Health Monitoring Damage Detection Systems for Aerospace written by Markus G. R. Sause and published by Springer Nature. This book was released on 2021 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: This open access book presents established methods of structural health monitoring (SHM) and discusses their technological merit in the current aerospace environment. While the aerospace industry aims for weight reduction to improve fuel efficiency, reduce environmental impact, and to decrease maintenance time and operating costs, aircraft structures are often designed and built heavier than required in order to accommodate unpredictable failure. A way to overcome this approach is the use of SHM systems to detect the presence of defects. This book covers all major contemporary aerospace-relevant SHM methods, from the basics of each method to the various defect types that SHM is required to detect to discussion of signal processing developments alongside considerations of aerospace safety requirements. It will be of interest to professionals in industry and academic researchers alike, as well as engineering students. This article/publication is based upon work from COST Action CA18203 (ODIN - http://odin-cost.com/), supported by COST (European Cooperation in Science and Technology). COST (European Cooperation in Science and Technology) is a funding agency for research and innovation networks. Our Actions help connect research initiatives across Europe and enable scientists to grow their ideas by sharing them with their peers. This boosts their research, career and innovation.

Download or read book Acoustic Metamaterials and Phononic Crystals written by Pierre A. Deymier and published by Springer Science & Business Media. This book was released on 2013-01-13 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Fundamentals of Physical Acoustics written by David T. Blackstock and published by John Wiley & Sons. This book was released on 2000-04-24 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: AN AUTHORITATIIVE, UP-TO-DATE INTRODUCTION TO PHYSICAL ACOUSTICS Easy to read and understand, Fundamentals of Physical Acoustics fills a long-standing need for an acoustics text that challenges but does not overpower graduate students in engineering and physics. Mathematical results and physical explanations go hand in hand, and a unique feature of the book is the balance it strikes between time-domain and frequency-domain presentations. Fundamentals of Physical Acoustics is intended for a two-semester, first-year graduate course, but is also suitable for advanced undergraduates. Emphasis on plane waves in the first part of the book keeps the mathematics simple yet accommodates a broad range of topics: propagation, reflection and transmission, normal modes and simple waveguides for rectilinear geometries, horns, inhomogeneous media, and sound absorption and dispersion. The second part of the book is devoted to a more rigorous development of the wave equation, spherical and cylindrical waves (including the more advanced mathematics required), advanced waveguides, baffled piston radiation, diffraction (treated in the time domain), and arrays. Applications and examples are drawn from: * Atmospheric acoustics * Noise control * Underwater acoustics * Engineering acoustics * Acoustical measurements Supplemented with more than 300 graphs and figures as well as copious end-of-chapter problems, Fundamentals of Physical Acoustics is also an excellent professional reference for engineers and scientists.

Download or read book Smart Structures and Materials written by B. Culshaw and published by Artech House Publishers. This book was released on 1996 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book introduces the enabling concepts that make up the so-called smart structure and presents a number of brief case studies to illustrate the applications of these concepts. It examines the domains of the individual technologies and defines the challenges faced by the integrator. The book is particularly effective for the potential system user who needs a good technical general background on the subject and is also useful for students and researchers in contributory technologies who want to better understand the context of their work. Consultants in civil and structural engineering will also find it of interest.

Download or read book Adhesive Bonding of Aircraft Composite Structures written by Welchy Leite Cavalcanti and published by Springer. This book was released on 2021-06-04 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is open access under a CC BY 4.0 license. It presents the results of the ComBoNDT European project, which aimed at the development of more secure, time- and cost-saving extended non-destructive inspection tools for carbon fiber reinforced plastics, adhered surfaces and bonded joints. The book reports the optimal use of composite materials to allow weight savings, reduction in fuel consumptions, savings during production and higher cost efficiency for ground operations.

Download or read book Launch vehicle Dynamics written by Harry L. Runyan and published by . This book was released on 1961 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: