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 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 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 Designing Quiet Structures written by Gary H. Koopmann and published by Elsevier. This book was released on 1997-10-13 with total page 261 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is the first of its kind. It provides the reader with a logical and highly quantitative means of including noise as a parameter in the early design stages of a machine or structure. The unique and unified methodology builds upon the familiar disciplines of acoustics, structural dynamics and optimization. It also exemplifies the art of simplification - the essence of all good engineering design. Strategies for designing quiet structures require extensive analytical and experimental tools. For computing the sound power from complex structures the authors recommend a new 3-D, lumped parameter formulation. This fully developed, user-friendly program can be applied generally to noise-control-by-design problems. Detailed instructions for running the application are given in the appendix as well as several sample problems to help the user get started. The authors also describe a new instrument: a specially developed resistance probe used to measure a structure=92s acoustic surface resistance. As an example, the procedure is outlined for measuring the valve cover of an internal combustion engine. Indeed, throughout the book the reader is presented with actual experiments, numerical and physical that they can replicate in their own laboratory. This is a must-have book for engineers working in industries that include noise control in the design of a product. Its practical and didactic approach also makes it ideally suited to graduate students. First text covering the design of quiet structures Written by two of the leading experts in the world in the area of noise control Strong in its integration of structural dynamics, acoustics, and optimization theory Accompanied by a computer program that allows the computation of sound power Presents numerous applications of noise-control-by-design methods as well as methods for enclosed and open spaces Each chapter is supported by homework problems and demonstration experiments
Download or read book Application of Acoustic Black Holes To Rotorcraft Structures for Vibration and Noise Control written by Robert Veltre and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
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 Architectures of Sound written by Michael Fowler and published by Birkhäuser. This book was released on 2017-10-23 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: Architects are used to designing visually. In order to expand their basic design tools, this book explores the interactions between sound, space, hearing, and architecture. To this end, the author uses contemporary and historic buildings and projects, but also fictional, philosophical, and theoretical approaches – the idea is not only to define sound as a source, but also as an instrument of architectural space. By introducing a metatheory of "critical hearing", designers are able to acoustically test their projects and contribute to their design with auditive input, already at the design stage.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 700 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book The Dictionary of Aerospace Engineering written by Utku Taşova and published by Entropol. This book was released on 2023-11-03 with total page 1032 pages. Available in PDF, EPUB and Kindle. Book excerpt: Propelling Understanding: Your Launchpad to Aerospace Engineering Excellence The realm of aerospace engineering is a confluence of science, ambition, and human endeavor, encapsulating the relentless pursuit of pushing boundaries and transcending terrestrial limitations. It is a domain that continually stretches the fabric of what is possible, melding imagination with the rigors of engineering precision. The Dictionary of Aerospace Engineering, with its extensive compilation of 6,000 meticulously curated titles, serves as a cornerstone for those engaged in this dynamic field, offering a wellspring of knowledge and a pathway to mastery. Embarking on the pages of this dictionary is akin to launching into a voyage through the core principles, advanced methodologies, and the ever-evolving technologies that are the hallmarks of aerospace engineering. Each entry is a beacon, illuminating complex terminologies and nuanced concepts, aiding both the seasoned engineer and the aspiring practitioner in navigating the vast expanse of aerospace engineering knowledge. The Dictionary of Aerospace Engineering is not merely a repository of terms but an edifice of understanding. It is a conduit through which the intricate and the arcane become accessible, where challenging concepts are decoded into comprehensible insights. This dictionary is an endeavor to foster a shared lexicon, to enhance communication, collaboration, and innovation across the aerospace engineering community. This comprehensive reference material transcends being a passive dictionary; it is a dynamic engagement with the multifaceted domain of aerospace engineering. Each term, each title is a testament to the relentless spirit of inquiry and the unyielding drive for innovation that characterizes the aerospace engineering sector. The Dictionary of Aerospace Engineering is an invitation to delve deeper, to engage with the lexicon of flight and space, and to emerge with a richer understanding and a sharpened expertise. It’s a portal through which the uninitiated become adept, the curious become enlightened, and the proficient become masters. Every term, every phrase is a step closer to unraveling the mysteries and embracing the challenges that propel the aerospace engineering domain forward. As you traverse through the entries of The Dictionary of Aerospace Engineering, you are embarking on a journey of discovery. A journey that will not only augment your understanding but will also ignite the spark of curiosity and the drive for innovation that are the hallmarks of excellence in aerospace engineering. We beckon you to commence this educational expedition, to explore the breadth and depth of aerospace engineering lexicon, and to emerge with a boundless understanding and an unyielding resolve to contribute to the ever-evolving narrative of aerospace engineering. Through The Dictionary of Aerospace Engineering, may your quest for knowledge soar to new heights and may your contributions to the aerospace engineering domain echo through the annals of human achievement.
Download or read book NASA SP written by and published by . This book was released on 1992 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1968-03 with total page 926 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Building News and Engineering Journal written by and published by . This book was released on 1859 with total page 1206 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 NASA Activities written by and published by . This book was released on 1976 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book N A S A Activities written by U.S. National Aeronautics and Space Administration and published by . This book was released on 1975 with total page 632 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Art Journal written by and published by . This book was released on 1890 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vol. for 1867 includes Illustrated catalogue of the Paris Universal Exhibition.
Download or read book The art journal London written by and published by . This book was released on 1890 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt:
