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 Proceedings of the 2nd International Conference on Mechanical System Dynamics written by Xiaoting Rui and published by Springer Nature. This book was released on with total page 4383 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Recent Trends in Wave Mechanics and Vibrations written by Zuzana Dimitrovová and published by Springer Nature. This book was released on 2022-10-06 with total page 1217 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume gathers select proceedings of the 10th International Conference on Wave Mechanics and Vibrations (WMVC), held in Lisbon, Portugal, on July 4-6, 2022. It covers recent developments and cutting-edge methods in wave mechanics and vibrations applied to a wide range of engineering problems. It presents analytical and computational studies in structural mechanics, seismology and earthquake engineering, mechanical engineering, aeronautics, robotics and nuclear engineering among others. The volume will be of interest for students, researchers, and professionals interested in the wide-ranging applications of wave mechanics and vibrations.
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 Graded Elastic Metamaterials for Energy Harvesting written by Jacopo Maria De Ponti and published by Springer Nature. This book was released on 2021-03-02 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents a complete framework for energy harvesting technologies based on graded elastic metamaterials. First, it provides a comprehensive survey of state-of-the-art research on metamaterials for energy harvesting and then explores the theoretical wave mechanics framework, going from inhomogeneous media to graded elastic metamaterials. The framework can be used to thoroughly analyse wave propagation phenomena in beams, plates, and half-spaces and to investigate the effect of local resonance on creating bandgaps or wave mode conversions. All these concepts converge together with piezoelectric materials in the study and design of piezo-augmented arrays of resonators. The energy harvesting performances of the graded metamaterials are then compared to conventional solutions, in order to quantify their advantages for applications.
Download or read book An Experimental Exploration Study of Acoustic Black Holes in Thick Plates written by Emily Stimson and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: An Acoustic Black Hole (ABH) is an effect that occurs when a structure contains a power-law tapered thickness. This profile will create a means for vibrations to be focused into a thinner region of the structure, where the addition of a lossy material can help efficiently dissipate the vibrational energy, essentially "trapping" the vibrations. Embedding a set of damped ABHs into a structure then creates a metastructure with good vibration and noise reduction characteristics, but with a lower weight than traditional add-on treatments. For this project, four 1" thick aluminum panels with various ABH orientations, lengths, minimum thicknesses, and types are explored using experimental modal analysis and laser vibrometry. Each of the four panels contained one or multiple ABHs, labeled as an ABH or multi-grid panel, were compared to the mode shapes and loss factors of a Baseline panel. The frequencies for each of the first modes shapes, or "cut-on" frequencies, for the ABH and multi-grid panels all occurred at lower frequencies compared to the Baseline panel; even after adding a layer of polyurethane for damping to the Baseline and ABH panels, there was an observable downward shift in each panel's "cut-on" frequency compared to the undamped Baseline panel. All of the panels exhibited several different modal behaviors including: modes that were dominated by the geometry of the panel and the boundary conditions, modes that were dictated by the embedded ABHs in the panel, and a mixture between the two. This led to the investigation for the types of mode classifications: global, local, and mixed modes. Then comparing the general shapes, movements, and radiation efficiencies of the mode shapes to the likes of a piston, dipole, or quadrupole source. The panels' loss factors aided in this exploration, due to similar global and mixed modes appearing in the lower loss factor range, while particular locally focused modes were seen with loss factors clearly above the rest.
Download or read book Proceedings of the 6th China Aeronautical Science and Technology Conference written by Chinese Aeronautical Society and published by Springer Nature. This book was released on 2024-01-07 with total page 711 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains the original peer-reviewed research papers presented at the 6th China Aeronautical Science and Technology Conference held in Wuzhen, Zhejiang Province, China, in September 2023. Topics covered include but are not limited to Navigation/Guidance and Control Technology, Aircraft Design and Overall Optimisation of Key Technologies, Aviation Testing Technology, Airborne Systems/Electromechanical Technology, Structural Design, Aerodynamics and Flight Mechanics, Advanced Aviation Materials and Manufacturing Technology, Advanced Aviation Propulsion Technology, and Civil Aviation Transportation. The papers presented here share the latest findings in aviation science and technology, making the book a valuable resource for researchers, engineers and students in related fields.
Download or read book Structure Borne Sound written by L. Cremer and published by Springer Science & Business Media. This book was released on 2013-03-09 with total page 591 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Experimental Investigation of the Effect of Model Scale on Structural joint Damping written by David G. Stephens and published by . This book was released on 1967 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Damping of Vibrations written by Z. Osinski and published by CRC Press. This book was released on 2018-05-08 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: This monograph seeks to strengthen the contributions of Polish scientists and engineers to the study of problems of mechanical vibrations and noise. It presents research covering such topics as: structural damping; internal damping in composite materials; and noise attenuation in working machines.
Download or read book Topics in Modal Analysis II Volume 6 written by R. Allemang and published by Springer Science & Business Media. This book was released on 2012-04-28 with total page 652 pages. Available in PDF, EPUB and Kindle. Book excerpt: Topics in Modal Analysis II, Volume 6: Proceedings of the 30th IMAC, A Conference and Exposition on Structural Dynamics, 2012, is the sixth volume of six from the Conference and brings together 65 contributions to this important area of research and engineering. The collection presents early findings and case studies on fundamental and applied aspects of Structural Dynamics, including papers on: Aerospace, Acoustics, Energy Harvesting, Shock and Vibration, Finite Element, Structural Health Monitoring, Biodynamics Experimental Techniques, Damage Detection, Rotating Machinery, Sports Equipment Dynamics, Aircraft/Aerospace.
Download or read book Vibration of Continuous Systems written by Singiresu S. Rao and published by John Wiley & Sons. This book was released on 2019-03-06 with total page 816 pages. Available in PDF, EPUB and Kindle. Book excerpt: A revised and up-to-date guide to advanced vibration analysis written by a noted expert The revised and updated second edition of Vibration of Continuous Systems offers a guide to all aspects of vibration of continuous systems including: derivation of equations of motion, exact and approximate solutions and computational aspects. The author—a noted expert in the field—reviews all possible types of continuous structural members and systems including strings, shafts, beams, membranes, plates, shells, three-dimensional bodies, and composite structural members. Designed to be a useful aid in the understanding of the vibration of continuous systems, the book contains exact analytical solutions, approximate analytical solutions, and numerical solutions. All the methods are presented in clear and simple terms and the second edition offers a more detailed explanation of the fundamentals and basic concepts. Vibration of Continuous Systems revised second edition: Contains new chapters on Vibration of three-dimensional solid bodies; Vibration of composite structures; and Numerical solution using the finite element method Reviews the fundamental concepts in clear and concise language Includes newly formatted content that is streamlined for effectiveness Offers many new illustrative examples and problems Presents answers to selected problems Written for professors, students of mechanics of vibration courses, and researchers, the revised second edition of Vibration of Continuous Systems offers an authoritative guide filled with illustrative examples of the theory, computational details, and applications of vibration of continuous systems.
Download or read book Experimental Investigation of Vibration Damping in Linear and Nonlinear Vibration written by Giovanni Ferrari and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The main tool for the dynamic analysis of continuous structures is today modal analysis, which applies to lightly dampened structures undergoing small amplitude vibrations. Vibration energy in real structures is always partially lost because of internal material dissipation, Coulomb friction, interaction with fluids and even in presence of passive and active dampers. This dissipation is integrated in modal analysis by the use of a modal damping ratio for each normal vibration mode. A linear viscous or equivalent damping model underlies the use of modal damping ratios and preserves mode superposition in the study. The use of modal damping in linear vibrations is also practically profitable, as real structures tend to show small damping values that vary with the natural modes. However, the estimation of modal damping ratios is impossible a priori, and experimental measurement is necessary. Modern design practices are imposing the use of thin lightweight structures, often in contact with fluids, which easily undergo large amplitude vibrations; stricter safety regulations, in turn, may require the estimate of vibration amplitudes closer to resonance. In these cases, modal parameters remain valid with very good approximation, freeing the industry from the adoption of more complex theories. Modal damping, however, cannot be extended to nonlinear large amplitude vibration: as soon as vibration amplitudes exceed the characteristic dimension of the system, the prediction of vibration amplitude fails altogether. Even under the assumption of stationary vibrations, experimentally determined damping values appear dependent not only on the normal mode of vibration, but also on the vibration amplitude. Provided the availability of suitable know-how, it was decided to undertake a wide experimental characterization of the trend of damping values of thin walled shells and plates during large amplitude forced vibrations, bridging the lack of relevant literature. In order to give general character to this experimental activity, several cases were taken into account: metallic materials, composites and rubbers, in presence and in absence of fluid-structure interaction. The increasingly common smart materials and smart structures, composites for which vibration damping is tuned according to the designer's wish, feature active or semi-active damping. In presence of fluids and active elements, damping can grow to large values or can instead destabilize the system by feeding, not removing, energy. The study of modal damping in case of active vibration amplitude mitigation was therefore included as well. Through this wide range of experiments, a better comprehension of nonlinear damping was sought empirically. Since no other means were available for geometrically nonlinear vibrations, modal damping was applied unchanged to match with experimental results the vibration amplitude predicted by nonlinear models at one specific resonance. As expected, the values had to be changed to reproduce the vibration amplitude given by different force levels of stepped-sine excitation. The dependence on excitation amplitude seemed to follow an auspicious trend across a wide range of cases. Furthermore, different expressions of damping in the nonlinear field were used with respect to the traditional viscous (modal) damping formulation. This is particularly suitable for specific materials (e.g. elastomers showing a viscoelastic behavior) or configurations. Relevant experimental results, however, were not more general than the ones obtained employing modal damping, which indicates the great complexity of the problem. Actually, some evidence seemed to suggest that the equivalent values of damping in the nonlinear field are also influenced by the energy transfers between vibration modes. While damping has been seldom or never investigated previously in case of internal resonances, an estimate of its values in this situation led to additional insight." --
Download or read book Mechanical Vibrations written by Michel Geradin and published by John Wiley & Sons. This book was released on 2015-02-16 with total page 616 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mechanical Vibrations: Theory and Application to Structural Dynamics, Third Edition is a comprehensively updated new edition of the popular textbook. It presents the theory of vibrations in the context of structural analysis and covers applications in mechanical and aerospace engineering. Key features include: A systematic approach to dynamic reduction and substructuring, based on duality between mechanical and admittance concepts An introduction to experimental modal analysis and identification methods An improved, more physical presentation of wave propagation phenomena A comprehensive presentation of current practice for solving large eigenproblems, focusing on the efficient linear solution of large, sparse and possibly singular systems A deeply revised description of time integration schemes, providing framework for the rigorous accuracy/stability analysis of now widely used algorithms such as HHT and Generalized-α Solved exercises and end of chapter homework problems A companion website hosting supplementary material
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 Surface Acoustic Waves in Inhomogeneous Media written by Sergey V. Biryukov and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface Acoustic Waves in Inhomogeneous Media covers almost all important problems of the interaction of different types of surface acoustic waves with surface inhomogeneities. The problems of surface acoustic wave interaction with periodic topographic gratings widely used in filters and resonators are under careful consideration. The most important results of surface wave scattering by local defects such as grooves, random roughness, elastic wedges are given. Different theoretical approaches and practical rules for solving the surface wave problems are presented.
Download or read book Dynamic Equivalent Modeling of Acoustic Metamaterials written by Nansha Gao and published by Springer Nature. This book was released on 2022-10-17 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book derives physical models from basic principles, studies the effect of equivalent models on the dynamic characteristics of phononic crystals and acoustic metamaterials, and analyzes the physical mechanisms behind vibration and noise reduction. It first summarizes the research status of vibration and noise reduction, and research progress in phononic crystals and acoustic metamaterials. Based on this, one-dimensional periodic beam, two-dimensional thin plate with circular hole, and corresponding gradient structures are introduced, and their dynamic characteristics are discussed in detail. Therefore, different equivalent methods for different models are proposed through theoretical analysis, modal analysis and transmission rate analysis. Finally, a Helmholtz-type acoustic metamaterial, i.e. a multi-layer slotted tube acoustic metamaterial, is studied. Aiming at the low-frequency band gap of this model, a theoretical model for solving the inverse problem of acousto-electric analogue equivalent is proposed, and the effect of structural parameters on the low-frequency band gap is studied using this equivalent model. This book closely revolves around how to conduct equivalent research on artificially fabricated periodic structures. The methods and conclusions presented in this book provide a new theoretical basis for the application of artificial woven periodic structures in the field of low-frequency vibration reduction and noise reduction and are also an innovation in the discipline of vibration and noise control. This book is suitable for undergraduate students, graduate students and teachers in vibration and noise majors in universities, and can also provide references for engineering and technical personnel in related fields.
