Vibro-Acoustics of Lightweight Sandwich Structures PDF Download

Author: Tianjian Lu
Publisher: Springer
ISBN: 3642553583
Category : Science
Languages : en
Pages : 350

View

Book Description
Vibro-Acoustics of Lightweight Sandwich Structures introduces the study of the coupled vibration and acoustic behavior of lightweight sandwich structures in response to harmonic force and sound pressure. This book focuses on the theoretical modeling and experimental investigation of lightweight sandwich structures in order to provide a predictive framework for vibro-acoustic characteristics of typical engineering structures. Furthermore, by developing solution tools, it concentrates on the influence of key systematic parameters leading to effective guidance for optimal structure design toward lightweight, high-stiffness and superior sound insulation capability. This book is intended for researchers, scientists, engineers and graduate students in mechanical engineering especially in structural mechanics, mechanics and acoustics. Fengxian Xin and Tianjian Lu both work at the School of Aerospace, Xi’an Jiaotong University.

Author: Anders Nilsson
Publisher: Springer
ISBN: 9783662531389
Category : Science
Languages : en
Pages :

View

Book Description
This is a set of Three volume books:Vibro-Acoustics, Volume 1, Second Edition; Vibro-Acoustics, Volume 2, Second Edition; Vibro-Acoustics, Volume 3, Second Edition. This three-volume book gives a thorough and comprehensive presentation of vibration and acoustic theories. Different from traditional textbooks which typically deal with some aspects of either acoustic or vibration problems, it is unique of this book to combine those two correlated subjects together. Moreover, it provides fundamental analysis and mathematical descriptions for several crucial phenomena of Vibro-Acoustics which are quite useful in noise reduction, including how structures are excited, energy flows from an excitation point to a sound radiating surface, and finally how a structure radiates noise to a surrounding fluid. Many measurement results included in the text make the reading interesting and informative. Problems/questions are listed at the end of each chapter and the solutions are provided. This will help the readers to understand the topics of Vibro-Acoustics more deeply. The book should be of interest to anyone interested in sound and vibration, vehicle acoustics, ship acoustics and interior aircraft noise.

Author: Anders Nilsson
Publisher: Springer
ISBN: 3662479346
Category : Science
Languages : en
Pages : 453

View

Book Description

Author: Anders Nilsson
Publisher: Springer
ISBN: 3662478072
Category : Science
Languages : en
Pages : 385

View

Book Description
This three-volume book gives a thorough and comprehensive presentation of vibration and acoustic theories. Different from traditional textbooks which typically deal with some aspects of either acoustic or vibration problems, it is unique of this book to combine those two correlated subjects together. Moreover, it provides fundamental analysis and mathematical descriptions for several crucial phenomena of Vibro-Acoustics which are quite useful in noise reduction, including how structures are excited, energy flows from an excitation point to a sound radiating surface, and finally how a structure radiates noise to a surrounding fluid. Many measurement results included in the text make the reading interesting and informative. Problems/questions are listed at the end of each chapter and the solutions are provided. This will help the readers to understand the topics of Vibro-Acoustics more deeply. The book should be of interest to anyone interested in sound and vibration, vehicle acoustics, ship acoustics and interior aircraft noise. This is the first volume, and covers the following topics: Mechanical systems with one degree of freedom, Frequency domain, Waves in solids, Interaction between longitudinal and transverse waves, General wave equation, Wave attenuation due to losses and transmission across junctions, Longitudinal vibrations of finite beams, Flexural vibrations of finite beams, Flexural vibrations of finite plates.

Author: Jiaxue Yan
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
Abstract: Honeycomb structures are widely used in many areas for their material characteristics such as high strength-to-weight ratio, stiffness-to-weight, sound transmission, and other properties. Honeycomb structures are generally constructed from periodically spaced tessellations of unit cells. It can be shown that the effective stiffness and mass properties of honeycomb are controlled by the local geometry and wall thickness of the particular unit cells used. Of particular interest are regular hexagonal (6-sided) honeycomb unit cell geometries which exhibit positive effective Poisson's ratio, and modified 6-sided auxetic honeycomb unit cells with Poisson's ratio which is effectively negative; a property not found in natural materials. One important honeycomb meta-structure is sandwich composites designed with a honeycomb core bonded between two panel layers. By changing the geometry of the repetitive unit cell, and overall depth and material properties of the honeycomb core, sandwich panels with different vibration and acoustic properties can be designed to shift resonant frequencies and improve intensity and Sound Transmission Loss (STL). In the present work, a honeycomb finite element model based on beam elements is programmed in MATLAB and verified with the commercial finite element software ABAQUS for frequency extraction and direct frequency response analysis. The MATLAB program was used to study the vibration and acoustic properties of different kinds of honeycomb sandwich panels undergoing in-plane loading with different incident pressure wave angles and frequency. Results for the root mean square intensity IRMS based on normal velocity on the transmitted side of the panel measure vibration magnitude are reported for frequencies between 0 and 1000 Hz. The relationship between the sound transmission loss computed with ABAQUS and the inverse of the intensity of surface velocity is established. In the present work it is demonstrated that the general trend between the STL pressure response and the inverted intensity metric have similar response characteristics over both the stiffness frequency region and the resonance frequency region, showing that an increase in IRMS corresponds to a decrease in STL. The ABAQUS model was used to verify the MATLAB program for natural frequencies and mode shapes, and to compute the STL on the top surface of the honeycomb sandwich structure. Resonant peaks in the frequency response of intensity and STL are identified with natural frequencies and mode shapes of the honeycomb sandwich structure. A unique feature of this research is the ability to apply the time-harmonic acoustic pressure as a load on the transmitting surface of the honeycomb sandwich panel with variable incident angle ranging between 0° to 90°. When the incident angle is nonzero, the pressure load is complex valued, with sinusoidal distribution, and frequency dependent. The finite element implementation of the complex-valued variable incident pressure distribution is programmed in MATLAB to give complete control of the angle, frequency and distribution. Commercial finite element software such as ABAQUS has limited ability to directly apply frequency dependent and distributed real and imaginary pressure distributions in a direct steady state frequency analysis over a large number of frequency evaluations. In the present work, IRMS results for a family of honeycomb sandwich panels with systematic increment in internal cell wall angle, subject to incremental changes in incident angle pressure loads are studied and compared. Results show that for honeycomb sandwich panels with both positive and negative internal cell wall angle, on average, intensity for the nonzero incident angles is higher than the 0°normal incident angle. For the honeycomb sandwich panels with positive internal angle, the intensity consistently increases with larger nonzero incident angles. Furthermore, under the same incident angle pressure load, the intensity of honeycomb panel with positive internal angle is consistently larger than honeycomb panels with negative internal angles.

Author: Andreas Mayr
Publisher: Logos Verlag Berlin GmbH
ISBN: 3832526986
Category : Architecture
Languages : en
Pages : 321

View

Book Description
The work reported in this thesis addresses the problem of structure-borne sound transmission in buildings. Vibrating sources, such as services plant and domestic appliances, transmit vibro-acoustic power, causing noise complaints by occupants in rooms removed from the source room. There is not yet an accepted practical method of predicting the installed power into floors or supporting walls, and thence the resultant sound pressure in rooms. This study concentrates on the prediction of the installed power from mechanical installations in lightweight buildings composed of framed and ribbed plates. To identify the characteristics of such receiver elements, a field survey has been undertaken, which involved measurement of the point and transfer mobilities of common wall and floor structures. It is shown that the range of measured values of receiver point mobility is surprisingly small and that the constructions investigated often displayed thin plate-like characteristics, with relatively small spatial variations in point mobility. These field measurements give support to the notion of averaging over contacts. This single equivalent receiver mobility has been assembled both from measured data and from the approximate method and then used in combination with single equivalent source data, to yield an approximate prediction of the installed power. The agreement obtained between the exact and approximate values allowed consideration of a practical implementation of the approximate prediction method, based on a reception plate method which yields the activity and mobility of the tested machine as single equivalent values.

Author: Luyao Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description
Sandwich structures with decent sound insulation and absorption properties have been widely used in the engineering fields such as aerospace engineering, marine engineering and civil and construction engineering. Investigations on the acoustic behavior of sandwich structures is of practical importance, not only for engineers but to researchers in the field. A numerical study of the vibro-acoustic and sound transmission loss (STL) of an aluminum honeycomb core sandwich panel with fabric-reinforced graphite (FRG) composite face sheets is performed in the present research. The honeycomb sandwich structure, faced with an FRG composite face sheet, has acoustic advantages over other types of sandwich structures commonly used in the field. The effects of different boundary conditions and geometric properties of the FRG faced honeycomb structure on the stiffness of the structure are evaluated. The effects of the stiffness on the acoustic performance of the structure are investigated. Truss core sandwich panels filled with sound absorbing materials are also studied numerically for the panels' vibration responses and STL behavior. The performances of a polyurethane (PUF)-foam-filled truss core sandwich panel and a wood-board-filled truss core sandwich panel are compared. The wood based sandwich panel shows advantages with compatible acoustic performance and environmental-friendly characteristics over the PUF foam panel. The acoustic behavior of the wood-based porous media, with varying airflow properties, are investigated. The most significant factor affecting the vibro-acoustic responses of the panel are identified. The wood-based-porous-medium-filled truss core sandwich panel with various face sheet materials are analyzed. A truss core 2 sandwich panel is designed with the optimal combination of wood-board and face sheet materials. Numerical models, based on the sandwich theory, are established based on the assumption the sandwich core is an orthotropic structural layer. The radiated sound power from the panel is quantified with the Rayleigh integral method. A random diffuse field is used as an incident sound source and is derived with the finite element method using ACTRAN. The numerical results generated with the implementation of the models are validated with experimental data available in the literature. The findings provide guidance for selecting and designing honeycomb core and truss core sandwich panels with decent acoustic properties for engineering applications. The developed approach presents practical significance for quantitatively evaluating and designing sandwich panels with high efficiency and effectiveness, when the acoustic and vibrational performance of the panels need to be considered.

Author: Yu Xiong
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
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.

Author: Alice Cicirello
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description

Author: Richard Lee
Publisher:
ISBN: 9780494852477
Category :
Languages : en
Pages :

View

Book Description