Sound Transmission Loss Analysis of a Double Plate-Acoustic Cavity Coupling System with In-Plane Functionally Graded Materials

In this paper, the isogeometric analysis (IGA) is employed to develop an acoustic radiation model for a double plate-acoustic cavity coupling system, with a focus on analyzing the sound transmission loss (STL). The functionally graded (FG) plate exhibits a different material properties in-plane, and the power-law rule is adopted as the governing principle for material mixing. To validate the harmonic response and demonstrate the accuracy and convergence of the isogeometric modeling, ANASYS is utilized to compare with numerical examples. A plane wave serves as the acoustic excitation, and the Rayleigh integral is applied to discretize the radiated plate. The STL results are compared with the literature, confirming the reliability of the coupling system. Finally, the investigation is conducted to study impact of cavity depth and power-law parameter on the STL.

Vibration and sound transmission loss characteristics of porous foam functionally graded sandwich panels in thermal environment

This study investigates the vibration and acoustic properties of porous foam functionally graded(FG)plates under the influence of the temperature field.The dynamics equations of the system are established based on Hamilton's principle by using the higher-order shear deformation theory under the linear displacement-strain assumption.The displacement shape function is assumed according to the four-sided simply-supported(SSSS)boundary condition,and the characteristic equations of the system are derived by combining the motion control equations.The theoretical model of vibro-acoustic coupling is established by using the acoustic theory and fluid-structure coupling solution method under the simple harmonic acoustic wave.The system's natural frequency and sound transmission loss(STL)are obtained through programming calculations and compared with the literature and COMSOL simulation to verify the validity and reliability of the theoretical model.The effects of various factors,such as temperature,porosity coefficients,gradient index,core thickness,width-to-thickness ratio on the vibration,and STL characteristics of the system,are discussed.The results provide a theoretical basis for the application of porous foam FG plates in engineering to optimize vibration and sound transmission properties.

Tunable low frequency band gaps and sound transmission loss of a lever-type metamaterial plate

A novel metamaterial plate with subwavelength lever-type resonators is proposed to obtain low frequency broadband band gaps and good sound insulation performance.The band structure is theoretically derived,and the validity of the theoretical method is verified by the finite element method.The formation mechanisms of the band gaps are illustrated by the analysis of the effective dynamic mass density and group velocity.The effect of the lever ratio on the band gaps is analyzed.The results indicate that as the lever ratio increases,the first band gap shifts to lower frequencies,while the bandwidth is widened.Moreover,the sound insulation performance of the proposed metamaterial plate is evaluated via examining the sound transmission loss(STL).Compared with the metamaterial plates without lever accessories,the proposed metamaterial plates with a suitable lever ratio have better sound insulation performance at low frequencies.

Analytical Study on the Rate of Sound Transmission Loss in Single Row Honeycomb Sandwich Panel Using a Numerical Method

Honeycomb structures have recently,replaced with conventional homogeneous materials.Given the fact that sandwich panels containing a honeycomb core are able to adjust geometric parameters,including internal angles,they are suitable for acoustic control applications.The main objective of this study was to obtain a transmission loss curve in a specific honeycomb frequency range along with same overall dimensions and weight.In this study,a finite element model(FEM)in ABAQUS software was used to simulate honeycomb panels,evaluate resonant frequencies,and for acoustic analysis.This model was used to obtain acoustic pressure and then to calculate the sound transmission loss(STL)in MATLAB software.Vibration and acoustic analysis of panels were performed in the frequency range of 1 to 1000 Hz.The models analyzed in this design includes 14-single row-honeycomb designs with angles of−45°,−30°,−15°,0°,+15°,+30°,+45°.The results showed that a-single row and−45°cell angle honeycomb panel in the frequency range of 1 to 1000 Hz had the highest STL as well as the highest number of frequency modes(90 mods).Furthermore,the panel had the highest STL regarding the area under the STL curve(dB∙Hz).The panels containing more frequency mods,have a higher transmission loss.Moreover,the sound transmission loss is more sensitive to the cell angle variable(θ).In other studies,the STL was more sensitive to the number of honeycomb cells in the horizontal and vertical directions,as well as the angle of cells.

Effects of mounting positions and boundary conditions on the sound transmission loss of panels in a niche

The sound insulation performance of railway car body structures is critical for the control of rail vehicle interior noise.In sound transmission loss(STL)measurements,a niche with a large depth is necessary to allow for mounting the wide range of thicknesses of railway car body panels and for the mechanical isolation of the two rooms.In this study,two typical interior floor panels are tested in a series of mounting conditions and mechanical boundary conditions.The change of STL results during measurement is also predicted by an STL prediction model based on the finite element method.At lower frequencies,the STL results are influenced by both the mounting positions and the mechanical boundary conditions.At higher frequencies,the STL results are mainly influenced by the mechanical boundary conditions.Differences between the panel in the infinite baffle and niches at the resonance and off-resonance frequencies are different.Considering both the effects of mounting positions and mechanical boundary conditions,the existence of the cavity amplifies the STL difference caused by the mechanical boundary conditions.

Topology optimization of chiral metamaterials with application to underwater sound insulation

Chiral metamaterials have been proven to possess many appealing mechanical phenomena,such as negative Poisson's ratio,high-impact resistance,and energy absorption.This work extends the applications of chiral metamaterials to underwater sound insulation.Various chiral metamaterials with low acoustic impedance and proper stiffness are inversely designed using the topology optimization scheme.Low acoustic impedance enables the metamaterials to have a high and broadband sound transmission loss(STL),while proper stiffness guarantees its robust acoustic performance under a hydrostatic pressure.As proof-of-concept demonstrations,two specimens are fabricated and tested in a water-filled impedance tube.Experimental results show that,on average,over 95%incident sound energy can be isolated by the specimens in a broad frequency range from 1 k Hz to 5 k Hz,while the sound insulation performance keeps stable under a certain hydrostatic pressure.This work may provide new insights for chiral metamaterials into the underwater applications with sound insulation.

An experimental investigation on sound transmission loss and vibration reduction of a vessel in water

Experimental results of sound transmission loss in a range of frequency through bubbly curtains were obtained, where the air content was in a wide range by means of varying pressure differences and the diameters of the pores of bubble-produce apparatus . Vibration reduction of a vessel in water due to the bubbly curtain was found.

Micro arc oxidation and electrophoretic deposition effect on damping and sound transmission characteristics of AZ31B magnesium Alloy

Micro arc oxidation(MAO) and electrophoretic deposition(EPD) process are employed to fabricate a dense coating on magnesium alloy to protect it from corrosion in engineering application. The EPD film changes the damping characteristic of magnesium alloy, and both the MAO and EPD process change the bending stiffness of samples being treated. Damping loss factor(DLF) test and sound transmission experiments were carried out for AZ31 B magnesium alloy with coating fabricated by MAO and EPD processes. The results indicate that DLF is improved in frequency range from 0-850 Hz. Bending stiffness of the samples is improved with MAO and EPD treatment. As a result, the sound transmission loss(LST) is improved in the stiffness control stage of the sound transmission verse frequency curve. To the samples by electrophoresis process, the LST is improved in frequency range from 2500-3200 Hz, because the damping loss factor is improved with EPD process. The results are useful for the surface treatment to enhance the damping loss factor, LST and widespread application of magnesium alloy while improving the corrosion resistance.

Friction Stir Welding Effect on Transverse Rigidity and Sound Transmission Characteristics of AZ31B Magnesium Alloy

AZ31B magnesium alloy was subjected to friction stir welding with various welding parameters. The equivalent Young's moduli of the friction stir welded samples and the base material were obtained by the three-point method, and their transverse rigidities were obtained as well. Furthermore, the sound transmission characteristics of those samples were experimentally studied by four-microphone impedance tube method. The experimental results indicate that the transverse rigidities of the friction stir welded samples were only 79%, 83% and 92% of those of the base material, respectively. The sound transmission losses of the processed samples were also lower, which was largely due to the reduction of transverse rigidities induced by the decrease of equivalent Young's moduli.

Power transmission through double-walled laminated composite panels considering porous layer-air gap insulation

The acoustic behavior of double-walled laminated composite panels consisting of two porous and air gap middle layers is studied within the classical laminated plate theory （CLPT）. Thus, viscous and inertia coupling in a dynamic equation, as well as stress transfer, thermal and elastic coupling of porous material ave based on the Biot theory. In addition, the wave equations are extracted according to the vibration equation of composite layers. The transmission loss （TL） of the structure is then calculated by solving these equations simultaneously. Statistical energy analysis （SEA） is developed to divide the structure into specific subsystems, and power transmission is extracted with balancing power flow equations of the subsystems. Comparison between the present work and the results reported elsewhere shows excellent agreement. The results also indicate that, although favorable enhancement is seen in noise control particularly at high frequencies, the corresponding parameters associated with fluid phase and solid phase of the porous layer are important on TL according to the boundary condition interfaces. Finally, the influence of composite material and stacking sequence on power transmission is discussed.

Propagation of acoustic waves in a fluid-filled pipe with periodic elastic Helmholtz resonators

Helmholtz resonators are widely used to reduce noise in a fluid-filled pipe system. It is a challenge to obtain lowfrequency and broadband attenuation with a small sized cavity. In this paper, the propagation of acoustic waves in a fluid-filled pipe system with periodic elastic Helmholtz resonators is studied theoretically. The resonance frequency and sound transmission loss of one unit are analyzed to validate the correctness of simplified acoustic impedance. The band structure of infinite periodic cells and sound transmission loss of finite periodic cells are calculated by the transfer matrix method and finite element software. The effects of several parameters on band gap and sound transmission loss are probed.Further, the negative bulk modulus of periodic cells with elastic Helmholtz resonators is analyzed. Numerical results show that the acoustic propagation properties in the periodic pipe, such as low frequency, broadband sound transmission, can be improved.

Low frequency acoustic properties of bilayer membrane acoustic metamaterial with magnetic oscillator

A bilayer membrane acoustic metamaterial was proposed to overcome the influence of the mass law on traditional acoustic materials and obtain a lightweight thin-layer structure that can effectively isolate low frequency noise. The finite element analysis（FEA） results agree well with the experimental results.It is proved that the sound transmission losses（STLs） of the proposed structures are higher than those of same surface density acoustic materials. The introduction of the magnetic mass block is different from the traditional design method, in which only a passive mass block is fixed on the membrane. The magnetic force will cause tension in the membrane, increase membrane prestress, and improve overall structural stiffness. The effects of the geometry size on the STLs are discussed in detail. The kind of method presented in this paper can provide a new means for engineering noise control.

Sound insulation performance of plates with interconnected distributed piezoelectric patches

This paper deals with the sound insulation performance of a thin plate with interconnected distributed piezoelectric patches. Piezoelectric patches are periodically bonded on the surfaces of the plate in a collocated fashion, and are interconnected via an inductive circuit network. This piezoelectric system is termed as piezo-electromechanical（PEM） plate in the paper.Homogenization methods are involved under a sub-wavelength assumption to analytically develop the dynamical equations for the PEM plate. The dispersion relationships and energy densities of the wave modes propagating in the PEM plate are studied; the sub-wavelength assumption is verified for the simulations in this paper. The coincidence frequency of the PEM plate is researched, and results show that the coincidence frequency of the PEM plate will disappear at certain circumstances; mathematical and physical explanations are made for this phenomenon. The disappearance of the coincidence frequency is used to optimize the value of inductance, for the purpose of improving the sound transmission loss of the PEM plate.

Sound Insulation Performance of Pyramidal Truss Core Cylindrical Sandwich Structure

Recently,cylindrical structures have been exploited in various fields due to their excellent mechanical properties.With the increase in the application of cylindrical shell structures,researchers are paying more and more attention to its acoustic performance and sound insulation applications.By inserting the pyramidal truss lattice into the cylindrical shell structure,a cylindrical sandwich structure is obtained and the sound insulation performance of the structure is investigated.The space-harmonic expansion method and the principle of virtual work are employed to establish a theoretical model for the acoustic analysis of cylindrical sandwich structures.The vibro-acoustic coupling is taken into account by imposing the velocity continuity condition at the fluid-solid interface.The sound transmission loss(STL)performance of the structure is examined by establishing both theoretical and finite element models.Subsequently,the influence of various parameters on sound transmission loss is researched and analyzed.