جستجوی مقالات مرتبط با کلیدواژه "افت انتقال صوت" در نشریات گروه "مکانیک"

In this article, an attempt has been made to estimate the amount of sound transmission loss in a flat oval channel by applying the approach of statistical energy analysis. Correct estimation of sound transmission loss in an air conditioning channel is of great importance due to the harmful effects of noise pollution in the environment on human health. Simulation with the statistical energy analysis method is a powerful approach to estimate sound and vibration in problems in which we deal with complex and multi-part systems; is considered. In this method, first, a system is divided into several subsystems, and then by writing a matrix equation that includes the energy exchanges between subsystems and energy loss coefficients; It is investigated from the perspective of vibration and sound estimation.On average, the model presented in this research is able to estimate the sound transmission loss in different dimensions of the air conditioning channels according to the experimental results in the accuracy range of ± 2.5 dB. Considering that it seems that the results obtained from modeling with this method are in good agreement with the experimental data; The results of this research can be used as an efficient approach to estimate noise in oval shaped channels stretched in different lengths.

Nowadays, composite panels are widely used in various industries, and the study of the behavior of these panels under acoustic vibrations is one of the important cases in engineering analysis. Also, the effects of incidence and azimuthal angles and Mach number are investigated and the calculated critical frequency and sound transmission loss are validated with other works. The results show that the critical and coincidence frequencies and sound transmission loss are influenced by factors such as the orthotropic behavior of the panel and its thickness, incidence and azimuthal angles, sound wave Mach number, and transverse shear flexibility. Based on the resulting graphs, increasing the incidence and azimuthal angles causes the enhancement of the critical frequency and sound transmission loss, while the orthotropic parameter has the opposite effect. On the other hand, increasing the Mach number and decreasing the thickness of the panel reduces the sound transmission loss and increases the critical frequency of the panel. Also, with the increase of the transverse shear flexibility of the panel, the critical frequency is increased. The trends of coincidence frequency changes are also similar to the mentioned trends of critical frequency with respect to the effective parameters except for the incidence angle. According to the presented results, the coincidence frequency of the panel, unlike the critical frequency, decreases with the increase of the incidence angle.

In this study, it is assumed that the outer shell of the sandwich has a core made of functional calibrated materials with piezoelectric patches and the inner shell is made of layered composites. Double-walled cylindrical shells have three external, internal and middle acoustic environments and are exposed to acoustic waves with a specific angle of effect. The dynamic equations of the structure are derived using the hypothesis of first-order shear displacement field of shells and Hamilton principle and together with the fluid / structure boundary conditions form the final equations. Using the Fourier series expansions of the input, return, and output sound pressures and shell displacements, the dynamic equations are discretized to form a state matrix. After validating the results with existing articles, finally the effects, voltage applied by piezoelectric patches, percentage of functional materials, angle of fibers used in composites, types of composite materials, number of piezoelectric patches and angle of impact on the structure of sound transmission behavior It has been evaluated in a certain frequency range. Finally, the voltage parameters applied by the piezoelectric patches, the percentage of functional materials, the angle of the fibers used in the composites, the types of composite materials, the number of piezoelectric patches and the angle of impact increased the sound loss.

In this study, sound transmission loss of a cylindrical shell made out of functionally graded materials with an arrangement of piezoelectric patches is investigated in the framework of the first-order shear deformation theory. Also, power law model is utilized to take into account material characteristics distribution along the thickness of the shell. It is noteworthy that both outer and inner piezoelectric patches are used as actuator and sensor. The structure is immersed in an acoustic medium of air and is subjected to acoustic waves with certain incident angle. The derivation of vibroacoustic equations in the form of coupled relations is realized by implementing Hamilton’s principle in conjunction with fluid/structure compatibility conditions. An analytical method is exploited to solve the coupled vibroacoustic governing equations with Fourier series. After validation study, parameter studies reveal the effects of the functionally graded index, incident angles, external electric voltage, and characteristics of piezoelectric patches on the sound transmission loss behavior of the structure in a certain frequency domain. Results indicated that with increasing the power law index, sound transmission loss decreases in the low-frequency region. Also, the applied voltage is able to improve the sound transmission loss especially in high-frequency region.

Double-walled structures are widely used in various industries such as aerospace, marine, and automotive. Therefore, in this paper, the sound transmission in these structures is investigated. Due to the influence of rotation and shear parameters by increasing the thickness of the cylindrical shell, the Newton-based three-dimensional theory of elasticity is used. In order to solve the governing equation of motion for a cylinder, it is assumed that the displacement field is the sum of the gradients of a scalar potential field and the curl of a vector potential field. As a result, the shell motion equation becomes two separate wave equations, which solve the displacement field. To confirm the obtained equations, the present results are compared with the results of other researchers in this field that have been obtained with other theories such as classical shell theory. Finally, the effect of various parameters such as properties and thickness of the fluid layer, Mach number, and material of the cylinders are investigated. The results show that in double-walled structures with the air gap, the acoustic impedance (the speed of sound multiplied by density) of the fluid is the main and effective factor in sound control. Any fluid with more Acoustic impedance behaves better in sound control and improves sound transmission loss.

Vibroacoustic behavior of graphene reinforced composite plate (GRCP) is studied to investigate the sound transmission loss (STL), Due to the importance of the behavior of the structure against sound waves. Many materials have been used to increase the stiffness and improve the vibroacoustic behavior of sandwich structures. which in recent years, Graphene has prompted many researchers to use it in sandwich structures. Governing equations are derived based on three-dimensional elasticity and state vector method is used to solve equations of motion. To evaluate the validity of the results from previous studies, two studies that have examined the sound transmission loss of plate have been used. To find the effective parameters on the amount of plate STL, changes in graphene weight fraction, plate thickness, incidence angle, thickness of graphene nanoplatelets (GPLs) and width of GPLs are investigated. Finally, numerical results show that adding a small amount of GPLs to the composite matrix increases its stiffness and thus improves the behavior of the structure against the pressure of sound waves. Also, Increasing the plate thickness has a good effect on the STL, and increasing width of GPLs with constant length has no effect on the vibroacoustic behavior of the structure.

A theoretical model is proposed to study the sound transmission loss of a truncated conical shell with porous layer. The isotropic thin-walled conical shell is excited by an oblique incident plane sound wave, which impinges on the outer surface of the shell. The governing equations of the shell motion are obtained by Love’s theory, and a convergent power series solution is applied to obtain the exact dynamic response of the shell. An equivalent fluid model based on Biot’s theory is considered to describe the wave propagation in the porous material. The model results are firstly validated against the results of prior studies. Then, the effects of several design parameters such as different boundary conditions at the ends of the shell, cone angle, incident sound wave angle and material properties of the shell are studied on the characteristics of the sound transmission loss. The proposed model can provide an effective tool in the acoustic design stage of the truncated conical shells. In addition, the transmission loss is obtained in the presence of the porous layer with two different configurations. The results generally show desirable performance of the porous layer in the sound insulation ability.

In this paper, the Three-dimensional (3-D) theory of elasticity has been used for sound transmission loss (TL) of a thin-walled cylindrical shell with infinite length. This structure is excited by an obliquely plane wave. Governing equations of the thin shell have been derived in radial, axial, and circumferential directions. Then, Helmholtz decomposition is applied to solve the equations. Therefore, the displacement field is considered in terms of Lame potential functions This method describes the vibrational behavior of the shells more accurately than other theories, including the classical theory and the first and third order of shear, due to the consideration of the effects of rotation and shear. A comparison of the present method results with those obtained from classical shell theory (CST) indicates an excellent agreement. However, at the high frequencies the classical encounter insufficient accuracies as a result of increasing the rotational terms as well as shear wave effects. The results show that with increasing shell thickness, due to increased flexural stiffness of the shell, the sound transmission loss has increased. By increasing the Mach number, due to the negative stiffness, reduces the sound transmission loss in the stiffness-controlled region and conversely increases the sound transmission loss in the mass-controlled region due to damping in the structure. Finally, it is shown that the critical and coincidence frequencies increase with the growing up Mach number.

With the development of urbanism and the airports, construction of highways around cities, noise pollution caused by the traffic of vehicles, landing and take off the airplane has become one of the most harmful effects on the habitants around the highways and urban areas. In order to prevent these damaging effects, or in other words, for reducing the transmission of the noises from streets to the residential buildings, it can be used from sound absorbing material around the highways. A number of 4 mixture designs have been investigated in this study in order to reduce sound transmission through concrete, including control sample and 3mixture designs of recycled rubber with sizes of 1–3 mm. The rubber has been used as a replacement of 5,10, and 15 percent of sand. First, 7,14 and 28-day strengths of concrete have been measured and then, sound transmission losses through the samples have been measured at the range of 63–6300 Hz by using impedance tube of the transfer function. The results indicate a reduction in the transmission of sound in samples containing rubber at high frequency ranges, which, given the reduction of environmental losses, makes use of this type of concrete in airports and freeways.

In the present study, the available methods of predicting the sound transmission loss through infinitely long double-walled cylindrical shells with porous layer are developed to analytically compute the sound transmission loss in triple-walled sandwich cylindrical shells in the presence of an external fluid flow. Loves’ shell theory and Lee’s method based on Biot’s theory are used to describe the motions of thin isotropic triple-walled cylindrical shell and wave propagation in the porous media, respectively. The vibro-acoustic problem for the most complicated configuration of the triple-walled sandwich cylindrical shell is formulated and solved by the transfer matrix method with appropriate boundary conditions. The total transmission loss in a diffuse field is calculated and validated by considering the effect of total internal reflection. Then the transmission loss of triple-walled cylindrical shell is compared with its double-walled counterpart of the same weight. The results generally show a superior performance in sound insulation for the case of triple-walled shell, considerably at mid-high and high frequency regions. Moreover, ten typical configurations, which involve different coupling methods between the walls and porous layers, are considered to completely study the effect of various configurations on the sound transmission properties. As will be shown, a configuration with the largest number of air gaps in its structure provides better performance in sound transmission reduction almost at the entire frequency range. The effects of external fluid flow and azimuthal angle are also studied on the sound transmission loss.

In this paper, sound transmission loss through double-walled orthotropic cylindrical shells based on three-dimensional elasticity theory is investigated. Hence, the purpose of this paper is to analyze the effect of the acoustic wave incidence under two different angels on sound transmission loss through the shell. The present model is a double-walled orthotropic cylindrical shell immersed in a fluid with an infinite length, whereas the acoustic plane incident waves impinge upon the shell with two different angels of θ and δ. The state space method is used to investigate the laminate approximated model along with transfer matrix approach for modeling both walls of cylindrical shell. In order to consider the two different angles of θ and δ, the corresponding wave equations have been modified according to the wave numbers. Comparing the results obtained from presents study with those of other researchers shows an excellent agreement between the results. Moreover, the effects of different parameters on sound transmission loss through the shell have been evaluated. The results show an enhancement of sound transmission loss in double-walled cylindrical shells rather than single-walled cylindrical shells particularly in high frequency range. Also, the results indicate the dependency of sound transmission loss on both of two θ and δ angels. In other word, the variety of two incident angles may cause the significant variations in sound transmission loss.

The objective of this paper is representation an analytical solution to calculate sound transmission loss (TL) of infinite thick transverse-isotropic cylindrical shell immersed in a fluid medium with an uniform external airflow and contains internal fluids where external sidewall of the shell excited by an oblique plane wave. In order to derive the governing equations the third-order shear deformation theory (TSDT) is used. Also، equation of motion of shell is obtained using Hamilton''s principle. With solving shell vibration equations and acoustic wave equations simultaneously، the exact solution for TL is obtained. Transmission loss resultant from this solution is compared with those of other authors. The results also indicate that TSDT is more powerful than FSDT and CST، especially in high frequency and less R/h.

In this paper, the acoustical treatment of double-panel structures lined with poroelatic materials is predicted using analytical method in order to study the effective usage of the various boundary conditions of porous layer and to identify the effective parameters on the transmission loss of the multilayer systems. Therefore, inertia and viscous coupling along with thermal and elastic coupling should be considered in transfer stress dynamic and stress-strain relationships for an elastic porous material based on Biot theory. Then, the governing equations of the wave propagation in an elastic porous material are briefly considered and the general forms for the stresses and displacements within the porous material are given. Applying various boundary conditions and solving these equations with Matlab code simultaneously, the transmission loss of these structures is calculated. The results from the analytical method are compared with the SEA madel and the experimental data with excellent agreement is observed. Finally, the influence of effective parameters of this structure with various boundary conditions on the transmission loss of the multilayer systems is studied. The results have been shown that the transmission loss of double-panel structures lined with a layer of porous material can depend critically on the method of mounting the porous layer to the facing panel.

There is a main problem that the noise generated in air intake system may be disgusting. Statistical energy analysis is a suitable method for acoustical - vibration analysis of structures in high frequency range. In this paper, the air intake system of an engine compartment is modeled using SEA. The transmission loss through the intake duct is calculated with importing CAD model and creating subsystems at high frequency range. In order to verify the results, a simple model of double walled cylindrical shell is modeled in Auto- SEA, and the results are compared with those of analytical ones. In addition, comparing the results of fully modeled of intake systems with experimental data available shows a good accuracy of results especially in high frequency range. Furthermore, the influence of inserting porous material is studied. Finally, the influence of some other parameters such as the thickness of the porous layers on the transmission loss of thesystem is investigated.

An analytical study is conducted in this paper to determine the characteristics of sound transmission through laminated composite double-walled thin cylindrical shells with infinite length. It is assumed that the external and internal fluid media surrounded the shells, and there is fluid existence in the annular space between them. A uniform flow exists with a constant velocity in the external medium. An exact solution is obtained by solving the classical shell equations and acoustic wave equations simultaneously. Transmission losses obtained from the numerical solution in this paper are compared with the results of other investigators for composite single-walled cylindrical shell. Comparison revealed good agreement. Finally, the effects of different source conditions, structural, fluid and gap properties as well as flight conditions on TL have been studied for a range of values, specifically; incident angle of the plane wave, Mach number and flight altitude of aircraft, thickness and curvature of shells lay-up stacking sequence and damping.

Automobile manufactures are persistently trying to develop comfort of passengers by improving different specification such as decrease of sound level in engine compartments. There is a main problem that the noise generated in air intake systems may be disgusting. Statistical energy analysis is a suitable method for acoustical- vibration analysis of structures in high frequency range. In this paper, the air intake system of an engine compartment is modeled using SEA. The transmission loss through the intake duct is calculated with importing CAD model and creating subsystems at high frequency range. In addition, comparing the results of fully modeled of intake systems with current experimental data, shows a good accuracy of results especially in high frequency range. Furthermore, the influence of inserting porous material is studied.