Investigation on sound transmission through thick-wall cylindrical shells using 3D- theory of elasticity in the presence of external and mean air-gap flow

2016 ◽  
Vol 24 (5) ◽  
pp. 975-1000 ◽  
Author(s):  
K Daneshjou ◽  
R Talebitooti ◽  
A Tarkashvand
Keyword(s):  
Cylindrical Shell ◽  
Mach Number ◽  
Transmission Loss ◽  
Equations Of Motion ◽  
Sound Transmission ◽  
Theory Of Elasticity ◽  
Air Gap ◽  
Thick Wall ◽  
Mean Flow ◽  
Double Wall

This paper studies the effects of an external mean flow and an internal air-gap mean flow on sound transmission through a double-wall thick cylindrical shell. Due to the major influence of some effective terms such as membrane, bending, transverse shearing and rotational inertia on thick-walled shell, three-dimensional theory of elasticity is used to obtain the governing equations of motion. Therefore, Newton’s second law is utilized to develop the equilibrium equations for an infinitesimal element in cylindrical coordinates. Then, the equations of motion related to the circular hollow cylinders are solved using Helmholtz potentials for arbitrary values of physical and geometrical parameters. In addition, by coupling of both inner and outer shells, a modal transfer matrix is created. This modal matrix stands for the global dynamic equilibrium of the double-wall cylinder. Moreover, the sound transmission Loss of the double-wall cylinder excited by an acoustic oblique plane wave with two angles of incident (i.e. elevation and azimuth angles) is predicted. Due to lack of studies in the field of sound transmission through the thick-walled shell, the results obtained in this study are compared with those from other researchers for a thin cylindrical shell. These results indicate an excellent agreement in comparison with each other. Furthermore, the results reveal that with thickening of the shell, critical and coincidence frequencies are getting closer to ring frequency. Moreover, the effects of external and air-gap flows on TL behave in similar way whereas the Mach number is positive. In addition, an improvement of transmission loss can be found whereas the Mach number is negative; particularly this enhancement is more specified for the external flow. Finally, the results indicate that where both external and air-gap fluids simultaneously flow in opposite directions [Formula: see text] the TL is significantly enhanced. However, for the case where these two fluids flow in the same direction [Formula: see text] the TL is decreased.

Control of sound transmission into a hybrid double-wall sandwich cylindrical shell

2021 ◽  
pp. 107754632098213
Author(s):  
Seyyed M Hasheminejad ◽  
Ali Jamalpoor
Keyword(s):  
Cylindrical Shell ◽  
Shell Structure ◽  
Transmission Loss ◽  
Sliding Mode ◽  
Circular Cylindrical Shell ◽  
Sound Transmission ◽  
Sound Field ◽  
Air Gap ◽  
Sound Transmission Loss ◽  
Double Wall

A 3D analytical model is formulated for diffuse sound field transmission control through a smart hybrid double concentric sandwich circular cylindrical shell structure in presence of external and internal air gap mean flows. The multi-input multi-output sliding mode control is applied to enhance the sound transmission loss characteristics via direct control action of a uniform force piezoelectric actuator layer along with semi-active variation of the stiffness/damping characteristics of the electrorheological fluid core layer incorporated in a non-collocated configuration within the external or internal shell structure. Extensive numerical simulations examine the uncontrolled/controlled diffuse field sound transmission loss spectrums in a broad frequency range for single-wall and hybrid double-wall sandwich shells at selected external and air gap Mach numbers. The proposed smart hybrid active/semi-active double-wall configuration is demonstrated to provide satisfactory overall acoustic insulation control performance with much lower operative energy requirements. Limiting cases are considered, and validity of the formulation is verified against the available data.

Functionally graded viscoelastic core characteristics on vibroacoustic behavior of double-walled cylindrical shells in a subsonic external flow

2022 ◽  
pp. 107754632110467
Author(s):  
Shohreh Reaei ◽  
Roohollah Talebitooti
Keyword(s):  
Cylindrical Shell ◽  
Transmission Loss ◽  
Excitation Frequency ◽  
Shear Deformation Theory ◽  
Sound Transmission ◽  
Functionally Graded ◽  
Loss Coefficient ◽  
Sound Transmission Loss ◽  
Polymeric Foam ◽  
The Core

The present study is concerned with an analytical solution for calculating sound transmission loss through an infinite double-walled circular cylindrical shell with two isotropic skins and a polymeric foam core. Accordingly, the two-walled cylindrical shell is stimulated applying an acoustic oblique plane wave. The equations of motion are derived according to Hamilton’s principle using the first-order shear deformation theory for every three layers of the construction. Additionally, by the aid of employing the Zener mathematical model for the core of polymeric foam, mechanical properties are determined. To authenticate the results of this study, the damping of the core layer goes to zero. Therefore, the numerical results in this special case are compared with those of isotropic shells. The results prove that the presented model has high accuracy. It is also designated that decreasing the power-law exponent of the core leads to improving the sound transmission loss through the thickness of the construction. Besides, in addition to probe some configurations versus alterations of frequencies and dimensions, the convergence algorithm is provided. Consequently, it is realized that by increasing the excitation frequency, the minimum number of modes to find the convergence conditions is enhanced. The results also contain a comparison between the sound transmission loss coefficient for four different models of a core of a sandwiched cylindrical shell. It is comprehended that the presented model has a transmission loss coefficient more than the other types of the core at high frequencies.

scholarly journals Analyzing and evaluation of effective parameters on sound transmission loss of the triple-layered acoustic panels with sound-absorbing middle layer

2015 ◽  
Vol 4 (2) ◽  
pp. 250
Author(s):  
Nader Mohammadi
Keyword(s):  
Boundary Condition ◽  
Porous Material ◽  
Elastic Layer ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Air Gap ◽  
Acoustic Properties ◽  
Sound Transmission Loss ◽  
Static Young’S Modulus ◽  
Wide Range

In this research, a triple-layered acoustic panel with sound-absorbing intermediate layer materials is modeled analytically in order to calculate the sound transmission loss in the normal incidence field. This information provides an appropriate platform for optimum noise control. In this paper, porous material is used as an absorbent layer between two elastic panels. In modeling these triple-layered panels, theory of wave propagation in porous materials is used and bounded boundary condition of the first elastic layer and unbounded boundary condition of the second elastic layer is applied. To validate the model, the results of this model are compared with the results of the Bolton. Comparison of results revealed very good compatibility. Here, the effect of the length of the air gap between the elastic layers, density and the material of the elastic plate, the thickness and vibro-acoustic properties of the intermediate porous material on the values of transmission loss is investigated.In a wide range of frequencies, increasing air gap, density of elastic panels and porous layer thickness, increase the transmission loss up to 10 dB. At frequencies above 10 kHz, a reduction in porosity, static Young's modulus, the loss coefficient, increasing bulk density of the solid phase, the factor of geometrical structure and viscosity of porous material, increase the sound transmission loss up to 15 dB.

Investigation of power transmission across laminated composite doubly curved shell in the presence of external flow considering shear deformation shallow shell theory

2017 ◽  
Vol 24 (19) ◽  
pp. 4492-4504 ◽  
Author(s):  
R Talebitooti ◽  
MR Zarastvand ◽  
HD Gohari
Keyword(s):  
Shear Deformation ◽  
Shallow Shell ◽  
Shell Theory ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Laminated Composite ◽  
Sound Transmission Loss ◽  
Effective Parameters ◽  
Mean Flow ◽  
Doubly Curved

This study applies shear deformation shallow shell theory to inspect the acoustic behavior of laminated composite infinitely long doubly curved shallow shells subject to a radiating oblique plane sound wave. Herewith, a procedure is developed to investigate sound transmission loss through this shell, clarified as a ratio of incident power to transmitted power in the existence of mean flow. In a further step, displacements are developed as a linear combination of the thickness coordinate to designate an analytical solution based on shear deformation shallow shell theory. Consequently, an exact solution for sound transmission loss is brought forward by combining acoustic wave equations as a result of wave propagation through this shell with doubly curved shell equations of motion. Afterwards, the accuracy of the present formulation (shear deformation shallow shell theory) is determined by comparing the achieved results with those available in the literature and some assumptions associated with the geometric specifications of the plate are investigated. Finally, because of the remarkable achievement of the current formulation results in reduction of noise transmission into such structures, some effective parameters on sound transmission loss are used in numerical results, to solve this problem.

scholarly journals Optimization of Sound Transmission Loss through a Thin Functionally Graded Material Cylindrical Shell

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Ali Nouri ◽  
Sohrab Astaraki
Keyword(s):  
Cylindrical Shell ◽  
Functionally Graded Material ◽  
Transmission Loss ◽  
Minimum Weight ◽  
Sound Transmission ◽  
Functionally Graded ◽  
Sound Transmission Loss ◽  
Softening Effect ◽  
Important Concern ◽  
Graded Material

The maximizing of sound transmission loss (TL) across a functionally graded material (FGM) cylindrical shell has been conducted using a genetic algorithm (GA). To prevent the softening effect from occurring due to optimization, the objective function is modified based on the first resonant frequency. Optimization is performed over the frequency range 1000–4000 Hz, where the ear is the most sensitive. The weighting constants are chosen here to correspond to an A-weighting scale. Since the weight of the shell structure is an important concern in most applications, the weight of the optimized structure is constrained. Several traditional materials are used and the result shows that optimized shells with aluminum-nickel and aluminum-steel FGM are the most effective at maximizing TL at both stiffness and mass control region, while they have minimum weight.

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