K. Daneshjou

Iran University of Science and Technology, Teheran, Tehrān, Iran

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Publications (35)30.89 Total impact

  • K. Daneshjou · M. Bakhtiari · H. Parsania · M. Fakoor
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    ABSTRACT: • We introduce a new method to solve complex heat conduction problem.
    No preview · Article · Jan 2016 · Applied Thermal Engineering
  • K. Daneshjou · R. Talebitooti · A. Tarkashvand
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    ABSTRACT: In this paper, the transmission loss (TL) of a thick-walled shell under obliquely plane incident wave is investigated considering three dimensional (3-D) theory of elasticity. Governing equations of the thick shell have been derived in radial, axial, and circumferential directions. Then, Helmholtz decomposition is used to solve the equations. Therefore, the displacement field is considered in terms of Lame potential functions. A comparison of the present method results with those obtained from classical shell theory (CST), first and third-order shear deformation theories (FSDT, TSDT) for this special case of the thin shell indicates an excellent agreement. Moreover, the comparison of present method with these theories for a thick shell having R/h=20 reveals good conformity at low frequencies. However, at the high frequencies these classical and higher order shell theories encounter insufficient accuracies as a result of increasing of the rotational terms as well as shear wave effects. The results of the present method show that with thickening the shell, the critical frequency is getting closer to the ring frequency. Consequently, the mass low controlled region is going to be completely removed which leads to significant enhancement of the TLs. Finally, the obtained numerical results demonstrate that the transmission loss is considerably decreased at the frequencies greater than the resonance frequency by increasing Mach number of the external mean flow.
    No preview · Article · Dec 2015 · International Journal of Mechanical Sciences
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    R. Talebitooti · K. Daneshjou · M. Kornokar
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    ABSTRACT: This paper proposes an extension of the full method to investigate sound transmission through poroelastic cylindrical shell. The “extended full method” is presented based on Biot theory with considering the 3-D wave propagation in a cylindrical shell. Contrary to previous methods, it could be applicable for both poroelastic cylindrical shells and double-walled cylindrical shells lined with poroelastic materials with an excellent accuracy. In the extended full method, the well-known Helmholtz decomposition is used to obtain the displacement fields, solid stresses and the fluid pressure. In order to verify the results of the poroelastic cylindrical shell the porosity goes into zero with eliminating the fluid phase of the poroelastic material. Thus, the results are compared with those of TLs for isotropic shell with high accuracy. The results also indicate that enhancing the porosity of the poroelastic cylindrical shells efficiently leads into decreasing the TL. It is also designated that with doubling the thickness of the poroelastic shell, the TL is improved about 6 dB in a broad-band frequency. Also, the present method is investigated for the case of a double-walled cylindrical shell composed of isotropic skins and poroelastic core. The first-order shear deformation theory is applied to modeling the isotropic shells. The results indicate that presented method is more accurate than simplified method, particularly in the case of small radius cylindrical shells. Moreover, the results indicate that with increasing the radius of the shell, the double-walled cylindrical shell behaves in a same trend as a double-walled flat plate.
    Full-text · Article · Nov 2015 · Journal of Sound and Vibration
  • K. Daneshjou · M. Bakhtiari · R. Alibakhshi · M. Fakoor
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    ABSTRACT: A straightforward implementation is applied to solve heat conduction equation for a 2D hollow cylinder made of orthotropic functionally graded material (FGM) in the presence of time-dependent heat source. All material properties are considered to vary continuously within the cylinder along the radial direction with arbitrary law. The transient solution can be obtained by augmented state space method, which leads to carry out the results easily, based on laminate approximation theory in the Laplace domain, and then the results obtained are converted into the time domain by applying the numerical Laplace transform inversion. By this method, the solution of heat conduction problem is obtained for general boundary conditions which can be included various combinations of arbitrary temperature, flux, or convection. Comparison of obtained results with special cases in the literatures shows the capability of the new presented method. Finally, in the presence of time-dependent heat source, the effects of circumferential to the radial thermal conductivity coefficient ratio and heat source size on temperature field are graphically shown.
    No preview · Article · Oct 2015 · International Journal of Heat and Mass Transfer
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    K. Daneshjou · M. Talebitooti
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    ABSTRACT: This paper focuses on an analysis of free vibration of thick rotating stiffened composite cylindrical shells with different boundary conditions. The analysis is performed on the basis of a three-dimensional theory by using the layerwise-differential quadrature method (LW-DQM). The equations of motion are derived employing Hamilton’s principle. In order to accurately allow for the thickness effects, a layerwise theory is used to discretize the equations of motion and related boundary conditions through the thickness of the shells. Then, the equations of motion and the boundary conditions are transformed into a set of algebraic equations by using the DQM in the longitudinal direction. This study demonstrates the applicability, accuracy, stability, and fast rate of convergence of the present method in free vibration analyses of rotating stiffened cylindrical shells. The presented results are compared with those of other shell theories obtained by conventional methods and with a special case where the number of stiffeners approaches zero, i.e., an nonstiffened cylindrical shell, and excellent agreements are achieved. Finally, some new results are presented, which can be used as benchmark solutions for future investigations.
    Full-text · Article · Mar 2014 · Mechanics of Composite Materials
  • K. Daneshjou · M. Talebitooti · R. Talebitooti
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    ABSTRACT: The generalized differential quadrature method (GDQM) is employed to consider the free vibration and critical speed of moderately thick rotating laminated composite conical shells with different boundary conditions developed from the first-order shear deformation theory (FSDT). The equations of motion are obtained applying Hamilton’s concept, which contain the influence of the centrifugal force, the Coriolis acceleration, and the preliminary hoop stress. In addition, the axial load is applied to the conical shell as a ratio of the global critical buckling load. The governing partial differential equations are given in the expressions of five components of displacement related to the points lying on the reference surface of the shell. Afterward, the governing differential equations are converted into a group of algebraic equations by using the GDQM. The outcomes are achieved considering the effects of stacking sequences, thickness of the shell, rotating velocities, half-vertex cone angle, and boundary conditions. Furthermore, the outcomes indicate that the rate of the convergence of frequencies is swift, and the numerical technique is superior stable. Three comparisons between the selected outcomes and those of other research are accomplished, and excellent agreement is achieved.
    No preview · Article · Apr 2013 · Applied Mathematics and Mechanics
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    ABSTRACT: This paper presents effects of boundary conditions and axial loading on frequency characteristics of rotating laminated conical shells with meridional and circumferential stiffeners, i.e., stringers and rings, using Generalized Differential Quadrature Method (GDQM). Hamilton's principle is applied when the stiffeners are treated as discrete elements. The conical shells are stiffened at uniform intervals and it is assumed that the stiffeners have similar material and geometric properties. Equations of motion as well as equations of the boundary condition are transformed into a set of algebraic equations by applying the GDQM. Obtained results discuss the effects of parameters such as rotating velocities, depth to width ratios of the stiffeners, number of stiffeners, cone angles, and boundary conditions on natural frequency of the shell. The results will then be compared with those of other published works particularly with a non-stiffened conical shell and a special case where angle of the stiffened conical shell approaches zero, i.e. a stiffened cylindrical shell. In addition, another comparison is made with present FE method for a non-rotating stiffened conical shell. These comparisons confirm reliability of the present work as a measure to approximate solutions to the problem of rotating stiffened conical shells.
    Full-text · Article · Mar 2013 · Latin American Journal of Solids and Structures
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    ABSTRACT: In this article, an approximate solution using differential quadrature method is presented to investigate the effects of thermo-mechanical loads and stiffeners on the natural frequency and critical speed of stiffened rotating functionally graded cylindrical shells. Transverse shear deformation and rotary inertia, based on first-order shear deformation shell theory (FSDT), are taken into consideration. The equations of motion are derived by the Hamilton's principle while the stiffeners are treated as discrete elements. Material properties are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fraction of the constituents. The temperature field is assumed to be varied in the thickness direction. The equations of motion as well as the boundary condition equations are transformed into a set of algebraic equations applying the DQM. The results obtained include the relationship between frequency characteristics of different power-law index, rotating velocities, thermal loading and amplitude of axial load. To validate the present analysis, the comparison is made with a number of particular cases in literature. Excellent agreement is observed and a new range of results are presented for stiffened rotating FG cylindrical shell under thermo-mechanical loads which can be used as a benchmark to approximate solutions.
    No preview · Article · Feb 2013 · Journal of Thermal Stresses
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    Behzad Babaei · Mahmood M. Shokrieh · Kamran Daneshjou
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    ABSTRACT: This paper studies the resistance characteristics of double-layered targets by using two different materials including steel and aluminum. Four types of double-layered targets are considered: aluminum–aluminum, aluminum–steel, steel–aluminum and steel–steel. Using these four targets, penetration tests are carried out on 1mm-thick plates with blunt nosed projectiles. A compressed gas gun was used to launch projectile within the velocity range from 50 to 400m/s. Standard steel projectile for perforation of steel and aluminum plates has been used when the aspect ratio, that is L/D, of the projectile is 8 and projectile is cylindrical flat-ended. The initial and residual velocities of the projectile were measured, and reported. Also, numerical simulations of some of the experimental tests are carried out using the non-linear finite element code LS-DYNA. A slightly modified version of the Johnson–Cook constitutive equation and fracture criterion was used to simulate material behavior. The predictions of the Ipson and Recht analytical model are compared with the obtained results. The correlation between the analytical, the numerical and the available experimental results demonstrates that the numerical method is a very accurate and effective analysis technique in perforation of multi-layered metallic targets.
    Full-text · Article · Dec 2011 · Materials Science and Engineering A
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    K. Daneshjou · H. Ramezani · R. Talebitooti
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    ABSTRACT: A study on free harmonic wave propagation in a double-walled cylindrical shell, whose walls sandwich a layer of porous materials, is presented within the framework of the classic theory for laminated composite shells. One of the most effective components of the wave propagation through the porous core is estimated with the aid of a flat panel with the same geometrical properties. By considering the effective wave component, the porous layer is modeled as a fluid with equivalent properties. Thus, the model is simplified as a double-walled cylindrical shell trapping the fluid media. Finally, the transmission loss (TL) of the structure is estimated in a broadband frequency, and then the results are compared. Key wordstransmission loss–porous media–cylindrical laminated composite shell
    Full-text · Article · Jun 2011 · Applied Mathematics and Mechanics
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    ABSTRACT: This work presents an analytical solution for acoustic transmission through relatively thick FGM cylindrical shells using third order shear deformation theory (TSDT). An infinitely long FGM cylindrical shell composed of metal and ceramic with power-law distribution of volume fraction through the thickness is considered. The shell is immersed in a fluid with an external airflow and an oblique plane wave impinges on the external sidewall of the shell. Comparing the results of present study with those of previous models (CST and FSDT) for thin shells, similar results are observed due to limited effects of shear and rotation on transmission loss (TL). However, for relatively thick shells where the shear and rotation effects become more important in lower R/h, TSDT presents more accurate results caused by its higher order model. In addition, the results show proportional change in TL according to distribution of material properties through the thickness of FG cylindrical shells.
    Full-text · Article · Dec 2010 · Composite Structures
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    ABSTRACT: Recently, in army and civilian applications, multi-layered plates are ordinary used, like marine hulls and aerospace vessels. In this article, the resistance traits of double-layered aluminum targets are investigated by applying three different projectiles. The masses of projectiles are 3.156 gr but aspect ratio (means L/D) of these projectiles are 1, 2.37 and 8; and projectiles are cylindrical flat-ended. We found an estimation procedure based on the contexts of the conservation of impulse-momentum law and conservation of energy. For verifying the maximum resistant performance of multi-layered targets, we employ the submitted Ipson and Recht analytical model in this paper and compare these results with our experimental results. In the last section, we demonstrate our numerical simulations by using the explicit finite element code Ls-dyna. The Johnson and Cook [1] constitutive relation and failure criterion have been employed as material model for the target plates. Only of the model and cylindrically shaped projectile is initially located 1 mm away from the target in simulation. We used explicit 3D structural solid elements for both projectile and target. Incidentally at this investigation planar surfaces, localized influence of target and projectile are considered. The rigid body motion, all thermal phenomena and friction of the front target are neglected. Eventually, if the target is double-layered, the highest resistant performance is obtained when the projectile's aspect ratio is l and the target resistance reaches minimum whilst projectile aspect ratio is 8.
    Full-text · Conference Paper · Jan 2010
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    K. Daneshjou · M. Shahravi

    Preview · Article · Dec 2009 · Journal of Mechanical Science and Technology
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    Kamran Daneshjou · Majid Shahravi
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    ABSTRACT: The wavelet scaling functions of spline wavelets are used to construct the displacement interpolation functions of triangular and rectangular thin plate elements. The displacement shape functions are then expressed by spline wavelet functions. A spline ...
    Preview · Article · Nov 2009 · Engineering With Computers
  • K. Daneshjou · R. Talebitooti · A. Nouri
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    ABSTRACT: Analytical study is conducted in this paper to understand the characteristics of sound transmission through cylindrical shell with free layer damping (FLD) treatment. It is assumed an infinitely long circular cylindrical shell subjected to a plane wave with uniform airflow in the external fluid medium. The damping layer applied on the surface of the shell is represented by HN model with frequency-dependent specifications. An exact solution is obtained by solving the Markus equations of FLD shells and acoustic wave equations simultaneously. As the pressure and displacement terms are expressed in series form, an iterative procedure is founded to cut them with an appropriatenumber of modes. Transmission losses obtained from the solution are compared with “modal-impedance method” for an especial case of untreated shell. Eventually, the numerical results show the effects of stiffness, loss factor and thickness of damping material, and also incident wave angles on TL curves.
    No preview · Article · Sep 2009
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    Behzad Babaei · Kamran Daneshjou · Majid Shahravi
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    ABSTRACT: Newly, multi-layered plates have become commonplace in both military and civilian applications, such as marine hulls and aerospace vessels. This paper studies the resistant the performance of perforation of multiple targets and studies the resistance characteristics of targets having the same total thickness and sequence of layers in multiple targets of special bulkheads and shell plating of navy ships. The analysis of double-layered target penetration shows that maximum resistance can be obtain for very low first-layer thickness. An estimation procedure is established based on the concepts of the conservation of impulse-momentum law, and conservation of energy. In the present work predictions of the proposed analytical model are compared with our experimental results that were 80 ballistic tests. Experimental results of P.Elek et al.[1] are adopted to check the maximum resistant performance of multi-layered targets. The results of the verification are good in terms of agreement for impact velocities ranging from 400-950 m/s. The standard steel projectile for perforation of steel plates has been used when the aspect ratio (i.e. L/D) of the projectile is about 1.3 and projectile is cylindrical flat-ended. In the final part, our numerical simulations by using the explicit finite element code Ls-Dyna [2] are presented. Introduction The case of penetration of a rod-like projectile into a metallic homogeneous target is well characterized experimentally and theoretically. Surprisingly, the case of a multi-layered target consisting of different metals has not yet been investigated adequately. This subject lacks essential experimental data for validation of theoretical and numerical models. Consequently, in the present work predictions of the Recht and Ipson's [3] analytical model and also P.Elek's [1] analytical model are compared with those of the numerical simulations (by using the explicit finite element code Ls-Dyna [2]) and our experimental tests. Additional information obtained by thoroughly studying the behavior of multiple targets, including the effects of target configurations, layer number, the thickness of each layered target and the target mechanical properties, are needed to understand unusual phenomena produced when penetration occurs in combined targets in contact, and to ascertain the ballistic limit velocity [4]. Moreover, a clear understanding of the role of the various components in a multi-layered target system is lacking so an estimation procedure is established based on the concept of the conservation of momentum, momentum-impulse law and energy. This paper studies the resistance characteristics of targets having the same total thickness and sequence of layers in multiple targets of special bulkheads and shell plating of Navy ships. Mines et al.[5] in 1998 described low-velocity impact tests on square panels made with two polymer composite sandwich construction, consisting of woven glass vinyl ester skins with a core mat core and woven glass epoxy with a honeycomb core. Woodward and Cimporu [6] in 1998 studied deformation and energy absorption in homogeneous, two-ply and multi-ply aluminum alloy laminates in order to gain insight into the mechanics of perforation as a function of ply thickness and number. In 1998 Ben-Dor et al.[7] studied high velocity penetration of a 3-D rigid sharp projectile entering a ductile layered target with an air gap between the plates and investigated the ballistic resistance of multi-layered targets based on an the assumption about localized projectile-target interaction. Nemes et al. [8] in 1998 studied the effects of laminate parameters on penetration of graphite/epoxy composites. Lamontage et al. [9]in 1999 studied normal and oblique hypervelocity impacts on carbon fiber/peek composites. In 1999 Mines et al. [10] studied the high velocity perforation behavior of polymer composite laminates with impact perforation velocities ranging up to 571 m/s. In 2000, Liu et al. [11] studied the impact perforation resistance of laminated and assembled composite plates made of glass fibers and an epoxy matrix and investigated the joining stiffness and perforation threshold of a composite plate assembled using various joining techniques, identified an efficient way to assemble thin composite laminates to achieve a high perforation threshold, and explored the feasibility of replacing costly thick laminated composite plates with assembled composite plates. Vaidya et al. [12] in 2000 described an innovative integrated hollow (space) E-glass/epoxy core sandwich composite construction that has several multi-functional benefits and advantages in terms of weight and bending stiffness. Gellert et al. [13] in 2000, used a simple model to explain bi-linear behavior, to provide a basis for geometrical scaling of composite ballistic perforation data, and to interpret the influence of material parameters and bond strength on the ballistic resistance of glass–fiber-reinforced plastic (GRP) composite plates of varying thickness. Espinosa et al. [14] in 2000 described the enhanced ballistic resistance of confined multi-layered ceramic targets to long rod
    Full-text · Conference Paper · May 2009
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    Kamran Daneshjou · Majid Shahravi · Behzad Babaei
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    ABSTRACT: Ricochet of steel long-rod projectile from oblique steel plates with a finite thickness was investigated numerically by using a full 3D explicit finite element method. Critical ricochet angles for various impact velocities and strengths of the target plates were calculated. Numerical simulations were predicted that critical ricochet angle increases with decreasing impact velocities and that higher ricochet angles were expected if higher strength target materials are employed. In this paper at first, the ricochet analytical models are studied so as to give a keen sense of how the critical obliquity for ricochet varies as a function of the initial conditions of the ballistic engagement and in next section predictions of the proposed analytical model are compared with our experimental results that was 50 ballistic tests. Numerical simulations of some of the experimental tests are carried out using the non-linear finite element code Ls-Dyna[1]. The parameters considered in the simulations are the impact velocity, impact angle oblique plate thickness, rod and target material and aspect ratio of projectile. Finally we can say the agreement between simulation, experimental results and analytical predictions is excellent and it is found that the numerical code is able to describe the physical mechanisms in the perforation events with good accuracy. Introduction It is well known that a projectile impacting on a suitably inclined surface can bounce back from the surface or partially penetrate it along a curved trajectory on the impacted surface with a reduced velocity. Some numerical [2] and analytical [3,4] studies are carried out for the penetration of long rod projectiles into oblique plate target in order to investigate the interaction of the projectile with the oblique plate and the induced projectile rotation. Further development of the analytical model for a full 3D geometry seems to be a formidable task due to the complexity of the physics involved in the ricochet, which includes large-scale high-strain-rate elasto-plastic of the projectile and the target plate, together. The erosion of projectile and target, occurring in a very short period of time. The obliquely spaced modern armor structures, which impose transverse disturbances, such as asymmetrical loading, to the long rod projectile, are designed against such tremendous threats [5]. It is known that the protection effectiveness of thin targets against long rods is strongly dependent upon the impact obliquity. There are several parameters that govern the interactions such as the impact velocity, the L/D of the projectile, the plate thickness, and the gap thickness. Since the effect of these parameters on the protection efficiency of the obliquely spaced armor structure is not investigated systematically until now, there exist no specific design guidelines.
    Full-text · Conference Paper · May 2009
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    Kamran Daneshjou · Majid Shahravi
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    ABSTRACT: Ricochet of a tungsten long-rod projectile from oblique steel plates with a finite thickness was investigated numerically using two explicit finite element methods. These two methods are Lagrange and smooth particle hydrodynamic (SPH). Three distinctive regimes resulting from oblique impact depending on the obliquity, namely simple ricochet, critical ricochet and target perforation, were investigated in detail. Critical ricochet angles were calculated for various impact velocities and strengths of the target plates in Lagrange and SPH methods. It was predicted that in every two methods, critical ricochet angle increases with decreasing impact velocities and that higher ricochet angles were expected if higher strength target materials are employed. The experimental results are discussed and compared with results predicted by the simulations and existing two-dimensional analytical model Through Investigation of the angles in which projectile only ricochets, both SPH and Lagrange methods represent approximate alike results. But in the cases that projectile begins to crack in head region out of high impact angles, the SPH method yields better results. One other advantage of the SPH against the Lagrange method is that no erosion happens though the method and therefore all the particles caused by impact are clearly seen. This means better satisfaction of the principle of conservation of mass. Therefore the correlation between the numerical results and the available experimental and observed data demonstrates that the SPH approach is an accurate and effective analysis technique for long rod ricochet phenomena in ricochet of tungsten rod with RHA target.
    Preview · Article · Mar 2009 · Engineering With Computers
  • K. Daneshjou · M. Shahravi
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    ABSTRACT: The ricochet of eroding long rods, from steel targets, is investigated by a series of three-dimensional numerical simulations in explicit finite element code. These are compared with the predictions of our analytical model and experimental results for ricochet. This approach is different than the rigid body treatment by A. Tate. Also it uses a new penetration velocity equation to predict critical ricochet angle. Critical ricochet angles were calculated for various impact velocities and strengths of the target plates in these approaches. It was predicted that critical ricochet angle increases with decreasing impact velocities and that higher ricochet angles were expected if higher strength target materials are employed. New model's results show a better agreement with numerical results and experiments, rather than Tate and Rosenberg models.
    No preview · Article · Mar 2009 · JOURNAL OF MECHANICS
  • K. Daneshjou · A. Nouri · R. Talebitooti
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    ABSTRACT: Circular thin orthotropic shells have many applications in the aerospace industry such as aircraft, missile and launcher. An analytical study is conducted in this paper to understand the characteristic of sound transmission through an orthotropic cylindrical shell. The shell is assumed to be infinitely long and is subjected to a plane wave with uniform airflow in the external fluid medium. An exact solution is obtained by solving the first-order shear deformation and acoustic wave equations simultaneously. The transmission losses (TLs) obtained from the numerical solution are compared with those of other authors. Additionally, in comparison with the classical thin shell theory (CST), the first-order shear deformation theory (FSDT) calculates with the best degree of accuracy. Numerical results are used to show the effects of fiber direction, geometrical properties, Mach number and material properties.
    No preview · Article · Jan 2009 · Aerospace Science and Technology