K. Daneshjou

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

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Publications (25)9.75 Total impact

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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.
    Latin American Journal of Solids and Structures 03/2013; 10(2):349-390. · 1.24 Impact Factor
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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.
    Journal of Thermal Stresses 02/2013; · 0.73 Impact Factor
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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.
    Applied Mathematics and Mechanics 01/2013; 34(4). · 0.65 Impact Factor
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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
    Applied Mathematics and Mechanics 01/2011; 32(6):701-718. · 0.65 Impact Factor
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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.
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing - MATER SCI ENG A-STRUCT MATER. 01/2011;
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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.
    Composite Structures. 01/2010;
  • 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.
    Journal of Mechanics. 09/2009; 25(03).
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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.
    Engineering With Computers 03/2009; 25(2):191-206. · 0.60 Impact Factor
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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 ...
    Engineering With Computers 01/2009; 25:411. · 0.60 Impact Factor
  • Kamran Daneshjou, Majid Shahravi
    Eng. Comput. (Lond.). 01/2009; 25:191-206.
  • 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.
    Aerospace Science and Technology - AEROSP SCI TECHNOL. 01/2009; 13(1):18-26.
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    K. Daneshjou, M. Shahravi
    Journal of Mechanical Science and Technology 01/2009; 23(12):3485-3485. · 1.09 Impact Factor
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    Kamran Daneshjou, Ali Nouri, Roohollah Talebitooti
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    ABSTRACT: Composite structures are often used in the aerospace industry due to the advantages offered by a high strength to weight ratio. Sound transmission through an infinite laminated composite cylindrical shell is studied in the context of the transmission of airborne sound into the aircraft interior. The shell is immersed in an external fluid medium and contains internal fluid. Airflow in the external fluid medium moves with a constant velocity. An exact solution is obtained by simultaneously solving the first-order shear deformation theory (FSDT) of a laminated composite shell and the acoustic wave equations. Transmission losses (TL) obtained from numerical solutions are compared with those of other authors. The effects of structural properties and flight conditions on TL are studied for a range of values, especially, the Mach number, stack sequences, and the angle of warp. Additionally, comparisons of the transmission losses are made between the classical thin shell theory (CST) and FSDT for laminated composite and isotropic cylindrical shells.
    Applied Mathematics and Mechanics 08/2008; 29(9):1165-1177. · 0.65 Impact Factor
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    K Daneshjou, R Talebitooti, A Nouri
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    ABSTRACT: Due to the high levels of noise into the modem launchers, the structural-acoustic coupling problem is an important subject in the area of vibro-acoustic analysis. In this paper, analytical study is conducted on oblique plane wave incident upon a flexible orthotropic double-walled thin cylindrical shell to understand the characteristic of sound transmission. External and internal fluid media surround the shells and there is fluid (air) in the annular space between them. A uniform flow moves with a constant velocity in the external fluid medium. The wave equations represent the fluid media and the Sanders equations describe the motions of the two shells. On the internal and external shell surfaces, the equations of fluid-structure interaction are considered. An exact solution is obtained by solving the classical shell equations and acoustic wave equations simultaneously. As, the pressure and displacement terms are expressed in infinite series form, an iterative procedure is constructed in each frequency. This convergence algorithm presents the advantage of best accuracy. Transmission losses (TLs) obtained from numerical solution are compared with those of other authors. Eventually, the numerical results are used to show the effects of, orthotropy ratio, geometrical properties, air gap specifications, Mach number, material and fluid properties. UN MODELE ANALYTIQUE POUR LA TRANSMISSION DES ONDES ACOUSTIQUES PAR LES DOUBLE PAROIS ORTHOTROPIQUES CYLINDRIQUES RESUME En raison du haut niveau de bruit produit par les lanceurs modernes, Ie probleme de couplage acoustique-structure est un sujet important dans les etudes vibro-acoustique. Dans cette etude avec une approche analytique, les caracteristiques des ondes acoustiques reflechissant d'une double paroi flexible orthotropique cylindrique ont ete etudies. Sur les surfaces externes et interieures, les equations de fluide-structure ont ete resolues. La solution exacte est obtenue par la solution simultanement des equations de paroi et de l'onde acoustique. Comme la pression et les termes de deplacement sont exprimes dans la forme de serie infinie, une procedure iterative est construite dans chaque frequence. Les pertes de transmission (TLs) obtenues de la solution numerique sont comparees avec ceux d'autres auteurs. Finalement, les resultats numeriques sont utilises pour montrer les effets de rapport orthotropique, proprietes geometriques, les specifications de les pace entre parois, Ie nombre de Mach, les proprietes de materielle et de liquide. Transactions ofthe CSME Ide fa SCGM
    03/2008;
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    K Daneshjou, R Talebitooti, A Nouri
    [Show abstract] [Hide abstract]
    ABSTRACT: Due to the high levels of noise into the modem launchers, the structural-acoustic coupling problem is an important subject in the area of vibro-acoustic analysis. In this paper, analytical study is conducted on oblique plane wave incident upon a flexible orthotropic double-walled thin cylindrical shell to understand the characteristic of sound transmission. External and internal fluid media surround the shells and there is fluid (air) in the annular space between them. A uniform flow moves with a constant velocity in the external fluid medium. The wave equations represent the fluid media and the Sanders equations describe the motions of the two shells. On the internal and external shell surfaces, the equations of fluid-structure interaction are considered. An exact solution is obtained by solving the classical shell equations and acoustic wave equations simultaneously. As, the pressure and displacement terms are expressed in infinite series form, an iterative procedure is constructed in each frequency. This convergence algorithm presents the advantage of best accuracy. Transmission losses (TLs) obtained from numerical solution are compared with those of other authors. Eventually, the numerical results are used to show the effects of, orthotropy ratio, geometrical properties, air gap specifications, Mach number, material and fluid properties. UN MODELE ANALYTIQUE POUR LA TRANSMISSION DES ONDES ACOUSTIQUES PAR LES DOUBLE PAROIS ORTHOTROPIQUES CYLINDRIQUES RESUME En raison du haut niveau de bruit produit par les lanceurs modernes, Ie probleme de couplage acoustique-structure est un sujet important dans les etudes vibro-acoustique. Dans cette etude avec une approche analytique, les caracteristiques des ondes acoustiques reflechissant d'une double paroi flexible orthotropique cylindrique ont ete etudies. Sur les surfaces externes et interieures, les equations de fluide-structure ont ete resolues. La solution exacte est obtenue par la solution simultanement des equations de paroi et de l'onde acoustique. Comme la pression et les termes de deplacement sont exprimes dans la forme de serie infinie, une procedure iterative est construite dans chaque frequence. Les pertes de transmission (TLs) obtenues de la solution numerique sont comparees avec ceux d'autres auteurs. Finalement, les resultats numeriques sont utilises pour montrer les effets de rapport orthotropique, proprietes geometriques, les specifications de les pace entre parois, Ie nombre de Mach, les proprietes de materielle et de liquide. Transactions ofthe CSME Ide fa SCGM
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    K. Daneshjou, M. Shahravi
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    ABSTRACT: 3D numerical simulations were performed in order to further investigate the role of penetrator strength in the interaction of long-rods and oblique targets. 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 with a full 3D explicit finite element method for various impact velocities and strength of target plates and projectiles. Numerical predictions were compared with existing two-dimensional analytical models and test results. It was predicted that critical ricochet angle increases with decreasing impact velocity and that higher ricochet angles were expected if higher strength target materials are employed. But there are differences between analytical models and 3D numerical simulation results or test results. The causes for these discrepancies are established by numerical simulations which explore the validity of the penetrator strength parameter in the analytical model as a physical entity. As a matter of fact, in this paper we first investigate the role of penetrator dynamic strength using two-dimensional simulation which resulted in different penetrator strengths out of different impact velocities. Next, by applying these amounts for penetrator strength in Rosenberg analytical model the critical ricochet angle is calculated. Finally, a comparison between the present analytical method with the 3D simulation and test results shows that the new analytical approach leads to modified results with respect to Rosenberg ones. KeywordsCritical ricochet angle-Penetrator strength-Numerical solution-Long-Rod
    Journal of Mechanical Science and Technology 01/2008; 22(11):2076-2089. · 1.09 Impact Factor
  • K. Daneshjou, A. Nouri, R. Talebitooti
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    ABSTRACT: Composite structures are often used in aircraft because of advantages offered by a high strength to weight ratio. Sound transmission through an infinite laminated composite cylindrical shell is studied in the context of the transmission of airborne sound into aircraft interior. The shell is immersed in an external fluid medium and contains an internal fluid, and airflow in an external fluid medium moves with a constant velocity. The different parameters were used to see how laminate specification affected noise transmission. An exact solution is obtained by solving the vibration equation of laminated composite shell and acoustic wave equations simultaneously. Transmission losses (TLs) obtained from numerical solution are compared with those of other authors. The effects of different source condition, structural properties and flight conditions on TL are studied for a range of values, especially, incident angle of the plane wave, Mach number and flight altitude of aircraft, stack sequences, angle of warp and damping.
    Archive of Applied Mechanics 05/2007; 77(6):363-379. · 1.04 Impact Factor
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    ABSTRACT: In this paper, classical thin shell theory is used to analyze vibration and critical speed of simply supported rotating orthotropic cylindrical shells. The eeects of centrifugal and Coriolis forces due to the rotation are considered in the present formulation. In addition, axial load is applied to cylinder as a ratio of critical buckling load. Finally the eeects of orthotropic ratio, material and geometry of the shell as well as axial loads on bifurcation of natural frequency are investigated.
    03/2007; 4.
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    Kamran Daneshjou, Majid Shahravi, Mohamad Rahimzadeh
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    ABSTRACT: In this paper the penetration depth of long-rod electromagnetic projectiles on semi-infinite targets are studied with numerical approach. And the role of nose profile was studied. The results obtained from this investigation were compared with the recent studies. For the targets and projectile were considered to be made of soft metals. All the results were compared with two analytical models: Tate and Vahedi. These two models don't consider the role of nose profile. The target is constrained to have no movement and the projectile doesn't pass through the target. The impact velocity of the projectile was considered as a variable and the results were compared together and they were in good agreement with other studies in this field.
    Journal of Solid Mechanics and Materials Engineering 01/2007; 1(5):635-643.
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    K Daneshjou, A Nouri, R Talebitooti
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    ABSTRACT: Laminated composite shells are increasingly being used in various engineering applications, including aerospace, mechanical, marine, and automotive. In this paper, sound transmission through an infinite laminated composite cylindrical shell is studied in the context of the transmission of airborne sound into aircraft interior. The shell is immersed into an external fluid medium and contains internal fluid, while the airflow in external fluid medium is moving with a constant velocity. Modal impedance method, along with the first-order shear deformation theory (FSDT), is used to calculate the transmission loss (TL), considering three directions of the shell. The TL obtained in this study is compared with that of thin laminated composite obtained by others. The effects of structural properties and flight conditions on TL are studied for a range of values, especially, Mach number, aircraft flight altitude, shell thickness, and warp angle. Comparisons of the transmission loss are made among classical shell theory (CST) and FSDT for laminated composite and isotropic shells, which show close agreements.
    Mech. & Aerospace Eng. J. 12/2006; 2(2).