Yazar "Rahmanian, Mohammad" seçeneğine göre listele

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    Nonlinear analysis of functionally graded skewed and tapered wing-like plates including porosities: A bifurcation study
    (Elsevier Sci Ltd, 2021) Farsadi, Touraj; Rahmanian, Mohammad; Kurtaran, Hasan
    In the present study, nonlinear panel flutter and bifurcation behavior of functionally graded ceramic/metal winglike tapered and skewed plates are investigated. Porosities are distributed over the cross-section of the functionally graded structure. The flutter speed, limit cycle oscillations, and bifurcation diagrams of the functionally graded plate with two types of geometrical non-uniformities being skewness and taperness are explored. Nonlinear structural model is utilized based on the virtual work principle by including the von-Karman nonlinear kinematic strain assumption. The first order shear deformation theory is employed to consider the transverse shear effect in the structural model. First-order linear piston theory is used to model the aerodynamic loading while the generalized differential quadrature method is employed to solve the governing equations of motion. Time integration of the final ordinary equations of motion is carried out using the Newmark average acceleration method. Different volume fractions are investigated to enhance the flutter instability margins and post-flutter behavior of functionally graded plates. Results demonstrate that the volume fraction and porosity coefficients have significant effects on dynamic behavior and limit cycle oscillation amplitudes.
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    Nonlinear flutter of tapered and skewed cantilevered plates with curvilinear fiber paths
    (Academic Press Ltd- Elsevier Science Ltd, 2021) Rahmanian, Mohammad; Farsadi, Touraj; Kurtaran, Hasan
    Aeroelastic stability of tapered/skew variable stiffness composite cantilevered plates are considered in the current study at flutter and post-flutter regions. The variable stiffness behavior is obtained by altering the fiber angles continuously according to a selected curvilinear fiber path function in the composite laminates. Flutter speed, limit cycle oscillations (LCOs), and bifurcation diagrams of tapered/skewed plates are obtained at two different fiber path functions. Nonlinear structural model is utilized based on the virtual work principle. Fully nonlinear Green's kinematic strain relations are used to account for the geometric nonlinearities and the first order shear deformation theory (FSDT) is employed to generalize the formulation for the case of moderately thick plates including transverse shear effects. One prominent target of the present study is to determine how the variable stiffness parameters affect the nonlinear behavior. Consequently, one may find the best fiber path with improved flutter and post-flutter characteristics for tapered/skew plates in supersonic flow. First order linear piston theory is used to model the aerodynamic loading. In order to get a reliable solution, the Generalized Differential Quadrature (GDQ) method is employed. Moreover, time integration of the equations of motion is carried out using the Newmark's average acceleration technique. It will be shown that taperness/skewness as well as variable stiffness lamination parameters have significant effects on the aeroelastic stability margins. In addition, the post-critical behavior is found to be periodic or quasi-periodic at all the presented simulations with no specific route to chaos. (c) 2021 Elsevier Ltd. All rights reserved.
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    Nonlinear lay-up optimization of variable stiffness composite skew and taper cylindrical panels in free vibration
    (Elsevier Sci Ltd, 2021) Farsadi, Touraj; Rahmanian, Mohammad; Kurtaran, Hasan
    In the present study, the fundamental natural frequencies of curvilinear fiber composite skew and taper cylindrical panels are optimized applying genetic algorithm (GA). Later, the fundamental amplitude-dependent nonlinear frequency behavior of the optimized curved fiber layup configurations is studied and compared with the reference unidirectional fiber layup. The variable stiffness behavior is obtained by altering the fiber angles continuously according to the curvilinear fiber path function in the composite laminates. A nonlinear structural model is utilized based on the virtual work principle. Green?s nonlinear kinematic strain relations are used to account for the geometric nonlinearities and the first-order shear deformation theory (FSDT) is adopted to generalize the formulation for the case of moderately thick cylindrical panels including transverse shear deformations. The goal is to determine how the variable stiffness parameters affect the linear and nonlinear free vibration behavior of the skew and taper cylindrical panels. Consequently, one may find the optimum fiber path with improved structural characteristics for the cylindrical panel. Eight-layered composite skew and taper cylindrical panels at two different boundary condition sets are considered in this research. Generalized Differential Quadrature (GDQ) method of solution is employed to solve the nonlinear governing equations of motion. Numerical results demonstrate the degree of effectiveness for fiber angle paths, boundary conditions, and geometrical non-uniformities on the fundamental frequencies of the cylindrical panel. Eventually, optimum fiber angles of each layer in free vibration analysis are presented.
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    Nonlinear stability of multilayered graphene platelet-reinforced functionally graded wing-like plates
    (Springer Wien, 2022) Farsadi, Touraj; Rahmanian, Mohammad; Kurtaran, Hasan
    Nonlinear panel flutter and post-flutter behavior of wing-like, taper, and skew plates made of functionally graded (FG) multilayered graphene platelet-reinforced polymer composite (GPL-RPC) are investigated in this study. Using two types of geometrical non-uniformity, skew and taper, the flutter boundary, limit cycle oscillations, and bifurcation plots of functionally graded GPL-RPC plates are reported. The graphene platelet (GPL) nanofillers are assumed to be dispersed uniformly or non-uniformly in the matrix and in the thickness direction. All GPL distribution patterns of UD, FG-O, FG-X, and FG-A are considered. The modified Halpin-Tsai micro-mechanical model and the rule of mixture are utilized to determine the effective material characteristics of GPL-RPC layers. In order to obtain the nonlinear mathematical model for the non-uniform plates, Von-Karman kinematic strains descriptions are used along with the virtual work principle and Hamilton's expression. To generalize the structural model, a first-order shear deformation theory (FSDT) is used. The well-recognized first-order piston theory is also utilized to account for the aerodynamic loading description. In the end, governing differential equations of motion are projected to their equivalent algebraic representation by means of the generalized differential quadrature method (GDQM), which is then followed by a time integration using the Newmark's average acceleration scheme. The goal of current research is to find how the GPL weight fraction affects the flutter instability margins and post-flutter behavior for FG GPL-RPC cantilevered plates at several proposed distribution patterns.
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    Reduced order nonlinear aeroelasticity of swept composite wings using compressible indicial unsteady aerodynamics
    (Academic Press, 2020) Farsadi, Touraj; Rahmanian, Mohammad; Kayran, Altan
    Nonlinear dynamic aeroelasticity of composite wings in compressible flows is investigated. To provide a reasonable model for the problem, the composite wing is modeled as a thin walled beam (TWB) with circumferentially asymmetric stiffness layup configuration. The structural model considers nonlinear strain displacement relations and a number of non-classical effects, such as transverse shear and warping inhibition. Geometrically nonlinear terms of up to third order are retained in the formulation. Unsteady aerodynamic loads are calculated according to a compressible model, described by indicial function approximations in the time domain. The aeroelastic system of equations is augmented by the differential equations governing the aerodynamics lag states to derive the final explicit form of the coupled fluid-structure equations of motion. The final nonlinear governing aeroelastic system of equations is solved using the eigenvectors of the linear structural equations of motion to approximate the spatial variation of the corresponding degrees of freedom in the Ritz solution method. Direct time integrations of the nonlinear equations of motion representing the full aeroelastic system are conducted using the well-known Runge–Kutta method. A comprehensive insight is provided over the effect of parameters such as the lamination fiber angle and the sweep angle on the stability margins and the limit cycle oscillation behavior of the system. Integration of the interpolation method employed for the evaluation of compressible indicial functions at any Mach number in the subsonic compressible range to the derivation process of the third order nonlinear aeroelastic system of equations based on TWB theory is done for the first time. Results show that flutter speeds obtained by the incompressible unsteady aerodynamics are not conservative and as the backward sweep angle of the wing is increased, post-flutter aeroelastic response of the wing becomes more well-behaved. © 2019 Elsevier Ltd