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Öğe An experimentally validated numerical method for investigating the air blast response of basalt composite plates(Taylor & Francis Inc, 2020) Susler, Sedat; Kurtaran, Hasan; Turkmen, Halit S.; Kazanci, Zafer; Lopresto, ValentinaNonlinear air blast response of basalt composite plates is analysed by using a generalized differential quadrature (GDQ) method, which requires less solution time and decreases the complexity compared to finite element method. A test environment that contains a shock tube is designed and set to experiment on the transient response of blast loaded laminated plates. Experimental and numerical results show a good agreement in terms of displacement, strain, and acceleration versus time. The responses of glass/epoxy, Kevlar/epoxy, and carbon/epoxy composite plates are also investigated by using GDQ method and the results are compared with the basalt/epoxy composite plate and discussed.Öğe Crashworthiness Optimization of Nested and Concentric Circular Tubes Using Response Surface Methodology and Genetic Algorithm(Latin Amer J Solids Structures, 2018) Usta, Fatih; Eren, Zana; Kurtaran, Hasan; Turkmen, Halit S.; Kazanci, Zafer; Mecitoglu, ZahitIn this study crashworthiness optimization of nested and concentric circular tubes under impact loading is performed by coupling Finite Element model, Response Surface Models and Genetic Algorithm. Specific Energy Absorption (SEA) and Crash Force Efficiency (CFE) are used in crashworthiness optimization since these criteria are important indicators for evaluating crashworthiness performance. Length and thickness of three concentric tubes as well as radius of one tube are adopted as design variables which are effective parameters on SEA and CFE. To reduce the computational cost of the optimization procedure, simple and computationally cheap Response Surface Models are created to replace finite element analyses in further calculations. The Non-dominated Sorting Genetic Algorithm -II (NSGAII) is applied to obtain the Pareto optimal solutions. Optimization results are presented for different selected designs that indicate relative importance of multi-objective functions. Results show that the total weight of the vehicles can be reduced by using nested tubes comparing to single tubes with identical masses. These designs can be adopted for use in practice.Öğe Design optimization of modified re-entrant auxetic metamaterials reinforced with asymmetric edge cells for crushing behavior using the Taguchi method(Springer Heidelberg, 2022) Usta, Fatih; Zhang, Zhennan; Kurtaran, Hasan; Scarpa, Fabrizio; Turkmen, Halit S.; Mecitoglu, ZahitThis work describes the compressive failure behavior and optimization of modified hierarchical re-entrant auxetic metamaterials reinforced with asymmetrical edge cells. The mechanical behavior of these metamaterials is parametrized against the width, thickness and angles of the cells. A Taguchi design (L27 (3(boolean AND)13)) has been performed to determine the effect of the eight geometric factors on the maximum compressive strength (specific strength), mean crushing force (MCF), specific energy absorption (SEA) and Poisson's ratio of the metamaterials. An analysis of variance (ANOVA) has been also performed to find out the relative significance and contribution percentage of each parameter from a statistical standpoint. The results show that the cell wall angle between the lateral and inclined ribs of the re-entrant unit cells has the largest effect on the compressive strength and absorbed energy of the structure that exhibits a percent variation of 82.5%, 30.0%, 85.9% and 75.1% in specific strength, MCF, SEA and Poisson's ratio, respectively. Moreover, the size of slot width and thickness, especially in the inclined struts, have a considerable effect on the mechanical performance compared to the angle of asymmetrical cells. Lastly, two samples from the optimization design table showing the best and worst mechanical responses are manufactured by using 3D printing and are tested under compression loading. The effects of the design factors on the deformation mechanisms and mechanical responses have been discussed by comparing the experimental and FE simulation results. The results show that the deformation mechanism of the asymmetrical unit cells and inclined struts play a key role in the resistance of the structures under compressive loads.Öğe Dynamic analysis of moderately thick composite cylindrical panel subjected to moving load(Gazi Univ, Fac Engineering Architecture, 2018) Kurtaran, HasanIn this study, dynamic behavior of moderately thick symmetrically laminated composite cylindrical panel under moving load is investigated using Ritz solution approximations. Hamilton's principle (also referred to as dynamic version of Virtual work principle) is used to derive the equation of motion. First order shear deformation theory is used to consider transverse shear effect. Time integration of equation of motion is carried out using implicit Newmark average acceleration method. Parametric study is conducted in order to investigate the dynamic behavior of composite cylindrical panel for different velocities of moving load, curvature ratios, stacking schemes and boundary conditions.Öğe Flutter improvement of a thin walled wing-engine system by applying curvilinear fiber path(Elsevier France-Editions Scientifiques Medicales Elsevier, 2019) Farsadi, Touraj; Asadi, Davood; Kurtaran, HasanIn the present study, the aeroelastic behavior of a wing-engine system modeled as composite Thin Walled Beam (TWB) with curvilinear fiber path is investigated. The variable stiffness is acquired by constructing laminates of TWB with curvilinear fibers having prescribed paths. In order to account the effect of chordwise and spanwise locations, mass, and thrust force of engine on the aeroelastic characteristics of TWB, the novel governing equations of motion are obtained using Hamilton's variational principle. The paper aims to exploit desirable fiber paths with improved aeroelastic properties for different wing-engine configuration. Ritz based solution methodology is employed to solve the equations with coupled incompressible unsteady aerodynamic model based on Wagner's function. Numerical simulation results which conform to previously published literatures are presented for validation purposes. Although different curvilinear fiber paths can be introduced to enhance flutter instabilities for each wing-engine configurations, there exists an ideal placement of engine on the wing considering only the engine mass, and the engine mass and thrust force, simultaneously. A comprehensive insight is provided over the effect of parameters such as the lamination fiber path and the effect of engine positions with different mass and thrust values on the flutter speed and frequency. (C) 2019 Elsevier Masson SAS. All rights reserved.Öğe Fundamental Frequency Optimization of Doubly Curved Aerospace Structural Panels via Variable Stiffness Concept(2020) Farsadi, Touraj; Kurtaran, HasanThe fundamental natural frequencies of curvilinear fiber composite doubly curved panels are optimized. Doubly curved panels are used in numerous components of the structural frames of aerospace vehicles. The variable stiffness performanceis achieved by changing the fiber path to the curvilinear fiber path function in the composite structures. The structural model is developed based on the virtual work rule. The target is to attain the best fiber paths with maximum fundamental frequencies. An eight-layer composite doubly curved panel with two forms of boundary conditions is considered as anexample in this research. The boundary conditions include; CCCC, FCFC. Von-Karman kinematic strain relations are utilized and the FSDT is used to generalize the equation for the doubly curved panel. Generalized Differential Quadrature (GDQ) theory of solution is applied to solve the differential governing equations of motion. Numerical results reveal the efficiency of the curvilinear fiber path concept on the frequencies of the doubly curved panel. The optimum fiber path function of each layer is offered for the free vibration study.Öğe Fundamental frequency optimization of variable stiffness composite skew plates(Springer Wien, 2021) Farsadi, Touraj; Asadi, Davood; Kurtaran, HasanIn this study, natural frequencies and vibrational mode shapes of variable stiffness composite skewed plates are optimized applying a genetic algorithm. The variable stiffness behavior is obtained by altering the fiber angles continuously according to two selected curvilinear fiber path functions in the composite laminates. Fundamental frequency and related mode shapes of the plates are optimized for two different fiber path functions using the structural model obtained based on the virtual work principle. A three-layer composite skewed plate with four types of boundary conditions and different plate geometries is considered as case study in this research. Diverse sweptback angles as well as different aspect ratios are considered as various plate geometries. The present study aims to calculate the best fiber path with maximized fundamental frequency or in-plane strengths for a composite skewed plate. The generalized differential quadrature method of solution is employed to solve the governing equations of motion. Moreover, the linear kinematic strain assumptions are used, and the first-order shear deformation theory is employed to generalize the formulation for the case of moderately thick plates including transverse shear effects. Numerical results demonstrate the effect of the fiber angles, boundary conditions, and diverse geometries on the natural frequencies of the composite plate. The optimal fiber angles of each layer are presented for the above cases in free vibration analysis. It is verified that the application of optimized curvilinear fibers instead of the traditional straight fibers introduces a higher degree of flexibility, which can be used to adjust frequencies and mode shapes.Öğe Geometrically nonlinear transient analysis of laminated composite super-elliptic shell structures with generalized differential quadrature method(Pergamon-Elsevier Science Ltd, 2018) Akgun, Gokce; Kurtaran, HasanIn this study, geometrically nonlinear dynamic behavior of laminated composite super-elliptic shells is investigated using generalized differential quadrature method. Super-elliptic shell can represent cylindrical, elliptical or quasi-rectangular shell by adjusting parameters in super-ellipse formulation (also known as Lame curve formulation). Geometric nonlinearity is taken into account using Green-Lagrange nonlinear strain-displacement relations that are derived using differential geometry and theory of surfaces. Transverse shear effect is considered through the first-order shear deformation theory. Equation of motion is obtained using virtual work principle. Spatial derivatives in equation of motion is expressed with generalized differential quadrature method and time integration is carried out using Newmark average acceleration method. Several super-elliptic shell problems under uniform distributed load are solved with the proposed method. Effects of layer orientations, boundary conditions, ovality and ellipticity on dynamic behavior are investigated. Transient responses are compared with finite element solutions.Öğe Large Displacement Static Analysis of Composite Elliptic Panels of Revolution having Variable Thickness and Resting on Winkler-Pasternak Elastic Foundation(Latin Amer J Solids Structures, 2019) Kalbaran, Ozgur; Kurtaran, HasanNonlinear static response of laminated composite Elliptic Panels of Revolution Structure(s) (EPRS) having variable thickness resting on Winkler-Pasternak (W-P) Elastic Foundation is investigated in this article. Generalized Differential Quadrature (GDQ) method is utilized to obtain the numerical solution of EPRS. The first-order shear deformation theory (FSDT) is employed to consider the transverse shear effects in static analyses. To determine the variable thickness, three types of thickness profiles namely cosine, sine and linear functions are used. Equilibrium equations are derived via virtual work principle using Green-Lagrange nonlinear strain-displacement relationships. The deepness terms are considered in Green-Lagrange strain-displacement relationships. The differential quadrature rule is employed to calculate the partial derivatives in equilibrium equations. Nonlinear static equilibrium equations are solved using Newton-Raphson method. Computer programs for EPRS are developed to implement the GDQ method in the solution of equilibrium equations. Accuracy of the proposed method is verified by comparing the results with Finite Element Method (FEM) solutions. After validation, several cases are carried out to examine the effect of elastic foundation parameters, thickness variation factor, thickness functions, boundary conditions and geometric characteristic parameter of EPRS on the geometrically nonlinear behavior of laminated composite EPRS.Öğe Large displacement transient analysis of FGM super-elliptic shells using GDQ method(Elsevier Sci Ltd, 2019) Akgun, Gokce; Kurtaran, HasanCurrent work concentrates on large displacement dynamic analysis of super-elliptic (SE) shells made of functionally graded materials (FGMs) employing generalized differential quadrature (GDQ) technique. SE shells can be in quasi-rectangular, elliptical or cylindrical shell forms according to the parameters in super-ellipse formulation. In this paper, large displacements are considered through Green-Lagrange nonlinear strain-displacement relationships derived for SE shells with full nonlinearity in transverse shear. Present solution is based on first-order shear deformation theory (FSDT). Virtual work principle and GDQ method are utilized to derive equation of motion and to express spatial derivatives existing in equation of motion, respectively. Newmark average acceleration method is employed in the solution of equation of motion. By solving various FGM super-elliptic (FGM-SE) shell problems, effects of FGM material properties (using different ceramic/metal pairs like Alumina/Steel (Al2O3/Steel), Zirconia/Aluminum (ZrO2/Al), Alumina/Aluminum (Al2O3/Al), Zirconia/Monel (ZrO2/Ni-Cu) and Silicon Nitride/Steel (Si3N4/Steel)), SE geometric characteristics (ellipticity and ovality) and boundary conditions on dynamic response are investigated.Öğe Non-linear transient response of porous functionally graded truncated conical panels using GDQ method(Elsevier Sci Ltd, 2021) Akgun, Gokce; Kurtaran, Hasan; Kalbaran, OzgurPresent study deals with large displacement transient dynamic response of truncated conical panels made of Porous Functionally Graded Materials (P-FGMs) using Generalized Differential Quadrature (GDQ) method. In this study, geometric non-linearity is taken into consideration through Green-Lagrange non-linear strain-displacement relations. First order shear deformation theory (FSDT) is utilized to take transverse shear effects into account. Virtual work principle is used to derive the equation of motion. The solution methodology utilizes GDQ method for spatial discretization of the variables. Newmark average acceleration method is implemented in time integration. Effects of different types of porosity distribution, porosity ratio and conical parameters on non-linear transient behavior of truncated conical panels are investigated for functionally graded material made of Zirconia/Aluminum (ZrO2/Al) considering various volume fraction coefficients.Öğe 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, HasanIn 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.Öğe Nonlinear flutter of tapered and skewed cantilevered plates with curvilinear fiber paths(Academic Press Ltd- Elsevier Science Ltd, 2021) Rahmanian, Mohammad; Farsadi, Touraj; Kurtaran, HasanAeroelastic 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.Öğe Nonlinear flutter response of a composite plate applying curvilinear fiber paths(Springer, 2020) Farsadi, Touraj; Asadi, Davood; Kurtaran, HasanIn the present study, nonlinear flutter and post-flutter behavior of a variable stiffness composite wing-like plate is investigated. The variable stiffness is obtained by varying fiber angles continuously according to a selected curvilinear fiber path function in the composite laminates. Flutter speed, limit cycle oscillations and bifurcation diagrams of the composite plate are explored for three different fiber path functions using the nonlinear structural model obtained based on the virtual work principle. The paper aims to exploit the ideal fiber paths with enhanced aeroelastic flutter and post-flutter properties for a composite plate in supersonic flow speed. First-order linear piston theory is applied to model the aerodynamics, and generalized differential quadrature is employed to solve the governing equations. Von Karman nonlinear strain theory is used to account for the geometric nonlinearities, and first-order shear deformation theory is employed to consider the transverse shear effects in the structural model. Time integration of the equation of motion is carried out using the Newmark average acceleration method. Different curvilinear fiber paths are introduced to enhance flutter instabilities and post-flutter behavior of the composite plate. Results demonstrate that the fiber orientation has a significant effect on the dynamic behavior of the plate and the asymmetric properties as well as the behavior of the limit cycle oscillation. © 2019, Springer-Verlag GmbH Austria, part of Springer Nature.Öğe 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, HasanIn 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.Öğe Nonlinear stability of multilayered graphene platelet-reinforced functionally graded wing-like plates(Springer Wien, 2022) Farsadi, Touraj; Rahmanian, Mohammad; Kurtaran, HasanNonlinear 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.Öğe Nonlinear transient dynamic analysis of laminated composite parabolic panels of revolution with variable thickness resting on elastic foundation(Elsevier Sci Ltd, 2019) Kalbaran, Ozgur; Kurtaran, HasanIn this article, nonlinear transient behavior of laminated composite Parabolic Panels of Revolution Structure(s) (PPRS) with variable thickness resting on elastic foundation is investigated using Generalized Differential Quadrature (GDQ) method. Winkler-Pasternak model is used to represent elastic foundation. Linear, arch, sine and cosine thickness functions are used to express variable thickness. In transient analyses, First Order Shear Deformation Theory (FSDT) is used to consider the transverse shear effects. Nonlinearity is taken into account using Green-Lagrange nonlinear strain-displacement relations considering deepness effect. Virtual work principle is used to derive the equations of motion. Partial derivatives in the equation of motion are expressed with GDQ method and time integration is carried out using Newmark average acceleration method. Several problems are solved and compared with finite element results in order to validate the proposed method. After validation, effects of thickness functions, thickness variation parameter, geometric characteristic parameter of PPRS, boundary conditions, elastic foundation parameters as well as composite lamination scheme on nonlinear transient dynamic behaviour of PPRS are investigated.
