Aerospace Science and Technology
Mahdi Karami Khorramabadi; Ali Reza Nezamabadi
Abstract
In this paper, the buckling behavior of functionally graded simply supported nanocomposite beams reinforced by nano clay is studied. The specimens were prepared and the experimental tensile and buckling tests are carried out. The elastic modulus of epoxy/clay nanocomposite for functionally graded and ...
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In this paper, the buckling behavior of functionally graded simply supported nanocomposite beams reinforced by nano clay is studied. The specimens were prepared and the experimental tensile and buckling tests are carried out. The elastic modulus of epoxy/clay nanocomposite for functionally graded and uniformly distributed of nanoclay are estimated through a model based on the genetic algorithm approach. The results show that GA can be considered as an acceptable optimization research technique to identify Young’s modulus of nanocomposites with maximum accuracy. For simply supported beam, the first order shear deformation beam theory is applied for displacement field and the governing equations are derived by using Hamilton principle. The influence of nanoparticles for functionally graded and uniform distribution on the buckling load of a beam is presented. Comparison study is conducted to assess efficacy and accuracy of the present analysis. A comparison for theoretical analysis with the experimental results demonstrated the high accuracy.
Aerospace Science and Technology
Seyed mohammad navid ghoreishi; Nabi Mehri-Khansari; Houman rezaei
Abstract
Regardless of the initiation or propagation procedure of crack in a gas turbine blade, the precise expectation of the fracture behavior, such as mixed-mode Stress Intensity Factors (SIF), plays a significant role in acquiring its operational life. Therefore, multilateral three-dimensional fracture solutions ...
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Regardless of the initiation or propagation procedure of crack in a gas turbine blade, the precise expectation of the fracture behavior, such as mixed-mode Stress Intensity Factors (SIF), plays a significant role in acquiring its operational life. Therefore, multilateral three-dimensional fracture solutions are required, including real-based mixed-mode loading (I/II/III) conditions and geometrical considerations. In this study, three-dimensional semi-elliptical crack in a gas turbine blade with various geometrical parameters and inclination angles under mixed-mode loading (I/II/III) conditions were investigated based on the employing finite element techniques and analytical procedure. In this context, the semi-elliptical crack has been considered in the critical zone of the rotating blade to achieve the effect of crack aspect ratio, rotational velocity, crack location, and mechanical properties. Fluid Solid Interaction (FSI) analysis was also performed in addition to solid functional enriched elements. Structural simulation is done at the speed of 83.776 m/s based on CFD simulation. The results indicated that Al Alloys blade shows a profitable resistance in crack propagation. Moreover, as the crack domain is near the location of x/c= 0.25 and 1.9 of crack front, the mode II SIF will be independent of rotational velocity and the blades' mechanical properties. Similarly, for the location of x/c= 1.1 in crack front, the mode III SIF is independent of rotational velocity and blades' mechanical properties.
Aerospace Science and Technology
Hossein Faveadi; Ali R. Davari; Farshad Pazooki; Majid Pouladian
Abstract
Flight simulation is a powerful and usefull instrument in design, testing, evaluation and validation of aircrafts; The results of aerolastic simulation along with rigid simulation can be used in the many areas of designs, such as modification or optimization, stability analysis and evaluating field test ...
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Flight simulation is a powerful and usefull instrument in design, testing, evaluation and validation of aircrafts; The results of aerolastic simulation along with rigid simulation can be used in the many areas of designs, such as modification or optimization, stability analysis and evaluating field test data; It can be said that the use of simulation in the fields of design and optimization, especially during the initial and detailed design, should be considered more than other fields; In this research, by use of simulation, the effect of some design parameters such as slenderless ratio, maneuvering acceleration, propulsion curve, natural frequency of the structure, aerodynamic load distribution , etc. On issues such as flight and tracking behavior, stability and collision accuracy, has been examined; In cases such as: evaluating the initial error or veviation of the thurst vector or its curve, rolling speed, tracking of control commands, etc. aerolastic simulation gives a more realistic output compared to rigid simulation; Further more in cases such as investigating the effect of aerodynamic load distribution or stiffness ans and mass distribution, only aerolastic simulation is able to respond. Accordingly, the main orientation of this research is to develop an approach with acceptable accuracy and speed in order to simulate elastic projectiles in order to achieve some of the mentioned goals; However, due to the wide range of effective parameters and their interaction, in this study, only the role of thrust and body rigidity has been examined.
Aerospace Science and Technology
Hadi Hamedani; Ahmad Mamandi
Volume 14, Issue 2 , October 2021, , Pages 30-51
Abstract
In this paper, the effects of different rotational speed functions in the elastic-plastic deformation and stress analysis of a rotating annular thin disk of functionally graded material (FGM) in Reddy model is studied using the analytical and FEM methods. In this regard, differential equations governing ...
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In this paper, the effects of different rotational speed functions in the elastic-plastic deformation and stress analysis of a rotating annular thin disk of functionally graded material (FGM) in Reddy model is studied using the analytical and FEM methods. In this regard, differential equations governing dynamic equilibrium for displacements and stresses in the elastic region of the FGM rotating disk have been derived using the theory of elasticity in plane stress condition and have been solved by the shooting method. Then, the equations governing the distribution of plastic radial and circumferential stresses on the disk have been extracted using the Prandtl-Reuss theory of plasticity and based on the Ludwig hardening law in conjunction with the von Mises yield criterion. Also, by modeling the annular thin disk in the environment of finite element software ANSYS, the results obtained from the elastic analytical solution and the finite element numerical solution have been compared to each other and to the results reported in the literature for specific cases and validated accordingly. The effects of variation of the disk geometric parameters, functionally graded material power index as well as different type of the time-dependent rotational speed functions such as the constant speed, exponential, and accelerated/decelerated linear, quadratic, and square root functions on the elastic behavior of the disk and distribution of radial displacement, and also distribution of radial, circumferential, and shear stresses on the disk have been studied. Moreover, the results of plastic analysis have been presented for distribution of radial and circumferential stresses on the disk.
Aerospace Science and Technology
M.E. Golmakani; M. Moravej; M. Sadeghian
Volume 14, Issue 2 , October 2021, , Pages 66-79
Abstract
In this paper, the nonlinear thermal buckling of moderately thick functionally graded cylindrical panels is analyzed based on the first-order shear deformation theory (FSDT) and large deflection von Kármán equations. The highly coupled nonlinear governing equations are solved using the ...
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In this paper, the nonlinear thermal buckling of moderately thick functionally graded cylindrical panels is analyzed based on the first-order shear deformation theory (FSDT) and large deflection von Kármán equations. The highly coupled nonlinear governing equations are solved using the combination of dynamic relaxation approach with the finite-difference discretization method at various boundary conditions. The material properties of the constituent components of the FG shell are considered to vary continuously along the thickness direction based on simple power-law and Mori-Tanaka distribution methods, separately. The critical thermal buckling load is considered based on the thermal load-displacement curve derived by solving the incremental form of nonlinear equilibrium equations. In order to consider the accuracy of the present results, a comparison study has been carried out. The effects of the boundary conditions, rule of mixture, grading index, radius-to-thickness ratio, length-to-radius ratio and panel angle are studied on the thermal buckling loads. It is observed from the results that in high values of radius-to-thickness ratios, there is no difference between the values of critical buckling temperature differences for linear and nonlinear distributions.
Aerospace Science and Technology
Ali Davar; Mahdi Mehrabani; MohammadReza Zamani; Mohsen Heydari Bani; Jafar Eskandari Jam
Abstract
The composite lattice cylindrical shells are analyzed in this research while they are subjected to transient dynamic loading. The equilibrium equations for the composite cylindrical shell are expressed in terms of classical shell theory. Additionally, due to the discontinuous distribution of stiffness ...
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The composite lattice cylindrical shells are analyzed in this research while they are subjected to transient dynamic loading. The equilibrium equations for the composite cylindrical shell are expressed in terms of classical shell theory. Additionally, due to the discontinuous distribution of stiffness and shell mass between reinforcing ribs and their proximity to one another (empty or filled with filler material), this issue has been expressed using an appropriate distribution function. On the basis of Lowe's first approximation theory, the strain-displacement and curvature-displacement relationships are considered. The Galerkin method is used to calculate the natural frequencies and shapes of structural modes for the boundary conditions, as well as the transient dynamic response of the composite cylindrical lattice shell to lateral impulsive loading applied extensively and uniformly on a specific rectangular surface. The convolution and a method for summing the effects of the modes are also obtained, and the obtained results are validated using references and ABAQUS finite element software. The effects of various parameters on free and forced vibrations are investigated, including geometric ratios, material properties, cross-sectional dimensions and distances, and lattice configuration. Finally, the effect of strengthening the cylindrical shell with lattice structures is investigated.
Aerospace Science and Technology
Pooya Yousefi Khiabani; Ali Nouri; Enayatullah Hosseinian
Abstract
In this paper, a semi-analytical solution for three-dimensional transient analysis of an annular plate with piezoelectric layers is investigated. The core is a functionally graded material with an exponential distribution. This method, which is a combination of the state space method, Laplace transform ...
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In this paper, a semi-analytical solution for three-dimensional transient analysis of an annular plate with piezoelectric layers is investigated. The core is a functionally graded material with an exponential distribution. This method, which is a combination of the state space method, Laplace transform and its inversion, and the one-dimensional differential quadrature method, is used to obtain the response of three-dimensional motion equations plate and the stress-displacement relations of the state space equations obtaining an analytical solution in the direction of the thickness and by applying the differential quadrature method to the equations of state space, a semi-analytical solution of the plate is obtained. To obtain a solution in the time domain, the Laplace transform and its numerical inversion are used. Analyzing the convergence of the present method, the obtained numerical results have been compared with the results of articles and with results obtained from using finite element analysis. Various parameters were studied including boundary conditions, piezoelectric properties, voltage applied to the actuator, the ratio of core thickness to layers, the ratio of outer to inner radius, and the functionally graded material variations index.
Aerospace Science and Technology
ali Vahedi; Mohammad Homayoun Sadr; Saied Shakhesi
Abstract
Epoxy is among the most important polymers, which is extensively employed in various technologies and applications. Nevertheless, epoxy polymers present low thermal conductivities and thus the enhancement of their thermal conductivity is an important research topic. Carbon nanotubes (CNTs) owing to their ...
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Epoxy is among the most important polymers, which is extensively employed in various technologies and applications. Nevertheless, epoxy polymers present low thermal conductivities and thus the enhancement of their thermal conductivity is an important research topic. Carbon nanotubes (CNTs) owing to their excellent thermal conductivities have been widely considered for the enhancement of the thermal conduction of epoxy polymers. In this work, we developed a combined molecular dynamics finite element multiscale modelling to investigate the heat transfer along CNT/epoxy nanocomposites. To this aim, the heat transfer between the CNT and epoxy atoms at the nanoscale was explored using the atomistic classical molecular dynamics simulations. In this case, we particularly evaluated the interfacial thermal conductance between the polymer and fillers. We finally constructed the continuum models of polymer nanocomposites representative volume elements using the finite element method in order to evaluate the effective thermal conductivity. The developed multiscale modelling enabled us to systematically analyze the effects of CNT fillers geometry (aspect ratio), diameter and volume fraction on the effective thermal conductivity of nanocomposites. Our results suggest that the interfacial thermal conductance between the CNT additives and epoxy polymer dominate the heat transfer mechanism at the nanoscale.The obtained findings in this study provide good vision regarding the enhancement of thermal conductivityof polymeric materials using highly conductive nanofillers.
Aerospace Science and Technology
Sina Jahandari; Ahmad Kalhor; Babak Nadjar Araabi
Abstract
This paper presents a novel approach to modeling of jet transport aircraft. Initially, basic mathematical models of jet transport are derived. Afterwards by focusing on the bank angle system of the jet transport, considering the aileron as the input, adverse methods of identification are utilized to ...
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This paper presents a novel approach to modeling of jet transport aircraft. Initially, basic mathematical models of jet transport are derived. Afterwards by focusing on the bank angle system of the jet transport, considering the aileron as the input, adverse methods of identification are utilized to estimate parameters of the system in an online manner. Then, effects of different types of noise on identification process are analyzed. Eventually, effects of time varying parameters are discussed. Recursive least squares method and its extended version, covariance resetting and forgetting factor methods were the fundamental tools in the system identification process of jet transport. Comprehensive simulations are presented and cast some light on effectiveness and disadvantages of different approaches.
Aerospace Science and Technology
Sina Jahandari; Ahmad Kalhor; Babak nadjar Araabi
Abstract
This paper addresses the adaptive control problem of an aircraft and focuses on the task that the pitch angle of the aircraft is required to follow the desired path. Considering the elevator deflection angle as the input and the pitch angle as the output, a mathematical model of the aircraft is derived ...
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This paper addresses the adaptive control problem of an aircraft and focuses on the task that the pitch angle of the aircraft is required to follow the desired path. Considering the elevator deflection angle as the input and the pitch angle as the output, a mathematical model of the aircraft is derived to specify the structure of the system. Three diverse deterministic self-tuning regulators are designed using direct and indirect methods. Assuming that the system is unknown, recursive least squares method is applied to estimate parameters of the system or that of the controller’s. Diophantine equation and minimum degree pole-placement methods are utilized to calculate the control law. Not only do simulation results clearly demonstrate the privilege and effectiveness of the proposed approaches, but also comprehensive discussion is presented to distinguish advantages and disadvantages of them.
Aerospace Science and Technology
Milad Noorabadi; Rahnama Malihe; Ghasemi Mohammad Amin; Jafar Eskandari Jam
Volume 12, Issue 2 , October 2019, , Pages 1-9
Abstract
In this paper the energy absorption capacity of stiffened circular composite tube is considered. The governing equations and dynamic equilibrium are first derived and then solved. Additionally, a finite element model of reinforced circular composite tube structure is modeled. At the following, the effects ...
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In this paper the energy absorption capacity of stiffened circular composite tube is considered. The governing equations and dynamic equilibrium are first derived and then solved. Additionally, a finite element model of reinforced circular composite tube structure is modeled. At the following, the effects of various parameters such as structural geometry, number of rings and stingers on mechanical behavior of such tubes are considered. The Stiffened cylinder is under axial loading and internal pressure, and boundary conditions for both sides of the cylinder are considered as simple supports. Results show increasing in the amount of energy in the stingers while the number of stingers increases, and decreasing in the amount of total energy while the number of rings and stringers are increase. Total strain energy and the strain energy created in structural elements increase by increasing the ratio of radius to thickness. The analytical solution results are in good compatibility with the results achieved from the finite element method.
Aerospace Science and Technology
Sajjad hajirezayi; Ali nouri; Enayatollah Hosseinian
Volume 12, Issue 2 , October 2019, , Pages 49-60
Abstract
Till now, various models have been proposed in literature to simulate the behavior of riveted structures. In order to find the most accurate analytical method in modeling the dynamic behavior of riveted structures, a comparison study is performed on several of these models, in this research. For this ...
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Till now, various models have been proposed in literature to simulate the behavior of riveted structures. In order to find the most accurate analytical method in modeling the dynamic behavior of riveted structures, a comparison study is performed on several of these models, in this research. For this purpose, experimental modal analysis tests are conducted on a riveted plate to verify the efficacy of the analytical models. Moreover, finite element model updating is used to reduce the difference between analytical and experimental results. First, the material properties of plates are optimized using the experimental results obtained from modal tests of a simple plate. Next, the optimization is performed for the physical properties of rivet. At the end, it is concluded that the fastener model proposed by Rutman can bring about the most accurate results when it is used in combination with solid plates and gap elements in the contact region.
Aerospace Science and Technology
S. Amir M. Ghannadpour; M. Barekati
Volume 12, Issue 1 , March 2019, , Pages 15-26
Abstract
In this paper, a method based on Chebyshev polynomials is developed for examination of geometrically nonlinear behaviour of thin rectangular composite laminated plates under end-shortening strain. Different boundary conditions and lay-up configurations are investigated and classical laminated plate theory ...
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In this paper, a method based on Chebyshev polynomials is developed for examination of geometrically nonlinear behaviour of thin rectangular composite laminated plates under end-shortening strain. Different boundary conditions and lay-up configurations are investigated and classical laminated plate theory is used for developing the equilibrium equations. The equilibrium equations are solved directly by substituting the displacement fields with equivalent finite double Chebyshev polynomials. Using this method allows one to analyze the composite laminated plates with combination of different boundary conditions on all edges. The final nonlinear system of equations is obtained by discretizing both equilibrium equations and boundary conditions with finite Chebyshev polynomials. Nonlinear terms caused by the product of variables are linearized by using quadratic extrapolation technique to solve the system of equations. Since number of equations is always more than the number of unknown parameters, the least squares technique is used to solve the system of equations. Some results for angle-ply and cross-ply composite plates with different boundary conditions are computed and compared with those available in the literature, wherever possible.
Aerospace Science and Technology
Mahdi Fakoor; Seyed Mohammad Navid Ghoreishi; Mohamad Aminjafari
Volume 12, Issue 1 , March 2019, , Pages 27-37
Abstract
In this paper, a combination method has been developed by coupling Multi-Objective Genetic Algorithms (MOGA) and Finite Element Method (FEM). This method has been applied for determination of the optimal stacking sequence of laminated composite plate against buckling. The most important parameters in ...
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In this paper, a combination method has been developed by coupling Multi-Objective Genetic Algorithms (MOGA) and Finite Element Method (FEM). This method has been applied for determination of the optimal stacking sequence of laminated composite plate against buckling. The most important parameters in optimization of a laminated composite plate such as, angle, thickness, number, and material of each layer are considered in the proposed method. These optimization processes have done for 3 types of compressive loads and optimal stacking sequences and Pareto front for each kind of compressive loads are determined. Unlike estimation methods like response surface and simple analytic methods, in the proposed optimization algorithm, objective functions are calculated directly by FEM software which leads to precise results. The results of proposed algorithm are validated against existing data in literature. The effects of different boundary conditions and aspect ratio of plate on Pareto front in buckling of a laminated composite plate are also studied.
Aerospace Science and Technology
Enayatollah Hosseinian; Ali Nouri; Majid Zia
Volume 12, Issue 1 , March 2019, , Pages 53-63
Abstract
In this paper, nonlinear vibration analysis of functionally graded piezoelectric (FGP) beam with porosities material is investigated based on the Timoshenko beam theory. Material properties of FG porous beam are described according to the rule of mixture which modified to approximate material properties ...
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In this paper, nonlinear vibration analysis of functionally graded piezoelectric (FGP) beam with porosities material is investigated based on the Timoshenko beam theory. Material properties of FG porous beam are described according to the rule of mixture which modified to approximate material properties with porosity phases. The Ritz method is used to obtain the governing equation which is then solved by a direct iterative method to determine the nonlinear vibration frequencies of FGP porous beam subjected to different boundary conditions. The effects of external electric voltage, material distribution profile, porosity volume fraction, slenderness ratios and boundary conditions on the nonlinear vibration characteristics of the FGP porous beam are discussed in detail. The results indicate that piezoelectric layers have significant effect on the nonlinear frequencies. Also it is found that the porosity has a considerable influence on the nonlinear frequency and these effects increased especially when the electric voltage is applied.
