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In this article, nonlinear thermomechanical analysis of transient vibrations and buckling stability of shallow composite bicurve shell under thermal loading has been performed. Both the geometric nonlinearity of the structure and the nonlinearity of material properties resulting from temperature changes in the analysis have been used. First-order shear theory and Hamilton's principle were used to derive the crustal motion equations and boundary conditions. In the following, the Ritz method is used to solve these equations. In order to distribute the temperature inside the shell, it is assumed that the temperature changes with time and coordinates only along the thickness. In addition, the effect of important parameters such as the effects of layering order, curvature and thickness of the shell on the temporal evolution of temperature and deflection of flat composite shell and bicurved under thermal boundary conditions has been studied. In order to validate the results, The deflect of center a homogeneous square plate under thermal loading was compared with the research results mentioned in the literature. Also, the results of thermal dynamic buckling of the composite shell under thermal load show that by decreasing the thickness of the shell, the elapsed time until the threshold of dynamic buckling is decreased. The necessary and sufficient conditions for the occurrence of dynamic buckling phenomenon are the absence of transverse loading and the application of the clamped boundary condition. It is also necessary to include nonlinear effects to find the buckling response.

Aerodynamic interference is one of the phenomena that occurs when two flying objects pass near each other. In this case, the change in the pressure distribution on objects passing near each other causes a change in the aerodynamic forces. In this research, the numerical investigation of the flow field between two narrow bodies at a close distance and the pressure changes along them at supersonic speeds is done. The simulation was done in two-dimensional and three-dimensional form, and the k-omega sst was used to model the flow turbulence. The two slender bodies were placed next to each other at speeds of Mach 1.5, 3, and 4.5 and at intervals of 2, 3, and 4 times the diameter of the body. they were examined in two modes with relative motion and without relative motion. The results show that as the free flow velocity increases, the shock wave deforms from bow to oblique and is reflected between the two bodies.  Also, as the flow Mach number decreases and the distance between two slender bodies increases, the reflected shock wave becomes weaker. At Mach 1.5 the shock wave reflection between two bodies is not very noticeable, while at Mach 4.5 the shock wave is well reflected between two bodies. In the state of relative motion of two slender bodies, separation occurs at the shock wave reflection points and the number of shock wave reflections decreases compared to the state without relative movement.

The main design goal of thermal control subsystem is to keep the temperature of the satellite equipment within specified margins. Satellite experienced extreme hot and cold conditions during the mission, so it is difficult to choose the materials and surface coatings for these conditions. If design is done to deal with hot conditions, satellite power for keeping warm in cold conditions is increased and this is while supply of required power for heating the satellite in cold conditions is one of the important design concerns. Due to restrictions in space systems for power supply, the value of power for thermal control subsystem should be optimal. This paper describes the process of designing a thermal control subsystem of small satellites using a simple model. In the present study, the thermal design is done by using the optimal choice for the radiator cover. This design has been done in a way that the least amount of heater power is required. For this purpose, optimization and linear programming have been used. Simulation results show that satellite temperature in warm and cold conditions is in the range and this method significantly reduces the amount of required power heater.

Various types of dynamic instabilities in mechanical systems are one of the most important disruptive factors in such structures. Therefore, an accurate study of dynamic instability in beams, as one of the fundamental engineering structures, is of great importance. In this paper, dynamic instability problem of beams made of Functionally Graded Materials (FGM) is investigated. For this purpose, the first-order shear deformation (or the Timoshenko) beam theory with the effects of geometric nonlinearity is considered. Thus, the proposed model has the ability to determine mechanical behavior of thin and thick beams. By considering the energy functions of the system, and implementing the Hamilton’s principle, the governing equations are obtained along with different types of common boundary conditions. The Differential Quadrature Method (DQM), as one of the best-known numerical methods, is used. The nonlinear partial differential equations are written in the form of equivalent ordinary differential equations. Then, considering the harmonic responses for the system, the differential equations are converted to a set of nonlinear algebraic equations. Finally, in order to study the important parameters, various numerical examples are provided. The obtained numerical results are compared with the literature and thus, the validity of the presented formulation and solution methodology is revealed. Also, a comparative study between linear and nonlinear kinematic models shows that the importance of geometric nonlinearity of the model is quite significant.

In this paper, for the first time, a nonlinear analysis of the dynamic instability of a relatively thick curved structure equivalent to a composite wing layer is performed. For this purpose, the wing structure of the aircraft is considered as a relatively thick curved beam and modelling has been done using first-order shear theory. Van Carmen's large non-linear strain relationships have been used in strain components in a curved line environment. One of the most complex instability modes is axial excitation of the curved beam under a harmonic dynamic load despite a static constant value. These static loads (positive or negative) and dynamic harmonic load coefficient have a significant relationship with static buckling load. Considering the dynamic axial load, the dynamic equations governing the system and the equations of the boundary conditions are obtained using the Hamilton principle and the method of calculating the changes, and to solve them, the generalized numerical differential squaring method is used. Also in this paper, for the first time, by solving the final algebraic nonlinear equations, the stability region of a relatively thick curved beam is determined as changes in the excitation frequency in terms of dynamic load. To determine the effects of different parameters on natural frequencies, critical buckling load and beam stability range, different modes including different linear and nonlinear kinematic models, different values of static load, length to beam thickness ratio and radius of curvature along with beam types Flat and curved composite layers have been considered. As one of the most important results, the results show that considering different combinations of fibbers, the amount of curvature as well as the geometric nonlinearity of the material is important and will have a great impact on the predicted responses for the dynamic instability region.

In this study, an anlytical exact solution for tow-dimensional steady-state heat transfer in cylindrical sandwich panel made of graphite-epoxy and poly urethane foam is presented. these sandwich panel is cylindrical shape and simulated a ground to air rocket. the symmetry heat transfer in the longitudinal and radial directions is presented. Finding the most possible solution based on complex boundary conditions and parametric studies is one of the innovative aspects of the present study. To find the most complete solution, Matlab and Abaqus software were used. For this purpose, first the cylinder was reliably analyzed in Abaqus software and then using the formulas of Strom-Liouville theory and Fourier transform heat transfer in Matlab software and the results were compared. Finally, the temperature distribution for each composite layer with the desired fiber angle between the temperature distribution for the zero and 90 angles is presented.

An existing solution for using tactical solid fuel rockets for space purposes is to add a blast tube to the nozzle. Equipping the nozzle with a blast tube, in addition to creating space to add the required subsystems, also makes it easier to stabilize and control the system. To get the best performance from a nozzle, various changes must be made to the nozzle structure.In the present study, the existing nozzle is first analyzed from a geometric and aerodynamic point of view using numerical solution in order to achieve performance and efficiency. Then in order to add the blast tube, two new geometries of the mentioned nozzle are designed and according to the prevailing conditions, the changes in velocity, pressure and temperature of the flow through the nozzle have been studied. The results show that the addition of blast tube causes a decrease in total pressure of less than 2%, which is acceptable considering the benefits obtained.

The use of new materials with suitable mechanical and physical properties in aerial structures can be a good alternative to materials that are commonly used (aluminum alloys, composites, etc). The use of magnesium alloys for various applications and predicting their behavior in simulation software requires complete and accurate identification of the properties and mechanical parameters of the material. One of these identification procedures is digital image correlation method. In this research, the first magnesium plate is prepared in different directions of rolling and then using two-dimensional digital image correlation method, the complete distribution of strain field during uniaxial tensile test in different directions of rolling is extracted and finally strain in three directions of length, width, thickness and anisotropy coefficient in terms of effective strain were calculated. Furthermore, for the first time using the virtual field method, elastic and plastic constants such as modulus of elasticity, Poisson ratio, strength coefficient, strain hardening exponent and yield stress for magnesium sheet in different directions of rolling were calculated.

The role of the nozzle in stability and guidance is very basic and the type of nozzle design has a great impact on the performance of the missile. In the present study, in order to create stability and easier control of the missile and to use the space created to add subsystems, it is intended to add blast tube and thermal insulation and calculate its thickness. For this purpose, a sample nozzle of the existing solid fuel rocket has been considered to add a blast tube and has been numerically analyzed. Then, two new designs of nozzles with and without using blast tube are presented and Using the existing relations analytically, the thickness of the insulators in each case is calculated and The simulation is based on it. Finally, a transient two-dimensional heat transfer analysis was performed in cylindrical coordinates for points inside the nozzle shell (behind the liner and insulation). The results show that increasing the thickness of insulation to a certain extent reduces the temperature of the nozzle shell. In the convergent-divergent nozzle designed with blast tube, this value is 0.11 in the convergent part, 0.07 in the blast tube, 0.068 in the throat and 0.11 in the divergent part. The results also show that unlike the convergent part of the nozzle, in the throat, blast and divergent parts, after passing the effective insulation thickness, the passage of time no longer has a significant effect on the nozzle shell temperature.

In this study, the vibration and stability analysis of functionally graded (FG) doubly curved panels reinforced with nano-graphene platelets (NGPLs) embedded by piezoelectric layers under the influence of aeroelastic force are investigated. Multilayer sandwich doubly curved panel makes of porous materials reinforced with nano-graphene platelets are considered. The NGPLs are assumed to be uniform and non-uniform distribution, as well as three types of targeted porosity distribution that change continuously along the thickness in each layer. This structure is always under influence of external fluid flow and modeled by the piston theory. Based on the higher-order shear deformation theory, the governing equations of motion of doubly curved panels reinforced with NGPL are obtained using extended Hamilton’s principle. Galerkin method is employed to transform the partial differential equations of motion into the ordinary equations. The effect of advanced materials including various patterns of porosity distribution, porosity coefficients, distribution or dispersion of nano graphene platelets, NGPL weight fraction, as well as the effect of structural geometric dimensions on vibrations and dynamic instabilities of structures are studied.

In the present study, optimum design of a semi-active oleopneumatic shock absorber equipped with MR valve in order to use in the airplane main landing gear will be discussed. In the first phase of design, based on the force-displacement diagram design criterion and considering a maximum value of gas pressure, dimensions of the main cylinder, piston cylinder, orifice width, valve radius, and length are determined in the passive state of shock absorber. In the following and in the second phase of design, by the use of obtained information from the first phase, and according to performance criteria of MR valve and the principle of using the maximum working capacity of MR fluid without magnetic saturation of MR valve, the optimum design of MR valve in the constant volume and the active state of shock absorber will be done. In the design procedure, the effect of geometric parameters on shock absorber force is also examined and will be shown that orifice width is the most effective and sensitive geometric parameter in this regard. Optimum design of airplane main landing gear MR shock absorber based on performance criteria of MR valve and investigating the effect of MR valve parameters on shock absorber forces and magnetic properties of valve are the novelties of this research. Due to the importance and the application of MR shock absorber, the results and the achievements of the present study can be used in other industries, in addition to the airplane landing gear as a specific case study.

In this article, vibration and supersonic flutter analyses are studied for trapezoidal sandwich panels. Functionally graded trapezoidal panel as well as reinforced sandwich panel by graphene nano platelets are considered. It is assumed that the graphene platelet (GPL) nanofillers are distributed in the matrix either uniformly or non-uniformly in the direction of thickness. UD, FG-X, FG-V, FG-O and FG-A are the distribution patterns of GPLs. Based on the Kant higher-order theories, the dynamic equations of sandwich panels reinforced with graphene nanoplates  are obtained using extended Hamilton’s principle. Dynamic pressure is estimated according to the quasi-stable theory of supersonic piston. Then, using a transformation of coordinates, the governing equations and boundary conditions are converted from the original coordinates into new computational ones. Finally, the differential squares method (DQM) to obtain the natural frequencies, the shape of the modes, and the critical aerodynamic pressure is used. The effect of different porosity distribution, porosity coefficients, distribution of graphene nanoplates, weight fraction, geometry of graphene nanofillers and geometric dimensions on natural frequencies and system instability behavior are studied.

In this paper, free and forced vibrations of a cylindrical sandwich shell with orthogonal stiffeners using high-order theory were analyzed. The sandwich structure is consists of two orthotropic composite face sheets and a flexible foam core and longitudinal and environmental stiffeners. The face sheets and core are perfectly glued together and there is no relative displacement between them at the interfaces. To analyze this shell under simply supported boundary conditions, the face sheets’ displacements are based on Kant's third-order theory and in the core, the second Frostig’s model is used. The Rayleigh-Ritz method to solve free vibration and the assumed modes method to analyze forced vibration were used. In the forced vibrations section, sinusoidal loading is applied uniformly and radially to the shell. The vibrations of the stiffened sandwich shell are simulated with Abaqus software. Finally, the effect of various parameters as length to radius ratio, thickness to radius ratio, core thickness to total thickness, structure and material of face sheets and core on the vibration response of the structure has been investigated. To validate, the results of free and forced vibrations obtained from the present analysis were compared with the results of other references and Abaqus software.

Shape Memory Alloys (SMAs) are a group of intelligent materials which have distinct and superior properties compared to other alloys. The stress-strain behavior of these materials involves two specific nonlinear phenomena, namely the Shape Memory effect and the quasi-elastic effect. The behavior of the alloy whilst subject to these two phenomena is such that after it enters the plastic state, the material will regain its original form. The research is based on the modeling of these two behaviors of memory alloys in the ABAQUS software using UMAT code. In this study, the simulation of buckling and post-buckling of sandwich panels have been investigated. Preparing a UMAT memory alloy properties code, enables the designer to use any ABAQUS features to analyze the behavior of smart structures made with the shape memory alloy. Also, in this research, the first buckling critical force of the first five modes for different percentages of the alloy in the shell and core have been studied, and then the effects of volumetric percentage change of alloys, distance from neutral axis, fiber angle variations, and finally stability and post-buckling behavior of the memory alloy as the result of initial strain have been investigated. The investigations have shown large changes in the shape memory alloy due to the great recovery stress during the phase shift.

The main purpose of this study is to design a microblowing system to reduce the drag force of an aircraft with SC(2)-0710 supercritical airfoil. For this purpose, the subsonic turbulent flow around the airfoil is simulated by the Fluent software. The numerical simulation has been investigated in cruise conditions at the Mach number of 0.4-0.6 and attack angle of 0º-3º. The turbulent flow is simulated using the SST k-ω turbulent model, and the UDF code is written in C programming language to apply the microblowing technique. The numerical results have been compared with the available experimental and numerical data, and they have had in accordance with each other. The results showed that the friction drag coefficient decreases with increasing the blowing fraction. On the other hand, in attack angle of 0º-2º, the increase in blowing fraction causes to increase the pressure drag coefficient of the airfoil with its microblowing compared to the airfoil without it. In fact, the microblowing has created the reverse effect on the pressure field around the airfoil. The results have been examined for six microblowing positions. It was detected that the greatest reduction in the total drag coefficient has occurred when microblowing has been located near the leading edge on the suction side. Also, it was observed that the lift force decreases by applying the microblowing, but the selected position has the least effect on reducing the lift coefficient. Besides, the results showed that the suitable results (that is, the lowest drag force) have been attained at the attack angle of 3º. Finally, after the numerical studies, the proposed system is designed, and assembly and disassembly maps have been provided.

Vibratory energy in direct contact with different members of the body, in a certain frequency range, can be risky. On the other hand, the maneuvers that the pilot conducted during the flight and the sudden accelerations of g entering the plane on the head and neck, the spinal cord and other organs of the body have adverse effects and disrupt the physiological and psychological actions of the pilot. The first, in this research by choosing a suitable model of the human body and then by extracting the motion equations, using the MATLAB software, the displacement, velocity and acceleration equations for each member of the body are obtained. The new work in this research is putting on the model of seat with cushion made of  foam, cushion made of viscoelastic and with cushion made of viscoelastic despite the pilot's seat suspension system that has a non-linear springs and dampers. The results indicate that at high acceleration of g, the pilot's suspension system has the best performance in damping and absorbing the energy of the system. For small movements that at low frequencies in the range of 0 to 30 Hz are occurred, the seat suspension system is not responding and to check this state, we must examine the functions of biodynamics and plotting them in two states of the body in sitting position and body in sitting position on a foam pad. In this case, the results indicate that in the apparent mass diagram, the use of cushion made of foam caused peak shift in this chart from a frequency in the range of 5 Hz to a frequency in the range of 13 Hz. Therefore, the presence of cushion for health is absolutely necessary.

In this research, the combustion chamber of the liquid propellant engine has been simulated numerically by the computational fluid dynamics (CFD) method. After the simulation, several methods have been proposed to improve the combustion. These include using baffle inside the combustion chamber, increasing the equilibrium ratio and the nano catalyst. In each of these methods, the combustion temperature, mass fraction of fuel and oxidizer, mass fraction of combustion products and mass fraction of pollutants were calculated and compared with a simple chamber. The results showed that using these methods increases the combustion heat by 28.36%, reduces fuel mass fraction by 27.91%, increases mass fraction of complete combustion products including water and nitrogen, and reduces NOx pollutant mass fraction by 26.85 as it is known that NOx pollutant is a product of incomplete combustion and generally reducing it results in better combustion.

In this article, the vibrational behavior of a spinning cylindrical thick shell carrying spring- mass systems and conveying viscos fluid flow under various temperature distributions is investigated. This structure rotates about axial direction and the formulations include the coriolis and centrifugal effects. In addition, this system is conveying viscous fluid, and the related force is calculated by modified Navier–Stokes relation considering slip boundary condition and Knudsen number. The modeled cylindrical thick shell, its equations of motion, and boundary conditions are derived by the principle of minimum total potential energy and based on a new three-dimensional refined higher-order theory (RHOST). For the first time in the present study, attached mass-spring systems has been considered in the rotating cylindrical thick shells conveying viscous fluid flow. The accuracy of the presented model is verified with previous studies. The novelty of the current study is consideration of the rotation, various temperature distributions, mass-spring systems and conveying viscous fluid flow implemented on proposed model using RHOST. Generalized differential quadrature method (GDQM) is presented to discretize the model and to approximate the governing equations. In this study the simply supported conditions has been applied to edges and cantilever boundary conditions has been studied in x=0, L. Finally, the effects of the velocity of viscous fluid flow, angular velocity, temperature changes and spring-mass systems on the critical speed, critical velocity, critical temperature and natural frequency of the structure are investigated.

In this paper, at the first time, free vibration and buckling analysis of the cylindrical sandwich panels whit flexible cores and Magneto-Rheological Fluid Layers for simply supported boundary conditions are studied based on an improved higher order sandwich panel theory. In order to validate the results, the obtained results were compared with those obtained using finite element ABAQUS software. In this investigation, the effects of magnetic field, geometrical parameters such as the length to radius ratio, the core thickness to panel thickness ratio, MR layer thickness to panel thickness ratio and Fiber angle on the natural Frequency, buckling Load and loss factors of sandwich structure were investigated. The results suggest that the natural frequencies, critical buckling loads (eigen values) and the modal transverse displacements (eigen vectors) of the cylindrical sandwich panels whit flexible cores and Magneto-Rheological Fluid Layers in the face sheets are strongly influenced by the intensity of the applied magnetic field.

In this research, behavior of a cylindrical sandwich panel with the flexible core in different boundary conditions, under the influence of follower force are studied. For this purpose, using the theory of the first-order shear deformation, and the principle of Hamilton, the governing equations have been extracted and by using generalized differential quadrature method (GDQM)are solved. The obtained results indicate that by considering simplicity of present method compared to the other methods in the analysis of stability problems of the cylindrical sandwich panel, the present results have the acceptable accuracy.Also, the results review show that the flutter phenomenon occurs in the free and clamp boundary conditions and for other boundary conditions only the divergence phenomenon or static buckling occurs.Another significant result is that increasing the number of composite layers, makes the flutter phenomenon in the cylindrical sandwich panel with the flexible core occurs later

This article for the first time is concerned with effects of parameters as local smart stiffness and smart attached mass dimensions of dynamic behavior of thick laminated plates with attached mass. In deriving governing equations, Gark-Kant’s higher order theory is used and effects of SMA and attached mass`s stiffness taken into account and finally vibration equations of thick plate carrying attached mass contain SMA is reached by using Hamilton`s principal. Then by means of Galerkin method, mass and stiffness matrices are extracted for achieving to a standard eigenvalue vibration problem. In this problem simply supported boundary condition is used for each four edges. Some important parameters such as ratio of local stiffness to stiffness of host structure and smart attached mass dimension on main frequencies of laminated thick plate is studied. A Comparative result with those in published references is presented. These numerical results show that local stiffness due to smart attached mass has a great role on dynamic behavior of thick laminated plates that if SMA didn`t active properly or ignore the effect of attached mass`s stiffness the dynamic response of system will have a lot of changes.

One of the designers concerns is structural failure as a result of stress concentration in the geometrical discontinuities. Understanding the effective parameters on stress concentration and proper selection of these parameters enables the designer to achieve a reliable design. In the analysis of perforated orthotropic plate, the effective parameters on stress distribution around cutouts include fiber angle, load angle, curvature radius of the corner of the cutout, rotation angle of the cutout and at last material of the plate. This paper tries to examine effective parameters on stress analysis of infinite orthotropic plate with central pentagonal cutout with imperialist competitive algorithm (ICA) introduced the optimum parameters to achieve the least amount of stress around the cutout. Like other evolutionary algorithms, ICA is becoming an important tool for optimization and other complex problem solving. The results reported in this review provide evidence of performance achievement of the ICA in terms of both computing time and quality of solution. In this paper, an analytical method has been used to Lekhnitskii theory for circular and elliptical cutouts. Finite element numerical solution is employed to examine the results of present analytical solution. Overlap of the results of the two methods confirms the validity of the presented solution. Results show that by selecting the aforementioned parameters properly, less amounts of stress could be achieved around the cutout leading to an increase in load-bearing capacity of the structure.

In this paper, the behavior of free vibrations and buckling of the thick cylindrical sandwich panel with a flexible core and simply supported boundary conditions using a new improved ýhigh-order sandwich panel theory were investigated. An axial compressive load is applied on the edges of the top and bottom face sheets simultaneously. The formulation used the third-order polynomial description for the displacement fields of thick composite face sheets and for the displacement fields in the core layer based on the displacement field of Frostig's second model. In this model, there are twenty seven degree of freedom. The transverse normal stress in the face sheets and the in-plane stresses in the core were considered .For calculated exact solution, according to thick face sheets, all of the stress components were engaged. The equations of motion and boundary conditions were derived via the Hamilton principle. Moreover, the effect of some important parameters such as those of thickness ratio of the core to panel, the length to radius ratio of the core, cumferential wave number and composite lay-up sequences on free vibration response and buckling of the panel were investigated. In order to validate the results, the obtained results were compared with those obtained using finite element ABAQUS software. The advantage of this paper is simplicity, considering face sheets as thick, exact solution and the considering of important terms such as (1_c/R_c ) in equations.

In this paper, the behavior of curved sandwich beam with a soft flexible core, under low-velocity impact, loaded with environmental thermal effects by pursuing the use of the high order shear deformation theory of sandwich structures is investigated. The Sandwich beam is comprised of composite sheets and foam core. The boundary condition is simply supported by probability of circumferential deflection. Two degrees of freedom for mass- spring model was used for modeling the impact phenomena. In the presented formulation, the first order of shearing deformation theory is used for sheets,the core Displacement field is considered unknown and then by using elasticity theory and compatible condition in the core, sheets common face and the relation of stress-strain core deflection are determined. In order to derive the governing equations of beam structure, the Hamilton principle was used. For validation, the results obtained from this research are compared with the results of other researchers and also the numerical result of ABAQUS software. The comparison of results shows good agreement. The effects of various parameters like impact velocity and mass, environmental temperature, core and sheets thickness and materials on core and sheets deflection and core stress and impact force were studied. The obtained results showed that increasing environmental temperature has a slight effect on impact force, but more effect on beam dynamic response. It is also shown that with increasing the hardness of beam, the energy absorption is reduced.