Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 07 14 Cooperative path planning for leader – follower formation of Multi UAV based on the minimum energy consumption for load transportation Cooperative path planning for leader – follower formation of Multi UAV based on the minimum energy consumption for load transportation 3327 3340 3523 10.22060/mej.2019.15994.6245 FA Hossein Kiaee Mechanical Engineering, Malayer University,Malayer Hamidreza Heidari Mechanical Engineering, Assistant Professor, Malayer,Iran Journal Article 2019 03 13 Today, unmanned aerial vehicles are highly considered for both military and commercial fields due to low cost, high maneuverability, and good survival. One of the most important design challenges of multi-unmanned aerial vehicle systems is mission planning. In the broad class of unmanned aerial vehicles, Quadrotor is an important member. The capabilities of this vehicle in load transportation has attracted the attention of many research groups around the world. In this paper, path planning based on the minimum energy consumption is studied for load transportation. The purpose of the present study is to investigate the effect of proposed cost function in order to obtain optimal path for transporting loads based on reducing the energy consumption of quadrotors. The results indicate the 35.29% energy consumption of multi unmanned aerial vehicle compared to the energy consumption of an individual quadrotor. This also leads to an increase in load carrying capacity. On the other hand, the leader- follower formation is preserved until the end of the path based on the defined relationships. The simulation results illustrate the power and efficiency of the method to overcome the high nonlinearity nature of the problem such as path optimization of multi-rotor helicopters. Today, unmanned aerial vehicles are highly considered for both military and commercial fields due to low cost, high maneuverability, and good survival. One of the most important design challenges of multi-unmanned aerial vehicle systems is mission planning. In the broad class of unmanned aerial vehicles, Quadrotor is an important member. The capabilities of this vehicle in load transportation has attracted the attention of many research groups around the world. In this paper, path planning based on the minimum energy consumption is studied for load transportation. The purpose of the present study is to investigate the effect of proposed cost function in order to obtain optimal path for transporting loads based on reducing the energy consumption of quadrotors. The results indicate the 35.29% energy consumption of multi unmanned aerial vehicle compared to the energy consumption of an individual quadrotor. This also leads to an increase in load carrying capacity. On the other hand, the leader- follower formation is preserved until the end of the path based on the defined relationships. The simulation results illustrate the power and efficiency of the method to overcome the high nonlinearity nature of the problem such as path optimization of multi-rotor helicopters.

https://mej.aut.ac.ir/article_3523_939314105ce8701e67489642ef4d49e8.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 08 22 Determination of the Flutter Instability Boundary of a Composite Wing Using Support Vector Machine Determination of the Flutter Instability Boundary of a Composite Wing Using Support Vector Machine 3341 3352 3553 10.22060/mej.2019.16011.6249 FA Mojtaba Farrokh Faculty of Aerospace Engineering, K. N. Toosi University of Technology, Tehran, Iran 0000-0003-2811-8310 Mohammad Reza Fallah Faculty of Aerospace Engineering, K. N. Toosi University of Technology, Tehran, Iran Journal Article 2019 03 16 The main goal of this article is to train a support vector machine in order to determine the boundary of the composite wing aeroelastic instability. Aircraft wing is modeled as a cantilever beam with two degrees of freedom with thrust as a follower force and mass of the engine. For structural modeling of composite wing the layer theory has been used and in the aerodynamic model, the flow has been assumed to be unsteady, subsonic and incompressible. Using the assumed mode method, the wing dynamic equations of the motion have been derived by Lagrange equations. Linear flutter speed according to the eigenvalues of the motion equations has been calculated. The process of flutter speed calculation has been converted to a computer code in which the number of layers, angle of fibers in each layer, the mass of the engine, and the thrust are input variables and the flutter speed is its output. Determination of the instability boundary using this conventional method is time consuming. In this article, a support vector machine has been adopted to reduce the calculation cost. The results indicate that support vector machine can be used in determining the boundary of the wings flutter instability as an accurate and fast tool. The main goal of this article is to train a support vector machine in order to determine the boundary of the composite wing aeroelastic instability. Aircraft wing is modeled as a cantilever beam with two degrees of freedom with thrust as a follower force and mass of the engine. For structural modeling of composite wing the layer theory has been used and in the aerodynamic model, the flow has been assumed to be unsteady, subsonic and incompressible. Using the assumed mode method, the wing dynamic equations of the motion have been derived by Lagrange equations. Linear flutter speed according to the eigenvalues of the motion equations has been calculated. The process of flutter speed calculation has been converted to a computer code in which the number of layers, angle of fibers in each layer, the mass of the engine, and the thrust are input variables and the flutter speed is its output. Determination of the instability boundary using this conventional method is time consuming. In this article, a support vector machine has been adopted to reduce the calculation cost. The results indicate that support vector machine can be used in determining the boundary of the wings flutter instability as an accurate and fast tool.

https://mej.aut.ac.ir/article_3553_e250c59336b505ed411d455abaa30b4d.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 10 26 Rapid and optimal design of a tail-sitter VTOL ducted fan using a neural network and PSO algorithm Rapid and optimal design of a tail-sitter VTOL ducted fan using a neural network and PSO algorithm 3353 3368 3656 10.22060/mej.2019.16388.6352 FA M. Navabi Shahid Beheshti University Shahram Hosseini Shahid Beheshti University Hadi Shanei Khaje Nasir Toosi University of Technology Journal Article 2019 05 20 Considering the optimal performance and new applications of the ducted fans, especially in unmanned aerial vehicle missions, this paper aims to provide an optimal and rapid method for designing aerial vehicles based on new mathematical and analytical tools which improved and accelerated many of the long engineered processes. In this new fast design method, an initial design is carried out based on the momentum theory. Then by connecting the matrix laboratory and a ducted fan design code software, several optimal design schemes for the duct are extracted by the particle swarm optimization and direct algorithm. The parameters search domain in the algorithm is obtained from the initial design with the momentum theory method and the various results of optimization software, in the case. Finally, in order to obtain the final duct design, according to the optimized information, a multilayer perceptron neural network using an error backpropagation algorithm is trained which in order to obtain the optimal training samples and the network output validations, the neural network is trained and test by 28 airfoils sample. In the redesign loops, without a time-consuming optimization, the trained neural model can extract the duct parameters very quickly, based on the constraints of structure, control design, and mission targets. Considering the optimal performance and new applications of the ducted fans, especially in unmanned aerial vehicle missions, this paper aims to provide an optimal and rapid method for designing aerial vehicles based on new mathematical and analytical tools which improved and accelerated many of the long engineered processes. In this new fast design method, an initial design is carried out based on the momentum theory. Then by connecting the matrix laboratory and a ducted fan design code software, several optimal design schemes for the duct are extracted by the particle swarm optimization and direct algorithm. The parameters search domain in the algorithm is obtained from the initial design with the momentum theory method and the various results of optimization software, in the case. Finally, in order to obtain the final duct design, according to the optimized information, a multilayer perceptron neural network using an error backpropagation algorithm is trained which in order to obtain the optimal training samples and the network output validations, the neural network is trained and test by 28 airfoils sample. In the redesign loops, without a time-consuming optimization, the trained neural model can extract the duct parameters very quickly, based on the constraints of structure, control design, and mission targets.

https://mej.aut.ac.ir/article_3656_14678db82874f1456031fcc05a3afaf6.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 09 28 Single and Multi-objective Optimal Control Design by Genetic Programming and Comparison with Riccati Equation Solutions Single and Multi-objective Optimal Control Design by Genetic Programming and Comparison with Riccati Equation Solutions 3369 3382 3601 10.22060/mej.2019.16014.6258 FA Adel Mohamamdi Faculty of Mechanical Engineering, University of Guilan, Rasht, Iran Nader Nariman-zadeh Department of Mechanical Engineering, Faculty of Mechanical Engineering, University of Guilan, Rasht, Iran Ali Jamali Faculty of Mechanical Enginnering, University of Guilan, Rasht, Iran Journal Article 2019 03 19 Gaining the function of control signal that transfer the system states from initial to desired final conditions is one of the main issues related to the optimal control of modern systems. Optimal control signal is usually obtained by numerical solution (such as dynamic programming algorithm) or analytical solution (like Hamilton-Jacobi-Bellman or Riccati equations approaches) of a single-objective performance index which is a weighted combination of control effort and the fitness of system’s states. However, choosing proper weight coefficients in these approaches needs a lot of trial and error in addition to experience. In this papers, such time consuming procedures are eliminated by using Genetic programming in single and multi-objective optimization process to find those closed-form mathematical solutions of optimal control problems. In this way, it would be readily possible to trade-off among the objective functions using the obtained pareto-front of those solutions based on the needs of the control system designer. It will be shown that in the case of same weighting factors, the solution of the Riccati equation would also be obtained using the approach of this paper Gaining the function of control signal that transfer the system states from initial to desired final conditions is one of the main issues related to the optimal control of modern systems. Optimal control signal is usually obtained by numerical solution (such as dynamic programming algorithm) or analytical solution (like Hamilton-Jacobi-Bellman or Riccati equations approaches) of a single-objective performance index which is a weighted combination of control effort and the fitness of system’s states. However, choosing proper weight coefficients in these approaches needs a lot of trial and error in addition to experience. In this papers, such time consuming procedures are eliminated by using Genetic programming in single and multi-objective optimization process to find those closed-form mathematical solutions of optimal control problems. In this way, it would be readily possible to trade-off among the objective functions using the obtained pareto-front of those solutions based on the needs of the control system designer. It will be shown that in the case of same weighting factors, the solution of the Riccati equation would also be obtained using the approach of this paper

https://mej.aut.ac.ir/article_3601_62e7f2e090fe150ef8deb4466fdc81b3.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 10 06 Simultaneous Optimization of a Convex Sole as a Foot and Hip Trajectory for a Biped Robot with an Ankle without an Additional Degree of Freedom Simultaneous Optimization of a Convex Sole as a Foot and Hip Trajectory for a Biped Robot with an Ankle without an Additional Degree of Freedom 3383 3396 3621 10.22060/mej.2019.16121.6282 FA Fateme Ghafouri BMMS Lab., Mechanical Engineering Dpt., Yazd University Mohammad Hadi Honarvar Faculty member / Mechanical Engineering Dpt., Yazd university 0000-0002-4464-7194 Mohammad Mahdi Jalili Bahabadi Faculty member / Mechanical engineering dpt., Yazd University Journal Article 2019 04 14 Foot geometry greatly affects gait characteristics and it determinants. This research deals with analyzing gait when foot-ground contact occurs on a convex curve namely sole curve. Designing sole curve is also included in this work, targeting least energy consumption during walking on a flat ground. The famous point mass model has been improved to a model with a moving contact point on a convex sole without adding an extra degree of freedom. As the convex sole is added to the model, motion reconstruction is needed because of the effects of the model’s geometry on optimized gait cycle. Therefore, in this research, simultaneous optimization has been done to find the optimized sole shape and hip trajectory. To avoid high computational cost, optimization variables have been coded into vectors with limited dimensions and obtained by using particle swarm optimization and steepest descent algorithm together. Kinematic constraints and requirements of a continues, repetitive and symmetrical locomotion have been driven and satisfied during optimization. The results have been shown that optimization of the sole shape and hip trajectory has great effects on the cost function Foot geometry greatly affects gait characteristics and it determinants. This research deals with analyzing gait when foot-ground contact occurs on a convex curve namely sole curve. Designing sole curve is also included in this work, targeting least energy consumption during walking on a flat ground. The famous point mass model has been improved to a model with a moving contact point on a convex sole without adding an extra degree of freedom. As the convex sole is added to the model, motion reconstruction is needed because of the effects of the model’s geometry on optimized gait cycle. Therefore, in this research, simultaneous optimization has been done to find the optimized sole shape and hip trajectory. To avoid high computational cost, optimization variables have been coded into vectors with limited dimensions and obtained by using particle swarm optimization and steepest descent algorithm together. Kinematic constraints and requirements of a continues, repetitive and symmetrical locomotion have been driven and satisfied during optimization. The results have been shown that optimization of the sole shape and hip trajectory has great effects on the cost function

https://mej.aut.ac.ir/article_3621_c5b270a763686e776039618cc709f3a6.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 10 10 Design and Kinematics Analysis of a Novel Cable Driven Parallel Active Joint Design and Kinematics Analysis of a Novel Cable Driven Parallel Active Joint 3397 3410 3628 10.22060/mej.2019.16308.6332 FA Mohammad Hosein Ghadiri Department of Mechanical Engineering, Parand Brabch, Islamic Azad University, Parand, Iran. Rambod Rastegari Department of Mechanical Engineering, Parand Brabch, Islamic Azad University, Parand, Iran. Journal Article 2019 05 12 Cable driven parallel mechanisms have a vast range of advantages and application due to their minimal mass and inertial effects. Normally they consist an outer fixed frame and an inner mobile platform. In this paper, a completely novel configuration of these mechanisms has been presented. In this configuration outer frame is considered as mobile platform and inner frame has been fixed. The mobile frame is attached to the fixed frame by the 8 cables and moves through the tensioning and lengthening of the cables. This new structure can be applied to the wrist mechanism, motion simulators, power balances, haptic interfaces, and etc. Since the parallel mechanism is a closed system, forward kinematics cannot be solved analytically. Several methods can be used to solve the forward kinematic of parallel mechanisms, including numerical optimization methods, in which the Newton-Raphson numerical method is used here. cables must always be in tension. Hence, a tension optimization algorithm is presented and, by solving this algorithm for all possible positions, the workspace of the mechanism is obtained. The results show that the Newton-Raphson method has an appropriate convergence rate and the tension algorithm is capable of determining the forces of the cables in the desired range. Cable driven parallel mechanisms have a vast range of advantages and application due to their minimal mass and inertial effects. Normally they consist an outer fixed frame and an inner mobile platform. In this paper, a completely novel configuration of these mechanisms has been presented. In this configuration outer frame is considered as mobile platform and inner frame has been fixed. The mobile frame is attached to the fixed frame by the 8 cables and moves through the tensioning and lengthening of the cables. This new structure can be applied to the wrist mechanism, motion simulators, power balances, haptic interfaces, and etc. Since the parallel mechanism is a closed system, forward kinematics cannot be solved analytically. Several methods can be used to solve the forward kinematic of parallel mechanisms, including numerical optimization methods, in which the Newton-Raphson numerical method is used here. cables must always be in tension. Hence, a tension optimization algorithm is presented and, by solving this algorithm for all possible positions, the workspace of the mechanism is obtained. The results show that the Newton-Raphson method has an appropriate convergence rate and the tension algorithm is capable of determining the forces of the cables in the desired range.

https://mej.aut.ac.ir/article_3628_3e524bf740dc8cfd3f49bd3e96daee6e.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 10 14 Design of Three-dimensional Robust Guidance Law Using Adaptive Dynamic Programming with Input Saturation Constraint Design of Three-dimensional Robust Guidance Law Using Adaptive Dynamic Programming with Input Saturation Constraint 3411 3424 3634 10.22060/mej.2019.16834.6451 FA Saeid Khan Kalantari Isfahan university of technology Iman Izadi Department of Electrical and Computer Engineering, Isfahan University of Technology Farid Sheikholeslam Department of Electrical and Computer Engineering, Isfahan University of Technology Journal Article 2019 07 27 In this paper, a three-dimensional robust guidance law for an interceptor considering input saturation and first-order dynamic for the autopilot system is designed. To attain this goal, first, modeling of the system in three-dimensional spherical coordination using engagement basics has been derived and after that, the appropriate cost function for a collision of interceptor and target considering actuator constraints and in absence of target movement information has been formulated. According to robust control literature for achieving this type of guidance laws, Hamilton-Jacobi-Isaacs differential equation inequality should be solved which unfortunately does not have a closed-form solution in our problem. Therefore, to overcome this challenge, using adaptive dynamic programming theory for solving acquired Hamilton-Jacobi-Isaacs, an algorithm for designing robust guidance law has been presented. Simplification of the differential inequality and also satisfying the robustness of the controller to different unknown target movemnts, are the most important features of the proposed algorithm. Various simulations for targets with different movements and comparison of the proposed method with conventional augmented proportional navigation, show the effectiveness of the designed three-dimensional robust guidance law. In this paper, a three-dimensional robust guidance law for an interceptor considering input saturation and first-order dynamic for the autopilot system is designed. To attain this goal, first, modeling of the system in three-dimensional spherical coordination using engagement basics has been derived and after that, the appropriate cost function for a collision of interceptor and target considering actuator constraints and in absence of target movement information has been formulated. According to robust control literature for achieving this type of guidance laws, Hamilton-Jacobi-Isaacs differential equation inequality should be solved which unfortunately does not have a closed-form solution in our problem. Therefore, to overcome this challenge, using adaptive dynamic programming theory for solving acquired Hamilton-Jacobi-Isaacs, an algorithm for designing robust guidance law has been presented. Simplification of the differential inequality and also satisfying the robustness of the controller to different unknown target movemnts, are the most important features of the proposed algorithm. Various simulations for targets with different movements and comparison of the proposed method with conventional augmented proportional navigation, show the effectiveness of the designed three-dimensional robust guidance law.

https://mej.aut.ac.ir/article_3634_e2eabaf96372e20a9e3d4b5f83723a61.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 10 16 Optimal Vibration Reduction of the Flexible Shaft-Disk-Blades System Using a Set of Nonlinear Energy Sink Optimal Vibration Reduction of the Flexible Shaft-Disk-Blades System Using a Set of Nonlinear Energy Sink 3425 3444 3639 10.22060/mej.2019.16274.6319 FA Jafar Aghayari PhD Candidate, Faculty of Mechanical & Energy Engineering, Shahid Beheshti University, Tehran, Iran Pedram Safarpour Faculty of Mechanical &amp; Energy Engineering,Shahid Beheshti University Abbas Rahi Assistant professor, Faculty of Mechanical &amp; Energy Engineering, Shahid Beheshti University, A.C., Tehran, Iran 0000-0002-7123-1741 Saeed Bab Department of Mechanical Rotary equipment, Niroo Reseach Institute, Tehran, Iran Journal Article 2019 05 05 In this paper, the application of nonlinear energy sinks for indirect vibration reduction of the blades in a flexible shaft-disk-blades system of a real steam turbine is conducted. 37 packets of seven-connected blades are mounted on the disk. The cyclic symmetric finite element analysis is employed to perform frequency analysis of this system. For the 11th mode, which is a combination of the second bending mode of shaft and the third bending mode of disk-blades, a two degrees of freedom reduced order model is identified. Nonlinear energy sinks with a small mass, an essential nonlinear stiffness and a linear damping are installed on the reduced order model in the anti-node position of the disk. The Runge-Kutta method is used to solve the nonlinear equations of motion numerically. Optimum stiffness and damping of the absorbers are determined to minimize the vibration amplitude of the blades. The results show that the occurrence of strongly modulated response around the resonance leads to the desired vibration reduction of the blades. If the absorbers have large nonlinear stiffness or low damping, a saddle-node bifurcation and a wide island is appeared in the negative detuning frequencies, and the blade could experience large amplitude periodic oscillation. In this paper, the application of nonlinear energy sinks for indirect vibration reduction of the blades in a flexible shaft-disk-blades system of a real steam turbine is conducted. 37 packets of seven-connected blades are mounted on the disk. The cyclic symmetric finite element analysis is employed to perform frequency analysis of this system. For the 11th mode, which is a combination of the second bending mode of shaft and the third bending mode of disk-blades, a two degrees of freedom reduced order model is identified. Nonlinear energy sinks with a small mass, an essential nonlinear stiffness and a linear damping are installed on the reduced order model in the anti-node position of the disk. The Runge-Kutta method is used to solve the nonlinear equations of motion numerically. Optimum stiffness and damping of the absorbers are determined to minimize the vibration amplitude of the blades. The results show that the occurrence of strongly modulated response around the resonance leads to the desired vibration reduction of the blades. If the absorbers have large nonlinear stiffness or low damping, a saddle-node bifurcation and a wide island is appeared in the negative detuning frequencies, and the blade could experience large amplitude periodic oscillation.

https://mej.aut.ac.ir/article_3639_ba304f3809ed31d0ad97b5a2b5df2a39.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 07 15 Nonlinear Flapping-Torsional Free Vibration Analysis of Rotating Beams Considering the Coriolis Force Nonlinear Flapping-Torsional Free Vibration Analysis of Rotating Beams Considering the Coriolis Force 3445 3462 3525 10.22060/mej.2019.16013.6251 FA Hadi Arvin Department of Mechanical Engineering, Faculty of Engineering, Shahrekord University Journal Article 2019 03 16 The nonlinear free flapping-torsional vibration of rotating beams is investigated in this paper. The presented equations are based on the exact geometrical formulation in conjunction with the Cosserat theory for rods. The equations of motion are reduced to the flapping and torsional equations of motion for symmetric rectangular beams by neglecting the shear deformation. The governing equations are coupled to each other with the non-homogenous boundary conditions. By employing the direct method of multiple scales the effective nonlinearity coefficients of nonlinear natural frequencies are extracted. After validation of the current results, the effects of the rotating speed on the type and the value of the effective nonlinearity coefficient of natural frequencies are examined. The sign of the effective nonlinearity coefficient demonstrates the softening or hardening treatment of the corresponding nonlinear natural frequencies. It is concluded that ignoring the flapping-torsional coupling due to the Coriolis force, for odd modes makes some errors in the magnitude of effective nonlinearity but the type of nonlinearity is predicted correctly. On the other hand, in the even modes for average to high rotation speed in addition to incorrect estimation of the magnitude of effective nonlinearity the different type of nonlinearity is also predicted. The nonlinear free flapping-torsional vibration of rotating beams is investigated in this paper. The presented equations are based on the exact geometrical formulation in conjunction with the Cosserat theory for rods. The equations of motion are reduced to the flapping and torsional equations of motion for symmetric rectangular beams by neglecting the shear deformation. The governing equations are coupled to each other with the non-homogenous boundary conditions. By employing the direct method of multiple scales the effective nonlinearity coefficients of nonlinear natural frequencies are extracted. After validation of the current results, the effects of the rotating speed on the type and the value of the effective nonlinearity coefficient of natural frequencies are examined. The sign of the effective nonlinearity coefficient demonstrates the softening or hardening treatment of the corresponding nonlinear natural frequencies. It is concluded that ignoring the flapping-torsional coupling due to the Coriolis force, for odd modes makes some errors in the magnitude of effective nonlinearity but the type of nonlinearity is predicted correctly. On the other hand, in the even modes for average to high rotation speed in addition to incorrect estimation of the magnitude of effective nonlinearity the different type of nonlinearity is also predicted.

https://mej.aut.ac.ir/article_3525_da9e6a4a4aeca98588e4dd77ceb37695.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 08 13 Free and Forced Vibration Analysis of Piezoelectric Patches Based on Semi-Analytic Method of Scaled Boundary Finite Element Method Free and Forced Vibration Analysis of Piezoelectric Patches Based on Semi-Analytic Method of Scaled Boundary Finite Element Method 3463 3484 3547 10.22060/mej.2019.16027.6255 FA Naserodin Sepehry صنعتی شاهرود-مهندسی مکانیک Mohammad Ehsani New Technologies Research Center (NTRC), Amirkabir University of Technology Mahnaz Shamshirsaz New Technologies Research Center (NTRC), Amirkabir University of Technology 0000-0002-4400-4930 Journal Article 2019 03 17 Development of a precise mathematical model of piezoelectric patches plays an important role in comprehending their operational mechanisms as well as developing new techniques based on their coupled electro-mechanical behavior. While, high computational cost of available numerical methods which are able to simulate vibrational behavior of piezoelectric patches, especially at high frequencies, is considered as a serious challenge in this area. The purpose of this study is to use a novel semi[1]analytical method, called Scaled Boundary Finite Element Method, to analyze free and forced vibration of piezoelectric patches. In order to evaluate the accuracy of this method in modeling of different problems occurred in structural health monitoring and fracture mechanics, the free and forced vibration of a piezoelectric patch, a piezoelectric patch attached to an aluminum structure, a piezoelectric patch with a circular hole and a cracked piezoelectric patch was analyzed as four case studies. Comparison of convergence rate of scaled boundary finite element method and finite element method indicates that the former provides exact results with much less degrees of freedom. In addition, proper matching of results demonstrates the capability of scaled boundary finite element method to model a variety of problems accurately at a very low computational cost. Development of a precise mathematical model of piezoelectric patches plays an important role in comprehending their operational mechanisms as well as developing new techniques based on their coupled electro-mechanical behavior. While, high computational cost of available numerical methods which are able to simulate vibrational behavior of piezoelectric patches, especially at high frequencies, is considered as a serious challenge in this area. The purpose of this study is to use a novel semi[1]analytical method, called Scaled Boundary Finite Element Method, to analyze free and forced vibration of piezoelectric patches. In order to evaluate the accuracy of this method in modeling of different problems occurred in structural health monitoring and fracture mechanics, the free and forced vibration of a piezoelectric patch, a piezoelectric patch attached to an aluminum structure, a piezoelectric patch with a circular hole and a cracked piezoelectric patch was analyzed as four case studies. Comparison of convergence rate of scaled boundary finite element method and finite element method indicates that the former provides exact results with much less degrees of freedom. In addition, proper matching of results demonstrates the capability of scaled boundary finite element method to model a variety of problems accurately at a very low computational cost.

https://mej.aut.ac.ir/article_3547_e6ba70fc093b4ce912d769ede1ceeba8.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 09 12 Transient Response of Annular Sandwich Plate with Functional Graded Core Combined with Piezoelectric Layers Transient Response of Annular Sandwich Plate with Functional Graded Core Combined with Piezoelectric Layers 3485 3502 3570 10.22060/mej.2019.15617.6172 FA Habib Arabi Department of Mechanic , University Campus 2, University of Guilan, Rasht, Iran Ahmad Bagheri professor, Department of Dynamic-Control , Faculty of Mechanic, University of Guilan, Rasht, Iran Gholamreza Zarepour assistant professor, Department of Dynamic-Control , Faculty of Mechanic, University of Guilan, Rasht, Iran Journal Article 2019 01 16 In this study, the transient response of the symmetric annular sandwich plate, with functionally graded core and piezoelectric layers, is investigated. It is also assumed that the sandwich plate is under external harmonic force and electrical voltage. Based on the power function model, it is assumed that the properties of the core material vary in the direction of the core thickness. To express the displacement field, the third order shear deformation theory is used. By use of the Hamilton principle, the structural equations are obtained in terms of displacement components and solved using the differential quadrature method. Finally, the time response is evaluated in terms of variations in effective parameters such as internal radius, power function index, core thickness and external voltage. The simulation results showed that the amplitude of the oscillations decreases when the internal radius of plate to be increased, in the desired time interval. In addition, by increasing the index parameter of the power function, the time response range increases. Finally, by applying external electrical voltage, the vibration amplitude of plate reduced and this advantage is used in control of vibrating systems. In this study, the transient response of the symmetric annular sandwich plate, with functionally graded core and piezoelectric layers, is investigated. It is also assumed that the sandwich plate is under external harmonic force and electrical voltage. Based on the power function model, it is assumed that the properties of the core material vary in the direction of the core thickness. To express the displacement field, the third order shear deformation theory is used. By use of the Hamilton principle, the structural equations are obtained in terms of displacement components and solved using the differential quadrature method. Finally, the time response is evaluated in terms of variations in effective parameters such as internal radius, power function index, core thickness and external voltage. The simulation results showed that the amplitude of the oscillations decreases when the internal radius of plate to be increased, in the desired time interval. In addition, by increasing the index parameter of the power function, the time response range increases. Finally, by applying external electrical voltage, the vibration amplitude of plate reduced and this advantage is used in control of vibrating systems.

https://mej.aut.ac.ir/article_3570_43b52842663fa6e4100c72751d08de6f.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 06 25 Uncertainty Propagation Analysis in Free Vibration of Uncertain Composite Plate Using Stochastic Finite Element Method Uncertainty Propagation Analysis in Free Vibration of Uncertain Composite Plate Using Stochastic Finite Element Method 3503 3520 3485 10.22060/mej.2019.15892.6223 FA Mahdi Fakoor Hadi Parviz University of Tehran Arash Abbasi Iranian space research center Journal Article 2019 02 28 Material uncertainty is more widespread in composite material than the other engineering materials. This uncertainty makes response of these types of structures to be nondeterministic. In order to predict structural reliability, uncertainty in structural responses must be quantified. There is not a reported research in the literature studying free vibration of composite plate with spatially stochastic material properties. In this research, physical and mechanical properties of composite plate including tensile and shear modulus and density of the plate are modeled as stochastic Gaussian fields. Assuming exponential auto covariance kernels for aforementioned stochastic fields, they are discretized to two parts, including deterministic and stochastic parts employing Karhunen-Loeve theorem. Assuming linear form of strains, mechanical strains are defined applying first order shear deformation theory. Kinetic and potential energy of the composite plate is extracted using finite element formulation. Stochastic finite element formulation is derived employing Hamilton’s principle and Euler-Lagrange and equations are verified with the results in the literature for deterministic case. After verification of formulation, material uncertainty effects on uncertainty of natural frequencies are investigated using Monte Carlo simulation. Results show that there is a linear relation between coefficient of variation of uncertain properties and coefficient of variation of stochastic natural frequencies. Material uncertainty is more widespread in composite material than the other engineering materials. This uncertainty makes response of these types of structures to be nondeterministic. In order to predict structural reliability, uncertainty in structural responses must be quantified. There is not a reported research in the literature studying free vibration of composite plate with spatially stochastic material properties. In this research, physical and mechanical properties of composite plate including tensile and shear modulus and density of the plate are modeled as stochastic Gaussian fields. Assuming exponential auto covariance kernels for aforementioned stochastic fields, they are discretized to two parts, including deterministic and stochastic parts employing Karhunen-Loeve theorem. Assuming linear form of strains, mechanical strains are defined applying first order shear deformation theory. Kinetic and potential energy of the composite plate is extracted using finite element formulation. Stochastic finite element formulation is derived employing Hamilton’s principle and Euler-Lagrange and equations are verified with the results in the literature for deterministic case. After verification of formulation, material uncertainty effects on uncertainty of natural frequencies are investigated using Monte Carlo simulation. Results show that there is a linear relation between coefficient of variation of uncertain properties and coefficient of variation of stochastic natural frequencies.

https://mej.aut.ac.ir/article_3485_dfeb9598fbfb97cc6bbcc0aff2c785d6.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 09 28 Nanovoid dynamics based on temperature dependent Young modulus and void formation energy in Nickel: a phase field study Nanovoid dynamics based on temperature dependent Young modulus and void formation energy in Nickel: a phase field study 3521 3532 3600 10.22060/mej.2019.16169.6293 FA Mohammad Sadegh Ghaedi Mechanical Engineering Group, Pardis College, Isfahan University of Technology, Mahdi Javanbakht Isfahan University of Technology, Department of Mechanical Engineering Journal Article 2019 04 20 In the present work, a phase field method is used to study the growth/annihilation of nanovoids under thermal and mechanical loadings. To do so, the coupled system of the Cahn-Hilliard and elasticity equations is solved using the nonlinear finite element method in 2 dimensional. This coupling is due to the presence of elastic energy in the Cahn-Hilliard free energy and the dependence of total strain on the void misfit strain. The novel point in the present physical model is including the temperature dependence of elastic properties and void formation energy. Then, examples of nanovoid structure evolution are presented consisting of planar gas-solid interface formation and evolution, growth/annihilation of circular nanovoids at different temperatures, growth/annihilation of nanovoids under biaxial compression and at different temperatures and nanovoid structure evolution with initially, randomly distributed void pattern. The obtained results show a faster growth with larger amounts of void concentration at lower temperatures. Also, the stress field significantly varies during nanovoids growth/ annihilation especially inside the solid-gas interface and its value depends on the nanovoid size and the concentration. In the present work, a phase field method is used to study the growth/annihilation of nanovoids under thermal and mechanical loadings. To do so, the coupled system of the Cahn-Hilliard and elasticity equations is solved using the nonlinear finite element method in 2 dimensional. This coupling is due to the presence of elastic energy in the Cahn-Hilliard free energy and the dependence of total strain on the void misfit strain. The novel point in the present physical model is including the temperature dependence of elastic properties and void formation energy. Then, examples of nanovoid structure evolution are presented consisting of planar gas-solid interface formation and evolution, growth/annihilation of circular nanovoids at different temperatures, growth/annihilation of nanovoids under biaxial compression and at different temperatures and nanovoid structure evolution with initially, randomly distributed void pattern. The obtained results show a faster growth with larger amounts of void concentration at lower temperatures. Also, the stress field significantly varies during nanovoids growth/ annihilation especially inside the solid-gas interface and its value depends on the nanovoid size and the concentration.

https://mej.aut.ac.ir/article_3600_8d7628dd7a710c8638dbd22d4421ee46.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 10 12 Optimal Adaptive Super-Twisting Sliding Mode Control of an Lower Limb Exoskeleton Optimal Adaptive Super-Twisting Sliding Mode Control of an Lower Limb Exoskeleton 3533 3548 3631 10.22060/mej.2019.16292.6321 FA Majid Mokhtari School of Mechanical engineering, ShahidBeheshti University, Tehran, Iran Mostafa Taghizadeh shahid beheshti university Mahmood Mazare School of Mechanical Engineering, ShahidBeheshtiUniversity, Tehran, Iran. Journal Article 2019 05 08 Disturbance and bounded uncertainty are the most important factors which can be degrade efficient performance of the lower limb exoskeleton. While sliding mode control is a robust control approach against such disturbances, however, by applying the boundary layer in spite of chattering phenomenon, robust performance becomes feeble. In order to overcome this drawback, high order sliding mode algorithms like supper twisting has been proposed in which, chattering phenomenon is mitigated by eliminating the boundary layer. In this paper, an adaptive supper twisting sliding mode control is proposed for a lower limb exoskeleton robot in which the sliding variable and its derivative tend to zero continuously in presence of the disturbance and bounded uncertainty. In addition, the desired trajectory of the upper limb is determined so that in each moment the stability of the robot is guaranteed based on zero momentum point criterion. To achieve maximum stability and minimum error in tracking of the desired trajectories, the controller parameters and the upper limb desired trajectory parameters are optimized using the Harmony Search algorithm. Robot is modeled in ADAMS and then control inputs are applied to the Adams model. Finally, Performance of two controllers is compared. Simulation results reveal the effectiveness of the proposed controller rather than the optimal sliding mode controller. Disturbance and bounded uncertainty are the most important factors which can be degrade efficient performance of the lower limb exoskeleton. While sliding mode control is a robust control approach against such disturbances, however, by applying the boundary layer in spite of chattering phenomenon, robust performance becomes feeble. In order to overcome this drawback, high order sliding mode algorithms like supper twisting has been proposed in which, chattering phenomenon is mitigated by eliminating the boundary layer. In this paper, an adaptive supper twisting sliding mode control is proposed for a lower limb exoskeleton robot in which the sliding variable and its derivative tend to zero continuously in presence of the disturbance and bounded uncertainty. In addition, the desired trajectory of the upper limb is determined so that in each moment the stability of the robot is guaranteed based on zero momentum point criterion. To achieve maximum stability and minimum error in tracking of the desired trajectories, the controller parameters and the upper limb desired trajectory parameters are optimized using the Harmony Search algorithm. Robot is modeled in ADAMS and then control inputs are applied to the Adams model. Finally, Performance of two controllers is compared. Simulation results reveal the effectiveness of the proposed controller rather than the optimal sliding mode controller.

https://mej.aut.ac.ir/article_3631_fd4c2dc64ccb8496e6f1f94c85f30d06.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 10 14 Simulation of Biceps Femoris Muscle Growth Based on Stretch Using a Multiscale Model Simulation of Biceps Femoris Muscle Growth Based on Stretch Using a Multiscale Model 3549 3566 3633 10.22060/mej.2019.15643.6175 FA Saeed Javadi Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad Abdolrahman Jaamialahmadi Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad 0000-0001-8747-2884 Ali Reza Danesh Mehr Mechanical Engineering, Tehran University Mohaddeseh Azadvari Tehran University of Medical Sciences Saeid Nekoonam Tehran University of Medical Sciences Journal Article 2019 01 17 Understanding the process of muscle tissue growth is important to professionals who are involved in curing musculoskeletal disorders, physical medicine and rehabilitation specialists and orthopedic surgeons. This article investigates the development of a musculoskeletal cell and also determining the vulnerable areas of biceps femoris muscles due to passive strains applied on it. By decomposing the deformation gradient tensor to two parts, the elastic and growth, the finite growth relations have been applied for an isotropic hyperelastic muscle material behavior. Consequently, the continuum relations were combined with the growth evolution equation whrer a series of mechanobiological relations were obtained. To solve them, a FORTRAN user-defined material subroutine (UMAT) for the finite element Abaqus software was written and executed. The biceps femoris – long head muscle was simulated based on a 6-week period assuming as a cylinder with 10% increase in initial length. Results of the simulation indicate that maximum strains occur in the surfaces, not inside the muscle. They reach 1.045 near the proximal muscle-tendon junction in the posterior layer and 1.06 in distal muscle-junction in interior surface. Also, these results can help a correct and optimal treatment, patient’s rehabilitation and orthopedic surgeries. Understanding the process of muscle tissue growth is important to professionals who are involved in curing musculoskeletal disorders, physical medicine and rehabilitation specialists and orthopedic surgeons. This article investigates the development of a musculoskeletal cell and also determining the vulnerable areas of biceps femoris muscles due to passive strains applied on it. By decomposing the deformation gradient tensor to two parts, the elastic and growth, the finite growth relations have been applied for an isotropic hyperelastic muscle material behavior. Consequently, the continuum relations were combined with the growth evolution equation whrer a series of mechanobiological relations were obtained. To solve them, a FORTRAN user-defined material subroutine (UMAT) for the finite element Abaqus software was written and executed. The biceps femoris – long head muscle was simulated based on a 6-week period assuming as a cylinder with 10% increase in initial length. Results of the simulation indicate that maximum strains occur in the surfaces, not inside the muscle. They reach 1.045 near the proximal muscle-tendon junction in the posterior layer and 1.06 in distal muscle-junction in interior surface. Also, these results can help a correct and optimal treatment, patient’s rehabilitation and orthopedic surgeries.

https://mej.aut.ac.ir/article_3633_acf922154627f6788918f03c42b123cd.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 10 16 Study of Young’s Modulus and Failure Strength of Polyurethane-Based Binary Polymer Composite Structures Based on Stress-Strain Curve for Tissue Engineering Vascular Graft Application Study of Young’s Modulus and Failure Strength of Polyurethane-Based Binary Polymer Composite Structures Based on Stress-Strain Curve for Tissue Engineering Vascular Graft Application 3567 3582 3638 10.22060/mej.2019.16159.6288 FA Nafiseh Jirofti Chemical Engineering Department, University of Sistan and Baluchestan, Zahedan, Iran Davod Mohebbi-Kalhori Chemical Engineering Department, University of Sistan and Baluchestan, Zahedan, Iran Afra Hajdizadeh Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran Abdolreza Samimi aC Chemical Engineering Department, University of Sistan and Baluchestan, Zahedan, Iran Journal Article 2019 04 17 The coronary arteries are of the important cardiovascular diseases. The autograft is the main treatment for this problem, but in many patients, the autografts are not applicable. So, due to a large number of requirements, it needs to find suitable replacements for diseases of blood vessels. Nanomaterial structures are highly contributive in tissue engineering vascular scaffolds due to their ability in mimicking the nanoscale dimension of the natural extracellular matrix and the existing mechanical match between the native vessel and the structure. The aim of this research was developing and mechanically improving nanofibrous hybrid structures using blend electrospinning methods with different ratios of the polyethylene terephthalate, polyurethane and polycaprolactone. The morphological and mechanical properties of all fabricated structures were evaluated. The average fiber diameter, porosity, stress and Young’s modulus changes’ range in composite structures (polycaprolactone/polyurethane and polyethylene terephthalate/polyurethane ) were obtained 343 ± 94 to 382 ± 83 nm, 58.6 ± 3.12 to 81 ± 1.7 %, 2.66 ± 0.39 to 19.05 ± 3.2 MPa and 3.18 ± 0.09 to 41.4± 3.31 MPa, respectively. According to results, the fabricated scaffolds as well as polyethylene terephthalate/polyurethane structure exhibited suitable mechanical and biological properties and clinical requirements as a small-diameter vascular graft. The coronary arteries are of the important cardiovascular diseases. The autograft is the main treatment for this problem, but in many patients, the autografts are not applicable. So, due to a large number of requirements, it needs to find suitable replacements for diseases of blood vessels. Nanomaterial structures are highly contributive in tissue engineering vascular scaffolds due to their ability in mimicking the nanoscale dimension of the natural extracellular matrix and the existing mechanical match between the native vessel and the structure. The aim of this research was developing and mechanically improving nanofibrous hybrid structures using blend electrospinning methods with different ratios of the polyethylene terephthalate, polyurethane and polycaprolactone. The morphological and mechanical properties of all fabricated structures were evaluated. The average fiber diameter, porosity, stress and Young’s modulus changes’ range in composite structures (polycaprolactone/polyurethane and polyethylene terephthalate/polyurethane ) were obtained 343 ± 94 to 382 ± 83 nm, 58.6 ± 3.12 to 81 ± 1.7 %, 2.66 ± 0.39 to 19.05 ± 3.2 MPa and 3.18 ± 0.09 to 41.4± 3.31 MPa, respectively. According to results, the fabricated scaffolds as well as polyethylene terephthalate/polyurethane structure exhibited suitable mechanical and biological properties and clinical requirements as a small-diameter vascular graft.

https://mej.aut.ac.ir/article_3638_895daa408f494ad58006c47a30f51c1f.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 52 12 2019 07 30 Mechanical Behavior of Temperature-Sensitive Hydrogel Considering Functionally Graded Characteristics Mechanical Behavior of Temperature-Sensitive Hydrogel Considering Functionally Graded Characteristics 3583 3594 3535 10.22060/mej.2019.16172.6294 FA Mohammad Shojaeifard School of Mechanical Engineering, College of Engineering, University of Tehran, Iran Mostafa Baghani دانشگاه تهران-مهندسی مکانیک Journal Article 2019 05 01 Hydrogels are 3 dimensional polymeric networks containing cross-linked chains which respond severely to the exterior stimuli and absorb a great amount of solution and swell. The functionally graded temperature-sensitive hydrogel is one of the most applicable materials to be used in the industry. Thus, to study the mechanical behavior of these materials, an energy density function is introduced which includes network stretch energy and mixing part. Considering the properties variation along the thickness direction, bending of functionally graded temperature-sensitive hydrogels is solved analytically under plane strain assumption. Verifying the presented analytical procedure, the results of this approach is compared with the outcomes of finite element method. To solve diverse problems by finite element method, UHYPER subroutine has been verified in the free-swelling problem. Next, the radius and stresses are studied by both methods for functionally graded temperature-sensitive hydrogels. Finally, according to the importance of factors such as semi-angle and bending curvature in industrial designs, these factors are investigated by changing the temperature in a range of 320 to 288 Kelvin. The continuity of the radial and tangential stresses field is the other reason for utilizing functionally graded hydrogels, while the multi-layer hydrogels do not have continuous stress fields. Hydrogels are 3 dimensional polymeric networks containing cross-linked chains which respond severely to the exterior stimuli and absorb a great amount of solution and swell. The functionally graded temperature-sensitive hydrogel is one of the most applicable materials to be used in the industry. Thus, to study the mechanical behavior of these materials, an energy density function is introduced which includes network stretch energy and mixing part. Considering the properties variation along the thickness direction, bending of functionally graded temperature-sensitive hydrogels is solved analytically under plane strain assumption. Verifying the presented analytical procedure, the results of this approach is compared with the outcomes of finite element method. To solve diverse problems by finite element method, UHYPER subroutine has been verified in the free-swelling problem. Next, the radius and stresses are studied by both methods for functionally graded temperature-sensitive hydrogels. Finally, according to the importance of factors such as semi-angle and bending curvature in industrial designs, these factors are investigated by changing the temperature in a range of 320 to 288 Kelvin. The continuity of the radial and tangential stresses field is the other reason for utilizing functionally graded hydrogels, while the multi-layer hydrogels do not have continuous stress fields.

https://mej.aut.ac.ir/article_3535_b99d193b66a6542917d2b7bee52c2574.pdf