مجله مهندسی مکانیک امیرکبیر
سال پنجاه و سوم شماره 6 (شهریور 1400)

One of the main challenges in wind turbine application is short-term storage of output power. Hydrostatic transmission  systems, in addition to their advantages such as increasing the reliability of the system and ability to use high-efficiency synchronous generators, give the system the chance to install the short-term storage to elevate quality and amount of the output power. The short-term storage in wind turbines is important because that significant amount of power in a wind profile lies in turbulence, which can be exploited by using suitable short-term storage such as an accumulator. In this paper, the effects of employing accumulator on the hydrostatic power transmission system are investigated. First, the nonlinear dynamic model of the wind turbine system is obtained. Then the nonlinear dynamic equations are linearized around steady-state trajectory of the system. Control system is designed based on proportional-integral-derivative control method with switching capability overall operation regions. During various simulation scenarios with hydrostatic transmission without the accumulator and with different accumulator size, it is proved that employing accumulator in the wind turbine improves the quality and quantity of the output power. The results reveal that with right choice of the accumulator, output power of the wind turbine increases significantly.

The main purpose of this paper is to model and simulate flight dynamics for a flapping wing micro aerial vehicle dragonfly-like with two pair clap and fling mechanism and active rigid tail. This article simulates the flight dynamics of a micro aerial vehicle dragonfly-like that can also use tail movements for longitudinal stability. Initially, using Kane's method, the equations of motion of the longitudinal mode are obtained. Then aerodynamics forces of Delfly II micro aerial vehicle and gearbox simulation are added to the equations of motion. Also, a novel design for a flapping wing micro aerial vehicle dragonfly-like is presented, in which tail movement is similar to the movement of insect tails in longitudinal mode. In this work, the tail movement is not used as an elevator, but the rigid tail movement is used as a control torque. The difference in brush motor rpm leads to differential thrust and pitch moment generation, similar to a quadrotor. Finally, the dynamic equations and aerodynamics and gearbox are all linearized and presented as state-space equations. Also, the response of the open-loop linearized model is compared with the nonlinear response by creating suitable initial conditions for the brush motor rpm.

In this paper, modeling and control of a robotic carrier for the cleaning system of solar farms are presented. Since solar panels are placed in natural environments, there is always a problem of dust accumulation on the panels, which results in absorbed energy reduction. Hence, robotic cleaners can be used for solar panels. For relocation of the cleaning robot between solar panel rows, an automated carrier mechanism is required. Hence, a robotic system for cleaner displacement is introduced, and its dynamics modeling and control are presented. The robot kinetics and kinematics models have been derived and validated by ADAMS software. Hence, kinetics and kinematics model-based controllers are introduced for robot motion control. Using the kinetics model, a computed torque method controller is designed and simulated. For less computational effort, a transposed Jacobian controller is designed, using the kinematics model. Finally, to increase control performance, an modified transposed Jacobian controller is also designed. The desired trajectory is designed for the robot. Finally, for software verification and analysis, the controllers are simulated, using co-simulation of MATLAB Simulink and ADAMS model. The simulation results show the satisfactory performance of the controllers and can be used for further design analysis of the prototype.

Cable parallel robots usually require at least one additional actuator force in addition to degrees of freedom to keep the cables in all directions in the workspace, which solves an optimization problem to determine the cable tensile force. In this paper, a convex optimization problem is formulated on a parallel cable robot using optimization conditions through the Karush-Kuhn-Tucker theory and the analytical-iteration method to achieve a minimum force vector of actuators that has less computational time and volume. Where the lower and upper limits of the optimization variables are applied, respectively, to ensure that the cables remain in tension and take into account the saturation limit of the actuators or the rupture limit of the cables (whichever is less), and equal constraints that the relationship between actuator force and force are expressed in the moving platform, defined by the force of the actuators as the sum of the basic solution and the homogeneous solution, -located in the null space of the transpose of Jacobin matrix. Comparison of the results of analytical-iterative solution presented in this paper with numerical algorithms of MATLAB software optimization shows that this method is much faster than these algorithms to converge to the optimal response.

This paper proposes a novel method for depth perception based on the performance of the human eye in the landing phase navigation of a fixed-wing aircraft. The proposed system is designed for situations where visibility is limited, there is no necessary infrastructure at the airport or navigation instruments that have problems and provide incorrect information. The inertial measurement unit and digital elevation model data are integrated to estimate the position of the aircraft and simulate the landing area at more than 200 feet. Reducing the height to 200 feet, the forward-looking infrared camera data is added to the system input. So, the environment map is updated in real-time in landing. At this stage, to depth perception, accommodation cue of the human eye is added to the simulation. In this study, the post-rendering Gaussian method to implement depth of field is used. Simulation results evaluated by using the standard of quality measurement of the visual system of flight simulation training devices and the results confirm the accuracy of the proposed method in terms of resolution, the field of view, frame per second and latency.

In this paper, the effect of nonlinear energy sink on the dynamic behavior of a rectangular simply supported elastic plate at different azimuth angles is investigated. The plate under study is a thin rectangular plate to which a non-linear energy sink is connected and the supersonic flow of air passes over it. The research aims to improve the behavior of the plate by changing the spatial parameters of the nonlinear energy sink. Classical plate theory is used to obtain plate equations, and von Karman strain-displacement relations are used to consider the nonlinear geometric effect. Modeling of supersonic aerodynamic flow will be based on first-order piston theory. The Kelvin-Voigt model is also used for non-linear energy sinks. The equations were extracted from Lagrange's method and then discretized by Rayleigh-Ritz method and solved by fourth-order Runge-Kutta method. In order to investigate the effects of nonlinear energy sink, the time history curves, phase portraits, Poincaré maps and bifurcation diagrams are used. The results show that using nonlinear energy sinks, the behavior of the plates, which in some cases is very complex, can be changed to a simpler behavior. In some cases, using a non-linear energy sink near the center of the plate is not appropriate.

The use of structural vibration is one of the bridge health monitoring approaches which is often costly, time-consuming. The response of a passing vehicle includes the bridge response so that it is used for extracting the bridge modal parameters. In this paper, the transmissibility measurement of a passing vehicle is employed in order to identify the bridge mode shape indirectly. As the sensor is embedded on the axle of the vehicle, recording the signal is fulfilled during the vehicle passage and there is no need to stop the vehicle. On the other hand, there is white noise assumption in most other techniques, but excitation characteristics are not considered in the proposed method which is another advantage. In the numerical simulation, the bridge is assumed to be Euler Bernoulli and the vehicle is modeled as a 4DOF system. Solving the vehicle-bridge interaction equations, the acceleration of all degrees of freedom are obtained. Afterwards, the mode shape is identified by applying the short time transmissibility measurement on the acceleration. Since the performance of the indirect methods in real cases is associated with many obstacles and challenges, a setup for experimental verification of the proposed method has been designed and constructed in a laboratory. Numerical simulations and experimental results indicate the capability of the proposed method for indirect identification of bridge mode shape.

This paper presents a combined use of active chassis systems to enhance vehicle roll and yaw stability using semi-active suspension and active braking systems. The designed active braking system based on sliding mode control reduces the probability of vehicle rollover by decreasing the longitudinal velocity and lateral acceleration. Also, a semi-active suspension is proposed through fuzzy control method to improve the vehicle roll stability, which attenuates the effect of lateral acceleration on roll angle and roll rate. The lateral load transfer ratio is selected as the rollover index based on roll angle and lateral and roll accelerations. A vehicle dynamics model is built in the ADAMS environment, which includes subsystems of steering, braking and front and rear suspension, tire model and body. Also, the nonlinear characteristics of tires, bushings, springs and dampers are considered in the model. So, it can accurately express the dynamics performance of the vehicle. The control algorithm is evaluated under step steer and lane change maneuvers utilizing MATLAB and ADAMS co-simulation. Simulation results show that the proposed system with combined controllers can effectively improve the vehicle yaw stability and the rollover prevention compared with the only active braking and semi-active suspension systems.

The inertial navigation system is a dead reckoning system, thus initial alignment for an inertial navigation system plays an important role in the accuracy of it. In this paper, a novel approach for initial alignment in an inertial navigation system with increased speed and accuracy is proposed. This method has two stages, which integrates the Kalman filter and a high order sliding mode observer. In the inertial navigation system, leveling misalignment angles reach the steady-state faster than the azimuth misalignment angle does, which means the azimuth alignment takes a considerable time for initial alignment. Therefore, in this paper at the first stage estimations of state variables of the system are obtained using the Kalman filter and whenever all variables (except azimuth alignment) reach steady-state, the second stage begins. In the second stage, the estimation which is obtained by the Kalman filter is used as the input to design an equivalent system with unknown inputs for inertial navigation system. A high-order sliding mode observer is then used to estimate the states of a system with an unknown input for estimating the azimuth alignment angle. This method not only increases the speed of estimation but also has comparable accuracy.

The thin-walled beams are widely adopted in different structural components ranging from civil engineering to aeronautical applications due to their conspicuous characteristics. A slender thin-walled beam loaded initially in compression may buckle suddenly in flexural–torsional mode since its torsional strength is much smaller than bending resistance. In this paper, flexural-torsional stability and free vibration analyses of axially functionally graded tapered I-beam resting on Winkler elastic foundation are assessed. Considering the coupling between the flexural displacements and the twist angle, the motion equations are derived via Hamilton’s principle in association with Vlasov’s thin-walled beam theory. The differential quadrature method is applied to solve the system of differential equations and to acquire the critical buckling loads and natural frequencies. To validate the obtained results, at first, homogeneous tapered I-beam in the absence of elastic foundation was analyzed and compared with a finite element solution using ANSYS and other available benchmarks. Afterward, the numerical outcomes for axially graded non-prismatic I-beam resting on elastic foundation are reported in graphical form to find out the impacts of axial load position, beam’s length, end conditions, web and flanges tapering ratio, material gradient index, Winkler parameter and spring position on the non-dimensional buckling loads and vibration frequencies.

Owing to current status of global energy consumption and greenhouse gases emission, investigation of energy demand in different sectors seems to be necessary. Meanwhile, International Energy Agency  reports imply that a considerable share of global energy use is consumed in transport sector. Thus, conducting the vehicle energy demand and influential parameters has become a demanding topic, especially in recent years. The current study investigates the vehicle energy demand considering the power losses due to tire slip. To achieve this, vehicle resistant powers are rewritten by taking the modified tire power loss into account and after that, two different passenger vehicles are chosen and simulations are performed in three well-known driving cycles. Energy demand of the selected vehicles significantly increases in a more aggressive driving cycle which comprises higher levels of longitudinal acceleration and speed. According to the results, considering the power loss due to tire slip would improve the calculation accuracy of tire losses up to 6 percent and in case of a more aggressive driving cycle and/or increased resistant forces, energy loss due to tire slip would be increased.

In this study, energy absorption behavior of cellular structures such as foams will be investigated. In this paper, developing microstructural modeling of cellular structures and analyzing their plastic behavior through the finite element method is the main goal. In this research, a unit cell is first developed for numerical computation reduction as well as modeling that has the desired foam statistical properties, and then the dynamic behavior of this unit cell under simulated impact will be analyzed. An analytical method to obtain the compressive strain value of the foams with the help of numerical solution results will be presented. In other words, using the analytical method, the finite element method and the simulation will be evaluated. Then, using simulated experiments, a model using the response surface methodology  to obtain the compressive strain will be presented and the results of this model will be evaluated by numerical method. The results of this study showed that it is possible to model and analyze the energy absorption of the foams using the method presented in this study and as a result, suitable structural equation for microstructural analysis of foams can be obtained in future researches.

In this paper, the reliability of rectangular plates without holes and containing a central circular hole under static tensile load has been studied. To investigate the initiation and evolution of damages, continuum damage mechanics approach together with finite element has been used. Constitutive equations with scalar damage have been obtained for the plate and implemented in finite element code, ABAQUS.  To analyze the probability of failure the first/second order reliability methods have been used and then, limit state function and random variables according to the continuum damage mechanics model obtained. The force-displacement curves for various sizes of the hole are obtained. With the addition of a central hole in a plate with a diameter of 2 to 10 mm, failure load is reduced by approximately 60 to 80%, which is consistent with the concepts of stress concentration. Finally, the probability of failure of each plate with different hole sizes is approximated and sensitivity analysis on the coefficient of variation is performed. The reliability of the specimen with a diameter of 10 mm has the lowest value, while the plate without a hole has the highest value and among the random variables, the critical damage is the most effective one in reliability.

The purpose of this paper is to present an analytical model for analyzing the penetration process by aspherical noseshape cylindrical on the kevlar/elastomer and the kevlar/epoxy composites and comparing them with each other using the energy method. To investigate this issue, energy absorptionequations forlinear andnonlinear materials are analyzed as a criterion for the performance of matrix-reinforced fabric. In this predicted model, the dependence of the ballistic behavior of the first and second layers of the composites on each other during the impact is considered. In this presented model, the components of energy absorption include the initial kinetic energy of the projectile, the kinetic energy of the projectile, the kinetic energy of the composite cone ahead of the tip of the projectile, the energies absorbed by primary and secondary yarns, the energies absorbed by the delamination among the layers and the cracking of the matrix, the energy dissipated by plugging of the layers is calculated during impact. The results of this study show a positive effect of elastomer use on thermoset matrix in composite. Also, analytical results are validated with the experimental results of previous studies and the perturbation analysis is done to examine the reason for error.

Numerous failure models for prediction of the load-carrying capacity of cracked and notched laminated composites have been of interest to researchers in the field of fracture mechanics. The cause of the importance of this subject was the extensive use of notched composite laminates in aerospace industries in the last decades. In this investigation, it was tried to predict the load-carrying capacity (critical failure load) of U-notched laminated composite specimens with various layup configurations under pure mode II loading (in-plane shear loading) conditions, by utilizing a simple and novel concept proposed recently by the authors. The new composed criteria have been proposed in the field of orthotropic fracture mechanics for the first time. For this aim, by using a newly proposed concept, namely the virtual isotropic material concept, and combining it with two well-known brittle fracture criteria in the field of linear elastic fracture mechanics, namely the maximum tangential stress and the mean stress criteria, the experimental results of the failure of the U-notched laminated semi-circular bend composite specimens under pure mode II loading condition, were theoretically predicted by using new last-ply-failure load curves. It was revealed that the experimental results are in good agreement with the theoretical predictions.

In this paper, the mechanical behavior of dual phase steel has been investigated in the macro and micro scales as experimentally and numerically. In order to study the influence of stress states on the mechanical behavior and fracture strain of DP600, four different specimens were tested under different stress states. Afterward, the obtained microstructure images by light microscope, were utilized to generate a 3D representative volume element based on the real microstructure. The microstructure images were converted to a 3D RVE model by image processing and finite element codes in Matlab and Abaqus commercial software, respectively. Then, the ability of the micro mechanical model to predict the macro mechanical behavior was evaluated under different stress states. The results demonstrate the micro mechanical model is able to predict the macro mechanical flow curve under different stress states except for shear. Finally, the influence of stress states on the stress to strain partitioning rate and the local plastic strain at fracture point were assessed. The results show stress-strain partitioning and local plastic strain are strongly dependent on stress state.

Additive manufacturing includes emerging methods that with reduced production time and ability to produce parts with complex geometry, are now widely used in variety of industries. Fused deposition modeling process is one of the most popular methods of additive manufacturing and so far, a lot of research has been done to model and improve the mechanical behavior of the parts produced by this method. The purpose of this research is to conduct an experimental study to model and investigate the effect of fused deposition modelling process variable on fatigue behavior of poly-lactic acid components, along with the development of numerical tools to predict this behavior. This paper uses the Taguchi algorithm to design experiments for experimental study. By performing fatigue testing on the sample and analyzing the result, the optimal value of the desired variable, as well as their effects are determined that the variable of fill density, nozzle temperature and layer thickness have the highest impact on fatigue life, respectively. The finite element simulation is performed by assuming assumption and its results are evaluated with the values of the optimized sample fatigue test. The result of experimental modeling and finite element simulation show that the models presented predict the poly-lactic acid components parts fraction with R-Sq 96.3% and 98.7% fatigue behavior, respectively.

In this study, plastic deformation of the metallic bipolar plate with serpentine flow field was investigated during stamping process. Strain path and thickness distribution in 304 stainless steel bipolar plate with the thickness of 0.1 mm were determined. To this aim, the process was simulated by the commercial finite element code. The validity of the result was evaluated by comparing the experimental and numerical thickness distribution and force-displacement curve which represent 4.76 and 3.85% prediction error, respectively. According to the results, flow of the material has significant effect on the thickness distribution of the central and lateral channels, and the thickness reduction percentage of the central channel in longitudinal, diagonal and transverse direction is much more than that of lateral one. Maximum thickness reduction (critical area) in central channels is placed in longitudinal direction (33% at channel side) while the diagonal direction is considered as critical direction for lateral channels. Due to the existence of the equibiaxial tension strain path in diagonal direction, significant thickness reduction is observed in both the side and the rib zone of the channels.

The friction stir spot welding has shown great potential for joining low-ductility aluminum to high-strength steels. In the last decade, wide researches were done to achieve high strength and tool life enhancement in friction stir spot welding. The electroplastic effect, with its environmentally friendly nature and high efficiency, has resulted in a reduction of flow stress and tool wear, improvement of plasticity and material flow for various processes. On the other hand, adding nanoparticles to the friction stir spot welded area joint increased the tool wear despite the improved strength. In this paper, the joint strength and spindle output power are investigated in electroplastic friction stir spot welding process for joining of AA6061-T6 with 1 mm thickness to DP590 steel sheet of 1.5 mm. A 2K design was used for statistical analysis considering four parameters of rotational velocity (1000, 2000 rpm), dwell time (2, 4s), electrical current (250, 500A), and adding SiC reinforcing nanoparticles. A quantitative study of the current density was performed by the finite element code with thermal-electric coupling. Results showed that electroplastic effect had a compatible impact with nanoparticles on strength improvement by accelerating the occurrence of dynamic recovery and recrystallization, and neutralized the negative effect of nanoparticles on tool life since created joints with failure loads above 7 kN.

Friction stir welding is a solid-state bonding technique based on two factors, a pressure greater than the material yield stress and large plastic deformation. The final joint between parts takes place in different welding geometries by using these two factors. The grain sizes in the weld areas are influenced by recovery, recrystallization, and grain growth. In the current research, using an analytical-numerical method based on finite element simulation of friction stir welding of AA6061-T6 alloy, the grain sizes in various welded areas have been predicted. The finite element simulation has been performed based on the coupled Eulerian-Lagrangian approach using ABAQUS software and the results have been verified by experiments. The predicted results were in good agreement with the experimental results. Due to the concentration of heat and plastic flow in the central region of the weld, the stirring region had the most microstructural changes and the grain size in this region decreased more sharply than other different areas of the weld. As the rotational welding speed increases, recrystallization phenomena in the central weld area increases. With increasing the translational welding speed, grain size increased in different welding areas. This increase occurred more severely in the central area of the welded joint.