نشریه مهندسی مکانیک مدرس
سال هفدهم شماره 10 (دی 1396)

Due to unique properties, lattice composite structure are used extensively in aviation, marine and automotive industry. In this research, experimental and numerical investigation of the free vibration of composite sandwich plates with triangular grid has been studied. For the fabrication of this plates, silicone mold, filament winding, and hand lay-up method were used. Stiffened plates and simple plates are fabricated, separately. Then, composite sandwich plates with triangular grid were created by attaching the two parts together. The modal test is done on the plates and natural frequencies have been extracted.The comparison of numerical and experimental results showed that there is a good agreement between them. By using Taguchi method, a parametric study was performed on the vibrational behavior of sandwich plates with triangular cores via three parameters that such as stiffeners’ number, stiffener thickness and skin thickness. The results show that the natural frequency of sandwich plates with triangular grid has a most sensitive to the stiffener thickness, and least sensitive to stiffeners’ number. The sensitivity of natural frequency is almost identical to stiffener thickness and skin thickness.To evaluate the efficiency of sandwich plates with triangular grid, the natural frequency of sandwich plates are compared with simple plates in the different boundary condition. The results show that the natural frequency of sandwich plates with the triangular grid is 133% and 138% higher than an equivalent simple shell at free and clamp boundary condition, respectively.

In this paper, optimal trajectories of soft landing on the Moon are designed based on different landing strategies. For this purpose, the problem of soft landing is defined as an optimal control problem to minimize fuel consumption and solved by a combinational direct method. The used solution method in this paper is a combination of direct collocation method, nonlinear programming, differential flatness and B-spline curves. In this method, by using differential flatness, dynamic equations of landing are expressed by the minimum number of state variables in the minimum dimensional space. Also, state variables are approximated by B-spline curves, and control points of these curves are considered as optimization variables of the nonlinear programming problem. By simultaneously using of differential flatness and B-spline curves, the number of variables and constraints of the optimal control problem decrease significantly and the problem is solved with high accuracy and speed. In the paper, three different strategies for soft landing on the Moon are investigated. These strategies are defined based on direct or indirect landing from the parking orbit and separation of horizontal braking and vertical descent phases. According to achieved optimal trajectories, by indirect landing from an intermediate orbit, the space vehicle can be landed on the Moon with the minimum fuel consumption. Also, by separation of horizontal braking and vertical descent phases, a more applicable landing trajectory can be achieved.

Numerous studies have been devoted to motion control of wheeled mobile robots in recent years. Among them, trajectory tracking has received much attention.. A feed-forward and feedback control structure for trajectory tracking is used to circumvent the limitation of Brockett’s theorem. Feed-forward control is calculated according to the reference trajectory, it can not compensate instrumentation and initial state errors, therefore a feedback controller is utilized as well. In this paper a model predictive controller is used as the feedback controller. Since the initial state is not often matched to the desired trajectory, rapid tracking of the trajectory in early steps is very important. In this paper a model predictive controller with laguerre functions and another one with exponential data weighting is used to reduce tracking error in early steps. According to simulation results, reference trajectory tracking is improved through laguerre functions in model predictive controller.

Shape memory alloys are a category of smart materials which exhibit large deformations under temperature or magnetic stimuli due to micromechanical changes. These alloys offer a good potential in design of control systems, sensors and actuators due to two main effects called shape memory effect and superelastic effect. Main advantages of these systems are their small scale, low weight, low activation power, long life and high power to weight ratio. On the other hand, the main disadvantage of thermal ones is their low actuation frequency. In this work, inspired by human arm muscles, a new actuator is designed and its actuation time is minimized utilizing the thermoelectric effect. The process requires simultaneous analysis of heat transfer, constitutive equations, phase transformation and also the dynamic equations of the actuator. The dynamic response of the designed actuator is compared with the similar experimental data available in the literature and finally it is shown that, the actuation time of the proposed actuator can be reduced at least 50% thanks to the Peltier effect.

Equal channel angular rolling process (ECAR) is one of the newest processes in the severe plastic deformation methods (SPD) that changes the mechanical properties of the sheet metal. In this study, the effects of ECAR process have been investigated on the corrosion behavior of the pure commercial copper samples. Five routs have been applied on the samples to investigate the mentioned parameters. Also, the corrosion rates were examined by the polarization and electrochemical impedance methods. The results show that the process has destructive effect on corrosion resistance of the samples. The results from SEM examination indicates that, with increasing the number of passes, the surface corrosion increases too and with increasing the passes pitting corrosion is clearly visible. Although with increasing the number of passes the uniformity of corrosion can be seen and positional mode is exited. Generally, the corrosion increases from the first pass to the second pass. Also, the more diameter and depth of corrosion is observed with increasing the pass number. The corrosion increase at the third pass and the corrosion type is pitting corrosion and uniform corrosion in the sample.

Condensation phenomena in steam flow, can cause droplets with different sizes to form. For an exact prediction of two phase flow behavior, it is necessary to consider the effects of all droplets with different sizes on the steam. In this paper, nucleation equation in an Eulerian–Lagrangian framework has been used to analyze one–dimensional flow of wet steam in a supersonic convergent–divergent nozzle. Polydispersed and monodispersed radius methods for modeling the formed droplets are compared. In polydispersed method, all the formed droplets in the spontaneous condensation zone, are retained in the calculations, without being merged with other groups; but in monodispersed method, all groups are merged, and only one group with averaged radius is retained in the calculations. The polydispersed method has an advantage and can predict the complete droplet spectra. Results of comparing the two methods with experimental data indicates that the predicted radius in the polydispersed method, in every four investigated cases, is closer to experimental data, than that of monodispersed method.

In recent years, capability of FPGA hardware for accelerating the solution of differential equations has attracted wide attention. However, complexities associated with the implementation and development of these equations on FPGA has precluded the wider application of this hardware among the users in the field of CFD. In this research, a software framework has been developed, which enables users to develop an FPGA based coprocessor for solving implicit PDE equations, quickly and with minimum complexity. Using this framework, the user defines the solution network and the algebraic equations, and the framework manages other operations such as construction of the solver IP, interface between the CPU and the coprocessor, memory layers and links among various parts. The framework consists of different sections for defining the architecture of the coprocessor using HLS and VIVADO software, and the links with CPU consisting of operating system drivers and operational functions for adjusting initial and boundary conditions and receiving the results through the PCIe port. Simplicity of the developed framework has been demonstrated by the construction of a coprocessor for solving two-dimensional Laplace equation. Comparison of speed of solution on CPU with the FPGA based coprocessor shows a 22-fold increase in the speed of solution of Laplace equation, and if fixed point operation is used in the construction of the coprocessor, the speed will even increase 65-fold.

The energy harvesting of a piezoelectric cantilever beam is obtained from the excitation of vibration modes. Vibration modes have strain nodes where the strain distribution changes in the direction of the beam length. Covering the strain nodes of the vibration modes with continuous electrodes effects a cancellation of the voltages outputs. The use of segmented electrodes avoids cancellations of the voltage for multi-mode vibration. The theory of Gauss law is presented for the voltage response due to the electro mechanic coupling. The effective parameter in the voltage response is the modal coupling term. This parameter depends on geometry, material, piezoelectric coefficients and the Eigen function of bending slope. If the slopes of the electrodes boundaries are close together, the electric response of vibration mode is very small. The resistive load affects the voltage and generated power. The optimum resistive load is considered for segmented and continuous electrodes, and then the power output is verified. One of the effective parameters on energy harvesting performance is the existence of concentrated mass. This topic is studied in this paper. Resonance and off-resonance cases are considered for the harvester. In this paper, both theoretical and experimental methods are used for satisfactory results.

In this paper, a hypersonic inlet for operating at Mach 5.0 is designed and analyzed numerically. The main axis of this study is a series of three-dimensional simulations with the accuracy of 10E-06 which are applied to determine the effects of the highly developed boundary layer on the performance of inlet for three different study cases. The basic inlet concept is designed by integration of double ramp compression surface and inlet duct which can reduce the free-stream Mach number to the range of 2.0. The most important factor that it affects the performance of the hypersonic inlet system, is the developed entropy layer on the fuselage of the flight vehicle. Ingestion of this layer results in thermal gradients and pressure recovery losses. The bow shocks at the nose and the leading edges are the main sources of this low kinetic energy layer. Using the k-ω turbulence model in the numerical simulations have resulted in a reliable estimation of the boundary layer. In the current context, shock structures, shock-boundary layer interactions, flow quality at the end of the diffuser and also the effects of using sidewalls on the performance of the hypersonic inlet are the main goals of the simulations and the related results are summarized

Automatic transportation systems nowadays play a key role in decreasing human errors and accelerating traffic flow. To implement controllers aiming at optimizing commute in terms of comfort and safety demands a rigorous modeling of the system. An accurate full-scale model will result in a more precise and reliable simulation. On the other hand, the growing number of vehicles and consequent rise in accidents associated with lack of driver attention highlights the need for driver assistant systems whereby more driver convenience, reducing accident, safety and comfort could be provided. In the present study, a complete nonlinear model of longitudinal vehicle dynamics has been chosen in order to make the model more compliant with reality and to minimize simulation and control uses errors. In the control section, a novel approach to developing an adaptive cruise control system is proposed in which the host vehicle acceleration is not only influenced by target car motion but also by the macroscopic motion of the traffic flow. The results indicate that the pile up resulted from sudden braking could be avoided by using a predictive control over vehicle acceleration which takes account of the motion of both front car and traffic jam. In the low level control section, a fuzzy control based on tracking error minimization is employed to maintain desired acceleration through calculating throttle angle and brake pedal. Such control command is then applied to the longitudinal model so as to appraise the select model performance in the driver assistant system.

With development of micro-electromechanical phase shifter, the study of deformation and instability of micro-switches is very important. The static behavior and pull-in instability of the clamped-clamped micro-beam subjected to local electrostatic loads which is used in DMTL phase shifter is investigated. Taking into account of nonlinear effects caused by radius of curvature for the first time, the nonlinear differential equation of the system is obtained using Euler-Bernoulli beam theory and effects of small sizes by employing the principle of virtual work. By considering the local electrostatic static voltage applied on the micro-beam, the governing partial differential equation is further discretized with the aid of Galerkin’s method, and the effect of system parameters on static deflection and pull-in voltage of the micro-switches are investigated. It is found that curvature nonlinearity has a great effect on the mechanical behavior of the micro-switches. Increasing this parameter leads to hardening behavior in the micro-switches, and also static deflection is decreased with respect to linear beam theory. The results also indicate that with an increase in the applied voltage, nonlinear strains increase and nonlinear effects caused by radius of curvature will be significant. For instance, when the stiffness parameter is increased from 0 to 10, maximum deflections of the micro-switches for applied voltages of 1V, 2V and 3V decreases about 7.7%, 35.8% and 48.6 %, respectively.

In this paper, position control is addressed for a pneumatically actuated 6-DoF Gough-Stewart parallel robot. At first, dynamic model of the pneumatic system of each link of the robot which comprises a pneumatic actuator and a proportional electrical control valve is extracted. Unknown parameters of the obtained dynamic model consisting friction force, viscous coefficient and the parameters of the valve are identified by employing an evolutionary algorithm. Then, position control of the robot’s pneumatic actuator is performed based on designing Backstepping-Sliding Mode controller according to the nonlinear dynamic model of the pneumatic system. Moreover, kinematic equations of the 6-DoF parallel robot are achieved and a novel method is proposed, the so-called Geometry-based Quasi-Forward Kinematic, to the end of calculating the position of the end-effector of the robot without using expensive position sensors. Accordingly, kinematic closed-loop control of the parallel robot, which is based on simultaneous joint space and task space control, is investigated for trajectory tracking using potentiometers, a rotation sensor, and based on the computed position of the end-effector by the proposed method. Desired sinusoidal trajectories with pure motions and also complicated trajectories are tracked in which error of positions and rotations are lower than 2 (cm) and 3 (deg), respectively. The results reveal that the trajectory tracking control of the pneumatic 6-DoF Gough-Stewart parallel robot is performed properly based on the proposed control strategies and the novel method for calculating the position of the end-effector.

In this research, analytical and numerical investigation of the ceramic- metal FGM beam under low velocity impact is carried out by first order shear deformation beam theory. The mass and stiffness matrixes are proposed by combination of Energy method, Ritz and Lagrange method. Also, simulating of low velocity impact on the ceramic- metal FGM beam is carried out by ABAQUS software that the beam is divided about 30 layers in thickness direction in ABAQUS software to create a functionally graded beam. Maximum contact force between impactor and beam in analytical model and ABAQUS software are 1062 and 1039 N with 2.21 percent difference and maximum impactor displacement in analytical model and ABAQUS software are 0.0104 and 0.0108 mm with 3.85 percent difference. Finally, the effect of FGM function types include the combination of exponential and polynomial functions, impactor velocity 1, 2 and 3 m/s, impactor radius 8, 12.7 and 16 mm and simply and clamped supported boundary condition are investigated on the contact force and indentation histories. The maximum and minimum contact forces are belonging to first and third order polynomial function and maximum and minimum indentations are belonging to third and first order polynomial function.

The poor formability of Mg results in crack and failure in workpiece material during rolling process and limits its applications in different industries. Numerical modeling of the process can guarantee that the required product properties are met with a minimum production cost. The numerical modeling of the rolling processes requires the coupling of several models including different physical phenomena such as the deformation of the workpiece with its thermo-metallurgical evolution and the thermal evolution of the rolls with its mechanical deformation. On the other hand, in finite element modeling of the rolling process, the meshes of the workpiece are often highly distorted. The high distortion in meshes decreases the confidence in the predicted results. Many formulations based on the viscoelasticity behavior of workpiece material are encountered in the literature to model the rolling process, each with their pros and cons. This present work introduces the Coupled Eulerian-Lagrangian (CEL) formulation, in which the workpiece is divided into three regions (unrolled, in rolling deformation, rolled) to simulate material flow during the process. The comparison of the results with the literature shows that the temperature and strain fields are well predicted by the proposed model. All of the simulations have been done in the two-dimensional mode with ABAQUS/Explicit software.

In this article, the influence of process parameters on warm deep drawing of PVC/fiberglass composite laminates (FRP) is investigated through the experimental tests. Fiberglass reinforced polymer (PVC) composite laminate sheets are new emerging materials that have many potential applications. FRP/composites provide high strength to weight ratios exceeding those of aluminum or steel. For the experimental tests, composite samples with [0/90]2, [0/90]4, [-30/30]2, [-30/30]4 lay ups were produced in using film stacking procedure. Statistical analyses based on Taguchi's method are used to reduce the number of experiments and to investigate the effect of process variables on the output results. The results show that the two variables of temperature and blank holder force have the most influence on output parameters. Furthermore they demonstrate that a high interaction between the forming temperature and blank-holder force is required to remove the wrinkling.

In this study, microstructure and mechanical properties of 7068 aluminum alloy matrix nanocomposite reinforced with 0.1, 0.3, 0.5, 0.7 and 1 wt.% graphene nano plates (GNPs) produced by stir casting and ultrasonic treatment have been investigated. Ultrasound device equipped with a cooling system with high power was used for mixing alloy and nanoparticles. Also the microstructure was investigated by scanning electron microscope. The microstructural studies revealed that GNPs addition reduces the grain size, but adding high GNPs content (1 wt.%) does not change the grain size considerably. Further investigations revealed that the addition of GNPs increases tensile strength. At high GNPs contents (1 wt.%), the presence of GNPs agglomerates on grain boundaries were found that causes decrease the tensile strength. The optimum amount of nanoparticles is 0.5 wt.% GNPs. The average ultimate tensile strength (UTS) of the specimens before and after extrusion processes increases from 212 MPa to 374 MPa. Adding of 0.5 wt.% GNPs and extrusion process make about 76% enhancement in tensile strength compared to that of unreinforced aluminum alloy.

With growing environmental pollution and concerns about fossil fuel depletion worldwide, there is an urgent need to find a solution for this problem. Using alternative fuels, such as natural gas, which can burn much cleaner than petrol or gasoline and as an advantage, it’s much cheaper than other conventional fuels and is much more widely available than oil in our planet. The most effective way we can utilize this alternative fuel in the common internal combustion engine, is by means of direct injection technology. Before natural gas can be utilized in common automotive engines, it’s necessary to conduct simulations and thus optimize these engines to maximize output power prior being built. Optimizing engines can only be achieved through simulation. KIVA-3V is a well-accepted engine simulation tool, recognized by industrial users and researchers. KIVA-3V lacks the ability to simulate gaseous fuel injections as it’s only designed to deal with liquid fuels. In this research, researched the governing equations on gas injections and used them to develop a numerical code for KIVA-3V to enable simulation of gaseous injections. We validated our modified version of KIVA-3V with two different sets of experimental data which we previously had. We showed our modified KIVA-3V code can effectively simulate gaseous injections producing very exact results. The gaseous fuel considered in this research is pure methane.

In this paper the principles of simultaneous measurement of three orthogonal force vectors Fx, Fy, Fz and three orthogonal torque vectors Mx, My, Mz to design a six axis force/torque sensor are considered. At first, a new index (η) for a qualitative comparison of six-axis force/torque sensors is proposed and then, cross-coupling error of several sensors presented in previous studies is evaluated and compared by using the new index. In the following, a systematic method for designing the six-axis force/torque sensor is described using numerical optimization procedure. This method is based on interactive interface between the SQP algorithm created in MATLAB and FEM analysis in ANSYS software. The geometry of sensor structure is selected to be a modified Maltese cross type. Principle cross-coupling error is chosen as the objective function to optimize four geometrical design variables of the sensor structure. Also, strain gauge sensitivity, maximum applied stress and geometric sizes of the sensor structure as constraints are formulated in problem. Results show that principle cross-coupling error of the optimal sensor design is less than 1.49% with a high moment to force specification (0.1 N.m/N).

Peristaltic phenomenon is widely used for biologically tissues such as the digestive and excretion of urine systems. Fingered and roller pumps, hoses and internal pumps, pumps for waste management in the nuclear industry are also working on the wavy walls rules. Hence, in this paper, the magnetic hydrodynamic flow of nanofluids inside a curved porous channel, with peristaltic walls and within the internal heat source has been studied. In the present study, the flow is incompressible and the governing equations, including flow, heat and mass transfer are obtained by using an assumption of long wavelength. For solving the equations, the central finite difference approximation algorithm and Keller-box method are utilized. Heat transfer is reduced due to the presence of a magnetic field. Also, increasing the power of the heat source and the Darcy number reduces the heat transfer. Increasing porosity in the environment increases the heat transfer. Increasing the power of the heat source is accompanied by a reduction in velocity in the central line of the channel in the corrugated mode.
In this paper, by using the numerical solution results, the effect of various parameters such as source term, Darcy number and porosity on the velocity, distribution of temperature, the function of the magnetic force, increase the pressure on the wavelength, Nusselt number and also the flow trapping phenomenon has been studied.

Gas turbines are among the most important power generation equipment in industries. One of the methods to enhance the performance of this equipment is the aerodynamic performance optimization of its stator and rotor blades. This paper presents an automatic aerothermodynamic optimization platform for the optimization of 3D stator blade geometry in axial-flow gas turbines using open-source software. This platform can be used for 3D aerothermodynamics optimization of 3D blades and includes parametric 3D modeling, mesh generation, CFD simulation, and implementation of optimization algorithm. 3D models are formed from 2D sections defined by Bézier curves and connected by spline stacking curve. Simulation of flow field includes the solution of compressible viscous flow on structured multi-block grid using parallel processing. Genetic algorithm is used as optimization algorithm. 45 optimization variables govern blade thickness variation in five sections and blade lean, sweep, and twist. Total pressure is selected as objective function and the result of optimization shows 5% decrease of total pressure loss coefficient in the blade. The use of open-source software in the optimization platform provides maximum customization capability to the user. The application of this platform for stator blade optimization shows that the platform can be used for aerothermodynamic optimization of turbomachines effectively.

Many people suffering from neuromuscular diseases, have some degree of limitations in their walking pattern. Knee-Ankle-Foot Orthoses (KAFOs) help correct patients’ gait pattern by supporting knee and ankle joints. Patients with quadriceps muscle weakness suffer from some restrictions in extension as well as in controlling their flexion during the gait cycle because of abnormal stiffness pattern of the knee joint. This paper addresses patients with quadriceps muscle weakness by designing an appropriate orthosis utilizing two different mechanisms for the stance and swing phases. Stance phase mechanism locks knee joint movement from the initial-contact up to the end of mid-swing phase and with regards to the orientation of the foot after mid-stance phase, the knee joint can flex freely. The required moment to reproduce the stiffness of a normal knee joint is calculated using the OpenSim software package in conjunction with the data collected from the motion analysis of each patient.
The required moment to modify the stiffness of the knee joint for two patients with different levels of muscle weakness was reproduced using a torsional spring. By designing patient-specific orthosis, the stiffness profile of normal joint for each patient with distinct level of muscle weakness can be reproduced, allowing patients to experience smother gait cycle. Using this orthosis not only improves the patient’s gait cycle but also prevents potential damage to healthy muscles.

Quadrotor is a Flying robot which can fly vertically and has a simple structure. Because of nonlinear dynamics of the system, Stability of the control process has an important role in this robot. In this paper, a neural controller is designed to stabilize the quadrotor. The neural controller is used to stabilize the attitude of the quadrotor. We first designed a PD controller using Ziegler Nichols method, then an online learner neural controller is trained for tuning the parameters of this PD controller. To verify these controllers first a simulation performed in the Simulink environment of the Matlab. In addition to simulation we have practically implemented these control methods on a Quadrotor test bench. Practical implementation results demonstrate the effectiveness of the presented method.

Blowby phenomenon of fuel-air mixture from cylinder-piston crevices, which occurs due to difference of in-cylinder and connected crevice pressures, influences engine performance. In the current work, experimental data of gasoline fuelled motoring condition at equivalence ratio of 0.9 were collected from a single cylinder research engine using skip spark technique. A relatively simple non-thermodynamic polytropic-base model was introduced and orifice-volume theory was coupled it; and gas flow through crevices was studied. From positive points of the model, it can be implied that the model predicts cyclic blowby without performing complex heat transfer and thermodynamic calculations. A verified thermodynamic simulation model including blowby sub-model was used to validate the polytropic-base model. Cylinder pressure evaluated by the thermodynamic model had good agreement with the measured pressure in the gasoline fuelled motoring condition at the equivalence ratio. First, in the polytropic-base model, output cylinder pressure of the thermodynamic simulation model was defined instead of experimental cylinder pressure and its blowby was evaluated. Then entering experimental cylinder pressure at equivalence ratio of 0.9 to the current model, cylinder mass and blowby to crevices were evaluated and compared with the predictions of the thermodynamic model. A very good agreement was observed between the obtained results and the results of the thermodynamic model. The new model showed maximum 6.88% cylinder mass lost around peak pressure position decreasing to 0.45% along the late expansion stage.

Thermal run-away of lead acid batteries is one of the destruction modes of lead-acid battery. This phenomenon is a thermal-fluid dynamics instability problem that needs to be solved via direct numerical procedures. High-order simulation of lead-acid battery is the first step of direct numerical simulation (DNS) methods for research on thermal run-away phenomenon. In this study, due to simple geometry of lead-acid-cell, spectral methods which are very common in DNS simulation of thermal and fluid dynamics instability problems is implemented on lead-acid cell. A full cycle of discharge, rest and recharge process of a lead-acid cell is simulated by Chebyshev spectral collocation method combined with fourth order Runge-Kutta time integration. Due to complexities, the simulations are performed to find the possible numerical difficulties of this method as the first step. Two coarse and fine grids with Chebyshev polynomials of 8 and 12 order are selected to perform numerical simulations. Comparison of the error shows that the accuracy will be decreased up to 200 times just by adding two points to grid. Also numerical results show that this method is sufficiently able to predict the cell behavior in the high rates of cell current. The results indicate that spectral methods and Runge-Kutta time integrations are promising tool for direct numerical simulation of lead-acid batteries to study complex physical phenomena such as thermal run-away problem.

Attitude control of the UAV’s is basis of the of many control systems such as position control, trajectory traking, traking moving targets and obstacle avoidance. Hence, one of the most important parts of the UAV's control is designing an appropriate and efficient controller, so that system being able to eliminates or reduces external disturbances, mechanical underactuation, changes in the model or physical parameter and interactions between its subsystems. In this paper, the attitude control problem is studed. For this purpose, the dynamics model of a quadrotor is derived by using Newton-Euler mtethod and the required parameters of the model such as moment of inertia, thrust and drag torque coefficient identified by experimental methods and an actual physical sample. Then, modidied PID and sliding mode controllers are designed to provide attitude traking for quadrotor and performance of these controllers is investigated in the presence of disturbance and sensors noise. Finally, the desgned cotrollers are implemented on a real 3DOF system and the experimental results are compared with the simulation results.

In this study, a galloping-based energy harvesting system is designed using a nonlinear energy harvesting sink (NES). In doing so, electromechanical equations of motion for the energy harvesting system are derived and the theoretical results are validated with experimental results. Then, three steps are presented to make system work efficiently. In the first step, several cross-section geometries for the bluff body are investigated and the results are verified by the Harmonic Balance Method. These results indicate that isosceles triangular section can harvest more energy than the other ones. In the second step, effect of changing the electrical load resistance on electromechanical behavior of the system is investigated and it is demonstrated that the maximum energy is harvested for load resistance values of more than 1 MΩ. In the third step, influence of changing the tip mass on the system is studied and it is shown that increasing the tip mass leads to increase the output voltage while the bluff body amplitudes remain constant. Consequently, the system is designed to work with the maximum possible tip mass which is about 35.3 gr. Finally, this system with a bluff body of isosceles triangular section can generate 700 mV using the load resistance value of 10 MΩ in the wind speed of 2.5 m/s. This system with the total mass of less than 500 gr and low-amplitude oscillations is designed to work properly in low wind speeds and presents an efficient application for low-power energy harvesting systems.

Micro end-milling is one of the main manufacturing processes of creating miniaturized parts which are increasingly demanded in many industries. Using tools with diameter less than 1 mm results in rising the so-called “size effect” and problems due to ploughing at low feeds per tooth. It is therefore crucial to estimate value of minimum chip thickness which helps to reduce or eliminate the ploughing. In this study role of scaling down is investigated with regard to milling operation in micro- and macro-scale. A titanium alloy Ti-6Al-4V is used as workpiece. Two-flute endmills with diameters of 0.8 and 2 mm are used representing micro and macro-scale, respectively. Effects of axial depth of cut and feed rate as input parameters were evaluated on such output characteristics as specific cutting energy, microhardness, surface roughness, topography and chip formation. Results show higher values of microhardness and specific cutting energy in micro-scale. Microhardness and specific cutting energy in micro-scale were found to be 6 times and 150% greater than the macro-scale, respectively. The study suggests that minimum chip thickness can be varied approximately between 0.25 and 0.49 of the cutting edge radius.

The radios of particles in Dissipative Particle Dynamics (DPD) method is investigated numerically taking into account size and type of conservative force. In the most of previous studies, the DPD particles have been considered as a point center of repulsion with zero radios and hence sphere size is prescribed by the creation of a structure of frozen DPD particles. Although only in ideal gas state or zero conservative force the DPD point particle is meaningful and with conservative force the DPD particles have an intrinsic size which is assigned by the spherical impenetrable domain occupied by each particle when immersed in a sea of other particles. At first the appropriate method should be define to calculate the size of DPD particle. Different methods including Stokes-Einstein relation, Stokes law and radial distribution function (RDF) are studied and it is concluded that according to limitation of Stokes-Einstein and Stokes relations the RDF is the best method for evaluation of DPD particle size. In the following, the trend of DPD particle size changing and their distribution in the system with linear and exponential conservative force examined. At the end we demonstrate that the employing of exponential conservative forces for the colloid-colloid and colloid-solvent interactions but keep the conventional linear force for the solvent-solvent interactions achieve a well-dispersed suspension with different particle sizes without extra computation

In this paper, cold roll forming process of a high strength steel pipe using four types of flower pattern including circular, edge, double radius and reverse bending is simulated with finite element method in MSC Marc Mentat software. Due to importance of quality of final pipe and in order to achieve the desired geometry in high strength steel pipes, selecting the appropriate flower pattern to design the pipe roll forming production line is considered. Using finite element simulation results, deformation of sheet in this process is studied and effect of flower pattern type on geometry of final product, which includes curvature distribution, spring back and thickness distribution of pipe, is investigated. Results show that implementing reverse bending flower pattern, leads to reduction in deviation from mean curvature at edge of the sheet up to about 65 percent. Thickness distribution analysis shows that circular and edge flower patterns cause upsetting and thinning of edge of the sheet up to 0.2 millimeters, respectively. But, use of double radius and reverse bending patterns cause average thickness of edge to be well adjusted to reach 2.8 millimeters. Also, circular flower pattern has the lowest value of spring back in terms of variation of mean relative curvature of 0.69 percent and edge deviation of 0.15 millimeters. To validate the finite element simulation, experimental tests were designed and conducted using one forming stand. By comparing resultant data of experimental tests with simulation results, validity of finite element simulation confirmed.

Partial differential equations are needed in most of the engineering fields. Analytical solutions to these equations cannot be derived except in some very special cases, making numerical methods more important. Alongside advances in science and technology, new methods have been proposed for solution of partial differential equations, such as meshless methods. Recently, the generalized exponential basis function (GEBF) meshless method has been introduced. In this method the unknown function is approximated as a linear combination of exponential basis functions. In linear problems, the unknown coefficients are calculated such that the homogenous form of main differential equation is satisfied in all points of the grid. In order to solve nonlinear equations, Newton-Kantorovich scheme is first used to linearize them. The linearized equations are then solved iteratively to obtain the result. In this paper, time dependent problems in solid mechanics have been investigated. In order to examine performance of the proposed method, linear and non-linear problems in solid mechanics are considered and the results are compared with analytical solutions. The results show good accuracy (less than 1 percentage error) of the presented method.

Underbalanced drilling and managed pressure drilling with foam have been gained attention of the world oil companies due to its many benefits. The advantages of this method include oil and gas production during drilling, high-speed drilling, drill bit life increase, better cutting transfer and reduced formation damage. In this paper cutting handling by foam was investigated in which foam was assumed to be a homogeneous, single-phase, compressible and non-Newtonian fluid whose rheological properties can be well described by power law model. The assumptions and governing equations of transient two-fluid model were expressed in Euler-Euler coordinate for fluid-particle (foam-cuttings). The upstream method is used to discretizing the equations and the results of the numerical solution are reported in the form of pressure, speed, cutting concentration, quality and density of the foam logs along the well. The impact of back-pressure, ROP, injection rate of gas and liquid, shape and size of cuttings, water influx and oil production on cutting concentration and bottom-hole pressure have been investigated. With increasing parameters such as back-pressure, liquid and gas flow rate, size of the cuttings and ROP, bottom hole pressure and cutting concentration increases. Cutting concentration decreases with increasing liquid and gas flow rate and increases by increasing back-pressure, cutting size and ROP. For validating, the results of the numerical solution are compared with field data obtained from well FR-1 located in the Santa Catarina state of Brazil which show about 16.5 percent errors.

In this research, a general mixed mode I/II fracture criterion is developed for fracture investigation of orthotropic materials. Various experimental tests show that cracks always propagate in an isotropic medium and along fiber direction in orthotropic materials. With a novel material model titled an Equivalent Reinforced Isotropic Model (ERIM), fracture criterion can be extended for investigation of fracture in orthotropic materials. This inspires that fracture in orthotropic materials follows the fracture mechanism in isotropic materials. This new criterion is developed based on extension of MTS which is widely used for isotropic materials. Also in this research the effects of T-stress in fracture of some specimens has been studied. A comparison between available experimental observations and theoretical estimation implies on capability of developed criterion for predicting both crack propagation direction and fracture instance, wherein the achieved fracture limit curves are also compatible with fracture mechanism of orthotic materials. It is also shown that non-singular T-stress term has a significant impact on orthotropic material failure, especially when the second mode is dominant mode. It is shown that unlike isotropic materials, fracture toughness of orthotic materials in mode I (K_IC) cannot be introduced as the maximum load bearing capacity and thus new fracture mechanics property, named here as maximum orthotropic fracture toughness in mode I (├ K_IC ┤|ortho) is defined. Considering ease of access, wood is used as experimental specimen for the purpose of comparing the results.

In this paper the modeling of combined heat and power (CHP) system driven by Stirling engine has been discussed. The system consists of one beta type Stirling engine as the prime mover, heat recovery system, power generator and the auxiliary boiler. The analysis of the Stirling engine is a non-ideal adiabatic analysis. To increase the accuracy of modeling, the frictional and thermal losses of Stirling engine are considered in comparison of other previous studies and the non-ideal adiabatic analysis is performed using a developed numerical code in MATLAB software. For model validation, the operational and geometrical specification of the GPU-3 Stirling engine was used and the results were compared with experimental results and other previous models. Then, one beta-type Stirling engine was proposed as prime mover in cogeneration system for building applications. The use of the cogeneration systems in building applications becomes more common, which system from the perspective of the fuel consumption and pollution emission, have a significant advantage in comparison with the other conventional systems. For this purpose, the effects of engine frequency, regenerator length, and heat source temperature on fuel consumption and pollution emission of system were examined and proper engine design parameters were selected. Finally, the electric power and thermal power were achieved 11263 W and 21653 W, respectively, with reduction in fuel consumption and pollution emission of 37% and 42%, respectively.

Heat transfer through the internal supports of the cryogenic fluid tanks is an important issue in the tank design and manufacture. On the other hand, the internal supports strength should be enough to stand safely against the forces applied to the internal tank. From the heat insulation point of view, most of the polymers are suitable materials to use in the internal supports. But the low mechanical strength of the most of the polymers limits the life of the supports made from polymers. In this paper, a new composite support made from steel and polymer is presented for the internal supports. Multilayered design of the steel part of the presented supports controls the heat transfer through this part by adding more thermal contact resistance (TCR) to the heat flow path. An analytical model is developed to calculate TCR between layers of the steel part at various pressure and temperature conditions. A thermo-mechanical coupled finite element (FE) model is developed for the proposed support and solved by ANSYS FE code. Temperature distribution and heat flux of the presented support are investigated by FE analysis results. Heat flow through the new support design is compared with the heat flow of the supports constructed with polymer blocks. Comparison of the heat flow results shows that the amount of heat transferred to the cryogenic tank through the internal supports in the static loading condition decreases when using proposed composite design instead of polymer blocks.

In recent years, the importance and requirements for high-quality energy and water has been increased significantly, and this trend will strongly continue. One of the promising solution for the water scarcity's problem is desalination of the oceans salt water by thermal methods, and if the required thermal energy is provided by wastes of a thermal power plant it will be competitive with other methods. In this paper, a combined cycle including solid oxide fuel cell (SOFC) and gas turbine is used as thermal resource. Here, combination of these two systems beside of multi effect desalination (MED) system leads to reduce in energy consumption, pollutant emissions, investment and operation and maintenance cost, as well as increase of efficiency in comparison with the conventional individual systems. Exergetic and economic analysis using a computer program in EES software was performed. The results proposed a system with thermal and exergy efficiency of 60 % and 57%, respectively. The system expenditures and revenues were estimated, and the effect of two important design parameters, i.e. operational temperature and current density of fuel cell, on exergy efficiency and levelized cost of electricity were investigated. Consequently, the reliability and availability of the proposed system are calculated as 0.842, using the Markov method. It is seen after reliability analysis and availability calculation the exergy and energy efficiency is reduced and LCOE increased by 8.8%.

FLDs, in fact are the range of strain combinations which identify the beginning of local necking. Different parameters such as sheet thickness, structural defects, temperature, loading direction, forming speed and etc. have influence on these diagrams and one of the most effective parameters is forming speed and it has a direct connection with press speed in sheet forming. In this research FLD are calculated for aluminum 6061 sheets with 3mm thickness in rates of 20, 100 and 200 mm/min experimentally and simulated in the rates of 20, 100, 200, 500 and 800mm/min. In order to do the experimental tests, bulge test is conducted in sheets in six different sizes according to standard by hydraulic press and built steel die. Also numerical modeling was done using the Abaqus finite element software and the maximum strain gauge criterion by entering the Johnson Cook data. Experimental and modelling results verify is studied by surveying the tearing location and errors between FLDs and result showed that experimental and numerical data are compatible with acceptable errors. It was observed that by increasing forming speed FLD increases, in a way that by increasing the press speed from 20 mm/min to 200 mm/min, FLD increases for 30 percentage. This variation can have different reasons such as friction effect and interaction effects between die and sheets, because at the low forming speed (of less than 100 1/s for strain rate) and at the room temperature, the effect of strain rate and mass inertia are minimal.

In this paper, optimization phase angle of alpha Stirling engine performed step by step method. After studying on the operation of various types of Stirling engines, the effect of the phase angle on the power and efficiency of Alpha Stirling engines was studied. The kinematic modeling of volumetric compression and expansion volumes has been done by ADAMS software. Then, the linearization of the thermodynamic equations was carried out on the basis of analysis of the isothermal and five-volume adiabatic stirling cycles to obtain the initial solution of its effective parameters on the power and efficiency. To optimize the phase angle between compression and expansion pistons, stepwise numerical solution of the stirling cycle was performed. Comparison of numerical solution with experimental data indicates an error rate of less than 5.3%. The simulation results show the optimum phase angle of 103 °. At this optimal angle, the results indicate an increase of 4.8% of the output power rather than the output power at a 90 ° pre-aligned angle. Simulation results indicate an improvement of 1.2% of the Alpha Stirling engine efficiency by adjusting this phase priority angle to the efficiency at 90 °.

In researches on ducted wind turbines, in order to consider the effects of the duct, the solution process is dependent on parameters which arise from experimental tests or computational fluid dynamics. In the present study, our goal is to present a method for considering the effects of the duct and hub on the wind turbine enclosed in a duct without needing to costly experimental tests or time-consuming numerical simulations. For this purpose, the potential flow method which requires only lift and drag coefficients as input parameters is used. The surface vorticity method and the lifting line theory based on the Biot-Savart law are implemented as a numerical method to analyze the performance of the ducted horizontal axis wind turbine. The proposed method is programmed in the MATLAB software. The validation is carried out with experimental result of the DONQI horizontal axis wind turbine. The results are in good agreement with experimental data in the literature. The output power of the ducted wind turbine is compared to the same bare wind turbine to show the effect of the duct on the performance of the wind turbine. The power curve is illustrated that the ducted wind turbine produces more power than an unducted wind turbine in the same condition.

Oscillating flow is one of the most important characteristics of flow in stirling engine heat exchangers. In this study reciprocating flow in stirling engine cooler is investigated numerically. Numerical solution is based on finite volume and pressure based algorithm by using the commercial CFD code fluent. A Shell and tube type heat exchanger used as cooler. The working fluid, gas flows inside the tubes while the cooling fluid, water flows around the tubes. The heat transfer coefficient, temperature difference between tube walls and working fluid, Nusselt number and friction coefficient are calculated for Helium, Carbon dioxide and Nitrogen at different operating pressure and oscillating frequency. The Nusselt number, heat transfer coefficient and temperature difference between tube walls and working fluid increase with increase of operating pressure or oscillating frequency while Friction coefficient decreases. Helium has the highest heat transfer coefficient and friction coefficient and the lowest temperature difference between tube walls and working fluid. At the highest operating pressure and oscillating frequency, Carbon dioxide has the highest Nusselt number and the lowest Friction coefficient. Finally empirical equations for Nusselt number and friction coefficient are proposed for Helium, Carbon dioxide and Nitrogen, the error of the equations are within 0.23-8.07% when the range of kinetic Reynolds number is 2.96-212.50.

One of the main challenges of simulating virtual objects by haptic devices is instability, especially in simulating stiff objects. In this paper, a stability criterion for a haptic device is derived using Lyapunov approach. The haptic device is modeled as a mass and viscous friction, which has to simulate the touching a virtual environment (VE) with specified stiffness and damping. Dynamic equations and state-space equations are derived with assumption of small values of sampling time, time delay and virtual damping. A Lyapunov function is proposed, consisting of summation of kinetic and potential energy of the system, plus two unknown terms. Each one of these two unknown terms is a function of one system states (i.e. position and velocity). These two functions are determined so that, from one side the Lyapunov function be positive definite, and from the other side the stability criterion is reached with putting time derivation of the Lyapunov function negative. The stability condition determined by this method is a linear criterion between maximum permissible virtual stiffness, virtual damping of the VE, physical damping of the haptic device, sampling time and time delay, and is consistent with the results of previous researches with linear methods. The importance of the presented analysis in this paper is that this method can be extended by adding new terms to the Lyapunov function, to remove some limitations and to take into account nonlinear effects. Presented criterion and its results are verified by experiments on KUKA robot.

Studying the behavior of composite materials reveals that various types of failure modes occur when material experiences different loading conditions, which may have a significant impact on performance and properties of a structure. In this research, we study the mechanical response of orthogonal multi-layers by considering different failure modes at micro-scale and their development in macro-scale. For this purpose, the effect of the emergence and growth of fiber separation and subsequent formation of matrix cracks are investigated in the micro-scale. Furthermore, interlayer separation caused by leaving the matrix are studied in macro-scale. To model the separation of fiber matrix which is the first dominant failure mode, the sticky area method is used. The model verification and obtained results are compared with the previous research. Then, XFEM method is used to take into account the failure mode of matrix. Finally, using of the sticky area method, we are able to simulate the separation of matrix layers. The FE-program Abaqus via its user scripting interface (Python) are employed in this research for modeling of fibers embedded into matrix.

In the present paper, heat transfer and entropy generation in Rayleigh-Bóenard convection of nanofluids subjected to a magnetic field within an enclosed cavity is studied by adopting the lattice Boltzmann Model. The left and the right walls are smooth and insulated against heat and mass. The bottom wavy wall is heated, while the top flat wall is maintained at the cold temperature. The variation of density is slight thus; hydrodynamics and thermal fields equations are coupled using the Boussinesq approximation. The density and energy distribution are both solved by D2Q9 model. The study have been carried out for Rayleigh number 103, 104 and 105, Hartmann number 0, 30, 60 and 90 and volume fractions of 0 up to 0.04 for Cu, CuO and Al2O3 nanoparticles in base pure water fluid. Results show that the Nusselt number and entropy generation increase with the increment of Rayleigh number and nanoparticles volume fraction, but those decrease by the increment of the Hartmann number. The enhancement of magnetic field augments or plummets the effect produced by the presence of nanoparticles on heat transfer and entropy generation at different Rayleigh numbers. In addition, it is shown the greatest effect of nanoparticles on heat transfer and entropy generation is observed by addition of Cu nanoparticles and the least is function of Ra number. This study can, provide useful insight for enhancing the convection heat transfer performance by considering of energy losses within enclosed cavities with Rayleigh–Bóenard convection nanofluid under influence of magnetic field.

A new method is proposed for implementing the no-slip/no-penetration conditions on the irregular immersed boundaries in the vorticity-streamfunction formulation of the incompressible viscous fluid flow. Time integration is performed using a semi-implicit method such that in each time step the vorticity-streamfunction equations are changed to a Helmholtz and a Poisson’s equation. Some singular source terms are added to the right hand sides of these equations, in the solid region, such that the desired boundary conditions can be satisfied. The singular source terms are found, using the inverse problems method, such that the desired boundary conditions of the vorticity-streamfunction equations be satisfied. Since the fast Poisson’s solvers are used, the method is high performance, with the computational effort of O(NlogN); and it is also flexible because it can be applied easily to the complex geometries. The method is applied in simulation of the fluid flow around a square solid obstacle, placed in a channel, and the agreement of the results with the other benchmark results are shown.

In this paper, a numerical algorithm based inverse method is used to estimate effective diffusion coefficient by using experimental tracer distribution. The Algorithm uses factitious experimental data which are produced by adding noise to numerical data obtained from direct problem. A comprehensive model (Diffusion-Convection-Reaction) is used to derive PET tracer distribution in tumor tissue with microvasculature network. This model was used because of considering all transport phenomena in tissue. In this work to achieve accurate distribution of tracer in tumor tissue, convection diffusion reaction equation which is a PDE is implemented. The proposed tracer in this work is Fluorodeoxyglucose (18F). Solution of inverse problem for estimating effective Diffusion Coefficient is based on minimization of least squares norm. In this work Levenberg-Marquardt technique is applied. Solution of parameter estimation problem require calculation of sensitivity matrix which elements are sensitivity coefficients. Sensitivity coefficients shows differentiation of Tracer concentration with respect to Effective Diffusion coefficient variation is calculated using first derivation of concentration equation. The equations of concentration distribution and sensitivity coefficients are solved using Finite volume method. The results show that the numerical algorithm is able to estimate the effective diffusion coefficient in tissue.

Energy saving, low robot mass to carried mass ratio, more ability to work in various environments, easier delivery of parts and lower production costs in flexible robots make these robots more attractive than rigid robots to many researchers and industries. But due to nonlinearities in flexible robot system and high vibration in operation points and also more sensitivity against external disturbances, control of these robots is more difficult and complex. In this paper a controller for a flexible link manipulator based on fractional calculus is practically implemented. At first the dynamic model of a single flexible-link robot is introduced. Then various controllers such as fuzzy control, PID control, and fractional order PID torque control are practically implemented on a single flexible-link robot made in laboratory, and then the performance of each controllers in decreasing of arm vibration in final desired point and tracking error reduction are investigated. Further, to compare the robustness of the designed controllers, a same constant disturbance is applied to all controllers and their performance are compared. Finally, the simulation results and experimental results show that the fractional order PID torque controller has the best results among the implemented controllers.

In this study, interference fit process and its influence on fatigue life of holed specimens made of AISI4340 hardened steel were investigated experimentally. For this purpose, Tungsten carbide pins were fitted into the steel samples and putted under fatigue test with zero load ratio and 10 Hz frequency. These experiments were done for specimens with 5 interfence levels and two repetition. Results revealed that the compressive force required for interference fitting the pin in hole increases as the interference size goes up. The peak force was observed when the pin reached bottom of specimen and the maximum plastic deformation occurred. 3D finite element modeling of interference fit showed that distribution of residual stress on the hole wall and far away from it were compressive and tensile respectively. Moreover, results of fatigue experiments showed increasing the specimens fatigue life up to 1.5% interference fit. In this level, fatigue life is 2.5 times greater than specimen without fitting. However, by increasing interference up to 2%, increasing trend of fatigue life is stopped. Analysis the fracture surface of samples showed that the fatigue cracks are initiated from edge of the hole at specimens with press fit. While crack initiation site was in the middle plane of hole for specimens without fitting.

In this paper, using a hybrid compression-absorption refrigeration system for providing cooling demand of air condition and fridges for meat, fish vegetable and dairy preservation, simultaneously on a ship is proposed. Cooling demands for air condition and fridges are in each ship. So, the use of proposed system can be considered in all ships and is not limited to a special one. Exhaust gases of auxiliary engine are applied as a heat source for absorption section. The results show that exhaust gases heat recovered is higher than the demand of generator on all ranges of engine loads. Unlike main engine, auxiliary engines are always on and don’t depend on the movement of ship. So, exhaust gases of auxiliary engine as a heat source is an appropriate and permanent heat source for generator of absorption section. Based on energy, exergy and environmental analysis, a comparative performance analysis of proposed system and conventional system (vapor compression refrigeration system) has been carried out. The results show that based on tropical condition, fuel consumption and total irreversibility of proposed system are respectively 91.6% and 26.6% less than conventional system. Using a hybrid compression-absoption refrigeration system in comparison to vapor compression refrigeration system causes 64834 $ annual saving due to reduction in CO2 emission penalty(cost).

In the present study, the available methods of predicting the sound transmission loss through infinitely long double-walled cylindrical shells with porous layer are developed to analytically compute the sound transmission loss in triple-walled sandwich cylindrical shells in the presence of an external fluid flow. Loves’ shell theory and Lee’s method based on Biot’s theory are used to describe the motions of thin isotropic triple-walled cylindrical shell and wave propagation in the porous media, respectively. The vibro-acoustic problem for the most complicated configuration of the triple-walled sandwich cylindrical shell is formulated and solved by the transfer matrix method with appropriate boundary conditions. The total transmission loss in a diffuse field is calculated and validated by considering the effect of total internal reflection. Then the transmission loss of triple-walled cylindrical shell is compared with its double-walled counterpart of the same weight. The results generally show a superior performance in sound insulation for the case of triple-walled shell, considerably at mid-high and high frequency regions. Moreover, ten typical configurations, which involve different coupling methods between the walls and porous layers, are considered to completely study the effect of various configurations on the sound transmission properties. As will be shown, a configuration with the largest number of air gaps in its structure provides better performance in sound transmission reduction almost at the entire frequency range. The effects of external fluid flow and azimuthal angle are also studied on the sound transmission loss.