نشریه مهندسی مکانیک مدرس
سال هفدهم شماره 11 (بهمن 1396)

The robot has to adapt its movement with the various condition of surfaces and ensuring the stability with the proper motion of its bust and legs in order to be able to move on different surfaces. A lot of basic parameters of the gait can be expressed by the planned seven-linked bipedal robot. One of the issues that have always attracted the attention of researchers, in this field, is to predict the motion path that guarantees the stability and minimizes the energy. In this study, parameter optimization being used which means that at the first, joint angles are defined as a parameter functions and then with respect to kinematics constraints that define maximum and minimum of joint angles, the problem of motion obtained in the way that maximizing stability of robot and minimizing energy and puts the robot in the permitted stable region. Also, we tried to have zero moment point scale used to calculate the stability of robot. Experimental tests in order to motion analysis for walking healthy were performed and the results were validated. Finally, due to the presented model and predicted path, the robot can move like a person. Comparison of experimental results and the result of presented model were used in each step to validate the accuracy of the proposed method.

In this study, the effects of using pure water, water/ethylene glycol mixture with 50:50 wt% and pure ethylene glycol as the working fluids on the energy and exergy efficiencies of a photovoltaic thermal (PVT) system are experimentally investigated. Moreover, the performance of the PVT systems are compared with a conventional photovoltaic (PV) system. The experiments are performed on a selected day in August at the Ferdowsi University of Mashhad, Mashhad, Iran (Latitude: 36° and Longitude: 59°). The investigated parameters in this study are: the photovoltaic cells temperature; output electrical and thermal powers; electrical and thermal energy efficiencies; output electrical and thermal exergies; and electrical and thermal exergy efficiencies. Based on the results, the PVT system with water/ethylene glycol mixture increases the output electrical power by about 5.41 % compared to that of the PV system. Furthermore, the results indicate that using pure water in the PVT system enhances electrical and thermal energy efficiencies compared to those of pure ethylene glycol and water/ethylene glycol mixture, whereas the overall exergy efficiency of PVT systems with pure water and water/ethylene glycol mixture working fluids are approximately same.

Compressor and their blades are one of the most important parts of gas turbines. Based on recent reports, failure of compressor’s blades was one of the major cause in malfunctioned t56 gas turbines. In this study, propagation rate of a crack within the compressor blade of a T56 jet engine has been investigated. To this end, centrifugal and aerodynamic forces acted upon the blade has been calculated and their corresponding stress field has been simulated in ANSYS software. Spots at the maximum risk of foreign object damage and corrosion had been located, and their bending and tension stresses had been calculated via employed simulation. Subsequently, an initial half elliptical crack has been created on all of previously located spots, and their stress intensity factor using Raju-Newman method has been determined. Finally, by using Paris law fatigue life and crack growth rate of each cracks has been extracted, individually. Results indicate a drastic decrease in fatigue life of blades when crack located close to the blade’s root. Furthermore, cracks located on the suction surface has remarkably shorter fatigue life than those which are located on pressure surface, in comparison.

Fatigue is one of the most important phenomena in the life determination of parts in various industries. The life determination of the part through the test procedures, due to the real loading (spectral loading) is very complicated. Thus, it is necessary to equalize the fatigue real cycle to test cycles applicable in the laboratory. In this paper, by using the available equations in equalization of fatigue cycles, some equations have been studied for the load spectrum. Then the deviation percentage of these equations has been investigated for two very applicable materials in aviation industries (Aluminum 7075-T6 and Steel 4130) by means of block loading spectrum. It has been observed that the errors is very large and not acceptable in some situations. After that, in order to decrease the errors, a new method has been proposed to determine the number of equivalent cycles in fatigue test, considering equalization of the real load and converting it to an applicable load in the laboratory. In this equalization process, constant amplitude loading was obtained for a sample loading block for each of the mentioned materials in such a way that the rate of fatigue damage to be equal to the real loading. Finally, some standard specimens have been tested by fatigue loading and has been observed that the new proposed procedure is capable to predict the fatigue life. The maximum error is equal to 5.5 per cent.

Hybrid joints (Metal–Composite) is being used more and more in aerospace industry due to their low weight and high strength. Dynamic study of this joint, owing to limitation of increase in screw’s preload in composite substructure, has certain importance. Effective factors on nonlinear behavior of the joint are low preload of the screw and high excitation force amplitude on the structure. Layer Element Model has been used to better the description of joint’s behavior in recent years. In this study effects of nonlinear behavior of joint on the structure has been investigated using 2D layer element theory in two divisions: increase of damping and decrease of stiffness which result in nonlinearity. Stiffness characteristics of the joint was modeled with normal stiffness and damping characteristics of the joint with structural damping in shear direction. Nonlinear frequency response function for two preload and two excitation force was extracted and nonlinear finite element model for stiffness and damping of the joint is suggested by High-order polynomial approximation in terms of response amplitude. Effects of increase of excitation force amplitude and decrease of screw’s preload on increase of nonlinearity was extracted by this finite element model. Results indicate that presented nonlinear finite element model corresponds closely to nonlinear vibration tests.

In this study, design of a novel robust control method for three-link underactuated biped robot which can satisfy appropriate constrains on the robot and cause the stability and rhythmic movement of the robot, is presented. Due to the wide use of sensors and actuators in mechanisms and robots, and existence of noise and also uncertainty in the system components or other error stemming from unmolded dynamics in the system or unwanted disturbances acting on them, there is an essential need for employment of robust control methods. In order to apply locomotion’s constrains to the system, the feedback linearization method is used. Additionally this method is combined with the sliding mode method to obtain a robust control method. The other purpose of the study is the complete elimination of chattering phenomenon. To this end, the control method is combined with the backstepping method. Finally, the exponential stability of the method, which is called FLBS, is proved, and the stability of the obtained walking cycle is shown using the Poincare map. In the robot modeling procedure, the contact between the swing leg and the ground is considered to be rigid and instantaneous. The underactuated nature of the robot and the importance of the role of contact in stabilizing the robot movement are taken into account in this study. Finally, simulations based on this control method are performed which show the exponential stability of robot movement, elimination of chattering and robustness against either disturbances or uncertainties.

In order to accurately calculate the critical force and time of manipulation, the influence of different input parameters on output parameters should be analyzed. The EFAST statistically-based method is one of the accurate and fast methods of sensitivity analysis. Previous studies have been conducted regarding the effect of different parameters on critical force and time of two-dimensional manipulation, using various methods including graphical, differential and statistical methods. In this study, for the first time, with the use of EFAST sensitivity analysis method, the effect of six dimensional input parameters including length of cantilever, width of cantilever, thickness of cantilever, tip height, radius of nanoparticle and tip radius on eight output parameters including critical force and time of manipulation in four modes of sliding along X axis, sliding along Y axis, rolling along X axis and rolling along Y axis, is analyzed in three-dimensional manipulation. The final obtained results demonstrate that the parameter of “thickness of cantilever” is the most influential parameter on critical forces of manipulation, and the parameter of “tip height” is the most influential one on critical times.

In the present study, a new thermal comfort model based on cutaneous thermoreceptors has been developed by using non-Fourier heat transfer in biological tissue. The new model considers the concept of finite propagation speed of thermal disturbance by using non-Fourier equations. Since biological tissues consist of complicated and nonhomogeneous structure, the heat process is different from other materials. The dual phase lag (DPL) bioheat transfer model describes two time relaxations is a case of non-Fourier heat transfer application in biological tissue. In this study, the mentioned model has been utilized to evaluate the temperature distribution at the depth of skin thermoreceptors. The new thermal comfort model has been verified by comparisons with experimental data where a good agreement has found. As thermal response of the human cutaneous thermoreceptors depends on temperature and its change rate at the depth of thermoreceptors; therefore, it is very important to estimate these parameters with a good accuracy. In this paper, the previous models improved and effect of non-Fourier heat transfer on temperature derivative is investigated. It is found that the DPL model has a significant effect on change rate of temperature and thermal response of cutaneous thermoreceptors.

In situations involving large zeta potential, the classical Poisson-Boltzmann theory of electrolytes breaks down and a modified Poisson-Boltzmann equation which takes into account the finite size of the ions must be utilized. In addition, most biofluids cannot be treated as Newtonian, therefore, simultaneous effects of finite size of the ions and non-Newtonian behavior of the fluid in combined electroosmotic and pressure driven flows have been examined in the present study. The Governing equations are solved by a finite-difference-based numerical procedure in a rectangular microchannel. The ion size is introduced into the modified Poisson-Boltzmann equation by the steric factor, which allows considering the ions as point charges or finite sizes. Considering the ionic finite size, generally enhances the velocity of the shear-thickening fluid, while reduces the velocity of shear-thinning fluid. The Cross sectional aspect ratio is also considered and it was found that the adverse pressure gradient greatly affects the velocity profile, when aspect ratio increases, while velocity profile is less sensitive to aspect ratio variations in favorable pressure gradients. Furthermore, friction coefficient of both shear thinning and thickening fluids increases with the increase in zeta potential for point charge model, which for finite size charges decreases. Cross sectional averaged velocity reduces under steric effects for shear thinning fluids at large zeta potentials, while it is slightly influenced by shear thickening fluids.

The design of a robust controller for the automatic landing system is investigated for an unmanned fixed-wing aircraft based on an external navigation system. Since landing is the most difficult phase of flight, the major accidents are occurring in the phase. So, providing a high-precision automatic landing system in presence of environmental disturbances is very important for UAVs landing. The used landing navigation system is founded on a portable land-based laser-optics system which can track the UAV and calculate the altitude and direction of it toward the center of runway. However, the navigation system is external; sending them to the UAV can be done with a delay. In this regard, UAV’s control systems must be designed such that the stability of aircraft is satisfied based on information of navigation system with considering the model uncertainty, noises, disturbance and navigation delay. So in this paper, a new robust stabilizer controller is suggested for UAVs to overcome these challenges with considering some limitation in the structure of the controller. Finally, simulation results based on laboratory software in the loop been presented. The results are indicating the capability of using proposed method for automatically landing of UAVs.

In this paper, a new design approach for an admittance control method is presented to deal with the environmental disturbances for user-in-charge exoskeletons. Since the challenge of maintaining the stability of the robot and the human is met by the user, environmental disturbances as a set of external forces should be considered. However, the proposed control methods have already ignored the issue and focused on presenting a desired dynamic relation between the interaction forces and the robot motion. This paper aims to find a control solution to maintain the desired behavior of the classical controllers in response to the interaction forces as well as to deal with disturbances properly. For this purpose, a control structure is developed by substituting an impedance control method for the low-level layer of an admittance controller. A simulation on an exoskeleton leg is conducted to evaluate the performance of the proposed controller in comparison with the classical control methods for user-in-charge exoskeletons. In contrast to conventional control methods, the results shows that the proposed controller can deal with both the interaction forces and the disturbances properly as the consequence of establishing different dynamic mappings for each of them.

In this paper, ferrofluid flow in a closed cooling loop without any mechanical pump has been simulated. The flow of the ferrofluid in the closed loop is resulted from applying a non-uniform magnetic field and the thermo-magnetic effect of the ferrofluids. The ferrofluid consist water and different volume fractions of iron oxide nanoparticles with nanoparticle diameter of 13nm. The two phase mixture model and the control volume technique have been used in the present study. The applied non-uniform magnetic field is resulted from an electromagnetic solenoid and the steady and also the transient modeling of the flow in the cooling loop from start point (stagnant ferrofluid in loop) have been carried out. The obtained results show that by applying magnetic field and also by taking advantage of temperature dependent property of the magnetic susceptibility, a flow of ferrofluid is created in the loop and by increasing the heat input (heater power) in the loop, the flow rate in the loop is increased. Moreover, the results show that by having a cold source (for rejection of produced heat) with higher constant temperature, the flow rate in the loop increases. Furthermore, the flow rate in the cooling loop is increased as the volume fraction of the nanoparticles in the base fluid increases. The mentioned cooling loop can be used in the electronic cooling systems.

The goal of this research is to design and build a solar adsorption chiller operated by activated carbon / methanol. Continuous refrigeration systems are able to produce cooling continuously. This paper examines the effect of activated carbon particles on the performance of a continuous adsorption chiller device. The source of this chiller is through sunlight and supplied by a parabolic collector that does not need to track sunlight. The system operates with two adsorbent beds that, when one is adsorbed, the other is desorbed. The experiments were carried out in Yasuj during three different days in the month of Bahman for three hot water input to the chiller 38℃, 34℃ and 30℃. The average ambient temperature during the experiment is 18℃. Experimental results shows that for the total energy input, 13MJm-2, the average performance factor of the chiller is when the inlet temperature of the hot water of the chiller is 38℃, 34℃ and 30℃, respectively, of 0.123, 0.103 and 0.10. For Previous temperatures the average specific cooling power of the device was obtained at 88Wkg-1, 65Wkg-1 and 50Wkg-1 respectively.

Today by usage of the simulation of normal tissue and the process of material diffusion in body, the place of tumor can be predicted. By considering the tumor tissue, its growth can be evaluated. The fluid flow in the capillary, its effects on the adjacent tissue and the diffusion of molecules from capillary wall are considered in these kinds of simulation. Cancer cells due to the high rate of dividing cells, have a low level of oxygen. This lack of oxygen is called Hypoxia, so by using of different invasive and noninvasive manners, the amount of oxygen is measured in the body. The PET device indicates the oxygen distribution by use of special tracers in the several parts of body. In this essay by considering a real capillary network, the blood flow had been simulated, then by taking to the account of its effects on the tissue, oxygen pressure and the concentration of tracer had been simulated at the same time. At the end, the concentration of free and bind tracer is shown and its changes by the time is analyzed.

This paper presents an experimental and numerical investigation of phase change material melting in a rectangular enclosure. The aim of this research is the study of the effect of the tilt angle of the enclosure on the flow structures and the melting rate. In the experimental section, the visualization of the melting process is carried out by the photography of the phase change material through a transparent enclosure. Then, the image processing of the photographs is performed to calculate the instantaneous liquid fractions. The variation of the solid-liquid interface by tilting the enclosure clearly implies the evolution of the flow structures in the liquid phase. Numerical simulation is performed using the enthalpy-porosity approach for tilt angles of 90, 45 and 0o and wall temperatures of 55, 60 and 70 oC. The results show that by decreasing the tilt angle from 90o to 45o and 0o, the melting times are 52% and 37% less than that of the vertical enclosure. Melting time reduction in the inclined enclosure is due to the formation of the vertical flow structures and thermal plums in the liquid phase. By Increasing the Stefan number from 0.36 to 0.43 and 0.55 the thermal energy storage increase by 5.4% and 13.8%, respectively. Also, a correlation is developed to predict the thermal energy storage in the tilt enclosures using nonlinear regression.

Forming limit diagrams (FLDs) are useful tools for prediction of the instability of sheet in metal forming. The goal of this study is to evaluate the formability of 260 brass alloy sheets under various strain rates (particularly at high strain rate). Three types of experimental procedure were developed: Nakazima test (for determination of the FLD at quasi-static condition), hydrodynamic forming (for determination of the FLD at intermediate strain rate) and Electrohydraulic forming (for determination of high strain rate FLD). Electrohydraulic forming (EHF) is a high velocity sheet metal forming process in which two or more electrodes are positioned in a water filled chamber and a high-voltage discharge between the electrodes generates a high pressure to form the sheet. Arbitrary Lagrangian Eulerian (ALE) formulations coupled with fluid–structure interaction (FSI) algorithms (that are available in the advanced finite element code LS-DYNA) were used to the numerical simulation of process and design of sheet metal specimen geometries. It was found that the forming limits of brass 260 in EHF increased more than 11% relative to the quasi-static. In addition, the formability of this material under the hydrodynamic loading is 4% higher than quasi-static values.

In this study, the effect of chaotic advection on laminar mixing is analyzed experimentally and numerically. Mixer includes two circular rotors and a circular stator in the way that rotational speed of each rotor could be controlled by time. This kind of mixer is widely used in the food and pharmaceutical industry. The performance of the mixer was investigated experimentally with dye injection and image recording. Moreover, the effect of chaotic flow on mixing numerically is studied qualitatively and quantitatively with Lagrangian fluid particle tracing, calculating the stretching rate of fluid elements and Poincare sections. The experimental results indicate that as a result of applying sinusoidal perturbation on rotational velocity of rotors, weak mixing zones will disappear with the passage of time, and fluid particles will be distributed uniformly in the surface of the mixer. Numerical simulation shows that the mixer flow is sensitive to initial condition when rotational velocity of rotors is variable, and this is one of important factors in chaotic flow. Further, calculation of stretching rate of fluid elements indicates that average exponential value of fluid elements stretching in the chaotic flow is two times more than non-chaotic one. This research, based on scientific concepts and theoretical application of chaos in fluid mechanics, denotes that the efficiency of low-speed mixers in highly viscous fluid mixing is increased without any increase in the consuming energy.

In this article, the nonlinear controller design of a hypothetical air vehicle using model-free adaptive control method is presented. The progress of industries in the last decade leads devices and processes to be more complicated and larger. For that reason one of the main problems of industries is modeling of these devices and processes that most of the industries are using PID controller because of simplicity, no need to any design and low computation. One of the solutions of problems caused by modeling is using data-driven control methods that control systems only with online data of the system is model-free adaptive control. This method has unique features that make it preferable from other data-driven methods like, no need to system identification, online estimation of parameters and condition of the system, simple and adaptive structure, low computation than other online methods and independency from the structure and dynamics of the system. In this article, simulate three forms of this method applied to pitch channel of a hypothetical air vehicle have implement and compared with PID controller. Comparison of The stability of this controller and PID applied with input noise and uncertainties to the system has done and finally for industrialization , system with first order actuator is considered. The obtained results demonstrate that the full form of model-free adaptive control has so much better response than PID.

In hovering, the deputy satellite must use fuel regularly to maintain a constant distance from a source point. Since the amount of fuel in satellites is a key element, it has also a great value to optimize its consumption. The system speed and the time of reaching stability are also other important elements that have been studied in this study. For this purpose, three useful controllers are used. These controllers are LQR controller, Pole Placement and sliding mode controller. In the following, these controllers were optimized using particle swarm optimization algorithm in order to compromise the amount of fuel consumption and the time of reaching stability. Comparing the final results shows that the sliding mode controller can be the best option for optimizing hovering system.

This paper presents an isogeometric analysis approach for static and free vibration analysis of laminated composite plates covered with piezoelectric layers using the Reissner-Mindlin theory. Isogeometric analysis (IGA) aims at simplifying the Computer Aided Design (CAD) and Computer Aided Engineering (CAE) by using the functions describe the geometry (CAD) and the unknown fields (Analysis). The isogeometric approach has here been employed that utilizes the Non-Uniform Rational B-Splines (NURBS) of quadratic, cubic and quartic orders to approximate the variables defining geometry as well as the unknown functions. Using the Reissner-Mindlin first order shear deformation theory requires the C0-continuity of generalized displacements and the NURBS basis functions are well suited for this purpose. The electric potential is assumed to vary linearly through the thickness for each piezoelectric sublayer. To alleviate the shear locking problem, a stabilization technique is employed in the stiffness formulation. Since study of the performance and accuracy of IGA in solving laminated composite plates is one of the main objectives of this article. Several numerical examples are presented and compared with those available in the literature. The obtained results indicate desirable accuracy and efficiency of the proposed approach.

In the new sheet metal forming process as incremental sheet forming and spinning forming, this is not perfectly true in Marciniak-Kuczyinski model to assume that sheet deformation occurs in the plane-stress state indispose there are normal compressive stress and through-thickness stress. In this type of forming processes, the obtained limit strains refer to improving the sheet forming. However, in researches the effects of through-thickness shear stresses, also known as out-of-plane shear, has been studied less. The generalized forming limit diagram is a great curve that includes all six components of the stress tensor. In this paper, the effect of normal comprehensive and through-thickness shear stresses on the limit strain AA6011 aluminum sheet using a modified M-K and the anisotropic Yield function, Hill 48 and by using numerical solutions of nonlinear equations, Newton-Raphson method. The first the forming limit diagram was drawn with the assumption that the through-thickness shear stresses and then the effects of normal comprehensive stress and through-thickness shear stress on the limit strains were proved and the generalized forming limit curves were obtained. The results show that forming limits can be increased significantly by both normal compressive stress and through-thickness shear stresses. Also, the effects of normal stress on increasing the formability of sheet compared with the effects of through-thickness shear stress is greater.

In this paper, shape and size of the Crack Tip Plastic Zone (CTPZ) are investigated for orthotropic materials based on Tsai-Hill and Hoffman yield criteria under various loading conditions and plane stress state for an infinite and central-cracked plate. It is assumed that the size of CTPZ is negligible verses the crack length for all loading conditions. For instance, the CTPZ is determined for orthotropic Boron-Epoxy and isotropic steel and effect of the crack’s axis angle on the CTPZ is analyzed for different loading conditions. The loading conditions were selected to obtain the CTPZ for mode I, mode II and combination of mode I and II. Dimensionless area of the CTPZ concept is used to compare the results obtained from Tsai-Hill and Hoffman yield criteria. The results show that in the same loading conditions, the size of CTPZ of Boron-Epoxy on Tsai-Hill yield criterion was smaller than on Hoffman yield criterion and this disagreement is less than the 10% and 13% based on the dimensionless area and radius of the CTPZ respectively. In a specific loading condition, the dimensionless radius of the CTPZ of isotropic materials is unique; however, it depends on the mechanical characteristics in orthotropic materials.

The tractor-trailer system is a wheeled mobile robot (WMR), including one wheeled unit named tractor that is equipped with actuators and one or some wheeled units named trailer that are connected to each other with a passive joint. As a special case, in this paper, the system locomotion is by tractor, and trailer is completely passive. In this paper, we develop the kinematic model of tractor-trailer; so the inputs of system are supposed to be tractor angular velocity and trailer linear velocity. Because of pure rolling condition between wheel and ground surface, we encounter a nonholonomic system. In this paper Model Predictive Control (MPC) is used in control designing of Tractor-Trailer for the first time and the goal is trajectory tracking of trailer position. First, the kinematic equations of tractor-trailer are developed. Then a feasible reference geometrical path is considered. After linearizing the system equations around reference path and using MPC that is an optimal control based method, a tracking controller is designed that minimizes a predefined cost function. Considering actuator saturation in system inputs, we solve a constrained optimization problem using numerical methods. The controller designed in this paper, will be compared against classic controller PID and its better performance is presented. Finally, the effectiveness and robustness of controller against disturbances and parameter uncertainties is proved using MATLAB results.

Fractography of drop weight tear test (DWTT) specimens has received great attention by researchers in recent years due to the complex fracture surface of this test specimen. In this research, macroscopic characteristics of fracture surface of spiral seam weld in API X65 pipeline steel are investigated for the first time using chevron-notched DWTT specimensTest specimens were machined from an actual steel pipe of API X65 grade with an outside diameter of 1219mm and wall thickness of 14.3mm. Then chevron notch of 5.1, 10 and 15mm depth was placed in the center of each specimen and test samples were fractured under dynamic loading of 7m/s. Fractography of the fracture surface of test specimen with 5.1mm notch depth (as typical of test samples) showed that cleavage flat fracture initiated from the notch root (where stress intensity factor was high). Cleavage fracture changed immediately to ductile shear fracture, deviated to one side of specimen and grew extensively in heat affected zone, and finally terminated in base metal. Delaminations were observed in shear fracture area almost parallel to crack growth direction. After that, shear lips and inverse fracture appeared in hammer impacted area. By calculating the percent shear area from standard formulations, it was found that test specimen had above 95% shear area, and ductile fracture was the dominant fracture mode implying the fitness of tested steel for application in high-pressure gas transportation pipelines.

In this paper, by defining a novel analytical derivation method for a composite beam, using the suitable assumptions, the stiffness coefficients and torsional rigidity (shear modulus) for single-cell and multi-cell thin walled layer wise composite sections of a beam are calculated. The results are presented in the form of Maple and FORTRAN codes in order to calculate these parameters in a timely manner. These parameters are used for the preliminary structural analysis of the beam. The nonlinear Euler Bernoulli beam assumptions are used to derive the stress-strain and strain-curvature relations. Next, by using the potential energy and elastic curvature relation for elastic beams, the stiffness parameter is calculated. Then, the equivalent torsional rigidity is introduced for single and multi-cell thin walled layer wise composite sections, using the stiffness parameter. To verify the validity of the computations, the results are compared with the numerical results obtained from a finite element analysis. The results show that applying this method for the calculation of the torsional rigidity of single and multi-cell thin-walled composite sections is a viable method and is very useful in obtaining a suitable, initial analytical approximation in the preliminary design of engineering structures, particularly in that of composite structures utilized in aerial industries.

In this paper, evaluation of cylindrical targets embedded in an elastic matrix is studied using resonance scattering theory (RST). For this purpose, the finite element simulation of ultrasonic wave scattering from the embedded cylinders propagated in elastic matrix is used for resonance ultrasonic spectroscopy (RUS). To involve the frequency effects of measurement system, the modified short-pulse method of isolation and identification of resonances (MIIR) is employed to calculate the resonance modes and frequencies of the elastic target. To examine the validity of the proposed method the backscattered resonance spectrum for an embedded steel cylinder in an epoxy matrix is calculated and the numerical results are compared with the experimental and mathematical results. The FE-based resonance ultrasonic spectroscopy method is employed to investigate the behavior of far field backscattered resonance frequency spectrum for two embedded adjacent elastic cylinders. Using the proposed method to calculate the backscattered resonance spectrum from two embedded adjacent cylinders, it was shown that changing the center-to-center distance of adjacent cylindrical targets shifts the n=4 resonance frequency and changing the receiver position affect the n=3 and n=4 resonant mode frequencies.

Interference fit process, as a popular method, is used in aerospace and automotive industries. General investigation of interference fit has been conducted on plain hole extensively. Nevertheless, interference fitted holes are practically subjected to bolt clamping force which may have different fatigue behavior than the plain hole. The objective of the present study is to extend the present knowledge about the fatigue behavior of interference fitted holes by investigating the subsequent bolt clamping force effect based on the experimental and numerical results. In this paper, Al-alloy 7075-T6 is utilized for fatigue test specimens. In relation to fatigue tests, three dimensional finite element analyses were used to explain the experimental results. By using finite element method, the interference fit process; bolt clamping and subsequent remote cyclic loading were simulated. The fatigue critical stresses on bolt clamped interference fitted (BIF) samples were compared with the corresponding stresses for interference fitted samples. The pre-stress distribution due to interference fitted hole, and its redistribution after bolt clamping forec and its interaction with remote loading were estimated The fatigue test results demonstrate that bolt clamping force applied on the interference fit plays positive effect on fatigue behavior and prolongs the fatigue life. The biggest life improvement for bolt preloads of 3409 and 6818 N is 2.5 and 7 times compared to the only interference fitted specimens, respectively.

This paper aims at proposing an algorithm for collision-free motion planning of two wheeled mobile robots. The proposed approach relies on discrete motion planning, convex optimization and receding horizon control (RHC) concepts. The proposed algorithm is employed for motion planning and control of a mobile robot in order to pass through an unknown environment both in simulation and practical implementation. In this regard, CVX package benefited from the Gurobi solver is employed to solve the optimization problem in the simulation. Moreover, in order to perform a collision-free motion planning, corresponding Robot Operating System (ROS) package with the intended mobile robot is employed to cooperate with the provided motion planner package. The provided package utilizes educational license of Gurobi optimizer solely to speed up solving proposed optimization problem and its built in branch and bound for Mixed Linear Integer Programming (MLIP). In order to keep the linear form of the constraints, a combination of the Velocity Obstacle (VO) in the first horizon and Bug method concept for the rest of the horizons is used. Obtained results show the reliability of this algorithm for safe collision avoidance. The reported results reveal this fact that by considering the maximum velocity of the E-puck, obtained computational time is less than 0.004 sec. in each stage which is fast enough for robot motion planning tasks.

The method of fundamental solutions is a boundary-type mesh-free method, which is very suitable for problems with unknown or moving boundaries. In this paper, the method of fundamental solutions is employed for shape optimization in torsion problems. The objective of this work has been to find optimum corners radii of hollow cross-sections under torsion for minimizing the maximum stress. First, it is shown that for the optimum value of the corner radius, the maximum shearing stress on the outer boundary should be equal to the shearing stress at internal corner. Considering this fact, a suitable objective function is defined and then it is minimized using the Levenberg-Marquardt method, which is a gradient-based optimization method. The configuration of collocation and source points has a very important effect on the accuracy of the solution in the method of fundamental solutions. Here, a two-constraint method is used for proper configuration of source and collocation points. To verify the accuracy of the developed code for torsion analysis of hollow members using the method of fundamental solutions, an example with a hollow elliptical domain is presented. The obtained numerical results are compared with the results of exact solution, which show a very good agreement. The optimum values of corners radii for members with square, rectangle and trapezoid cross-sections and different thicknesses have been successfully found. Then, using the obtained results, a formula for the optimum value of the radius of internal corners of hollow rectangle cross sections is constructed.

This paper focused on the vehicle path planning in the highways and complex urban environments. At first, obstacles and road lines have been detected by sensors of the intelligent vehicle, thereupon the vehicle will be find the safe areas using the time distance method developed in this paper. Then, an appropriate path close to the intelligent decisions about human being would be chosen through the developed algorithm. There is the possibility of collision to surrounding vehicles in the areas where changing the lane is needed. Therefore, to prevent collision, a five orders polynomial curve is offered for each lane change maneuver. The reached maneuver is optimized based on the vehicle dynamic and allowed lateral acceleration. Finally, a suitable path to pass quite safely and without any collision through the obstacles is suggested. At the end, two main and different simulation scenarios included the lack of collision is verified by MATLAB software and the obtained path is controlled by the sliding mode controller. These simulations indicated effectiveness of this method. The lateral acceleration is obtained in allowed range for comfort of occupants in these scenarios.

Recently, robotic systems are widely used in surgery, due to their characteristics such as having high precision, being tireless and making no mistakes. They are especially suitable for operation on hard tissue, as the bone is stationary and does not change shape and therefore preoperative planning of the system is much more straightforward. Nevertheless, proposed robotic systems for surgery on skull bone are still in the research stage. In this study, by considering the requirements of craniotomy surgery, a Remote Center of Motion spherical mechanism is used in design and prototyping of a surgical system. The kinematic equations and Jacobian of the mechanism are calculated analytically and later verified through software simulation. Detailed design and force analysis helped selection and use of appropriate AC servo motors for actuation. An aluminum prototype is fabricated out of CNC machined parts. Performance of different connection methods between PC and the robot were tested and a combination of them is proposed for higher reliability and speed. Finally, a software library is generated in LabVIEW environment to simplify the connection with servo motors and utilization and control of the robotic system.

In this paper, the effect of expander and the internal heat exchanger is investigated in transcritical carbon dioxide direct-expansion geothermal heat pump. In this regard, a comparison is performed between four cycles. The four cycles are: (1) the cycle with expansion valve, (2) the cycle with expander, (3) the cycle with expansion valve and internal heat exchanger, (4) the cycle with expander and internal heat exchanger. The present numerical model has been investigated performance analysis of the four cycles under study in different operating conditions in two district cases. The first study includes a specific heating load, and the second study is a constant evaporator loop length (ELL). Then model evaluates characteristics including coefficient of performance (COP), evaporator loop length and heating capacity of the four cycles under study. To examine the performance of the four cycles, a parametric study is performed to investigate the effect of different parameters such as difference between soil temperature and evaporator outlet temperature, water inlet temperature, water mass flow rate, gas cooler length. The results indicate that COP associated with the expander cycle is always higher than the values related to the expansion valve cycle. The use of internal heat exchanger in a cycle including an expansion valve always leads to a slight increase in COP. An internal heat exchanger has negligible effect on COP in the cycle with an expander but reduces the evaporator loop length.

Hydroforming is a convenient method for applying fluid to produce parts with high strength to weight ratio. Hydrodynamic deep drawing assisted by radial pressure with inward flowing liquid process is considered as a type of hydroforming. In this method, radial and cavity pressures are two most important parameters, the values of which at any moment play an important role on the quality of final part. In this study, based on a hybrid method, the cavity and radial pressure paths in hydrodynamic deep drawing assisted by radial pressure with inward flowing liquid process are optimized. In this method, an adaptive simulation that is integrated with the fuzzy control system with the ABC algorithm is used to determine the optimized radial and cavity pressure paths. The achievement of a cup with least thinning and without wrinkling has been defined as the optimization goal. The validity of radial and cavity pressure paths obtained from optimization algorithm is verified through an experiment. Results showed that utilization of the optimized loading path yields the part with lower maximum thinning and without wrinkling.

Dielectric barrier discharge (DBD) plasma actuators are one of the new devices for active flow control, which has received substantial attention during the last decade. The performance of the actuator is optimum when it induces the highest velocity per unit of power consumption. Since the induced velocity and the power consumption of the actuator depend on many different variables, finding the optimal set, which results in the best performance, is of immense importance. In this paper, in order to optimize the performance of these actuators, at first, by using full factorial design of experiments the effect of electrical variables (including voltage and frequency) and geometrical variables (including the gap between electrodes, dielectric thickness, and covered electrode width) on induced flow velocity and power consumption in steady actuation is experimentally investigated. Then, by using the multi-layer perceptron neural network, a model is created for the ratio of induced velocity to power consumption. The model is validated both statistically and experimentally. The results indicate that the coefficient of determination for training and test data is higher than 95 percent. Finally, the surrogate model is optimized by genetic algorithm and the optimal value of electrical and geometrical variables is determined. In order to validate the result, an actuator is designed based on the optimal set of variables and it’s ratio of velocity to power is measured to be 29.71 (m/s)/(kW/m). The difference of 3 percent between the measured and the predicted value demonstrates high accuracy and correctness of the proposed model and method.

One of the most important achievements of the Carnot was creating a limit for heat engines; this limitation is a criterion for measuring and comparing the performance of heat engines. Classical thermodynamics studies completely the equilibrium and reversible processes but transfer phenomena effects have been ignored, while in the real irreversible process, there are finite time processes and finite size systems. On the other hand, the close relationship between thermodynamics, fluid mechanic and heat transfer has caused thermodynamics to move from theoretical analysis toward a comprehensive and real analysis. Another point is that all the practical processes are irreversible. This study analyzed the irreversible combined cycle in finite time thermodynamics. The combined cycle studied consists two endoreversible cycles and three thermal sources. The irreversibility has occurred between the subsystems and the thermal sources and sink on the system boundaries. By solving algebraic equations, obtained dimensionless total power and efficiency were calculated based on dimensionless variables. The MATLAB programming code is used to solve algebraic equations. Finally, it is obtained that the thermal efficiency and dimensionless total power functions of the heat sources temperature, working fluid temperature and thermal conductance. Also, the effects of each dimensionless variable were investigated to the proportion of dimensionless total power and efficiency. In this study, the parameter study has been used for improving the irreversible combined cycle in the finite time thermodynamics. In addition, Optimization results have shown that the maximum dimensionless total power and thermal efficiency associated with it are 0.086102 and 47.81%, respectively.

In this paper, natural convection heat transfer is numerically investigated in a square enclosure filled with power law non-Newtonian fluid model and central heat source for steady and quiet state. The top wall of the enclosure is thermally insulated and the vertical walls are at constant temperature of TC. The down wall of the enclosure also has four equal parts at constant temperature of TC and TH. The governing equations for the power-law fluid flow are solved with the numerical finite difference method based on the control volume formulation and SIMPLE algorithm. The results show that for small Rayleigh numbers the Nusselt number will not be affected by changes of the power law index but in Ra=106, thermal performance changes are more significant with the change in power law index. With a smaller the Rayleigh number in all indexs, the center of flow lines rotation, regarding to the axis parallel to axis Y, in the middle of the enclosure, will be more symmetrical. Also with stronger natural convection in the square enclosure, the average of Nusselt number for non-Newtonian fluid increase with increased power law index and improved thermal performance by increasing the Rayleigh number is impressive for the density power law fluid (n˃1). Results also show that the Rayleigh number for the start of natural convection in the square enclosure is reduced by increasing the power law index.

The sheet metals formability can be restricted by localized necking and internal cavitation. On the one hand, nucleation and growth of cavities during plastic deformation can increase the inhomogeneity of sheet metal and accelerate the localized necking. On the other hand, localized necking at the intervals between the cavities can lead to accelerate the joining and coalescence of the internal cavities. In this paper an analytical model based on Marciniak-Kuczynski (M-K) model and Gurson plastic potential function in order to exert the internal voids effect on localization necking has been developed. Stowell’s model was used to illustrate void growth behavior during plastic deformation. In order to examine the effect of the voids on localized necking, the void volume fraction was considered in the imperfection factor and the plastic volume constancy principle. The nonlinear system of equations was solved with the modified Newton-Raphson method using MATLAB software. This new analytical method (M-K-Gurson) was used to predict the forming limit diagram (FLD) of IF steel alloy sheets and the results were compared with those of other researchers. The results showed that the M-K-Gurson method predicted the FLD with better agreement comparing with experimental results. Thereafter, the effects of strain hardening exponent, anisotropy coefficients, geometrical imperfection factor, the void volume fraction and the void growth rate parameter on the FLD were investigated.

This paper attempts to predict the occurrence of central bursting defects in the plane strain extrusion process using upper bound method. For this purpose, the material under deformation is divided into three deformation zones. These deformation zones are separated from each other by the shear boundaries as the exponential functions. Then, an admissible velocity field, including the radial and the angular velocity components are developed for each deformation zone. Strain rates components are determined and mathematical relationships for internal, shear and friction powers are obtained. For a given process conditions, the total power toward geometrical shape of shear boundaries entrance and existence is optimized. Intersection position of the entrance and existence shear boundaries of deformation zone on centerline represents the occurrence of central bursting defects. The effect of process parameters, including semi die angle, reduction in area and friction factor on the defects and the extrusion force are investigated. The analysis results with the FEM simulation (Deform software) and the results of the published papers are compared. The results showed that increase of friction factor and increase the reduction in area decreases the probability of central bursting defects.

According to the development of non-contact three-dimensional measurement methods over the past two decades, along with the acceleration of scanning operations and the accuracy in measuring and significant development of their application in a wide range of fields (such as design, reverse engineering, quality control and inspection, medicine, documentation of objects, robotics, etc.), we have seen an increase in the amount of information obtained (points cloud) from the 3D scanner as the output of the scan operation. This raises restrictions on data management, data transfer, data storage, or even the development of real-time scanning methods. In this way, the need to compress and reduce the amount of data with the preservation of accuracy or minimum drop in accuracy and quality as one of the issues of interest in the post-processing of scanning operations has been revealed more than ever before. In this paper with presenting a new and distinct method for lossless compression on points cloud obtained from 3D scan operations in the form of an ordinary single-channel 2D image based on the image-based encoding techniques, we have evaluated the performance and effectiveness of the proposed method, while designing and constructing a non-contact 3D scanner with structured-light pattern based on the Gray code technique. The results show the accuracy and applicability of this method and the achievement of distinct compression rate [230:1] among other lossless compression methods of 3D data.

In this work growth and characterization of potassium chloride with nanodiamond is studied. Crystals were grown in Czochralski crystal growth method. KCl crystals are doped with 0.5, 1 and 1.5 percent nanodiamond (ND) impurities. Breaking cross sections of the pure and doped crystals were characterized by (scanning electron microscopy) SEM. As a result, increasing the doping percentage of the ND in the KCl crystal, leads to arising the surface roughness and nicks curvature on the fracture cross section of the crystal. It means that ND doping inside KCl crystal caused to increase mechanical hardness of the crystal and increasing the doping percentage results more mechanical resisting crystal. On the other hand, Vickers microhardness scale is used in this study. Hardness is too complex to be described by first principles. Based on the dielectric chemical bond theory, a semiempirical theoretical formulation of the hardness of pure and doped crystals is introduced. Analyzing of the results shows increasing of the nanodiamond doping leads to increasing of mechanical resistance of the samples.

In this paper, axial buckling of a composite cylindrical shell with and without a rectangular cutout is studied based on the first-order shear deformation theory. The equations are derived in a general form and can be converted to Donnell`s, Love`s, and Sanders` theories. To investigate the perforated shell, a physical domain is decomposed into several elements with uniform boundary and loading conditions in each element edges. In each element, the governing equations are discretized in both longitudinal and circumferential directions by the use of generalized differential quadrature method (GDQM). By assembling these discretized relations, a system of algebraic equations is generated. The boundary conditions at the shell and cutout edges, and the compatibility conditions at the interface boundaries of adjacent elements are also discretized by GDQM. Finally, the buckling load is calculated by an eigenvalue solution. To validate the presented method, the results of GDQM are compared with the available ones in the literature and also with ABAQUS finite element model. Then a parametric analysis is performed to investigate the effects of different parameters on the buckling behavior of the shells with and without cutouts. This study illustrates that the shell layup has a great effect on the buckling load of a shell. In addition, the influence of increasing the cutout size is not identical for different layups. However, the buckling behavior is independent of the shell material. Moreover, it was concluded that the shell with a square cutout has higher critical load than the one with a rectangular opening.

In variable refrigerant flow (VRF) heat pumps facing variable environmental conditions, the required load is achieved by means of compressor speed and expansion valve opening. Thus, this type of heat pumps is under transient conditions in addition to steady state conditions. Thus a detailed modeling is essential for an appropriate heat pump analysis and strategy. In the present paper, dynamic modeling of a VRF heat pump is conducted. For this purpose, dynamic modeling of heat exchangers is done via modified moving boundary method. Compressor and expansion valve are modeled in steady state as their thermal transient conditions are much faster compared to heat exchangers. Finally components models are coupled in MATLAB software. Validations indicate the present model with 5.3 percent error is more accurate than the previous studies (10 percent error). By investigating of compressor speed and expansion valve opening variations effect by the present model, it is concluded that transient conditions on system performance such as COP and generation are very effective compared to steady state conditions and these effects depend on the type and size of variation and in this article 15 percent difference is achieved. These conditions must be considered in system strategy, otherwise system real generation and model prediction will be different and consequently thermal comfort will be disturbed. Thus an accurate dynamic model is necessary for all steady and transient conditions and the present model can be utilized.

In this study, the inverse heat transfer problem of the estimation of unknown heat flux imposed on the boundary of a one-dimensional slab is solved by the genetic algorithm and two modified versions of this algorithm and the results obtained from different versions of the genetic algorithm are compared with each other. These two modified versions are developed based upon genes rearrangement approach. In this approach, an additional cost function is added to the conventional genetic algorithm to increase its computational efficiency. The results obtained by using errorless simulated temperature measurements show that modified genetic algorithms can improve the convergence and accuracy of the inverse solution in comparison with the conventional genetic algorithm and they give accurate estimations for the supposed heat flux even by using a small number of generations and moderate population size. The results show that modified genetic algorithm (2) provides better response to all the parameters of the solution evaluation in comparison with the conventional genetic algorithm and other modified version. In addition, in this study, the effect of adding Tikhonov regularization term to the objective function on the stability of the solution is investigated. Although only a simple one-dimensional problem has been solved in this study to demonstrate the approach of genes rearrangement, but this approach is expected to succeed in the inverse solution of complicated multidimensional problems.

The performance of cement paste as the reinforcing element in walls and transferring pipes in oil wells is of considerable importance. It is known that the mechanical properties of hardened cement can be altered under high pressure and temperature of oil well; the gravity of this change has an important role in the stability and service life of the well. This paper investigates the mechanical properties of hardened cement and GO-reinforced cementitious composites at molecular scale under the surrounding conditions similar to those of an oil well using molecular dynamics method. Results in nano scale revealed a decreasing pattern in mechanical properties of calcium silicate hydrate with increasing temperature of the oil well. However, pressure increment in the conventional range of the oil wells did not show any noticeable effect on hardened cement properties. Using GO proved to be beneficial to the calcium silicate hydrate, drastically improving its mechanical properties. Results concluded that GO nanoparticle can act as reinforcing elements in the cementitious matrix. The outcome of this research can provide more insights on the application of GO in the oil well cementitious matrix, in an ideal molecular conditions and thus passed over GO agglomeration, non-homogenous dispersion and impurities in the macro scale.

Today fiber metal laminates (FMLs) by having good mechanical properties and low weight have been attention. The use of shape memory alloy (SMA) in the FMLs causes these alloys, under mechanical cyclic loading, by creation reversible hysteresis loop, can absorb or waste mechanical energy and causes amelioration of resistance against buckling instabilities of FMLs. In this study, the effect of increasing pre-strain and embedment SMA wire in far and near layers to neutral axis of FML, under static buckling were investigated. FMLs were contained epoxy resin and glass fibers and 2024-T3 Aluminum alloy. To investigate effect of pre-strain of SMA, the pre-strain of 1, 2 and 3 percent with fixed quantity 6 wires in these FMLs were tested. Due to investigate the position of embedment, the quantity of 4 wires with fixed 3% pre-strain, in far and near layers to neutral axis, are used. The results showed that the increase of pre-strain due to creation more tension of SMA during the fabrication of the specimens and the tendency of wires to return to its original shape during the test makes the structure more resistant against pressure loading. Also, the wires were placed in layers far from the neutral axis of the specimen as compared to near the neutral axis due to the greater effect of the bending resistance of the specimen during the buckling and the effect of the better return properties of SMA wires, causes to increasing resistance against instability and load tolerance limit in FMLs.

In this paper, a linear dynamic model for a reaction wheel is identified using experimental analysis. To do this, online input-output data of reaction wheel is sent and received by CAN protocol working with the frequency of one mega bit per second. The experimental hardware consists of reaction wheel, processing board, CAN protocol, and LabVIEW monitoring. Modeling assumes the reaction wheel and its inner control circuit as a black box and takes into account the practical considerations. Initially, behavior of the reaction wheel is examined using test signals for velocity and acceleration as inputs. After that, the test signals are replaced by Chirp and PRBS signals and the output results are saved. According the results obtained in the tests, ARMAX and ARX linear dynamic models are assigned to the motor and different orders of these models are compared with each other to reach the appropriate order of the models. Furthermore, a delay is also incorporated in the model and its proper order is determined by the simulations. Finally, to validate the proposed model, the outputs of the model and plant are compared followed by exerting a new test signal. The results indicate a good agreement between the proposed model and the practical behavior.

The present study investigates the surface energy of metallic nanoplates as the most basic thermodynamic concept of nanostructures using one of the most efficient available computational tools in the field of nanoscience i.e. the molecular dynamics simulations. Whenever physicochemical properties of nanostructures are discussed, the surface energy is one of the key parameters. This parameter has the utmost importance at nanoscale since at this scale the surface to volume ratio is very large and thus there is a significant difference between nanoscale properties and the engineering scale properties. In this study, the surface energy of gold and silver metallic nanoplates using molecular dynamics simulations are investigated and shown to be dependent on size. The surface energy of metallic nanoplates with different thicknesses were calculated and it was shown that for very thin metallic nanoplates with sufficiently small thickness in the order of a few nanometers, the surface energy is dependent on the thickness of nanoplate and the surface energy decreases by reducing the thickness of the nanoplate. By analyzing the excess energy of different layers in very thin nanoplates, it was found that this size-dependent behavior is due to the reduction of excess surface free energy density in surface layers and its increase in the inner layers that overall reduces the surface energy of nanoplate.