نشریه مهندسی مکانیک مدرس
سال هفدهم شماره 5 (امرداد 1396)

Cooperation and autonomy are among the most important aspects of unmanned systems through which greater use of these system is possible. Most applications in civil market is related to government organizations requiring surveillance and inspection, such as coast guards, border patrol, emergency services and police. A cooperation algorithm is developed and simulated in this research for autonomous UAVs to track a dynamic target in an adversarial environment. First, a mathematical formulation is developed to represent the area of operation that contains various types of threats in a single framework. Then a search point guidance algorithm is developed by using a rule-based approach to guide every UAV to the way points created by the cooperation algorithm, with the requirements of completing mission, avoiding restricted areas, minimizing threat exposure level, considering the dynamic constraints of the UAVs and avoiding collision. The cooperation algorithm is designed based on a variable formation which depends on a cost function. The efficiency of the team is improved in the terms of increasing the area of coverage of the sensors, flexibility of the UAVs to search for better trajectories in terms of restricted area avoidance and threat exposure minimization, and improving the estimation. Finally, the performance of the algorithm is evaluated in a MATLAB environment, which includes the dynamics of vehicles, the models of sensor measurement and data communication and the discrete execution of the algorithms. The simulation results demonstrate that the proposed algorithms successfully generated the trajectories that satisfy the given mission objectives.

We know, cantilevers are based for the most of the MEMS components, in this paper, the fabrication process of SiO2 micro cantilever array based on bulk micromachining technology is introduced. The results of which can be used to fabricate of SiO2 micro cantilever sensors. The micro-cantilever fabrication process is implemented in the 13th stage with two glass and talcous masks and it is also suspend by wet release technique. The main advantages of the proposed method can be expressed no need for advanced deposition equipment, design with minimum mask, fast and simplicity in implementation of the micro cantilever, avoid of complexity release from sacrificial layer, release the micro cantilever at environment temperature, low cost price and finally possible to implement in microelectronics research laboratories with limited equipment. The SiO2 micro cantilevers fabricate with 1and 2µm thickness, 50, 100, 150, 200, 250, 300, 350 and 400μm lengths, and 20 and 40µm widths. The resonant frequency and the spring constant values are also calculated for different materials (Si3N4, Si, Au, SiO2, Al and SU8) with various sizes. The SEM images results show that the lithographic process is correctly done on the roughness of the backside substrate, the fabrication process and Si etching operations controls are performed suitable, and micro-cantilevers are suspended with negligible stress.

One of the disadvantages of drag driven vertical axis wind turbines, is low aerodynamic performance of the turbine which is mainly due to adverse torque of the returning blade. A recently introduced design suggests using opening/closing blades for the rotor to eliminate the negative torque of the returning blade. In this study, the aerodynamic performance of the newly proposed turbine has been investigated experimentally and numerically. The experimental measurements are performed in a subsonic open-jet type wind tunnel facility. However, the numerical simulations are performed using the Ansys-Fluent commercial software, using the Multiple Reference Frame model (MRF). The effects of the number of blades (3, 4 and 6-bladed), end plates and turbulence intensity on the torque and power coefficients are examined in details, in several Reynolds numbers. Results show that the new rotor has no negative torque in one complete revolution and the 3-bladed rotor has the best aerodynamic performance, in a manner that, it reaches a maximum power coefficient of 0.21 at TSR=0.5. Although increasing the number of blades decreases the output torque oscillations, it also decreases the average power coefficient of the rotor. Results also show that, Reynolds number does not have significant effects on the average power coefficients of the rotors, in the studied range of Reynolds numbers, 7.7×104 ≤ Re ≤ 1.2×105.

in recent years, Variety of analytical methods have been used to calculate the output piezoelectric energy, but it is new something the use of finite element method and compared using analysis software with numerical methods. And also check the types of circuit connection of piezoelectric layers So in this article particular form of numerical analysis method is called separation of variables method compared with the finite element method, To take advantage of these methods is to be determined. The model is a Bimorph beam with two piezoelectric layers and a central elastic layer. This Bimorph beam starts vibrating at various frequencies as a result of base excitation. First, frequency behavior of the Bimorph beam is simulated using the separation of variables method. In this method, the equations of motion in parallel and series connection of piezoelectric layers are obtained as separate parameters. The coupled mechanical and electrical equations are derived using the solution of equations obtained from the separation of variables method. Finally, the output voltage, current and power are obtained in terms of frequency.
Then, the Bimorph beam is modeled based on finite element method using ABAQUS software. after the illustrating Output voltage, current and power diagrams is illustrated for a certain range of frequencies and the results of the finite element method and the steady state method are compared to validate the model.

Wearable robots are robots which are used for rehabilitation or augmentation by human. Recently, there has been an increasing interest in the development of wearable devices to assist elderly as well as patients, soldiers and many other persons for movement assistance and power augmentation. On the other hand, a realization of wearable robot which has the same degree of freedom of a human is not easy from considerations about a size and weight of device. This study is about a lower limb assist robot that consist of just an actuator on each of legs. In this paper after a brief review on wearable robots and their applications, a suitable design of robot which is named RoboWalk presented with inspiring from Honda weight compensation system. In the following kinematics and dynamics modeling of system presents with using of denavit-hartenberg parameters and validates with ADAMS software results. Results with high accuracy has been achieved. It’s necessary to evaluate main foundation of design of robot which is an assistant force in the direction of foot reaction force that has been achieved with the accuracy of 0.02 radians. finally effect of change in user’s weight, position of center of mass and friction of walking assistant robot component is examined in this study.

Individuals with high levels of disability like patients with cervical spinal cord injury, are highly dependant on their relatives for daily life needs. Hence, this problem decreases the quality of life of this individuals and their relatives. New technologies such as robotics have the potential to help these kind of patients and give them some degree of independence. The first step in design and implementation of robots which have the capability of helping disabled people is to design a user interface that can receive user’s commands and transfer these commands into the robot environment. In this paper, a haptic user interface has been designed and implemented to serve patients with cervical spinal cord injury. In this user interface, user’s head angles have been extracted using a gyroscope sensor and then transferred into the computer simulation environment in which the robotic arm is graphically simulated and the user can control the arm using his/her head movements through a novel control pattern. A haptic unit has also designed and implemented to produce resistive torques against head movements to help user to physically sense the weight of gripped objects and the collision of the robotic arm with obstacles. The performance of haptic user interface evaluated using three sets of tests subject to two healthy individuals. Finally, obstacle collision detection tests was 100 percent successfully while heavy and light object recognition tests were 83 percent and heavy, medium and light object recognition tests were 72 percent successful.

The occurrence of damage is considered as an unavoidable fact in fibrous polymers. For this reason, the self-healing systems could extend the service life time of materials by implementing the concept of autonomous or induced repair. In the present study, a self-healing E-glass fibers/epoxy composite based on micro-vascular channels has been designed and fabricated. The specimens were fabricated via the hand lay-up route, while the fabrication of micro-vascular channels was conducted through the removing of solid preforms. Due to the lack of previous studies about the utilization of anhydride resin-hardener system with lower viscosity and also their controllable miscibility in comparison to the amine systems, in the present work, these materials were selected as healing agent for repairing the primary defects created in the structure. For this purpose, mico vascular channels containing two various parts of epoxy resin and anhydride hardener (2, 3.2, and 3.7 Vol.% with respect to the matrix part) were incorporated in the structure of composites. The flexural behavior of the specimens was assessed during the different time span (0, 4, 8 and 11 days) from the primary damage creation. After the defect creation in the structure, the healing agents present in the micro vascular channels are flow into the defects and after the combining with catalysis dispersed in the matrix, local polymerization process and restoring of properties are started. According to the obtained results in this research, the highest flexural strength recovery of 46% was observed for the specimen with 3.2% healing agent after 8 days.

Butt weld friction stir welding of steel sheets with thicknesses of less than 1 mm has been known as one of the most important challenges in recent years. In this work, butt weld friction stir welding of IF (Interstitial free) steel with the thickness of 0.7 mm is studied experimentally. For this purpose the effects of rotational and travel speeds of the tool on the strength and hardness of welded joints is investigated. Mechanical strength of the joints is evaluated with uniaxial tensile test. Also, in this paper the microstructure evolutions of welded joints of IF steel sheets with the thickness of 0.7 mm are studied. The results show that with increasing in rotational speed and decreasing in travel speed of the tool, the tensile strength of welded joints will be increased. In addition, with increasing in rotational and travel speeds of the tool, the hardness of welded zone is increased. The results of microstructural investigations show that the microstructure of welded zone is improved with increasing in rotational and travel speeds of the tool. The results of EBSD analysis show that no significant changes have been occurred in the left side of stir zone in comparison to center of stir zone. Also, it is shown that the fraction of high angle grain boundaries in the center of stir zone has been increased than the left side of stir zone (from 25 % up to 48 %).

Network Control Systems (NCS) arise in many real-world applications and they have been an active area over recent decades. Using NCSs instead of traditional controllers has led to significant decrease in costs, weight and power of installations, also increase in reliability of control systems. Despite these advantages, NCSs confront various challenges, such as time varying delays and data packet dropouts in control data transfer which leads to instability. In this paper, the stability analysis and stabilizing with state feedback are studied for NCSs which includes time varying delays in state equations. This goal is achieved by introducing a new functional and using the Lyapunov-Krasovskii approach. Then, an accurate estimation of derivative of functional is obtained by applying Wirtinger and Reciprocally convex combination inequalities. In the proposed method, a stability criterion is derived with less conservatism and complexity. Afterwards, the problem of controller design is examined in which the state feedback controller is designed based on stability criterion. Finally, the dynamic model of the satellite as an examples is used to demonstrate the advantages of proposed method which illustrates our proposed method has desirable influence in decreasing conservatism of results and leading to better performance.

In this work, axial vibration of nanorod was analyzed based on two phase integro-differential nonlocal elasticity theory using isogeometric method. Two phase integro-differential nonlocal elasticity theory not only shows the nonlocal property in an integrated manner based on kernel weight function, but also combines local and nonlocal linear curvature for a two phase nonlocal elastic material. The new isogeometric approach combines finite element method with computational geometry and can present an accurate geometric model for the problem. Also, using b-spline basis functions with arbitrary continuity order, it can be a better alternative for classical finite element methods. The obtained results indicated that isogeometric approach was superior to finite element method in term of speed and convergence quality. Moreover, in this model, the effects of phase and nonlocal parameters on the natural frequencies of the nanorod were investigated and it was shown that increase of parameters of local phase and nonlocal length scale, respectively, increased and decreased the values of natural frequencies of nanorods. Finally, for two special cases, asymptotic frequencies for a single type of nonlocal rod, two phase integro-differential was obtained and the results were compared with corresponding available differential Eringen results.

Signal processing has a key role in signal based fault diagnosis in rotating machinery for finding beneficial discriminating features. Task of Signal processing is conversion of the raw data into beneficial features to facilitate the diagnostic operations. the features should be robust regarding noise and working condition of the machine and simultaneously sensitive to the machine defects. Therefore, assignment of more efficient analyzing techniques in order to achieve more beneficial features of the signal and faster and more accurate fault detection is taken into consideration by researchers. In order to finding such features, the current research applies at first wavelet packet denoising and then applies wavelet packet based Hilbert transform as well as improved Hilbert-Huang transform separately to decompose vibration signal into narrow frequency bands in order to extracting instantaneous frequencies. The findings show that the wavelet packet based Hilbert transform generates better results in comparison to the improved Hilbert-Huang transform in detecting frequencies of the broken rotor bar fault.

Ultrasonic Assisted Magnetic Abrasive Finishing (UAMAF) is the combination of magnetic abrasive finishing (MAF) and ultrasonic vibrations to finish the surfaces in nanometer scale. In this work, the experimental setup for UAMAF was prepared to finish inner surface of tube workpiec. By using experimental setup, the effect of experimental parameters such as ultrasonic vibrations, mesh number, the type of abrasives (SiC and diamond) and finishing time has been investigated on the changes in the surface roughness of AL6061 tube workpiece. The experimental results showed that the use of ultrasonic vibrations has a significant effect on reducing the surface roughness. The changes in surface roughness increases with the mesh number from 90 to 800 and finishing time from 30s to 5 min. Among two types of abrasives, diamond showed the best performance in finishing. Optical microscopy images showed that the dominant finishing mechanism in MAF for coarse grains (with mesh size of 90 and 120) is two body and for fine grains (with mesh size of 220, 400 and 800) is three body. In UAMAF for both of the coarse and fine grains the dominant finishing mechanism is three body.

Investigation of spike stall formation and its propagation in a low-speed axial-flow compressor is the main aim of this study. Experimental measurements are performed in a low speed axial compressor test rig. Measurement parameters include instantaneous velocity and static pressure at the stall inception process. For this purpose several hot wire probes and a high response pressure transducer is used in data acquisition procedure. Instantaneous fluctuations of velocity at upstream of the blade row show that spike stall inception is accompanied by flow separation from the leading edge of the rotor blade and formation of a vortex subsequently. This vortical structure extends over the blade span. Stall cell propagates with a circumferential speed lower than rotor wheel speed which is equal to 66% of rotational speed in this compressor. Furthermore, wavelet frequency analysis is employed for detail investigation of spike disturbances and capability of this method in distinguishing the spike stall is presented. Wavelet analysis, by representing the temporal variation of frequency spectrum, shows dominant phenomena in the transient process from stable operation to the stall inception condition.

In the present study, microstructure and wear resistance of in-situ composite coatings TiC-Al2O3 and TiB2-TiC-Al2O3 product by gas tungsten arc welding process on AISI 304 austenite stainless steel were investigated. For this, a paste of the mixed powders of 3TiO2-4Al-3C and 3TiO2-4Al-B4C was provided and applied on the surface of AISI 304 austenite stainless steel substrate, then fused using gas tungsten arc welding process. The microstructural features and phase characterization of the cladded samples were investigated using optical and electron microscopy and X-ray diffraction analysis. The mechanical properties of clad layers were studied by Vickers microhardness and pin-on-disk wear tests. The microstructural investigations of cladded layers indicated that high heat input during welding led to high temperature synthesis and formation of significant reinforcing particles on the surface of steel. Also, the cubic TiC particles formed separately or inhomogeneously nucleated on Al2O3 particles in the austenitic matrix of 304 stainless steel. Likewise, the formation of TiB2 particles was approved with X-ray diffraction analysis. The rei

In single-body converters of ocean wave energy, oscillations of a floating body (buoy) serve as the main driving force for electricity generation. Buoy geometry optimization is known as an approach to enhance the efficiency of these converters. In the present research, the process of wave energy absorption in point absorber converter is modeled as a spring-damper system. Two geometries are considered for the buoy of the converter (conical and spherical-cap). The effects of buoy geometry on its dynamics in the nonlinear wave are investigated and comparison of these effects on dynamic performances of the modeled converter are reported. Equalization of environmental conditions and modeling of the two models were discussed, and a new equalization method was proposed. Effective wave energy on each model was calculated based on geometrical characteristics of the corresponding buoy. Then, the models were hydrodynamically analyzed via boundary element method by taking the diffraction theory as the governing theory. The incident wave was assumed to be a second-order Stokes wave.
Results were obtained in both time and frequency domains and validated against the results of available research. Maximum dynamic responses of the restrained buoy with spherical-cap geometry in heave and surge (vertical and horizontal directions, respectively) were found about 4.4% and 11.3% higher than the conical buoy, respectively. The average percentage of absorbed wave energy by the modeled converter with spherical-cap buoy was about 2.2-2.5% higher than that of the other model. The average percentage of absorbed energy by the models were predicted to range within 20-24%.

Piston effect is an important mechanism of heat transfer in a supercritical fluid flow under microgravity condition. In this study, a Lattice Boltzmann Model (LBM) has been introduced to simulate the piston effect. Variations of diffusion coefficient has been accounted for by adding a corresponding term to equilibrium distribution function. To calculate the intermolecular forces and compressibility in the LBM, a van der Waals equation of estate has been employed. Boundary conditions corresponding to compressible LBM at the presence of van der Waals forces have been set to eliminate the speed jump at the wall. It has been shown that such boundary conditions provide high accuracy in problems involving forces with an error of second order of magnitude in terms of space. The developed thermal LBM together with compressible LBM have been applied to simulate the heat transfer to supercritical fluid flows. The piston effect has been modeled by considering van der Waals inter molecular forces. The errors associated with each of the schemes used have been evaluated. A comparison between a pure conduction case and heat transfer due to piston effect has been made. It has been shown that the heat transfer occurs faster once the piston effect is in effect.

In current study turbulent flow around a 3D square cylinder is modeled using large eddy simulation and shear stress k-ω turbulence modeling for three values of Reynolds numbers 5000, 46000 and 69000. The flow and sound field simulations are conducted by using fluent commercial software. Sound pressure level in the acoustical far field and on the surface of the square cylinder at incidence are evaluated for six angles of attack. Flow induced sound at far field is predicted by employing FWH analogy while sound pressure level over the surface model is directly estimated by measuring the unsteady surface pressures. The results of the present study showed good agreement with the available experimental results. The fluctuating lift and drag forces acting on the square rod and flow turbulence are the main sources of the acoustic field generation. It is noticed that the minimum of drag coefficient, mean and root mean squared (rms) value of lift coefficient, and sound pressure level in acoustical far field occurred at 13 angle of attack. The maximum Strouhal number occurred at 13o angle of attack. The Strouhal number for all angles of attack is noticed to be independent of the flow Reynolds number. Both turbulence models considered in this study predict the acoustic and flow features within an acceptable accuracy.

This paper aims at investigating the effect of heat input in resistance spot welding on microstructure and mechanical behavior of 2304 duplex stainless steel, as a promising candidate for automotive application. The results showed that due to rapid cooling rate inherent to resistance spot welding, the ferrite-austenite phase balance is destroyed and nitride-type precipitates are formed within the ferrite grains. The amount of austenite in the weld nugget was a function of welding current, as the most important factor affecting welding heat input. Increasing welding current increased the austenite volume fraction from 4 to 18%. Moreover, the nitride precipitation was reduced upon using higher welding currents. Investigation of weld mechanical performance during the tensile-shear loading showed that increasing welding current enhances both load bearing capacity and energy absorption capability. The maximum achievable peak load and energy absorption of 2304 duplex stainless steel resistance spot welds were 25 kN and 40 J indicating a superior weldability.

In recent years, metallic multilayer material have been attention of many researchers and different industries. Cold roll bonding is one of the method for produce layered composite that compared to other composite manufacturing methods are more economically and have the ability to produce layered composite with different material. In this research, for the first time and according to ASTM-E561 and using compact tension specimens investigated plane stress fracture toughness for thin three-layer Al/Cu/Al composite sheets produced by Cold Roll Bonding Process. The fracture toughness is an important parameter in the design that their analysis can predict crack growth and life for material has crack. In addition to the fracture toughness, mechanical properties and tensile fracture surfaces were evaluated by using of uni-axial tensile test, micro hardness and scanning electron and optic microscopy, respectively. Results of carried out tests, showed the value of tensile strength, microhardness and fracture toughness for Al/Cu/Al layered composite compared to initial Al 5052 and pure Cu, increased that the main cause of this increase is applied high strain and cold working. Value of fracture toughness for Al/Cu/Al layered composite received 38.7MPa.m1/2 that compared to initial Al5052 and pure Cu, 81% and 165% enhanced, respectively. Results of SEM demonstrated that ductile fracture mechanism govern for Al/Cu/Al composite such as initial samples, but the difference is that dimples for composite layers shallower and smaller compared to initial samples.

One of the most important machining processes in the field of orthopedic surgeries and biomedical engineering is the drilling process. Applying excessive forces on the bone tissue, it can be caused cracking and damage bone tissue during the drilling process. In this paper, it is produced an improved analytical model based on early work done by Bono and Ni, Chandrasekharan, and Lee to predict the thrust force in the bone drilling process. In this model, the cutting action at the drill point is divided into three regions: the primary cutting lips, outer portion of the chisel edge (the secondary cutting edges), and inner portion of the chisel edge (the indentation zone). All three regions have been investigated for the cutting process by the analytical model. In order validating the model, some experiments performed on the fresh bovine bone. Feed rate and rotational speed are adapted as the effective parameter in the drilling process, The statistical model to obtain the mathematical model and provide interaction diagrams of input variables experiments, to response surface methodology and experimental investigation of bone drilling have been offered. Comparing the analytical model and experimental results show good agreement. From both analytical model and experiments, it is can conclude that with decreasing feed rate and increasing rotational speed, thrust force on the bone tissue decreases.

In this study, based on the third-order shear deformation theory the equations of motion are obtained to analyses the deformation of a long and slender composite beam. The beam has initial geometric imperfection and subjected to impact load. The impact procedures are applied by rigid body with a specific speed, off-center and at a certain distance from the beam's surface. Hamilton’s principle and the von-Karman nonlinear strain-displacement relationship are used to obtain the equations of motion that they are based on displacement and in a set of coupled nonlinear partial differential equations in dynamic mode. The generalized differential quadrature Method (GDQM) is used to discretize the obtained equations and convert them into a set of ordinary differential equations. Newton-Raphson iterative scheme is employed to solve the resulting system of nonlinear algebraic equations. Then, by solving the equations of the system, the effects of initial geometric imperfection on the beam’s deflection have been studied. Also the effects of mass and the initial velocity of the impactor on the beam’s deformation are investigated. The results of this research show that an increase in the amount of the initial velocity and mass of the impactor entail an increase in the beam deformation.

Coverage of ground stations by satellites is a very important factor to access geographic, geotechnical and strategic information. This is generally achieved by one or more satellite with specified position and navigation. In this regard, in the area of low altitude orbits regional or global coverage of the Earth's surface is achieved utilizing various mathematical methods to change the position and arrangement of satellites. In this study, the arrangement of certain number of satellites is performed to reach maximum coverage. It is assumed that the satellite constellation is in the symmetrical Walker pattern. In this regard, taking into account the situation of user and determining the initial position of satellite in system, Geometric Dilution of Precision (GDOP) parameters are calculated utilizing a new model. The innovation in this new presented model is employing GDOP in an inverse manner. GDOP is a geometric standard that the less related values for it represents more accuracy in determining the amount of coverage. In this study the effects of compression of the earth as well as chamfer are considered. The calculations are presented for specific geographic areas and only for one day. The results show that by taking advantage of new computing model, the coverage area will dramatically increase. By organized employing of all the satellites in the constellation, with the best received Information from satellites, better coverage can be achieved.

In the present paper, a hybrid filter is introduced to simultaneously preserve the stability and accuracy and also to eliminate unwanted oscillations in the numerical simulation of shock-containing flows. The fourth-order compact finite difference scheme is used for the spatial discretization and the third-order Runge-Kutta scheme is used for the time integration. After each time-step, the hybrid filter is applied on the results. The filter is composed of a linear sixth-order filter and the dissipative part of the fifth-order weighted essentially non-oscillatory scheme. Using a shock-detecting sensor, the hybrid filter reduces to the linear sixth-order filter in smooth regions and to the fifth-order weighted essentially non-oscillatory filter in shock regions in order to eliminate unwanted oscillations produced by the non-dissipative spatial discretization method. The filter performance and accuracy of the results are examined through several test cases including the linear wave equation and one- and two-dimensional Euler equations of gas dynamics. The results are compared by that of a hybrid filter which is composed of the linear sixth-order and the second-order linear filter and that of the fifth-order weighted essentially non-oscillatory scheme.

Gravitational search algorithm (for the first time) has been used for two-objective optimization of airfoil shape, in this article. 2D compressible Navier-Stokes equations with Spalart-Allmaras model has been used to simulate viscous and turbulent flow. First, efficiency and accuracy of the optimizer sets have been evaluated using inverse optimization. Objective functions were differences between drag and lift with their corresponding values of the NACA0012 objective airfoil, as a set of airfoils randomly were chosen as starter airfoils, in this case and the aim was to obtain the airfoils that satisfy the considered objective functions. In direct optimization, gravitational search algorithm that has been used in the present work, has achieved proper parameters (related to the Parsec method) and consequently has found optimized airfoils with maximum lift and minimum drag objective functions. This algorithm starts to slove using a set of airfoils and it is directed towards the airfoils that provide the mentioned objective functions. Comparison of the results (Pareto fronts) shows better and more proper performance of the gravitational search algorithm rather than particle swarm optimization algorithm and former researches (done using other meta-heuristic algorithms) for aerodynamic optimizations.

In this study, error back-propagation neural network is used for fault detection of composite plate with delamination damage. At the first step of the fault detection process, a free vibration analysis of laminated composite plates is performed based on numerical finite element method and the natural frequencies of individual modes is obtained for different delamination models (size, geometry and location of the delamination region). Then natural frequencies extracted from the model are considered as the input parameter and the size, geometry and location of the delamination region are also considered as the output parameters of the neural network. 8-layers composite plate is modeled based on the three-dimensional elasticity theory and considering hexagonal brick elements. So, transverse shear deformations effect is taken into account in the modeling of composite plate. ABAQUS software capabilities are used for modeling because of the complexity of process governing on the composite plate with delamination. The numerical results obtained by the finite element method are compared and validated with available numerical and experimental data. Two training methods including Levenberg - Marquardt and Error propagation flexible algorithm are used to train the neural network and compare responses. Predicted results by Levenberg – Marquardt training method are in very good agreement with the values obtained by the finite element method. After training the neural network, the model generalization is used for predicting and detecting of the damage in composite plate.

The present study proposes a novel numerical method for fatigue life prediction under non-proportional loading. This method is employed for fatigue life estimation of different materials including 1045 Steel, 30CrNiMo8HH, Titanium TC4, extracted AZ31B Magnesium and Aluminum alloy 6061 under both proportional and non-proportional loadings. Basis of the method is developed in the framework of two numerical modifications. The first modification modifies fatigue damage parameters by correlating damages quantities of non-proportional loading to the proportional one. The second modification uses the same equation as the first one, but the corresponding damage coefficient is replaced by the additional hardening coefficient. In addition, these modifications are applied to fatigue damage parameters including maximum shear strain, SWT, Fatemi-Socie, and Babaei-Ghasemi model and also verified against experimental observations available in literature. Furthermore, the obtained results are discussed in details and also are compared to the non-modified findings. Moreover, the variation of the fatigue life prediction error is calculated for the aforementioned models. Finally, the results show considering and implementation of these modifications significantly improves the accuracy of the predicted fatigue lives for all the studied cases.

Catalyst layer is one of the important components of PEM fuel cell that its modeling and optimization can have a significant effect on the performance and the price of fuel cell. Despite successes were obtained to improve the fuel cell performance but still the slow reaction of oxygen in the cathode catalyst layer and mass transfer limitations are the main factors that reduce the efficiency and the performance of PEM fuel cell. The aim of this paper is modeling the cathode catalyst layer with homogeneous and agglomerate models and comparison with together. The governing equations are including oxygen diffusion equation, electrochemical reaction rate equation, transport equations of protons and electrons and auxiliary equations that solved by Matlab software and validated with experimental and numerical data available in the literature. The results show that at constant porosity, with increasing the agglomerate radius and thickness of ionomer film around agglomerate, the activation loss is increased and the concentration is reduced therefore the fuel cell performance is reduced. By more decreasing the radius of agglomerate, the fuel cell performance curve base on the agglomerate model approach to the performance curve base on the homogenous model.

Laser cutting is one of the modern methods for cutting. In this method heat affected zone width and microstructure changes as a result and also sheet deformation are very low in comparison to other thermal methods and a fine cut is the result. The control of heat-affected zone (HAZ) during laser cutting of titanium sheets due to low thermal conductivity and high tendency to chemical reaction is of great importance. In this paper, the effect of some of the most important laser cutting parameters, including the type of assistant inert gas, stand-off distance, cutting speed and power on HAZ width was assessed in CW CO2 laser cutting of Ti-CP sheets, using Taguchi L16 orthogonal array. Metallography of the cut samples, effects of cutting parameters and optimal conditions of cutting were investigated. Taking into consideration the test results, it is suggested to select the highest possible cutting speed for thin Ti-CP sheets and provide the required severance energy by controlling the laser power. The use of helium instead of argon also showed a significant impact on the reduction of HAZ width. Finally, microstructure and hardness changes are presented.

Guidance of an underwater vehicle in the wake of target due to the complexity of guidance in water and also sensor limitations, is still the most important homing guidance method. Disadvantages of wake guidance can be mentioned as zigzag motion for rediscovering the wake in its path which according to the decreasing linear speed of approaching the target, sometime it doesnt reach the target and collision fails. Therefore various ideas, with both positive and negative aspects, have been introduced to improve movement in the wake path. According to complexity of the wake model and also its instability in order to extract its parameters, makes it a very nonlinear phenomenon and guidance in it is a problematic in underwater vehicle. Since the wake detection area by the sensor is not enough widespread, wake is just discovered in the near of itself. Hence the real wake path is not detectable and therefore advanced guidance method is not available. For this reason, it is suggested to use a method of unknown path tracking for the wake guidance. This guidance law consists of two parts of path estimation and nonlinear guidance. The estimation method is performed using particle filter that has the ability to estimate nonlinear paths. The stability proof of nonlinear guidance method is done by Lyapunov.

Thermal energy storing technologies are a new approach in reducing energy costs, managing demand side, pick shaving and increasing portion of renewable energies in energy production. In spite of lots of advantages of thermal energy storage techniques, there are still major challenges in the path of Latent heat thermal storages (LHTS). One of the challenges is the low charge and discharge rate of heat transfer in LHTS. In the current study charging rate of a shell and tube LHTS is numerically studied by enthalpy-porosity numerical technique. Exact positioning of the heat transfer tubes and thermal fins has great impact on the natural convection flows. In this study effect of increasing heat transfer tubes (HTF), lower positioning of tubes in four tubes configuration, changing upper tubes distance and using interconnected axial fins has been studied and compared to each other. Moreover, velocity and temperature contours have been analyzed. Results demonstrated that increasing number of tubes could not solve the slowing rate of charging at the end of process and tubes need to be positioned lower in the tube. In addition, it was observed that heat transfer axial fins can decelerate convection flows and develop stationary areas inside the shell. Prediction results revealed by lowering tubes and closing them to the shell wall, introduced in this article, it is possible to decrease charging time of 0.95 of storage capacity to one fourth of similar time in a one tube LHTS.

Prediction and prevention of wrinkling are very important in tool design and determining the effective parameters in sheet metal forming processes. In forming metallic cups, wrinkling generally occurs in the two regions of flange and wall. The control of wrinkling in flange area is not so difficult by controlling the blankholder pressure, but it is difficult in the wall region because the sheet is not supported in this area. In this paper, using a geometric method based on numerical simulation, the wrinkling in the wall of the symmetric conical parts in the developed hydrodynamic deep drawing with radial pressure and inward flowing liquid is investigated. In the process, two independent pressure supplies have been used for forming the sheets. Due to the nature of the process, the effects of radial and cavity pressures on wrinkling have been investigated. In addition, the effects of material, initial blank thickness and punch velocity on wrinkling in wall area were investigated. To verify the results of the simulation, several experimental tests have been done on the St13 and copper sheets. Good agreement between the simulation and experimental results shows the reliability of this method in the wrinkling study. It was also demonstrated that increasing the maximum radial pressure or decreasing cavity pressure leads to increasing wrinkling. Additionally, wrinkling was decreased with increasing blank thickness. Moreover, it was shown that wrinkling simulation is much depended on input parameters such as punch velocity and appropriate element size

Quadrotors are types of Unmanned Aerial Vehicles (UAVs) which have unique features compared to conventional aircrafts because of its vertical take-off and landing capability, flying in small areas and its high maneuverability. Also the relatively simple, economical and easy flight system of quadrotors, makes it to widely used as a good platform for development, implementation and testing a variety of control methods. One of the robust control methods is sliding mode control. In spite of the high capabilities of this approach, it has a main problem which is high frequency switching of the control signal witch is known the chattering phenomenon. In the past several decades, fractional order differential equations have been implemented in engineering application field, including controllers design and provided the possibility of using controllers for improving the performance of system. In this paper, a fractional order sliding surface has been employed for designing sliding mode control rule for quadrotors. The main objective of this study is to improve the performance and reduce the chattering phenomenon in sliding mode method. In this regard, by introducing sliding 〖PD〗^α surface, the control rule is designed in two different modes of 0

In this paper, the effect of new control tools on the behavior of the parachute and its performance is studied by applying a compulsive stimulus in flow field. Modeling simulation and analysis performed with Ansys Fluent. A general geometry is proposed and simulations are carried out to indicate the effect of those stimuli on the flow behavior, parachute performance and high pressure areas on parachute. For the simplicity, the assumptions of axisymmetric and rigid wall of the parachute are used. Due to the large range of motion of fins compared to adjacent cells and also the importance of quality of mesh in the vicinity of the solid boundary, spring-based smoothing method for local and area remeshing are employed. In this way, the mesh quality for presenting the boundary layer and vortex generated in the solid surface are enhanced. The results depicted that using spherical arch geometries versus circular sector or parabolic geometries lead to some advantages. Permittivity of disk at the end of the parachute, has been triggered to increase the general drag coefficient dramatically up to around two times larger. Despite the existence of stimulation on a large area, flow field experience a total pressure drop. On the other hand if the stimulus does not exist the area is much smaller.

Minimum quantity lubrication (=MQL) technique has many technological and economic advantages in grinding operation. It not only improves general grinding performance such as surface integrity, grinding forces and wheel wear but also, it is eco-friendly technique because of its small consumption of cutting fluid. Despite these advantages, MQL technique has a serious thermal problem in grinding operations due to small amount of cooling. To overcome this problem combination of hybrid nanofluid and ultrasonic vibration has been suggested. Nanofluid can increase heat transfer from workpiece/wheel interface due to its high thermal conductivity. Also ultrasonic machining can decrease heat generation due to its reciprocating mechanism and reduction of time and length of contact between grain and workpiece. In this research hybrid Multi Walled Carbon Nano Tubes (=MWCNT) (with high thermal conductivity) and Al2O3 (with good lubrication effect) nanofluid has been utilized. The results have been shown that combination of MQL and UAG leads to decreasing of maximum grinding temperature up to 60.2% in comparison to dry grinding (from 254ºC to 101ºC). Moreover, friction coefficient and tangential grinding force have been reduced up to 35.9 and 69.2 percent respectively. Furthermore, any burning has not been observed with combinations of these techniques while severe burning has been observed in dry grinding. Surface morphology analysis has been shown decrease of plastic deformation and side flow. And finally the generated chips have been shown similarity of cutting mechanism in in the utilized techniques and conventional cutting fluids.

Gas turbine power and thermal efficiency increase with inlet temperature. Considering the temperature limitations for the alloys used in gas turbine components, employment of techniques for reduction of these components temperatures seems to be an essential subject. Based on the research conducted on this subject, among all the proposed methods, rib cooling yields higher heat transfer coefficient and among various types of ribs, V-shaped ribs have higher heat transfer compared to angled rib. The purpose of this feasibility study is to investigate the two proposed ribs for use in gas turbine from heat transfer and fluid flow view and compare their thermal performance. In this work, 3-D numerical simulation has been performed for V-shaped ribs with an angle of 〖60〗^° for the two cases of staggered and inline ribs in two opposite walls in a rectangular channel. Experimental results have been used for validation. The results indicate an enhancement of ~22% in heat transfer if V-shaped ribs with an angle 〖60〗^° and downstream orientation are located in staggering form in two opposite walls of a channel. In this case, an increase of 10% is observed for pressure drop, however, its thermal performance increases 12% which is positive and considerable.

Lost foam casting is a new method for casting complex parts. This method, in addition to its technical and economic advantages over the traditional methods, has environmental benefits and therefore has been of special interest. In this study, the effects of foam density, pouring temperature, and coating viscosity were studied, which are the most important factors affecting porosity and hardness in the lost foam casting method. The Taguchi method, signal to noise ratio and analysis of variance were used to design experiments and determine the optimal levels of each variable. All the considered variables were evaluated in three levels using L9 orthogonal array Taguchi analysis. Results showed that foam density of 20 kg/m3, pouring temperature of 740° C and coating viscosity of 20 sec were the optimal values for the variables due to creating appropriate condition between thermal decomposition and foam evaporation with speed of melting advancement and exhaust gas through the pores in the coating and creating lowest porosity (2.6%) and highest hardness value (27.7 HRA). Foam density and pouring temperature were the most influential parameters on the porosity and hardness with the impact factors of 64.58% and 56.35%, respectively.

Optimum design and performance improvement of the Heat Recovery Steam Generator (HRSG) have noticeable effects on the thermal efficiency of the combined cycle power plants. Therefore, HRSG must be designed in such way that maximizes the heat recovery and improves the overall performance of the plant.
In this paper, a method for design and optimization of a triple pressure HRSG is proposed. It is shown how to simultaneously optimize the operating and geometric design parameters of the HRSG by using the constructal theory. Considering the minimum total entropy generation as the objective function, the optimum parameters in the HRSG unit are derived by using the genetic algorithm method under the fixed total volume condition. Optimized total volume is derived by converting the exergy destruction to cost of entropy generation in order to compare with the capital cost and the results show that there is a trade-off between them. Also, aspect ratios of the units, the heat transfer area for each component of the HRSG and thermodynamic properties are significant features of the flow configuration inducted by the Constructal design. Furthermore, the effects of changing in the temperature and flow rate of hot gas on the optimal values of the total volume, power and steam production are determined.

One of the very important issues in designing hand prosthesis is to consider their cover or cortex. The purpose of this research is to design a cover to have a similar behavior, as much as possible, to the human natural skin, in power transmission and deformation pattern. A layer made of Lorica®, which has similar properties to natural skin, has been added to the conventional cover which composed of three layers. Using finite element analysis Software, ANSYS V.15, the new four-layered cover has been investigated on three dimensional model of the hand prosthetics with different thickness for the outer layer, and the pattern of deformation and internal stresses in the prosthesis are measured. Optimal thickness of the outermost layer is evaluated due to stress and strain distribution and their transformation to prosthesis metallic core. The relationship between the thickness of this layer and the distribution of stress and deformation of the cover is not linear and direct and the thickness of 1.5mm shows better results among the measured values in this section. In this study, the fourth layer was added to improve the frictional and elastic properties of formerly used prosthetic covers, and its effects on stress and strain distribution in the prosthesis was investigated. It is determined that due to lack of linear correlation between the thickness and stress distribution, the optimal thickness of each layer must be selected based on design limitation like the ability of embedding tactile sensors in future for the minimum thickness.

Nowadays, Hybrid Electric Vehicles (HEVs) are introduced in order to reduce fuel consumption and emissions. The issue that is very important in HEVs, is how to split power between main components of powertrain. Best energy management can be obtained when all future conditions are available. With the advancement of the intelligent systems, access to the road conditions, traffic and other online information has been provided up to the limited prediction horizon. In this paper, a combination of predictive control and Dynamic Programming methods have been used for obtaining online sub-optimal trajectory. Change in the state of traffic in the path has great effect on reduction of fuel consumption. Therefore, According to the state of traffic, a fuzzy logic system is proposed for the online estimating of the vehicle speed. Unlike many energy management methods that use historical data, the proposed strategy leads to reducing the dependence of the controller on the drive cycle. The simulation is implemented on a Plug-in Hybrid Electric Vehicle with parallel structure. The proposed method is compared with Dynamic Programming and instantaneous optimization. Evaluation of results shows that the proposed method, while simplicity and avoiding complicated mathematical relationships, in addition to fuel consumption reduction compared with instantaneous optimization, can manage SOC, properly. The results of this method are close to the global optimal solution of Dynamic Programming.

Nowadays, the world is facing to increasing loss of fossil resources, energy crisis and environmental problems. On the other hand, diesel engines due to wide application in various sectors such as transport, agriculture, industry, etc., are the main sources of emissions and fuel consumption. Accurate measurement of fuel consumption and engine pollution is time-consuming and costly. Hence, the main objective of this study was to develop proper linear regression models of some important performance parameters of ITM285 tractor engine based on engine torque and engine speed. Experiments were carried out in 11 levels of primary engine speed (1063, 1204, 1346, 1488, 1629, 1771, 1818, 1913 and 2054 rpm) by 10 N.m steps of torque from zero (no load) to full load. The measured parameters include fuel consumption mass flow, exhaust temperature, instantaneous engine speed, maximum and mean exhaust opacities. Four different linear regression models were used to estimate the parameters. The results of regression models performance evaluation showed that quadratic model had the highest efficiency and the lowest RMSE for all parameters. The maximum and minimum effects of engine torque were on exhaust temperature and instantaneous engine speed, respectively; while, this result was completely reverse for primary engine speed. The results of regression models evaluation showed a high adaptation between the output of each model and the desired output. Also, the fuel mass flow and exhaust temperature were highly correlated to the maximum and mean exhaust opacity with correlation coefficients of 0.96 and 0.99, respectively.

In this research dynamic instability and nonlinear vibration of a clamped-clamped micro-beam sandwiched with piezoelectric layers based on parametric excitation in sub-harmonic region is investigated. The equation of motion is derived based on Hamiltonian principle, and non-dimensionalized using appropriate non-dimensional parameters. Applying a harmonic AC voltage to the piezoelectric layers results in the time varying of the linear stiffness of the micro-beam. The resultant motion equation in non-dimensional form is discretized to single degree of freedom model using Galerkin technique. The governing equation is a nonlinear Mathieu type ODE, and the periodic attractors are captured based on the shooting technique. The nonlinearity of governing equation is due to the geometric nonlinearity which originates from the clamped-clamped boundary conditions. The effect of various parameters including, magnitude of the nonlinear stiffness, damping coefficient, the frequency and the amplitude of the harmonic excitation on the parametric resonance region is investigated. The results depict that increased damping coefficient leads to the decreased aria of the parametric resonance region. It is concluded that the magnitude of the nonlinear stiffness, does not affect on the area of the resonance region, however it considerably influences on the amplitude of the parametric resonance.

In this paper, a fractional order backstepping type of fast terminal sliding mode controller is proposed for controlling a micro-electro-mechanical triaxial gyroscope with parameter uncertainty and internal and external disturbances. To compensate uncertainties and also incoming disturbances to the system used combination of sliding mode and backstepping robust nonlinear controllers. In the proposed approach, the sliding surface is selected in the form of fractional order. To increase the speed of convergence the system states to equilibrium points or the error to zero, the fast terminal sliding mode controller is used. The globally stability of the closed loop system will prove by Lyapunov stability theorem. Also in addition to the above proposal controller, a fractional order backstepping sliding mode controller designed and implemented for the gyroscope system. In order to evaluate the performance of designed controllers, these controllers compared with backstepping sliding mode controller and the backstepping fast terminal sliding mode controller. The results shown that the proposed controller has a faster transient response than the other controllers. Another advantage of the proposed controller is simplicity designed and implemented, increase system stability and acceptable tracking than the other controllers. Also unlike the other two controllers the chattering phenomenon completely removed in the fractional order designed controllers.

The use of automatic systems for space exploration can dramatically decrease the cost of desired mission. One of the structures that has previously been utilized for space exploration is the wheeled rovers. Wheeled rovers have wide work space and can move with a proper velocity. Their mechanisms are simple and are energy efficient. In the most of the previous studies, it has been assumed that the wheeled robot chassis is rigid. However, if the wheeled robot motion on relatively rough terrain is required then it should be equipped with flexible suspension. Also, in most of the earlier studies, the nonlinear friction between the wheels and ground has not been modeled. Consequently, in this paper, the dynamics equations of a wheeled robotic system with flexible suspension is derived. To model the friction and wheels slip, the Dugoff friction model is utilized. Considering the wheels torque as inputs, a novel two-layer driver is proposed. Adopting the suggested algorithm, the control of pitch angle is possible. In the first layer, the motion of the system is adjusted using modified multiple impedance approach. Also, in the second layer, which is called local controller, the actuating torque of wheels are adjusted so as the output forces/torques of the first layer can be realized. The obtained simulation results support the merits of the proposed new motion strategy control.

In this paper, the Wave Finite Element Method (WFEM) is developed for modelling of stress wave propagation in one-dimensional problem of nonhomogeneous linear, anisotropic micropolar rod of variable cross section. For this purpose, the WFEM equations are developed based on the micropolar theory of elasticity. Two kinds of waves with fast and slow velocities are detected. For micropolar medium, an additional rotational Degree of Freedom (DOF) is considered besides the classical elasticity’s DOF. The method proposed in this paper is implemented to solve the wave propagation and impact problems in micropolar rods with different layers. The results of the proposed method are compared with some numerical and/or analytical solutions available in the literature, which indicate excellent agreements between the results.

Drilling is one of the most critical mechanical process in oil and gas industry in which its operational parameters should properly be tuned to reduce drilling time and consequently enhance efficiency of the drilling process. The main objective in this paper is to present a new method to regulate and optimize the Rate of Penetration (ROP) of the system with top drive rotary motor torque in drill string. The paper presents a formulation of a robust receding horizon controller to track piecewise constant references. To achieve this, a tube-based Robust Model Predictive Control (RMPC) is introduced in which the tubes are based on reachable sets. A drilling system is assumed as a test bed for evaluating the performance of the proposed control scheme. The assumed drilling system is modeled as a linear system with additive bounded uncertainties by using Bourgoyne and Young model which is known as a complete mathematical drilling model. The most important novelty part of this manuscript corresponds to integration of both tracking and regulatory objectives in one control framework. Simulations demonstrate the effectiveness of the stability and robust characteristics the proposed RMPC scheme in terms of its stability and robust characteristics with respect to the usual control approaches.

Stress urinary incontinence (SUI) is characterized by the involuntary transurethral leakage of urine caused by an increase in abdominal pressure in the lack of an adequate bladderý ýcontraction that raises the vesical pressure to a level that exceeds urethral pressureý. ýAdult women are most commonly affected by SUI which is believed to be caused in part byý ýinjuries to the pelvic floor sustained during childbirthý. ýDespite the large number of women affected by SUIý, ýlittle is known about the mechanisms associated with the maintenance of urinary continence in womený. ýThe work in this ýresearch ýfocuses on studying the behavior of the bladder and the dynamics of the urine during an increase in abdominal pressure like a coughý. ýThe computational model is developed by using the Finite Elements Method (FEM) and Fluid-structure interaction (FSI) techniques. ýThe results show a good accordance between the clinical data and predicted values of the computational models. ýSimulated pressure is more accurate in the model in which non-linear material properties are utilized. The results of the computational methods indicate that by using numerical techniques and simplification of the physics of biological systems, clinical results can be reached in virtual environments in order to understand pathological mechanisms.

The objective of this paper is to obtain acoustical behavior of air flow around 65° sweep back cropped, 66°/42° cranked arrow and 53° diamond delta wing configuration by using large eddy simulation approach with 0.17 of smagorinsky-lilli coefficient. It is worthy to mention that the root chord of the wings is 360 mm. Validation of the aerodynamics coefficient is performed using available experimental results which showed good agreements. CFD simulations were performed for 15 degree angles of attack at a Mach number of 0.147 and a Reynolds number of 1.2 million based on the root chord. Acoustic measurements such as power spectral density, acoustic pressure, sound pressure level and sound amplitude, were taken using 3 microphones in the wake region of the mentioned wings. The amount of sound pressure level of microphone which is placed at 1.835 meter from apex of above wings in the range of Strouhal 0 to 1 is, 22 to 66, 10 to 73 and 9 to 44 which indicates aeroacoustic behavior of the diamond delta wing, is more better than cropped and cranked arrow delta wing.

The contour method is a new approach to measure the residual stress and use to provide a two-dimensional map of residual stresses. In this study, residual stresses were measured in the rods which produced by hot extrusion with high reduction cross section. The rods material was 6061 aluminum alloy and the effect of annealing heat treatment has been studied on the rods. For this purpose, residual stress has been evaluated before and after annealing heat treatment and the uncertainty of the contour method calculated. The results indicate that in the rods that produced by hot extrusion with high reduction cross section, tensile residual stress is created in the rod core and by moving along radius changed to compressive residual stress such that the surface is balanced via tensile and compressive stress. The maximum tensile residual stress is formed on the rod center and performing annealing heat treatment causes to high reducing residual stress. Also the uncertainty investigation determined, the uncertainty was almost uniform on the surface and displacement error and model error sources have a same effect on the uncertainty of contour method.

Nowadays, two-layer sheets have many applications in various industries due to their superlative characteristics. Characteristics such as weight and formability of two-layer sheet depend on the material and the thickness of the layers which compose the two-layer sheet. Plastic instability and occurrence of localized necking limit the forming of the sheets. Forming limit diagram is used to evaluate the formability of sheet. In this paper, a multi-objective genetic algorithm is applied to optimize the thickness ratio of layers in Al3105-St14 two-layer sheet. The optimal model minimizes the weight and maximizes the formability of two-layer sheet simultaneously. Forming limit diagram of two-layer sheet is determined by analytical model based on Marciniak and Kuckzinsky (M-K) method using Barlat and Lian non-quadratic yield criterion. Experiments are also carried out on Al3105-St14 two-layer sheet in order to examine the validity of the theoretical results. Pareto-based multi-objective optimization is used in order to make the objective function of weight per unit area minimized and the objective function of formability maximized. The Pareto front provides a set of optimal solutions. In addition, the knee point as the most satisfactory solution from Pareto-set is determined using minimum distance method.