Modares Mechanical Engineering
Year:2017 | Volume:16 | Issue:11 |Papers Count:58

This paper presents a fast and efficient aerodynamic optimization method for megawatt class wind turbines. For this purpose WP_Baseline 1.5 MW wind turbine is used as a test case. Modified particle swarm optimization (PSO) algorithm is used in this study. PSO parameteric studies are conducted, to increase both efficiency and speed of optimization cycle. Since in aerodynamic optimization, it is very desirable to limit the number of the variables, in this study geometric class/shape function transformation technique (CST) is used for blade geometry parameterization and the appropriate order of shape function polynomial is proposed for S818, S825 and S826 airfoils. Improved Blade Element Momentum (IBEM) theory is implemented for wind turbine power output estimation, and validated with experimental and Computational Fluid Dynamic (CFD) data of AOC wind turbine. The aerodynamic data needed for IBEM is provided by XFoil software. XFoil output data for pressure coefficient and wall shear stress which are validated against experimental and CFD data, are applied as the aerodynamic input data for IBEM method.The twist, the chord and 3 types of airfoil for all sections of the turbine blade are optimized using IBEM method. Optimization is performed with realistic constraints to produce feasible geometry. The performance of the final optimized geometry is simulated via 3D steady incompressible Navier–Stokes equations coupled with Transition SST Model CFD simulation to predict the performance improvement.The results show about 6 percent power enhancement for WP_Baseline wind turbine.

Numerical investigations of the effects of ocean water waves on the structures and also the devices designed to capture energy from waves, mainly require proper generation of desired water waves with Specific features. In this study, a numerical method for generation of nonlinear irregular waves is proposed for viscous flow simulations based on Navier-Stokes equations. The numerical method is based on a control-volume approach where a two-step projection method is used to solve the governing equations. In this regard, the motion of the flap-type wavemaker inside the water is simulated using the fast-fictitious domain method, the VOF method is used to capture the free surface evolutions and highviscosity regions are employed to damp the reflecting waves. First, various methods of wave generation for the numerical wave tanks, available in the literature, are reviewed and next, three waves with different wave steepness are simulated to demonstrate the capabilities of the proposed method. Results show that the method can effectively produce irregular waves, from linear waves up to the steep nonlinear ones. Furthermore, shallow to deep water waves can be generated with reasonable accuracy using the proposed method.

Nowadays, modern windows with standard caulking are used in most buildings. Study of air infiltration and caulking these windows in several ways such as energy, indoor air quality, thermal comfort and pollution entering in the building is important. This study consists of two parts, first the airtight performance of various window gaskets is experimentally investigated. For this purpose, 8 different types of gaskets are used and modern window gap is simulated, and air infiltration rates are measured at different pressure differences. The results show that the airtight performance of various gaskets is different. Also, experimental results are fitted by power law equation, and relations and coefficients are used to calculate air infiltration rate of modern windows (sealed windows), respectively. In the second section due to the very low air infiltration rate of the experimental results, indoor air quality is assessed by numerical modeling methods. In the sample model, air infiltration of modern windows as ventilation and human breathing as a source of CO2 is simulated. Indoor air quality is weighed by the CO2 concentration in the interior space. The results show that the air infiltration of window gaps to ensure air quality during the 8 hours is insufficient. Then, assuming uniform distribution of CO2 in the sample space, and solving the transfer species equation for the problem situation, analytical equation for evaluating indoor air quality were achieved. Analytical results match numerical simulation results exactly. The results of this study can be very useful for HVAC engineers.

In this study, fatigue growth of external surface cracks on the autofrettaged cylinders under bending is investigated. Autofrettage is a process in which a thick-walled cylinder subjected to internal pressure with known amount, causing some portions on the inner zone of the cylinder deformed plastically. In this case, removing the pressure causes compressive residual stresses on the inner layers and tensile stresses on the outer wall. The goal is increasing the fatigue durability of the product by inducing residual compressive stresses into materials, but along with this, there are adverse tensile stresses which can decrease the life due to the outer defects. In this paper, the external cracks are in the forms of halfelliptical, semi-elliptical and semi-circle. Samples made by aluminum 2024 alloy. The cylinders were autofrettaged up to 40 and 60 percent. Cracks were located in circumferential direction and normal to cylinder axis. The numerical simulations were performed by finite element method. Experimental data and numerical results were compared. Results show that the number of load cycles to fracture, in the 60% autofrettaged cylinders are smaller than those for 40% and also smaller than the state without autofrettage. Distribution of stress intensity factor along the crack front is symmetric and crack grows in its initial plane which indicating the dominance of the first mode of failure during the crack growth.In all samples, after some steps of the growth, crack front transforms to the semi-elliptical shape until complete fracture.

The attenuation of mechanical load is one of the most effective approaches in wind turbine components cost reduction, and improving the control system reduces mechanical loads with minimum effort. In modern wind turbines, electrically-excited synchronous generators are mostly applied in direct-drive structure. In current research, generator field voltage along with the blade pitch angle is employed for tower load reduction in a novel multivariable-adaptive control structure. The controller is designed based on the extracted model with aerodynamic, vibratory and electrical interactions. The centralized multivariable structure is chosen to simultaneously reduce rotor speed fluctuations and tower vibrations.Since the nonlinear wind turbine model is complex, the controller is designed via optimization process.The nonlinear aerodynamic behavior of blades influences the closed-loop performance in different operating condition; therefore controller is adapted to the condition by employing gain-scheduling method. The effects of signal noise, digital control and higher-order dynamics of electrical system might defect the closed-loop stability. The designed controller is implemented on a wind turbine simulator which includes the previously-mentioned effects. By comparing the performance of the multivariable adaptive controller with a two input-one output multivariable controller, it is proven that the mechanical loads acting on tower have been greatly decreased.

In this study a numerical model based on the finite element method is used to simulate the behavior of human lumber spine. Due to lack of realistic models, in the present work a lumber spine model is generated from Computational tomography (CT-Scan) images by Mimics 17 software. Also, according to the wide range of loading conditions, to achieve realistic results, optimized loads acquired from other researches are used. Human lumber spine model which is used in this study consists of five vertebrae, five discs, and all ligaments. Model is loaded under statical conditions and calculated with ANSYSAbaqus 16 (Simulia Inc., Providence, USA) software. Obtained results are compared with other numerical simulation results and experimental measurements which are reported in other researches.Numerical modeling consists of six cases as follows: intervertebral rotation, interadiscal pressure and facet joint forces under the axial rotation and lateral bending with compressive follower force loadings.In all cases, intervertebral rotation, interadiscal pressure and facet joint forces are reported.Comparisons show that obtained results have good agreement with experimental measurements.Therefore, results show that realistic model with optimized loadings predicted the behavior of lumber spine more accurate than other numerical models.

Nowadays, use of modified compartmental model in order to estimate the transmission of tracer to the cells or cancerous tissues is used extensively. The modified compartmental model includes two parts, one to predict the mass transfer from vessels and a compartment to describe metabolism occurring inside the tissue. In the modified compartmental model, the kinetic rate constants can be obtained by estimating the parameters between the compartments. The tracer uptake is the main method used to diagnosis of cancerous tissues from other tissues. Today, most physicians use the standard uptake value (SUV) to study the amount of tracer uptake in cancer suspicious regions in order to have a more accurate recognition of cancerous and normal tissues. In this paper, the comprehensive evaluation of different uptake methods based on experimental data is performed. The Patlak graphical analysis method and standard uptake value method are used to predict the tracer uptake into the tissue. A comparison between the uptake parameter resulted from the two mentioned methods with the uptake parameter obtained by modified compartmental model in a rat shows the appropriate degree of accuracy of the Patlak method in distinguishing the cancerous tissues from the normal ones.

Supercritical fluids have substituted non-super critical fluids in some areas of industry because of their unique characteristics and have been the subject of numerous experimental, numerical and analytic studies since their discovery. In this study laminar natural convection between a hot vertical tube with constant temperature and supercritical carbon dioxide with uniform temperature at inlet is simulated by utilizing a numerical model. The simulation is a two-dimensional, pseudo-transient numerical model based on finite volume method. The main objective of this study is to investigate and analyze the effect of severe property variations of supercritical carbon dioxide on the flow and temperature field of natural convection that ultimately affect heat transfer rates with respect to non-critical natural convection.Numerical simulations have been carried out for temperature and pressure ranges of 305K to 312K and 7.5MPa to 9MPa respectively. Span and Wagner’s multi-parameter equation of state have been used directly to determine carbon dioxide properties around pseudo critical temperature for the first time.Results indicate an increased rate of total heat transfer up to 160% near pseudo-critical temperature and 118% in other temperatures for supercritical natural convection with respect to ideal gas assumption.

In this paper, the modified couple stress theory is used to study static and dynamic pull-in instability of a general model of a nano-cantilever under a sudden applied DC voltage in the presence of the surface effects. A partial part of the nano-cantilever is subject to the electrostatic and capillary forces. Euler-Bernoulli theory is used to model the beam and the equation of motion is derived by using Hamilton’s principle. The governing equations are transformed into a non-dimensional form and then solved using finite element method (FEM). The results, obtained using FEM are compared with the data available in the literature and found in good agreement. Basic parameters for engineering design at the nanoscale, such as deflection and pull-in voltage have been calculated for both of the dynamic and static modes.The results of dynamic analysis of the beam show that as the voltage increases, the beam goes into an oscillating mode with large amplitudes just before pull-in phenomenon occurs and the beam collapses into the substrate (fixed electrode). Moreover, it is found that a decrease in the length of the fixed electrode (increase of the partially affecting parameter), the increase of the fringing field effect, the size effect and the surface effect increases the pull-in voltage of the nano-cantilever beam.

Injection of drug micro particles into arteries is one of the stenosis treatments. Micro particles scattered in blood flow collide with plaques, the drug is absorbed to treat stenosis. Since the collision of drug particles with artery wall depends on blood flow pattern, the efficiency of this method relies on guiding drug particles to stenosed site, otherwise it would require much higher drug dose for the patient, which has various side effects. Applying magnetic field and guiding drug particles to the target area extensively increases efficiency of the treatment and lessens side effects. In the present study, efficiency of using drug particles in vertebrobasilar system to treat atherosclerosis with and without applying magnetic field has been investigated. Ansys-Fluent commercial software has been used for numerical simulation. Results indicate applying magnetic field plays an important role in drug particles circulation as drug captivation surges almost 16-fold. Injecting location and the particle diameters have also been examined and found to be important in the treatment effectiveness.

One of the main topics in the field of robotics is the formation control of the group of robots in trajectory tracking problem. Using organized robots has many advantages compared to using them individually. Among them the efficiency of using resources, the possibility of robots' cooperation, increasing reliability and resistance to defects can be pointed out. Therefore, formation control of multibody robotic systems and intelligent vehicles have attracted considerable attention, this is discussed in this paper. First, kinematic and kinetic equations of a differential drive wheeled robot are obtained.Then, reference trajectories for tracking problem of the leader robot are produced. Next, a kinematic control law is designed for trajectory tracking of the leader robot. The proposed controller steers the leader robot asymptotically, following reference trajectories. Subsequently, a dynamic control algorithm for generating system actuator toques is designed based on feedback linearization method. Afterwards, formation control of the robots has been considered and an appropriate algorithm is designed in order to organize the follower robots in the desired configurations, while tracking control of the wheeled robot.Furthermore, the stability of the presented algorithms for kinematic, dynamic and formation control laws is analyzed using Lyapunov method. Finally, obtained results for different reference paths are presented which represent the effectiveness of the proposed controller.

In the present study, the convergence behavior of the direct simulation Monte Carlo (DSMC) method is extensively explored. The Simplified Bernoulli Trials (SBT) collision algorithm is applied to simulate a one-dimensional nano Fourier heat conduction problem, which consists of rarefied gas confined between two infinite parallel plates with unequal temperatures. The investigations compares the Soninepolynomial coefficients ak calculated from the DSMC results with theoretical predictions of the Chapman-Enskog (CE) theory. In addition, the convergence behavior of the wall heat flux and the ratio of the DSMC-calculated bulk thermal conductivity (KDSMC) to the infinite-approximation of CE theoretical value (K) is studied. The numerical accuracy of the DSMC method is found to be restricted with regard to three parameters: time step, cell size, and number of computational particles per cell. The dependency of the SBT collision algorithm on these discretization errors has been investigated in comparison with the standard collision algorithm, i.e., no time counter (NTC). The results indicate that SBT can achieve analytical solutions of the Sonine polynomials using fewer particles per cell than NTC.Moreover, in the SBT algorithm, the effective parameter in the convergence is Dx/Dt ratio, which should be adjusted accurately. This study shows that by decreasing the number of particles per cell to even one particle in a constant Dx/Dt setting, the SBT algorithm accurately predicts solutions where the NTC algorithm fails.

In the present paper, a DSMC solver is utilized to study the effects of wall heating/heater plates on performance parameters of microthruster systems. The solver uses local Knudsen number based on the gradient of flow properties to distinguish the molecular and continuum region. This solver uses theory of characterisitcs for determination of inlet and outlet boundary conditions. Proper cell dimensions, number of particles per cell, and grid study are carried out to guarantee the accuracy of simulations.Three typical micropropulsion systems are studied. All three systems have a microchannel and a converging-diverging micronozzle. The first type is cold gas micropropulsion system, the second type is a microthruster with wall heated channel, the third type is microthruster with heater plates inside. The first type is considered as reference case and two other systems are compared with type1. It is observed that heating the walls in microthruster type2 accelerates the flow and increases the specific impulse of the system. In micropropulsion device type3, heater plates increase downstream temperature of convergent-divergent nozzle and also elevate the specific impulse. Due to considerable mass flow rate decrease of system type3, its thrust is decreased whereas mass flow rate of system type2 is not decreased as much as type3 and therefore the thrust of microthruster type2 is more than type1 and type3. Hence the second microprolusion system configuration has higher performance parameters in comparison with two other systems. It is also observed that increasing wall temperature in microthruster type2 decreases the thrust and specific impulse sensitivity to temperature increase.

One of the new methods for reducing the vibrations of rotors with variable imbalance is implementing automatic ball balancer (ABB). Although the ABB has numerous advantages, it has one major deficiency; increasing the rotor vibration amplitude at transient state that limits the use of this type of balancers. In the previous studies for diminishing the mentioned deficiency, a new type of ball balancer which is called the ball-spring ABB is introduced, and the dynamic behavior of Jeffcott rotor equipped with the ball-spring ABB is investigated. In the Jeffcott rotor model the gyroscopic effect is not considered, however, in practice and in many applications, due to asymmetry which comes from the offset of the rotor from the shaft mid-span, the gyroscopic effect is generated. In such conditions, the results of Jeffcott model are not reliable and dynamic behavior of the ball-spring ABB should be investigated in the presence of gyroscopic effect. In this paper by considering the asymmetry in the rotor-shaft system and taking into account the gyroscopic effect, the equations of motion of a rotor equipped with the ball-spring ABB are derived. The time responses of the system are computed and based on the Lyapanov first method, the stable regions are extracted. The results show that not only does the gyroscopic effect not affect on the performance of the ball-spring ABB, but also the magnitude of the Eulerian angles of the rotor equipped with the ball-spring ABB is less than those the rotor equipped with the traditional one.

ual stresses and distortion are of the main disadvantages of welding process which determining the amount and distribution of them have great importance in the design of structures, especially in the space industry. In this study, a finite element method is used to analyze the thermo- mechanical behavior of a spherical shell due to TIG welding. The spherical shell is made of titanium alloy (Ti-6Al-4V) with 2 mm thickness. The modeling of welding process is based on an uncoupled thermomechanical coupling. TIG welding is examined for six cases based on current intensity and welding progress speed setting the voltage on 12 V in all cases. Distribution of temperature and residual stresses caused by TIG welding of the titanium spherical shell have been extracted and compared among the six different cases. The effects of current intensity and welding progress speed on shell distortion and residual stress have been investigated. The results showed that increasing the current intensity and decreasing the welding progress speed have the most effects on longitudinal residual stresses which the amount of this increasing reached to %44 for decreasing the welding progress speed. Welding distortion increases to maximum %132 by increasing current and decreasing welding progress speed.

Object grasping by robot fingers with purely rolling constraints is one of the most interesting issues under consideration by many researchers. In earlier studies, the main goal was the manipulation of object under purely rolling constraints to reach the final stable configuration. In this paper, in addition to deriving kinematic and dynamic equations of the system dual fingers robot and grasping semicircular object on the horizontal plane with rigid hemi spherical fingertips under pure rolling constrained, we investigate object manipulation on desired path maintaining dynamics stability. Modified multiple impedance control is used for object manipulation and robot fingers by considering the required reforms in this control law. In this method multiple impedance control is performed by applying the desired behavior of the entire system, including fingers and object, and dynamics stability condition is satisfied.In this way power adjustment and that these forces arrive in the right place largely effective in minimizing slip is the fingers on the surface object. The results of simulations show the eligible object manipulation and dynamics stability by robot fingers under pure rolling grasp.

In this research, based on nonlocal elasticity theory, static and dynamic analysis of an elastic homogeneous nanotube conveying fluid with clamped - clamped boundary conditions is investigated.The nanotube is under electrostatic actuation and magnetic field with considering the surface effects, mechanical and thermal force. Transverse displacement of the nanotube consists of two parts static and dynamic displacement. In this study, the static displacement is calculated by using the weighted residual method and instability and vibration frequency is analyzed by applying the generalized differential quadrature method. By applying a voltage greater than the critical value (called Pull-in voltage) the nanotube may undergo instability. In this investigation, the effect of various parameters such as velocity of fluid, length scale parameter, magnetic field, electrostatically voltage, effects of surface layer and thermal loading on the static displacements, natural frequency and Pull - in voltage of the nanotubes conveying fluid has been studied. Finally, the validity of the results by comparing them with the results of the numerical methods in previous research is investigated, in which there is very good agreement between the results of the present work and previous studies. The results show that the length scale parameter is significant parameter in the system's Pull - in voltage and its increasing lead to decreasing the Pull-in voltage. Also, it is shown that the dimensionless frequency and the static displacements, respectively, is decreased and increased with increases in the applied voltage.

In this paper the effect of artificial noise on the performance of nonlinear system identification method in reconstructing the response of a cantilever beam model having local nonlinearity is investigated. For this purpose, the weak form equation governing the transverse vibration of a linear beam having a strongly nonlinear spring at the end is discretized by using Rayleigh-Ritz approach. Then, the derived equations are solved via Rung-Kutta method and the simulated response of the beam to impulse force is obtained. By contaminating the simulated response to artificial measurement noise, nonparametric nonlinear system identification is applied to reconstruct the response. Accordingly, intrinsic mode functions of the response are obtained by using advanced empirical mode decomposition, and nonlinear interaction model including intrinsic modal oscillators is constructed. Primary results show that the presence of noise in the response highly affects the sifting process which results in extraction of spurious intrinsic mode functions. In order to eradicate the effect of noise on this process, noise signals are used as masking signals in the advanced empirical mode decomposition method and intrinsic mode functions corresponding to the noise are extracted. Based on this approach, the dynamic of the noise in the response is identified and noise reduced signals are reconstructed by the intrinsic modal oscillators with suitable accuracy.

In this paper, design of an adaptive controller, as a combination of feedback linearization technique and Lyapunov stability theory, is presented for a parallel robot. Considering a three degree-of-freedom parallel mechanism of the robot, which serves pure translational motion for its end-effector, kinematic and constraint equations are derived. Then the dynamic model of the constrained system is extracted via Lagrange’s method to be used in the robot control. Two optimized trajectories are designed for the endeffector in the presence of some obstacles using harmony search algorithm to be tracked by the robot.An objective function is defined based on achieving the shortest path and also avoiding collisions with the obstacles keeping a marginal distance from each obstacle. The first trajectory is a 2D path with four circular obstacles and the second is a 3D path with three spherical obstacles. Performance of the designed controller is simulated and studied in conditions including external disturbances and varying system parameters. The results show that the proposed adaptive controller has a suitable performance in control of the end-effector to track the designed trajectories in spite of external disturbances and also uncertainty and variation of the model parameters.

With regard to daily developments in technology, application of carbon nano tubes (CNTs) in manufacturing of many devices and equipment is widely promoted. Many sensors, nanomachines, and developments in oil, petrochemical and aerospace technologies are some of CNTs applications.Considering the importance and wide range of these applications, recognition and investigation of CNTs behavior is extremely significant. CNTs have a slight natural curvature, hence they are predominantly subjected to different transverse loads. In this research, based on nonlocal elasticity theory, possibility of snap-through and bifurcation behaviors of arch shaped CNTs due to sinusoidal load distribution and on elastic foundation are investigated and corresponding graphs are plotted. To obtain buckling critical loads, essential stability equations are derived. Finally, the results of classic theory are compared with the results of nonlocal theory and it is indicated that the dimensionless scale parameter (l), has a key effect on possibility of buckling and its type occurring. According to the results and plotted graphs, in most cases, increase in dimensionless scale parameter (l) has led to increasing the possibility of bifurcation phenomena; some other cases helped to transition from snap-through to bifurcation, meaning that the possibility of the snap-through phenomena happening has been reduced.

Time-of-Flight Diffraction (TOFD) technique is a well-known inspection method used in ultrasonic nondestructive evaluation. This inspection technique is based on the time of arrival of the diffracted echoes from the tips of planar discontinuity. This is in contrast with the conventional ultrasonics which rely on the amplitude of specular reflections received from discontinuities. Like any other technique, ToFD has its limitations. In this paper, the finite element method is employed to evaluate the planar defects using ultrasonic time-of-flight diffraction method. The commercially available software ABAQUS/Explicit is used to simulate the ultrasonic wave behavior in the wedge transducers, specimen and wave interaction with the embedded planar defect. The CPE4R plane strain element is employed for discretization of the steel specimen and wedge transducers. The CINPE4 infinite element is also used on the wedge side walls for reducing unwanted echoes and noise reduction inside the ultrasonic wedge.The wave attenuation of the Plexi-glass wedge is simulated as the mass and stiffness proportional damping model. Evaluation and sizing of various defects show that, the accuracy of the proposed method is within acceptable range compared to the conventional ToFD method.

One of the most important factors in surveillance systems using robots is the complexity and unpredictability of the robot trajectories. This becomes more vital in hostile conditions where the robot trajectory is being followed by another agent. Therefore, random or chaotic sequences can be used in motion planning of surveillant robots. However, chaotic sequences would be more effective due to their deterministic nature. Moreover, the intrinsic robustness and ergodicity of chaotic systems, compared to random functions, would be another advantage to be considered in surveillance systems which require comprehensive coverage. In this paper, a method is proposed for chaotic motion planning for boundary surveillance and implemented to a quadrotor robot. Quadrotor robot is introduced as an appropriate choice for boundary surveillance application due to high maneuverability and aerial functions. The chaotic trajectory is produced using Henon map. Then the dynamics of the system is derived and a sliding mode controller is designed for such chaotic motion. Finally, the dynamics of the robot and the proposed controller are simulated to generate the chaotic trajectories for two cases. The performance of the proposed algorithm is discussed according to unpredictability and staying in the allowable region. A circular path and a non-smooth path are considered for simulation examples.

In this paper, using both linear and nonlinear identification methods based on iterative and recursive least-square, the performance of a backstepping control system of a quadrotor in the presence of uncertainties is improved. At first, the dynamic model of a quadrotor is introduced and descriptive equations are presented in an appropriate state-space in order to design a controller based on backstepping method. Then the backstepping controller is designed using virtual controller for trajectory tracking. In this control system, the control performance is not satisfactory because of the physical uncertainties existed in quadrotor. Consequently, an online identification method is introduced and used to improve the performance of the controller. In this regard, some parameters, which are linear in the model structure, are identified by least square error technique and iterative least square method is used for identifying other parameters. The results indicate that the steady-state error is decreased and the ability of tracking of a desired trajectory in the presence of uncertainties is increased. Furthermore, the results demonstrate the stability of roll and pitch angles, while the method prevents the vibration of control forces.

Inertial navigation system has drift error in underwater applications. Use of DVL with Kalman filter for position and attitude correction is common. Using velocity data decreases drift error in position estimation but this error exists and increases linearity with time. In this article the navigation system consists of inertial measurement unit (IMU) and a Doppler velocity log (DVL) along with depth sensor.By use of magnetic field measurement and earth magnetic field map a new measurement is generated.Discrete extended Kalman filter with indirect feedback is used for tightly coupled integrated navigation algorithm. This algorithm is based on inertial navigation error dynamics. This paper demonstrates the effectiveness of algorithm through simulation. The procedure of simulation is done by sensor data generation. Arbitrary trajectory with specific kinematic characteristic (linear and angular velocity and acceleration) is generated. Sensor data is produced by adding noise and bias to kinematic characteristic of trajectory. Simulation results reveal that the new algorithm with use of magnetic data and earth magnetic field map decreases the drift error in comparison to conventional INS-DVL integrated navigation algorithm.

A variety of numerical methods were developed for the wave propagation analysis in the field of structural health monitoring. In this framework, meshless methods are suitable procedure for the analysis of problems such as damage initiation and its propagation or the fracture of materials. In this study, Hermit-type radial point interpolation method (HRPIM) is investigated for the numerical modeling of flexural wave propagation and damage quantification in Euler-Bernoulli beams using MATLAB. This method employs radial basis function (RBF) and its derivatives for interpolation which leads to Hermitian formulation. The evaluation of performance and capability of HRPIM is based on the comparison between the captured HRPIM ang benchmark signals using the root mean square error (RMSE) and reflection ratio from damage. The algorithm of damage quantification is the analytical solution which relates the reflection ratio to the damage extent. In this study, Gausian-type RBF is utilized and the number of field nodes, the size of support domain, shape parameters of RBF, the number of polynomials in the interpolation formula, the arrangement of background cells and the number of Gaussian points in damage length are the effective parameters on results. Based on the evaluation, the acceptable values and range of theses parameters are presented for correct modeling.

Nowadays the use of Drug Eluting Stents (DESs) is considered as a successful method for the treatment of coronary artery blockage. In order to study the impact of the presence of topcoat on heparin-eluting stents efficacy, two designs (with and without drug free topcoat) have been compared. Moreover, here the importance of the plasma flow as a controversial topic among researchers has been studied. In order to have more realistic working heart, plasma flow is considered a pulsatile function. Also, the injury of the coronary artery penetrated to a depth of media layer during angioplasty. Volume-averaged porous media equations which describe the drug release dynamics are employed and solved numerically by Finite Volume Method (FVM). Results put the amount of strut penetration in the forefront of importance. Local drug pharmacokinetics experiences significant changes by strut passing through endothelium, intima and Internal Elastic Lamina (IEL) and being contiguous with media layer.Although the plasma flow decreases/increases the amount of concentration level and subsequently decreases/increases the amount of drug mass in media/adventitia layer, the results show that these effects are not significant. Among other findings, it is notable that the presence of topcoat has a negligible effect on the release characteristics.

Equal channel angular pressing (ECAP) is one of the most effective processes to produce ultra-fine grain (UFG) and nano-crystalline (NC) materials. Commercially pure titanium (CP-Ti) has significant potential to be used as a biomedical and implant material because it shows excellent biocompatibility properties. This material has the low static and dynamic strengths. By applying the ECAP process, the strength of CP-Ti could be developed. The elastic recovery during unloading or spring-back phenomenon is one of the most sensitive parameters in sheet and bulk metal forming processes. This phenomenon leads to some unfavorable geometrical and dimensional changes in the final products and it must be decreased. In this study CP-Ti of Grade 2 is ECAPed at the room temperature via a channel angle of 135o for 3 passes. The microstructural analysis and mechanical tests such as the tensile and three-point bending tests are all performed on the ECAPed CP-Ti. The microstructural evolution reveals that by applying the ECAP, coarse grain (CG) structure develops to UFG structure. Moreover, the results of the mechanical tests show that applying the ECAP significantly increases tensile and bending strengths of the CP-Ti. Investigation of spring-back in three-point bending of unECAPed/ECAPed CPTi is conducted by experimental and finite element simulation methods using the Abaqus software. The results of this study reveal that by applying the ECAP, spring-back values increase. Thus, to eliminate the disadvantages of spring-back phenomenon, this should be considered in design and manufacturing of products including bent made of ECAPed material.

In hydromechanical deep drawing process, the traditional matrix is replaced by pressurized fluid, and the final shape is determined based on the shape of a rigid punch. It is necessary to change the fluid pressure within the allowed working zone during the process to prevent the workpiece from rupturing and wrinkling. Working zone curve represents the range of maximum available drawing ratios without rupture under the highest chamber pressure. In this paper, hydromechanical deep drawing of square cups made of aluminum-steel double layer sheets are studied by experiments and finite element simulations. In order to detect the rupture onset in simulations, experimental forming limit diagrams were obtained using aluminum/steel double layer sheet. Experimental data were used to validate the finite element model. The effects of process parameters such as thickness of the various layers, prebulge pressure, chamber pressure and the friction coefficient were investigated on the working zone and the process window. The numerical results show that an optimum amount for the drawing ratio exists for each prebulge pressure. Also, with increasing the chamber pressure, shrinkage is reduced on the flange area. By increasing the friction between the sheet and matrix or the sheet and blank-holder, working zone becomes smaller; while with increasing the friction between the sheet and the punch it becomes larger. Experiments were performed for different drawing ratios to evaluate the numerical results and good agreement was observed.

Structural-integrity assessments of pipelines play a key role in the design and safe operation of pipeline systems. Gas pipelines currently experience internal transmission pressures up to 15 MPa in low ambient temperatures. Combination of high strength and good toughness is essential for the steels and welded joints used in pipelines. In this study, theK IC toughness has been determined for base metal and seam weld of a pipe of grade API X65, following the ASTM E1820 standard. The API X65 steel is the most commonly used pipe material in Iran high-pressure gas transportation pipelines. The fracture toughness tests employed side-grooved and fatigue pre-cracked compact tension specimens, extracted from the original pipe, to determine the crack growth resistance curves based on the unloading compliance method using the single specimen technique. From these, K IC values of 302 MPam0.5 and 262 MPam0.5 were obtained for base metal and seam weld, respectively. These results produce toughness data which serve to evaluate and compare crack growth resistance of base metal and seam weld metal and to determine the critical sizes of acceptable cracks in pipelines.

Electrospray is an atomization method which produces monodisperse and fine droplets by applying a high potential difference between a nozzle and a counter electrode. Therefore liquid meniscus shows different behaviors when flow rate or applied voltage varies in the electrospray method. Here we report experimental study of these modes based on observation of the liquid meniscus shape emitted from the nozzle. The formation of different modes is reported and forces acting on the meniscus in each mode is discussed. In this work classification of electrospray modes is reviewed for a wide range of flow rates, between0- 80ml/h, and voltage, between 0-8.5kV. Electrospraying of ethanol is studied as a promising clean fuel for a wide range of voltages and flow rates. Formation of dripping, sibling, spindle, micro spindle, intermittent cone jet, oscillating jet, precession, cone-jet, multi jet, simple jet and ramified jet modes are observed. It should be noted that throughout this study such as identification of mode shapes has been done based on taking photos of electrospray phenomenon using the method of shadowgraphy, and this method has been done by using a high speed and a high resolution camera. In present configuration, for all flow rates, the dripping and sibling mode is utilized for all of voltages which are lower than 3kV, for voltages between 3-4kV the spindle mode will be seen and for the voltages which are more than 5.5kV the multi jet mode will be observed. There are the other mode shapes for voltages between 4-5.5kV.

Integration of airframe and propulsion system is one of the most challenging steps in flight vehicle design cycles. In this paper, a three-dimensional supersonic inlet based on the wave-derived geometry technique has been designed and analyzed. Although the considered method was created for hypersonic forebodies, the idea is fully operational for the low supersonic inlet design at Mach 1.6. The inlet concept in this paper is formed from predefined profile elements which are used to generate the threedimensional geometry in an oblique shock pattern. By this approach, the curved corner of the inlet entrance edge can generate the same shock as the main compression surface and also these curved surfaces provide the optimum transition between entrance geometry and compressor face which is important for the airflow quality and propulsive efficiency. The new concept has been validated by a series of accurate CFD simulations with completely structural grid domains. The major inlet' s performance factors like total pressure recovery, flow distortion and mass flow capture ratio are calculated. The concept and its accurate numerical simulations create a baseline for more advanced designs and researches about the three-dimensional inlets and geometry transition techniques between the different sections of duct.

This paper studies path generation using manual guidance procedure for industrial robots by considering real-time singularity avoidance. Main feature of the proposed approach is singularity avoidance by variating impedance control parameters in preset distance from singularity in order to warn operator.Robot end-effector is equipped with a force sensor which the operator grasps, thereby producing the desired path. The desired end-effector path is generated by operator’s manual guidance for applications such as welding and spray painting and is recorded by robot controller. Robot singular configuration is possible during the manual guidance. So real-time detection of singularity position and orientation have to be considered during path generation because it can lead to unexpected high robot joint velocity. This problem is not safe due to physical human-robot interaction. Manipulability ellipsoid method is utilized for singularity identification. The method can be utilized on-line due to its simple and low calculation process. On the other hand, the end-effector velocity is saturated in a specific value in the approach considering safety issues. Two main advantages of the proposed approach are real-time application and high safety because of the singularity avoidance. Experiments are applied on a SCARA robot to study the effectiveness of the proposed approach. Experimental results show the ability of proposed approach in dealing with singularity problem during the manual guidance.

Dynamic analysis of structures is of significant importance in a variety of applications. Modal parameters identification can be utilized in resonance frequency estimation, fault detection and its diagnostics in many industrial applications from automobile to aerospace and satellite industries. To perform the vibration tests utilizing shaker, test sample should be connected to shaker using fixture. No fixture can reproduce a perfectly rigid boundary condition; at some frequencies the interaction between the fixture and the structure will become important, causing the modes of the assembly to be considerably different from the fixed-base modes that would be predicted by an idealized finite element model. However, it would be very convenient to be able to estimate the fixed-base modes of a structure experimentally so they could be used to update or validate the model for the structure. In this paper, two degree of freedom model is considered for the system and optimal shape for fixture is designed based on the analytical analysis. Mode shapes and frequencies of fixture are investigated numerically and compared with experimental results. Effect of connection torques on the system dynamics such as power spectral density and natural frequencies is studied by performing different experimental analyses.

In this research the transient flow analysis in viscoelastic pipes considering Fluid Structure Interaction has been performed utilizing a newly developed formulation of Transfer Matrix Method in frequency domain. To obtain this extended form of TMM, mathematical processes were accomplished. Time domain governing equations have been transformed to frequency domain and then a suitable matrix form of them is used to study transient flow due to sudden valve closure. Obtaining a set of algebraic equations instead of integral equations and the ability to analyze this phenomenon without the need to solve complex convolution integral, are some of the benefits of the frequency domain tools that have been applied in this research. To verify the model, initially two cases of rigid and elastic pipe wall have been analyzed. Results showed good conformity compared to experimental data and available analytical solution. Then having a set of reliable experimental data of transient flow in VE pipe, MatLab code was adopted to the model and here also results were in good agreement with the experimental results.Moreover, it has been shown that this model will be a suitable tool for parametric analysis and for determining the critical situations of the system. The results obtained from this research prove that using frequency domain tools will lead to an effective and precise model for simulating the transient flow characteristics in VE and also normal transmitting pipelines.

Nowadays utilization of hydroelectric power as renewable energy source is developed in the world.Using very low head axial turbines in rivers is one of the ways to obtain this energy. In this research, design and optimization of an axial hydraulic turbine with very low head (2.9m) was done. The first step in the optimization of turbine is generation of a suitable initial geometry. For this purpose one dimensional design approach based on Euler law was used. Development of computation algorithms is very efficient and suitable in hydraulic turbine design and performance investigation. In this research mesh was generated with mesh-ANSYS software and then the default domain was simulated by solving the 3-D Navier Stokes equations through the runner passages in the CFX software. Optimized geometry is obtained by optimization of Drag to Lift coefficient ratio for different blade midspans. For parameterization of airfoils, the “CST” method and for extraction of flow characteristics of airfoils XFOIL software were utilized. Then airfoil coefficients were corrected using fminsearch algorithm in MATLAB software to minimize the Drag to Lift ratio. The results show that the efficiency in design point is increased by 2.4%.

Hybrid laser-arc welding is a new welding process which has received particular attention in various industries because of its technological and economic advantages. This process combines a laser beam and an electric arc to incorporate the advantages of both laser and arc welding processes. The main goal of this paper is to evaluate the performance and ability of hybrid Nd: YAG laser-TIG welding compared to lone laser welding process for welding of aluminum foam sandwich (AFS) panels of AA6082. To this aim, a set of experiments for both laser and hybrid laser-TIG welding were done to investigate the effects of welding parameters including laser power, arc current and welding speed on weld dimensions.Then, appropriate welding parameters for the laser and hybrid laser-TIG welding of AFS panels were calculated by statistical analysis. The results show that laser power threshold for creating the keyhole was less in hybrid laser-TIG welding than lone laser welding. Moreover, increasing the laser power and decreasing the welding speed result in increasing both the weld depth and width. But, with increasing the arc current, the weld depth remains almost unchanged and only the weld width increases.Comparing the laser and hybrid laser-TIG results show that adding a 100 A arc to a 2000 W laser source can increase the welding speed from 2 to 3 m/min which proves the high ability and efficiency of hybrid laser-TIG welding process.

In this paper, the effect of adding a hydrophobic micro porous layer (MPL) at the cathode side of a PEM fuel cell on the cell performance is investigated. For this purpose, a three dimensional two-phase nonisothermal simulation of cathode side layers of a PEM fuel cell which includes gas channel, gas diffusion layer (GDL), hydrophobic micro porous layer (MPL) and catalyst layer (CL) has been performed. The governing equations of fluid flow in the fuel cell are solved with a multiphase mixture model via developing a code and distribution of velocity, pressure, temperature, species concentration and liquid water saturation at the various layers of the cathode side of fuel cell are obtained.Furthermore, the effect of physical and wetting properties of MPL including thickness, porosity, contact angle and permeability on saturation level and performance of the fuel cell are studied. The results show that by adding an extra micro porous layer between GDL and catalyst layer because of differencing in the wetting properties of the layers, a discontinuity appears in the liquid saturation and species concentration at the contact surface of them. In addition, according to the obtained results, increasing the MPL porosity causes liquid water saturation to decrease and improves the cell performance. While increasing the MPL thickness decreases the cell performance. In order to validate the results, the performance curves calculated by single and two-phase simulations were compared with experimental results and good agreement was found between them.

Nowadays, movement of micro/nano particles has been attracted considerable attention to manufacturing different devices in micro/nano scale and medical and biological applications. Atomic Force Microscope Probe is widely being used for precise small scale movements. During nanomanipulation, micro/nano particles can be moved to a desired destination with high accuracy using Atomic Force Microscope while in contact mode with precise probe control. In this article, by selecting a proper amount of torque applied to the probe tip, deviation from the center and movement of probe have been investigated to ensure the contact between the probe and micro/nano particle. Different liquid environments (water, alcohol, and plasma) with different micro/nano particles including biological and non-biological have been used for this investigation. In addition, using sliding mode control, Atomic Force Microscope Probe was used in different environments such as water, alcohol, and plasma.Obtained results showed that the time needed to control different micro/nano particles in plasma was shorter than that of in water; also the time needed in water was shorter than that of in alcohol.

Galloping of cables is a kind of self-excited vibration and is characterized by high amplitude and low frequency. In this paper for investigating the nonlinear galloping of an inclined cable, considering flexural and torsional stiffness, a cable-beam model is used. The iced cable is formulated under the effects of combined wind flow and support motion. Assuming low sag to span ratio and using physical parameter values of the cable, the governing equations of motion are obtained as classical equations of the perfectly flexible cable, plus a further equation governing the twist motion. These two degrees of freedom system is discretized via the Galerkin method, by taking one in-plane and one out-of-plane modes as trial function. Two resulting non-homogeneous ordinary differential equations are coupled and contain quadratic and cubic nonlinearities in both velocity and displacement terms. By using multiple scale method for 1: 1 internal resonance, a first order amplitude-phase modulation equation, governing the slow dynamic of the cable is obtained. In this paper the wind speed and the eccentricity of the iced section are set as control parameters. Without considering the eccentricity, the value of amplitude is increased as the wind speed is increase. But considering the eccentricity, it is reduced to first increasing and then decreasing the amplitude.

The hysteresis nonlinearity of the Magnetic Shape Memory Alloy (MSMA) actuator limits its control applications. To tackle the problems, usually the hysteresis behavior of these materials is modeled.Prandtl-Ishlinskii (PI) model is more practical in this area because of its simplicity and having analytical inverse. Two versions of this model, entitled: rate-independent model and rate-dependent model, have been developed. Experimental results show that with increasing input frequency, the shape of hysteresis loops is amplified. In this study, by using experimental test setup, the input voltage is applied to the MSMA actuator at frequencies 0.05- 0.4 Hz and the displacement output is captured by a proximity position sensor, Also the MSMA behavior is modeled by generalized rate-dependent Prandtl-Ishlinskii (GRDPI) model and modified generalized rate-dependent Prandtl-Ishlinskii (MGRDPI) model. The modified version of the model is presented by the authors to enhance the ability of the GRDPI model for describing the asymmetric and saturated hysteresis behavior in MSMAs by hyperbolic tangent function in the model output. For training of the mentioned models, the actuation frequencies 0.05 and 0.2 Hz are selected and the model parameters of each model are also obtained by using Genetic Algorithm (GA).For validation of the models the hysteresis loops at frequencies 0.1, 0.3 and 0.4 Hz are selected. The result shows that, due to using hyperbolic tangent function in the model output, the modified version of the GRDPI model can describe the hysteresis behavior in MSMAs more accurately.

The present paper aims to evaluate a class of discontinuous Galerkin methods for modeling of coupled flow and mass transport equations in porous medium. Various combinations of primal discontinuous Galerkin methods were used for discretization of the coupled nonlinear system of flow and mass transport equations in a saturated porous medium and a fully implicit backward Euler scheme was applied for temporal discretization. The primal DGs have been developed successfully for densitydependent flows by applying both Cauchy and Dirichlet boundary conditions to the mass transport equation. To avoid the errors arising from non-compatible selection of DG methods for flow and mass transport equations, only compatible combinations were applied. To linearize the resulting nonlinear systems, Picard iterative technique was applied and a slope limiter was used to eliminate the nonphysical oscillations appeared in solution. For the purpose of consistent velocity approximation, Frolkovic-Knabner method was used. Three benchmark problems were simulated for validation and verification of the numerical code, which the results from the simulations show a good accuracy and low numerical dispersion for the model. Finally, to highlight the significance of consistent velocity approximation, a hydrostatic test problem was prepared.

In the present study, AM60 magnesium alloy was cast and then subjected to hot extrusion process.Next, Multi Directional Forging (MDF) experiments with six pass numbers were conducted to investigate the influence of the operation on the microstructure and mechanical properties of these alloys. The shear punch test (SPT) and Vickers microhardness test were employed to evaluate the mechanical properties of the extruded and MDFed samples. Both the shear yield stress (SYS) and ultimate shear strength (USS) obtained from the shear punch test increased just after two passes but decreased with further pressing, although it was expected that the grains become finer with increasing the pass number. After two passes USS increased from 121.58 MPa to 142.42 MPa. This rise and fall indicates that texture softening overcame the strengthening effects of the grain refinement. The Vickers microhardness was measured across the cross sections of the extruded and MDFed samples, the results of this test also confirm this. The average microhardness of the extruded and MDFed samples were found to be respectively 73.50, 85.93, 82.26 and 77.83 HV for the extruded and 2, 4 and 6 passes of MDFed, which confirms SPT results. Optical micrographs showed that processing by MDF reduces the grain size from 11.22 to 1.91 mm after 6 passes.

Due to necessity of increasing performance in new generations of the humanoid robots, in this paper, a novel power transmission mechanism to actuate the ankle joint of a humanoid robot is presented in order to increase the motion speed of SURENAIII humanoid robot. Also, the energy consumption of the proposed and the previous mechanisms are studied. In the proposed mechanism, the actuators of the ankle joint are located in the shank link. Then, a combined timing belt-pulley and a harmonic drive module are exploited for power transmission for the pitch joint. Also, the roll joint drive has employed a roller screw. In order to validate the design procedure, the simulation results of the robot are compared with the experimental data. The results reveal that the dynamic model is fairly matched to the real behavior of the robot. Also, the revolutionary genetic algorithm is employed to optimize the effective path planning parameters with respect to the minimum knee joint energy consumption. This optimization procedure which is employed in robot walking on flat terrains consists of straight motion and ensures the robot's stability. As a result, the optimal path planning parameters for proposed mechanism are obtained in such a way that the actuating torques of lower-body of SURENAIII are decreased. Also, the proposed mechanism can be achieved using lighter motors and makes the robot faster by means of mass reduction of foot.

The present study probes the nonlinear free vibrations of viscoelastic polymeric composite plate reinforced by carbon nanotubes. For this purpose, Kelvin-Voigt model is utilized. Moreover, the equations of motion are extracted by the Hamilton principle and take Von Karman nonlinearity into account. In order to solve and analyze nonlinear free vibrations, the researchers utilized multiple scales method. Using this method, the normal nonlinear frequencies of the system were obtained and the impact of various factors such as dampness coefficient, material viscosity and carbon nanotubes volume fraction were investigated. Besides, the thickness-dimension ratio of the plate and its impact on the normal frequency was also studied. The findings of the study highlighted that an increase in the ratio of plate’s thickness to its length causes an increase in the normal nonlinear frequency of the plate.Additionally, as the volume fraction of the carbon nanotubes increases, system’s normal nonlinear frequency increases as well. Finally, the impact of different distribution of carbon nanotubes on the normal nonlinear frequency and system’s time response was also probed. As was observed, nonlinear frequency for FG-O distribution was more than that of for the uniform distribution, but the trend was reverse for FG-X distribution.

In this paper a new high order element is proposed for analysis of beams with shear deformation effect.In each node of this element there exist translation and rotation degrees of freedom. The element’s formulation is based on the first-order shear deformation theory (FSDT). For this aim, displacement field of the element is selected from fifth order. Moreover, the shear strain is varied as quadratic function throughout the element. It is worth noting that the quadratic function can be used for axial displacement field. By employing curvature and shear strain relations of Timoshenko beam theory, the exact and explicit shape functions of the displacement fields are obtained. By utilizing these shape functions, beam elements’ stiffness matrix is also calculated. Finally, several numerical tests are performed to assess the robustness of the suggested element. The results of the numerical testes prove the absence of the shear locking and high accuracy and efficiency of the proposed element for analysis of beam and frame structures. It should be mentioned, due to utilizing fifth order function for displacement field, the proposed element calculates the exact solution for displacements and internal forces throughout the element for triangular distributed loads.

By using the initial estimation of CO concentration in enclosed parking lots, the designer could design a ventilation system with assurance of producing good air quality. In this paper, the practical correlation of CO increasing due to cars and time in enclosed parking lots is proposed. The proposed model is represents the variation of CO concentration in parking lot according to functional parameters. In addition to air flow ventilation, the effect of CO removal effectiveness on the air quality of enclosed parking lots is expressed in the proposed relation.

In this article, the effects of helicopter main rotor blade tip geometric shapes on the aerodynamic of hover flight are analyzed. Aerodynamic coefficients, vortical flows and vortex wakes are discussed.Fluent software with implicit finite volume method has been used for numerical simulation process. The grids are structured. Experimental results of the Caradonna and Tung have been used for aerodynamic validations. In this investigation, the flow has been considered turbulent, compressible, and viscous. The results of several RANS models for a specific rotor have been compared and the standard k-e turbulent model is finallyselected. The Roe method with second order scheme was selected. Thirteen different geometrical shapes on the tip of the blades have been presented and the results of the models have been compared. These studies show that the blades of BERP IV, Blue edge, Actual, Bell-214 and BERP III produce maximum thrust and MIL-17, Sikorsky RH-53D, Tapered, Bell-412, Sikorsky SH-3D and ComancheRAH-66 produce minimum torque and also the blades of BERP III and IV, Ogee and Bell-214 produce maximumtorque.