نشریه مهندسی مکانیک مدرس
سال شانزدهم شماره 12 (اسفند 1395)

Magnetic shape memory alloys (MSMAs) are a new class of smart materials that exhibit characteristics of large recoverable strains and high frequency. These unique characteristics, make MSMAs interesting materials for applications such as actuators, sensors, and energy harvesters. This paper presents a two-dimensional phenomenological constitutive model for MSMAs, developed within the framework of irreversible continuum thermodynamics. To this end, a proper set of internal variables is introduced to reflect the microstructural consequences on the material macroscopic behavior. Moreover, a stress-dependent thermodynamic force threshold for variant reorientation is introduced which improves the model accuracy in multiaxial loadings. Preassumed kinetic equations for magnetic domain volume fractions, decoupled equations for magnetization unit vectors and appropriate presentation of the limit function for martensite variant reorientation lead to a simple formulation of the proposed constitutive model. To investigate the proposed model capability in predicting the behaviors of MSMAs, several numerical examples are solved and compared with available experimental data as well as constitutive models in the literature. Demonstrating good agreement with experimental data besides possessing computational advantages, the proposed constitutive model can be used for analysis of MSMA-based smart structures.

Flow around a circular cylinder placed in an incompressible uniform stream is investigated via two-dimensional numerical simulation in the present study. Some parts of the cylinder are replaced with moving surfaces, which can control the boundary layer growth. Then, the effects of the moving surfaces locations on the power and drag coefficients are studied at various surface speeds. The flow Reynolds number is varied from 60 to 180. To simulate the fluid flow, the unsteady Navier-Stokes equations are solved by a finite volume pressure-velocity coupling method with second-order accuracy in time and space which is called RK-SIMPLER. In order to validate the present written computer code, some results are compared with previous numerical data, and very good agreement is obtained. The results from this study show that some of these surfaces reduce the drag coefficients and the coefficient of the total power requirements of the system motion. The optimum location and the speed of the surfaces which cause the minimizing the power coefficient are also obtained; By observing the results it is found that in all Reynolds numbers, the minimum power coefficient or in other word, the optimum drag coefficient is occurred at surface angle of 70 deg.

Selecting tool materials, tool sizes and determining the cutting parameters presents a great challenge in machining operations especially in high speed machining processes. In this study effect of feed rate which is one of the important machining parameters and tool size on tool life in high speed machining of Ti-6Al-4V alloy were investigated. Fixed cutting speed of 200 m/min, feed rate of 0.03 and 0.06 mm/tooth together with axial cutting depth of cut 5.0 mm, and radial cutting depth of cut 1.5 mm were employed as the cutting parameters. TiAlN TiN coated tungsten cemented carbide insert in two different size was used during machining operations. Flank wear land measurement was taken by using a toolmakers’ microscope and recorded accordingly throughout machining processes. The results showed during the machining employing both feed rate and using smaller tool size chipping occurred on the tool nose along with gradual tool flank wear. Also by increasing the feed rates utilizing the smaller size of tool highly affected tool life compared to employing the larger one during the high speed machining operations. Reduction the feed rate by 50 percent increased the tool life of smaller tool size by 200 percent.

In this numerical study, three dimensional laminar flow, heat transfer and other thermal characteristics of a microchannel heat sink, consisting of seven isosceles triangular microchannels, have been investigated. For this purpose, conduction in the solid parts has been considered and two different horizontal inlet/outlet (I-type) and vertical inlet/outlet (U-type) arrangements have been considered. Simulations have been performed for a constant heat flux of 125 kWm-2 entering from the substrate. In previous studies flow of water in rectangular microchannles has been considered, but in this study CuO-water nanofluid has been utilized. The effects of the Brownian motion of nanoparticles and variation of thermophysical properties of the nanaofluid with termperature have been considered and their importances studied. The results show that with increasing pressure drop, the heat sink performance in terms of heat transfer, thermal resistance and uniform temperature distribution at subtrate improves for the two nominated arrangements. Also increasing the volume fraction to 2% improves the heat sink performance, but as it increases further the thermal resistance and the non-uniformity of temperature at the bottom plate enlarge with no heat transfer improvement. Making comparison with the results of the previous studies on the effect of inlet/outlet arrangement proves that the thermal performance is affected by both of the inlet/outlet arrangement as well as the shape and geometry of the microchannels. For the heat sink of this study with triangular microchannels the performance of the I-type arrangement is better than the U-type arrangement.

In the current research, laminar flow and heat transfer of viscoelastic fluid in an axisymmetric sudden expansion whit expansion ratio of 1:3 is investigated. Finite volume method and PISO algorithm are used for numerical simulation of flow and heat transfer of viscoelastic fluid. As well as, for study the effect of elasticity property of polymeric fluid flow, nonlinear Phan-Thein-Tanner (PTT) rheological model is used. Most of the researches which has been done in this field are focus on investigating hydrodynamic parameters of flow like study the effect of Reynolds number and elasticity property on vortices length, so due to the scarcity of comprehensive study about the heat transfer of viscoelastic fluid flow in sudden expansion, performing present study seems necessary. Considering some of the rheological and thermodynamic properties of viscoelastic fluid as function of temperature is the other innovations of current study, which because of the sensitivity of some of the viscoelastic properties to temperature, considering this hypothesis for solving energy equation seems essential. The results of numerical simulation shows that the maximum quantity of local Nusselt of sudden expansion for downstream wall is approximately where vortices are finished and the procedure of velocity variation is like smooth pipe. Also, whit increasing Reynolds number that led to enhancing length and intensity of vortices, the maximum local Nusselt in sudden expansion region move further toward downstream.

This paper presents a numerical study using two-fluid model in order to compare the effect of hydrodynamic and hydrostatic models for pressure correction term in two-fluid model in modeling gas-liquid two-phase flows to provide a more accurate model. Two-fluid model is solved by Godunov Approximate Riemann Solver. The two-fluid model is applied using both hydrodynamic pressure correction term and hydrostatic pressure correction term for four sample examples including Water Faucet Case, Water-Air Separation Case, Toumi’s Shock Tube Case, and Large Relative Velocity Shock Tube Case. Hydrostatic pressure correction term is neglected for vertical geometry, therefore, in this geometry; two-fluid model cannot be hyperbolic. Thus, hydrostatic pressure correction term is not a stabilizing term. Also, in horizontal pipe and for atmospheric conditions, hydrostatic pressure correction term presents better results than hydrodynamic pressure correction term. But, in non-atmospheric conditions, hydrodynamic pressure correction term presents better results. Therefore, in order to select a suitable pressure correction term for two-fluid model, we consider geometry (vertical or horizontal) and flow conditions (atmospheric or under-pressure). Also, hydrodynamic pressure correction term in two-fluid equations system is hyperbolic in a boarder range than hydrostatic pressure correction term.

In this paper, the mechanical behavior of the Graphene Oxide (GO)/ epoxy nanocomposites has been investigated under different strain rates. To reach this goal, GO nano sheets were synthesized through Hummers method (a chemical method) and then GO/epoxy nanocomposite was prepared using the solution-based method. Standard specimens test were made from nanocomposite. In order to study the static and dynamic behavior of material, the static pressure test and the split pressure hopkinson bar test were performed on the specimens, respectively. The results showed that the stiffness and the strength of epoxy increase with adding GO to it. It was found that the behavior of epoxy is dependent on the strain rate so intense that its dynamic strength is more than static one about 50%. Furthermore, the effect of GO in low strain rates is more than high strain rates such that adding 0.3% weight ratio of GO increase the strength of epoxy by nearly 20% and 5% in 0.01 s^(-1) and 1100 s^(-1) of strain rates, respectively. In addition, the comparison of Scanning Electron Microscopy (SEM) images from the fracture surfaces of neat epoxy and its composite showed that the surface toughness of nanocomposite is more than epoxy’s.

In this article, cavitation flow around axisymmetric projectiles with ringed and non-ringed cavitator has been investigated using control volume and boundary element methods. In the numerical method, the homogeneous equilibrium approach as well as the zwart model, for modeling the mass transfer and forming the system of equation, have been used. In the boundary element approach with dipole distribution on the body and cavity surfaces and source distribution on the cavity surface, the right conditions were set for using the Green's theorem in solving the potential flow. Moreover, some source components were imposed on the cavitator surface in order to add the hole effects. The validation procedure for both methods has been done by analytical and experimental data. In general, the results of this research are presented in two parts. In the first part, hydrodynamic properties of ringed cavitator such as cavity dimensions, intended forces, flow behavior and etc are analysed deploying the numerical methods based on Navier Stokes equations. In the second part, the boundary element method has been used for the analysis of the cavitation flow around practical geometries with ringed cavitator. The most important finding of this study is reduction of the cavity dimensions and also an increase in the force on the projectile during the use of annular cavitator. In addition, as a result of this study, two equations for maximum length and maximum diameter of the formed cavity on the cylindrical body in relation to the cavitation number and hole diameter have been provided.

Due to the rapid growth of manufacturing industry and increased competition among companies, the need to produce parts with free-form surfaces with lower cost and higher accuracy is felt. Nowadays beside all of the great benefits of 5-axis CNC machines the use of 3-axis CNC machines are more common in industry because of the high capital investment, high operating and maintenance cost, the low dynamic stability and their complex programming in 5-axis machining. Therefore it is preferred using 3-axis machines in industry where it’s possible. Since the inability of machining some complex parts by 3-axis machines, the 3axis machining technology has been proposed. In this paper, a new method has been used to determine the tool appropriate orientation for 3axis machining. In the proposed method, visible and invisible points of the surface and the shortest tool length are calculated for the workpiece and finally performed surface partitioning. The minimum number of tool orientation result from this methods reducing overall machining time and the boundaries between machining partitions to improves the surface quality. A 3axis machining of an impeller perform and evaluate the efficiency and surface accuracy by the use of a coordinate measuring machine.

This paper investigates the vibration behavior of fluid conveying viscoelastic pipe rested on non-uniform elastic Winkler foundation. The Kelvin-Voigt model is employed to consider the viscoelastic behavior of the pipe. Using the Galerkin’s method, the eigenvalue problem for the simply supported fluid conveying viscoelastic pipe is extracted. The effects of the fluid velocity, the viscoelastic constants and the foundation parameters on the complex eigenvalues and the divergence and the flutter instability of the fluid conveying viscoelastic pipe are studied and discussed. It is found that including the viscoelastic behavior to the pipe material alters the trend of the instability of the fluid conveying pipe, i.e., the first and the second modes divergence and the coupled mode flutter for the elastic pipe change to the first mode divergence, the second mode flutter and the second mode divergence for the viscoelastic pipe, respectively. The structural damping causes the velocity of the divergence instability at the higher modes to be increased. Also, because the viscoelasticity of the pipe affects the different vibration modes in different manner, therefore, the pipe dose not exhibit a coupled-mode flutter. Moreover, the non-uniformity of the foundation stiffness alters the first divergence velocity. The results are verified through comparing them with those reported in the literature.

In this paper, an adaptive robust tracking control system for an unmanned quadrotor is designed .Quadrotor placed in category of rotary wing aerial vehicle, and it is an under actuated and inherently unstable system. Also the dynamic model of system is nonlinear and along with the Uncertainty, therefore it is required to design a robust control system for stabilization and tracking the desired path. This system must be capable to retain the quadrotor balance in the presence of the disturbance, undesired aerodynamical forces and Measurement error of constant parameters. The suggested controller in this paper consists of two inner and outer control loops. Inner loop controls the Euler angles and outer loop is for control the quadrotor position and translational motion, and calculating the desired angles for trajectory tracking. In this paper by utilizing the adaptive sliding mode, the controller has been designed which is no need to be given the uncertainty range and the upper bound of it will be estimated as a scalar number. In order to prevent from diverging adaptive parameters, the sigma-modification is used in adaption laws and also to achieve suitable performance in various load, the total mass is estimated adaptively. The control design is based on the Lyapunov theory and the robust stability of system in the presence of the disturbance have been shown.

In this study, the effects of frequency, height and wavelength of progressive gravity waves on vibration and energy absorption of the single- and two-degree of freedom Bristol oscillating cylinder systems have been investigated experimentally and numerically in different depth of water. The experiments were carried out in channel equipped with both a paddle-type wave-maker and wave features measurement tools. Numerical simulations were conducted in COMSOL software assigned to simulate interactions between physical environments for turbulent flow. Making a comparison between the numerical and experimental conclusions compared to the other researcher's results demonstrates a desired matching in a wide range of wave's parameters. It can be seen in findings that changing in depth of submerged objects from free surface of water has considerable influence on their vibration behavior, so that by rising in depth, the oscillations amplitude increases to a maximam and then decreases. The obtained results indicate the different effects of relative depth under the submerged buoy on the efficiency of the single- and two-degree of freedom systems; so that increasing water height causes rise in the efficiency of single degree of freedom systems, but it doesnt have considerable influence on two degree of freedom systems. The results also show that expanding the wave-maker frequency for a constant height of water in channel causes to rise in energy and height of the generated waves so that oscillations amplitude of submerged buoy rise in vertical and horizontal line.

One of the common ways to reduce vibration in the structures is to add a thin viscoelastic material layer to the structure. By appropriate using of viscoelastic materials one may increase modal loss factor of the structure and reduce unfavorable structural vibration which is a main cause of fatigue and failure in the structures. In this paper, low velocity impact response of sandwich plate with magnetorheological fluid core is investigated. Hamilton principal is used to obtain the governing equation of motion for sandwich plate. Free vibration problem of the sandwich plate is solved using the Navier solution method. Classical lamination theory is used to analyze the mechanical behavior of the composite laminate in the facesheets. Only shear strain energy of the core is considered and viscoelastic behavior of the MR material was described by complex shear modulus approach as a function of magnetic field intensity. Furthermore, analytical solution for impact force is obtained by a two degree of freedom spring mass model. For three different stacking sequence of face layers, contact for history and variation of maximum impact force and it’s corresponding time by magnetic field intensity is investigated. The results show considerable effect of variation in magnetic field intensity on maximum impact force and it’s corresponding time.

In this study, hydrodynamic behavior of four-sided wind tower attached to parlor and courtyard of a scaled model form existing historical house with wind incident angel as variable was numerically investigated. Hazire-ei house wind tower, which has six channels with rectangular cross section, integrated with parlor and courtyard is considered among the most typical ones in the vernacular architecture of Yazd city. This article seeks to investigate the performance of four-sided wind tower regarding suction and supply amount of air and the way it was used as a vernacular solution for natural ventilation in order to provide engineers with design guidelines for contemporary use. Numerical study was conducted on a 1:25 scaled model and for 13 wind incident angels with 15 degrees intervals and interested parameters are mass flow rate and flow direction in each channel. A structured mesh was generated and ANSYS Fluent software was used for numerical simulation. Numerical modeling results were validated against experimental tests conducted on the same scaled model and good agreement was observed. Results indicate that in 68.5% of incident angels, four-sided wind tower acts as sucking the air out of building and in other incident angels with approximately equal amount of supply and extract rate, it operates as an air exchange unit. Accordingly it can be concluded that putting aside stack effects, four-sided wind towers in dry regions of Iran are mostly employed for heat dissipation elements rather than inducing outdoor cool breezes.

In this study, the control problem of a knee rehabilitation robot is examined. The main drawback of rehabilitation facilities, such as continuous passive motion, is the lack of feedback from the interaction force between the robot and patient leg. This means that if during the exercises, an unvoluntary motion by patient is generated, the increased interaction force can then damage the patient leg. The interaction force is increased because the robot tries to hold the patient leg along the prescribed reference path. In the current paper, to realize the compliant behavior of the robot, the concept of admittance along with two control methods including adaptive model reference and integral backstepping will be utilized. Adopting admittance control method, the robot will deviate the prescribed path so that the interaction force can be decreased. The obtained simulation results reveal the good performance of the robot even in the presence of noisy sensory data. Additionally, it has been shown that the proposed combined admittance and backstepping controller has better performance, in terms of tracking error and decrease of interaction force, as compared with the model adaptive reference model.

Locomotion regulation of a robot according to path conditions is one of the main interests in the robotics, because it enables the robot to move in unknown environments. This can be realized using inspiration from the human and animal's bio-mechanism in generating various motion patterns called central pattern generator (CPG). These motion patterns are called “gaits” and changing between the motion patterns is called “gait transition”. Many models have been proposed to model CPGs and used for trajectory generating of various mobile robots. In this paper, a type of CPG network called 4-cell CPG model is studied to generate the rhythmic signals of the ankle joints in a bipedal locomotion gaits. This model is composed of four coupled identical cells whose internal dynamics is described by the Morris-Lecar nonlinear differential equations and the couplings between the cells follow the diffusive type. The generation of various locomotion gaits depends on the adjustment of the phase differences between rhythmic signals produced by the cells. The phase differences, in-turn, are obtained via properly adjusting the coupling weights between the cells. Here, we exploit a non-dominated sorting genetic algorithm (NSGA-II) to find the best set of coupling weights for maximally approaching the desired phase differences of the primary bipedal gaits of walk, run, two-legged jump, and two-legged hop. Also, some secondary bipedal gaits, especially one that called “hesitation walkˮ, are obtained by symmetry breaking bifurcations of the primary gaits. The “hesitation walkˮ has already predicted in [28], however the authers could not generate it.

This Paper, with the help of the device was made in this university as "rapid prototyping device base on direct metal laser melting", study interaction of metal powder apparent density and heat transfer experimentally. Selective Laser Melting (SLM) is a direct fabrication of part through layer by layer powder deposition and successive laser beam irradiation. One of the important properties of the SLM is thermal conductivity and thermal diffusivity of the metal powder. In this paper, thermal conductivity and diffusivity of metal powder with various apparent densities were studied. According to the method of measuring (the difference between two temperatures), The tests showed the dependence of thermal properties to metal powder apparent density. Changes in apparent density was established through the pressure applied to the raw powder bed. Because achieve to desirable apparent density through proper distribution is much expensive. This study was done in range of apparent density 44.75% to 56.4% compared to the density of pure iron. Comparing the samples produced in different densities it was understood that the pressure applied to the raw powder bed with the optimum point of arrest. In fact, the best quality of the manufactured parts, in density of about 46% was obtained.

Derivation of temperature distribution, at the different sections of nose, to select the material, component, and sensitive system installation at inside of it, implicates to specifying the induced aeroheating to the nose surface. This parameter with surface temperature and recess due to surface ablation must be corrected at next time steps of flight trajectory. The different methods, to estimate or calculation of aeroheating, were created whereas the most accurate method for this purpose is numerical solution of fully navier stocks, chemical dissociation and ionization of air, mass conservation of species, turbulence modeling, combustion modeling due to surface ablation, nose heat transfer equations with time marching finite volume algorithms simultaneously. Utilizing these solvers for flight trajectory is snail, and it’s required the high computational memory. Therefore, the finite difference method is used, and the governing equations are translated to curvature coordinate by mapping terms. By using this translation, to solve the governing equations, the space marching solvers can be used. Therefore, in this research, the more accurate estimation of temperature distribution for 3-D nose of supersonic and hypersonic vehicles was presented by using the numerical space marching solvers such as viscous shock layers and viscous boundary layer methods. Therefore, the comprehensive code was created to this purpose. The results of this code were validated by using the temperature telemetry results of flight tests. The relative error of the results was less than 10 percent.

Dynamic modeling, simulation and control of a quadrotor using feedback linearization and PID controller based on MEMS sensors’ experimental dat
˜یÏå [English]
The purpose of this article is dynamic modeling of a quadrotor and control of its Roll and Pitch angles based on the experimentally measured sensors data. So, after driving nonlinear model of quadrotor equations, the control of the quadrotor’s angular situation was simulated using PID and feedback linearization algorithms. Due to the widespread application of MEMS sensors in measuring the status of various systems and to have a more realistic simulation, sensors data was measured and used in simulation of controllers. Due to errors of MEMS sensors, vibration of motors and airframe, being noise on outputs, Kalman filter was used for estimation of angular situation. As one of the purposes of this paper was the use of its results in actual control of a quadrotor, motor model was used to determine PWM control signals. The results obtained from simulation in Simulink showed good performance of both controllers in controlling roll and pitch angles

Investigating the effects of process parameters on forming forces and defects formation in tube spinning process of AA6061
˜یÏå [English]
Tube spinning or flow forming process is used for manufacturing of seamless tubes widely put into service in advanced industries. The ideal flow for materials entering the deformation zone in this process is extrusion-type flow in axial direction. Very localized deformation zone which is confined by outer materials and forming tools is very important aspect of this process. Therefore, development of defects during the deformation process with undesirable flow of materials can be easily occurred. The main reason of undesirable flow of materials is choosing inappropriate process parameters which results in arising various geometrical and dimensional defects. In this paper, the effects of process parameters on formation and growth of different defects and their correlations with material flow and forming forces in tube spinning of AA6061 was investigated by using design of experiment (DOE) method. The results of experiments show that by applying the optimized values of reduction and feed rate per revolution, these defects can be controlled. Also, by comparing the experimentally measured and theoretically calculated forming forces it can be shown that the larger the deviation of measured forces from calculated ones gets the more severe formation of defects and undesirable materials flow becomes.

Numerical study of the effect of stenosis on the hemodynamic parameters in branch of LAD coronary using 0D/3D coupling ˜یÏå [English]
Stenosis in coronary artery and the other cardiac diseases such as Atherosclerosis is major cause of death in the world. Numerical simulation of blood flow can help medical evaluation to curve arteries have been stenosis. The purpose of this paper is to find the effect of arteries stenosis on the hemodynamic parameters by simulation of blood flow in LAD branch of coronary artery. The computational domain has been determined from CT images of human heart. In this study, blood is assumed to be homogeneous, Newtonian and the blood flow assumed to be pulsatile. In order to more realistic modeling of flow and pressure, Seven–element lumped model has been used in coronary artery outlet, in order words the 0D and 3D models are coupled together. The results indicate that the calculated flow wave is the minimum in systolic phase and maximum in diastolic phase in coronary artery, in contrast with Aorta. On the other hand, by increasing the stenosis percent from 30 to 60 percent, no significant drop of flow has been observed in the state of rest, and it has been validated with experimental results. The results indicate that with increasing stenosis, time average wall shear stress in the stenosis region increases, while it decreases before and after the stenosis, also the investigation of oscillating shear index indicates that in the state of 60% of stenosis and in the main downstream branch, it has the maximum value, that is indicative of the presence of turbulent flow in this region.

The position of the planets for the planetary gear systems are in two forms of equally and unequally spaced. This paper investigates free vibration of the planetary gear with unequally spaced planets. The planetary gear set of this study is modeled as set of lumped masses and springs. Each component such as sun gear, carrier, ring gear and planets possesses three degrees of freedom and considered as rigid bodies. Bearing and mesh stiffnesses are modeled in the form of linear springs. Generally, planet, rotational, translational, distinct and degenerate modes are five vibration modes of the planetary gear systems. The results show that the translational mode for the system with numbers of even equally and unequally spaced planets, is different and rotational and translational modes have the same characteristics for the both systems. For the system with numbers of even unequally spaced planets, the natural frequencies of the translational modes have multiplicity one. When the numbers of the planets of the system are odd and the position of them is unequally spaced, the rotational and planet modes are generating and the natural frequencies of the translational modes are not appears. For the distinct and degenerate modes of the system with unequally spaced planets, the planets only have the rotational motion.

In the present paper, a numerical study is performed for analysis of 3D effects of geometrical parameters namely microchannel depth, eccentricity and sizes of rotors and operational parameter namely pressure difference on flow flux and efficiency by LBM. In investigation of simultaneously variation effect of geometrical parameters namely rotors eccentricity and microchannel depth is observed in all depths, increasing the eccentricity, both flow flux and efficiency increased. Also, in a constant eccentricity both flow flux and efficiency increased. In the next investigation that simultaneously effect of geometrical parameters namely rotors sizes and microchannel depth is discussed determined that in all depths, decreasing the rotors sizes, flow flux decreased. But for efficiency, it became less in the lower depths and increasing depth the efficiency increased. In final, the effects of operational parameter of pressure difference and geometrical parameter of microchannel depth on flow flux and efficiency has been studied. As the results show, increasing the pressure difference, flow flux linearly decreased so that it became zero at the certain pressure. Moreover, efficiency variations vs. pressure difference parabolically is observed.

In electromagnetic motors, increase in output torque leads to increase in rotor inertia. Various robotics applications, especially haptic interfaces, oblige convenient dynamic performances of electromagnetic motors which are strongly in turn influenced by the rotor’s inertia. In the present paper, a robust control method for a viscous hybrid actuator is developed which supplies a desired varying torque while maintaining a constant low inertia. This hybrid actuator includes two dc motors with the shafts coupled through a rotational damper using a viscous non-contact coupler. This coupling method is based on Eddy current to provide the required performances. The large far motor eliminates or reduces the inertial forces and external dynamics effects on the actuator. The small near motor provides the desired output torque. Since the system is essentially linear, the applied robust control method is based on Hꝏ and parametric uncertainties and physical constraints including motors’ voltages saturation, rotary damper’s speed saturation, fastest user’s speed and acceleration applied to the actuator and force sensor noise are considered in its design. Also the robust method of µ-synthesis for the system in presence of parameteric uncertainties and other physical constraints are studied. The implementation of the controller on a 1 dof haptic interface model validate the achievement of the desired performances.

Solar humidification-dehumidification desalination is one of the most practical methods for water desalination in small scale for regions far from cities and low population. The aim of this study is manufacturing and simulation of a solar humidification-dehumidification desalination system with capacity of 20 lit/day. This system consists of humidification and dehumidification units¡ solar air and water heaters. To this end¡ at first this system is explained and modeled. Then¡ manufacturing process of solar air heaters¡ and different parts of desalination system is investigated. After the manufacturing process of the desalination system¡ this system is experimentally tested and the effect of pertinent parameters¡ such as the temperature of inlet water and air to humidifier; inlet water temperature and flow rate to dehumidifier on the performance of the system and distillate product is investigated. The results show that the effect of water temperature on the fresh water produced in more than air temperature. Moreover¡ using the chilled water¡ which its temperature in the range of well temperature¡ in the dehumidifier inlet leads to an increase of 31 % in the fresh water produced. Also¡ the best water flow rate to the dehumidifier inlet is 0.12 kg/s. Finally¡ experimental and simulation results are compared with each other and good consistency is seen.

In this paper¡ the stress intensity factor for an internal circumferential crack in a thick-walled cylinder has been determined. The cylinder has been subjected to an axisymmetric thermal shock on the outer surface according to the dual phase lag theory. The uncoupled¡ quasi-stationary thermoelastic governing equations have been assumed. The temperature and stress fields have been solved analytically in the Laplace domain and its Laplace inversion transform has been obtained numerically. Using weight function method¡ the stress intensity factor for mode-I has been extracted. Temperature¡ stress and stress intensity factor of hyperbolic and dual phase lag theories have been compared and the effects of heat flux and temperature gradient time relaxations on the temperature¡ stress and stress intensity factor have been studied. According to the results¡ the dual phase lag temperature distribution is different in comparison with the Fourier model. Also¡ the stress intensity factor for dual phase lag model is significant larger than Fourier one. Moreover¡ the maximum stress intensity factor in dual phase lag model occurs for a crack that the peak of stress wave reaches to its tip. Results show assumption of adequate heat conduction model for structure design under transient thermal loading is critical.

In the present work¡ an inverse design algorithm called Ball-Spine (BSA) is developed as a quasi-3D method on the meridional plane of a centrifugal pump impeller with rotating frame and incompressible viscous flow within it¡ with the aim of improving its performance. In this method¡ numerical analysis of viscous flow on a thin plane of flow between two blades using a 3D viscous flow solver is combined with BSA¡ which modifies hub and shroud geometries. Namely¡ instead of solving inviscid quasi-3D flow equations in the meridional plane¡ full 3D Navier-Stokes equations is solved on the thin plane of flow. To show the validity of the present work¡ centrifugal pump is numerically evaluated and numerical results are compared with experimental results¡ and flow field in the meridional plane of pump impeller is obtained using quasi-3D method. By studying the algorithm in the rotating geometry and choosing static pressure and reduced pressure as target parameters the ability of performance of the algorithm is assessed. After that¡ the new impeller geometry is obtained in conformity with the modified pressure distribution¡ by defining target pressure distribution on the hub and shroud surfaces of the conduit and trying to eliminate excess pressure gradients. Obtained results indicate good rate of convergence and desirable stability of BSA in the design of rotating conduits with incompressible viscous fluids. By using the above-mentioned optimization method following results was observed: increase of static pressure along streamline¡ 1% of increase in the pump total head¡ delay in impeller cavitation inception.

In this paper¡ the behavior of cylindrical shells with uniform thickness and functionally graded thickness distributions subjected to axial quasi-static loading is investigated experimentally and subjected to axial impact is investigated experimentally and numerically. Steel cylindrical shells with uniform thickness and functionally graded thickness distributions have same inner diameter¡ length and weight. Cylindrical shells are impacted by the drop hammer apparatus and experimental axial force-time curves are obtained by using a load cell; in addition¡ impact simulations are done by Abaqus finite element software. The effect of thickness distributions on the shortening¡ energy absorption¡ buckling shape and axial force-time curve of cylindrical shells is investigated. It is found that for axial quasi-static loading¡ a change in thickness distribution of cylindrical shell is able to convert the buckling shape from mixed buckling (a combination of axisymmetric and diamond modes) to progressive buckling¡ also for axial impact loading¡ a change in thickness distribution of cylindrical shell can affect the number of complete folds. The studies also suggest that at same impact energy¡ functionally graded thickness distribution cylindrical shell compared with uniform thickness distribution cylindrical shell absorbs approximately the same energy with more shortening and transforms less mean load and peak load to under protected specimen¡ thus¡ functionally graded thickness distribution cylindrical shell is a better energy absorption specimen. It is found that there is a good agreement between the experimental and numerical results.

The detection of changes in the dynamic behavior of structures is an important issue in structural safety assessment. Deployment and servicing of marine and coastal structures such as piers in the marine environment with constantly changing¡ requires understanding the dynamic behavior of these structures to prevent possible damage. Among the factors of uncertainty in understanding the dynamic performance of piers is uncertainties related to semi-rigid connection of deck to piles. According to this fact that the main mass of the structure is on deck¡ the connection of deck to piles is very important. In this study¡ experimental and numerical model of beach piers were studied. A Test on experimental modal analysis was performed to determine the response of structures. A numerical model of the structure prepared and theory of modal analysis was performed on it. Then¡ based on the finite element model updating of structure approach¡ identify and determine the percentages of semi-rigid connections. Results show this fact the connection isn’t fully rigid. According to the present method can be compared to determine the percentage of semi-rigid connections and prepare the finite element model with more adaptable to the experimental model. Updated results with this method were very close to the real model.

In this research with utilization various neural networks models¡ the relationship between the amount of water production and the temperature of the vapor with different weather conditions¡ time of day and several water debit in desalination system equipped whit linear solar parabolic concentrator was investigated. The results showed that static and dynamic networks can be modeled the process of production fresh water with high accuracy. Static neural network can do the modelling process with higher speed than dynamic neural network. However it seems that the amount of error with using dynamic networks was reduced in process modeling. Coefficient of determination (R2) for training¡ validation and testing in static networks were 0.9898¡ 0.9899 and 0.9889¡ respectively. While coefficient of determination (R2) for training¡ validation and testing in dynamic networks were 0.9922¡ 0.9894 and 0.9901¡ respectively. Also the amount of mean square error (MSE) in static network for training¡ validation and testing was 0.0011¡ 0.0027 and 0.0024¡ respectively and for dynamic networks was 0.0018¡ 0.0007 and 0.0004¡ respectively. Comparison between dynamic and static networks show that the dynamic networks can be predicted the production of fresh water and vapor temperature according to changes in atmospheric parameters accurately than the static networks.

The present study was undertaken to design and analyze three different configurations of SOFC (solid oxide fuel cell) and MGT (micro-gas turbine) hybrid system. The first presented configuration is a hybrid system with one fuel cell which considered as a basic mode. Two other configurations are considered with two fuel cells that mounted upstream of the turbine in series and parallel forms. The aim of the current study was thermodynamic analyze of designed hybrid systems and achieving the optimum fuel consumption factor for fuel cells that used in hybrid systems. Therefore¡ other performance parameters such as turbine inlet temperature¡ compressor pressure ratio and the number of cells¡ which play an important role in implementation of SOFC and gas-turbine¡ were parametrically analyzed and the obtained optimum values were used in analyzes. In this regard¡ the parameters associated with electrochemical processes within cells considered as a function of their chemical and thermodynamic conditions¡ and their modeling code combined with the modeling code of micro gas turbine cycle. The results of this study revealed that fuel utilization factor has direct impact on the SOFC/MGT hybrid system performance. Also we demonstrate that the optimal fuel utilization factor for basic mode hybrid system was 0.85¡ hybrid system with 2 series fuel cells were obtained 0.7 and 0.8 respectively and hybrid system with two parallel fuel cells were calculated to be 0.85. Moreover¡ the SOFC/MGT hybrid system with two series fuel cells account for the highest electrical efficiency and was selected as the most efficient configuration.

In this paper¡ by defining a new paradigm for nonlinear aerodynamic equations of flow separation and static stall¡ a new form of nonlinear aeroelastic equations for two degrees of freedom airfoils (torsional and bending) are presented. Structural equations are based on the nonlinear mass-spring model; include the nonlinear quadratic and cubic terms. Aerodynamic equations are obtained by combining the unsteady Wagner model and the nonlinear lift coefficient-angle of attack for simulating stall using a cubic approximation. Hamilton’s principle and Lagrange equations were used to derive the aeroelastic equations. The obtained integro-differential nonlinear aeroelastic equations are solved using a new time-history integration method. The aeroelastic behavior of the airfoil is compared in both unsteady and quasi-steady flow. Using the time-history method compared to the phase space method leads to fewer equations. The results show that the aeroelastic behavior of airfoil with a linear structure¡ using a nonlinear aerodynamic theory for the stall¡ causes oscillations with a limit cycle in unsteady and quasi-steady flow compared to other linear aerodynamic theories. Also¡ the use of the cubic curve instead of the piecewise linear curves which is commonly used in other references¡ although¡ causes an apparent complication of the equations¡ reduces the computational time due to faster convergence in solution and makes the reduction in errors. The results show that the use of nonlinear aerodynamic static stall not only reduces the instability velocity¡ but also reduces the amplitude of limit cycle oscillations in both unsteady and quasi-steady regimes.

In recent years¡ knee diseases are spread especially in elderly people. Since performing daily activities such as walking and running¡ the knee supports the weight of the body¡ there is more likely to be injured. This issue is more important for elderly people who have weak muscles and almost all elderly people suffer from knee pain. One way to help this people in order to move normally is to use a wearable device to aid the knee. In this article¡ a passive wearable robot will be designed to improve the strength of the elderly who suffers from the knee pain. The robot uses the compliance elements to increase the power of the knee joint in parts of a cycle. This robot will be developed based on a Stephenson II six-bar mechanism. Using this mechanism has the advantage of producing the similar motion to a knee. In other words¡ this mechanism produces the linear and rotational motions simultaneously. Additionally¡ more compliance elements can be added to improve the performance of the wearable robot. The optimal dimensions of the robot will be Through the kinematics analysis and also the derivation of the dynamics equations and the numerical validations of these equations¡ the performance of the robot will be considered. The performance of the robot mounted on the leg is compared with the human. Obtained results show that the less power is required when a wearable robot is used. This proves the merits of the designed robot to be used for the elderly.

In this study¡ a Lattice Boltzmann Method (LBM) has been developed to calculate the distribution of a scalar quantity¡ like temperature¡ in a natural convection flow field under the condition of varying fluid thermal conductivity. The standard form of an LBM usually considers the fluid properties to be constant without any source term in conservation equations. The model developed is to account for variation of thermal conductivity with temperature in the presence of an external heat source. The proposed model has been examined against various case studies. It is shown that it is capable of modeling the extremely nonlinear problems. To magnify the nonlinear term in the natural convection case of under study¡ the radiation and other thermal sources have been used. The multiple relaxation time scheme has been applied to assure the solution stability. Using Chapman-Enskog analysis¡ the error associated with the proposed model has been estimated. The part of error which was not due to variations in the fluid properties¡ may be eliminated by introducing a correction term in higher order terms in Chapman-Enskog analysis. In addition¡ it has been shown that the correction term associated with the fluid conductivity variations¡ create an error of second order in terms of Knudsen number and is negligible. The present LBM model has an error of the second order of magnitude with respect to time.

In the present study¡ for the first time¡ adsorbent bed of SWS-1L/water adsorption chiller with rectangular and trapezoidal finned flat-tube heat exchanger with has been simulated three dimensionally based on the distributed parameters model and finite volume method. Effects of some important parameters on the chiller performance such as bed averaged pressure¡ temperature and uptake variations with cycle time have been examined for better understanding of bed dynamic behavior. Also¡ a comparative study between two different configurations of adsorbent bed including rectangular and trapezoidal fins has been conducted based on identical adsorbent mass. For this purpose¡ bed temperature¡ uptake and pressure distributions as well as the vapor flow patterns at the end of heating cycle phases and also effects of fin height and spacing on the system performance have been studied. In this investigation at fixed bed length of 20mm¡ fin height and spacing variations have been examined in the range of 8-20mm and 3-12mm¡ respectively. Results indicated that the system performance with rectangular and trapezoidal adsorbent beds are almost similar except for those conditions which fin spacing is 3mm and fin height are 14¡ 20mm. For the mentioned dimensions¡ the specific cooling power (SCP) of rectangular beds are almost 5% and 17% (for fin heights of 14 and 20mm¡ respectively) better than those of trapezoidal beds. Maximum and minimum SCP of adsorption chiller with flat-tube heat exchanger were obtained about 882 and 163W/kg for the smallest and the largest bed geometry and operating conditions considered in this study.

The empirical mode decomposition method is a new technique to obtain constitutive components of a signal. Applicability to all kinds of signals including non-stationary and nonlinear is a main feature of this method. So far¡ many researches have been done in the literature to eliminate or reduce effects of multiple sources of errors such as stop criteria¡ end effects and interpolation function. This article focuses on end effects error which many of previous solutions have been proposed based on symmetry or similar methods to decline it. The proposed combined method using auto-regressive (AR) models for short sections of signal edges¡ forecasts tails of maximum and minimum envelops. Some of first intrinsic mode functions are initially calculated as a result of AR model application. The methods based on symmetry are then used to continue sifting algorithm for remaining signal that has no enough extremums to employ AR model. Finally¡ by executing some examples¡ more accurate results obtained from proposed method are compared with those achieved from the mirror method. Noise is also added to signal time history in the last example¡ to simulate a more realistic situation.

The dynamic stability of single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) embedded in an elastic medium subjected to combined static and periodic axial loads are investigated using Floquet–Lyapunov theory and bounded solution theory. An elastic Euler- Bernoulli beam model is utilized in which the nested slender nanotubes are coupled with each other through the van der Waals (vdW) interlayer interaction. The Galerkin’s approximate method on the basis of trigonometric mode shape functions is applied to reduce the coupled governing partial differential equations to a system of the extended Mathieu-Hill equations. Applying Floquet–Lyapunov theory and Rung-Kutta numerical integration method with Gill coefficients¡ the influences of number of layer¡ elastic medium¡ exciting frequency and combination of exciting frequency on the instability conditions of SWCNTs and DWCNTs are investigated. A satisfactory agreement can be observed by comparison between the predicted results of Floquet–Lyapunov theory with bounded solutions theory ones. Based on results¡ increasing the number of layers¡ and elastic medium¡ dynamic stability of SWCNTs and DWCNTs surrounding elastic medium increase. Moreover¡ the instability of CNTs increases by increasing the exciting frequency.

In order to detect damage in a large-scale and complicated structure¡ there is need to exact nonlinear numerical modeling that its results have been analyzed using a method of system identification. In this way¡ the extended finite element model (XFEM) based on cohesive crack model (XFEM Based Cohesive Crack Segments) for concrete material as a reliable model is used for investigating real responses of Karun 3 concrete dam against applied loads and damages. In this model¡ whole of the structure is potentially under damage risk¡ while there is no initial crack. The dam is numerically modeled and analyzed using the finite element method (FEM) and XFEM Based Cohesive Crack Segments respectively¡ and the dam is analyzed under the seismic excitation. Then¡ for specification of crack effects and nonlinear behavior¡ the structural modal parameters and their variation should be investigated based on structure response for obtaining damage initiation time and its location by using system identification based on continuous Wavelet (CWT) transform. Results show that the dam natural frequencies decrease after the crack is formed¡ where decrease in longitudinal and vertical responses are more than the transversal response decrease. Moreover¡ crack width and its exact location are specified precisely from comparing the intact and damaged crest and central cantilever vibration modes. Therefore¡ the combination of XFEM Based Cohesive Crack Segments and CWT is useful procedure for structural health monitoring of concrete arch dams.

Thin revolved shells are intersetted in many engineering applications¡ in particular dubbly curved shells. In this research¡ linear and nonlinear buckling analyses (with consideration of geometrical non-linearity) are performed on two different types of elliptical shells known as Oblate and Prolate which are under external hydrostatic pressure. These shells are made of homogeneous steel. ABAQUS (a well-known finite element software) is used for performing the simulations. Several important parameters affecting the buckling behaviour of these revolved elliptical shells are investigated in detail such as the ratio between minor and major radii¡ the percentage of nonlinear buckling value and the shell thickness magnitude on buckling load capacity. The results show the significant effect of shell geometrical dimensions¡ the magnitude of nonlinear buckling value as an initial imperfection and the shell thickness variations on the buckling load capacity. Finally¡ it is also observed that the Oblate shell results in a remarkable reduction in the load capacity compared to the other shell type used in this study. To verify the validity of the results¡ a comparison is made between the present FEM results and the available theoretical studies and a good agreement is observed.

Lamb waves are certain type of ultrasonic waves that can propagate in thin plates. Lamb waves are particularly useful in testing large plate-shaped structures. Moreover¡ due to extensive flexibility in modeling sophisticated structures¡ finite element modeling (FEM) has been used in numerous Lamb wave studies. Due to the complexity of the scattering problem¡ interpretation of results is not easy. FEM helps us to better understand the complex issues that are associated with the scattering phenomenon. In this paper¡ we first consider a number of different finite-element modeling approaches that can be used for modeling Lamb waves and among them¡ we choose the best model that can provide both good accuracy and high computational speed. We then use this approach for modelling the scattering of Lamb waves from a through-thickness cylindrical hole in a large plate. This study has applications in structural health monitoring and defect sizing in plates. It is found that a 2D planar finite element model has the lowest computational cost and an accuracy of better that 95%. To verify the FEM results¡ experimental measurements are also conducted on an aluminum plate in which a through-thickness cylindrical hole is machined. The FEM results agree very well with those obtained from the experiments. It is concluded that by using this model¡ the position and properties of defects could be easily determined in plate structures.

Tube multi-point hydroforming is a new flexible forming technology for manufacturing of various tubular parts that presented and investigated in this paper for first time in the world. In this process¡ one die is enough to deform tubes to different shapes by utilizing high pressure fluid. In conventional hydroforming¡ it is necessary to manufacture different dies for producing different geometrical parts. This requires higher process time and cost. In present novel¡ tube multi-point hydroforming is investigated via FE simulation and experiments. In this process a new die based on multi point forming were designed and manufactured. Due to good formability of brass 70/30¡ a bulged tube and a rectangular tabular cross section of brass with initial thickness of 2mm are produced by applying this die to the process. The main difference between multi-point die and conventional dies is substituting the rigid surface by wide spaced pins. By adjusting the pins height¡ different tubular cross sections could be produced. This process is simulated and verified experimentally and defects are predicted. In order to decrease these defects an elastic layer of polyurethane is used. According to the simulation¡ maximum decreases in thickness are 11% and 17% for the bulged and rectangular cross section samples. These results are matched with the experiment.

Cylindrical shells are commonly used in various industries such as manufacturing airplanes¡ missiles¡ pipelines¡ bicycles¡ submarines¡ different automobile devices¡ decorative structures for buildings etc. They have extensive applications in industries because of their low weight¡ high resistance and ease of use. While working¡ these structures undergo various forces such as axial¡ torsional¡ internal pressure¡ or a combination of different loadings. Cylindrical shells with different openings are under the effect of tension concentration and instability of structure due to their geometric disconnections. The study of pore effects on load carrying and buckling behavior of cylindrical shells has been¡ and still is¡ among the manufacturers and designers’ concerns. In this paper¡ the buckling of cylindrical shells with seam¡ with lozenge or circular openings under axial load has been investigated using numerical and laboratory methods. The shells are of steel (standard: No: 1.0110 ST 37¡ DIN) which is one of the most common materials used in various industries including traditional and industrial construction¡ gas¡ oil and petrochemical industries. The effect of different openings on the buckling load of shells has been analyzed¡ and the obtained results have been compared with those obtained in the lab using Abacus software.

The wind is one of developing sources of renewable energy in recent years. Wind power often is unusable at peak times. Therefore¡ a storage system or backup power is always necessary. In this study¡ a hybrid system was applied for a wind turbine to provide the reliable power. The hybrid system consisted of four main components: a wind turbine¡ electrolyzer¡ hydrogen storage and fuel cell. The extra electricity produced in fewer demand hours by wind turbine was conducted to a hydrogen and oxygen generator system. Hydrogen were stored in a tank. Then¡ hydrogen was introduced to a fuel cell unit in order to produce electricity at peak times (when the electricity produced by wind power was less than demand). The hydrogen production rate by alkaline electrolysis as well as the electricity production by PEM fuel cell was investigated. The maximum hydrogen produced by the system per hour average was 304 ml and the power produced by the fuel cell was 1008 mW. After the construction of the prototype¡ a case study for this system was done in Kouhin area.

In this research¡ counter-current two phase flow is investigated adiabatically in vertical Plexiglas tubes with internal diameters of 60 mm¡ 80 mm and 110 mm. All of tubes have the same height of 2 m. So far¡ there have been few studies on counter-current flows in large diameter tubes. Water and air flow downward and upward through the tubes¡ respectively. Superficial velocities of air and water ranges are 1.77-7.17 m/s and 0.05-0.11 m/s for 60 mm tube¡ 0.99-4.03 m/s and 0.03-0.09 m/s for 80 mm tube and 0.55-2.26 m/s and 0.01-0.05 m/s for 110 mm tube. In addition to reverse flow¡ other main regimes can be observed as slug¡ churn and annular in the tubes. Our efforts in drawing the flow patterns map were aimed at minimizing uncertainties at the boundaries. Based on the obtained experimental results¡ slug and annular regimes gradually comprise smaller regions of the flow map as the tube diameter increases. However¡ churn regime contains larger area of the flow pattern maps. Moreover¡ Kelvin – Helmholtz instability is observed in tubes and experimental and analytical results represent appropriate consequent in comparison. Eventually¡ validation of experimental flow patterns map accomplished by theoretical results.

Accumulation of plastic strain during cyclic loading is one of the main reasons for fatigue failure. In order to predict the fatigue life of plates¡ it is necessary to calculate the accumulated plastic strain and the affecting parameters carefully. In this study¡ a combination of nonlinear isotropic and nonlinear kinematic hardening model (modified Choboche) was implemented in the commercial finite element code of ABAQUS¡ by using a FORTRAN subroutine to calculate the accumulation of strain in samples made from thin plates of aluminum. In this regard experimental¡ strain controlled and stress controlled cyclic tests were carried out¡ and the required coefficients for simulating the hardening behavior of aluminum alloy 2024-T3 were obtained and the accumulation of plastic strain was simulated at different uniaxial loading condition. The comparison of the experimental and the predicted results shows that¡ the determination of optimal coefficients for combined nonlinear isotropic and nonlinear kinematic hardening model (modified Choboche)¡ has an adequate ability to predict the experimental results. The obtained results also show that¡ increasing stress amplitude and mean stress increase the strain accumulation. The results from 4 types of cyclic loading indicate that the stress ratio has a direct influence on the strain rate when the maximum applied cyclic load is kept the same¡ and an increase in stress ratio increases the accumulation of plastic strain. Moreover¡ the rate of strain accumulation at the first cycles is high while it is reduced by increasing the number of cycles.

In this paper¡ the preferred regions of pulse-width pulse-frequency (PWPF) modulator parameters are obtained based on zero-input¡ static¡ and dynamic analysis in the presence of sensor noise as an input noise to PWPF modulator. The design parameters are reduced to 3 by using the quasi-normalized equations of PWPF modulator. Therefore¡ the results are applicable for grouped parameters¡ regardless of the value of each parameter¡ separately. Moreover¡ the computational burden is highly decreased¡ especially in a statistical analysis. The input noise of the modulator is constructed by a low pass filter driven by a white Gaussian noise. The fuel consumption and number of thruster firings are considered as performance indices. The modulator output frequency is also limited to 50 Hz. The preferred regions of quasi-normalized system are extracted based on eliminating the upper 30% (and 10%) of the plotted graphs for the above-mentioned performance indices. Finally¡ the preferred regions can simply be viewed in our resulting curves¡ i.e.¡ normalized hysteresis plotted versus normalized PWPF on-threshold for different values of modulator time constant. Each of these curves is plotted for a specified value of input noise power spectral density.

In this study Large Eddy Simulation method has been employed in order to investigate the effects of blade rotation direction of downstream turbine in two co-rotating and counter-rotating configurations. The acquired results are in good agreement with presented experimental data in literatures. Counter-rotating configuration is used in order to investigate the effect of blade rotation on the efficiency of downstream wind turbine. The results show that the efficiency of downstream wind turbine is increased about 4 percent without any change in wind farm layout and type of wind turbines. The upstream wind turbine absorbed a portion of wind energy. Hence stream wise velocity is decreased and lateral velocities are increased in downstream direction. The flow behind the upstream turbine is rotated in same direction with downstream turbine in a counter-rotating configuration. This is why the efficiency of downstream turbine is increased in a counter-rotating configuration. The results of the present study show that streamwise velocity profile is almost identical in both configurations¡ while¡ lateral velocities are changed considerably. In other words¡ a better efficiency of wind farm could be due to the lateral velocities. Hence¡ the efficiency of wind farm could be increased by decreasing the distance between two consecutive wind turbines in a counter-rotating configuration.

The present article deals with analytical modeling of boring bar dynamics as well as identification of unknown parameters for the dynamic model. Experimental modal analysis is utilized to measure the Frequency Response Functions (FRFs) of cutting tool. Using the analytical methods of modal analysis theory¡ dynamic parameters of boring bar (i.e. natural frequencies¡ damping ratios and modeshapes) are extracted from curve fitting of experimental FRFs. A new physical configuration is proposed¡ in order to accurately estimate the dynamic response of boring bar in time/frequency domains. In the proposed dynamic model¡ boring bar is modeled as an Euler-Bernoulli beam with flexible support and tip mass. The mechanical properties (i.e. modulus of elasticity and density) are considered to be constant along beam length. The flexibility of boring bar''s clamping interface is modeled by linear translational/torsional spring elements. Particle Swarm Optimization (PSO) is utilized to identify the unknown parameters of dynamic model. The parameters include translational/rotational clamping stiffness and dimensionless correction factors for boring bar''s diameter/tip mass. These parameters directly control the mass/stiffness distribution of proposed dynamic model. The FRFs obtained from updated model of boring bar are compared with experimental FRFs. It is shown that¡ by optimal selection of unknown parameters¡ boring bar FRFs can be accurately calculated at any point along its length. Hence¡ by incorporating the dynamic model of passive/active actuator into the proposed dynamic model¡ the stability lobes of dampened boring bars can be predicted.

In this paper¡ by introducing of development of two approaches based on the relative map filter (RMF); it has been tried to improve simultaneous localization and mapping (SLAM). The implementation of Extended Kalman Filter SLAM (EKF-SLAM) in large environments is not practical due to large volume of calculations. On the other hand¡ the observation and motion models of many robots are nonlinear and these cause the divergence of EKF-SLAM. The basis of RMF is relative distances between landmarks; therefore its equations are independent from the robot motion model. Also¡ the robot observation model can be linearly defined and its convergence is guaranteed. Despite these features¡ the relative filter proposed methods are faced with the problem of ambiguity in absolute positioning of robot and landmarks. In this article¡ ILPE (Improved Lowest Position Estimation) and IMVPE (Improved Minimum Variance Position Estimation) methods are introduced. In these methods¡ the ambiguity problem in localization and mapping of robot and landmarks are solved by sequential switching between absolute and relative spaces. The calculation volume of these methods does not depend on the number of landmarks and depends on the average number of landmarks observed in each scan of the robot. In this paper¡ the equations and the required algorithm to find the position of landmarks and robot are presented. Moreover by simulation¡ the performance and efficiency of the proposed methods are discussed in comparison with the previous methods including EKF-SLAM.

Nowadays, multilayered sheet metals are used in order to achieve a wide range of favorite mechanical, physical, thermal and electrical properties. The laser beam passage over the sheet creates extreme temperature changes which can lead to a change in chemical properties and microstructures. Due to the wide application of these materials in chemical and corrosive environments, corrosion tests were carried out on two-layered SUS304L/copper C11000 and three-layered SUS430/copper C11000/steel SUS430 sheets subjected to various laser passes. Ytterbium fiber laser is used and the governor mechanism during the process is TGM. The changes of microstructures were revealed by metallography. Corrosion resistance of steel layer in three-layered sheet subjected to laser was dropped due to the martensite and oriented ferrite grain size reduction in HAZ. There is no change in microstructure and corrosion behavior of copper layer and the second steel layer due to the HAZ low penetration depth. There is no change in microstructure and corrosion behavior of steel layer in two layered sheet due to the austenitic microstructure. Penetration depth of HAZ in two-layered sheet is limited to a small part of its steel cross section. So, there is no change in microstructure and corrosion behavior of copper, and corrosion is the same all over the copper layer in all specimens.

In this paper, boundary layer control technique is investigated on the NREL-5MW offshore baseline wind turbine blade with numerical simulation of linear DBD plasma actuator in a three-dimensional manner. This wind turbine uses pitch control system to adjust its generated power above its rated speed; but below that the controller is not in function. In the current study, operating condition is set such that the control system is off. Plasma actuator consists of two electrode and dielectric material. One of these electrodes is connected with the air and the other one is encapsulated with the dielectric material. When the necessary high-level AC voltage is applied to electrodes, electric field forms around the actuator and an induced wall jet forms with the ionization of the air around the actuator. Electrostatic model is applied to simulate the effects of plasma actuator and the resulted body force is inserted into flow momentum equations. In the present study, three different control cases are studied. Results show that in all cases, using this actuator leads to improvement of the velocity profile in controlled section, which influences on pressure distribution and results in rotor torque increment. Finally, increasing in torque leads to grows in produced power of the wind turbine. The most increment in output power occurs, when the actuator installed near the root of the blade in the spanwise direction and before low-speed region in the chordwise direction.

In this experimental study dynamic viscosity of hybrid engine oil (5w-50)-Cuo-MWCNT nanofluid for volume fractions of 0.05, 0.1, 0.25, 0.5, 0.75 and 1 percent of nanoparticles for temperatures of 5, 15, 25, 35, 45, 55 °C has been measured. This hybrid nanofluid has been prepared utilizing the two steps method. For viscosity measurement, the Brookfield viscometer has been used. The experimental measurments indicate that by increasing volume fraction of nanoparticles the viscosity increases; also by increasing the temperature the viscosity decreases. Based on the experimental results the maximum and minimum viscosity increases with volume fraction increase from 0.05 to 1 at a constant tempearture are 35.52 and 12.92 percent, respectively, relating to 55 and 15 °C. Measurement of the nanofluid viscosity with different volume fractions, shear rates and tempeartures indicate its Newtonian behavior. A new temperature and volume fraction dependent viscosity correlation, developed in this study to be used in numerical simulations, shows very good agreement with experimental results.

Supercritical carbon dioxide refrigeration is a proposed system to provide extremely low temperatures. The waste heat from the gas-cooler is noticeable. So, it can be used as a promising heat source in other systems like multi-effect-desalination system (MED), in order to provide cooling and fresh water, simultaneously; as well as reduction of power consumption. In this paper, the energy analysis and comparison of two novel combined systems are carried out. The combined systems consist of CO2 refrigeration system and two MED's models, the Boosted model and the water preheaters (PH) model. The effect of operating parameters such as evaporator temperature, ambient temperature and compressor outlet pressure on system performances are studied. Results showed that for both combined systems, by decreasing the evaporator temperature or increasing the ambient temperature, the coefficient of performance (COP) and the distilled water flow rate, decreases and increases, respectively. On the other hand, increasing the compressor outlet pressure would increase COP and decrease distilled water flow rate up to an optimum point. Also, MED-Boosted could produce more fresh water compared to MED-PH. In order to decrease the power consumption of the combined system two methods are presented. In two compressors method the COP enhances 6.2% compared to the base system (consists of one compressor and an expansion valve). However, the produced fresh water would be reduced by 60%. On the other hand, the expander method could improve the COP by 23.4%, compared to the base system, while the amount of distillated water decreases less than 8%.

Considering the daily increase of consumption and expense of nonrenewable energies such as natural gas and electricity, application of clean and renewable energies such as solar thermal energy nowadays has been highly taken into consideration. In this research, at first, simple steam Rankine cycle and two different configurations of combined steam and organic Rankine cycles with parabolic trough solar collector as heat source are simulated from energetic and exergetic point of view. First configuration was basic steam rankine cycle with parabolic trough solar collector (PTSC) as heat source, and other configurations of the combined cycle worked as follows: In the second configuration (combined cycle with intermediate heat exchanger), with the increase of steam condenser pressure, heat dissipation in condenser is used as heat source for bottoming organic Rankine cycle and in the third configuration (combined cycle without intermediate heat exchanger), reduced-temperature solar fluid moving output of steam rankine cycle acted as the organic Rankine cycle heat source. Simulation results in the basic input state show that third configuration has the maximum amount of work and irreversibility and second configuration has the minimum amount of work and irreversibility which in this case, increase in the steam cycle condenser pressure leads to the reduction of work of combined cycle with intermediate heat exchanger, even lower than the simple steam cycle. On the other hand, second configuration has the maximum solar energy and exergy efficiency among three configurations which is due to the reduction of collector area required in this configuration.

In this research, subcooled flow boiling of water and water-based nanofluid in the different channels cross sections with the same hydraulic diameter is simulated. The subcooled flow boiling of water in the channels is studied by Euler – Euler model. The results of this part was matched with the experimental data very well. To study the effects of nanoparticles in the subcooled boiling flow, copper oxide nanoparticles with 40 nm in diameter were injected at the inlet to the flow. The nanofluid subcooled boiling is simulated by considering three phases, liquid, vapor and nanoparticles. The water and vapor interaction is simulated by Euler-Euler approach; and the motion of nanoparticles in the continuous fluid is modeled by Euler – Lagrange model. Water, vapor and nanoparticles were considered continuous fluid, dispersed fluid and dispersed solid, respectively. After model validation, boiling of nanofluids was modeling in different channels. Volume fraction and temperature variations is obtained along the channels. The results showed that, at low concentrations of nanoparticles (0.001 kg/s) rectangular channels and at higher concentrations (0.005 kg/s) square channels have the greatest changes in vapor volume fraction compared to pure water boiling.

Nowadays, emerging more advanced computer systems made it possible to simulate and model complex problems even with higher accuracy. Regarding lower time and cost, the use of simulations instead of physical experiments is increasingly considered as an alternative method in the analysis and optimization of process performance. The importance of such methods becomes more significant when talking about micro-processes, since there are lots of difficulties in experimental measurements as a results of scaling problems by scaling down from macro to micro. In this study, a 3D model is developed using Deform-3D software for prediction of micromilling process behavior. Effects of cutting parameters on such characteristics as cutting forces, temperature distribution and tool wear are investigated. To check the validity of the model, force results of simulation are compared with the measured ones. A high level of correlation exists between the obtained simulation and measured results which shows that the 3D developed model has good capability to predict process behavior.

Recently, tubular flames are considered due to their advantageous in geometry of the flame. The major importance of tubular flame is its uniform temperature distribution. Therefore, it may reduce thermal fluctuations along the combustion chamber. In this paper, a non-premixed tubular flame is simulated numerically under various operational conditions. A solver is developed in openFOAM and numerical results are validated against the experimental measurements. Also, temperature distribution and concentration of major species of the flame in the middle of the burner are investigated and compared using global and DRM22 as chemical kinetics. In addition, stability of the flame in air presence as oxidizer has been studied. Results show that by increasing oxygen mole fraction in oxidizer, the equivalence ratio of the steady tubular flame region decreases and the flame will be established uniformly in equivalence ratio near the extinction limit. If pure oxygen is used as oxidizer, flame temperature will be increase strongly and tubular flame can be stable for equivalence ratio between 0.1 and 0.2. Thereupon carbon dioxide from the flue gases is added to the oxidizer to control the flame temperature changes. Establishment of steady tubular flame in presence of carbon dioxide is simulated too. Results show that by decreasing oxygen mole fraction, the equivalence ratio of the steady tubular flame region increases and the stability zone becomes wider

One of the main difficulties in employing fully coupled algorithms for solving Navier-Stokes equations is the high computation cost of coefficient matrix determination and solving the linear equation system. Therefore, the number of required iterations and computational costs may be reduced by increasing the convergence rate. This article deals with the formulation and testing of an improved fully coupled algorithm based on physical influence scheme (PIS) for the solution of incompressible fluid flow on cell-centred grid. The discretisation of improved algorithm is investigated and fully clarified, by comparing the methodology with two similar schemes. For a better insight, two benchmark problems are solved. The first problem is a steady lid-driven cavity with different Reynolds numbers between 100 and 10000. The second problem is steady flow over a backward facing step for the specified Reynolds number of 800. The history of residuals for present and previous methods are compared, in order to demonstrate the performance of the new discretization scheme. It is worth mentioning, the presented method is based on nine cells discretization. Therefore, the computational costs and memory usage of the proposed method are almost the same as previous ones. The results indicate that, the improved method converges in fewer iterations in comparison with prior methods. The new scheme can be utilized for development of the computational fluid dynamics solvers based on cell-centred grid arrangement.

In this study, energy and exergy analysis of a two bed adsorption cooling system have been performed. Silica gel-water has been chosen as the adsorbent-refrigerant pair. Analysis is performed for evaluating the effect of operating conditions on the optimal timing and then on the maximum value of the SCP, COP, effectiveness and the minimum value of internal irreversibility and external irreversibility. A lumped parameter mathematical model and a global optimization method called the particle swarm optimization have been used to reach this purpose. In this model, internal and external irreversibility have been calculated with the new method without calculating irreversibility of the cycle internal component. Energy analysis showed that maximum of SCP increases with the increase of the mass flow rate and heat source temperature. Furthermore, an increase in the heat source temperature causes an increase in the COP, but an increase of the mass flow rate causes a decrease in the COP. Exergy analysis reviled that depending on the mass flow rate and heat source temperature, 65-90% of input exergy was expended by internal irreversibility, 1–20% were expended by external irreversibility and 8-14% is transferred to the cold reservoir in evaporator. It is concluded at the low-temperature heat source if the mass flow rate is chosen less than 0.6 kg/effectiveness at heat source temperature 75 is more than 65 and vice versa.

In the present work, a novel electromagnetic actuation flexible-valve micropump using the fluctuating elastic wall is proposed, based on one-way lymph transfer mechanism. A time dependent magnetic field is used for actuating the magnetorheological elastomer (contractible) wall. Two flexible valves are located in two terminals of microchannel in order to filter bidirectional flow and generate one-way fluid flow. Water properties are used for simulation and the maximum Reynolds number is not exceeded from 30, Womersly number is lower than 1 in all cases. Knudsen number is much less than unity, therefore no-slip condition is valid at walls. A fully coupled magneto-fluid-solid interaction approach using time dependent study of two-dimensional incompressible fluid flow is performed. All solid parts follow Hook’s law and simulation is carried out using finite element approach by COMSOL Multiphysics software. A parametric study is conducted and the effect of key geometrical, structural and magnetical parameters have been examined on the net pumped volume. Present micropump is able to generate unidirectional flow and propel net volume of fluid left to right, and the net pumped volume of fluid is affected by design parameters. The proposed design can serve in a wide range of microfluidic applications for example, flow rate and total mass transfer are completely controllable. At the end of the study, an optimum geometrical design based on initial model is proposed. The final design is capable to transmit nearly two times of net volume compare to initial model and more than three times of the previous design.

In recent years, Mg alloys have received much attention as a promising candidate for raw material in biodegradable vascular stent. Forming of Mg alloys is difficult because of poor workability of them at room temperature. Hence this presents a technological barrier to the fabrication of initial micro-tube for a biodegradable stent. With regard to high biodegradability of the magnesium alloy WE43 to manufacture biodegradable stent, it has been selected as initial with casted structure. In this study, for enhancing mechanical properties and attaining micro tube a combination of equal channel angular pressing (ECAP) with extrusion and micro extrusion was used and Mg bars were fabricated to high-quality micro-tubes with refined microstructure. Fine-grained size billets of the WE43 alloy were obtained by one-pass of ECAP. The processed Mg bar was extruded into a bar with 5 mm in diameter. Finally, a UFG and high strength micro tubes with an outside diameter of 3.4mm and a wall thickness of 0.25mm were successfully produced by micro extrusion process. Mentioned processes were simulated using finite element (FE) simulations. The result shows the grain size of Mg incredibly reduced after this combined method and mechanical properties were significantly improved.

Prediction of the behavior of T-shaped chambers due to its high complexity has always been of great interest researchers. In this article, based on experimental data and genetic programming, the optimal model was presented for mixing process response. To get system’s behavioral equations, first, by using the experimental results and by changing the input variables System, input – output data is extracted. In order to predict the behavior of the system, the equation of input – output data, is derived using genetic programming. To design the structure of genetic programming trees, multi-objective optimization with two objective functions are taken into consideration: model inaccuracy and complexity of structure. By minimizing the objective function at the same time, we are looking for simple equations (minimizing the complexity of the structure) and increasing the accuracy of modeling (minimizing the error). In order to achieve a less complex equation, depth of the generated trees in structure of genetic programming will be minimal. By using multi-objective optimization, optimum set of points have presented. Comparing the results obtained from the models and real data represents a very good match.

The robotic sensor deployment task to achieve maximum converge is one of the main phases in feasibility studies and development of communication infrastructures and environment monitoring systems. In this article, a new approach is proposed to treat the maximum coverage in 3D vector spaces. For this purpose, a new geometric strategy is first presented to compute the area covered by an individual sensor. To maximize the coverage of the robotic network, the fractal search algorithm was employed. This population-based evolutionary algorithm has been proposed based on the growth of the random fractal and demonstrates a robust performance in tackling constrained and unconstrained optimization problems. Then, based on several scenarios and by considering spatial constraints, the efficiency of the fractal search optimizer was compared with other methods in terms of robustness, running time, quality of the coverage results, convergence rate, as well as the statistical test of Wilcoxon. The comprehensive assessment and analysis of the results certify better performance of the proposed approach to maximize the coverage in 3D vector spaces. The proposed approach can obtain the optimal deployment and coverage of the robots by the best convergence rate and computational and statistical precision.

Today, composite materials have extensive use in aerospace automotive and defense industries compared to metals, because of their high strength to weight ratio and good corrosive resistance. Machining of these materials regard to their composite structure is complicated. Achieve optimal machining conditions, depending on the needs, according to the type of fiber and resin used in composites, need proper analysis and careful investigation. In this study, composite pipes made of glass-epoxy to a thickness of 5 millimeters, which are often used in the body of Aerospace structures, produced by hand lay-up and their surface roughness after turning process is measured. In order to obtain the minimum roughness in the turning process, tool type in two modes, and cutting speed, feed rate, and depth of cut are studied at three different levels. So Taguchi experimental design method and experimental test samples on roughness the results analysis and performed by minitab software. Finally, concluded that the minimum value of the surface roughness is obtained by tools with chip-breaking levels, cutting speed 100 m/min, feed rate 0.05 mm/rev, and the depth of cut 1.5 mm.

Cell injection system in medicine used to inject the materials into the cells. The injection system consists of Injector and rotating plate. The controller sets height, position and orientation of the rotating plate. The proposal of this article is to replace SCARA robot injection tool and it included ability in desired position tracking and applied to time-varying force. In recent articles the control system applies to the rotating plate of Cells and this method can cause the damaging risk. The proposed method is fixed plate and to increase the success rate, the robot had been controlled. The parameters of environmental models are estimated by nonlinear proposed models and by using the recursive method, the minimum of squares errors will be optimal. The voltage strategy can control robot actuators. This method is simpler and free from the manipulator dynamics. In all recent studies, the impedance control is based on the torque control method and the proposed method of this article is applying the impedance control using voltage control. The robust adaptive impedance controller is designed in the presence of uncertainties. The simulation's results demonstrate desired performance of the proposed method

In this paper, concentrated and distributed compressive loading quasi-static tests were conducted on sandwich structures with empty and foam filled honeycomb core. The sandwich structure used in this research were formed by aluminum plate and aluminum 5052 honeycomb structure. Foam used to fill the honeycomb structure was polyurethane foam with a density of 137.13 kg / m3.Concentrated loading quasi-static tests were performed by flat ended penetrator with a diameter of 10 mm and universal machine. Also distributed loading quasi-static tests were carried out by universal machine. In distributed loading, force is applied uniformly to the entire structure surface. Displacement rate was 2 mm/min for both types of loading. The purpose of this paper was to study the filler material effect on energy absorption and destruction shape of sandwich structure, as well as comparison of the two types of loading in unfilled and foam filled honeycomb core sandwich panels. The results of quasi-static tests showed that filler material has positive effects on increasing energy absorption in both concentrated and distributed loading. Polyurethane foam as filler material of honeycomb structure used in sandwich panel core increase specific absorbed energy of sandwich panel with foam filled core proportion to empty honeycomb core sandwich panel structure in concentrated and distributed loading by 6% and 29% respectively.

In this paper, experimental comparison between conventional burner and porous burner in domestic purposes as stove, according to Iranian National Standard No. 10325 has been carried out. This comparison between the conventional burner available in the Iranian market and its equivalent porous burner is done. First, flammability of the porous silicon carbide burner was investigated. The results showed that the flame is formed when the equivalence ratio is less than 1, so the best performance equivalence ratio was around 0.7. By changing the distance between the pot and the burner and also changing the pot diameter, it was found that for a pot with 26 cm diameter and burner distance of 1 cm, porous burner efficiency increases to 55%. The comparison between the conventional burner and optimum situation porous burner showed that at the same factors like power, distance between the pot and the burner, the pot diameter, the burner diameter, measuring tools and the same method, porous burner efficiency is 1.5 times more than conventional burner. In conventional burners CO and NOX pollutant are 8-26 and 8 times more than porous burners. Due to higher efficiency and lower emissions, conventional burners can supersede porous burners for domestic purposes.

Single point incremental forming is a new and flexible method for 3D parts production of sheet metal. In this way, a hemispherical tool forms incrementally the sheet being clamped in perimeter. Because of the nature of localized deformation in this process, the formability is higher and forming forces are lower as compared to traditional sheet metal forming process. However, in this method dimensional accuracy is somewhat low due to spring back and bending occurred in boundaries. Recently, the incremental forming process using frictional heat has been developed. In this research, the experimental effect of generated heat by friction stir of the tool on dimensional accuracy in components of AA3105 sheet has been studied at high rotational speeds. By this method, due to friction movements of tool, the temperature of formation area rises while fixing the general temperature of sheet by spraying cooling liquid. Then, the sheet has low strength in contact region with tool while it has high strength in other areas. As a result, the force imposed on the sheet as well as the undesirable plastic deformation will decrease. Also, by decreasing the yielding stress, elastic strain and spring back decreases as well. An increase in formability because of softening of forming area is another contribution of this strategy. This idea has been studied by production of some parts of truncated-pyramid geometry and changing rotational speed from 1000 to 7000 RPM. The results show that at speed higher than 3000 RPM, formability and dimensional accuracy of the parts increase.

In recent years, energy harvesting from ambient sources in order to use for low-powered electronics has been considered by many researchers. Wind energy, solar energy, water energy, mechanical energy from vibrations, etc are common sources of ambient energy. In this paper, optimization of energy harvesting from ambient vibration using magnetic shape memory alloy is presented. To this end, a clamped-clamped beam coupled with MSMA units is considered. A shock load is applied to a proof mass which is attached to the middle of the beam. As a result of beam vibration a longitudinal strain is produced in the MSMA. This strain changes magnetic flux inside the coil connected to MSMA and as a result, an AC voltage is induced in the coil. To have a reversible strain in MSMA, a bias magnetic field is applied in the transverse direction of MSMA units. The Euler-Bernoulli model with von Kármán theory and a thermodynamics-based constitutive model are used to predict the non-linear strain and magnetic response .Finally, Faraday's law of induction is used to predict the output voltage. After obtaining the governing equations, a design optimization is performed to find the optimal shape and configuration of the energy harvester together with the effects of proof mass and bias field.

Pulse wave velocity often used as an indicator clinically for diagnosis of cardiovascular diseases. This assumption is well grounded in the physics of pulsatile flow of an incompressible fluid where it is fully established that a pulse wave travels faster in a tube of stiffer wall, the wave speed becoming infinite in the mathematical limit of a rigid wall. in this paper we point out that pulse wave velocity in a stiffer tube is strictly valid only when the wall is free from outside constraints, Which is used as the outer boundary condition (tethering: the degree to which the vessel wall is surrounded by tissue). In this paper, using the equations of blood fluid and vessel walls and using analytical solutions and the use of tethering as outer boundary conditions pulse wave velocity is investigated. In previous research pulse wave velocity has been obtained just for the tethering zero and one, But in the study pulse wave velocity investigated for tethering different degrees of tethering and for three different material wall viscoelastic, elastic and stiff. With this research, it is clear the changes of pulse wave velocity with change of degrees of tethering and change of material wall ,This results is a great help for use of pulse wave velocity as an clinical index to predict arterial stiffness.

A numerical-analytical modeling technique was presented for predicting instantaneous energy absorption with axial tidal turbines in unsteady water flow. The goal of present paper is introducing a fast and stable integral solution approach with unique solution. This technique employs steady-state CFD data to approximate transient performance of axial tidal turbine in unsteady external flows. This solution technique was designed for modeling axial tidal turbine with convergent-divergent duct in water flow with unsteady boundary conditions. The governing equations for fluid flow were derived in the form of integral equations. The equation of one-degree of freedom motion for rotor was solved with fourth-order Runge-Kutta method and variation of parameters approach. CFD data for rotor and duct of axial tidal turbine were inserted as boundary values in integral equations of fluid flow. Two transient analytical equations were employed for approximating rotor torque and back pressure coefficient of tidal turbine. The results of integral solution approach were compared with transient CFD data in ANSYS-Fluent software. Many numerical simulations were performed to determine duct dimensions for maximum power enhancement in an axial tidal turbine.

Topology optimization of the heat transfer quality in two-dimensional heat conduction problem at enclosure as one of the typical thermo-physical problems has always been quite important. In this paper a level set-based topological optimization procedure of two-dimensional heat conduction problem include point and speared thermal on computational domain load using finite elements method is developed. In level-set method, all structural boundaries are parameterized by a level of dynamic implicit scalar function of higher order. Changes of this function can easily model the detachment and attachment of dynamic boundaries in topology procedures. The same shape functions of finite elements analysis are employed to approximate the unknown temperatures and geometry modeling of the design domain. The objective function is to minimize thermal power capacity and sensitivity analysis on some heat conduction problems is investigated to deal with the topology optimization using level-set method with the finite elements scheme. Finally, topology optimization results of 3 heat conduction problems under both include point and spread thermal load cases are presented to demonstrate the validity of the proposed method. The proposed method lead to a significant reduction of the computational cost and time and it can be applied to a wide range of topology optimization problems arising from the heat transfer.

In aircrafts with multiple wings, control surfaces, and stabilizers, the stabilizing fins located at the tail provide stability for the boosting. In such aircrafts, the vortices resulting from the flow around upstream wings and control surfaces usually weaken the stabilizers’ performance. The nature of the form of grid fins makes them less sensitive in comparison with planar fins. Accordingly, the performance can be improved by substituting grid fins for planar fins. This paper simulates the flow field around the different models of planar and grid fins by applying finite volume methods using hybrid grid near the airplane’s body. At first, the flow field around a model with available experimental results was simulated to achieve the appropriate model of turbulence model. Then, two set of planar stabilizers, i.e. PL1 and PL2 and one set of grid stabilizers were designed for an aircraft with wings and control surfaces in a way that aerodynamic coefficients of the fins are equal to each other. However, they demonstrate different aerodynamic coefficients when installed on the aircraft as stabilizers. The simulation was run at Mach numbers 0.6, 0.7, and 0.8 and attack angles 0, 2, 4, and 6 degrees. The results indicate that pitch moments and normal force coefficients of the planar fin are lower than the grid fin in both models. Moreover, the performance of the planar fin as a stabilizer will be improved if its chord’s length is decreased and its span is increased.

In this paper, the effect of high frequency induction welding parameters on the weld quality of welded pipes is studied. In this purpose, process parameters such as current, frequency and edge shape of the weld connection and their effects on the heat distribution are investigated. Experimental investigation is performed by using tensile test, metallography, and micro hardness. This reveals three regions with different grading and various thermo-mechanical treatments. The results show that the grain size decreases about 27 percents as the edge shape is improved. By conducting thermo-magnetic analysis, different current intensities and frequencies are evaluated in the creation of appropriate temperature distribution. The results show that with increasing the current and frequency, the heat-affected zone is expanded and other areas become smaller. The maximum increase of the average temperature in the weld edge, was about 42 percents from 1250 to 1500 amperes per unit increase of the frequency. Micro-hardness test is used to detect micro-structural phases of the weld zone.By comparing the results of the metallography and micro-hardness tests, more uniform weld width was observed with modified edge of the in welded samples. The results represent 18 percents of decrease in the weld width of the modified samples in comparison with samples without edge preparation.

In this research, ammonia-water regenerative Rankine cycle driven by solar energy and LNG as it’s heat sink in condenser, is simulated from the energy, exergy and exergoeconomic point of view. A relatively new method is used to implement pinch temperature difference in heat exchangers which causes improving of the thermodynamic performance and output power of the system. Also heat exchangers are simulated by using heat transfer correlations of shell and tube heat exchanger in details. The results of based condition showed the suitable performance of natural gas cycle from the thermodynamic and exergoeconomic point of view and notifies the importance of using the natural gas cycle. Solar collector and condenser of ammonia-water cycle because of their high cost value, are introducing as the components that shoud be more concidered from the exergoeconomic viewpoint. The parametric analysis results show that in high inlet pressure of ammonia-water turbine, the exergy efficiency and the total cost of the system heve more suitable values while the net output power of the system decreases. Also by changing the ammonia mass fraction, changing of output parameters has a complicated patern. Finally by increasing the pinch temperature difference in heat exchangers, the decreased amount of system’s thermodynamic performance is more than the amount of system’s economical performance improvement.

The cavity problem always has been considered as a classic and fundamental problem. Specific materials like Bingham viscoplastic which is sort of Non-newtonian fluids shows resistance in a certain range of stress, calling yield stress, and almost acts like rigid body in this limited area. In case of increase applied stress, flows like fluid. Considering heat transfer in this type of material and investigate it, yield stress and viscosity variations with temperature as in practice we face will not be far-fetched. In the present work the numerical solution of the problem of Bingham material inside lid-driven cavity, investigating fluid flow and heat transfer in view of the changes in material properties has been done and results have shown with change in dimensionless numbers and parameters of Re=10-1000, Bn=1-2000, Pr=0.01-100 and E=5000-50000. In this study, using the finite volume method to discretize governing equations and the use of collocated grid, effect of viscosity and yield stress dependence to temperature compared with independence mode and then distribution of horizontal and vertical components of velocity, yield areas and flow inside cavity, center of vortex and then heat transfer due to the stream lines next to side walls, have been analyzed.

The current paper deals with the cyclic softening/hardening and strain ratcheting behavior of circular steel tubes under repeated inelastic pure bending. A relatively simple closed-form solution is proposed to tackle the problem. Key physical features involved are the elastic after-effect, accumulated cyclic (creep type) ovalisation of the cross-section, cyclic plasticity including the Bauschinger effect, cyclic softening/hardening of the material and ratcheting effect. The moment-curvature formulation of the tube is derived in an ovalised configuration. Tvergaard stress-strain relation is used to describe the elasto-plastic stress–strain relationship of the material. This continuous nonlinear constitutive model considerably abridges the solution. A combined nonlinear kinematic/nonlinear isotropic hardening rule is used to describe the cyclic uniaxial stress-strain. The analysis of the low cycle pure inelastic bending of the tube is performed under a curvature-control regime. The cycle by cycle growth (creep type) in the ovalization of the cross-section is modeled using a modified version of the Bailey–Norton creep law. The model predictions are examined against a number of available test data on the inelastic monotonic and cyclic bending of tubes and reasonable agreements are observed.

The considerable amount of internal combustion engine waste heat through exhaust gases and the capability of adsorption cooling system to be driven by waste heats cause adsorption cooling systems to be interesting for vehicle air conditioning. Low specific cooling power of these systems leads them to be bulkier with respect to other cooling systems. Therefore, practical use of these system has been a challenge. One of the methods to enhance the system performance is adsorber bed optimization which is only feasible by numerical simulations. Hence, an exhaust waste heat driven adsorption cooling system with longitudinal finned-tube adsorber is simulated three dimensionally and considering heat and mass transfer details. Also, both the intra-particle and inter-particle mass transfer resistance has been taken into account in governing equations in order to study the effect of adsorbent particle diameter on the system performance. Results show that among the examined geometrical configurations, bed with 20 fin numbers and fin height of 10 mm is the optimum case corresponding to the maximum specific cooling power. In addition, adsorbent particle diameter in the range of 0.3-0.4 mm is the most suitable diameter for the adsorber bed packed with zeolite13x grains.

In the recent decades, due to environmental sustainability, abundance, availability and appropriate thermo-physical properties, natural refrigerants are being considered with potential of substitute refrigerants. In this study, Propylene (R1270), Propane (R290), Isobutane (R600a), R407c, R410a, R12, R22 and R134a have been investigated as refrigerant in common refrigeration systems. In the case studies, the thermodynamic and technical parameters of the cycle, using above mentioned refrigerants, have been investigated for common refrigeration systems in temperature range of -30°C to 10°C in the evaporator, and also for heat pump systems with a temperature range of 45°C to 60°C in the condenser. Finally, Propylene was introduced as a refrigerant to replace with synthetic refrigerants in the above mentioned temperature ranges in common refrigeration cycles.