Modares Mechanical Engineering
Year:2019 | Volume:19 | Issue:6 |Papers Count:25

In the present work, a novel microchannel configuration is proposed to improve the cooling performance of a capillary-driven microfluidic system. In this approach, the possibility of meniscus formation inside the microchannel is increased for a wide range of operating temperature by controlling the capillary and viscous forces. The proposed microchannel consists of three sections. The first section is a narrow part of microchannel to control the pressure drop. The second section of microchannel is an evaporator. The meniscus is formed in this section due to balance of the capillary and viscous forces. It can move along the microchannel until the entrance of the third section of microchannel. The third section is a wide part of microchannel. The meniscus cannot move further in this section due to decreasing the capillary pressure. The evaporation rate from meniscus is estimated by using the thin film evaporation theory. Results show that the heat flux up to 30-100 W/cm2 (at the range of 70-100⁰ C) can be dissipated by the evaporation mechanism from a hydrophilic membrane.

In the present work, an investigation and simulation of the air flow, containing solid suspended particles in the actual impactor is done studied; particles under investigation are in the micron range. The results of this work can be illustrated by simulating the motion of particles in an actual impactor, investigating the effects of temperature changes on the surrounding environment, and the impedance plates on the accumulation efficiency. In the first part, by deriving the governing equations for this phenomenon and choosing the appropriate numerical method for solving these equations, the path of particles motion is simulated. By determining the path of the particles, it is possible to determine the number of particles deposited on collecting plate, and then according to the mentioned relations, the collection efficiency is obtained for a laboratory experiment, which compared with laboratory values. This comparison indicates the acceptable accuracy of the chosen employed method. In the next section, by selecting particles with different densities, effect of the environment temperature and inlet air variations by assuming constant plate temperature, and collector plate temperature variation on the impactor efficiency have been investigated. The results show that the particle density affects the efficiency of impactor, and reduces the diameter of cut from 2. 2 to 4. 2 in micrometer range. Due to the increased viscosity of the air, the heating of impactor’ s environment reduces the efficiency of impactor. The results showed that temperature variation of the collection plate could also change the particle collecting efficiency.

In the present study, CFD simulation of Transit-time ultrasonic flowmeter with the PZT-5J piezoelectric sensor was modeled for light, heavy, and medium crude oil by the wave equation in the acoustic wave propagation path and finite element solving method in the unsteady state and it was implemented, using COMSOL Multiphysics 5. 3 software. Different samples of light, heavy, and medium crude oil at different temperatures were modeled and simulated under constant pressure, using CFD tools. the maximum received voltage and speed of sound in samples were calculated by the proposed model. To evaluate the accuracy of the proposed model, the simulation results were compared with the empirical data obtained from the experimental work of the researchers. The average values of the maximum voltage of received signals for an ultrasonic flowmeter containing light, heavy, and medium light crude oil samples are 0. 9491, 1. 0115, and 0. 943 v, respectively. The difference between the simulation results and the experimental data for the speed of sound in the light, heavy, and medium crude oil samples was at most about 0. 2336%, 0. 4339%, and 0. 1378%, respectively. Therefore, the high costs of designing and optimizing the transit-time ultrasonic flowmeter for crude oil can be reduced, using the proposed model.

In this study, we derived the rotating airfoil aeroelastic system of equation considering Loewy aerodynamics. To this end, we define the local coordinate system on airfoil and reference coordinate on the hub. We define the free air velocity vector and the airfoil rotating speed vector according to the reference coordinate. So, the Kinetic and Potential energies are derived based on linear stiffness and linear damping according to the Hamiltonian principle. Wakes behind the rotating blades form into the helix. Therefore, we form the aeroelastic equation of motion with Loewy aerodynamic which compensates the wake effects. Stability analysis is performed by the well-known P-K method. Flutter speed and stability boundary are estimated. Comparing the results of stability analysis and the reference validates the applied method. Furthermore, we proposed the PID Control to suppress the flutter speed. Pitch angle is the PID controller input and command. The desired control criteria including settling time and error tolerance are selected to design PID controller. Unit step response shows that pitch angle response is under-damped. However, step response tracks input well. Besides, disturbance rejection by considering the gain from input to output to remain below the gain value is analyzed.

In the current paper, the flutter of a circular cylindrical shell containing an internal fluid while subjected to supersonic external flow has been investigated. It is noted that the internal fluid is formulated through a simple and novel model, in which the fluid is only represented by the free surface as well as the surrounding structural degrees of freedoms. To this end, a computational Fluid-structure interaction (FSI) model within the framework of the finite element method is developed. The internal liquid is represented by a more sophisticated model, referred to as liquid sloshing model, and the shell structure is modeled by Sanders’ shell theory. The aerodynamic pressure loading is approximated by the first-order piston theory. The initial geometric stiffness due to pre-stresses in the initial configuration stemming from the fluid hydrostatic pressure, internal pressure, and axial compression load is also considered. The validity of the derived formulation is established, using some verification examples. The obtained results reveal as the filling ratio is increased from 0 to 1, the flutter speed increases first as the filling ratio is increased and reaches the maximum value at the 0. 5 filling ratio; then, it decreases when the filling ratio is further increased and reaches the critical value of an empty shell at the 1. 0 filling ratio.

In this paper, the laminar and fully developed flow with heat and mass transfer in a fuel cell channel with rectangular cross-section is investigated. The rectangular channel is straight and has a porous wall and three non-porous walls. The governing equations including the momentum and energy equations solved by a two-dimensional code (quasi-three-dimensional), and the velocity, pressure and temperature distribution curve along the channel, and non-dimensional flow parameters such as the friction coefficient and the Nusselt number in different aspect ratios are calculated and plotted. For the flow, the non-slip boundary condition is used and for the heat transfer, the usual boundary conditions in the fuel cell is used, so that on the porous wall, the constant heat flux boundary condition is used and on three other non-porous walls, constant temperature boundary condition is used. The results show that for a given aspect ratio, the friction coefficient in the injection condition is greater than suction condition, and by increasing the amount of injection and suction, the difference between them increases. In addition, the value of friction coefficient for unit aspect ratio 1 (square cross-section) is minimal for suction and ejection. The value of the Nusselt number is minimal at unit aspect ratio for both suction and injection. Also, the distribution of velocity and temperature along the channel as well as the dimensionless distribution of these two parameters along with injection and suction and without it in different aspect ratios are plotted and discussed.

This paper presents a new method to design stabilizing and tracking control laws for a class of nonlinear systems whose state space description is in the form of polynomial functions. This method employs the nonlinear model directly in the controller design process without the need for local linearization about an operating point. The approach is based on the sum of squares (SOS) decomposition of multivariate polynomials which is transformed into a convex optimization problem. It is shown that the design problem can be formulated as a sum of squares optimization problem. This method can guarantee globally exponential stability of the nonlinear system with less conservatism than other linearization based methods. Also, a sum of squares technique is used to evaluate the stability of closed loop system state with respect to exogenous input. The nonlinear dynamic model of air vehicles can usually be expressed by polynomial nonlinear equations. Therefore, the proposed method can be applied to design an air vehicle autopilot. The hardware in the loop (HIL) simulation is an important test for evaluation of the aerospace control system before flight test. The HIL results using designed controller for a supersonic air vehicle are presented. The results from HIL is compared to the software simulation that the appropriate consistency of results shows the efficiency of the proposed method in the air vehicle autopilot control loop.

Parallel robots have a lot of advantageous compared to their counterparts, serial robots, such as higher accuracy, more load to weight ratio, and higher stiffness, which contribute to their various, and precise applications. Stiffness of the robot, as one of the most crucial parameters which should be considered in design procedure of the robot, ensures optimal accuracy respect to the desired application. In this paper, an experimental study is investigated on evaluation of the robot’ s stiffness and the errors corresponding to compliance of the mechanism, which indicate the displacement of end-effector of the robot with respect to external imposed forces. The aim of this paper is to evaluate the stiffness and the errors due to the softness behavior of the mechanism of a 3 degree of freedom (3-DoF) parallel robot; for this end, the amount of transfer of the final executor to the applied load is simulated. First, the 3-DoF decoupled robot is introduced and its features are expressed and the stiffness of the mechanism is modeled using Finite Element Method (FEM). Then, stiffness behavior of the mechanism is determined in different positions of the end-effector by considering predefined boundary conditions. In order to evaluate the obtained model of the robots’ stiffness, a novel experimental setup is developed to measure the stiffness of the mechanism. By employing the setup, stiffness behavior of the robot is measured in different conditions. Finally, the output results of the stiffness model are compared to the experimental tests. The results reveal that the 3-DoF decoupled parallel robot shows a proper stiffness behavior. Hence, it can be employed in various applications with high precision.

Sloshing phenomenon is one of the complex problems in free surface flow phenomena. Numerical meshless methods as a new method can be used to solve this problem. In these methods, the lack of a mesh and complex elements for the domain of problems due to the change in geometry of the solution over time provides a lot of flexibility in solving numerical problems. In the previous researches, the sloshing problem in reservoirs was solved, using the Laplace equation with respect to the velocity potential, but the solution to this problem with pressure equations has not much considered; therefore, using the pressure equations and a suitable lagrangian time algorithm, generalized exponential basis function method has been developed for dynamic stimulation reservoirs. The approximation is solved, using a meshless method of generalized exponential basis functions and the entire domain of problem will discrete to a number of nodes and then with appropriate boundary conditions, the unknowns are approximated. In this study, linear and nonlinear examples have been solved under harmonic stimulation, in two-dimensional form of rectangular cube tanks, and the results of them have been compared with the analysis solving methods, other numerical methods, and experimental data. The results show that the present method in two-dimensional mode is very noticeable compared with other available lagrangian methods because of accuracy in solving problem and spending time.

One of the main concerns of the world today is reduction of energy resources and rising prices. To counter this, most countries in the world are looking for new solutions to reduce the need for energy in various fields. Energy consumption in buildings has a significant share of the annual energy consumption of countries. About 40% of energy consumption of Iran is annually consumed in heating, cooling, and other building needs. Therefore, this sector has a significant potential for improving infrastructure and reducing energy consumption. One of the building components that plays a significant role in the loss of thermal energy is window. Using multiglazed windows filled with ideal gases, a lot of wasteful energy in the building can be reduced. In this paper, the effect of using different multi-glazed windows to reduce building heat losses has been investigated. Effect of number of layers, kind of ideal gas and its thickness, and also kind of frame has been studied in this paper. To investigate these factors, thermal losses of a typical building is simulated in the Carrier software. Also, conduction heat flux passing through multi-glazed windows for different filling gases is calculated by Fluent software. Based on the results, three-glazed window with Krypton gas has the best performance in reducing heat loss of the building and its application improves thermal performance of a single-pane window up to 66%.

The present paper presents the results of the thermodynamic and economical study of the use of synthesis gas from a biomass gasification reactor instead of natural gas at a synchronous power plant. First, the analysis of the system at the Pars khodro factory, which is fed with natural gas, was done, and the use of a gasifier for the synthesis of natural gas for the replacement of natural gas is investigated. The results of thermodynamic analysis indicate that the increase in the percentage of biomass fuel moisture had a slight effect on CH4 and N2 in synthetic gas, but it has a relatively modest effect on CO and CO2 and also low thermal value. By using a gasifier reactor, a natural gas consumption of 4468316cubic meters per year will be saved. The results of economic analysis indicate that due to the price of natural gas of 700Rials per cubic meter, the purchase price of electricity is 650Rials per kWh, the number of years of operation of 7 years and the profit rate of 7%, the net present value is at the zero frontier and this investment is at the threshold of being economically feasible. But if the rate of profit is to be raised, the lower the natural gas purchase price, or the lower price of electricity purchase, the improved system from the economic point of view is not profitable. In this regard, at a profit rate of 7%, the price of the biodegradable fuel is at most equal to 100, 000 rials per ton, the net present value is at the zero frontier and the investment will have economic justification, But in larger quantities of biomass, investment will not be economically profitable.

Thermal and hydrodynamic behavior of a laminar flow of water within a horizontal curved Vipertex tube with mixed convection heat transfer, in the range of low Grashof numbers, has been numerically studied. The curved horizontal Vipertex tube has geometry of 180o, fixed dimensionless radius of centerline curvature of 2R/D=6. 62, dimensionless roughness height e/D=0. 1, and a constant heat flux is exerted on the walls. The three-dimensional governing equations were discretized, using a finite volume method. To solve the problem, the computational fluid dynamics of ANSYS Fluent has been used. The results reveal that not only Grashof number and the buoyancy forces arising from it, but the mutual effects of the centrifugal and the buoyancy forces affect the thermal and hydrodynamic characteristics such as dimensionless axial velocity contours, secondary flow vectors, dimensionless temperature contours, heat transfer coefficient, and skin friction coefficient. So that, for a given Reynolds number, increasing Grashof number due to more interaction between buoyancy and centrifugal forces, results in temperature difference reduction in the Vipertex tube. Therefore, the buoyancy forces decrease and lead to the lower heat transfer coefficient, but in smooth curved tube increasing Grashof number leads to the higher heat transfer coefficient. Nevertheless, the Vipertex curved tube in very low range of Grashof and Reynolds, in each Grashof and Reynolds equally, has a higher heat transfer than a smooth curved pipe. The results also indicated that the skin friction coefficient in these types of tubes can be up to 3. 5 times higher than that of smooth one with a Grashof increase.

In this study, a constitutive equation based on the hyperbolic sine Arrhenius-type model has been developed to describe the hot deformation behavior of a Fe-17Cr-7Ni (17-7PH), semiaustenitic precipitation hardening stainless steel. The experimental data obtained from hot compression tests at temperature range of 950-1100 C and strain rates of 0. 001-1 s-1 were used to establish the constitutive equation. The material constants of α , A, n, and Q were calculated, using the developed model related to the applied strain by 6th order polynominal relationships. The average absolute relative error (AARE) and correlation coefficient (R) were used to evaluate the accuracy of the constitutive equation. The average values obtained for AARE and R were 5. 17% and 0. 9904, respectively. The results indicated that the developed constitutive equation can predict the flow stress behavior of the studied alloy with good accuracy over a wide range of experimental conditions. The model can be, therefore, recommended for analysis of hot deformation mechanism and microstructure evolution.

The optimal insulation thickness is a function of the insulation initial cost and the cost of energy carriers for the internal space heating and cooling due to heat transfer from the wall. In Iran, by allocating subsidies to the energy sector, tariffs for energy carriers are sensibly lower than global prices. In order to determine the insulation optimal thickness, energy carrier tariffs were considered variable according to consumption. Electricity and gas costs were divided into 4 ascending tariffs for low, moderate, high, and very high consumption cases. In addition, the case of energy carriers without subsidies was also examined as the 5th scenario. The outer wall consists of a typical hollow brick layer with 20cm thickness, insulated with an expanded polystyrene layer, placed at the outside. Heat load due to heat transfer from the external wall was calculated by using EnergyPlus simulation software in different geographical directions and different thermal insulation thicknesses in Tehran climate. The optimum insulation thickness was determined based on the total cost over the lifetime of 30 years. According to the results, in the first tariff, which refers to low-cost subscribers, the use of thermal insulation in some geographic directions does not allow the payback period over a lifetime. In other directions, economic savings are low and neglectable. For higher tariffs, the optimum insulation thickness increases. In the 2nd to 5th tariffs, the optimal thermal insulation thickness varies from 6 to 18cm. Also, the calculated payback periods of these configurations are between 6 and 28 years.

In this article, the flexural sensitivity and flexural resonant frequency of the atomic force microscope made of functionally graded materials is investigated by modified couple stress theory (MCST). In MCST, the size effect of the system is taking into account by means of the material length scale parameter. Microbeam is made of a mixture of metal and ceramic with properties varying through the thickness following a simple power law of n. In this work, due to the kinematic energy and potential energy of microbeam, the governing equations of motion and corresponding boundary conditions are derived on the basis of Hamilton principle by considering Euler-Bernoulli beam theory. Based on the results, it is clear that when the contact stiffness increases, the flexural sensitivity of the system decreases, and flexural resonant frequency increases. Moreover, when the microbeam thickness comes approximately close to material length scale parameter, the difference between MCST and classical continuum mechanic becomes significant. Furthermore, in low contact stiffness, increasing the power n reduces the flexural sensitivity of microbeam, while in high contact stiffness, increasing the power n increases the flexural sensitivity of the system. Results also show that at each value of contact stiffness, as ceramic volume fraction increases the flexural resonant frequency will be increased, too.

Different strategies are studied to control chemotherapy delivery in cancerous tumors. The main aim of control is to reduce cancer cells immediately and, at the same time, it is the least harm to the healthy tissue of the body. Besides, at the end of treatment, the amount of drug remaining in the patient’ s body should be as low as possible. Various control algorithms are applied on dynamic models with different orders. In this paper, a modern dynamic model for cancer with five ordinary differential equations by considering normal, endothelial and cancer cells, and the amount of two chemotherapy drugs and anti-angiogenic residues in the body is considered as state space variables and the rate of injection of two drugs as a control signals. After discussing the mathematical model of the system, the system is controlled by fuzzy controller with defining the rules along with fuzzifier and defazzifier by one of the control signals (rate of chemotherapy drug). This means that the rate of normal and cancerous cells counts as the input of the fuzzy controller and the amount of chemotherapy drug injections signal is the output. The simulation results show that in the last days of treatment, cancer cells have a downward trend, and normal and endothelial cells also tend to the healthy state. The solutions of the fuzzy controller are compared with the uncontrolled mode as well as the available experimental data. The results indicate that the system has met the permissible limits, which indicates the validity of the answer from the fuzzy controller.

Welding by laser beams is one of the essential parts of production process in automobile manufacturing used for joining plates. In this paper, for the first time, simulation of pulsed laser welding process of joining stainless steel to low carbon steel was carried out. For this purpose, at first, thermal analysis was carried out by finite element method and with exact definition of thermal resource; temperature profile and the dimensions of the melting area was gained as results. This was followed by mechanical analysis. The thermal analysis results were stored in a mechanical element as history to obtain the thermal conditions of the material. As results of this analysis, the strain of elastic and plastic as well as the amount of residual stress was obtained. The results show that low carbon steel passes through higher range heat in cooling process, because of higher thermal conductivity. Also, low carbon steel saves more residual stress due to higher yield stress. For validation of simulated model, two plates of 304 stainless steel with similar parameters with the simulated model were welded by laser welding. Comparing the results obtained from the experimental model with the simulated model shows a very good agreement.

In order to evaluate the ability of micropolar fluid model to simulate nanofluids, mixed convective heat transfer of a micropolar nanofluid in a square lid-driven cavity has been numerically studied. The governing equations were solved by finite volume method, using SIMPLE algorithm. In this paper, the effect of parameters like the Grashof number, the volume fraction of nanoparticles, and micropolarity ratio on the heat transfer of Al2O3-Water nanofluid have been investigated. Also, to calculate fluid viscosity and thermal conductivity coefficient of the nanofluid, the temperature-depended variable model was used, considering the Brownian motion of the particle. The results showed that the increase in Grashof number amplifies the buoyancy force and enhances the Nusselt number as well as heat transfer rate. Also, the increase in micropolar viscosity at low Grashof numbers intensifies the forced convection and increases the Nusselt number over the hot wall. However, at Gr=105, the increase in micropolar viscosity up to K=1 leads to the decrease in the amount of heat transfer, but its further increase entails the increase in heat transfer. Although the addition of nanoparticles to the fluid improves heat transfer rate, the extent of improvement at micropolar nanofluid is lower than that in the Newtonian nanofluid.

In this paper, a fuzzy clustering system is presented to display the flow field changes in the rotor outlet of centrifugal turbomachinery. What is important in the research done in the field of turbomachinery is the need for all the fields to properly understand the phenomena of flow inside the turbomachines, which has complexities. For this reason, the most advanced laboratory equipment is used in this regard, which is associated with issues such as time consuming, high costs, and a large number of required tests, and doubles the importance of simulating and observing current phenomena through artificial intelligence algorithms. The present system operates on the basis of fuzzy clustering so that the spatial data (from the PIV measurement system) by the number of specific clusters to the field display in the initial time; then, by applying changes to the cluster related to the time series (from the system measurement of LDA) that contains the recorded changes of the current during the time of the data mining, the new field data are obtained at a new time step and the clustering of the data shows the variation of the flow field in the fuzzy environment. In this paper, the flow field was investigated for 6 successive steps, and the results of the system output showed the variation of the flow field from the rotor rotation at different angles.

The present study investigated modeling and optimization of a multi-tube heat exchanger (MTHE) network considering the effect of different nanoparticles on the tube side. After thermal modeling in ε-NTU method, optimization was performed from the perspective of increasing effectiveness and decreasing total annual cost as 2 objective functions, using 8 designe parameters, including number of MTHE and particles volumetric concentration. In addition, optimizaation was performed at 3 various cold mass flow rates and different nanoparticles including AL2O3, CuO and ZrO2 and result were compared with the base fluid (water). The results show that the Pareto front was improved in nanoparticles case, and the rate of improvement in CuO nanoparticles case, especially in higher effectiveness and lower nanofluid mass flow rates is more significant compared with the other studied cases. In addition, because of the improved thermal performance of MTHE network in the nanoparticles case, the heat transfer surface area and consequently the volume of MTHE network for fixed values of effectiveness are significantly reduced. Finally, after display of the results of the design parameters versus effectiveness, sensitive analysis of particle volumetric concentration on the objective functions was performed for typical piont and the results were discussed.

Wire Electrical Discharge Machining (WEDM) is known as an advanced manufacturing process, especially for producing delicate and intricate shapes and cutting difficult-to-cut materials. Machining error on small arced path is an important problem associated with this process. The current paper investigates experimentally the machining errors of three-stage WEDM on the small straight and arced paths. To reveal the reason behind these errors and to compensate them, residual materials of each cutting stage on the straight and arced corner paths were separately measured and analyzed. Machining errors of each WEDM stage in both paths were accurately considered and the causes of these errors in the straight and small arced paths were experimentally and theoretically determined and discussed. Experiments showed that the roughing stage has such a serious deteriorating influence on the machining errors on the arced paths that it cannot be compensated in the following finishing stages. The spark angle domains of the roughing stage on the arced paths were calculated and the effects of these domains on the machining errors due to wire diversion from the programmed path were analyzed. In addition, this research proposes a novel guide in multi-stage WEDM by defining some machining concepts and developing equations for error calculation of WEDM finishing stages on these paths. The machining errors estimated by equations have consistency with the related experimental ones. Results of this study can be employed in the accurate WEDM cuttings.

The preference of fiber– metal laminate over metal and composite has been proved in lots of researches. In the present study, the main goal is to investigate an idea for impact resistance improvement of fiber metal laminates under high-velocity impact by numerical analysis and experiment. Due to the existence of various types of mechanisms for dissipating kinetic energy of projectile in contact with the target, in this research, it has been concentrated on one of them and by adding a rubber layer into AL/GL/GL/AL laminate, it has been allowed more bending to the aluminum layer thereby offering higher dissipating kinetic energy and increased special perforation energy. Materials used in this study are 2024-T3 aluminum alloy, woven glass/ epoxy prepreg and Nitrile butadiene rubber (NBR). All of the tests have been done by a highspeed gas gun in Tarbiat Modarres University and numerical analysis is done with Ls Dyna software. With numerical analysis, it is possible to achieve results such as contact force and different energies variations during the impact of the projectile with the target which cannot be achieved by experiment. The results show that by adding a rubber layer into the laminates, the aluminum layer bend more so more kinetic energy can be dissipated from the projectile. Hence, special perforation energy and ballistic velocity are increased effectively.

Near dry Electrical Discharge Machining (EDM) is one of the advanced methods for removing materials environmentally friendly. Combining the minimum quantity of lubricant (MQL) and vegetable oil not only reduces health hazarders and costs, but also improves the process. This research has been conducted on Mo40 steel and the mixture of vegetable oil and air has been used as dielectric. The effect of electric current variables, open circuit voltage, pulse on and off time and air pressure were studied on material removal rate (MRR), tool wear rate (TWR), and surface roughness (Ra), using the method of designing the central composition of the response surface. The results showed that the increase in ampere, pulse on time and open circuit voltage increase the MRR; also, increase of the pulse off time improves washing of the environment that prevent short-circuit and all had an effect on the MRR. Also, increasing the ampere and open circuit voltage leads to an increase in the TWR and increasing the pulse on time, as well as the increase in pulse off time, reduces the TWR. Increasing the air pressure reduced the dielectric density and increased the TWR. On the other hand, the increase in the ampere and the pulse on time as well as the open circuit voltage increased Ra and increase in the pulse off time and the air pressure reduced Ra. This method has led to an increase of 200% in MRR, 30% reduction in TWR, and 60% reduction in Ra compared to the kerosene immersion method.

Al6061 alloy is widely used in the industry; so, its welding with reliable methods is of great importance. In the fusion welding of these alloys, imperfections such as cracks, cavities, and segregations of alloy element may occur that necessitates the application of solid state welding processes such as friction stir welding method. In spite of the many advantages of the friction stir welding, several attempts have been made to improve the properties of the resulting joints. In this study, the effect of increasing the cooling rate and the effect of vibration during the process on the microstructure and mechanical properties of Al6061 welds are investigated. Also, the simultaneous effect of water circuling and vibration on the mechanical properties of the joints is evaluated The results showed that vibration due to increasing the strain and water circuling due to increasing the cooling rate reduced the grains size in the stir zone. Investigations revealed that cooling rate increment decreased the dissolution of Mg2Si precipitates significantly. The results of the tensile test showed that the strength of the joints increased due to the grain refinement as vibration was applied or when cooling rate increased. Also, when the vibration and coolant were applied simultaneously, the strength increased dramatically due to significant grain refinement and presence of Mg2Si precipitates. On the other hand, with grain refinement, the volume fraction of grain boundaries increases and, thus, the growth of the cracks decreases and correspondingly elongation enhances.

Today, Ducted Fan micro aerial vehicle has attracted much attention in the field of business and research due to the duct and, thus, the ability to be safe in enclosed environments. In order to real identify and practical help to control and implement the vehicle in various maneuvers, the experimental example of this VTOL MAV was built by Aerospace Engineering Department of Amirkabir University of Technology. In this research, in the first step, the modeling of the ducted fan is considered. In this way, after obtaining the dynamic model of the ducted fan, the parameters in this model are calculated, using empirical methods. In this regard, the aerodynamic coefficients of the control levels and the inertia of the ducted fan can be mentioned. In the second step, the controller design of the ducted fan is discussed. Ducted-Fan MAV control is one of the important issues in designing this fan due to inherent instability. The study of vehicle that reported shows that nonlinear dynamic inversion is an appropriate choice among control methods due to its successful empirical implementation on ducted fan. Thus, by choosing this method, the control system was designed to follow the desired command of the vehicle in the Simulink simulation environment. In this process, the position command is first applied to the ducted fan and converted by the controller to the command of state control actuators, after which these commands by changing the angles of the control levels of the ducted fan lead to the change in the angles of the ducted fan’ s side, the pitch, and the roll, and, thus, achieved a desired position. The results indicated that the desired command was correctly followed; also, the stability of the closed loop system was successfully accomplished by using dynamic inversion method for the Ducted Fan MAV.