مجله مهندسی مکانیک
سال چهل و نهم شماره 1 (پیاپی 86، بهار 1398)

The performance of the axial flow cyclone separator known as I-Sep, with the aim of separation of gas-liquid flow of air and water is analysed. The experimental tests which have been done in collaboration with Caltec Company in Cranfield University are compared with numerical tests in different gas volume fractions and inlet flow conditions. The sensitivity analysis of simulation to the droplet size with the Eulerian model are performed and it is shown that the efficiency of the separation increases and the pressure loss decreases by increasing the droplet size. For two inlet gas volume fractions, 90% and 97.5%, the simulation was performed using Eulerian and RSM models with 10 micron diameter droplets. The simulation results for the efficiency of separation and pressure loss were in well accordance with experimental results. For GVF equals to 97.5%, optimum value is 88% for 0.799 (kg/s) of inlet mass flow rate. For GVF equals to 90%, two maximum and one minimum point can be observed.

The aim of present study is numerical investigation of carbon dioxide injection effect on the flameless oxy- fuel combustion. For this purpose, different subjects have been analyzed such as various regimes composed in oxy- fuel combustion, temperature distribution and heat release in different values carbon dioxide injection, minimum amount of CO2 for injection in oxidizer and maximum carbon dioxide injected into oxidizer. The counter flow diffusion flame solver used to steady and axisymmetric simulations. Also, a base condition is used with preheating temperature equal 1400K to deliver results. The obtained results show that injection of carbon dioxide into the oxidizer to reduce the maximum and mean combustion temperature. In the carbon dioxide injection over 80 percent of oxidizer mole fraction, this injection causes the maximum and average temperature reduced than air- fuel combustion with nitrogen injection into oxidizer. As well as, this results indicate that prior to achieve flameless combustion the maximum amount of carbon dioxide injectable into the oxidizer is constant and does not change by increasing of preheating temperature.

In dense occupancy spaces, providing the proper conditions especially as indoor air quality is very important. On the other hand, in most air distribution systems, the ventilation performance and energy saving parameters are greatly influenced by the arrangements of supply diffuser positions. Therefore, in this study, the effects of supply diffuser positions on thermal comfort, indoor air quality and energy consumption in an amphitheater have been investigated. For this issue, a small amphitheater with 50 occupants has been modeled under the conditions that the linear air inlet diffusers located in four situations. The results indicate that the displacement ventilation can provide the proper conditions. However, by changing the location of supply diffuser positions, IAQ and occupants comfort can be improved. For example, for the inlet diffusers are located vertically on the floor, relative ventilation effectiveness is improved about 20% and CO2concentration is decreased about10% in comparison with the other cases.

In the present study, the non-Newtonian fluid flow with the temperature-dependent viscosity over a non-isothermal square cylinder is investigated. Carreau-Yasuda model is utilized to simulate the non-Newtonian properties of the fluid. Non-Newtonian Lattice Boltzmann method, with local computing features, is used to numerical simulate of momentum and energy equations. Grid analysis and validation of results have been successfully completed. Simulations are accomplished for a wide range of parameters including Reynolds number 10< Re < 50, Non-Newtonian index 0.3< n <1, and temperature-thinning index 0< b < 0.5. Simulations show that the proposed method is able to predict the shear- and temperature-dependent properties of Carreau-Yasuda non-Newtonian fluid flow. The results show that increasing of temperature-thinning index leads to reduction and increment of the drag coefficient and Nusselt number, respectively.

In this study, an analytical method based on energy balance equations has been presented to investigate the effects of rifling dimensions on the axial and angular velocities of the bullet. In this method, gun barrel has been considered as a control volume system that maximum pressure due to the detonation of explosive provides its input energy. Also, bullet velocity can be obtained using the calculation of absorbed energy terms by the system like energy due to friction between rifling and bullet along with taking into account the inner ballistic effective parameters. The obtained results of the presented model revealed that rifling twist-rate and barrel length are two important parameters which influence bullet velocity. Increasing these two effective parameters resulted in increasing bullet velocity over a particular range of values and after that has no important effect on bullet velocity. Comparison of the obtained theoretical results with previous experimental and numerical results in the literature showed a surprising agreement.

There are several methods to control an aircraft that one of them is lateral jet. The most important feature of this method is the proper operation at low dynamic pressures. In the present study, the new arrangement of side jets is experimentally by wind tunnel testing. The tests are performed on a standard model. In present scheme, two parallel jets are used at the top and two parallel jets at the bottom of the model. By this combination, pitching and rolling channels can be controlled. In the present study, pressure distribution in upstream and downstream of jet and in the middle of jets have been analyzed. To visualize the shocks, Schlieren method has also been used. The results are presented in the subsonic and supersonic flows, at positive and negative angles of attack. Reducing the pressure in midfield jets in the same position downstream of a jet and keep the pressure area at the upstream of jets are the advantages of this method. This property beside roll control increases the attractiveness of this method.

The current research introduces a rehabilitation active knee brace, equipped by a series elastic actuator, controlled by several patterns, each of them starts by a suitable foot situation in the walking gate. The proper condition to operate the control sub-programs is identified by referring to the signals, emitted by 4 micro-switches, which are installed into the corresponding shoe sole. An orthotics sample is made and its materialization constraints were analyzed. By planning a pilot project, the functionality of orthotic sample was evaluated in laboratory condition. The results indicates that the orthotic sample can be amplified 34 percent the maximum available torque of knee joint. In average, applying the proposed orthosis requires 46.54 W power during mentioned test conditions.

This article examines the factors affecting the optimal model of piezoelectric actuators’ placement around a hole in a plate under tension in order to reduce stress concentration. It has been provided a stiffness ratio in which the parameters affecting piezoelectric actuators’ placement around a hole are shown. this stiffness ratio is introduced with four parameters include modulus of elasticity, thickness of the plate, thickness of the piezoelectric actuators and voltage applied to piezoelectric actuators as the parameters affecting actuators placement around the hole. In this study PSO algorithm was used to examine the optimum placement of piezoelectric actuators. Next, using particle swarm optimization algorithm, a python code is developed to specify the best pattern for actuation around the hole for effect of different parameters. Using particle swarm optimization algorithm, the area and the best location of piezoelectric patches are investigated and the optimum pattern recognition around the hole is presented. Then, the effect of increasing the area of piezoelectric patches on stress concentration reduction is investigated for all percentage area of piezoelectric patches. To analyze the results, the solution of finite element on an experiment was used.

In this paper a level set-based topological optimization method is developed for determining the optimized topology based on the data obtained from solving two-dimensional heat conduction problem using finite elements method. In level-set method, all structural boundaries are parameterized by a level of dynamic implicit scalar function of higher order. Moreover, Allen-Chan equation has been used to update the design variables which have advantages compared to the classic method including letting new holes to be created during the optimization process, ability of removing the re-initialization step and the numerical stability of optimization process. In the present study, the objective function is to minimize thermal power capacity. Sensitivity analysis has been investigated on several heat conduction problems to optimize the topology using level-set and finite element methods. Finally, topological optimization results obtained from 6 heat conduction problems including point thermal load, spread thermal load, nonzero specified temperature on boundaries and the combination of these 3 cases have been presented to demonstrate the validity of the proposed method.

This paper performs a numerical investigation of the viscous dissipation effects on the laminar forced convection of a nanofluid within a horizontal parallel plate microchannel in the presence of a uniform magnetic field. A uniform heat flux and also a uniform magnetic field are applied to the middle section of the micochannel, while the entry and exit sections of the microchannel are thermally insulated. The finite volume method along with the SIMPLE algorithm is used to solve the governing equations. The effects of relevant parameters such as Reynolds Number, solid volume fraction, Hartman and brinkman numbers on the flow and temperature fields and the heat transfer performance of the microchannel are examined against numerical predictions. The results show that the rate of heat transfer decreases with an increase in the Brinkman number. The results also show that in the absence of viscous dissipation the increase of solid volume fraction and Hartman number enhance the heat transfer performance of the microchannel. However, these parameters play a different role in the presence of viscous dissipation.

The solar energy is one of the most promising options for electricity generation to be replaced for fossil fuels. Solar thermal power plants with central receiver system have major advantages compared to the other concentrating solar power systems. To increase the efficiency of these power plants an efficient power cycle, regarding the high temperature of the heat source, can be employed. Accordingly, in the present work, a combined Brayton-ORC is proposed for co-generation of heat and power. Thermodynamic evaluation including energy and exergy analyses for the power plant is conducted. The results show that the gas turbine inlet temperature and concentration ratio have the largest incremental effect on the both energy and exergy efficiencies. The recuperator has the largest exegy destruction and exergy destructin in ORCs’ pumps is the lowest one. Based on the input data, for the proposed combined cycle, first and second law efficiencies, can reach to 61.34% and 73.28%, respectively.

Fiber metal laminates are now very widely used in advanced industries such as the aerospace industry. After introduction of thesematerials, researchers had successfully overcome the disadvantages of metals like corrosion,composites materials such as lowimpact resistance. They combined advantages of metals,composites,used them in a hybrid structure simultaneously. One ofthe most important loading which a fiber metal laminate in aerospace industry is faced, is high velocity impact loading. In this study,it had been tried to increase impact resistance of fiber metal laminates using the exceptional properties of shape memory alloys.Therefore, nickel-titanium shape memory alloy wires are embedded between layers of basalt fiber reinforced epoxy composite andthese layers are entirely covered by two sheets of aluminum type 6061 in top,bottom. The results of high velocity impact testsindicate that by embedding wires, the energy absorbed by the sample,subsequently fracture resistance increases significantly,However, increasing the number of wires does not have significant effect on energy absorption,impact resistance of structure.

Machining and rolling processes are used to produce threads. The thread rolling process is more considered by the producers because of necessity to threads with high quality and strength in different industries. Other advantages of this process are producing without chips and wasting of material with high rate of manufacturing. Because of indicated geometry and small sizes of the threads studying on them is difficultly. As for increasing demands to accuracy, speed and optimization of manufacturing process the regard to the finite elements simulations of processes has been increased by the investigators. At this article making threads on St37 steel pipes has been done. For studying microhardness, texture of material and strength of threads made by thread rolling some tests were design and done. Then the results compared with process simulation results in ABAQUS commercial code and the results got by machining threading process. The results showed that the hardness and strength is significantly improved in the threads made by thread rolling and the hardness of these threads is higher than threads made by machining process.

Internal ballistics include the study of the combustion gases pressure. In the present paper, a numerical method is proposed to predict internal ballistic parameters such as pressure, temperature, velocity and friction force along the length of the weapon tube. The grid generation is done in the Gambit environment and after writing the appropriate code The simulation of the bullet movement inside the tube has been carried out and the behavior of the bullet inside the tube is initiated from the onset of the motion due to the combustion pressure until the bullet is available. It is famous that the ultimate goal in internal ballistic analysis is to determine the relation between speed and range. Here, the factors affecting the optimal speed achievement are fully described. Also, the movement of bullets inside the tube is shown using diagrams and contours. The most important results are about the upward and downward pressure and the temperature behind the bullet. Furthermore, the maximum temperature behind the bullet and its minimum at the tip of the bullet have occurred.

Networks of closed conduits containing pressurized fluid flow occur in many different instances throughout the natural and manmade world. The dynamics of such networks are dependent not only on the complex interactions between the fluid body and the conduit material within each fluid line, but also on the coupling between different lines as they influence each other through their common junctions. The forward modeling (time-domain simulation), and inverse modeling (system parameter identification) of such systems is of great interest to many different research fields. An alternative approach to time-domain descriptions of fluid line networks is the Laplace-domain representation of these systems. In this paper we will consider a pressured fluid line, and we will find an optimized upper bound to the pressure by using Laplace transforms to solve the related differential system.

SERN (Single Expansion Ramp Nozzle) nozzles often used in many aerospace vehicles with scramjet engines. Employment of SERN nozzles results in reducing the frictional drag and weight of nozzle and also they produce extra lift. A numerical study of supersonic gas flow in SERN nozzles is presented in this paper. The Navier-Stokes equations are solved with using a FORTRAN code. The governing equations are conservation of mass, momentums, energy and state equation of perfect gas for two dimensional compressible viscose flow. Equations are solved with using time-marching method. For verification, the results of recent numerical solution are compared with experimental results and results of Fluent and results of method of characteristics (MOC) and comparisons show good agreement with experimental results and other numerical solutions.

Gear pump is one the most common types of static type (positive displacement) pumps with properties such as small size and safe performance. These pumps are mainly used for handling high pressure fluids and flow measuring in hydraulic systems. The most important weakness of this type of pump is high leakage in high working pressures. So, it is important to study the leakage types and the ways to eliminate them in order to decrease the amount of energy lost. In this study, an external gear pump has been studied numerically, analytically and experimentally. Using FLUENT software, the pump leakage, efficiency and power consumption are studied numerically and then have been compared with the experimental data. The numerical results have a good agreement with the experimental data. The results show that the leakage due to a suitable central clearance does not reduce the pump performance. Moreover, this clearance causes the fluid to convey from the space between gears to the high pressure outlet zone without using any decompression slots on the side bearings of the pump. As a result, the flow rate and the pump overall performance are improved.

In this study, the inertial and non-isothermal flow of viscoelastic fluid has been simulated inside the symmetric planar channel with 1:3 sudden expansion. The non-linear form of Phan Thien-Tanner (PTT) has been used for modeling the rheological and complex behavior of the viscoelastic fluid. For creating the non-isothermal flow, temperature values are constant and different at the inlet and on the walls of the channel. To simulate the non-isothermal flow, the PISO algorithm is used and the governing equations are linearized by finite volume method (FVM). Also, fluid properties are a function of temperature and viscous dissipation term has been applied in the energy equation. The main purpose of this study is to investigate the effects of elastic property, inertial force and viscous dissipation on the flow pattern, pressure changes, pressure drop coefficient and loss coefficient for inertial and nonisothermal flow in the expanded part of the planar channel. The results of this study show that increasing the Reynolds number in the range of laminar flow creates an asymmetric flow pattern in the expanded part of the planar channel (unlike the sudden expansion pipe) which plays a major role on the distribution and drop of pressure in this part.

Electrohydraulic forming (EHF) is a high velocity sheet metal forming process in which two electrodes are positioned in a water filled chamber and a high-voltage discharge between the electrodes generates a high-pressure to form the sheet metal. In this work, extensive experimental tests have been designed based on design of experiments (DOE) technique to investigate the effective parameters in EHF. Discharge energy, stand-off distance, electrode gap and electrode diameter have been considered as effective input parameters. Response surface methodology (RSM) has been used to model and optimize the EHF performance with respect to drawing depth. Base on the results, it can be stated that maximum drawing depth is obtained when discharge energy is minimum and other two factors (stand-off distance and electrode diameter) are maximum. There also exists an optimum amount of electrode gap determined according to the process conditions.

Cavitating flow through the nozzle is numerically simulated by using the multiphase lattice Boltzmann method. The pseudo-potential Shan-Chen model is used to resolve inter-particle interactions, modeling phase change between the liquid and vapor phases and imposing the surface tension at the interface. The numerical algorithm implemented is simple for programming and efficient for simulation of multiphase cavitating flows comparing to the traditional Navier-Stokes solvers with complicated cavitation models. Efficiency and accuracy of the multiphase lattice Boltzmann method with Shan-Chen model for simulation of cavitating flows through the nozzle are examined by computing the cavitation inception, growth and collapse and the results obtained are compared with the existing numerical results in the literature. The study shows that the present computational technique is robust and efficient to predict the cavitation phenomena in the geometries studied.

In this research, forming of Bimetal (Al/St) square cups in hydrodynamic deep drawing assisted by radial pressure process has been studied aiming to investigate the parameters and their effects on the thickness of cups. At first, using finite element simulations by Abaqus software, different pressure paths were tried to form the square cup, and experiments were utilized to validate the results. The results showed that lower maximum pressure and lower punch velocity lead to tearing on the sheet contact area with the punch tip. Also, they demonstrated that at higher levels of pressures and punch velocities, the wall thickness distribution of the square cups depends on the pressure path. By applying the pressure path with the desired maximum amount, the square cups with high deep drawing ratio were formed. In the next step, the effect of several important parameters in terms of the desired pressure path was investigated using design of experiments, and the results were interpreted using ANOVA. Among the studied factors, direct effect of the punch tip radius and the interaction of the layers layout and thickness ratio had a significant effect on the minimum thickness of square cups. Finally, the optimal factor values were also obtained.

It is known that friction has a significant effect in determining the ballistic impact performance of woven fabrics. In this paper the ballistic behavior of Twaron Aramid fibers fabrics against high velocity impact of a cylindrical projectile is investigated. Dynamic explicit method using ABAQUS software is utilized to analyze the high-speed impact. For this matter 3D solid elements are used and a VUMAT material model based on maximum stress damage criterion is developed by FORTRAN program. Then using this model, the effects of the friction between yarns on energy absorption of the fabric is investigated. Results indicate that the amount of stress in the fabric is highly sensitive to the friction coefficient between the warp and weft fibers. Increasing the friction between fibers, causes the projectile energy to be distributed among a larger number of threads which increases the penetration time of the projectile in the fibers. In all models, except the case with one layer fabric, higher friction coefficients cause higher energy absorption in the fabric. Moreover, experimental tests were used to validate the model in this project the results have the agreement with the Correlation coeficient determination of 0.94, which verifies the accuracy of the simulation.

The behavior of a bubble in dielectric viscous fluid under electrical field is numerically studied using the lattice Boltzmann method base on the Shan-Chen model. Deformation of the bubble is considered including the effects of buoyancy and electric forces induced from the external applied electric field. A computer code is written to solve the problem, which includes solving the flow field and electric field. To validate the results of the flow field, two tests have been employed: the free-bubble rising test and the Laplace test. In order to check the results of the electric field, the deformation of static drop under electric field is compared with two-dimensional Taylor equation. The comparison of results between present study and previous researches shows that there is a good agreement between the results. The results reveal that the electric field affects and controls the shape, velocity, and location of the bubble. For positive discriminating function, the rising bubble velocity decreases by increasing the electric capillary number, while the reverse trend is observed for negative discriminating function. In higher Eotvos numbers, the increase of electrical field causes the bubble break up for positive discriminating function. Also, larger difference function leads to bubble break up at lower electrical capillary numbers.

Undoubtedly, the flight control system is one of the most important parts of an aeronautical vehicles that has duty of stability and achieve good performance in execution of commands. In flight control according to nonlinear dynamics, time varying and structural and parametric uncertainties of aeronautical vehicles, various control approaches use to achieve stability, good performance and reduce the effect of the uncertainties and modeling error. In this paper, autopilot software design were developed using nonlinear dynamics inversion controller to landing a UAV in two stages. Also, with using DSP hardware and CPU TMS320F28335, nonlinear dynamics inversion autopilot software were implemented and tested to real time PIL stage. Finally, nonlinear six-degree-of-freedom simulation results at real-time, confirm proper performance of implementation.

Composite materials due to their unique properties such as high specific strength and stiffness have gained many applications in automotive, aerospace, transportation and other industries. In this study, the effects of addinggraphene nanoplatelets (GNPs)in various weight percentages (0, 0.1, 0.2, 0.3, 0.4 and 0.5 with respect to matrix) on the flexuralbehaviorof carbon-fiber reinforced epoxy compositeswereassessed. For dispersion of GNPs into the polymer matrix, high speed mechanical stirrer andultrasonic waves were used. Hand lay-up method was used for fabricating the composites, and three-point bendtest for assessing their flexural behavior.Results demonstrated that the maximum improvement in flexural properties was obtained with the optimal amount of 0.4 wt.% of GNPs.The percent enhancements in flexural strength, flexural modulus,and energy absorptionwere 39, 135,and 47, respectively. Also, electron microscopy studies revealed that the addition ofGNPs had a great influence in improving the interfacial characteristics between the matrix and the carbon fibers.

Desalination of the brackish water using a passive solar still with a Phase change materials (PCMs) put under the basin liner of the distillation device is dealt with the help of transient mathematical models. To achieve an optimal system, genetic algorithm is used. In order to estimate the desalinated water in a year, the mass of fresh water in two days of midsummer (7 August) and the midwinter (4 February) was calculated as the typical days in summer and winter. It is assumed that the average amount of water produced in these two days will be repeated for all days at the year. The results showed that mass reduction of saline water is lead to Increase of desalinated water mass. A salt hydrate PCM that its thermal conductivity and density were 0.69 ୵௠.௄ and 1505 ୏୥௠య respectively was selected as the optimal PCM. This type of PCM had a higher thermal conductivity and density than other PCMs. The melting point of this type of PCM is 58°C, which is close to the maximum temperature that saline water reaches in the summer. According to considered limitations for inputs of genetic algorithms, water mass, PCM mass and thickness of the glass, 20 kg, 3.14 kg and 2.15 mm were selected respectively. The maximum amount of annual produced freshwater In optimal mode obtained 1632 kg per square meter of desalination.

In the present work a numerical study of a vertical finned tube heat exchanger in the case of laminar free convection of the ambient air flow was discussed. In this study different geometries of external longitudinal fins (rectangular, trapezoidal, and triangular) with four different temperatures of hot inlet fluid in the pipe was investigated. The simulation has been done with a three-dimensional model and finite volume method. In order to increase the efficiency of pre-selected fin, geometric parameters such as the thickness of the fin, the fin height and the number of fins have been examined and compared. Then the heat exchanger performance for different mass flow rates of hot fluid were evaluated. The result represents an effectiveness for optimal finned tube with a 10% increase compared with optimal reference model.

Photovoltaic panels receive, solar radiation energy, and directly converted into electrical energy. The aim of this study is to evaluate the changes in the electrical power and electrical efficiency by changing environmental condition that photovoltaic cells installed in. The experiment is done in Shahrekord, with a height of 2045 meters. The electrical output power and the efficiency over the four days continuously compared with the same condition, that, three days of this, is in a completely same condition and one day by installing a foil with the size of 12 square meters on the ground. The results show that with installing reflective foil, the radiant flux affects on the surface temperature. By cooling on the panel surface, the electrical power output is enhanced. The efficiency aluminum reflector is used when the maximum at least 5.37 % of the 13.11 percent. While on other days without reflector with the same conditions, minimum and maximum values 11.27 and 15.99 percent respectively.

When a vertical liquid jet impinges on a horizontal solid surface, the liquid will spread radially on screen until at a particular radius the supercritical flow converts to subcritical flow and circular hydraulic jump phenomenon occurs. In present study, this phenomenon was simulated for first time by using Open FOAM software and modified VOF method. Validation of simulation results was performed with the experimental data and the Watson's modified theory and Bohr's approximate solution. The effect of mass flow rate and downstream height were compared in terms of quality and quantity for Newtonian fluid (water) and non-Newtonian fluid (Herschel-Bulkley). The results show that the jumps associated with the Herschel-Bulkley (HB) have smaller radius in compare to water and have low sensitive to changes in flow rate and downstream height. Variation of jump radius in HB fluid decreases with increasing flow rate and downstream height.

Interest in applying flying robots especially quadcopters for civil purposes has dramatically grown in the last decade. In fact, since quadcopters are capable of vertical takeoff and landing (VTOL), they can be widely employed for nearly any aerial task where a human presence is hazardous or response time is critical. This paper is concerned with a tracking control design of a quadrotor via Pole Placement Technique based on presence of a diffeomorphism. To this end, after dynamic modeling of the flying robot using Newton-Euler equations, the state space form of the acquired final model as well as the signal controls are presented. Since the main objective of this work is to track the smooth reference signals, the differential equations described the dynamics of the system, based on our proposed approach, should be transformed from the state space into input-output space. So, the output controllability of the system, as well as the presence of a diffeomorphism between two state spaces are considered, respectively. Finally, a tracking control design via Pole Placement Technique, in the presence and absence of uncertainty, is proposed.

In this study, the buckling behavior of laminated composite plates with and without cutouts subjected to in-plane loading has been investigated. The composite plate with different cutout shapes is subjected to various types of in-plane compressive loads. A numerical study using finite element method (FEM) has been carried out to study the effect of various cutout shapes including circular, rectangular and combination of these two types of cutout shapes. Furthermore, the effects of plate aspect ratio, plate length/thickness (a/t), ply orientation and boundary conditions on the buckling behavior of laminated rectangular composite plates are all considered in the analysis. In order to have a basic reference in our study two analytical solutions based on CLT and FSDTmethods are also have been used to predict the buckling behavior of laminated composite plates without cutouts. An experimental method has been used to investigate the behavior of buckling loads of the composite rectangular composite plates with and without cutouts. Finally, the outcome results of the FE and experimental methods are compared.

In this study, natural convection from the exterior of a longitudinally finned vertical cylinder into the surrounding air was studied. For this purpose, an experimental model was designed and constructed and the necessary measurements were performed on this model. This model was also numerically simulated and in this case many different cases of fin length and fin number were studied and compared. It was tried to find the best thermal and economical case. Based on the results, heat transfer increases almost linearly with the number of fins and their lengths, but the most thermo-economically appropriate case was found to be the case of 8 fins with 10cm lengths. In this case, heat transfer would be about 2.5 times of the no-fin case at a small expense. For the purpose of verification, the numerical results were compared with the experimental results of this work and another work.

Aluminum and its alloys have an ever growing demand in many industries such as aerospace, automotive due to their high strength to weight ratio and corrosion resistance. In this research, in order to improve the wettability and distribution of nano-sized Al2O3particles within the matrix with low agglomeration and to achieve the good mechanical properties, injection of the milled nano- Al2O3/Al composite powder within the molten and mechanical stirring was used. Different mass fractions of nano alumina particles up to 0/3, 0/5, 0/7 and 0/9 wt% were injected into the melt under stirring. The microstructure and mechanical properties of the fabricated nanocomposites were studied. The density measurements showed that the porosity in the composites increased with increasing the mass fraction of Al2O3 Hardness, yield and ultimate tensile strengths of the composites increased with increasing Al2O3 particles up to 0/5 wt% The increase in mechanical properties can be explained by more uniform distribution of Al2O3 in the matrix, and grain refinement. The further addition of Al2O3 particles (>0/5%) particle agglomeration and porosity were the two important factors for decreasing strength and ductility.

In this paper, the simulation of fiber-laser drilling process of Inconel 718 superalloy with the thickness of 1mm is investigated through the Finite Element Method. The influence of process parameters i.e. laser pulse frequency (150 to 550 Hz), laser power (200 to 500 watts), laser focal plane position (-0.5 to +0.5 mm) and the duty cycle (30 to 70%) were investigated in 5 levels and two external parameters i.e. the hole's entrance diameter and hole taper angle, were observed to be the process output responses. By performing the statistical analysis, the input and output parameters were found to have a direct relation with each other. By an increase in each of the input variables, the hole's entrance diameter and the hole taper angel increase. Verification of model was performed by experimental results. The results of the conducted simulations and statistical analyses having been used, the laser drilling process were optimized by means of the desire ability approach. Finally, residual stress simulation of this process was carried out at optimum setting. The residual stress value on the surface of sheet is maximum (0.14 MPa) and this value decreases with increasing distance from the surface of the sample.

Argon or Gas-Tungsten Arc welding (GTAW) is known as an important method of joining metals in industrial applications. Due to the importance of the controlling welding-parameters to prevent any defect formation during the process; in this research, weld-current, pre-heating temperature and electrode-traveling speed are adopted as the input welding-parameters. Then, using the Grey Analysis Method, the effect of the aforementioned welding-parameters on the ultimate-strength, hardness and angular distortions of the welded joints are obtained and optimized. Grey-diagrams are plotted by calculating the Grey-ratio, Grey coefficient and Grey-degree. Finally, based on these diagrams, the effect of the welding-input variables is established in percent and the optimum values are obtained with the effect of input parameters on the output values. Experimental tests are carried out based on the optimum values for the input and output parameters to verify the results of the Grey analyses.

Using OpenFOAM, numerical simulations of two-dimensional flow past a stationary and harmonically pitching wind turbine airfoil at a moderate value of Reynolds number (400000) have been carried out in the current study. Wind turbine blades are subject to different oscillating motions due to unsteady flow around them. Therefore, sinusoidal pitching motion as one of the basic motions in an unsteady oscillation is needed to be thoroughly investigated. This helps to reduce the loads on blades occurring due to dynamic stall phenomenon. The aim of this numerical study is to enhance the accuracy in prediction and analysis of unsteady phenomena around an oscillating NACA 6-series airfoil at near- and post-static stall regions. The experimental data possessed by the presenting authors are considered for validation. In most cases as the results demonstrate, the numerical simulation along with turbulence modelling using k-ω-SST with low-Re correction can accurately capture the physical phenomena related to unsteady pitching motion and hence, highly precise aerodynamic coefficients and pressure coefficients around the airfoil will be obtained at different stall-wise regions.

Conventional machining of Inconel 718 superalloy due to specifications such as high hardness and low thermal conductivity, results in low surface quality and high cutting forces. In this research hybrid high pressure jet assisted machining process was employed to improve machining conditions of this superalloy. To obtain suitable conditions of process applying optimal range of jet pressure proportional to other process parameters is essential. Experiments were conducted in five jet pressures, 1, 50, 100, 150, 200 bar, three cutting speeds, 50, 75 and 100 m/min, two feed rates, 0.05 and 0.14 mm/rev, and 1 mm of depth of cut with full factorial designed to reach possibility of process parameters investigation. By executing the experiments, cutting forces and surface roughness were measured. In order to multi-objective optimization, NSGA-II was employed to artificial neural network models which were trained by genetic algorithm, and optimized jet pressure ranges proportional to other process parameters were obtained. The multi objective optimization results demonstrate that for feed rate of 0.05 mm/rev and cutting speed range of 50-100 m/min, optimal range of jet pressure is 80-109 bar.

In the present study the effect of porous fin on increasing free convection heat transfer rate in a square enclosure is studied numerically. The left wall of the cavity, to which the fin is attached, is assumed to be kept at higher temperature while the right wall is kept at a lower temperature. In addition, the horizontal walls of the cavity were considered insulated. Various pertinent parameters were employed, such as the Rayleigh number, Darcy number, fin inclination angle, porosity, length and position of the fin. CFD method is used to solve the governing equations of this problem. The results is reported in term of Nusselt number. The results of this investigation showed that the presence of a porous fin increases the average Nusselt number on hot wall when compared with the cavity without any fin, for various lengths, positions, and inclination angle of the fin. To achieve optimum heat transfer, the present results suggests that the porous fin should be placed either close to the bottom surface or in the middle of the vertical hot surface and an angle of 90 degree. The results also demonstrate that the increase in porous fin length will result in an increase in the average Nusselt number. It is also observed that increasing the porosity of the fin will increase the average Nusselt number of the hot wall.

Heavy fuel oil (Mazut) has high viscosity that doesn't flow at the ambient temperature and should be warmed up to flow. One of the fuel warming up solutions is the steam tracing system. In this method, a steam pipe with 3/4 or 1 inch diameter is installed in parallel with Mazut pipe connected with specific bounds. The condensate is collected using steam traps installed in a proper distances and returns to the condensate tank. In this paper, the heat transfer process is simulated numerically in the steam tracing system installed on the Masut pile lines using Ansys-Fluent commercial software. Mazut pipes are simulated in different conditions including the pipes without insulation, with insulation and with steam tracing & insulation, and then numerical results are compared to each other. In addition, the effects of different steam temperature on the Mazut viscosity are investigated. It is concluded that steam tracing system is not needed essentially for the short length pipes. Besides, using the steam tracing with the insulation will cause constant fuel oil temperature and this will be critical in cold ambient temperature. Moreover, increasing the steam temperature has little effect on the steam tracing system efficiency so that the higher steam temperature just leads to higher heat loss and reduces the overall efficiency of the system.

The main objective of this study is experimental tests and numerical modeling of forming and annealing processes of CuZn30 brass cylinder. In order to determine the grain size and shape, before and after heat treatment processes, metallography is conducted on the surface of the cylinder and during that, the impact of work hardening to change of the material yield strength, specified. Numerical Modelling of forming stages, have been conducted with the finite element method. The purpose of numerical simulation is to determine the effects of parameters such as friction coefficient, work hardening and anisotropic properties of primary sheet metal on limiting drawing ratio, force exerted on the drawing punch and final geometry. The results show that the friction coefficient have influence on the effective strain distribution, while work hardening exponent have little effect. Force exerted on the drawing punch is affected by changing the work hardening exponent. Some defects are caused in experimental samples, was analyzed by finite element method and the causes of appearing defects identified and were used in experimental tests. On the end, geometries obtained using simulations have been compared and verified with experimental tests. The output results show good agreement with experimental tests.