مجله مهندسی مکانیک
سال چهل و ششم شماره 3 (پیاپی 76، پاییز 1395)

Applying Roe’s scheme to solve the MHD equations leads to reduction of the numerical viscosity and growth of the accuracy. By increasing 2 dis I m ɺ in MPD thruster that accompanies strong expansion near the electrodes tips, Roe’s scheme has failed. In the zones where need more numerical viscosity, hybridizing Roe’s scheme with HLLE method provides a stable solution and limits the numerical viscosity in the other zones. To achieve a high-resolution method, new modification of MUSCL technique has been employed. This method is called OMUSCL2 technique which has lower dispersion and dissipation errors. For validation of developed algorithm, the Princetonfull-scale benchmark thruster, with cathode length of 7.62cm , mass flow rate of 6gr s and total discharge current of 15.3kA , has been simulated.The comparison of the predicted results of magnetic field and enclosed current with the measured data shows good qualitative and quantitative agreement.The calculated thrust is 52.67 N which showsabout6% difference compared with measured value. Furthermore, this simulation properly predicts the experimentally exhaust plume structure.

Todays, in Power Plant Industries, hydraulic coupling are frequently used for transmission of power from electromotors to pumps and fans. However, because of the oil trap in the coupling and continuous operation the properties of the oil change and early destruction of coupling happens. Consequently, this problem can be delayed by precise analysis of thermal and hydrodynamic behavior of coupling and also using a proper cooling system. Thus, in this paper, thermal and hydrodynamic behavior of a mixture of oil and air in a hydraulic coupling, because of the 3D-geometry and complicated flow, is simulated by FLUENT software. The aim of this study is to identify locations of the secondary flows and vortex which have the greatest role in heat-generation. Also, the areas of fluid and body with high temperature will be determined. In this simulation, the internal flow in the coupling is examined in 3D, two-phase, and turbulent conditions. The velocity and temperature distribution of the fluid flow and the temperature distribution on the body of coupling are analyzed. The results indicate that the maximum temperature is occurred at the outside diameter of turbine coupling, increasing the distance between the pump and turbine increases the thermal dissipation around 65KW and increases the maximum and mean temperature of oil, and displacing the fins can reduce the thermal dissipation around 8KW.

Without any doubt, energy production based on renewable energies is one of the most effective methods in the near future. Solar chimney power plant is a relative novel technology for electricity production from solar energy. The solar chimney power plant is a simple power plant which is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated thermal energy is converted into kinetic energy in the chimney and ultimately into electric energy using a combination of a wind turbine and coupled generator. In this study, a 3D-numerical method is used to evaluating of Stack height on solar chimney power plant operation and then presenting a matched relation between height and power generation. The results show that the stack height has direct influence on flow field characteristics and then on the power output of power plant.

In this study, changes in velocity and turbulence energy in the wake of a Peugeot model and the drag coefficient changes in an Unsteady Flow, with increasing vehicle speed (inlet velocity), are Measured and evaluated. The blow open circuit wind tunnel to simulate fluid flow is used. The maximum disturbances and nominal maximum speed of the device, respectively are, 0. 1% and 30 m / s. The inlet wind velocity has been increased continuously by an inverter that causes the changes in rotational speed of the wind tunnels electro motor. The results showed three different regimes in the velocity profile of the near wake model. With increasing distance from the model and with increasing velocity, three regimes in the wake are close to each other. Turbulence intensity is measured in the wake and drag coefficient decreased with increasing the flow Speed and reached to a minimum value and then increased.

In this paper buckling and free vibration behavior of functionally graded nanoplate resting on elastic foundation is investigated. Small scale effects are taken into consideration with employing elasticity nonlocal theory. The governing equations of functionally graded nanoplate are derived based on the Hamilton's principle and solved by using Navier method for boundary conditions simply support. Mechanical properties of the functionally graded nanoplate are assumed to vary continuously along its thickness according to a power law function. The elastic foundation is modeled as two parameter Winkler-Pasternak foundation. To show the accuracy of the present analytical solution, present results are verified with the results available in the literature. The effects of nonlocal parameter, power index, thickness, Winkler and shear module parameters on the critical buckling load and natural frequency of nanoplate are investigated. The results is shown that the natural frequency and critical buckling load decreases with increase in the aspect ratio, nonlocal parameter and index power. Also Winkler and Pasternak foundations lead to incre ase structure stiffness.

Micro turbines are indeed very small gas turbines (25-300 kW) that usually have thermal regenerator or recuperator to minimize the energy consumption. In currently working plants, the air entered into the compressor is compressed and then is preheated using the heat of turbine exhaust gases in a recuperator. One of the methods to enhance the performance of the gas turbine is using a heat exchanger to recover the energy of hot gases leaving from gas turbine. To recover heat in gas turbine industry different devices have been used. In general, heat recovery devices are divided into two groups i.e. i) regenerators and ii) recuperators. Regenerators act periodically and at the first time interval it absorbs the heat of turbine exhaust gas in the heat exchanger matrix and in the next time interval transfers heat to the cold dense air leaving the compressor. In contrast, Recuperators are heat exchangers that transfer heat into compressed air continuously and use the energy of exhaust hot gases. This paper investigates the thermodynamic of microturbine. The results show that adding a recuperator increases the cycle thermal efficiency significantly. Also this paper investigates the effect of recuperator materials on the micro-turbine performance and the turbine inlet temperature as the most effective factor to increase the performance. The thermodynamic equations were solved by an engineering software EES2013. Considering the results show that at the pressure ratio of 4.29 the thermal efficiency is maximum and adding a recuperator decreases the fuel consumption rate 45 percent in the combustion chamber.

This paper presents simulation results of gas leakage from damaged gas pipeline in steady-state, one dimensional and adiabatic flow with considering AGA equation of state. Damaged pipeline are considered as either complete failure or hole in the pipeline wall. Aim is to get the leaked gas flow rate from the damaged area with real gas properties and compare it with prefect gas. For this purpose, integral and differential methods for solving the governing equations with considering real gas properties were investigated and the result show that for considering variable compressibility factor along the pipeline, equations should be solved by the differential method. Damaged pipeline is considered in transmission line, Supply and distribution network. The results show that in the transmission line the predicted leaked gas mass flow rate using the perfect gas deviates from the real gas by -%9.26 and then real gas properties should be used in simulations. But in supply and distribution networks the deviations are respectively -%1.67 and %0.41 and then perfect gas properties can be used in simulations.

In past years, efforts to reduce the effect of wing tip vortices and reduce drag on aircraft has attra cted many scientists of the world. One of the important activities carried out in this regard is installation of winglet at the wi ng tip. Nowadays, purpose of many researches is to achieve the best installation of winglet at different angle of attack. Some paramete rs such as speed or angle of attack, changes in different phases of flight. In t his study winglet with two angles of 30 and 60 degr ees mounted on P3F aircraft half wing model and its effects on the reduction of drag compared with wing without winglet. Tests has been conducted at Shiraz University of Technology Wind tunnel at three speed s 15 , 20 and 25 m/s , and with different angle of attacks namely: 0 , 3 and 7 degrees. The results of experiments show the drag f orce reduction due to using winglet with different cant angles. It is also shown that by changing flight conditions, to achieve a fa vorable situation, we need to change the winglet ca nt angle. Based on the results, the winglet with 60 degree cant angle, decreases dr ag about 8 %. and with 30 degree cant angle, decrea ses drag up to 4 %.

Metal hydrides can be used for ambient cooling and heating because of their exothermic and endothermic reaction with hydrogen. This is the first attempt to investigate the cooling capacity of compressor driven metal hydride heat pumps (CDMHHP) using a two-dimensional model. In the last studies, only one-dimensional models have been used for studying the application of CDMHHPs. The simulation results have been compared with experimental results and a good agreement have been observed between them. Then the effect of compressor type and hydrogen adsorbent on the performance of heat pump have been investigated. The results show that the device efficiency significantly depends on compressor performance and using the two-stage compressor can improve the device performance compared with one-stage compressor. Also the use of LaNi5 and C5 alloys showed more cooling power in C5 alloy in the same operating condition whereas it takes more cost. Since the power consumption was equal to both alloys, the heat pump containing LaNi5 alloy with tree times larger compressor could generate the same cooling power provided by C5 alloy.

The present study is investigated to checking the effect of cooling film on turbine blade. The geometric model which is used in this study has the same dimensions with the one which was used for the experimental tests by Akkad [1]. At geometric simulation the semi-cylindrical and flat blade attached to it have been used for showing the front edge of the blade. Geometric model is gridded by GridGenTM software and fluid flow is simulated by FluentTM solver. Blowing ratio is defined as a ratio of the cooling mass flux and mainstream. Simulation is done for different values of 0.5 Blowing ratio and 1, and with the k-ε and k-ω turbulence model. It is assumed that the value of the free turbulence intensity at stream is 0/75%. The results show that the cooling film has more efficacies at downstream for low blowing ratio and also in the output adjacency of the cooling jet it can be observed that the blowing ratio growth causes to increase the efficacy of cooling film.

Total activity that is performed by the operator on the tractor seat, affects driver comfort, especially when the critical pressure distribution is in the region of buttocks, so driver posture plays an important role in comfort. Thus, research to model and optimize the angle of inclination of Massey Ferguson tractor seat in ABAQUS finite element software, in order to validate the seat modeling ,output results were compared with experimental results. In this model the tractor seat with five angles of 0, 5, 10, 15, and 20 degrees in the four stimulation acceleration 0.5, 1, 1.5 and 2 meters per second squared in frequency range of 3- 66 Hz was forced vibration and output accelerations in the contact areas of driver's body with seat in three different mass of Iranian Agriculture drivers were obtained from the finite element software .The results of the main factors and the interaction effects in mean variance analysis table on output acceleration in contact areas showed a range of angles of 10 to 15 degrees has been optimized for Massey Ferguson tractor seat, Because these angles in all contact areas of driver's body with seat has not big effect in creating uncomfortable.

In this paper, a new methodology is proposed for for active feedback control of drug administration in cancer chemotherapy. In this way, a nonlinear mathematical model is used to describe the dynamics between the tumor cells, immune-effector cells, and the cytokine interleukin-2 (IL-2). The proposed control method is based on the combination of takagi-sugeno fuzzy modelling, parallel distributed compensation and feedback linearization strategies. For this purpose, the control input has two components: a) a part is used to eliminate some nonlinear terms; b) another part is considered to stabilize the reminding nonlinear dynamical model. Then, the direct Lyapunov method is used for stability analysis and stabilizing controller design. Simulation studies on well-known benchmark problems demonstrate the effectiveness of the proposed method.

An automatic ball balancer can automatically balance the rotors with varying unbalance and doesnt need a control system to balance the rotor. These devices are used in rotating machineries that may be switched on/off several times a day, therefore reducing the balancing time becomes a necessary task. Also in practice, due to the offset of the rotor from the shaft mid-span, the gyroscopic effect is created. In one race auto-balancer, impact between balls may cause fracture of the balls and produce malfunction of the auto-balancer. These deficiencies solved by using double-race auto-balancer. Considering pervious researches reveal that the dynamic behavior of automatic double-race ball balancer under the gyroscopic effect as well as optimization of its parameters has not been investigated. In regard these, here, the dynamic behavior of automatic double-race ball balancer under the gyroscopic effect is investigated. The effect of damping ratio and the mass of balls of the automatic dynamic ball balancer on the stability and balancing of the system under the gyroscopic effect have been studied. Finally, using the genetic algorithm, the optimum values of these parameters to minimize the balancing time and converging the Euler angles to zero are obtained.

This article deals with MED-TVC desalination system modeling. Heat of exhaust gas from turbine with a recovery boiler was used in desalination plant to increase efficiency of existing thermal cycle. Use of waste heat leads to reduced fuel consumption and lower prices is to produce fresh water. Mass balance equations, energy and heat transfer of various components by MATLAB code was solved and an optimization process to increase performance and reduce the heat transfer area was performed. To optimize the modeling, genetic algorithm is used, and the results have been obtained with high accuracy. The results show the reduction of heat transfer area (effects and condenser) against increasing system performance.

In this study, numerical analysis of the effect of external flow turbulence and aspect ratio of building on the amount of opening discharge coefficient in natural ventilation is reviewed by modelling. The solution is the use of computational fluid dynamics (CFD) approach by Fluent Software and to understand taken properly of the result of numerical solution, the result of experimental solution that had been obtained by others is used. All the obtained results are gotten in three-dimensional space assuming steady state flow and incompressible fluid. Turbulent model was used is standard k-ε that has the most accommodation with experimental results. At the end of the study, this conclusion was reached that the amount of opening discharge coefficient is increased by increasing the number of Reynolds in opening and with increasing the width to length ratio of building the amount of discharge coefficient decreases. And finally it is concluded that by increasing of the turbulence of external flow, discharge coefficient decrease.

In this paper, the effects of inclination angle on natural convection heat transfer in a square enclosure filled with a water–Cu nanofluid in the presence of a magnetic field have beennumericallyinvestigated. A half of the bottom and left walls of the enclosure are adiabatic and a half of each of them are at a constant temperature T. The right wall is at temperature T and the top wall is adiabatic ( T>T ). Discretization of the governing equations is achieved through a finite volume method and solved with a SIMPLE algorithm. Prandtl number of the base fluid is considered to be Pr = 6.2. The results show that the heat transfer increases with an increase in Rayleigh number, but it decreases with an increase in Hartmann number. Increasing the volume fraction of nanoparticles, depending on the Rayleigh and Hartmann numbers may increases or decreases the rate of heat transfer. Also, the results show that the inclination angle can be used as a control parameter for heat transfer in the enclosure and the heat transfer rate has its minimum value for inclination angle at 45o.

In this paper the Lattice Boltzmann Method based on Brinkman-Forchheimer equation is applied to simulate flow past a square cylinder covered by a porous layer. The porous media effect is incorporated as a force term in the lattice Boltzmann equation. The method is tested against fully porous Poiseuille, Couette and lid-driven cavity flows. Upon comparing the results with the analytical and numerical data available in the literature, a satisfactory agreement is observed. Then, a detailed investigation on the flow past a porous covering square cylinder is presented. The Reynolds number ranges from 20 to 250 and Darcy number from 10-2 to 10-6 .The numerical results shows that selecting appropriate porous parameters can postpone vortex shedding and reduce Strouhal number and drag coefficient. Results show that the drag coefficient and Strouhal number are smaller for large Darcy number and small porous layer thickness. For low Reynolds number (

A variant to traditional liquid-phase sintering is to use prealloyed powders, which are heated to a temperature between the liquidus and solidus. The liquid forms inside the particles and spreads to the particle contacts. The liquid volume fraction increases with increase in sintering temperature and time and decreases rigidity of the sample. Beam bending test is the technique for measuring viscosity of the samples. In this paper, measurement of viscosity and its influence on the deflection behavior of LeadBronze pre-alloyed beam in different sintering temperatures was studied. Beam bending analysis is performed at various temperatures and times ranging from 845 to 865 °C. The midpoint deflection was measured by the in situ bending images. The viscosity as a function of the deflection rate, density, span length and height was measured by mathematical relations. It is concluded that increase in liquid volume fraction due to increasing temperature, decreases viscosity and then rigidity of the sample. Finally the deflection of Lead-Bronze beam as a function of time is linear and in the case of temperature is nonlinear and deflection rate increases with increasing time.

Investigations illustrate that fatigue behavior, corrosion resistance and failure behavior are one of the most common results affected by residual stresses. The shot peening process which causes compressive residual stress (CRS), is one of the ways to improve the performance of industrial components, especially weld joints with tensile residual stress. In the present paper, numerical analysis of parameters of shot peening process on residual stress distribution is employed on pre-stressed specimen. On one hand, the numerical simulation of this process is investigated. On the other hand, the surface CRS and the effective parameters of this process, by simulating it on the welded specimen, are investigated on and around the welding region. In each section, numerical results were verified not only with former numerical investigations but also with building a proper empirical specimen and measuring the stresses experimentally. Results illustrate the decrease of tensile residual stress or increase of CRS on the surface of the pre-stressed specimen after shot peening process. Moreover, it shows that parameters of the shot peening process have a significant impact on final stresses in the specimen. Besides, based on the results the maximum CRS goes up by increasing the diameter and velocity of the shot.

A variant to traditional liquid-phase sintering is to use prealloyed powders, which are heated to a temperature between the liquidus and solidus. The liquid forms inside the particles and spreads to the particle contacts. The liquid volume fraction increases with increase in sintering temperature and time and decreases rigidity of the sample. Beam bending test is the technique for measuring viscosity of the samples. In this paper, measurement of viscosity and its influence on the deflection behavior of Lead-Bronze pre-alloyed beam in different sintering temperatures was studied. Beam bending analysis is performed at various temperatures and times ranging from 845 to 865 °C. The midpoint deflection was measured by the in situ bending images. The viscosity as a function of the deflection rate, density, span length and height was measured by mathematical relations. It is concluded that increase in liquid volume fraction due to increasing temperature, decreases viscosity and then rigidity of the sample. Finally the deflection of Lead-Bronze beam as a function of time is linear and in the case of temperature is nonlinear and deflection rate increases with increasing time.

The subject of fossil fuel consumption and air pollution is one of the important Challenges in the world now, and the most important consumption and pollution reduction, since it use battery and electric motor beside combustion engine and because of this the engine can work with optimum its performance and brake energy regeneration. In this regard, this article main purpose is the performance comparison between electric hybrid and common gasoline cars using computer simulation. First common gasoline car was simulated for ECE and EUDC and Tehran highway driving cycles for the results validation and its fuel consumption was compared with the experimental. Also for more confidence of simulation results, the fuel consumption compared with results of another reference results that this vehicle had been simulated with other software in ECE and EUDC driving cycle’s. After ensuring software validation, full hybrid car with series structure and mild hybrid car with parallel structure designed and simulated in considered driving cycles. Results of simulation showed that the series full hybrid car fuel consumption in comparison with parallel mild hybrid one has 68.6% greater reduction in ECE driving cycle and 9.7% greater reduction in EUDC driving cycle and 29% greater reduction in Tehran driving cycle. Also the results of simulation showed that the series full hybrid car fuel consumption in comparison with gasoline car is 49% and in comparison with parallel mild hybrid one is 20% factor specific in big cities is fossil fuel cars exhaust emissions. Hybrid electric cars are one of the new technologies in fuel.

In this study, the aerodynamic parameters in static and dynamic mode of a blade in a MAV empirically study, the performance characteristic curves are extracted, and then the identification of propulsion system of a quadrotor is done. To supply needed data for identification process, a measurement setup is designed and built. The setup is able to measure all aerodynamic parameters of propeller and input and output of motor. In propeller modeling, all characteristic curves of propeller in static and dynamic mode is measured and analyzed. These characteristics include power, propulsion force and efficiency of blade is determined by the rotational speed of the motor. System identification is divided to two parts: propeller identification and motor identification. For identification of motor, recursive least square algorithm is used. Identified model for motor shows the relationship between voltage and angular velocity of motor. Finally, the review was done on the engine and propeller, the entire complex has been identified. Propulsion series linear model obtained in this study can be used in modeling quadrotor. Eventually identified motor is compared with identified motor by De Lellis. The comparison validated the identified motor at this research. Also the comparison of present that used model has one step and test to identification passive parameters. On the other hand, this model is very simple and efficient.

In the present work, numerical simulation with Reynolds stress model has been developed to study the thermal performance of square channel with various-shaped 90˚ ribs fixed on walls in staggered pattern. The simulations were performed for three type of rib shapes, i.e., square, trapezoidal, and trapezoidal with decreasing height in the flow direction. The Reynolds number is 25,000 and rotation number is 0.12. The simulation indicates the distribution of thermal performance in one period of ribs. The results show that features of the inter-rib distribution of heat transfer coefficient are strongly affected by the rib shape and trapezoidal ribs provide higher heat transfer enhancement and pressure drop than the other ones. Trapezoidal rib efficiency is 40.62% higher than smooth channel and 2.6% higher than square rib.

In this work, a novel solar greenhouse is investigated. The curved roof of this greenhouse is equipped with a special cover reflects NIR and lets PAR to pass, according to the fact that NIR is unnecessary for the photosynthesis process and PAR is vital for plants growth. Reflected NIR is concentrated in the focal line of curved roof. In the roof focal line, a pipe containing water and Phase Change Material (PCM) is improvised that gathers reflected Energy. Numerical analysis is done for solar irradiance on this greenhouse at 4 days from four different seasons. The results reported as temperature contours and stream lines. Studies reveal that by using a proper isolator in the walls, we can provide whole of needed heating energy all over the year with saved energy in the storage system and there will be no need to more cost for the heating purposes.