Sharif University of TechnologyScientia Iranica1026-309820520131001Spiral heat exchanger optimization using genetic algorithmSpiral heat exchanger optimization using genetic algorithm144514543402ENM.BidabadiSchool of mechanical Engineering, Iran university of Science and Technology, Narmak, Tehran, 16846, IranA. K.SadaghianiSchool of mechanical Engineering, Iran university of Science and Technology, Narmak, Tehran, 16846, IranA.Vahdat AzadSchool of mechanical Engineering, Iran university of Science and Technology, Narmak, Tehran, 16846, IranJournal Article20130729This paper investigates optimization methods based on genetic algorithms (GAs) for spiral heat exchangers. The purpose of designing heat exchanger depends on its application and could be total cost, heat transfer coefficient or both of them. The current targeting methods identify optimum points from both economic and thermodynamic views and capture a trade-off between two objectives. Optimizations using single objective functions are performed in order to investigate parameter behavior in two different applications of SHEs. Also this work takes care of numerous geometric parameters in the presence of logical constraints. Multi-objective and weighted function optimizations using genetic algorithm are developed in order to obtain a set of geometric design parameters, which lead to minimum pressure drop and the maximum overall heat transfer coefficient. Optimized heat transfer coefficient compared to its first value at basic design had a 13% increase and total cost in optimized case presents 50% reduction compared to the basic design. Also in trade-off cases, heat transfer coefficient and total cost have been improved up to 60% increment and 20% reduction respectively. Therefore, designing heat exchanger using presented optimal methods in this research are proposed as useful methods for designers, engineers and researchers.Sharif University of TechnologyScientia Iranica1026-309820520131001An Efficient Concept for Non-dimensionalizing the Duffing Equations Based on the Parameterized Perturbation MethodAn Efficient Concept for Non-dimensionalizing the Duffing Equations Based on the Parameterized Perturbation Method145514633403ENArefAfsharfardDepartment of Mechanical Engineering, University of Torbat-e-Heydarieh, Torbat-e-Heydarieh, IranAnooshiravanFarshidianfarDepartment of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, IranJournal Article20130727In this paper, ongoing studies to investigate nonlinear ordinary differential equations (ODE) are extended by presenting a new concept in non-dimensionalization process. This concept is illustrated with a practical example of nonlinear ODEs, which cannot reliably solve using the numerical methods. In this paper, two perturbation techniques are used to solve the problem. Effect of varying the dimensionless initial displacement on the accuracy of solution is investigated. It is shown that if the process of non-dimensionalizing is done appropriately, the calculated results will be extremely accurate. Moreover, a new concept called ″behavior of results″ is proposed to find accurate results.Sharif University of TechnologyScientia Iranica1026-309820520131001Some Considerations on Higher Order Approximation of Duffing Equation in the Case of Primary ResonanceSome Considerations on Higher Order Approximation of Duffing Equation in the Case of Primary Resonance146414733404ENS.A.A.HosseiniFaculty of Engineering, Kharazmi University, Mofatteh Avenue, P.O. Box 15719-14911, Tehran, IranJournal Article20130729Here, the higher order approximation of forced Duffing equation is studied. First, using the renormalization group method, the modulation equations of Duffing equation in the case of primary resonance is determined. The resulting modulation equations are identical with those previously obtained by method of multiple scales and generalized method of averaging. Second, the periodic steady state behavior of the solutions and the problem of spurious solutions in higher order approximation are considered. It is shown that depending on the truncation method of original phase and amplitude modulation equations, two types of frequency response equation may be obtained. One possesses spurious solutions for the case of softening nonlinearity and the other for the case of hardening nonlinearity. Furthermore, it is shown that the truncation of thefrequency response equation do not necessarily lead to more accurate results. Finally, by application of root classification of polynomials and Descartes' rule of signs, a criterion is presented to detect the existence of spurious solutions in any point of frequency response equation without solving it. This method is also applicable to other nonlinear systems.Sharif University of TechnologyScientia Iranica1026-309820520131001Heat and mass transfer by Natural convection around a hot body in a rectangular cavityHeat and mass transfer by Natural convection around a hot body in a rectangular cavity147414843405ENG. A.SheikhzadehUniversity of Kashan, Ghotb Ravandi Blvd, Kashan, 87317-51167, IranR.HeydariDepartment of Mechanical Engineering,University of Kashan, Ghotb Ravandi Blvd, Kashan, 87317-51167, IranN.HajialigolDepartment of Mechanical Engineering,University of Kashan, Ghotb Ravandi Blvd, Kashan, 87317-51167, IranA.FattahiDepartment of Mechanical Engineering,University of Kashan, Ghotb Ravandi Blvd, Kashan, 87317-51167, IranM. A.MehrabianDepartment of Mechanical Engineering, Shahid Bahonar University of KermanJournal Article20130729The simultaneous heat and mass transfer by natural convection around a hot body in a rectangular cavity is investigated numerically. The cavity is filled with air and the ratio of body’s length to enclosure’s length is assumed to be constant at 1/3. The differential equations for continuity, momentum, energy and mass transfer are solved using the Patankar technique. The results are displayed in the form of isotherms, isoconcentrations and streamlines and the effects of Rayleigh number, Lewis number and buoyancy ratio on average Sherwood and Nusselt numbers are investigated. The study covers a wide range of Rayleigh numbers, Lewis numbers, and buoyancy ratios. It is observed that by increasing Lewis number, the average Sherwood number increases and the average Nusselt number decreases. Additionally, by increasing the absolute value of buoyancy ratio, the average Sherwood and Nusselt numbers enhance. This work is a novel one in this field in the light of the geometry and the range of dimensionless numbers.Sharif University of TechnologyScientia Iranica1026-309820520131001Multivariable control of an industrial boiler-turbine unit with nonlinear model: A comparison between gain scheduling & feedback linearization approachesMultivariable control of an industrial boiler-turbine unit with nonlinear model: A comparison between gain scheduling & feedback linearization approaches148514983406ENHamedMoradiCentre of Excellence in Design, Robotics & Automation, School of Mechanical Engineering, Sharif University of Technology, Tehran, IranAriaAlastyCentre of Excellence in Design, Robotics & Automation, School of Mechanical Engineering, Sharif University of Technology, Tehran, IranMajidSaffar-AvvalDepartment of Mechanical Engineering, Amirkabir University of Technology, Tehran, IranFiroozBakhtiari-NejadDepartment of Mechanical Engineering, Amirkabir University of Technology, Tehran, IranJournal Article20130729Due to demands for the economical operations of power plants and environmental awareness, performance control of a boiler-turbine unit is of great importance. In this paper, a nonlinear multi input-multi output model (MIMO) of a utility boiler-turbine unit is considered. Drum pressure, generator electric output and drum water level (as the output variables) are controlled by manipulation of valves position for fuel, feed-water and steam flows. After state space representation of the problem, two controllers based on gain scheduling and feedback linearization are designed. Tracking performance of the system is investigated and discussed for three cases of ‘near’, ‘far’ and ‘so far’ set-points. According to the results obtained, using feedback linearization approach leads to the more quick time responses with a bit more overshoots (in comparison with the gain scheduling method). In addition, in feedback linearization strategy, input control signals (valves position) actuate in less time with less oscillations. It is observed that in the presence of an arbitrary random uncertainty in model parameters, the controller designed based on feedback linearization is more robust. Finally, according to the phase portraits of the problem, as the desired speed of tracking process is increased, dynamic system tends to demonstrate a chaotic behaviour.Sharif University of TechnologyScientia Iranica1026-309820520131001Analytical Solution for Large amplitude Vibrations of Micro-beams Actuated by an Electro-static ForceAnalytical Solution for Large amplitude Vibrations of Micro-beams Actuated by an Electro-static Force149915073407ENM.Baghani1School of Mechanical Engineering, College of engineering, University of Tehran, Tehran, IranA.Asgarshamsi2Department of Mechanical Engineering, Sharif University of Technology, Tehran, IranM.GoharkhahSchool of Mechanical Engineering, College of engineering, University of Tehran, Tehran, IranJournal Article20130727An analytical study using Variational Iteration Method (VIM) is carried out in order to investigate the vibrations of electro-statically actuated double-clamped and simply-supported micro-beams. Effects of applied voltage and residual axial load on the nonlinear natural frequency and deflection of the micro-beams are studied. It shows that pre-compression in micro-beams increases the amplitude of deflections for a specific applied voltage. Also, an increase in pre-tension motivates the micro-beam to show more nonlinear behavior in an applied voltage. Predicted results are compared with the experimental data available in the literature and also with numerical results which shows a good agreement. It is concluded that the second order approximation of the VIM leads to highly accurate solutions which are valid for a wide range of vibration amplitudes.Sharif University of TechnologyScientia Iranica1026-309820520131001Numerical Investigation on the External Compressible Flow around NACA m1 and NACA 0015 AirfoilsNumerical Investigation on the External Compressible Flow around NACA m1 and NACA 0015 Airfoils150815163408ENSasanAkbarpour1Department of Mechanical Engineering, Sahand university of Technology, Tabriz, IranMortezaGhorbani2Center for CFD Studies on Heat Engines, Cavitational Flows and Petroleum Industries,Department of Mechanical Engineering, University of Tabriz, Tabriz, IranJournal Article20130729The importance of the external flows around the airfoils got serious when the airplanes with high velocity crashed due to passing the critical Mach number. Those events caused to become clear the significance of the effects of the Mach number on the drag and lift forces. In this paper, the modeling of two standard airfoils for different angles of attack and various Mach numbers are. The external flows around the airfoil are solved by two turbulence models which are Splalart-Alamaras and k-ε models. Both of the airfoils have been modeling for Mach numbers from 0.8 to 1.2 and angles of attacks of 0 and 4 degrees. The pressure and drag coefficients, pressure force for both top and bottom walls of the airfoils are calculated by using the Spalart-Almaras and k-ε models. The results show that, the drag coefficient increases intensively when the Mach number is equal to one, then for a determined Mach number, the drag coefficient is stable. The drag force and coefficient of two above turbulence models in different Mach numbers are investigated and the location of the shock wave phenomenon for the airfoils NACA m1 and NACA 0015 with different angle of attacks is studied.Sharif University of TechnologyScientia Iranica1026-309820520131001Lattice Boltzmann simulation of natural convection in a nanofluid-filled inclined square cavity at presence of magnetic fieldLattice Boltzmann simulation of natural convection in a nanofluid-filled inclined square cavity at presence of magnetic field151715273409ENGH.R.KefayatiSchool of Computer Science, Engineering and Mathematics, Flinders University, Adelaide, AustraliaJournal Article20130729In this paper, the effect of a magnetic field on natural convection flow in a nanofluid-filled inclined square cavity has been analyzed by Lattice Boltzmann method (LBM). The cavity is filled with water and nanoparticles of copper at the presence of a magnetic field. This study has been carried out for the pertinent parameters in the following ranges: the Rayleigh number of the base fluid, Ra=103–105, the volumetric fractions of nanoparticles between 0 and 6% and inclined angle (θ) of the cavity between θ= -60°and 60°with interval of 30°.The Hartmann number varied from Ha=0to 30 while the uniform magnetic field is considered horizontally. Results show that the heat transfer is decreased by the increment of Hartmann number for various Rayleigh numbers and the inclined angles. Magnetic field augments the effect of nanoparticles at high Rayleigh numbers. Negative inclined angles simultaneously decline heat transfer toward θ=0°and the influence of nanoparticle.Sharif University of TechnologyScientia Iranica1026-309820520131001Numerical energy separation analysis on the commercial Ranque-Hilsch vortex tube on basis of application of different gasesNumerical energy separation analysis on the commercial Ranque-Hilsch vortex tube on basis of application of different gases152815373410ENNaderPourmahmoud1Department of Mechanical Engineering, Urmia University, Urmia, IranSeyed EhsanRafiee2Department of Mechanical Engineering, Urmia University of Technology, Urmia, IranMasoudRahimi2Department of Mechanical Engineering, Urmia University of Technology, Urmia, IranAmirHassanzadehDepartment of Mechanical Engineering, Urmia University, Urmia, IranJournal Article20130731In this numerical study, energy separation analysis of a Ranque-Hilsch vortex tube (RHVT) has been investigated for different conditions such as operation of machine under applying different inlet gases. The utilized gases in this study are nitrogen dioxide (NO2), carbon dioxide (CO2), oxygen (O2), nitrogen (N2) and air. The cooling and heating performance in a commercial vortex tube for the mentioned gases has been described in details and illustrated by different curves. The present three-dimensional (3D) computational fluid dynamic (CFD) model is a steady axisymmetric model that employs standard k-ε turbulence model to perform the computation procedure of results. Various key parameters including cold and hot exit temperature differences and energy separation rates are described numerically. The results show that NO2 enhances the greatest amount of cooling and heating capacity among investigated gases. Some of numerical results are validated by available experimental data. Furthermore,a comprehensivecomparison is performed in this article between two different kinds of boundary conditions for cold and hot exhausts i.e. pressure-outlet and pressure-far-field.Sharif University of TechnologyScientia Iranica1026-309820520131001Evaluation of the modified 3D free-surface Green’s function for potential flow in a numerical towing tankEvaluation of the modified 3D free-surface Green’s function for potential flow in a numerical towing tank153815493411ENA.AbbasniaDepartment of Marine Engineering, Amirkabir University of Technology, Tehran, IranMahmoudGhiasiDepartment of Marine Engineering, Amirkabir University of Technology, Tehran, IranJournal Article20130729What is derived in this paper is the potential flow around the marine structures in the numerical towing tank. The Green’s formula and image method is employed to solve the boundary value problem. The Green’s function satisfies the Laplace equation and the boundary conditions on the bottom, walls and free surface. The Green's function consists of three parts. The first part is correlated with spatial spacing between the source and a field point. The second part consists of the free surface disturbance. The radiation condition is dealt with in the third part to ensure that the waves vanish upstream of the source. An infinite series is obtained for each part of the Green’s function using the image method. Effects of the numerical towing tank’s width and depth on the solution are investigated, and the flow patterns due to the presence of a singularity with constant strength in the uniform flow are computed. Uniform motion of a submerged sphere and ellipsoid are simulated and compared with the analytical solutions and other numerical results. Wave profiles are computed for a sphere and an ellipsoid to show the effect of the tank width on the solution.Sharif University of TechnologyScientia Iranica1026-309820520131001A Novel Method for Simultaneous Control of Speed and Torque of the Motors of a Cable Suspended Robot for Tracking ProcedureA Novel Method for Simultaneous Control of Speed and Torque of the Motors of a Cable Suspended Robot for Tracking Procedure155015653412ENM. H.KorayemMechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, IranA.ImanianMechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, IranH.TourajizadehMechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, IranS.KhayatzadehMechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, IranM.MaddahMechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, IranA.TajikMechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, IranS.ManteghiMechanical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, IranJournal Article20130729In this paper, a new method is proposed for controlling the motors of ICaSbot (IUST Cable Suspended Robot) which is a modified version of crane aiming to object handling in industrial environments. In order to provide more accurate tracking, torque and speed of the motors are controlled simultaneously using inverse kinematics and inverse dynamics of the robot. The equations of the motors are evaluated as a look up table by conducting some special experimental tests and calibrations while their data sheets and motor parameters were not available. Required feed forward signal of the motors are estimated by the aid of inverse dynamics of the robot while its error are compensated by the aid of PID controller on the speed and torque of the motor. As a result, required (Pulse Width Modulation) PWM of the motor are exerted to produce a desired angular velocity while a specific amount of torque is applied on the motors. Not only the voltage of the motors is controlled using the mentioned PWM, but also the current are improved using the feedback control of the torques. PID gains are optimized using Ziegler-Nicholsmethod. By the aid of the mentioned combination of feed forward and feedback controlling terms of motor speed and torque, the desired trajectory is tracked with the highest possible accuracy. The efficiency of the proposed method is eventually proved by comparing the experimental tests with simulation results.