Impact Factor :
1.025
Q1(Year 2015)
ISSN : 1026-3098
e-ISSN : 2345-3605
Published Issues
Spiral heat exchanger optimization using genetic algorithm
2013
Abstract :
This 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.
Keywords :
Heat transfer, Spiral heat exchanger, Multi-objective, Optimization, Genetic algorithm
( 1209 Visit ) ( 218 Download )

An Efficient Concept for Non-dimensionalizing the Duffing Equations Based on the Parameterized Perturbation Method
2013
Abstract :
In 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.
Keywords :
Nonlinear ordinary differential equation; Perturbation method; Characteristic distance; Non-dimensionalization;
( 1251 Visit ) ( 157 Download )

Some Considerations on Higher Order Approximation of Duffing Equation in the Case of Primary Resonance
2013
Abstract :
Here, 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.




Keywords :
Perturbation method; Renormalization group method; higher order approximation; Primary resonance; Duffing equation.
( 781 Visit ) ( 60 Download )

Heat and mass transfer by Natural convection around a hot body in a rectangular cavity
2013
Abstract :


The 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.
Keywords :


Heat and mass transfer; Natural convection; cavity


( 1128 Visit ) ( 107 Download )

Multivariable control of an industrial boiler-turbine unit with nonlinear model: A comparison between gain scheduling & feedback linearization approaches
2013
Abstract :
Due 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.
Keywords :
Boiler-turbine, Nonlinear model, Multivariable control, Gain scheduling, Feedback linearization
( 989 Visit ) ( 90 Download )

Analytical Solution for Large amplitude Vibrations of Micro-beams Actuated by an Electro-static Force
2013
Abstract :


An 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.


Keywords :


Nonlinear; Vibration; Micro-beam; Variational Iteration Method


( 893 Visit ) ( 133 Download )

Numerical Investigation on the External Compressible Flow around NACA m1 and NACA 0015 Airfoils
2013
Abstract :
The 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.


Keywords :
Airfoil; Drag Coefficient; k-ε Model ; Mach Number; Spalart-Almaras Model


( 952 Visit ) ( 119 Download )

Lattice Boltzmann simulation of natural convection in a nanofluid-filled inclined square cavity at presence of magnetic field
2013
Abstract :
In 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.




Keywords :
Natural convection, Inclined cavity, Nanofluid, Magnetic field, Lattice Boltzmann method
( 1050 Visit ) ( 153 Download )

Numerical energy separation analysis on the commercial Ranque-Hilsch vortex tube on basis of application of different gases
2013
Abstract :
In 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.




Keywords :
Ranque-HilschVortex tube; Numerical study; Energy separation; Inlet gases
( 1316 Visit ) ( 196 Download )

Evaluation of the modified 3D free-surface Green’s function for potential flow in a numerical towing tank
2013
Abstract :
What 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.


Keywords :
The Source; Boundary-value Problems; Numerical Towing Tank; Green’s Function; Image Method
( 846 Visit ) ( 57 Download )

A Novel Method for Simultaneous Control of Speed and Torque of the Motors of a Cable Suspended Robot for Tracking Procedure
2013
Abstract :
In 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.
Keywords :
Cable Robot; DC Motor Control; Speed Control; Torque Control; PWM
( 1167 Visit ) ( 118 Download )

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Published Issues
2017
Transactions on Civil Engineering
Transactions on Mechanical Engineering
Transactions on Industrial Engineering
2016
2015
Transactions on Civil Engineering
Transactions on Mechanical Engineering
Transactions on Chemistry and Chemical Engineering
Transactions on Computer Science & Engineering and Electrical Engineering
Transactions on Industrial Engineering
Transactions on Nanotechnology
2014
Transactions on Civil Engineering
Transactions on Mechanical Engineering
Transactions on Chemistry and Chemical Engineering
Transactions on Computer Science & Engineering and Electrical Engineering
Transactions on Industrial Engineering
Transactions on Nanotechnology
2013
Transactions on Civil Engineering
Transactions on Mechanical Engineering
Transactions on Chemistry and Chemical Engineering
Transactions on Computer Science & Engineering and Electrical Engineering
Transactions on Industrial Engineering
Transactions on Nanotechnology

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