International Journal of Engineering
Volume:26 Issue: 12, Dec 2013

This study develops a fuzzy sliding mode controller (FSMC) based on a variable boundary layer. A fuzzy inference mechanism is used to on-line tune the thickness of the boundary layers of the controller. Minimum rule base has been used for the fuzzy inference system which results in low calculation effort. The aim of this paper is to design a controller which will eliminate the chattering of FSMC while maintains the robustness of the controller. To prove the effectiveness of this method, an experiment has been done using MATLAB/SIMULINK. In this experiment, the results of FSMC with auto-adjustable boundary layers are compared with the results of FSMC with fixed boundary layers and the results of FSMC with sign function. The results of the experiment confirm that the performance of fuzzy sliding mode controller based on auto-adjustable boundary layer method is superior to the fixed boundary layer method.

In this paper, the natural convection heat transfer of Al2O3-EG-water nanofluid in a rectangular cavity which is heated from the bottom and is cooled from the top has been investigated numerically. The governing equations for a Newtonian fluid have been solved numerically with a finite volume approach using the SIMPLER algorithm. The main focus of the current study is on the effects of variable thermophysical properties of nanofluid on the heat transfer in natural convection. The influence of pertinent parameters such as Rayleigh number (Ra=105-107) and volume fractions of nanoparticles (0≤Φ≤0.05) on the heat transfer characteristics of natural convection have been studied. The results have shown that the average Nusselt number is reduced by increasing the volume fraction of nanoparticles. To study the significance of temperature effect on thermophysical properties of nanofluid, the results obtained by using variable properties of nanofluid are compared with those of constant properties.

In this paper, the effect of air turbulence intensity on the flame structure in various radii and lengths of a flame holder numerically studied. Finite volume method is used to solve the governing equations. The obtained numerical results using realizable k-ε and β-PDF models show a good agreement with the experimental data. The results show that flame holder with greater lengths yield shorter flame lengths and higher flame temperature. Also, it is observed that by increasing flame holder radius, flame length slightly decreases at first and then it increases. When holder radius increases, flame temperature increases at first and thereafter decreases. The obtained results indicate that increasing air turbulence intensity results in considerable decrease in flame length, flame temperature, NO formation and temperature gradient in the flame zone.

In this research, at first, the natural frequencies of a cracked beam are obtained analytically, then, location and depth of a crack in beam is identified by neural network method. The research is applied on a beam with an open crack for three different boundary conditions. For this purpose, at first, the natural frequencies of the cracked beam are obtained analytically, to get the examples for training neural network. Then, inversely, the neural network which has been trained by obtained the natural frequencies came from analytically analysis, is used for obtaining the location and depth of the crack. The effect of numbers of natural frequencies as input of the network was evaluated on the prediction accuracy. Results and measure of errors show that the neural network is a powerful method to determine the location and depth of crack. Also, increasing the mode numbers of the natural frequencies give rise the prediction accuracy to be increased

This work deals with the three-dimensional magneto-thermo-elastic problem of a functionally graded truncated conical shell under non-uniform internal pressure and subjected to magnetic and thermal fields. The material properties are assumed to obey the power law form that depends on the thickness coordinate of the shell. The formulation of the problem begins with the derivation of fundamental relations of thermo-elasticity in the conical coordinate system. Subsequently the differential quadrature method (DQM) is employed to discretize the resulting differential equations and transform them into a system of algebraic equations. Numerical results are presented to illustrated effects of non-homogeneity properties of material and thermal loads on the distributions of displacement, stress, temperature and induced magnetic fields. Finite element method is used to validate the results of DQM for a functionally graded truncated conical shell which shows excellent agreement.

In this paper, the effect of various parameters on out-of-phase thermo-mechanical fatigue (OP-TMF) lifetime of A356.0 cast aluminum alloy is investigated. The studied parameters include maximum temperature, dwell time, and the thermo-mechanical loading factor. OP-TMF tests are conducted considering realistic running conditions of diesel engine cylinder heads. The maximum temperature varies between 200 to 275°C and the thermo-mechanical loading factor, which is the ratio of mechanical strain to thermal strain, is considered between 75 to 150%. The dwell time (or holding time) changes between 5 to 180 sec. at maximum temperature. The fracture surfaces of specimens are studied using Scanning electron microscope (SEM). These SEM images reveal that A356.0 alloy has a ductile behavior. The cyclic softening phenomenon is also observed during stress-strain hysteresis loops. The TMF tests results demonstrate that the dwell time bears no significant effect upon the lifetime. However, large influences for maximum temperature and the thermo-mechanical loading factor are depicted in the lifetime of A356.0 alloy.

Due to restrictions on the choice of relaxation time in single relaxation time (SRT) models, simulation of flows is generally limited base on this method. In this paper, the SRT lattice Boltzmann equation was used to simulate lid driven cavity flow at different Reynolds numbers (100-5000) and three aspect ratios, K=1, 1.5 and 4. The point which is vital in convergence of this scheme is how the boundary conditions will be implemented. Two kinds of boundary conditions which imply no-slip and constant inlet velocity, imposed in the current work. For square cavity, results show that with increasing the Reynolds number, bottom corner vortices will grow but they won’t merge together. Also the merger of bottom corner vortices into a primary vortex and creation of other secondary vortices was shown in the cases which the aspect ratios are bigger than one. Also at the case which the aspect ratio equals four, and Reynolds number reaches over 1000, simulations predicted four primary vortices, which were not predicted by previous SRT models. The results were confirmed by Previous MRT model.

In this experimental study, the effect of creating an air jet inside the combustion chamber by establishing an air-cell inside of the piston body at different injection timings in a DI diesel engine has been studied at 2000 rpm and full load operation. The performed tests include studying the Soot and NOx emissions, combustion and performance parameters. The obtained experimental results show that using an air-cell inside the piston causes in simultaneous reduction of Soot and NOx emissions, also advanced injection timing results in increasing of brake power and reduction of brake specific fuel consumption(bsfc) with increasing of maximum pressure in the combustion chamber and maximum value of heat release rate. Also, the results showed that the best time injection for air cell engine is 13 BTDC, in which the NOx and soot emissions decrease by 15% and 50%, respectively, while BSFC and power remains relatively unchanged.

The allocation of design tolerances between the components of a mechanical assembly and manufacturing tolerances can significantly affect the functionality of products and related production costs. This paper introduces Imperialist Competitive Algorithm (ICA) approach to solve the machining tolerance allocation of an overrunning clutch assembly. The objective is to obtain optimum tolerances of the individual components for the minimum cost of manufacturing. The results of ICA were finally compared with the Genetic Algorithm (GA). Based on the results, ICA has demonstrated excellent capabilities such as accuracy, faster convergence and better global optimum achievement.

This paper investigates the induced stresses in circular single deck roofs floating on seismically excited storage tanks. Equations of motion are derived using variational principle. Response of deck floating roofs is evaluated for two different classes of ground motions; near-source and long-period far-field records. Besides time histories and frequency contents for a specific tank, peak value diagrams of stress for tanks with different radii are illustrated. Results indicate two critical locations in the deck roofs: one near the center of the roof and the other along the deck-pontoon interface. It is shown that near-source ground motions produce larger stresses at the inner critical radius of the deck but far-field ground motions lead to larger stresses in deck-pontoon interface. The results could have practical implications in the design process of floating roofed cylindrical tanks.

In this article thermoelastic damping in nano-beam resonators is investigated based on nonlocal theory of elasticity and the Euler-Bernoulli beam assumptions. The governing equation of deflection of the beam is obtained from shear and moment resultants and stress–strain relationship of the nonlocal elasticity model and also the governing equations of thermoelastic damping are established by using, two dimensional non-Fourier heat conduction with one relaxation time based on continuum theory frame. Free vibration of the nano-beam resonators is analyzed using Galerkin reduced order model formulation for the first mode of vibration. In the present investigation a clamped-clamped nano-beam with isothermal boundary conditions at both ends is studied. This nonlocal nano-beam model incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect. The obtained results are compared with the numerical results of the classical thermoelastic models. Thermoelastic damping effects on the damping ratio are studied for the various nano-beam thicknesses and ambient temperatures. In addition to, the study includes computations for different values of nonlocal theory parameter. The results show that with increasing the amount of nonlocal parameter and also with decreasing the length of the nano-beam, difference of the results of classical and nonlocal theory increases.

This article deals with the mechanical analysis of a fixed-fixed nano-beam based on nonlocal elasticity theory. The nano-beam is sandwiched with two piezoelectric layers through it’s upper and lower sides. The electromechanical coupled equations governing the problem are derived based nonlocal theory considering to Euler-Bernoulli beam assumptions and based on the nonlocal piezoelectricity according to the electrostatic Maxwell’s equations. Two piezoelectric voltages are employed to tune the stiffness of the nano-beam. The obtained equations are solved by step by step linearization method and Galerkin’s weighted residual method. The obtained results are compared with the results of the local model, and also the effect of piezoelectric voltages on the non-locality of the model is investigated.

In this article, the radiated noise by a shock-absorber is studied. This particular shock-absorber is used in a heavy-gauge shearing line in order to stop the cut steel sheets. Three steps are followed to evaluate the propagated sound in the surroundings; first of all, the plate vibration response is specified after the impact. Secondly, the edges of the plate are substituted by a set of the monopoles to model the effects of the edges in the sound generation. Thirdly, Rayleigh integral equation is used to calculate the sound generated by the surfaces of the plate. The finite element method is also employed to simulate the problem.

In the present study, the aim is to optimize full and half toroidal continuously variable transmission (CVT) in order to minimize the vehicle fuel consumption (FC) in ECE driving cycle. First, the model of both CVTs’ efficiency is presented. The control strategy of CVTs speed ratio based on minimizing the vehicle FC is introduced, and the algorithm of calculating the vehicle FC is shown. Afterwards, both types of CVT are optimized using Particle Swarm Optimization method (PSO) with the aim of minimizing the vehicle FC in ECE driving cycle, and the optimized geometries are achieved. It is found that a remarkable fuel economy can be achieved through optimization of both types. The effects of the vehicle weight on the optimized geometries are examined. It will be shown that, the optimized geometry of full toroidal type isn’t strongly influenced by the vehicle weight, while the optimized geometry of half toroidal one varies through variation of the vehicle weight.In the present study, the aim is to optimize full and half toroidal continuously variable transmission (CVT) in order to minimize the vehicle fuel consumption (FC) in ECE driving cycle. First, the model of both CVTs’ efficiency is presented. The control strategy of CVTs speed ratio based on minimizing the vehicle FC is introduced, and the algorithm of calculating the vehicle FC is shown. Afterwards, both types of CVT are optimized using Particle Swarm Optimization method (PSO) with the aim of minimizing the vehicle FC in ECE driving cycle, and the optimized geometries are achieved. It is found that a remarkable fuel economy can be achieved through optimization of both types. The effects of the vehicle weight on the optimized geometries are examined. It will be shown that, the optimized geometry of full toroidal type isn’t strongly influenced by the vehicle weight, while the optimized geometry of half toroidal one varies through variation of the vehicle weight.

biodiesel may be economical if produced from inexpensive feedstock which commonly contains high level of free fatty acids (FFA) as an inhibitor in production of methyl ester. In this study a two-step process for biodiesel production from high FFA oil in a batch stirred tank reactor (BSTR) is developed. Oil sample extracted from spent bleaching earth (SBE) were utilized for biodiesel process. In the first step, FFA of the SBE oil was reduced to 3.01% through acid catalyzed esterification following by another reduction to less than 2%. Triglycerides resulted from both steps were transesterified with methanol (molar ratio 6:1) using an alkaline catalyst (1% wt/wt) to produce biodiesel. Major fuel properties of SBE biodiesel were measured to comply with ASTM and En standards. Therefore, an optimized process for production of biodiesel from a low cost high FFA source was accomplished.