INTERNATIONAL JOURNAL OF ENGINEERING
Year:2013 | Volume:26 | Issue:12 (TRANSACTIONS C: ASPECTS)|Papers Count:15

This study develops a fuzzy sliding mode controller (FSMC) based on a variable boundary layer. A fuzzy inference mechanism has been used to tune the thickness of the boundary layers of the controller online. To lower the rate of calculation of the controller, a minimum rule base has been used. The aim of this paper is to design a controller which is able to remove the chattering and maintains the robustness of controller simultaneously. To prove the effectiveness of this method, a simulation has been done using MATLAB/SIMULINK. In this simulation, the results of 3 controllers, FSMC with auto-adjustable boundary layers, FSMC with fixed boundary layers, and FSMC with sign function are compared. The results of the simulation 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 heated from the bottom and 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 the variable thermophysical properties of nanofluid on the natural convection heat transfer. The influence of pertinent parameters such as Rayleigh number (Ra=105-107) and volume fractions of nanoparticles (0£F£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-e and b-PDF models show a good agreement with the experimental data. The results show that the flame holders 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 first and decreases thereafter. The 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, natural frequencies of a cracked beam are obtained analytically. Also, the location and the depth of a crack in the beam are identified by neural network method, in this study. This research is applied on a beam with an open edge crack for three different boundary conditions. For this purpose, firstly, the natural frequencies of the cracked beam are analytically obtained to get the examples for training the neural network. Then, inversely, the trained neural network is used for obtaining the location and depth of the crack. The effect of the numbers of the 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 numbers of the natural frequencies causes 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 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 the out-of-phase thermo-mechanical fatigue (OP-TMF) lifetime of the A356.0 cast aluminum alloy is investigated. Studied parameters include the maximum temperature, the 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 275oC and the thermo-mechanical loading factor, which is the ratio of the mechanical strain to the thermal strain, is considered between 75 to 150%. The dwell time (or the holding time) changes between 5 to 180 sec. at the maximum temperature. Fracture surfaces of specimens are studied using the scanning electron microscopy (SEM). These SEM images reveal that the A356.0 alloy has a ductile behavior. The cyclic softening phenomenon is also observed during stress-strain hysteresis loops. TMF test results demonstrate that the dwell time bears no significant effect upon the lifetime. However, large influences for the maximum temperature and the thermo-mechanical loading factor are depicted in the lifetime of the A356.0 alloy.

In this paper, the single relaxation time (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. Due to restrictions on the choice of relaxation time in the single relaxation time (SRT) models, simulation of flows is generally limited base on this method and imposing a proper boundary condition will improve the capability and stability of this method. In this work, bounce back rule is imposed to consider no-slip boundary condition on solid walls and constant inlet velocity proposed by Hou was applied at the inlet side of the cavity. For a square cavity, results show that with increasing the Reynolds number, bottom corner vortices will grow but they won’t merge together. In addition, the merger of the 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. Furthermore, 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. In additon, 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. Furthermore, the results showed that the best time injection for air cell engine is 13BTDC, 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. ICA is a multi-agent algorithm with each agent being a country, which is either a colony or an imperialist. These countries form some empires in the search space. Movement of the colonies toward their related imperialist, and imperialistic competition among the empires, form the basis of the ICA. During these movements, the powerful imperialist are reinforced and the weak ones are weakened and gradually collapsed, directing the algorithm towards optimum points. The objective of present study is to obtain optimum tolerances of the individual components for the minimum cost of manufacturing using ICA. The results 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 in comparison with traditional GA.

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. These critical locations and their stress dependencies have not been reported in previous works. The results could have practical implications in the design process of floating roofed cylindrical tanks.

In this article, thermo-elastic damping in nano-beam resonators is investigated based on nonlocal theory of elasticity and the Euler-Bernoulli beam assumptions. To this end, governing equation of motion of the beam is obtained from stress–strain relationship of the nonlocal elasticity model and also governing equations of thermo-elastic damping are established using two dimensional non-Fourier heat conduction. 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 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 thermo-elastic models. Thermo-elastic damping effects on the damping ratio are studied for the various nano-beam thicknesses and ambient temperatures. In addition, 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 between the results of classical and nonlocal theory increases.

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

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, the 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, a model for both toroidal CVT efficiency is presented. A simulation model of the considered power train is described. The control strategy of CVT 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 each type. The effects of the vehicle weight on the optimized geometries are examined. It will be shown that, the optimized geometry of full-toroidal type is not 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) was 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.