Scientia Iranica
Year:2014 | Volume:21 | Issue:1 (TRANSACTIONS B: MECHANICAL ENGINEERING)|Papers Count:7

The movement of charged particles in an electrical field is of practical importance in filtration efficiency and in electrostatic coating. In this paper, both of these applications have been investigated computationally. For the case of filtration, a mathematical model is introduced for the electric filter, which is made of split type fibers. The filter was assumed to be composed of rectangular fibers arranged in a staggered array field. Simulation was conducted to study filtration efficiency. Single fiber efficiencies under various filtration conditions were calculated and compared with results obtained from semiempirical expressions. In the electrostatic powder painting, gas flow and particle flow fields inside a coating booth under given operating conditions are considered and the effects of particle size on their trajectories are studied. Steady state turbulent gas flow is simulated by solving incompressible Navier-Stokes equations and the standard k-e" turbulence model. The discrete phase of particles is modeled based on the Lagrangian approach. In both cases studied here, the flow field and the collection mechanisms were accurately simulated experimental observations.

In this study, the effect of the angle of attack on the aeroelastic characteristics of high aspect ratio wing models with structural nonlinearities in unsteady subsonic aerodynamic flows is investigated. The studied wing model is a cantilever wing with flag, lag and torsion vibrations and with large deflection capability, in accordance with the Hodges-Dowell wing model. An unsteady low speed incompressible air flow is assumed to include the flow time lags. Variations of the limit cycle amplitudes and frequency with free stream velocity at different angle of attacks are carefully studied. For the considered model, the angle of attack has little effect on utter velocity but its effect on limit cycle amplitudes and frequency is considerable. This study shows that the limit cycle amplitudes are very sensitive to variations in angles of attack.

This paper presents a methodology for solving shape optimization problems where the unknown is the shape of the problem domain. The proposed algorithm is based on minimization of the stress along the design boundary calculated by the Modified Fixed Grid Finite Element Method (MFGFEM). Using MFGFEM eliminates mesh adaptation and re-meshing processes, as needed in the standard finite element method, and reduces the analysis cost significantly. In this study, a new approach for computing the stiffness matrix of boundary intersecting elements is also presented and the optimal shape of the problem domain is obtained via a simple optimization algorithm. The performance of the proposed approach is investigated for shape optimization problems. It is concluded that the results of the present method are in good agreement with other analytical and finite element solutions.

A tribological investigation, in terms of the coefficient of friction and wear resistance of refined, bleached and deodorized palm olefin, was conducted using a pin-on-disk tribotester. Palm oil was selected as a candidate due to its superior tribological properties and its large production, which can lead to the mass production of bio-lubricant. The material of the pin and the disk is Titanium (Ti6Al4V). The experiments were conducted following the ASTM G99. The normal load was 9.8 N and the observation time was 1 hour. The sliding speeds were 0.25 m/s and 1 m/s. In this research, only 5 ml of the test lubricant was applied at the beginning of the experiment to investigate the capability of the lubricant to maintain its function. To make sure the lubricant does not subside due to the centrifugal force from the rotating disk, a groove was crafted on the disk. In this research, the coefficient of friction and wear rate were calculated. From the analyses, the coefficient of friction calculated for palm olefin was the lowest for both sliding speed conditions, while the wear rate obtained showed that it was efficient lubricating oil at low speed, with a high wear rate at high speed.

The most important part of the second law of thermodynamics is described as determining the value and source of wasted exergy in processes, and suggests concepts for reducing those losses in order to enhance efficiency. So, the main purpose of this paper is to study the effect of alcoholic additives, load and engine speed on combustion irreversibilities and second law efficiency. The mentioned alcoholic fuel is ethanol, which is combined with gasoline in different percentages of 5, 10 and 15%. The experiments have been done for 2500, 3000, 3500 and 4500 rpm, and 25%, 50% and 75% full load. The results show that, mostly, when alcoholic fuel is used, the combustion internal irreversibility increases and second law efficiency decreases, which is due to the increase in temperature difference between burned combustion products and unburned mixtures, but, an increase in load and engine speeds increases second law efficiency. Another important outcome of the present study is in demonstrating brake specific fuel consumption (bsfc) reduction, due to using recovered exergy from water, whose average value is 14.1%.

This paper presents a new method to generate the cam position commands required for manufacturing a cam profile by an open-architecture CNC machine. At first, the junction points of several connected PH quintic curves, as cam segments, are obtained based on the supposed desired follower motion. Consequently, the desired cam curve is represented via a multi-segment C2 PH quintic curve. After that, a new interpolation algorithm is proposed to generate the position commands required for machining of the cam. The designed cam-follower mechanism is performed for several case studies to evaluate the effectiveness of the employed curve representation and the proposed interpolation algorithm. The simulation results demonstrate that the proposed interpolation algorithm is capable of providing a smooth transition for all regions of the follower motion, and the obtained displacement, velocity, acceleration and jerk profiles match the corresponding desired profiles closely. Therefore, the newly advised interpolation algorithm with a uniform segmentation scheme is not only feasible for generating cam position commands, but also yields a satisfactory performance for the follower motion. Also, the non-uniform rotational segmentation of the cam curve causes the amount of kinematic characteristics of the follower motion to be significantly increased, compared to the corresponding desired profiles.

Conservation of mass, momentum, energy and state equations are recognized as basic mathematical models in analysis of the acoustic behavior of cavitation, as well as super cavitation. Also, it is known that the order of acoustic effects is not as high as that of hydrodynamics. Therefore, in this paper, initially, for comparing different terms of equations, using scale analysis, conservation equations are converted into dimensionless ones. Then, by comparing all conditions, coupled with weighting terms available in those equations, groups of parameters most appropriate with the hydrodynamics and hydro acoustics of the cavitating flow, are selected. By regarding acoustics as lower order phenomena, compared to the hydrodynamics of flow, and simultaneously using the perturbation method, two equations containing leading and first orders and different terms can be attained. Obtained results indicate that leading order equations represent the hydrodynamics of the cavitating flow, and first order equations indicate the acoustics of cavitation or supercavitation. Acoustic equations of the present study contain terms related to fluid viscosity, density and pressure changes, and background flow velocity. As acoustic equations are coupled with leading order equations, in order to find the noise of cavitation, equations of fluid flow for compressible flow should be resolved.