مجله مهندسی مکانیک
سال چهل و چهارم شماره 2 (پیاپی 68، پاییز 1393)

In this study, a numerical study of mixed convection of non-Newtonian fluid and magnetic field effect in constant heat flux boundary condition along a vertical wavy surface is investigated. A simple coordinate transformation to transform wavy surface to flat surface is employed. A cubic spline collocation numerical method is used for present analyses. The effec of magnetic field, amplitude wave length ratio
, the bouyancy parameter, generalized prandtl number and power law viscosity discussed and show graphically as skin friction coefficient, local and average Nusselt number.results show when imposing the magnetic field effect the local and average Nusselt number increase near the leading edge. Also with increasing the generalized prantle number the rate of heat transfer increase and the thermal and velocity boundary layer thickness decrease.

The Influence of landing impact and runway surface roughness on the airplane dynamics have always been considered by aircraft manufactures and researchers. But due to complexity of nonlinear models most of researchers have used linear models to simplify the problem. Also in the researches that nonlinear models have been used, influence of landing impact and runway surface roughness has been studied separately. In this paper, a nonlinear model has been used to model aircraft landing gear system. Also, the influence of both landing impact and runway surface roughness during landing has simultaneously investigated. The results show that considering both of these phenomena simultaneously, cause specific behaviors in systems response. Then the influence of shock absorber stiffness and damping on the airplane nonlinear dynamic during landing on uneven runway is investigated. The results show that there is possibility of loss of contact between the tire and runway for some values of landing gear parameters.

In this research, the influence of stacking sequence and nanoclay Closite30B on mechanical properties of 2D woven E-glass/epoxy laminated was investigated. The specimens of composite laminates with woven glass fiber (WR) were made with four various stacking sequences. They were composed with different weighted percentages of nanoclay such as 0.5wt.%, 1.5wt.% and 3wt.% in optimal specimen of composite laminates. For checking their properties, some points such as tensile test, flexural test and X-Ray diffraction were used. The study of their mechanical properties shows the specimens with ±45 angles had a significant improvement in comparison to other angles. Adding nanoclay caused improvement in mechanical properties of nanocomposite laminates in comparison to composite laminates. The best results were found on specimens with 0.5wt.% and 1.5wt.% nanoclay.

In this paper, modeling and optimization of a plate-fin heat exchanger for heat recovery in simultaneous heat and power generation systems has been studied. Design variables for the optimization of heat exchanger are hot and cold flow lengths, number of layers, pitch, lance length, thickness and fin height. Effectiveness and total annual cost of system (sum of the initial investment cost and performance) are considered as two contradict objective functions. Due to the increase of efficiency (favorite), heat and pressure loss (total annual cost) increase (unfavorable), so instead of a specific answer, it is needed to balance solutions to satisfy all of the objective functions, simultaneously. In this study, the multi-objective Bees Algorithm (MOBA) is used to improve both objective functions and the results are shown as a Pareto curve. Finally, in order to prove the effectiveness of the proposed algorithm, the results are compared with a case study from literature review that is better than the references results in some design points.

Replacement of port fuel injection strategy with direct fuel injection to the combustion chamber is one of the effective methods for fuel consumption and emission reduction. With this strategy the engine would have diesel engines low fuel consumption. Also it would have gasoline engines power. Determination of optimum fuel injection angle in a direct fuel injection stratified charge engine is the object of this research. In this view Iranian nation engine first simulated numerically as port fuel injection using KIVA-3V code. Inlet port injection strategy was replaced with direct injection one hereinafter simulation results was calibrated using experimental data. Then optimum fuel injection was determined for direct injection stratified charge engine. Simulation results show that flow velocity vectors are biger because of fuel direct injection to the cylinder. Ninthy degree is the best fuel injection angle for determined engine condition. In this way air fuel is mixed better. With this fuel injection angle in cylinder pressure and cycle work increased in comparison to other fuel injection angles. Also, unburned hydrocarbons, carbon monoxide and nitrogen oxide emissions reduced in comparison to other fuel injection angles.

Nowadays, AC-current plasma actuators are more preferred to the DC-current plasma actuators in active flow control. So far, almost no research work has been done on DC-current plasma actuator. In this paper, using a direct current power supply and different geometries, plasma characteristics of the both corona and DBD, were studied. Using the results of this study, it was found that the induced flow of the DC current corona is weaker than that caused by AC-current ones, and it has perpendicular components to the flow direction. Also, the induced flow of the DBD actuators is stronger than the corona ones.

The filtering efficiency is affected directly by the pressure drop throughout. In this study, pressure drop and other flow parameters throw the air filter of Peugeot 405 is modeled, numerically. Flow is supposed to be incompressible and turbulent. The k-
turbulent model was used along with first-order upwind scheme for convective terms discretizations. The obtained results show the range of pressure drop between 0.05% and 1.9% depending on the engine speed. This amount of pressure drop is negligible in comparison to the pressure drop in other parts of air feed system. Therefore, one can increase the power of filtering. The numerical results indicate the presence of vortices in the edges of inlet section of filter hose. This vortices leads to decreasing of filtering efficiency. For eliminating the vortices, some changes have been made on the cross section of inlet pipe and its junctin to inlet box. Then the new geometry was analyzed. The results confirm the remove of vortices and a rather small reduction in pressure drop.