مجله مهندسی مکانیک
سال چهل و سوم شماره 1 (پیاپی 65، بهار و تابستان 1392)

One of the important compartments in a submarine due to change of the depth is main ballast tanks (MBT). Submarines are usually designed in order to blow compressed air into main ballast tanks. In order to provide an exact model, it is required to determine the relation between weight and buoyancy with blowing air process. In the oceans with non-deterministic conditions, it is required to simulate and test these conditions in a virtual space by the aid of an exact and complete dynamic model. In this paper, a numerical modeling for air blowing into MBTs for a typical submarine is considered and verified with experimental results. The results were shown direct effects of tanks situation, submarine angle about pitch and yaw on air blowing into MBTs. Meanwhile, in case of rising, the submarine made rolling instability being smaller by increasing velocity.

The purpose of this article is investigating the simultaneous and mutual effect of numerical dissipations and vorticity confinement in the regions near and far from the surface. From one hand because of the numerical dissipations due to differencing method and truncation errors, the existence of artificial dissipation or diffusion property is inevitable. On the other hand vorticity confinement acts as a body force source term to the Euler equations, which this also add or subtract the amount of numerical viscosity. However, the effects of these properties are different and thus deeply consideration of these effects on each other and finally on the predictions and the speed of convergence seems to be necessary. The problem is set up for the compressible, two dimensional and steady and unsteady flow around the fixed and pitching NACA0012 airfoil at different angles of attack. From this point of view the attached and highly separated regions of the boundary layer are investigated. The overall goal is that, is it possible to achieve acceptable predictions using only Euler equations with vorticity confinement and suitable artificial dissipations with coarse grid meshes in comparison with Navier Stokes equations with turbulence models and very fine grids? The numerical predictions show that under these conditions with several try and errors satisfactory primary results could be obtained in much less running time.

In this study optimization of objective function of axial compressor by using Genetic Algorithm with weighted method has been investigated. The effects of variations in combination of different weighted coefficients of objective function on optimization have been carried out. The objective function contains linear isentropic efficiency and static pressure rise coefficient by considering mean stage diameter, angle of inlet air at rotor and flow coefficient. In each steps of optimization the fitness function is created by weighted coefficients and the new objective function is produced and the new optimization problem has been established. The effect of variations in weighted coefficients on objective function was studied. Results showed that the objective function has been reduced in each step which explains the optimization has been achieved.

This paper studies the effect of sintering variables such as sintering temperature and time on densification and shape distortion of Cu-28Zn prealloyed powder using response surface methodology. Sintered density and dimensional change was measured to calculate densification parameter, porosity percentage, and volumetric shrinkage and develop mathematical models, consequently. Adequacy of models was evaluated by analysis of variance, which corresponding to a 95% confidence interval. Obtained mathematical models are useful not only for high accuracy predicting of densification and shape distortion but also for selecting optimum sintering variables to achieve the desired properties.

Numerical and experimental evaluation of total drag of a quad cylinder in the vicinity of a flat plate is investigated. A quad of rectangular shape and later a quad with optimal drag are placed near and the inside of a turbulent boundary layer of a flat plate. The drag on the flat plate and the quad are measured separately and compared to the case when they are in similar flow field lonely. The experiment is performed by employing a low speed wind tunnel. The measuring device was a one Dyne accurate load cell. Conclusion is reaveled that when the obstacle closes to the flat plate, the total drag is reduced to a minimum and then increases again at very close to the plate. For the case of square cylinder the minimum distance is about 2.5 millimeter. The same conclusion is arrived to by reforming a numerical evaluation of the same flow fields and results are reported.

This paper presents an explicit finite-volume model which has been developed to study two dimensional incompressible natural convection in a square enclosure filled with Al2O3 Water nanofluid that operates under differentially heated walls. As boundary conditions of cavity, two opposite left and right walls were kept at constant but different temperatures. Also two opposite bottom and top walls were thermally insulated. The Navier-Stokes and energy equations are solved, numerically. Heat transfer and fluid flow are examined for parameters of non-uniform nanoparticle size, mean nanoparticle diameter, nanoparticle volume fraction, Grashof number, Prandtl number and different geometries of enclosure. At this work, for solving of the governing equations an explicit finite-volume procedure and a time-marching method are utilized, and the forth order rungkuta is used for discretizating time expressions. Also instead of the conventional algorithms of SIMPLE, SIMPLEM and SIMPLEC, an artificial compressibility technique is applied for coupling the continuity to the momentum equations. Results indicate that using nanofluid causes an increase in the heat transfer and the Nusselt number. Furthermore; by decreasing the mean diameters of nanoparticles, Nusselt number increases. By increasing R nano particle volume fraction, Nusselt number increases.

In this research the effect of Suzuki Vitara, L90, 206T3 and 206SD Peugeot resonators were investigated to verify vehicle sound level. Experiments were done in form of 4510 factorial by complete randomize design. Type of resonators in four levels, sound amplitude in five levels (0.05, 0.15, 0.25, 0.35 and 0.45) and excited frequency in ten levels (32, 64, 128, 256, 512, 1024, 2048, 4096, 8192 and 16384 Hz) were the factors of these experiments. Results showed that type of resonators and excited frequency had significant effects on vehicle of sound levels. Suzuki Vitara and L90 had maximum and minimum effect on decrement of vehicle sound levels, respectively.