Modares Mechanical Engineering
Year:2010 | Volume:10 | Issue:2|Papers Count:9

The most important application of explosive welding in cylindrical geometry is cladding of cylindrical surfaces in order to increase corrosion and wear resistance and also improving the mechanical properties of bimetal product. In this study, the explosive welding of bimetal tubes made of steel and Phosphor-Bronze was investigated using two explosives (TNT and Amatol 5-95) with different explosion velocity. At first the explosive window of two metals was achieved using the theoretical experimental relations, and then using different experiments, the key role of explosion velocity and also the position of selected parameters of explosive window in the metals weld ability were determined. At the end, the successful method of manufacturing of this bimetal tubes is presented and commented upon.

In end milling operation, cutting forces induce vibration on tool, work piece and clamping devices which affects surface integrity and quality of the product. In this process, to select the optimum end mill and machine tool, the prediction of exact cutting forces is of prime importance. In the present work, modeling and simulation of cutting forces in end milling operation are performed. Instantaneous chip geometry is predicted using a 3D simulation software, the effect of cutting depth and feed rate are calculated and cutting conditions are predicted before any machining operation.

In this article sub-grid modeling of Smagorinsky and Localized Smagorinsky Models are investigated. In modeling sub-grid scales, it is necessary to determine the Smagorinsky coefficient which is an experimental constant. Dynamic Models are developed to estimate this value more efficiently. In this research, the test filter is Gaussian, numerical method is based on the finite volume scheme, and a SIMPLE algorithm is used to evaluate the pressure. To perform computations on a personal computer, value of Reynolds number had chosen enough low to make a two dimensional modeling and comparison with respective experimental results possible.Comparison of numerical results shows high accuracy of the localized dynamic models. More numerical investigations reveal that although localized dynamic models need more computing time, but the higher resolution of the method makes it possible to use a coarser grid and hence compensate the extra CPU time.

Numerical solution for mixed convection combined with surface radiation in an inclined channel containing three protruding heat sourcesis investigated in this article. This combinationre present printed circuit boards in electrical equipments. Air is assumed to be the working fluid which is laminar, steady, incompressible and thermally and hydrodynamicaly developing. Governing equations are discretized using the F. V. method in a staggered domain and simple algorithm is used to couple velocity and a pressure. Numerical results presented for temperature and velocity contribution and maximum temperature that occur in chips for different valuesof fan velocity as Reynolds number 150< Re< 1400 and heat generated in chips as Grashof number 1< Gr < 1.2x107 and channel installation angel 0 <f< 90. Main emphasis in this article is comparison between vertical and horizontal design of electrical equipments. According to results in natural convection regime maximum temperature decreases as channel angel increase from 0 to 90 but in forced convection regime, maximum temperature increases 30 centigrade.

This paper presents a finite element solution for the static analysis of a multi-layers beam with and without piezoelectric layers. The beam is under large deformation. The virtual work principle and the Lagrangian update method (LUM) have been employed to study the static behavior of piezoelectric beams. Four-nodes element with two displacement degrees of freedom and one electrical degree of freedom has been used in this analysis.Finally, in order to prove the validity of the presented formulation and the solving process, the results are compared with the other available data.

This paper presents the effect of tilt angle on static and dynamic performance characteristics of two gaslubricated noncircular journal bearing configurations, namely two and four lobe bearings. The linearized system approach using finite element method is used to obtain both steady state and dynamic characteristics. The results of the investigation show that tilt angle has a significant effect on static and stability characteristics. With an increase in tilt angle, power loss is decreased while stability margins are increased.

A passive scalar is a property that is affected by the flow field without affecting it. In this paper, first, the governing equations on the turbulent flows are solved and the property of a passive scalar in two dimensions is numerically studied. Having the values of the velocity components, the governing equation on transport of a passive scalar is solved. To compute the turbulent velocity field, the Large Eddy Simulation (LES) method using Smagorinsky subgrid scale is invoked. The flow in a cavity has been the basis to validate the accuracy of the generated computer code. To ensure the compatibility between the flow and the transport of passive scalar fields a similar LES approach is used. As a three-dimensional numerical solution for a turbulent flow fields needs a massive computational time and efforts, therefore a two-dimensional simulation used for a proper saving. Instead, to validate the numerical results, the range of the Reynolds number of the flow is kept within the range of the two-dimensional measurements. Comparison of the numerical results and the experimental measurements in two-dimension reveals the high accuracy of the results and compatibility between the flow and passive scalar fields. Ability of developed scheme to accurately handle transport of a passive scalar is promising to extend LES method into the transport of more species and hence to simulate reacting flows.

In this research, biodiesel was initially produced from waste vegetable oil by transesterification reaction. The main properties of this fuel were compared with the ASTM D-6751 standard. Then, performance of MF-399 tractor engine was tested and evaluated by using 5 to 25 percent biodiesel and diesel blends. Test results showed that, the power and torque of MF-399 tractor engine were increased, using biodiesel and diesel blends. This is because of good combustion of biodiesel due to high oxygen content of this fuel. There was also a slight increase in the fuel consumption and specific fuel consumption of biodiesel and diesel blends due to low calorific value of biodiesel. Results show that the B5D95 blend has the best performance and the lowest increase in specific fuel consumption among the other blends. The fuel consumption and specific fuel consumption of B25D75 was lower than the B20D80 blend. Therefore, if the goal is using high amount of biodiesel, B25D75 blend is recommended for use in MF-399 tractor engine.