MODARES TECHNICAL AND ENGINEERING
Year:2006 | Volume:- | Issue:24 (SPECIAL ISSUE ON MECHANICAL ENGINEERING) |Papers Count:13

Two essential steps in numerical simulation of a flow field are discrimination of the computational space and discrimination of the governing partial differential equations (pde's). In the present work a triangular unstructured grid is utilized. Unstructured grids are recognized to be superior for complex geometries as well as for grid adaptation. For discrimination of governing pde's a finite element method is employed. This research presents a new implicit finite element method in a triangular unstructured grid. For convection term of Navier-Stokes equation a conservative upwind method is used, while a finite element method is used for viscous terms. Results are very promising for viscous flows inside a driven cavity.

MSRox is a wheeled mobile robot with two actuated degrees of freedom that has smooth motion on flat surfaces, and has the capability of climbing stairs and traversing obstacles and flexibility toward uphill, downhill and slope surfaces. MSRox with 82.916 cm in length, 54.10 cm in width and 29.249 cm in height has been designed to climb stairs with 10 cm in height and 15 cm in width; ever the less, it has the capability of climbing stairs up to about 17cm in height and unlimited width.In this paper, the motion systems and the capabilities of MSRox are described. Furthermore, experimental results of stair climbing and comparison of the results with others are presented.

The friction materials are generally consisted of homogeneous dispersed friction materials in a metallic based which produced via a process of compaction and sintering of metallic powders, hard materials, and if necessary lubricant. The role of these materials in the components is transferring kinetic energy to heat and generating torque (brakes and clutches).This research is a property investigation of effected parameters in manufacturing of bronze based friction materials which is used in heavy automotive clutch plates, helicopter brakes, and etc. Four compositions were selected for bronze friction materials and different parameters such as compaction pressure, sintering time and temperature on density, porosity, and hardness were studied. The nearest results to imported samples are: compaction pressure of 5 t/cm2, sintering time and temperature of 30 min. and 820 DC respectively. The wear resistant in [mal sample containing 2% of hardened additives was determined by ASTM G-I05 standard and compared with foreign samples. The sample containing WC had the closest property and microstructure with imported samples.

In this research behavior of bubble due to under water explosion and it's effects on ship structure have been studied. For determination of these effects field equations must be derived and solved them by mathematical simulation. Mathematical model is corn in follow, it show physical rules on impression of bubble oscillation on body ship. This model is solved by combination of Euler method, 5 steps Adams-Beshforse method and 4 step Adams-Moltone method for explaining the response of ship structure due to oscillation bubble. In order to agreement of solution way, stress-strain curves that obtained in this paper, is compared with experimental results. Also these results compared with FEMA results. Ship structure is modeled in ANSYS software in free beam form with variable mass and stiffness elements. Internal ship's equipments and buoyancy are modeled by local mass and spring.The effect of explosion depth and explosive mass on stress in ship structure is studied. These result show when explosion depth is increased, stress is decreased and when explosive mass is increased, stress is increased.  

Various thermo mechanical processes have been studied to improve the mechanical properties of 18Ni-Co-Mo steels. In this work, the effect of interpass aneal time on the mechanical properties of the 18Ni-Co-Mo steel was investigated, using the rolling experiments. Hot rolling process was performed in two passes. The reduction of area was 30% in the first pass at 1100°c. After first pass specimens were air cooled to second pass temperature (900°C) and held for various interpass time (2 sec, 5 min and 10 min). The second pass was performed at 900°C for 20% reduction of area. After that, the specimens were directly water quenched to retain the microstructure present at the second pass. Tensile and charpy tests samples were machined from hot rolled specimens. The results showed that grain size was decreased significantly at these conditions by increasing the interpass time from 2 sec to 5 min. This was attributed to the static recrystallization. With an increase in interpass time to 5 min, tensile strength was increased, without significant change in charpy impact energy. Increasing the interpass time from 5 to 10 min, increased austenite grain size. This was attributed to the grain growth. The results indicated that the interpass time of 5 min can be considered to obtain the maximum tensile strength.

The element free Galerkin (EFG) method, which is based on the moving least square (MLS) approximation, requires only nodal data and no element connectivity. These features make the method more flexible than the conventional FEM. Nevertheless, direct imposition of the essential boundary conditions in the EFG method is always difficult because the shape functions obtained from the MLS approximation do not have the Kronocker-delta property.A new method named "the complementary integral method" is proposed here to overcome this difficulty. The presented method is more consistent with the variational basis of the EFG method. Several numerical examples are used to illustrate the implementation and performance of the method.The numerical examples including the Poisson's equation and 2D static and dynamic elasticity problems show that the method converges fast with reasonably accurate result for both the unknown variables and its derivatives.

A 3-D finite element model is presented to study the thermo-mechanical response of thick plate weldments under different multi-pass welding sequences. The Anand's Viscoplastic Model is applied to simulate the mechanical response of weldments.The thermal modeling of welding zone is also carried by applying the isothermal melting pool approach. In this research the temperature dependency of thermal and mechanical properties of material is considered and the welding parameters such as arc movement, welding speed and welding lag between each sequence are simulated. Finally, in the FE model the addition of filler material into the welded zone is modeled using the Element Rebirth Technique (ERT). The accumulated results show that, on specific point as the number of layers of weld increases, a noticeable change occurs in the magnitude of maximum temperature and its time of reach. For the points near to the weld line, this change affects the amount of distortion, and the through thickness stress components but it has no significant effect on the residual stress components which may arise in the plane of plates.  

The complex and stochastic nature of the electro-discharge machining (EDM) process has frustrated numerous attempts of physical modeling. In this paper two supervised neural networks, namely back propagation (BP), and radial basis function (RBF) have been used for modeling the process. The networks have three inputs of current (I), voltage (V) and period of pulses (T) as the independent process variables, and two outputs of material removal rate (MRR) and surface roughness (Ra) as performance characteristics.Experimental data, employed for training the networks and capabilities of the models in predicting the machining behavior have been verified. For comparison, quadratic regression model is also applied to estimate the outputs. The outputs obtained from neural and regression models are compared with experimental results, and the amounts of relative errors have been calculated. Based on these verification errors, it is shown that the radial basis function of neural network is superior in this particular case, and has the average errors of 8.11% and 5.73% in predicting MRR and Ra, respectively. Further analysis of machining process under different input conditions has been investigated and comparison results of modeling with theoretical considerations shows a good agreement, which also proves the feasibility and effectiveness of the adopted approach.