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In this article, effects of Friction stir welding tool rotational and traverse speeds were studied on the temperature distribution, material flow and formation of defects in the welding zone. Computational fluid dynamics method was used to simulate the process with commercial CFD Fluent 6.4 package. To enhance the accuracy of simulation in this Study, the welding line that is located between two workpieces, defined with pseudo melt behavior around the FSW pin tool. Simulation results showed that with increase of FSW tool rotational speed to linear speed, the material flow in front of tool became more and dimensions of the stir zone will be bigger. The calculation result also shows that the maximum temperature and stir of the material was occurred on the advancing side. The computed results showed that with incompetent heat generation, insufficient material flow caused around the pin and defects formed in weld root. The computed results were in good agreement with the experimental results of other researchers. Based on the welding parameters that used in this simulation, the maximum strain rate is predicted between -4(S-1) to +4(S-1) in the stir zone.

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The existing studies of threshing process of combine harvesters adopt the assumption of constant mass, which is contradictory to the phenomenon of separation of grains and short stalks in actual threshing process. Therefore, the characteristics of threshing and separation are not accurately described. Aiming at this problem, this study established the tangential-longitudinal threshing and separation test-bed with tangential-flow device, auxiliary feed beater, and longitudinal-flow device of tangential-longitudinal-flow combine harvester and conducted experiments and analysis of rice threshing with feed rates of 5, 6, and 7 kg s^-1. The results showed that the changes in rates of material flow along the arc-length of concave in tangential-flow device and longitudinal-flow device were equal to the changes in rates of material density with time. In the process of variable-mass and constant-mass rice threshing, when the feeding rates were 5, 6, and 7 kg s^-1 in the test-bed, the flow rates from the tangential-flow device were 4.07, 5.01, and 5.95 kg s^-1, respectively. The average power consumption of the tangential-flow drum in variable mass threshing process was higher than that in the constant mass threshing process by 2.16, 2.73, and 3.09kW, respectively. The flow rate at the outlet of the longitudinal-flow device was 3.34, 4.04, and 4.72 kg s^-1, respectively. The average power consumption rate of the longitudinal-flow drum in variable mass threshing process was lower than that in the constant mass threshing process by 7.32, 10.44, and 12.17kW, respectively. The results of material flow rate and power consumption would offer the basis for the design of longitudinal-tangential flow threshing and separation device.

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In this research, the friction-stir welding (FSW) process was used for butt joining of AA2024-T351 and AA6061-T6 dissimilar alloys. Welding was carried out using a tool with frustum of pyramid pin. The effects of rotational and linear speeds of the tool on microstructure, macrostructure, and mechanical properties of joints were examined. The AA2024 alloy was located in the advancing side due to higher flow stress at higher temperature than the AA6061 alloy, which was located in the retreating side. Macro analysis showed that with a rotational to linear speed ratio of higher than 31.25 revolutions per millimeter the transverse joint section demonstrated tunnel hole defect. With an increase in heat input material flow on different depth levels of joint became more homogenous and the AA2024 alloy’s amount in the stir zone increased. Moreover, with rotational to linear speed ratio of higher than 40 revolutions per millimeter, the effect of deformation rate was dominant, whereas with lower ratios the effect of temperature on grain size in the stir zone was dominant. Application of offset to the tool during welding in the retreating side led to improvement of flow of materials in the stir zone and an increase in friction stir joint strength.

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Numerical simulation of multi material or multi-phase flows are one of the most challenging problems between computational fluid dynamics researches. The main difficulty of these problems is producing some unexpected and non-physical oscillation at material interface which causes entering some error in to computation domain. For eliminating this source of error, many sophisticated algorithm have been proposed recently. By neglecting diffusion processes, Euler equations and HLLC reimann solver are applied. In addition, Level set algorithm is implemented to track interferences between two materials. An accurate, easily developed and low computation cost algorithm, proposed by Abgrall and Karni, is used to prevent generating the oscillations in the interfaces. In the current work, the algorithm is developed to 2 dimensional algorithm. Afterwards, the result of 1 and 2 dimensional code are evaluated to verify the developed algorithm by some standard problems such as sod problem. Finally, shock –bubble (Air – Helium) interaction problem is simulated to investigate the effect of the algorithm in 2 dimensional simulation. The comparison shows that the code and its result have very good accuracy with very low computational cost.