Current Issue : October - December Volume : 2016 Issue Number : 4 Articles : 5 Articles
Artificial granite material has been used for construction of the high-precision machine due to superior damping ability.\nHowever, its lower material stiffness also lessens the application in fabrication of the machine tool. The purpose of this\nstudy was therefore aimed to verify the structure performance of the machine tool reformed with artificial granite material,\ninstead of the casting iron. To gain insight into the optimized configuration of the vertical columns and spindle head\nstock, the static and dynamic characteristics of the machine models with cast iron and granite composites were predicted\nfor comparison. With this, evaluations of the machine with different design were made to examine the experimental\nmeasurements on the prototype machine. According to the simulation results and experimental measurements,\nthe static stiffness of the machine tool reformed with granite material is comparable to the original casting machine, differed\nby 8% approximately. However, granite machine shows superior dynamic stiffness, about 0.5ââ?¬â??1.3 times of the conventional\ncasting machine. This study verifies the feasibility and effectiveness in fabrication of the machine tool with the\nartificial composite material and provides the improvements for further fabrications....
In this study, a novel magnetorheological brake with multi-pole and dual-gap configuration is presented to increase not\nmerely the torque output but also the range of controllable transmission torque while maintaining a compact structure.\nIn addition, the proposed magnetorheological brake design features several individual coils, and lower power consumption\nfor a desired torque output could be obtained by properly controlling the input currents in those coils. Theoretical\nresearch has been done in order to reveal the relationship between the novel structure and the output torque and\nobtain the mathematical formulas of the output torque. Then, based on the theoretical research, finite element analysis\nwas performed to optimize the structure, analyze the magnetic field distribution, and evaluate the capability of the\ndesigned magnetorheological brake. Finally, an optimization was performed to obtain the minimum power consumption\nfor a desired torque. The results show that the proposed magnetorheological brake can generate a considerable torque\ndensity in its dimensions while maintaining controllable power consumption by individual input currents....
Mechanical model with detailed design parameters of a rotor slewing bearing with the structure type of double-row\ntapered roller for supporting the rotor of the wind turbine was presented. The internal geometrical relationships of the\nrotor slewing bearing were established in the Cartesian coordinate system. The elastic contact deformations between\neach tapered roller and the raceways were expressed through the geometrical transformation. The mechanical model\nwas established using the equilibrium relations in the rotor slewing bearing. The safety factor and the fatigue life which\nrepresents, respectively, the ability of resisting the rolling contact plastic deformation failure and the rolling contact fatigue\nfailure of the rotor slewing bearing were obtained based on the solution of the mechanical model. Effects of the\ndetailed design parameters such as axial clearance, contact angle, and roller semi-cone angle on the carrying capacity of\nthe rotor slewing bearing were analyzed. The results show that right amount of small negative axial clearance, increase\nin contact angle, and decrease in roller semi-cone angle are advantageous for enhancing the carrying capacity of the\nrotor slewing bearing. This provides the basis for the reasonable value selection of the design parameters of the doublerow\ntapered roller slewing bearing for supporting the rotor of the wind turbine....
Aimed at studying the casing wear in the highly deviated well drilling, the experimental study on the casing wear was carried\nout in the first place. According to the test data and the linear wear model based on the energy dissipation proposed\nby White and Dawson, the tool jointââ?¬â??casing wear coefficient was obtained. The finite element model for casing\nwear mechanism research was established using ABAQUS. The nodal movement of the contact surface was employed\nto simulate the evolution of the wear depth, exploiting the Umeshmotion user subroutine. In addition, the timedependent\ngeometry of the contact surfaces between the tool joint and casing was being updated continuously.\nConsequently, the contact area and contact pressure were changed continuously during the casing wear process, which\ngives a more realistic simulation. Based on the shapes of worn casing, the numerical simulation research was carried out\nto determine the remaining collapse strength. Then the change curve of the maximum casing wear depth with time was\nobtained. Besides, the relationship between the maximum wear depth and remaining collapse strength was established\nto predict the maximum wear depth and the remaining strength of the casing after a period of accumulative wear, providing\na theoretical basis for the safety assessment of worn casing....
A design for the fail-safe mechanism of a guide vane in a Francis-type hydro turbine is proposed and analyzed. The\nmechanism that is based on a shear pin as a sacrificial component was designed to remain simple. Unlike the requirements\nof conventional designs, a shear pin must be able to withstand static and dynamic loads but must fail under a certain\noverload that could damage a guide vane. An accurate load determination and selection of the shear pin material\nwere demonstrated. The static load for various opening angles of the guide vane were calculated using the computational\nfluid dynamics Fluent and finite element method Ansys programs. Furthermore, simulations for overload and dynamic\nload due to the waterhammer phenomenon were also conducted. The results of load calculations were used to select\nan appropriate shear pin material. Quasi-static shear tests were performed for two shear pins of aluminum alloy Al2024\nsubjected to different aging treatments (i.e. artificial and natural aging). The test results indicated that the Al2024 treated\nby natural aging is an appropriate material for a shear pin designed to function as a fail-safe mechanism for the guide\nvanes of a Francis-type hydro turbine....
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