Current Issue : April - June Volume : 2017 Issue Number : 2 Articles : 6 Articles
The contra-rotating fan is an electromechanical device in which electromagnetic force and aerodynamic force coordinate\ntogether. Its operation process is affected by multiple factors and is also coupled with multiple variables. In order to further\nreveal its working mechanism, electromagnetic-fluid coupling model for contra-rotating fan was presented and relevant\nnumerical computations were performed by the combination of the motorsââ?¬â?¢ electromagnetic-field simulation and\nthe fanââ?¬â?¢s fluid-field simulation. Curves of electromagnetic torque and aerodynamic torque in time domain, respectively,\nfor two motors and two impellers of the fan were obtained, and then fast Fourier transform algorithm was used to analyze\ntheir harmonic components. Meanwhile, the resonance effect induced by the same-frequency components between\nthe harmonic electromagnetic and aerodynamic torques was investigated. Moreover, the impellerââ?¬â??motor interaction and\nmatching performance were explored so as to determine the optimal combination scheme of blade number in two-stage\nimpellers. The reasonableness of this scheme was validated experimentally. This heterogeneous physical-field simulation\nmethod targeted at electromagnetic-fluid coupling condition offers an important reference for optimizing the fan system....
Based on the elasto-hydrodynamic lubrication theory, a 2-degree-of-freedom nonlinear dynamic model of helical gears\nwith double-sided film is proposed, in which the minimum film thickness behaves as a function of load parameters, lubricant\nparameters, and the geometry of the contact. Then, the comparison of the hysteresis loops in different gear models\nshows the soundness of the presented model. Using numerical method, the time evolution of lubricant normal force,\nminimum film thickness, and lubricant stiffness is obtained in order to demonstrate the influence of the driving torque\nand pinion�s velocity. The results obtained in this article can contribute to the root cause for the gear vibration and show\nthat the hydrodynamic flank friction has almost no influence on the gear system....
The key parameters which caused the scoring failure of helical gears are operating load and speed. In this study, the\nsimulations using geometric meshing theory were carried out to investigate the effect of load and speed of warship\ntransmission helical gear system on thermal elasto-hydrodynamic lubrication. The numerical algorithm for the analysis of\nthree-dimensional thermal elasto-hydrodynamic lubrication used in this work has advantage that the film pressure and\ndistributions can be calculated from Reynolds equation for all mixed lubrication regions without any specific boundary\ncondition for the edge of solid contact region. Oil film pressure, film thickness as well as film temperature under different\nload and speed conditions were obtained and compared. In addition, experimental tests were conducted to determine\ngear surface temperature under different load and speed conditions. This work provided a guidance to understand\nthe load- and speed-dependent thermal elasto-hydrodynamic lubrication....
A Continuously Variable Transmission (CVT) is a type of transmissions that provides\na continuous range of speed ratios, thus it allows increasing the overall powertrain\nefficiency by running the engine at the optimal operating points. This paper\ninvestigates implementing a model based hydraulic pressure controller to achieve the\ndesired CVT gear ratio. A map of desired gear ratios was estimated using the Optimal\nOperating Line (OOL) strategy, which minimizes the engine fuel consumption according\nto a defined cost function and a set of systems constraints. The controller\nwas implemented in a complete vehicle model that includes driver, powertrain and\nroad load models. The model was subjected to two different driving cycles and the\nresults demonstrate the effectiveness of the control strategy and the pressure controller\nin keeping the engine at the most efficient operating regions....
In this contribution, a four-bar linkage having a variable input velocity is studied, traditionally it is assumed to be constant.\nThe advantages of a variable input velocity mechanism, in contrast to a mechanism driven by constant velocity, are the\nflexibility of the output motion (and/or improved kinematic and dynamic characteristics). The velocity of the crank is\ncontrolled in order to obtain the desired output motion at the coupler point. The input velocity trajectory and the controller\nparameters are considered as design variables, such that the kinematic and dynamic requirements are fulfilled.\nTwo numerical examples are provided to corroborate the result....
This article presents a multi-objective optimization to improve the hydrodynamic performance of a counter-rotating type\npump-turbine operated in pump and turbine modes. The hub and tip blade angles of impellers/runners with four blades,\nwhich were extracted through a sensitivity test, were optimized using a hybrid multi-objective genetic algorithm with a\nsurrogate model based on Latin hypercube sampling. Three-dimensional steady incompressible Reynolds-averaged\nNavierââ?¬â??Stokes equations with the shear stress transport turbulence model were discretized via finite volume approximations\nand solved on a hexahedral grid to analyze the flow in the pump-turbine domain. For the major hydrodynamic performance\nparameters, the pump and turbine efficiencies were selected as the objective functions. Global Pareto-optimal\nsolutions were searched using the response surface approximation surrogate model with the non-dominated sorting\ngenetic algorithm, which is a multi-objective genetic algorithm. The trade-off between the two objective functions was\ndetermined and described with regard to the Pareto-optimal solutions. As a result, the pump and turbine efficiencies for\nthe arbitrarily selected optimum designs in the Pareto-optimal solutions were increased as compared with the reference\ndesign....
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