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Enhancing the efficiency of gear systems is of significance to reduce fuel consumption and overall weight. Windage power losses become prevailing in high-speed gear systems, such as aero-engine applications. To avoid the shortages and limitations of commonly used methods (e.g. negative volume in dynamic mesh method and one moving object in sliding meshing method), this paper describes an unstructured overset computational fluid dynamics technology to simulate the airflow pattern in a gearbox and calculate the windage losses. A disk, a spur gear and a helical gear, spinning in the air at rotational speed up to 7200 r/min are studied respectively, the windage power losses obtained by the numerical method show good agreement with experimental data and analytical findings in the open literature. Meanwhile, the associated deceleration torques exerted by pressure and viscous forces on spinning gear surfaces are also determined. Furthermore, the overset method facilitates to estimate the windage losses of a non-meshing gear pair. The results of this paper indicate that the overset method can accurately predict the windage power losses and provide a new route to investigate the flow pattern surrounding the gears. This method can serve as an effective tool for engineering applications in the future. [ABSTRACT FROM AUTHOR]

The effect of fluid viscosity and material parameters of the damping layer on the natural frequency characteristics of a circular cylindrical shell covered with free damping layer immersed in a viscous acoustic medium is studied in the present paper. An equivalent method is applied to the damping layer coated on the surface of the cylindrical shell. Then, the wave equation for viscous flow field derived from the linear equations of continuity, Navier-Stokes and state, the Flügge's thin shell theory for the isotropic, elastic, thin cylindrical shell and the appropriate wave harmonic field expansions in association with the pertinent boundary conditions are employed to get the equations of motion and the characteristic equation in the coupled system. Subsequently, numerical analysis is applied to solve the characteristic equation for the coupled system at various material parameters and viscosity coefficients, the influence of which can be illustrated by the calculation results. [ABSTRACT FROM AUTHOR]

The viscosity and filtrate volume of drilling fluid were tested by changing the polyanionic cellulose content in drilling fluid. The effect of polyanionic cellulose on the viscosity and filtrate volume of drilling fluid was analysed. The test results showed that the viscosity of drilling fluid increases with increasing polyanionic cellulose content. When the polyanionic cellulose content is below 1·5%, the viscosity increases slowly, whereas the viscosity increases rapidly when the polyanionic cellulose content is above 1·5%. Equation ( ) is a fitting equation that shows the relationship between viscosity and polyanionic cellulose content. The filtrate volume of drilling fluid decreases approximately linearly with increasing polyanionic cellulose content. Equation ( ) is a fitting equation that shows the relationship between filtrate volume and polyanionic cellulose content. Polyanionic cellulose can effectively improve the viscosity and reduce the filtrate volume of drilling fluid. [ABSTRACT FROM AUTHOR]

Thermal visbreaking of inner Mongolia oil sand bitumen was conducted at several temperatures for different lengths of time in the laboratory. The viscosity of the thermally-treated oil was reduced dramatically with thermal treatment under the condition of adding 0.3 wt% anti-coking agent, the oil sand bitumen reacting at 410°C and 45 min. The kinematic viscosity (100°C) of visbreaking oil is reduced to 138.25 mm2·s-1 and the qualities of it are conformed to 7# Chinese Standard for Fuel Oil, which can directly be regarded as product. [ABSTRACT FROM AUTHOR]