Study On Pitch Bearing Of The Horizontal-axis Tidal Current Turbine

As the horizontal axis turbine is increasingly and widely used in the tidal current power stations,the horizontal axis turbine with variable pitch is universally regarded because of high efficiency and low starting velocity.An intensive analysis and study has been done in this paper to research the pitch bearing of horizontal-axis tidal current turbines.In this paper,optimal speed ratio coefficient and theoretical external load has been obtained by analysis of capacity usage ratio that effected by variable speed ratio coefficients.Then,based on analysis of theoretical working conditions,the external load that acting on the turbine impeller affected by speed of tide and wave,swaying of ship hull has been comparatively analyzed.Through the theoretical analysis,the relative velocity of impeller has been obtained on actual working conditions.According to the relative velocity,the load acting on turbine impeller has been analyzed under tidal impact condition,in fluid analysis software ANSYS-CFX.Thus the external load analysis has been done,and provided data support for next step study.Through analysis and comparing the characteristics of different kinds of bearings assembled in normal usage,four-point contact bearing has been selected and modeled.Several geometric parameters of the bearing has been discussed based on static bearing behavior,optimized through genetic algorithm.After optimization,ensured the bearing can be working normally under working conditions.After analysis and comparing the statics analysis of the bearing using the hertz theory and FEA,the geometric parameters are validated to be reasonable.The pitch bearing mainly suffers dynamic loads from impact of wave and tide when working in ocean.So transient dynamic analysis for the bearing has been taken to study above conditions.It is validated by the results of the FEA that the capacity of the bearing for anti-wave and impact resistance has certain resistibility.After study the strain and deformation that affected by impact loads,curves of stress-strain behavior of bearing in the load cycle has been obtained.By researching the fatigue life theory of bearings,the lifetime of the bearings of the variable pitch mechanism has been proposed and modified by analyzing all the conditions of swaying,impact of wave and tide,high reliability,material hardness,level of grease contamination,and a modified coefficient.It is verified by the FEM through the modified coefficient and S-N curve that the bearing has adequate service life.