Structural Analysis Of Horizontal Tidal Current Turbine Main Shaft

The tidal current turbine as a kind of energy conversion device is still in the initialresearch stage at present. It is different from traditional dam-tidal energy generationequipment and has little effect on marine environment. Nowadays, direct-drive tidal currentgeneration turbine which has advantages of small bulk, low noise and good heat dissipationhas become the trend of future turbine. As the critical connection part of direct-drive tidalenergy generation turbine, the shaft plays a role in transferring impeller torque and bearinghorizontal axial thrust and the weight of transfer component, its damage will seriously affectthe normal work of the unit. The structure analysis and research of the shaft of horizontal-axisdirect-drive tidal current generation turbine are presented in this paper.Based on the actual working conditions of Zhaitang island in Qingdao, the structuredesign of the turbine whose power is200kW is presented in this paper. Hydrodynamiccharacteristics analysis of the blade airfoil in the unit are presented according to momentumtheory and maximum energy capture theory of the impeller, the main design parameters suchas impeller power, torque and axial thrust are calculated when the turbine is under thecondition of nominal flow rate, these parameters provide data support for the shaft strength,stiffness, fatigue life and modal analysis.Firstly, structure design of a kind of horizontal-axis tidal energy generation turbine ispresented in this paper, the turbine select direct-drive pitch type, it is mainly composed of thepitch mechanism, the shaft transmission mechanism, the brake device and the generator. Theload analysis of the impeller is presented under hydrodynamic environment, then the power ofthe impeller, the rotational torque and axial thrust are calculated.Secondly, theoretical design and calculation of the shaft is presented and shaft size ofeach section is obtained. On the basis of the tidal load which is bore by impeller under theactual marine environment, the shaft strength and stiffness are checked with ANSYS software,the analysis results show that the design of the shaft structure meet the strength requirements.Then fatigue analysis model of the shaft is set up by the Palmgren-Miner linearcumulative damage theory. The material property and fatigue load spectrum of the shaft are set. The fatigue cumulative damage of the shaft is calculated under current dynamic loads.The analysis results show that the shaft can meet the15-year fatigue life requirements.Finally, The shaft vibration equation is deduced according to vibration theory ofmechanical kinetics, modal analysis of the shaft considering the impeller quality andcentrifugal force generated by impeller rotation is presented. The analysis results show thatthe front10stages natural frequency and external load vibration frequency of the shaft differ alot, so there is little opportunity to occur resonance in working condition and the runningcondition of the shaft is safe.The paper would provide theoretical support for independent development of high-powertidal current turbine. Meanwhile, it has significant practical value for the unite component’sdesign and analysis.