The Optimization Of Blade Design For Horizontal Axis Marine Current Turbine

The research object of this dissertation is blades of horizontal axis marine current turbine(HAMCT),whose efficiency and reliability are crucial to the operation of HAMCT.Aim at the characteristics of heavy load and huge weight,this work studies on the technologies to withstand and reduce the load by blade design and optimization.The work is mainly carried out in three aspects:firstly,the optimization of the hydrofoil specialized for HAMCT,as a result new hydrofoils with high strength are obtained;secondly,to conform the "high efficiency&low load" requirements for hydrodynamic shape of the blade design,the equivalent S-N curve model is presented,which can make a quick estimate of blade fatigue lifetime in the stage of blade design,and this fatigue lifetime is regarded as the quantization of load,so that the load-reduction optimization can be carried out in all working conditions and whole lifetime,thus to find balance between efficiency and reliability;thirdly,the structure and layer design of the blade,take blade weight as objective function,meanwhile take tip deflection,ultimate load,fatigue load and craft requirements as constraint conditions,the process of layer optimization reduces the design redundancy and blade weight,improve the stress distribution and the stiffness of the blade.The full text is divided into the following six chapters.Chapter 1 gives the research background,according to the characteristics of HAMCT,it is proposed to solve the axial load problem from the perspective of blade structure design and optimization.Subsequently,a review on hydrofoil,hydrodynamic design,structural design,and load reduction of HAMCT is made.Finally,the main research content of this paper is presented.Chapter 2 introduces the basic theory and research methods of the blade technologies of HAMCT.Part 1 of this chapter elaborates the blade element momentum theory.Part 2 presents a prototype designed by BEM theory which is suitable in low-velocity condition,and the feasibility of BEM applied to blade design and performance prediction was verified by sea test.In order to guarantee the convergence of the algorithm,in part 3 an amendment is presented when the BEM theory is not available,so that load prediction can be achieved in all working conditions.In part 4,the optimization tools based on genetic algorithm are introduced,including general genetic algorithm and NSGA-II multi-objective genetic algorithm.Chapter 3 presents an optimization process,which takes a multi-objective genetic algorithm as framework,on the shape of hydrofoil to improve the strength of hydrofoil while retaining its hydrodynamic performance,so that it can withstand the axial load.16 parameters are used to represent a hydrofoil,and maximum lift to drag ratio and principal moment of inertia are taken as objective functions for hydrodynamic performance and structure strength respectively.The process results in two new hydrofoils based on NACA 63421 and NACA 63430.The maximum lift-to-drag ratio of the new hydrofoils is the same as that of the original ones,meanwhile the main moment of inertia is increased by more than 30%.Chapter 4 presents the blade design of a 120 kW HAMCT to achieve maximum energy capture whose theoretical analysis and sea test are carried out.Based on the present work,a design method of "high efficiency&low load" is proposed.An equivalent S-N curve model is presented whereby the blade's fatigue lifetime is rapidly estimated along with a simplified load spectrum.The fatigue lifetime is taken as the quantification of axial load.Afterwards,using the maximum energy capture efficiency and fatigue lifetime of the blade as the objective functions,a multi-objective genetic algorithm was used to optimize the original blade.Finally,the optimized blades were analyzed using the Tidal Bladed tool,and the optimized blades were improved in their "low load" performance.Chapter 5 presents the layer design of a 120 kW HAMCT blade using general structure model,and the blade was subjected to field test and sea test.The result shows that general structure model can meet the request of ultimate load.Subsequently the deficiencies of the general model are analyzed and a new method specialized for HAMCT blade layer design is presented,which solve the problem that blade parts such as skin and spar are designed isolated and empirical formula of wind turbine are abused.The new method takes blade weight as objective function and tip deflection,ultimate load,fatigue load and craft requirements as constraint conditions.After layer optimization,the blade weight is reduced,the stress distribution is improved,and the stiffness is improved.The new structural layer design method combined with the "high efficiency&low load" hydrodynamic shape design in Chapter 4 can significantly reduce the blade weight.Chapter 6 summarizes the full text,and list the future work on HAMCT blade technologies.