| Tidal turbines are the major equipments for energy exploitation and utilization of tidal stream. In the development process of tidal turbines, how to effectively absorb the ocean energy is the most significant concern for research staff. Rational and effective stress analysis of the blades and the impeller can be the basis for the design of the key structures and the entire turbine. Related diffuser can improve the flow field, and make turbine get more energy from the flow. The strength of the frame structure can be assessed by the finite element analysis method, which can be provide a judge for its design.This thesis was based on the study of a tidal turbine with position-changeable blades. A brief summary of the working principle of the turbine structure was given. The advantages of the turbine on energy harvesting and use have been sumrized. The forces applied on the turbine impeller and the blades were analyzed in theory, which can be the basis for the design of the key components and the whole prototype in the follow-up.Based on the tidal current and geological conditions at the target site, the main technical parameters were determined; the study of material selection, corrosion preventions, seal design were completed; the impeller was designed using theoretical analysis, selection of the increaser, generators, water-lubricated bearings, and the couplings of the turbine system were completed.Using the Fluent, the pros and cons of three different types of diffusers were analysised, and the best type was been determined; the iMPacts of important parameters, such as the opening angle and radius of front plate, the radius of the back plate, on the performance of the diffuser were analyzed based on the corresponding rate-increasing and drag coefficient curves. It can be found that the arc diffuser can greatly increase the stream velocity, and improve flow field distribution, and then maximize abtain the tide energy. Thus, a viable way for indirectly increaseing the energy efficiency of the turbine has been provided.The frame structure was preliminary designed refered to the CCS "shallow water fixed platforms norms" in this paper; the aloads were computed; a simplified model was created and was studied by Finite Element Analysis (FEA) using ANSYS Workbench. For local area whose safety factor is less than the material allowable safety factor, the design was strengthened, optimized and calculated again; finally, the structures and design sizes which meet strength requirements were been determined. Fanally, the overall layout of a prototype (12kW) was completed, which could be the foundation for further research. |
