Study On Green Water On Floating Foundation Of Tidal Power Station

Tidal energy is one kind of renewable energy. Because of the larger energy density andpredictability comparing with wind energy, utilization of ocean tidal current has attractedwidespread attention of a number of research groups. Tidal energy will occupy the importantposition of immeasurable in the development and utilization of renewable energy. Now sometidal power stations have been completed in the corners of the world, its foundation structuretypes mainly in three forms-floating moored system, pile mounted system and seabedmounted/gravity based system. Floating moored system composed of submerged one andfloating one. Floating moored system is popular due to its convenient installation andmaintenance. Tidal power station with multi-mooring system works in a fixed place for a longtime exposing to the waves, flows and winds, so the risk on green water on its deck is fargreater than general ship with propeller and rudder which can change direction easily. Greenwater has a directly impact on power generation efficiency and security of floating tidalpower station. The green water sometimes destroys deck structure of the floating tidal powerstation, as a disastrous environmental load. There is big relationship between the volume ofwater on deck and floating foundation’ motion in waves. The paper focuses on the influenceof tidal turbine to the floating foundation and evaluates the probability of green water basedon potential theory, simulates green water with dynamic mesh method based on CFDtechnology.There are five parts in this paper:(1) Review and summarize the floating foundation oftidal power station and research issues on green water;(2) With the potential flow method,probability theory, evaluate how often the green water attacks the floating foundation of tidalpower station (involved with damping of tidal turbine);(3) Numerical wave tank wasestablished with the FLUENT based on CFD, which can simulate the floating foundation’smotion in waves for a long time;(4) Confirm reliability of Numerical method of green wateron a fixed offshore structure by means of comparing the results of Greco’s experiments ongreen water on fixed FPSO, then use this numerical method to simulate green water on thefoundation of floating tidal power station;(5) Simulate the process of green water on the freefloating foundation of tidal power station. Compare the movements of floating foundation among three cases: one is to take no consideration of influence of tidal turbine, another is totake consideration of damping of tidal turbine and the final one includes a comprehensiveconsideration of the influence of tidal turbine to the floating foundation (damping, added massand load acted on tidal turbine working in the water flow).During simulating green water with dynamic mesh method based on CFD technology,the motion of floating foundation in the wave shows the necessity to consider influence oftidal turbine to floating foundation. Floating foundation’s motion in wave with consideringtidal turbine damping is smaller than that without considering influence of tidal turbine tofloating foundation. The final case of taking a consideration of load acted on tidal turbine, thefloating foundation’s balance position-bow trim increase the risk of green water. It makessense to study the influence of tidal turbine to sea-keeping performance of floatingfoundation.