Analysis On 3D FSI Dynamic Response Of Offshore Wind Turbine Foundation

With energy depletion and environmental degradation, clean pollution-free and renewable energy has become the national focus of research and application. The wind is a new energy that more developed, which has been a leading renewable energy. China has a long coastline and abundant offshore wind resources. Electricity load centers are mostly concentrated in the eastern coastal areas. So offshore wind energy will surely become one of the main energy in the future sustainable development. The basis of wind turbine relates to the safety of the fans, and is considered as one of the factors which caused the high cost. So to develop new economic infrastructures is the main topic of offshore wind farm research. Infrastructure for offshore wind turbine design needs to consider the situation of the geological structure of the seabed, offshore distance, wind and wave load, ocean currents, ice and other effects.This thesis is based on the Yancheng Xiangshui wind farm project in Jiangsu Province, by means of numerical analysis, using the ADINA software to simulate, with selection of materials suitable for practical engineering constitutive model, to build a three-dimensional model which contains wind turbine/infrastructure/water and the seabed, and finally analysis the static and dynamic response of the overall structure considering the fluid-structure interaction.The main conclusions of this paper are:(1) This paper established a three-dimensional finite element model of offshore wind turbine sole pile foundation, and got the structure's natural frequencies and mode shapes with and without considering the water as potential fluid. After checking this sole pile foundation of 1.5MW wind turbine, it can avoid the range of 1P and 3P excitation frequency of impeller rotation, which meets the engineering requirements.(2) Static analysis shows that, the maximum settlement is 0.35m, appears at sludge layer near to the pile; wind load is the main source of horizontal displacement, which has little effect on the structure of settlement; the settlement and horizontal displacement of pile and wind tower are both very small, which has no effect on the structure stability.(3) Through the dynamic coupling analysis of structure and water flow, loading cycle flow velocity, the results are: large settlement displacement appears at soft mud layer, 90% of this settlement occurs in the first half cycle, which means that the first 2 seconds of this velocity load made the structure settle dramatically and increased slowly after that; When the velocity load direction equals to the wind load, the horizontal displacement grow significantly, while develop slowly at other time in the cycle; Contrast to the soil, the windward of the tower stress is larger than leeward.(4) Established a three-dimensional finite element model of offshore wind turbine tetrapod pile foundation, and got the structure's natural frequencies and mode shapes with and without considering the water as potential fluid. After checking this tetrapod pile foundation, it can also avoid the range of 1P and 3P excitation frequency of impeller rotation. The results also show that water has greatly reduced the lower part of frequency, which is often more harmful to the structure. When designing, we must avoid the frequency range of dynamic load.(5) Similar to the sole pile foundation, static analysis shows that, wind load has little effect on the structure settlement, and this is the main source of horizontal displacement. At the same time, the overall settlement decreased a little, so the tetrapod pile foundation is safer than sole pile.(6) Similar to the sole pile foundation, through the dynamic coupling analysis of tetrapod foundation, the settlement mainly happens at the first half cycle. When the acceleration turns from the minimum value to the maximum, the horizontal displacement grows quickly, while change slowly at other time in the cycle.(7) The statistic and dynamic analysis indicates that, for structures contain the dynamic loads such as wind turbine, dynamic coupling calculation must be carried out to verify the stability of the structure. Compared with the sole pile and tetrapod pile, settlement / horizontal displacement / stress nephogram / plastic zone has very similar laws, the bearing capacity of tetrapod foundation is clearly higher than sole pile, when does not count in the cost of construction.