Dynamic Coupling Analysis And Optimum Technology On Monopile Tripod Support Structures Of Offshore Wind Turbine

It is a consensus that energy development and environmental protection are of fundamental importance to the economical progress of every country. However, oil or other fossil energy is not renewable so it's crucial for the human race to concentrate their effort on the fresh and renewable energies. As a typical clean and sustaining energy, the wind turbine has been one of the top green energies which are developing fast; moreover, the wind turbine has been one of the most significant aspects in many countries'policy of sustainable development. Large-scale wind turbines have expanded from the land to the sea and been one of the hot issues of research and application because of the rich wind energy resource, high energy acquisition and less influence from the environment. The cost of the productivity of electricity is the bottleneck of the development of offshore wind turbines and the support structure is one of the key causes of the high investment; consequently, to conduct research about the dynamic and mechanical properties about the support structure of wind turbines and elect the economical and effective option has great significance.The thesis mainly focuses on the topic about the dynamic properties, response and optimization of the support structure of the wind turbine under environmental forces.The research in this thesis mainly includes the following aspects:Firstly, as the target, a monopile tripod structure has been elected as the target based on the calculation of various support structures. According to the properties of force, the range of natural frequency of the wind turbine has been determined. Additionally, FEM model has been established under the requirement of dynamical characteristics.Secondly, load from the wind turbine and the environment have been taken together to analyze the strengthen of the structural model; the static strengthen under the influence of extreme environmental load and different load combination from working wind turbine has been acquired; the stiffness and strengthen have been guaranteed through the comparison between the aforementioned results and the regulations from API. Furthermore, the research fulfills the dynamical effect from the single function from the loads because of wind turbine, wind, wave, current, ice or earthquake and gets the time history of the maximal displacement and equivalent stress in critical places of the structure. The data have proved the following conclusions factors which need special attentions while doing the wind turbine design: on the one hand, response of the wind turbine to the ice force is the biggest; on the other hand, forces and moments because of the operation of the wind turbine have heavy influences to the structure.Thirdly, taking the requirements about the stiffness, strengthen and dynamical properties of the monopile tripod support structure of the wind turbine as the constraints, using the outside diameters and thicknesses of the structure as the variables, the optimization of the steel volume which satisfy the design has been achieved. What's more, it has been discovered that the diameter of the intermediate column has the most importance to the natural frequency of the structure.