| As one kind of environmental-friendly and renewable energy,offshore wind power has a bright future.The location of wind turbine from offshore to deep sea is an inevitable trend.The installation and removal process of offshore wind turbine platform are critical parts of the whole life cycle of wind turbines,during which the dynamic response can directly affect the safety and expenditure of the construction.At present,fixed turbine installation technology has been widely used in China.However,there exists many other problems needed to be solved in the installation of submersible turbine.In this paper,an aided chains installation and removal method for semi-submersible wind turbine platform is proposed.In this method,some problems caused by dynamic response of submersible turbine platform in certain sea condition can be coped with.On this basis,an optimization plan of turbine installation and removal plan is provided.The main research contents and results of this thesis are as follows:(1)A preliminary design of a new quadruple float semi-submersible platform foundation is proposed and the corresponding basic parameters are determined.Based on the ANSYS finite element analysis model,the dynamic characteristics of semi-submersible platform foundation are analyzed in time domain.Then the dynamic response characteristics under different wave periods can be obtained during the process.Meanwhile,the time-history curve of sway,pitch and heave conditions as well as anchor chain tension can also be obtained under typical sea conditions and extreme sea conditions.By comparative analysis,it is found that semi-submersible platform can maintain stability under conditions mentioned above.(2)Based on this semi-submersible platform foundation,a kind of auxiliary installation method using aided chains is proposed.By calculating the dynamic response of the platform after installation,conclusions can be drawn that: the symmetrical arrangement of the aided chains will not affect the balance position of the platform;it can significantly improve the pitch response of the platform and slightly improve the heave response of the platform.Two different methods for removing aided chains are designed.The comparative analysis indicates that the symmetrical unloading method can maintain the symmetrical state of the platform and optimize the platform’s dynamic response and anchor chain stress.(3)Main factors which affect the dynamic response are studied while using the aided chains method to remove the anchor chain of the semi-submersible platform during the withdrawal process.By comparing the effects of aided chains of different stiffness on the dynamic response of the platform,it is pointed out that the aided chains can effectively reduce the sway and pitch extent of the platform when the anchor chain is removed.The excessively rigid aided chains will affect the natural frequency of the platform and may cause resonance under the influence of periodic waves.By comparing the effects of different pretensions of aided chains on the dynamic response of the platform when the anchor chain is removed under typical sea conditions,it is pointed out that increasing the pretension can effectively reduce the pitch response of the platform and slightly reduce the sway response to the platform.It is pointed out that the symmetrical removal of the anchor chain scheme can effectively reduce the pitch response of the platform.(4)In order to determine the safe construction period,it is pointed out that the installation of the aided chains cannot completely eliminate the influence from the sea state.Under high weave conditions,the tension of the aided chains will change dramatically,which is likely to cause the breakage of the aided chains and in turn can impede the installation.It is recommended to install the platform below sea level 3.By studying the removal process of the semi-submersible wind turbine platform under different sea conditions,it is concluded that under high weave sea conditions,the amplitude of the platform motion and the aided chains tension will increase,which will easily cause the aided chains to break.It is recommended the anchor chain removal operation of the platform should be carried out below sea level 4. |
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