| With the maturation of offshore wind energy technology and great development prospects of the offshore wind resources,it is necessary to develop the offshore wind energy for the renewable energy sources.Compared to the land wind energy,the construction of offshore wind energy is complicated system engineering.Because the installation of the wind turbine is affected by the climate,sea wave,water flow and other factors,which is one of the biggest difficulties during the installation process.When the offshore wind turbine is installed integrally,the wave-induced ship motions can cause the wind turbine to pendulate.Especially,the heave motion of the floating crane can lead to the multiple impacts between the wind turbine and the installation platform.Therefore,it is an urgent to ensure the installation process of wind turbine in safety and stability.Based on the background of offshore installation,the landing and docking technology of offshore wind turbine is investigated through the theoretical analysis and experimental study,which can provide the instruction for the development of practical installation.First,the 12-DOF coupled model between the floating crane and the wind turbine is built and the dynamic characteristic of the offshore wind turbine is analyzed and investigated.In the model,the 6-DOF motion of floating crane including the surge,roll,sway,pitch,heave and yaw are considered.And then,the 5-DOF motion of wind turbine including the roll,pitch and the yaw of the wind turbine,the sway angles in the xz plane and yz plane are considered in the model.In addition,the elastic stretch of the hoisting cable is introduced into the coupled model.What’s more,the displacement constraint from the installation platform is introduced into the model.Base on the above model,the dynamic model of the integral installation can be derived when the boundary conditions of coupled model are introduced according to the different installation scheme.Base on the coupled dynamic model of crane-wind turbine,the dynamic characteristic of wind turbine is studied during the integral installation,respectively.During the integral installation,the calculation is carried out to study the effect of these factors such as release height,release velocity,wave amplitude,wave frequency and wave angle.Then,the dynamic response of offshore wind turbine during the landing process is paid attention to.Then,dynamic model is established considering the sway of the wind turbine.In the model,the multiple impacts between the wind turbine and the installation platform and the tensioning and relaxing of the hoisting rope are considered.Meanwhile,the displacement constraint from the installation platform and the stroke constraint of the soft landing system are introduced into the model.This model is calculated using Baumgarte method.Then,the maximum release velocity is evaluated during the hoisting process.Last,the dynamic response of wind turbine is calculated under the composite excitation combined by the heave motion of the tip and release motion of the hook.Besides,the optimal performance of stiffness-damping element is investigated under these above excitation.Base on the analysis,in order to increase the range of application of the soft landing system in the harsh sea condition,a predictive control approach with multi-inputs multi-outputs is proposed.The characteristics and the validity of the control strategy are investigated.The reliability of this system may be reduced considering the extra power system in the active control approach.Aimed to reduce the acceleration of the wind turbine,the semi-active approach is presented by adjusting the orifice area of valve to change the damping characterics of the system.Compared with the results of the passive soft-landing system,the effectiveness of the two control approaches can be validated.The performance of these two approaches is calculated under different sea condition.Last,the simulation experimental set-up of the offshore wind turbine installation is designed according to the installation process.This experimental set-up consists of installation frame,hydraulic buffer,pulley,hoisting rope,motor and control system.Here,the wind turbine is assumed as a mass point and the buffer can be equivalent to be an element including the linear damping,quadratic damping and variable stiffness.Then,the dynamic model in the previous chapter can be simplified as test dynamic model of the landing process.Base on the principle of the minimum peak acceleration,the control voltage of proportional valve is optimal designed.The test data of the heave motion of floating crane is used as the system input.Three typical wave conditions of wind turbine installation,the simulation experimental is carried out to validate the effectiveness of the control approach.In this paper,this study and achievements can provide the theoretical basis and technical guidance for the installation of the offshore wind turbine and can contribute to the development of the soft landing system in the future. |
