Dynamic Characteristic Study Of A Novel Integrated Offshore Structure Consisting Of A Bottom Fixed Offshore Wind Turbine And An Aquaculture Cage

There are broadest coastlines and abundant marine resources in China.In recent years,the exploitation and utilization of marine resources,such as offshore wind power and marine fishery,have attracted more and more attention.Nowadays,the bottom fixed foundations are extensively applied in offshore wind farms in China,e.g.monopile,jacket foundation,tripod foundation and et al.Due to the complex environmental and geological conditions in coastal regions,the constructed offshore wind turbine(OWTs)are vulnerable to the cyclic wind,wave and current loads during the service period.In order to improve the reliability of OWTs,the substructure of OWTs is often bulky and expensive,and the underwater space cannot be sufficiently utilized.Meanwhile,the mariculture is profitable,and it is gradually moving into the deep sea.However,the development of deep-sea aquaculture has been delayed due to the difficulties in the power supply.Therefore,it is necessary to integrate the OWTs and mariculture to sufficiently utilize the ocean space and maximize the economic benefits.In order to realize the integrated development of OWTs and mariculture,this paper focuses on the following key issues:(1)An integrated offshore structure consisting of a monopile OWT and steel aquaculture cage is proposed,which is named as ISFC-OWT.The parameters of upper WT system are the same as those of the DTU 10-MW baseline WT.For the support system,a monopile substructure is employed to support the OWT,and a square mariculture is developed in combination with the additional three secondary piles.The fish nets are arranged on the side and bottom of the proposed aquaculture cage,and the available breeding space is about 90,000m~3.(2)Based on the relevant design specifications and standards of OWTs,mariculture and offshore platforms,the design methods and requirements for ISFC-OWT were summarized.Then according to the real recorded in southeastern offshore regions in China,the load combinations and partial load coefficients for the design of ISFC-OWT were determined.The finite element(FE)model of ISTC-OWT is established using member element in SACS,and the RNA is simplified as s concentrated mass with respect to the tower top.Further,the structural bearing capacities under multiple limit states were checked using the partial load resistance coefficient design method.(3)Using the screen method,a fish net hydrodynamic load model is established based on the equivalent of mass and stiffness.Combined with the fully coupled analysis and pile foundation linearization theories,the coupled analysis model of ISFC-OWT was established,which includes the rotor nacelle assembly(RNA),tower,substructure,fish net,soil-pile interactions and servo control.Based on the coupled analysis model,the dynamic characteristics of ISFC-OWT were discussed under typical wind and wave loads,and the coupling mechanisms were revealed.(4)Based on the coupled model,the vibration control strategy for ISFC-OWT is studied.According to the reductions of coupled responses,the mitigation effects of tuned mass dampers under normal operation and extreme conditions were investigated.The optimal vibration control strategies for ISFC-OWT are summarized.