Experimental Study Of Offshore Wind Turbine With Monopile Foundation Constructed In Clayey Site Subjected To Cyclic Lateral Load

While offshore wind power is increasing dramatically in China,domestic design standard for designing offshore wind turbine is still not available.Because offshore wind turbine suffers from sophisticated environmental loading during operation,lateral resistance of foundation is a design priority for offshore wind turbine.For monopile foundation,the design criterion mainly focuses on accumulated lateral deformation and nature frequency.In order to study the lateral behavior of monoplie foundation constructed in clayey site at the coastal area in China,this thesis conducted a series of analysis work,which includes:1)A field static pile test was conducted in an offshore site at the East China Sea.Based on the test results,lateral behavior of pile-soil system is analyzed.Besides,by using numerical back-analysis method,comparison between measured and suggested static p-y curve is carried out,and revised static p-y curve is proposed based on above analysis work.2)A cyclic loading device was manufactured,and marine clay was sampled from coastal site in the East China Sea.After that,a series of model tests were conducted.Based on the test results,analysis work were proposed,which includes accumulated lateral deflection of model pile,foundation stiffness and nature frequency,cyclic p-y curve,pore-water dissipation and softening zone.An empirical formula was also proposed to evaluate the accumulated lateral deflection of model pile.In addition,reduction factor for soil reaction of cyclic p-y curve was suggested based on the test results.3)A numerical model was conducted by combining FAST and ADINA,which could consider one-way coupled fluid-structure interaction of wind turbine and supported structure.Based on the proposed numerical model,a case study was carried out to estimate the dynamic behavior of a NREL 5MW wind turbine constructed in clayey site,which suggested that the influence zone of latera load concentrated in an elliptical area with 2 times of diameter paralleling to the loading direction and 1 times o fdiameter perpendicular to the loading direction.This paper fouces on studying the cyclic lateral behavior of monopile foundation constructed in clayey site and relative design method.The analysis work of in-situ pile test could,which has proposed a modified p-y curve,provide a resonable reference for other construction in adjacent area.A novel loading device has been designed and manufactured,and a series of indoor model tests have been carried out,which could provide useful instruction for cyclic design of monopile construced in clay site.Besides,a one-way coupled model considering dynamic fluid-structure interaction has been developed,which could partialy represent the strong coupled behavior between turbine-tower-foundation and environmental loading.In addition,design strategy of monopile foundation for scour protection and marine growth was summarized,and a detailed design case was proposed.Finally,proposed model test and numerical analysis could be used to assess the lateral resistance of monopile,which could also be used as a reasonable reference for monopile design in offshore site at China.