Study On The Safety Of Floating Container Of Bucket Foundation

With the proposal of China’s ’ carbon peak in 2030 and carbon neutralization in 2060’ strategy,offshore wind energy is gradually developing towards far-reaching sea areas and large capacity units.In this context,based on the efficiency of bucket foundation and the economy of gravity foundation,a new type of polygonal steel-concrete composite bucke foundation has be developed,and two practical engineering prototypes are demonstrated in Guangdong sea area.The installation process of steel-concrete composite bucket foundation is very simple,but it brings the problem of increasing self-weight,which makes the cost of the original shore prefabricated method increase sharply,and the conventional onshore prefabricated method and equipment are no longer applicable.Therefore,an idea of synchronous prefabricated multiple bucket foundations on offshore platforms is proposed.However,in the process of offshore construction of steel-concrete composite bucket foundation,the open skirt cannot rely on self-floating displacement and the overall floating stability of the foundation is insufficient.Based on the offshore wind power project in Guangdong,this paper proposes a technology to improve the foundation displacement and floating stability based on floating container.The hydrodynamic performance and structure of open bucket skirt-floating container and bucket foundation-floating container are studie.The specific research contents and conclusions are as follows:(1)Based on the example of hexagonal steel-concrete composite bucket foundation in Guangdong,the structural design of floating container for bucket foundation is studied.Firstly,according to the required buoyancy of the foundation and the hydrological data of the dock,the size of the floating container and the structure type are determined.Secondly,a set of hybrid pressure loading system is set up,which relies on gravity self-flow loading and compressed air loading to realize the floating and sinking functions of floating container auxiliary open bucket skirt and bucket foundation.Finally,the horizontal and vertical lifting points of the floating container are designed to meet the structural integrity and operational safety of the open bucket skirt-floating container and the bucket foundation-floating container.(2)Based on theoretical derivation and numerical simulation,the hydrodynamic characteristics of open bucket skirt-floating tank and bucket foundation-floating tank under different draft depths are analyzed.It is found that the structural stability of the open bucket skirt-floating container and the bucket foundation-floating container under different draft depths meets the requirements.The variation trend of six degrees of freedom with wave period is similar between bucket skirt-floating container and bucket foundation-floating container under different wave directions.The heave and pitch periods of the two structures increase with the increase of draft except for the inherent pitch period of bucket foundation-floating tank.(3)The motion characteristics of open bucket skirt-floating container and bucket foundation-floating container in irregular waves are numerically simulated and analyzed,and the control strategy of motion response of open bucket skirt-floating container and bucket foundation-floating container is proposed.The research shows that the draft depth,wave period and wave angle have effects on the maximum amplitude and acceleration of heave and pitch motions in three directions.The motion responses of the two structures are large when the water intake is 11.5 m,and it is recommended to work at the tidal level below 10 m.When the wave period is close to the inherent period of the structure,the two will resonate,increasing the motion response,and should be avoided as far as possible in practical operation.(4)Based on the load conditions of the floating container under the seated state and the floating state in the actual project,the influence of the upper and lower cabin pressure drainage on the structural strength of the auxiliary floating container is quantitatively analyzed,and the improvement effect of the local strengthening of the auxiliary floating container connector is explored.The finite element model of open bucket skirt-floating container was established for strength analysis.It is recommended to control the pressure of the upper cabin below 7.5 m water head when the upper cabin of the floating tank is aerated to discharge ballast water.When the ballast water is discharged by air from the lower cabin of the floating container,the pressure head of the upper cabin of the floating container is controlled to be 5-6 m,so that the stress of each structure is less than the allowable stress of the steel structure,and the ballast water can be discharged safely from the lower cabin of the floating container.The fixed boundary method is used to simulate the floating state of the open bucket skirt-floating container.By strengthening the local connection,the strength of each component of the floating container meets the requirements,and the safety of the offshore construction of the bucket foundation is ensured.