Study Of The Rotation Of Monopile At Seabed Under Lateral Loading

With the rapid development of economy,the energy problem is becoming more and more serious.Due to environmental protection and renewability,offshore wind energy has been paid more and more attention.Monopile foundation has become the most commonly used foundation form for offshore wind farms due to its advantages of simple structure,convenient construction.The load on monopile foundation for offshore wind turbine is very complex,including wave load,wind load and flow load.Under complex loads,it is inevitable for monopile foundation for offshore wind turbine to have larger deformation,which will affect the normal operation of the fan structure and cause safety problems.In order to ensure the normal operation of the fan structure,it is necessary to strictly control the deformation of the foundation.The deformation characteristics of monopile foundation for offshore wind turbine under lateral load is the foundation of the above research,and the core is the interaction between pile and soil.At present,p-y curve method is recommended by API and DNV to consider pile-soil interaction,and it is the most widely used nonlinear analysis method for lateral loaded piles.However,the existing p-y curve method is based on the test results of small size pile foundation,which is difficult to be applied to large diameter pile foundation.In practical engineering application,due to the rotation of pile foundation under load,there is a certain difference between the actual rotation at seabed and the theoretical rotation obtained by numerical calculation with p-y curve method.Therefore,it is particularly important to accurately evaluate the rotation of monopile foundation for offshore wind turbine under lateral load.In this paper,API specification p-y curve method,lateral static loading model test in sand soil,ABAQUS three-dimensional finite element numerical simulation and other methods were used to systematically study the deformation characteristics of monopile foundation for offshore wind turbine in sand under lateral static load.The main work and research results are as follows:(1)The nonlinear solution process of p-y curve method was deduced by finite difference method and compiled into MATLAB program to solve the nonlinear calculation problem of p-y curve.The influence of the number and spacing of pile elements on the lateral displacement of pile body was analyzed under the condition of different relative density of sand soil,pile diameters and depth-diameter ratios.According to the research results,the fitting formula for the optimal setting of the number and spacing of pile elements is obtained,which provides technical support for the design of monopile foundation for offshore wind turbine.(2)Deformation characteristics of monopile foundation under lateral static load are studied through lateral static loading model test in sand soil.Under the conditions of different relative density of sand soil,buried depth and loading height,the lateral displacement at mud surface and loading position of pile foundation is measured.The change curve of displacement at the mud surface and loading position with load is obtained directly,and the change curve of rotation at the mud surface with load is calculated.The test result and the calculation result of API specification p-y curve method are compared and analyzed.The calculation result of API specification p-y curve method is conservative and unsafe in the design of monopile foundation for offshore wind turbine monopile foundation.According to different loading height,burial depth and relative compactness of sand soil,the difference between them is about 0.05°~0.2°.(3)Three dimensional finite element numerical model was established by ABAQUS software based on lateral static loading model test in sand soil.The curves of the rotation and the lateral displacement at mud surface of monopile foundation under the action of lateral static load with the change of load are calculated.In addition,The numerical model are verified by the results of laboratory tests.The results basically agree with each other,indicating that the monopile foundation under different working conditions can be simulated and calculated according to the model.Through ABAQUS three-dimensional finite element numerical simulation and API specification p-y curve method,the influence of relative density of sand,pile diameter,buried depth,loading height on the deformation characteristics of monopile foundation for offshore wind turbine was studied.The difference between the actual and theoretical values of the rotation and lateral displacement at seabed of pile foundation is analyzed and a design chart is drawn to provide an effective reference for the design of monopile foundation for offshore wind turbine.