Study Of Bearing Capacity Of Suction Bucket Foundation In Sand For Offshore Wind Turbines

With the rapid development of China's economy and society,the demand for energy,especially clean energy,is increasing.As the fastest developing green energy in China,wind energy has a broader application prospect.However,with the rapid development of onshore wind power plant construction in China in recent years,the situation of "wind curtailment and power limit" has emerged due to the small size of source market,which is difficult to consume locally.Therefore,people begin to turn their attention to offshore wind power construction.In offshore wind farms that have been built at home and abroad,the construction cost of foundations accounts for about25% to 30% of the total cost.Therefore,the rational selection of foundations for offshore wind turbines is the key to the development and utilization of marine wind energy.As a novel type of Marine foundation proposed and developed in the past two decades,suction bucket foundation is more economical,environmentally friendly and reusable than traditional gravity foundation and pile foundation.Therefore,it has a good development prospect in the construction of offshore wind farms in China.At present,there are many research achievements on suction bucket foundation,but most of them focus on soft clay,which is not suitable for sandy soil.Therefore,this thesis mainly uses ABAQUS,a general-purpose finite element software,to conduct secondary development through FORTRAN programming,and study the bearing capacity characteristics of suction bucket foundation in sand.The influences of geometric size of foundation,relative density of sand soil and load combination mode on the bearing capacity of bucket foundation are discussed.The main conclusions are as follows:(1)A user subroutine is written for the secondary development of the software ABAQUS to simulate the stress dependancy of Young's modulus of sand with the change of pressure,and the numerical simulation of two in-situ test is conducted to verify the reliability of the finite element model used in this paper.The effects of mesh density and increment time on the numerical results are discussed.(2)Numerical simulation is carried out for a series of bucket foundations in sand with different relative density.The influence of loading height,different aspect ratio and sand compactness on the bearing capacity of suction bucket foundation and itsfailure mechanism is systematically discussed.The results show that the bucket foundation does not rotate around a certain point in the process of horizontal loading.In the early stage of loading,translation is dominant,while in the later stage,rotation is dominant.The position of rotation center is affected by load level,loading height and bucket foundation size,but it is generally loated at the depth of 0.7-0.9 times of the bucket foundation below the bucket lid.(3)The loading height affects the ultimate bearing capacity and initial stiffness of the bucket foundation-soil system.The horizontal bearing capacity decreases with the increase of the loading height,and the bearing of the bending moment with respect to the center of the top of the bucket gradually increases until the ultimate bending moment capacity is reached.The moments of the horizontal ultimate load of the bucket foundation with respect to the center of the bucket bottom under different loading heights are approximately the same,with an error of no more than 10%.Compared to the effect of the diameter of the bucket,the influence of the embedment depth of the foundation on its bearing capacity is more obvious.Through dimensionless analyses of the numerical results,the equations of failure locus in the lateral load-moment plane is obtained.(4)Based on the results of finite element numerical simulation,the distribution of earth pressure on various bucket wall is obtained when the foundation is unstable.Then based on the limit equilibrium theory of soil,a simplified calculation method of bearing capacity of the bucket foundation on sandy soil is developed,which can provide reference for preliminary engineering design.