Research On Mechanical Characteristics Of The New Pile-Bucket Combined Foundation For Offshore Wind Turbines

Driven by many factors such as energy security and climate change,global wind power is developing rapidly.With the continuous expansion of wind power development scale,onshore wind power is increasingly restricted by factors such as land resources,wind energy resources,and noise.Offshore wind power has become an important area for wind power development.For the development of offshore wind power,it is generally considered that the water depth of 50 m or less is suitable for fixed foundations,and the 50 m or more is suitable for the development of floating foundations.At present,global offshore wind farms are mainly distributed in offshore waters,and the water depth is generally below 30 m.The application of various types of fixed foundations is relatively mature.However,wind power development in the sea area between 30 m and 50 m water depth is still in its infancy.Due to the increase of the water depth and the single unit capacity of the unit,the load on the wind power foundation continues to increase.The safe and economical basic type has become a technical problem to be solved urgently for the development of offshore power.Aiming at the above problems,this paper proposes a new pile-bucket combined foundation structure for offshore wind power,and carries out research on shape optimization,static and dynamic characteristics,and bearing characteristics of foundation structure.The details are as follows:(1)Research on structural optimization design of the pile-bucket combined foundation.Starting from the actual project,the load of the foundation structure is analyzed and used as the input condition for the design.The structural form of the pilebucket combined foundation is proposed.ABAQUS finite element software is used to analyze the sensitivity of various parameters of the structure,the influence of structural parameters on the stress and displacement state of the overall structure is analyzed.Finally,a relatively better scheme is obtained.And,the construction process of the pilebucket combined foundation is briefly introduced.(2)Research on static characteristics and bearing characteristics of the pile-bucket combined foundation.Static characteristics analysis of bearing capacity and stability,foundation inclination and structural strength of this foundation.The inclination rate at the top flange of the foundation under the combined action of the limit load standard is6.2‰,which meets the engineering requirements.The maximum stress of the steel structure of the foundation under the load of the ultimate load structure strength check is 272.9MPa,which is less than the steel yield strength of 345.0MPa.According to the specific marine geological conditions,the ABAQUS finite element software is used to carry out the fine numerical simulation of the pile-bucket combined foundation and the bucket foundation.The bearing characteristics differences between the two foundations under different loading modes is compared and analyzed.Under the monotonic load,the pile-bucket combined foundation is at least 2 times higher than the bucket foundation for the horizontal ultimate bearing capacity and the bending moment ultimate bearing capacity.The vertical ultimate bearing capacity is similar.In the compound loading mode,with the increase of vertical load,the H-M envelopes of the two foundations first expand outward and then contract internally.(3)Dynamic characteristics calculation analysis of the pile-bucket combined foundation.The foundation structure,the tower and the whole machine is established.The calculation of structure's self-vibration characteristics and the structural resonance verification were carried out.The natural frequency of the first-order mode of the offshore wind turbine structure is 0.320 Hz,and the difference from the excitation frequency of the wind turbine unit is greater than 10% of the excitation frequency,so the structure will not resonate.The wind and wave random loads of the foundation under extreme conditions are simulated,and the dynamic response characteristics of the foundation under the coupling of these three kinds of random loads are analyzed.The results show that the maximum windward displacement of the top of the upper tower and the bottom flange of the foundation are 52.3cm and 10.1cm.Finally,the fatigue calculation of the foundation under normal operating conditions is carried out,and the maximum fatigue damage in the structure is 0.31,which meets the requirements of the code.