Research On Penetration And Sinking-leveling Of Multi Bucket Foundation For Offshore Wind Turbines

With the development of domestic offshore wind energy resources and the planning and construction of wind farms,the application of bucket foundations in wind farms can greatly reduce construction costs.The four-bucket foundation has advantages in resisting super-large horizontal loads.The research on the four-bucket foundation sinking installation mechanism is of great value to the application and promotion of the four-bucket foundation.In this paper,the main control factors such as suction penetration,critical sinking pressure and leveling strategy in the four-bucket foundation installation process are studied by model test,theoretical calculation and numerical simulation.The specific research contents and main results are as follows:(1)Based on the test of the four-bucket foundation in sand,the design method of the four-bucket foundation sinking and negative pressure was verified,and the substation negative pressure control system was studied.The research shows that the theoretical negative pressure can be used as the upper limit of the negative pressure value,and the negative pressure derived from the API sinking resistance can be used as the lower limit of the negative pressure value.The negative pressure sinking system with large initial negative pressure value has a more obvious effect on reducing the four-bucket foundation penetration resistance,and is more favorable for the four-bucket foundation sinking.(2)Based on the four-bucket foundation critical negative pressure test and theoretical calculation,the critical negative pressure at the time of the damage of the four-bucket foundation was studied.The research shows that the critical vacuum ratio of the non-dimensionalization test of the four-bucket foundation model is about 3times higher than the theoretical critical negative pressure considering the influence of seepage.When the internal and external permeability coefficient of the cylinder is between 5 and 6,the critical negative pressure value is close to the theoretical critical negative pressure value.The negative pressure will make the soil in the cylinder loose and the critical negative pressure value can be increased.(3)Based on the four-bucket foundation leveling test,the leveling strategy was studied.The study found that the greater the depth of the four-tube foundation,the more difficult it is to level,and even the ground soil is infiltrated.The "high-position bucket" leveling strategy has a clear target,but the leveling negative pressure safety reserve is low;the "high-position bucket + temporary bucket method" leveling strategy has a higher leveling safety reserve,but the non-leveling direction four-bucket foundation The dip has a greater impact.Combined with a single method of leveling measures,the critical negative pressure value is used as the upper limit of the negative pressure control,and a “mixing and leveling strategy” is proposed,which can achieve effective leveling of the four-bucket foundation.(4)Based on the finite element ABAQUS,the numerical simulation of the seepage field characteristics of different depths of the four-bucket foundation was carried out,and the calculation formulas of negative pressure loss and penetration resistance were derived.The research shows that the seepage field is symmetrically distributed around the geometric center axis of the four-bucket foundation.The distribution characteristics of the seepage field in each bucket are the same.The seepage fields between the cylinders have little influence on each other and gradually decrease with the increase of the depth of penetration.The sinking negative pressure loss mainly occurs inside the cylinder and increases as the depth of penetration increases.