钻井船插桩CEL数值模拟中的若干问题分析

Issues of numerical simulation of the spudcan penetration based on CEL method

依据模拟钻井船在不同场地条件下贯入阻力的离心模型试验结果及具体工程实例,对利用耦合欧拉-拉格朗日(CEL)有限元方法模拟钻井船在黏土、砂土、黏土下覆砂土、砂土下覆黏土及成层土场地插桩过程时,影响贯入阻力计算结果的几个因素进行了研究。结果表明,对于不同土层场地条件,有限元模型中欧拉区域范围对贯入阻力几乎没有影响。为确保CEL数值结果的精度,有限元建模时靠近桩靴部分设置为细网格区域,以外区域设置为粗网格区域;对于不同土层场地条件,减小细网格尺寸及增大细网格范围可以减小贯入阻力的振荡情况;经比较总结,细网格尺寸建议取0.05倍桩靴直径,细网格范围建议取2倍桩靴直径。采用位移控制模拟钻井船插桩时,桩靴贯入速率对黏土场地的贯入阻力影响较小,对砂土下覆黏土场地的贯入阻力影响很大,对一般成层土场地的贯入阻力有一定影响。经比较总结,建议在研究钻井船在不同土层场地的计算贯入阻力时,有限元模型的桩靴贯入速率取0.2 m/s。

According to the simulation of centrifuge model test of spudcan penetration in various soil profiles, several influencing factors of the penetration resistance are discussed using coupled Eulerian-Lagrangian（CEL） finite element method. Five typical seabed profiles commonly encountered in the field are considered： clay, sand, clay overlying sand, sand overlying clay, and layered soils. It is shown that different ranges of Eulerian domain barely affect the calculation results. To ensure the accuracy of the numerical results of CEL, fine mesh is defined near the spudcan and coarse mesh far away. For various soil profiles, the study confirms that decreasing the size of fine mesh or increasing the range of fine mesh can ease the vibration of the penetration resistance curves. By comparison, the size of fine mesh is proposed to be set as 0.05 times the diameter of the spudcan, meanwhile, the range of fine mesh is proposed to be set as 2 times the diameter of spudcan for various soil profiles. When the displacement control is adopted, the penetration rate has a little effect on the profile of clay, while a great effect on the profile of sand overlying clay. By comparison, a penetration rate of 0.2 m/s is selected in FEM when investigating the calculated penetration resistance in various soil profiles.