海上风机大直径单桩动态打桩过程数值仿真分析

Numerical Analysis of Dynamic Piling Process of Large-diameter Monopile of Offshore Wind Turbine

在海上风电场建设中,基础施工是项目建设中最重要的关键环节之一,因此研究超大直径单桩动态打桩过程中桩-土-水相互之间的耦合效应有非常重要的意义。分析了海上风机大直径单桩的动态打桩过程,以江苏启东H3海上风力发电场建设过程中的沉桩为工程背景,使用商用有限元软件LS-DYNA进行建模,基于多物质ALE流固耦合法,通过定义多物质材料和流固耦合关键字建立了流体(海水和土壤)和固体(桩体)之间相互作用的耦合机制。对动态打桩过程中土体的应力、应变、体积分数以及沉桩阻力的变化规律进行了仿真分析,发现在桩端附近的土体有明显的应力集中区,应力分量的等值线具有类似于“应力泡”的层状结构,这表明桩端土体具有类似球形的扩张形式。随着贯入深度的增加,桩端处的压应力也在逐渐增大,但各应力集中区的影响范围和等值线的轮廓形状变化不大,说明动态打桩过程对土壤的影响范围是有限的。每次击打过后,由于应力波的反射作用和土体受压缩出现的塑性屈服,桩体会先向下移动一段距离再向上回弹一段距离,从而导致沉桩阻力先增大后减小,直到下一锤击又开始。为海上风机大直径单桩的动态打桩过程提供了数值仿真建模参考和实用的分析方法。

In the construction of offshore wind farms,the foundation construction is one of the most important stages in the project construction.Therefore,it is of great significance to study the coupling effect between pile-soil-water in the dynamic piling process of large-diameter monopile.The dynamic piling process of large-diameter monopile of offshore wind turbine(OWT)was analyzed.The pile driving process during the construction of H3 offshore wind farm in Jiangsu Qidong has been taken as the engineering background,and the commercial finite element software LS-DYNA was used for modeling.Based on the multi-material Arbitrary Lagrangian Eulerian(ALE)fluid-solid coupling method,the coupling mechanism between the fluid(the seawater and the soil)and the solid(the pile)had been established by defining the keyword of multi-material group and fluid-solid coupling.Then the variational principle of soil stress,strain,volume fraction and pile driving resistance in the dynamic piling process had been simulated and analyzed.It was found that there was an obvious stress concentration area in the soil near the pile end,and the contour of the stress component had a layered structure similar to"stress bubble",which indicated that the soil at the pile end had a form of spherical expansion.As the penetration depth increased,the compressive stress at the pile end was gradually increasing,but the influence range of each stress concentration area and the contour shape of the contour line did not change much,indicating that the influence range of the dynamic pile driving process on the soil was limited.After each blow,due to the reflection of stress wave and the plastic yield of the soil under compression,the pile would first move downward for a certain distance and then rebound upward for a certain distance,thus causing the pile sinking resistance to increase first and then decrease until the next blow.The research provides numerical simulation modeling reference and practical analysis method for the dynamic piling process of large-diameter monopile of OWT.