横纵振荡对风电桩基局部冲刷的影响机理

Influence mechanism of horizontal and vertical oscillations of wind power pile foundations on local erosion

海上风电桩基的振荡对其局部冲刷的影响不容忽视。该文采用VOF(volume of fluid)两相流模型,对横纵振荡的风电桩基进行数值模拟。分析不同频率、振幅下的桩前和桩侧对称面在周期内流场分布、马蹄涡系变化和床面剪切应力,探究振荡桩基对局部冲刷的影响机理。研究结果表明:在振荡周期内,纵向振荡桩基桩前对称面内产生回流,在T/2时刻马蹄涡达到最大且床面剪切应力最大,不改变桩侧对称面内水流流动;横向振荡桩基会延展桩侧马蹄涡系,在T/2时刻马蹄涡最大但床面剪切应力最小,T时刻最大,不改变桩前对称面内水流流动。横向、纵向振荡会增大桩前和桩侧的床面剪切应力,加剧局部冲刷,当A=5 mm、f=2 Hz时,纵向振荡桩前对称面剪切应力较静止约增大0.75%,桩侧对称面约增大7%;横向振荡桩前对称面约增大2.5%;桩侧对称面约增大10%。

The impact of the oscillations of offshore wind power pile foundations on local scour cannot be ignored.The VOF two-phase flow model was used to numerically simulate the horizontal and vertical oscillations of wind power pile foundations.The flow field distribution,horseshoe vortex system changes and bed surface shear stress of the pile front and pile side symmetrical planes under the oscillation of different frequencies and amplitudes during the period were analysed,and the influence mechanism of the oscillating pile foundation on local scour was explored.The research results show that during the oscillation period,the pile foundation with longitudinal oscillation generates backflow in the front symmetrical plane of the pile.At T/2 time,the horseshoe vortex reaches the maximum and the bed surface shear stress is the maximum,while the water flow in the pile side symmetrical plane keeps unchanged.The pile foundation with transverse oscillation will extend the horseshoe vortex system on the pile side.The horseshoe vortex is the largest at time T/2 but the bed shear stress is the smallest and reaches the largest at time T,while the flow of water in the symmetrical plane in front of the pile keeps unchanged.Transverse and longitudinal oscillations will increase the bed shear stress both in front of the pile and on the side of the pile,intensifying local scour.When A=5 mm,f=2 Hz,the shear stress in the front symmetrical plane of the longitudinal oscillation pile increases by about 0.75%compared with the static state,and that on the pile side symmetrical plane increases by about 7%,the shear stress in the front symmetrical plane of the transverse oscillation pile increases by about 2.5%and that on the pile side symmetrical plane increases by about 10%.