波浪作用下海上风电伞式吸力锚基础周围冲刷演变机制

SCOUR MECHANISM AROUND UMBRELLA SUCTION ANCHOR FOUNDATION FOR OFFSHORE WIND TURBINE IN WAVES

以近海风电伞式吸力锚基础为研究对象,进行室内水槽试验和数值模拟,研究波浪作用下伞式吸力锚基础周围冲刷演变机制,分别基于Raaijmakers和Myrhaug模型,提出随机波浪小Keulegan-Carpenter数(KC)情况下伞式吸力锚基础周围平衡冲刷深度预测模型。结果表明:随机波浪下,波峰时形成的旋涡体系主导冲刷过程,此时基础上游逆压梯度最大,这有利于波浪边界层充分分离,形成马蹄形旋涡,马蹄形旋涡和桩侧流线压缩导致筒裙上游两侧约45°圆心角位置剪切流速最大,筒裙和锚枝的设置保护了该位置床面土体,使得最大冲刷深度位置位于锚枝之间。当KC采用KC_(s,p),且KC_(s,p)<8时,修正Raaijmakers模型预测的平衡冲刷深度Seq′与计算值具有较好的一致性,当KC_(s,p)>8时,预测值与试验值之间的误差变大,修正Raaijmakers模型过分估计了平衡冲刷深度。当KC_(rms),a<4,n=10时,修正Myrhaug平衡冲刷深度预测模型预测效果最好。

A series of wave flume experiments and numerical simulation were conducted under waves,so as to investigate the scour mechanism around umbrella suction anchor foundation(USAF)of offshore wind turbines.Then,two revised models were proposed according to the model of Raaijmakers and Myrhaug model respectively to predict the equilibrium scour depth around USAF for low Keulegan-Carpenter number(KC)under waves.The results indicated that the vortex system at wave crest phase is mainly responsible for the scour process under waves.What’s more,due to the combination of the horseshoe vortex and streamline compression,the maximum scour depth occurred at the upside of the USAF with an angle of about 45°corresponding to the wave propagating direction.The tube skirt and anchor branches play a role in protecting the scour around USAF to some extent.The revision model based on Raaijmakers’s model shows good agreement with the simulating results of the present study for KC_(s,p)<8.However,the gap between the predicting results and experimental data becomes large and the Eq.(25)overestimates the equilibrium scour depth to some extent for KC_(s,p)>8.The predicting results of another revision model based on the stochastic model are the most favorable for n=10 when KC_(rms)<4.