波流共同作用下沙质海床动力响应及其对大直径圆柱局部冲刷影响研究

Large diameter cylinder is widely used in offshore engineering, and its local scour is the one of prime reasons causing offshore coastal structures failure. Under the combined action of waves and currents, the fluctuation of water pressure in sandy seabed surround pier can inducing seabed liquefaction, aggravating sediment transport and local scour. The model experiment was carried out in wave current flume to study the mutual effects of waves and currents- large diameter cylinder -seabed. Therefore, wave height, flow field, suspended sediment concentration, seabed morphology, and pore water pressure in seabed were detailed measured. The sandy seabed dynamic response around large diameter cylinder were discussed under the combined action of wave and current, and the sediment movement mechanism around pier impacts by the flow properties and the pore water pressure in the seabed were analyzed. Meanwhile, the sediment movement mechanism was analyzed firstly by the means of wave dynamics, sediment dynamics, and marine soil mechanics. The corresponding transport rate and the computing methods of seabed shear stress were obtained secondly. The three-dimension water and sediment mathematical model of solid-liquid two-phase flow, lastly, are developed on the basis of curvilinear coordinates, adaptive mesh, and high accuracy free surface tracking technology. Under the action of wave flow, by synthesizing the result of experiment, calculation, and theoretical analysis, the relationship between seabed scour around the large diameter cylinder and seabed dynamic response was revealed, the mechanism of sediment incipient motion, transport, suspension around the large diameter cylinder was explored. Consequently, the mechanism of local scour and calculating method around the large diameter cylinder under the combined action of wave and current was obtained, which will provide the theoretical basis to the design of the offshore coastal structures.

近海大直径圆柱基础周围局部冲刷是建筑物破坏的主要原因之一。波流共同作用下的波动水压力可导致沙质海床液化，加剧泥沙输移和局部冲刷。在波流水槽中进行波流-大直径圆柱-海床相互作用模型试验，详细测量大直径圆柱周围波高、流场、悬沙浓度、床面形态、海床中孔隙水压力等，探讨在波流共同作用下大直径圆柱周围沙质海床的动力响应规律，分析大直径圆柱周围水流特性和海床内孔隙水压力对泥沙运动的影响机制。将水波动力学、泥沙动力学、海洋土力学相结合分析泥沙运动的力学机理，然后得到相应的输沙率和床面切应力计算方法，开发基于曲线坐标、自适应网格、高精度自由面追踪技术的固液两相流三维水沙数学模型。综合试验、计算和理论分析结果，探讨波流作用下大直径圆柱周围泥沙起动、推移、悬浮的机理，揭示波流作用下大直径圆柱周围床面冲刷与海床动力响应的关系，得到波流作用下大直径圆柱周围局部冲刷的机理和计算方法，为近海建筑物的建设提供理论支撑。

近海大直径圆柱基础周围局部冲刷是建筑物破坏的主要原因之一。波流共同作用下的波动水压力可导致沙质海床液化，加剧泥沙输移和局部冲刷。在波流水槽中进行波流-大直径圆柱-海床相互作用模型试验，设置了大直径圆柱与平底海床、大直径淹没圆柱与平底海床、圆柱与斜坡海床等多种工况，设定单纯波浪、波流叠加、孤立波等多种海况条件，详细测量结构周围波高、流场、床面形态、海床中孔隙水压力等。建立了一套基于雷诺时均方程控制的水动力数值模型，采用实测底床地形数据对大直径圆柱周围冲刷坑内的涡流结构进行数值模拟，得到大直径圆柱周围及冲刷坑内的涡流结构随时间的演变过程。将水波动力学、泥沙动力学、海洋土力学相结合，综合试验、计算和理论分析泥沙运动的力学机理，揭示了波流作用下大直径圆柱周围局部冲刷与海床动力响应的关系，提出了小KC数波流作用下大直径圆柱周围局部冲刷深度预测公式，提出了孤立波作用下圆柱周围局部冲刷深度预测公式，并研究了减冲桩防护墩桩局部冲刷的方法。研究成果可为高桩码头、海上风电基础、跨海大桥等工程的建设提供理论支撑。