波流作用下大直径淹没圆柱局部冲刷试验研究

水下大直径淹没圆柱在波流共同作用下的冲刷特性与非淹没情况有较大差别。在波流水槽中开展局部冲刷试验，将大直径淹没圆柱模型安装在中值粒径0.22 mm的平底沙床内，改变波浪波高和周期、水流流速和方向、圆柱淹没率，测量圆柱周围流速变化，记录柱周冲深发展历时，运用激光地形仪测量冲刷坑的地形形态，分析了淹没率S_r和相对高度h_c/D对准平衡冲深的影响。结果表明，相同入射波流条件下，随相对柱高h_c/D降低，冲刷发展速率、冲坑半径和深度都随之减小。当相对柱高h_c/D>1时，冲深随柱高增长速率较快直至达到临界值。准平衡冲刷坑呈"倒勺状"，沿圆柱左右两边呈对称分布，柱前呈半环状；圆柱正后方淤积成"马鞍状"沙丘。

Experimental study on local scour around large-diameter submerged cylinders under combined waves and current action

The characteristics of local scour around large-diameter submerged cylinders are quite different from the non-submerged ones under combined wave and current conditions. Local scour model tests are carried out in a wave-current flume. A submerged cylinder model was installed in a flat sand bed. The flow velocity around the model was measured,and the development of the scour depth was recorded under various waves,current velocities,current directions and submergence rates. A laser scanner was used to generate the geometry of the equilibrium scour hole. The influence of the submergence rate S_r and the relative cylindrical height h_c/D on the equilibrium scour depth is analyzed. The results show that under the same incident wave current conditions,as the relative cylindrical height h_c/D decreases,the scour development rate,the scour hole radius and the scour hole depth decrease. When the relative cylindrical height h_c/D is larger than 1,the scour depth increases rapidly as the cylinder height increases until a critical value of h_c/D is reached. The quasi-equilibrium scour hole is in the shape of a "flipped spoon". The scour hole is symmetrically distributed along the left and right sides of the cylinder. The front of the cylinder is a semi-annular scour hole. A "saddle-shaped" dune is formed due to accumulation of sand scoured away from the cylinder.