孤立波作用下淹没垂直桩柱局部冲刷试验研究

孤立波在近岸地区会引起剧烈的泥沙运动,导致采用淹没式桩基础的近海建筑物周围发生局部冲刷,严重影响近海建筑物的稳定性。采用中值粒径为0.22 mm的均匀沙在波浪水槽中布置平底沙床,在两种不同桩径条件下,对孤立波作用下淹没桩周围的冲刷发展过程进行了记录分析,探讨入射波高及淹没率对局部冲刷的影响,并从冲刷形态方面对比分析了孤立波与单向水流、规则波作用下局部冲刷的异同。结果表明:在相同淹没率条件下,随着入射波高的增大,桩周冲刷形态由双喇叭型向瞬态型冲刷形态发展;在相同入射波高条件下,桩高与桩径比h_c/D位于1～7范围内,淹没率对桩前最大冲刷深度影响不大,而桩后最大冲刷深度随淹没率增大而减小,并给出了淹没因子K_s与淹没率的多项关系曲线;孤立波与单向流作用下的淹没桩周围地形变化相似,而与小周期规则波作用下的地形变化差异较大。对实测数据进行多元回归得到冲刷深度的综合计算公式,经验证该公式计算值与实测值最大误差不超过7%。

Experimental study on local scour around the submerged vertical circular cylinder under solitary wave action

Solitary waves can cause intense sediment movement in the coastal area,resulting in local scour around the offshore structures that use submerged pile foundations,and seriously affecting the stability of offshore structures. On a flat sand bed with sediment median size of 0.22 mm in a wave flume,a series of experiment were conducted respectively for two cylinders with different diameters and different submergence ratios under the action of solitary waves with a range of incident wave heights. The evolution of scour around the cylinder was recorded and analyzed,and the profiles of the scour hole were compared between those formed under solitary waves and steady current,and between solitary waves and regular wave conditions. It is shown by experimental results that,under the same submergence ratios,the scour type changes from the Twin-Horn-Shaped to the Transient-Shaped as the wave height increases. Under the same incident wave heights and the h_c/D within the range 1—7,the equilibrium scour depth in front of the cylinder is independent on the submergence ratios,while the equilibrium scour depth behind the cylinder decreases with an increase in the submergence ratios,and coefficient K_s as a function of S is obtained. A significant difference is found in the profiles of scour holes formed under regular waves and solitary waves,but no obvious distinction is exhibited for scour under steady current. The comprehensive calculation formula of scour depth is obtained from the measured data. It is shown that the deviation between the values from the empirical formula and measured data is below 7%.