Experimental study on local scour around the submerged vertical circular cylinder under solitary wave action
摘要
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 hc/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 Ks 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%.