Experimental Study On Local Scour Of Submerged Cylinder Under Solitary Wave

With the continuous development and utilization of marine resources,in the construction of various offshore buildings,pile columns can be divided into two categories:non-submerged and submerged,gravity anchorage,underwater caisson,energy dissipation measures are considered underwater submerged structure.The local scour around the building seriously affects the stability of the structure and even leads to the slope and collapse of the building.Solitary wave will cause intense sediment movement and shoreline evolution in the coastal area.Therefore,the study of local scour around the submerged pile column under the action of solitary wave has important engineering value and theoretical significance.Based on the wave flume test,the local scour around the submerged pile column under the action of the solitary wave is studied.The experiment is carried out on the sand bed with flat bottom.The sand bed with the diameter of 0.22 mm is laid and the solitary wave is used.The hydrodynamic characteristics around the pile column,the development process of scour and the change of bed surface morphology were measured and recorded.The wave conditions,the submergence degree of the pile column,the structure type of the pile column and the diameter of the pile column were changed.The influence of the above.factors on local scour are analyzed.The experimental results show that the wave propagation is disturbed by the cylinder,the horseshoe vortex and the lee-wake are produced around the pile,and the semi-annular scour holes are produced in front of the pile and behind the pile,respectively,with the increase of the number of solitary waves.The semi-annular scour holes in front and behind piles gradually form circular scour holes.The geometric form of the scour hole around the pile consists of the vertical depth of the scour hole,the extension width and the slope of the scour hole.The maximum scour depth appears after the pile,and the slope of the scour hole changes dynamically in the scour development stage.The slope of the scour hole tends to a stable value when the scour is balanced.The shape of the scour hole around the pile under the action of solitary wave is similar to that of the scour hole around the pile under the action of unidirectional flow,but the position of the maximum scour depth is opposite,the difference of the scour form around the pile under the action of the solitary wave and the regular wave is great,but when the submergence rate increases,The scale of the scour holes around both piles tends to decrease.The inundation rate increases,the overcurrent capacity above the pile column increases,the flow around the pile column weakens,the intensity and duration of the horseshoe vortex and lee-wake decrease,the sediment transport capacity becomes weaker,and the scour hole scale becomes smaller,At hc/D>1,there is little change in the depth of the pile in front of the pile,but the depth behind the pile is still increasing.There was a positive correlation between the scour hole size and the surface grain size of the pile around the pile height.Under the same wave condition,the vortex strength and duration of the pile circumference are larger than that of the submerged structure,and the scour development rate of the non-submerged structure and the scale of the scour hole around the pile are larger than that of the submerged structure.However,the local scour around the pile column is similar to that around the pile in the two types of structure,both of which are connected ring scour holes with the back flushing depth greater than that of the pile front,and the diameter of the pile increases and the maximum scour depth around the pile increases.Based on the experimental data,the prediction formula of local maximum impact depth of submerged pile column under the action of solitary wave is obtained.