Experimental Study On Multi-bubble Motion Characteristics Of Underwater Explosion Under Different Boundary Conditions

Multi-bubble dynamics plays an important role in various engineering fields,such as seabed resource exploration,underwater missile attack,multi-bubble ice-breaking,and so on.The boundary conditions have a significant impact on the motion characteristics of bubbles,and the interaction between bubbles will produce some special bubble movement phenomena.Therefore,it is of academic significance and engineering value to explore the motion characteristics of multiple bubbles under different boundary conditions and reveal the coupling mechanism between multiple bubbles and boundary conditions.The experimental bubbles in this paper are produced by low voltage electric spark technology.By adjusting the distance between the initial centers of bubbles and the distance between bubbles and different boundaries,we can explore the influence of characteristic parameters on the multi-bubble fusion characteristics,water mound parameters and ice breaking effect.In this paper,the dynamics of two bubbles on the free surface,at the boundary of ship structure(wall and V-shaped structure)and near the ice layer are studied experimentally,and the pulsation between bubbles,water mound and ice-breaking phenomenon are observed.In this paper,six typical water mound phenomena are observed for the interaction between single bubble and free surface.The differences of the motion state and the parameters of the water mound between two vertically arranged bubbles and a single large bubble at some special moments near the free surface are investigated.It can be seen that the maximum volume of the fused bubble and the time to complete the jet are later,and the water mound at the same time will be higher and thinner.Then,the influence of the bubble spacing of two bubbles on bubble fusion and water mound parameters under the vertical layout condition is revealed,the results show that the increase in bubble spacingγbb leads to a decrease in the time when bubbles complete the jet.And the laws of bubble characteristic parameters(bubble spacing,bubble and free surface distance)on bubble motion and crown water mound parameters under the horizontal layout condition are summarized,the results show that with the increase of γbf,the time when the bubble reaches its maximum volume increases and the crown appears later;The bubble spacingγbb may not be the main cause of apron phenomenon.The water mound phenomenon caused by three bubbles is shown,and some suggestions are put forward for the application of water curtain anti-missile.Then,for the motion of two bubbles near the boundary of the ship structure,this paper selects the simplified wall and V-shaped structure as the boundary,showing some basic phenomena of the two bubbles under the boundary,such as fusion,jet,rupture,etc;The motion characteristics of two bubbles under the wall in horizontal and vertical arrangement are investigated,and some special physical phenomena are shown.Finally,the motion of bubbles at the boundary of layer ice and its ice-breaking effect are studied in this paper.First,it shows the movement characteristics of a single large bubble under a certain thickness of ice,and summarizes the main reasons for the ice fracture:the expansion wave formed by the shock wave reflected by the ice,which causes the ice to generate tension,resulting in the ice fracture.Then,the movement characteristics of two horizontal bubbles under the ice and the breaking effect of the ice were observed,and the fusion motion state of two bubbles near the ice with holes,the ice-breaking effect and the water mound phenomenon on the free surface were studied under different arrangements.