Numerical Calculation Of Gravity Current And Its Interaction With Structures

The gravity current phenomenon exists in many places in nature and in actual engineering.In meteorological research,the study of sea breeze forwards,cold mountain air,and sand storms belongs to the category of air gravity currents.In the geological research,the formation of the canyon and the avalanche on the bottom of the continental slope are also related to the formation of gravity currents.In environmental engineering,the leakage of harmful heavy gases and the accident of offshore oil tankers have formed gravity current causing environmental pollution.In marine engineering,the gravity current caused by the density difference between seawater and river water at the estuary is fast and destructive,which will have a greater impact on the installation and operation of marine engineering in this area.This paper mainly uses the research method of numerical calculation to compare the results of related model tests to verify the accuracy of the numerical model.The main researches are the interaction of gravity currents and multi-structures,the three-dimensional characteristics of gravity currents,the mechanical characteristics of structures under the submarine groove topography,and the motion response of mooring structures under the influence of gravity currents.Under the interaction of gravity current and multiple structures,the characteristics of the flow field of the gravity current,the change of head speed and the mechanical characteristics of the structure are studied.Change the spacing,the number,the density,the shape and the height of the structure,and study the changes of the characteristics.Studies have shown that changing the spacing,number,and height of structures can significantly change the velocity of the heads of different currents.When the structure is relatively compact,the force of the first structure is significantly higher than that of other structures.The force of the last structure due to the hydraulic jump phenomenon is still subject to greater resistance after the flow field enters a quasi-steady state.The three-dimensional CFD numerical simulation was used to study the three-dimensional motion characteristics of the gravity current,and the different flow field characteristics before and after it passed around the cylinder were studied.Studies have shown that the movement of the gravity current has obvious three-dimensional characteristics,and there is a horizontal spatial difference in the position of the head of the gravity current.After the gravity current head passes around the cylinder,a hydraulic jump phenomenon occurs.The flow of the left part of the structure keep the same characteristics with the flow before interacting with the structure.The right part of the structure,due to the occurrence of the hydraulic jump phenomenon,causes the height of the head of the gravity current to drop,which in turn makes the position of the mixed layer lower.The numerical method is used to study the load characteristics of structures with gravity currents under the special submarine terrain with submarine grooves,compare the different force characteristics of structures at different depths,and compare changes in force characteristics with or without a deceleration grid.Studies have shown that the structure at the bottom of the water tank is significantly different from the characteristics of the structure suspended in water,and it is only affected by the positive force.When the structure is in a high position,the resistance force of the lowdensity fluid dominant force acts on it,making it subject to negative resistance.The existence of the deceleration grid can effectively reduce the first maximum value of the resistance and the lift force of the structure,and the effect of reducing the lift force is significant,and at the same time,the force of the structure has a certain hysteresis.The motion response of the mooring structure under the action of gravity current is studied.The numerical calculation research method is used to study the effects of the changes in the depth of the structure and the change in the density of the gravity current on the motion response of the structure.Structures in the high-density fluid non-mixing zone are translated in the positive x direction and rotated clockwise,and structures in the lowdensity fluid non-mixed zone are translated in the negative x direction and rotated counterclockwise.The two working conditions have the same movement trend and the directions are completely opposite.The change of the density ratio of the gravity current does not change the movement trend of the structure,which affects the intensity of the structure's movement.The greater the density ratio of the gravity current,the greater the amplitude of the movement of the structure.