Study On The Hydrodynamic Characteristics Of Buoy-type And Solid-foam-type Anti-sloshing Techniques In A Tank

Liquid sloshing refers to the motion phenomenon of free surface in the container which is not fully loaded with liquid and is excited by external force.This phenomenon often occurs in the liquefied natural gas(LNG)tanks.When the external excitation frequency is close to the natural frequency of the liquid tank,violent resonance and great impact pressure in the tank will occur,which seriously threatens the structural safety of the liquid tank.Therefore,it is necessary to propose and study the promising anti-sloshing methodsBuoy-type anti-sloshing structure is proposed in this paper and based on the potential flow theory,the boundary element method is adopted to establish the three-dimensional rectangular tank model with a buoy-type structure and predict the natural sloshing frequencies and corresponding modes in liquid tanks.Effects of geometry parameters,including position,draught and radius of structure on natural sloshing frequencies are studied.The anti-sloshing effects of the buoy-type structure in tanks of different liquid depth are also analyzed.It is found that the natural sloshing frequencies in liquid tank with a buoy-type structure are generally lower than that without any structure.When the buoy-type structure moves close to and along the tank wall,the variation range of natural sloshing frequency is the largest.The effect of buoy-type structure with larger radius and draft on the natural sloshing frequency is more obvious.A solid-foam-type anti-sloshing techniques concept is proposed.And some experiments using foam balls with different diameters are conducted in the paper to investigate effects of foam on the hydrodynamic characteristics.The contact between foam with bigger diameter is considered as point contact due to shape restriction.As for foam with very small diameter,it is complete contact.So the study on foam with small diameter is based on changing foam thickness.When the tank is excited by different excitation frequencies,anti-sloshing effects of different foam thicknesses in three liquid depths is studied,which mainly inludes the reduction of steady wave height and dynamic pressure.And then excitation amplitude is changed in order to investigate the anti-sloshing effects of foam.It is found that foam can effectively suppress sloshing and reduce the pressure amplitude.The best choice of foam thickness is one tenth of the liquid depth.The tank is excited by larger excitation amplitudes,the foam can obviously restrain the wave breaking.The study on foam balls with bigger diameter is based on changing the number of foam-layer.The effects of the foam with different diameters and layers on the steady wave height and dynamic pressure in tanks with three liquid depths are firstly explored.Then effects of the contacts number between the foam balls and the mass of foam on free surface is studied by using the control variable method.It is found that the double-layer foam with a diameter of 0.01 m is the best choice,which can reduce the steady wave height by at least 55% and significantly weaken the nonlinear characteristics of liquid sloshing.Under the condition of same foam-layer thickness,the foam balls with smaller diameter always have better anti-sloshing effect than the larger ones.Under the condition of the same mass of foam laying on the free liquid surface,the more contacts between the foam balls,the better the anti-sloshing effect.