Numerical Simulation Of Nonlinear Liquid Sloshing In The Tank

As the demand for oil and natural gas increases, the size of the fluid contained cargo ship such as VLCC, FPSO, LNG and LPG increases. The security of these ships at sea has attracted significant attention in the fields of naval architecture and ocean engineering.Liquid sloshing is a kind of wave motion inside a partially filled tank which subjected to an external excitation force. It's a complex fluid motion with strong nonlinearity and randomicity. Sloshing occurs in almost all of the conditions except the full load and no load. When the behavior of sloshing becomes violent, it can lead to huge local impact load and cause structural damage. In order to design the tank walls under sloshing action's load and insure the stability of the ship, it's necessary to predict the liquid sloshing using numerical method.The main contents of the thesis are as follows:(1) The research of liquid sloshing with potential, viscous and experimental methods is systematically reviewed in present thesis. The numerical method for the free surface simulation is also presented.(2) The numerical method for liquid sloshing is discussed. The computational process of arbitrary Lagrangian-Eulerian (ALE) finite element method and boundary element method is introduced. The rationale of the VOF method is also introduced. All the methods are compared with the available analytical solution, good agreements are obtained.(3) The two-dimensional liquid sloshing problem in the horizontal excited tank is investigated. The ALE finite element method and the boundary element method are compared with the simulation of liquid sloshing with a honrizontal or vertical baffle. The effect of the baffle is checked.(4) The liquid sloshing problem in the three-dimensional rectangular tank under horizontal or roll excitation is simulated. The hydrodynamic force and moment acting on the tank wall are also computed. For liquid sloshing problem with baffles, the effects of baffles type, dimention and position are investigated.(5) The violent liquid sloshing problem in the three-dimensional rectangular tank under horizontal or roll excitation is simulated. The shallow-water effect is also studied. For liquid sloshing problem with baffles, the effects of baffle's type, dimention and position are investigated.Concluding discussions of the baffle's effect are shown as follows.(1) For liquid sloshing in a horizontal-exited tank, the transient amplitude of free surface elevation increases with the increase of baffle's depth and decreases with the increase of baffle's length when the tank is horizontal-baffled, the transient amplitude of free surface elevation decreases with the increase of baffle's height when the tank is vertical-baffled. The vertical baffle is a more effective way to reduce the sloshing amplitude than the horizontal baffle.(2) For liquid sloshing in a roll-exited tank, the transient amplitude of free surface elevation decreases with the increase of baffle's height when the tank is vertical-baffled, the transient amplitude of free surface elevation increases with the increase of baffle's depth and decreases with the increase of baffle's length when the tank is horizontal-baffled. The horizontal baffle doesn't work well when the exicitation becomes violent.(3) For liquid sloshing in a tank with a T-shaped baffle, the transient amplitude of free surface elevation decreases with the increase of baffle's height when the tank is under the horizontal-excitation. The T-shaped baffle doesn't work well when the tank is under the roll-excitation.