Investigation Of Nonlinear Dynamic Behavior For Tank Sloshing

Sloshing phenomenon is usually encountered engineering fields,such as liquid cargo ships in non-fully loaded navigation,liquid storage tanks in the earthquake or moving oil tank cars.Sloshing may induce violent impact pressures near the liquid free surface.The pressure may lead to the local damages or local yields of bulkheads,which could influence ultimate strength of tank.There are many factors have effects on sloshing pressure,such as excitation frequency,excitation amplitude,liquid viscosity,air compressibility,filling level and coupling between fluid and structure etc.Therefore,from perspectives of analytic,numerical and experimental method,it is very important to investigate the prediction of sloshing pressure and corresponding to influence factors thoroughly and in-depth.As above mentioned factors,this thesis carried out the following works:(1)By means of commercial CFD package FLUENT,effects of different turbulence models(κ-ε model,κ-ω model and Reynolds stress model)on sloshing pressures are numerically investigated.By comparing between experimental and numerical results,a more reasonable turbulence model which is used to predict sloshing pressure in numerical model is concluded.(2)Based on governing equations of fluid mechanics(continuity equation and N-S equation),the formula of the thickness of boundary layer is deduced.The ratio of energy dissipation induced by viscous effect is quantitatively investigated,which obtain from sloshing fluid inside and outside the boundary layer.Considering the computational model with and without a second set of boundary layer grid,the effect of boundary layer on sloshing pressure is also numerically investigated,and the corresponding mechanical mechanism is discussed.Carrying out a series of sloshing model tests validate the computational model with boundary layer grid can predict sloshing pressure effectively.(3)For two representative tanks,such as prismatic tank and rectangular tank,2-D and 3-D computational models with boundary layer grid are modeled.Adopting κ-ε turbulence model,effects of 3-D on sloshing pressure are investigated.(4)The parameters of impact pressure induced by sloshing and the corresponding rising time play an important role in dynamic response of bulkhead,and the parameters are connected with liquid viscosity.Therefor four liquids with different viscosity and identical density are designed for sloshing model tests and numerical computations,and effects of liquid viscosity on impact pressure and the corresponding rising time are quantitatively investigated.For sloshing of higher viscous liquid,mechanical mechanism of high-frequency oscillations around pressure peaks is analyzed.(5)Numerical simulation and model test are usually applied to forecast sloshing pressure in resonance.But it is high for computational cost and economic cost.Based on linear potential flow theory,the relationship among sloshing pressure,excitation amplitude and excitation frequency is investigated,and a semi-analytical formula to forecast impact pressure in resonance is constructed for different excitation amplitude and filling level.Also,the forecasting formula of sloshing pressure is validated by model tests and numerical simulations.(6)Numerical calculations for sloshing involving in fluid-structure interaction require substantially longer computing time whether adopting strong coupling algorithm or weak coupling algorithm.Based on the spring-mass mechanical model and considering elastic effect of bulkhead,a simplified mechanical model is proposed to handle sloshing problems involving in fluid-structure interaction for rectangular model.Effects of bending stiffness of bulkhead and filling ratio on modes of coupled system are investigated,and contributions of mass points to bending moment of bulkhead are also discussed.Finally,the proposed mechanical model is validated by the results,which are obtained from the computational results of fluid-structure interaction code ADINA and published data.The main innovations of this thesis are listed as followings.(1)A computational model proposed to predict sloshing pressure is more accurately.The model adopts κ-ε turbulence model and includes a second set of boundary layer based on the formula of boundary layer thickness.The numerical model provides guidance for establishing a computational model of sloshing simulations.(2)Effects of liquid viscosity on impact pressure and the corresponding rising time are numerically and experimentally investigated.Results demonstrate that high viscous liquid not only leads to obviously decrement of sloshing pressure and to obviously increment of rising time of impact pressure,but also entrains air from free surface into sloshing liquid and develops a mass of air pockets and bubbles.Eigenoscillations of bubbles lead to high-frequency oscillations around pressure peak.These conclusions are valuable information for dynamic response calculations of tank structures under impact loads.(3)Based on linear potential flow theory,a semi-analytical formula to forecast impact pressure in resonance is constructed for different excitation amplitude and filling level.The importance of this formula is to forecast sloshing pressures in other resonances if sloshing pressures are given in several resonances.(4)Based on spring-mass model and considering elastic effect of bulkhead,a simplified mechanical model is proposed to handle sloshing problems involving in fluid-structure interaction for rectangular model.The importance of this mechanical model is to improve computational efficiency for numerical calculation considering fluid-structure interaction effects.