Large Motions And Flutter Responses Of Ship In Waves

The strong nonlinear phenomena such as green water and slamming are easy to occur in ship navigation in rough sea,causing severe impact even serious damage on hull structure,which affects the stability and safety of ship navigation.Therefore,study on ship motion response and prediction of the impact load of green water and slamming is of great significance to the ship-form optimization and structure design.At present,the potential flow theory is widely used in the study of large motion,green water and slamming in the ship domain.Besides,the linear hydrodynamic theory based on the assumption of small amplitude wave and small motion is generally adopted in the engineering application of the shipbuilding industry.However,fluid viscosity can not be ignored under many circumstances.The research results based on potential flow theory have errors in the study of large amplitude motion.The study of water entry problem mainly focuses on the wedge model.In addition,there is less research on the problem of ship flutter response.Based on the above achievements and shortcomings,the following research work has been carried out.1.Green water problem.A three dimensional multiphase flow numerical model was established by using software FINE/Marine based on viscous flow theory.The BRICS(Blended Reconstruction Interface Capturing Scheme)compressible discrete scheme was adopted to reduce numerical diffusion near the free surface.The radiation problem of the Wigley hull was firstly simulated and the results were close to the experiment data.The reliability and accuracy of the numerical model were verified.Then,according to the important influence factors of green water such as wavelength and wave amplitude,simulations on Wigley ship under different wave conditions were carried out.The impact load on deck and superstructure was analyzed simultaneously.2.Water entry problem.According to the body plan of S-175 containership,the full-sized models of bulbous bow,parallel middle body and stern were established by software LS-DYNA respectively.The explicit finite element method(FEM)and the Arbitrary Lagrangian-Eulerian(ALE)algorithm were utilized to effectively track the boundary movement of material structure and avoid serious grid distortion.The simulation of a wedge was firstly carried out.The results were in good agreement with the published experimental data.The reliability and accuracy of the numerical model were verified.Then,based on the sinking velocities of local sections in published study,the water impact of three typical models are simulated.3.Flutter response problem.Taking the cuboid as the research object,the software LS-DYNA was used to simulate the stress of the rigid body and the elastic body during the motion.Based on the explicit analysis method,the fluidstructure interaction problem of the hull during the wave-facing voyage is simulated.The results show that green water is more likely to occur with relative wavelength of 1.2 and there are two impacts near the junction between deck and superstructure.The profile shape has great influence on the sinking velocity and slamming load,and the velocity can not directly reflect the pressure condition.The research results have some reference value for prediction of impact load on deck,slamming load and ship-form optimization.