Experimental And Numerical Research Of Box-Shape Ship Forced Rolling Hydrodynamics

With the growing attentions paid to ship rolling motion,it has been one of the hot topics in the field of ship hydrodynamic to determine the roll damping coefficients and find out the physical characteristics of the flow field when a ship rolls.The model test,empirical formula and the viscous flow numerical simulation are mostly used approaches in determination of roll damping.Model test provides the most visualized and effective method to determine the rolling damping.Furthermore,empirical formula used for roll damping prediction is also based on data from model testing.Numerical simulation using CFD is widely applied in the research of ship roll damping for its advantages such as low cost,the noncontact measurement of the field flow,etc..In this thesis,ship rolling hydrodynamics under forced rolling condition has been investigated by both model testing and numerical simulation.First the model test using a barge model is carried out where the model was forced to perform harmonic rolling by a self-designed forced roll equipment.Accuracy and reliability of this equipment was verified through this experiment.Roll hydrodynamic coefficients were obtained by analyzing experimental data.From which,the variations of the roll hydrodynamic coefficients under different roll amplitudes and roll frequencies was be analyzed,especially the roll damping coefficient.Meanwhile,the flow field around the ship model in forced roll testing was investigated by employing PIV(Particle Image Velocimetry)equipment.By capturing and analyzing movements of the particles,Velocity vector distributions were obtained,which further indicated the flow separation and vortex shedding around the bilge of the ship.Secondly,based on the VOF multiphase model,effects of the turbulence models,mesh quality,time step,etc.on the convergence and accuracy of the computation are studied respectively.Afterwards,the forced rolling numerical simulations are conducted according to the experiment conditions of the barge.Finally,the numerical simulations and model tests are compared,as well as the flow vorticity field measured by PIV and the flow vorticity field simulated by FLUENT.