Numerical Prediction Of Motion And Hydrodynamic Forces For A Ship Advancing In Regular Head Waves In Shallow Water

In recent years,with the development of ships towards larger scale,some navigational areas can no longer be regarded as deep water but shallow water;consequently,the ship hydrodynamic performances are under the shallow water effect.For a large ship advancing in shallow water,greater hydrodynamic forces acting on the ship bring about significant ship squat;when the ship is navigating in shallow water in waves,the vertical oscillatory motion induced by the wave effects further aggravates the risks of ship grounding.Therefore,predicting the motion and hydrodynamic performances of large ships advancing in shallow water under wave actions is of great significance for a safe navigation.In this thesis,the numerical wave tank is established by utilizing the CFD software STAR-CCM+.Taking the tanker KVLCC2 model and the containership DTC model as study objects,numerical simulations of the viscous flow around the ships advancing in regular head waves in open deep and shallow waters and in restricted water are conducted by solving the unsteady RANS equations based on the CFD method for viscous flows to predict numerically the ship vertical motion and the hydrodynamic force on the ship.Convergence analyses of the numerical results are carried out and the numerical uncertainty due to discretization is evaluated to verify the numerical method.For the open deep water condition,the ship motion and hydrodynamic forces of the KVLCC2 model advancing in regular head waves are computed by using the viscous flow method,and the numerical results have shown a satisfactory agreement with the model test results.Then,the inviscid flow around the ship is simulated based on the inviscid model to investigate the influence of fluid viscosity on the ship motion and hydrodynamic performances.The results have shown a minor influence of fluid viscosity on the ship motion and a certain influence on the added resistance in waves.For the open shallow water condition,the applicability of different wave models is studied first,and it is found that waves modeled by the fifth-order Stokes wave model are much more stable than those modeled by the linear wave model.Then,the wave propagation under different water depths is simulated,and perceptible but negligible dissipation of wave energy due to the effect of fluid viscosity is found.The numerical simulations of wave propagation have shown a stronger non-linearity of wave amplitudes of longer waves in shallower water.After that,the viscous flow around the KVLCC2 model advancing in regular head waves under different water depths and at different ship speeds is numerically simulated,the influences of water depth and ship speed on the ship motion and hydrodynamic performances are investigated,and the navigational safety is analyzed in the light of the dynamic underkeel clearance of the ship.The numerical results have shown that the peak value and the corresponding frequency of ship vertical motion decrease in shallower water,and a change in the variation trend of the added resistance in waves against the wavelength or the wave circular frequency in shallower water has been found,while the increase in the pressure resistance always contributes significantly more to the added resistance in waves than the increase in the frictional resistance under different water depths.Moreover,a significant reduction in the dynamic underkeel clearance of ship in longer waves in shallower water is also found,bringing about higher risks of ship grounding,but such risks can be effectively reduced when the ship is operating at a lower speed.For the shallow and narrow waterway condition,the ship motion and hydrodynamic forces of the DTC model advancing in regular head waves are predicted,and the numerical results have shown a satisfactory agreement with the model test results of the international benchmark study.Then,the viscous flow around the ship advancing in regular head waves in waterway of different widths are numerically simulated,and the influence of side wall on the ship motion and hydrodynamic performances is analyzed.It is found that the ship-bank interaction has a non-negligible influence on the mean attitudes of ship in waves and a significant influence on the added resistance in waves.In this thesis,the ship motion and hydrodynamics of the ships advancing in regular head waves in open deep and shallow waters and in restricted water are well predicted,the features of the viscous flow around the ships under different conditions are well captured,and the influences of water depth,ship speed and side wall on the ship motion and hydrodynamic performances are revealed.It offers a certain theoretical guidance to the safe navigation of a ship advancing in shallow water under wave actions.