Numerical Simulation Of Interactions Between Two Ships Under Wave Effect

Ships play a vital role in the development of marine resources.However,the waves in the ocean poses more challenge to the safety and reliability of the ship’s operations.Therefore,it is very important to study the interaction between waves and ships.With the development of ship technology,it is more common for two or more ships to work side by side.This thesis studies the wave force and motion characteristics of the two ships when the waves flow through the two ships.Based on the user-defined function in FLUENT software,a high-quality numerical wave tank is successfully constructed by the defining wave velocity at inlet and the wave-damping method,which can be agree well with the theoretical wave shape.The VOF(Volume of Fluid)multiphase flow model and the standard k-ε model were selected to simulate the wave environment.The validation of the selected models is conducted by the comparison with the experimental results in a similar environment.The thesis considers 6900 t cargo ship(referred to as "big ship")and 1600 t cargo ship(referred to as "small ship")as the research objects.The content of this thesis are finished: numerical simulation of fixed ships,heaving ships and ships in the heaverolling two-degree-of-freedom coupled motion under wave action.For the numerical simulation of the fixed ship in the wave,this thesis considers two influencing factors,namely distance between the ships and the wave level.Numerical simulations show that when the ships are stationary,the small ship will hinder the propagation of waves.The change of the wave surface will cause the drags of the two ships to be out of phase.Two peaks appear on the lift coefficient curves of the two ships.Drag and lift coefficients of the two ships are negatively related to the distance between the two ships.The drag coefficient is positively correlated with the wave level,and the lift coefficient is slightly negatively correlated with the wave level.For the numerical simulation of the ships heaving in the waves,this thesis adds the draft of small ship as a variable on the basis of simulation of the fixed ships.The numerical simulation shows that the hydrodynamic coefficients of the two ships have different changes under different wave levels.The flow field analysis is carried out with the big ship as the main research object.It is found that under the higher wave level,the drag coefficient of the big ship and the displacement of heave motion were positively correlated with the distance between ships and the draft of the small ship.At lower levels,the drag coefficient of the big ship is inversely related to the distance between the ships and the draft of the small ship.The movement displacement of the two ships is positively correlated with the wave level.For the numerical simulation of the ships heaving and rolling in the waves,this thesis takes the distance between the two ships as the main research variable.The numerical results show that the tendency of the hydrodynamic coefficients of both ships mainly depends on the law of the waves rising and falling on both sides of the small ship.At higher wave levels,the change trend of drag coefficient of the two ships with the distance is consistent with that in the simulation of the heaving ships.However,the shipped sea in some working conditions will affect the tendency of drag coefficient of the small ship.And the roll angle of the two ships will decrease as the distance decreases.At lower wave levels,the drag coefficient and roll angle of the big ship increase first and then decrease as the distance decreases while the drag coefficient of the small ship decrease first and then increase as the distance decreases.This is because of the changes in the law of the waves rising and falling on both sides of the small ship.The change trend of the roll angle at a longer distance is consistent with the drag coefficient.It decreases at a shorter distance as the distance decreases.In this thesis,the safe docking distance of the two ships is determined based on the roll experience.