A CFD-based Study On The Prediction Technique Of The Seakeeping Of Wave Piercing Catamaran

Wave piercing catamaran is one of the most developing ships in the field of high performance ship,which is not only excel at the speed and powering and the good seakeeping capacity,but performs well in the wide deck area of the conventional catamaran.Therefore,it has been widely used in the civil and military fields.However,the researchers have found that the negative effects of heave and pitch motion on the performance of ship comfort while the wave piercing catamaran is moving at high speed.Thus,the proper predictions on motion of the waving piercing catamaran in the waves are required in the initial ship optimization design.In the present studies,the deficiencies still exist in the prediction on the motion of wave piercing catamaran in the waves and the motion performance in the different wave angles.In the large amplitude motion,the repeated water entry and exit of the bows lead to the violent change of the instantaneous wet surface.In addition,the water entry of midbody causes the breaking wave phenomenon,as well as the strong nonlinear effect of the flow field,which results in the significance of the simulation of the details in the flow field in the process of motion.Based on the previous studies,this study has analyzed the motion of wave piercing catamaran in regular head waves by the means of the CFD-based 3D viscous numerical wave tank technique,as well as the nonlinear of motion and the variation of details in flow field.Furthermore,it makes the predictions on the motions in different wave direction angles.Firstly,a 3D viscous numerical wave tank is set up on the basis of CFD theories,which is made to calculate the ship seakeeping.And a valid numerical simulation on wave has been done by three dimensional numerical techniques of wave generation and absorption.Then,an application of overlapping grid on the seakeeping of ship has been studied through the introduction of overlapping dynamic mesh technique.In the meanwhile,the grid division method in the whole flow field is studied at last,such as the grid around hull,boundary layer mesh,the grid on the free surface,etc.,to obtain a set of optimized computing grid on seakeeping.Secondly,compared with the test value,the predictions have been made in this study onthe heave and pitch motion of a wave piercing catamaran ship model by three-dimensional numerical wave tank technique.Moreover,the law of relative motion of the ship,as well as the corresponding frequency and speed range of maximum response,has been obtained by estimating the motion phase and the natural frequency.In the meanwhile,a numerical analysis has been done to evaluate the effects of the wave piercing catamaran on the motions in the wave.Furthermore,the motion of nonlinear problems of the wave piercing catamaran in head waves has been studied,and the non-linear change of heave and pitch motion of the ship with different wave steepness has been achieved.The unsteady state flow near the free surface and the propeller nominal wake section and the analysis of non-linear characteristics of the flow field have been simulated in this study.Finally,the predictions on the motion of wave piercing catamaran in beam and the oblique waves have been made in this study,which has contained the three-freedom motion in different wave angles of 45 degrees,90 degrees,120 degrees and 135 degrees at zero advancing speed,and then compared the law of motion changes in different wave angles.