| In recent years,due to the increasing demand for development and transportation of marine resources,the actual sea area is not in a calm state,and most of them are in severe sea state.Therefore,it is necessary to study the motion response of ships sailing under bad sea conditions and the increase of resistance caused by waves.The study of wave added resistance is of great significance for the ship speed and economy of ships.The analysis of the ship's motion response under severe sea conditions is related to the safety of the ship,especially collaborative work of multi-vessel is increasing day by day.In this paper,a RORO ship and a 50000DWT semi-submerged ship are taken as the research object to solve the wave added resistance of the RORO ship and the semi-submerged ship,and the motion response of the two ships under coupling action.Based on the RANSE(Reynolds Averaged Navier-Stokes Equations)of incompressible viscous fluids and VOF methods,the wave added resistance under severe sea conditions is studied.The simulation of regular waves is realized under the computational fluid dynamics(CFD)software platform by instantaneously increasing the velocity of the fluid and the wave surface at the fixed wave boundary.In order to verify the reliability and accuracy of the numerical simulation calculation method,the calm water resistance coefficient and wave resistance coefficient of the international standard model KCS(KRISO Container Ship)are calculated,and compared with the model test results,the data are in good agreement.The relative error of total resistance coefficient of still water is 1.1%,the relative error of frictional resistance coefficient and ITTC-1957 is about 0.8%,and the average relative error value of wave resistance coefficient is 4.10%.Then,taking a RORO ship and a 50000DWT semi-submerged ship as the research object,the wave added resistance of the RORO ship and the semi-submerged ship in the range of 0.65 Lpp?1.15 Lpp is carried out.Based on the three-dimensional potential flow theory,the two-ship coupled motion response under severe sea conditions is studied.The two ships of the RORO ship and the semi-submerged ship are considered as the research object.The roll,pitch and heave RAO of two ships is calculated in the frequency domain when l=0-3m,which is transverse space of two ships.Due to the good maneuverability of the RORO ship,the bow of RORO ship is rotated by 0°-30° around the z-axis.The influence of the rotation angle r in the frequency domain on the roll,pitch and heave of the two ships under coupling active is analyzed.According to the analysis of frequency domain calculation results,the RORO ship is more prone to roll resonance in the two-ship coupled motion.In the study of the two-ship coupled motion response in the time domain,the PM spectrum was selected for research.Because the RORO ship is more prone to roll resonance,under the condition of h=1.25m-2.75m,the calculation and comparison analysis of the roll,pitch and heave of a single RORO ship and the RORO ship in two ships when l=3m,4m and r=0°?30°,the following conclusions are drawn:in the two-ship system layout of r=10°and r=15°,the roll value of RORO ship in the two ships with l=3m,4m is smaller than the roll value of a single RORO ship in the calculation period of 120s.Under the condition of h=1.25m?2.75m,Comparing and analyzing the roll,pitch and heave of the coupling motion when l=3m,4m and r=0°-30°.It is found that the effect of r on the roll,pitch and heave of the two ship coupled motion is much larger than l and h.By programming,under the condition of h=1.25m?2.75m,the maximum and minimum vertical relative displacement difference between the two ends of ramp when l=3m,4m and r=0°?30°,which is located at the stern of the RORO ship,the other end is located in the midship of semi-submerged ship.It is found that the possibility of the maximum vertical displacement difference is much higher than other cases in the layout of the two ship systems with r=20°.According to the time domain calculation and analysis of the coupled motion of the two ships when l=3m and 4m,under the condition of h=1.25m?2.75m.If the bow of the RORO ship is rotated a certain angle while the two ships are working together,the two-ship system layout of r=20° ought to be avoided as much as possible,it is recommended to choose the two-ship system layout of r=10°or r=15°. |
PDF Full Text Request