Experiments and CFD for ONRT Course Keeping and Turning Circle Maneuvering in Regular Waves

Abstract

CFD computations are validated for course keeping and maneuvering of ONRT ship hull advancing at Froude number 0.2 in regular waves. The course keeping computations are conducted for various wave headings (0, 45, 90, 135, 180 deg) with λ/L=1.0 and H/λ=0.02. The maneuvering computation is performed for a turning maneuver with 35 deg rudder deflection for the ship located initially in head waves with λ/L=1.0 and H/λ=0.02. The 6DOF motions/velocities and wave elevation are validated against available experimental data. For course keeping, the validation study focuses on the 0th, 1st and 2nd harmonic amplitude of motions/velocities. The effective and propeller power are also investigated using CFD results. For the turning maneuver, the validation study focuses on the characteristics of turning trajectory in waves and low and high frequency of motions/velocities. For course keeping, the 0th and 2nd harmonic of motions show an average error of 30%DR whereas 1st harmonic amplitude predictions show a smaller error with an average value of 12%DR over all the wave headings. For all harmonics, the largest error value was for the stern quartering wave and the smallest value was often for the head wave conditions. The study on the propeller performance in course keeping showed that the effective power required for the ship was largest in head waves, about 30% more than the power required in calm water. The effective power decreased by increasing the wave heading such that the values were close to the effective power in calm water for wave heading > 90 deg. The propeller efficiency was found to be higher in waves. The increase of the propeller efficiency was largest for wave heading of 45 deg, about 10% increase compared to calm water. For the turning maneuver, the trajectory was well predicted with E=2.9%D and 3.7%D for the advance distance and tactical diameter, respectively. The drift distance was under predicted by 9%D and the drift angle is predicted 87 deg whereas the experimental data shows 55 deg. The comparison of course keeping and turning showed the low frequency values are significantly affected by turning. The low frequency values of the experimental heave and pitch showed the wave is distorted by the ship motion for the second and third turning cycles. The high frequency values of turning and course keeping are similar for the heave and pitch motions and different for other motions/velocities. CFD shows good agreement for the high frequency values of heave, pitch and roll motions and low frequency values of most motions/velocities excluding heave and pitch.