URANS simulations for a free-running container ship: Part 2. Added power

Abstract

Part 2 reports the validation, local force and local flow study results for the free-running added power simulations whose conditions are the same as the self-propulsion test except for the increased propeller rotational speed and the presence of wave. When targeting the same mean Froude number in the wave condition, the propeller requires the increased propeller rotational speed for the operation at the low advance ratio due to the added resistance. The test is performed at five different wavelengths in head waves and four different headings in the oblique waves. For the validation study, the time series of the validation variables is decomposed with discrete Fourier transform to extract the harmonic values. Validation variables are global parameters, including motions, propeller thrust, and torque coefficients, added power variables, and self-propulsion factors which show reasonable agreement against the experiment results and produces a similar error from the self-propulsion simulation. The local force study shows that the added resistance mostly appears at the bow due to the bow plunging during the short head wave and resonance condition. The contributions of the gravitational force and the buoyant force are found to increase as the stern motion exceeds the bow motion during the long head wave condition. The oscillation of the propeller performances shows correlation with the first harmonic amplitude of the propeller inflow. Heave, pitch, and roll decay tests are performed prior to the main test to assess the natural frequencies of the ship. Same as Part 1, a discretized propeller is used.