Experimental investigation on turning characteristics of KVLCC2 tanker in regular waves

摘要

Manoeuvring performance of a ship in actual sea is significantly different from that in calm water due to wave loads. It is necessary to estimate the ship's manoeuvrabilities in waves at the early design stage for its safe operations. Several theoretical approaches have been attempted to estimate the manoeuvring performance of ships with considerations of wave loads in recent decades, but there are insufficient model test data for the validation of numerical results. In this study, free-running model tests are systematically performed for well-known KVLCC2 tanker. Model tests are carried out in a square basin, regular waves are generated with the variations of directions, lengths, and heights. In particular the wave lengths are selected at around the ship length. The number of propeller revolution is determined for the model speed corresponded to full-scale service speed in calm water, that rps is fixed in all runs. Therefore the loss of approach speed is observed depending on the encountered wave conditions. Encountered wave profiles are estimated by using relative wave heights data measured on the side of deck in real time, the rudder is always deflected at the moments when the wave crest passes on the midship of the model. The timing of rudder deflection has little influence on the low frequency manoeuvring motions of the model ship. Drifting distances of turning trajectories are relatively large when the wave lengths are below the ship length, and relative drifting angles between wave propagation direction and trajectory drifting direction are largest when the wave lengths equal to the ship length. Drifting distances and relative drifting angles increase with increasing wave heights. Although the trajectories at the early stage of turns are varied depending on encountered waves, drifting distance and angles during steady turns are similar if the wave height and length are identical. Based on the present test results, it is appropriate that the trajectory drifting distances and angles are defined as the magnitude and direction of a vector between two positions with the headings of 360 degrees and 720 degrees. Finally, the effects of velocity fluctuations on the trajectory drifts are analyzed in some cases.