Experimental and numerical evaluation of the added wave resistance for an ultra large container ship in shallow water

In this paper, the added wave resistance of an Ultra Large Container Ship (ULCS) in shallow water is investigated both experimentally and numerically. The experimental results come from a series of tests performed in the Towing Tank for Manoeuvres in Confined Water (co-operation Flanders Hydraulics Research and Ghent University) in Antwerp (Belgium) in 2016. Tests were executed for head and following waves, with two wave amplitudes, and using two different beam frames to attach the ship to the towing tank’s carriage. One of the frames restrained the heave and pitch motions while the other one allowed the free motion of both. The results of experiments outline the proportionality of added resistance on the square of the wave amplitude in shallow water conditions. Moreover, the expected behaviour of added resistance at different wave lengths can be observed: in long waves, the added resistance is tightly related to the ship motions, while in short waves it achieves an asymptotic trend. In following waves, a peculiar phenomenon is noticed: at moderate forward speeds a positive added resistance of substantial magnitude is measured for a specific, speed dependent interval of wave lengths. This phenomenon is investigated and preliminary ascribed to the interaction between the incident wave field and the return current originated by the motion of the ship in shallow water. Numerical simulations are performed with two potential codes: one based on strip theory and one 3D panel code. The 3D panel code performs better than the strip theory code. An in-depth analysis of the added resistance and vertical motions is performed, and the discrepancies of simulated added resistance with respect to experiments are mainly ascribed to the inaccuracies of numerical codes in the calculation of heave and pitch RAOs and phases.

Jaar van publicatie:2019