Parametric Roll: Hyghly Controlled Experiments fora an Innovative Ship Design

The present work is focused on ship’s parametric roll. In particular, a series of controlled experiments have been performed in order to obtain repeatable results both for the inception and the roll amplitude in parametric roll condition. The experiments have been performed for an innovative ship design (a tumblehome shape) in a towing tank provided by a flap-type wave maker. The model was tested in 3 DoF conditions, being roll, pitch and heave motions free and surge, sway and yaw restrained. The experimental work, which is the subject of the present paper, is part of cooperative research project between the IIHR (Iowa Institute of Hydraulic Research), the University of Trieste and the Italian ship model basin (INSEAN) (1, 2). All the experiments have been carried out in head waves at the INSEAN basin n. 2. The model motions were measured both by an optical motion tracker (Krypton) and a gyroscopic platform (MOTAN). Tests were carried out for three different metacentric heights in a range of speeds. Roll decay tests as a function of forward speed were before every experiment in waves in order to determine the natural roll frequency and the roll decay rate. The head waves experiments showed parametric roll excitation for different metacentric heights, wave steepness and Froude number. The repeatability of the obtained results, allows to use them as a benchmark for both CFD codes and theoretical models. This will be the subject of a future work, which is at present in preparation and involves other international collaborations beyond the ones listed here.