Full-scale URANS prediction of a vessel's transverse stability in wind and waves under lifting condition

Predicting a vessel’s motion response is important for the design as well as evaluating its operability and sustainability. This is often performed in towing tanks through captive model test. However, discrepancies exist between model-scale and full-scale results. Besides, quite often, the wind is not included in the test, resulting in unrealistic assumptions of static pressure and constant heeling lever from the wind. This paper presents a study on transverse stability under wind, waves, and lifting conditions, incorporating several series of URANS-based (Unsteady Reynolds-averaged Navier-Stokes) simulations in model scale and full scale. According to the results, scaling effect accounts for about 3~15% in terms of roll amplitude and it seems to be both frictional-force-related and wave-frequency-dependent. In calm water, wind force exerts limited influence on the vessel’s transverse stability. However, in regular beam waves especially in longer waves, a wind of 25 m/s increases the roll amplitude up to 53% and the extent of its influence appears to be wave frequency-dependant. The correlation between roll motion and wind/waves/lifting is complicated but their combination produces way more influence than any individual factor alone, indicating none of them should be neglected.