Hydrodynamics of Two Side-by-side Vessels Experiments And Numerical Simulations

Abstract

Side-by-side offshore oil offloading is routinely performed around the world. During these operations a shuttle is moored in close proximity to a floating turret-moored storage facility. Operational experience often dictates the limiting weather conditions for conducting such operations safely. In general no hydrodynamic analyses are performed to assess more quantitatively the threshold values and this has been accepted by the Industry. Owing to the nature of the LNG trade, reliability of each stage of the chain is paramount. In this context, the reliable modeling of the hydrodynamics and sea keeping of two side-by-side moored vessels during the offloading phase has become mandatory especially in view of the limited or lack of experience for operations that have not yet been performed. The hydrodynamics of two side-by-side vessels is more complex than for a single vessel. The difficulty lays in the hydrodynamic interactions, the shielding effects and the wave resonance observed in the gap between the two vessels. Experiments have been performed for variable distances between the two vessels. The model test campaign is described. The numerical results obtained with two diffraction packages able to deal with the wave resonance in the gap (WAMIT and HYDROSTAR) and hydrodynamic interactions are compared with the experiments.