Evaluation on the Hydrodynamic Performance of Small-Scale Buoys

The geometry of a buoy is a critical determinant of its hydrodynamic performance, directly influencing its stability and operational efficiency in marine applications. While extensive studies have investigated the dynamic response and mooring loads of large-scale buoys, the effect of geometric shape on the performance of small-scale buoys under transient deployment and steady towing conditions has not been quantified. This study presents a numerical investigation into the hydrodynamic characteristics of a small-scale streamlined buoy and a conventional cylindrical buoy, examining two critical operational scenarios: free water entry under self-weight and steady-state towing. The primary contribution of this work is the first quantitative comparison of these two geometries at small scale across both deployment and service conditions. The results indicate that during free water entry, the streamlined buoy sinks deeper than the cylindrical buoy at all density ratios. It also achieves a higher maximum ascent velocity. Under towing conditions, both the time-averaged drag and lift forces increase with velocity for both buoy types, with the cylindrical buoy experiencing a more pronounced increase. The wake of the streamlined buoy shows no significant vortex shedding at any velocity, whereas vortex shedding behind the cylindrical buoy becomes increasingly evident as velocity rises. With the increasing attack angle, the time-averaged drag force of the streamlined buoy increases moderately, while that of the cylindrical buoy rises markedly. As the buoy approaches the free surface, the time-averaged drag force increases slightly, while the absolute value of the time-averaged lift force rises substantially. The vortex on the upper side of the buoy, influenced by the free surface, exhibits reduced intensity, whereas the lower-side vortex becomes significantly stronger. For applications demanding high towing stability such as long-term ocean observation networks, communication relay buoys and navigation aids, the streamlined buoy performs better than the cylindrical buoy.