Multi-Phase Simulation of Droplet Trajectories of Wave-Impact Sea Spray Over a Vessel

Abstract

Sea spray, generated by ship-wave collisions, is the main source of marine icing. In certain, but not all, circumstances a cloud of spray forms after a wave impacts a ship. The spray cloud comprises numerous water droplets of various sizes. These droplets are dispersed and transported over the vessel deck by the surrounding wind and fall onto the deck or into the ocean under the effect of gravity. The motion of these droplets is important since they determine the extent of the spray cloud and its duration over the deck, which consequently affects the distribution of icing accumulation on a ship in freezing weather. In this paper, a multi-phase air-water simulation of droplet trajectory is used to predict the cloud motion of various size droplets. A smooth particle hydrodynamics (SPH) computational fluid dynamics (CFD) model is implemented and the simulation is accelerated using GPU computing. The field observation data is used to simulate the trajectory. The results of the simulations are compared with an available theoretical model and reasonable agreement is found. The inverse dependence of size and velocity for droplets after the breakup process is examined. The simulation results are consistent with the theoretical model in that neither the largest nor the smallest droplets reach the maximum height of the spray cloud, but the mid-size droplets do. The spray cloud spreads faster and crosses the front of the vessel quicker than predicted by the theoretical model. It is also found that the trajectory of a single droplet is significantly affected by surrounding droplets in a multi-droplet trajectory model. A mono-droplet theoretical trajectory model, therefore, is not as accurate as the multi-droplet CFD model.