Numerical detection of bubble creation and extinction events under a breaking wave using Optimal Network algorithm

Bubbles generated by breaking waves play a crucial role in coupling oceans with the atmosphere by enhancing gas transfer, heat exchange, and sea spray aerosol formation. In this study, we perform direct numerical simulations of wave breaking wherein the topology of the air-water interface is captured by a coupled level-set and volume-of-fluid method. We develop an Optimal Network (ON) algorithm, which is a parallel, Lagrangian bubble tracking algorithm that utilizes information on bubble position, shape, velocity, and volume to establish a network of non-conflicting maps quantified by pseudo-distance error norms, between lists of bubbles belonging to adjacent time instants. The ON algorithm is capable of categorizing events involving bubbles, aerated cavities, and filaments into continuity, fragmentation, coalescence, entrainment, and bursting at the sea surface. We apply suitable filters and dynamic task scheduling to reduce the computational complexity of detecting non-binary fragmentation and coalescence. By employing the ON algorithm as a post-processing tool, we obtain bubble trajectories and residence times, construct bubble history graphs, and detect all bubble creation and extinction events that span the spatio-temporal evolution of bubble plumes beneath breaking waves.