On the Dynamics of Floating Plastic Debris Under the Action of Waves on the Sea Surface. Numerical Modeling

Ocean plastic pollution poses a serious environmental threat to both natural ecosystems and human health. An important field of research on this problem is the development of the physical foundations and methods of remote sensing of plastic debris (PD). The plastic in the ocean and inland waters is largely associated with buoyant polyethylene (PE) films, which are expected to be located the water surface. However, everyday observations show that plastic objects, including PE films, are partially or completely submerged in the near-surface water layer, even though the density of these fragments is lower than that of water. This makes detecting plastic pollution using radar methods more challenging than might be expected. This paper is focused on numerical modeling of an initial stage of the dynamics of a buoyant plastic film placed on the water surface when an intense gravity-capillary wave (GCW) approaches the film. The modeling is performed using the open-source software “OpenFOAM”. It has been revealed that for a highly nonlinear GCW with a bulge structure near the wave crest, there is an “overflow” of water over the film with subsequent sinking of its edge. It has also been obtained that a buoyant PE film sank below the water surface rises slower in the presence of GCW than in the “no wave” case. The explanation of the film immersion effect is given based on the hypothesis that an averaged hydrodynamic force directed against the Archimedean force arises in the field of the orbital wave motions of the liquid particles.