Session: 08-05-02 Free Surface Flows II

Paper Number: 79108

79108 - Numerical Simulation of the Wave-Induced Drift of Floating Marine Plastic Debris Modeled as Discrete Particles 

Every year few million metric tons of plastic litter are entering our oceans. They are being transported in the oceans by several mechanisms (Longuet-Higgins [1953]). Amongst the most important ones being the wave-induced drift or the Stokes drift (Calvert et al. [2021]). The usual consideration of marine litter objects as Lagrangian tracers, being perfectly transported by the waves Stokes drift put us into considering the opposite. Additionally, these objects have finite sizes, various shapes and various plastic-to-water density ratios which potentially contribute to a non-Lagrangian tracer description of their transport. Amongst the best tools to study these issues are numerical simulations along with experimental wave tank validation. As a matter of fact, in this study, we use Basilisk (Popinet [2014]), a Direct Numerical Simulation (DNS) tool to solve the two-phase Navier-Stokes flow equations on an octree grid including the Volume-Of-Fluid (VOF) method for the free surface tracking. The waves are generated with a numerical wavemaker (Lande [2020]) to recreate the wave conditions in an experimental study that we performed (R. Clavert et al. [2021]). We use a Discrete Particle Model solver to account for the presence of plastic particles whether at the free surface or under it with the hypothesis of dilute suspension flow and therefore the particles are not modifying the flow structure. Particular care is dedicated to the implementation of body forces that are potentially present at the free surface such as pressure gradient and surface tension. The goal of our work is organised in three-fold: i) We first compare our simulation results directly with the experimental work that we carried out in an experimental wave tank which shows that relatively spherical floating inertial objects have an enhanced wave-induced drift when compared to a purely Lagrangian tracer. ii) Then we carry out several larger-scale tri-dimensional simulations of various sea states satisfying the JONSWAP wave spectrum. iii) Finally, the larger-scale simulations will help us to build a reduced model of marine litter Stokes drift that is dependent on their characteristic sizes, the water-to-particle density ratios and the wave characteristics. 

Presenting Author: Andriarimina Rakotonirina The Ocean Cleanup

Authors:

Bruno Sainte-Rose The Ocean Cleanup
Andriarimina Rakotonirina The Ocean Cleanup
Ton Van Den Bremer TU Delft
Yannick Pham The Ocean Cleanup