NUMERICAL SIMULATION OF THE WAVE-INDUCED DRIFT OF DISC-SHAPED FLOATING PLASTIC DEBRIS

Floating plastic debris poses a significant threat to the health of the world's oceans and ecosystems. Understanding the pathways of floating marine litter is crucial in designing effective solutions to mitigate this problem. The Ocean Cleanup aims to build simple but reliable numerical models to better predict plastic accumulation zones. In this context, a Lagrangian point-particle model has been developed that can help better understand wave-induced drift. The continuous and the discrete phase are coupled in a one-way fashion using a micro-scale Euler-Lagrange approach. The Maxey-Riley equation is modified to account for disc-shaped objects, variable submergence, and two-directional drag correlation. By comparing our numerical predictions with experimental work, we demonstrate that floating discs can experience up to 73% increased wave-induced drift compared to Stokes drift. We show that the non-Lagrangian behaviour of objects is mainly dependent on the water-plastic density ratio and its size compared to the wavelength. Two key physical mechanisms contributing to increased drift effects are investigated, both related to the particle's variable submergence. Finally, we provide an overview of the computational limitations and the model sensitivities that can help to improve the accuracy of numerical wave-induced drift predictions.