Investigating plastic waste transport in coastalareas with Smoothed Particle Hydrodynamics

Technological progress and increasing human activity are driving higher production levels, resulting in more waste being released into the environment, and in particular in the seas and oceans. The growing need to understand the transport and distribution mechanisms of marine debris has led to the development of various investigation methods, with extensive monitoring (both in situ and through remote sensing), laboratory experiments, and numerical modeling. Through the use of physical equations, real environmental data, and appropriate computational algorithms, numerical modeling in particular can bridge the gap between discrete experimental data and the complexity of the phenomenon, allowing its behavior to be described and predicted under more general conditions. The existing literature has primarily focused on oceanic dispersion models suitable for deep water and offshore investigations, while few studies address the coastal areas, due to the complexity introduced by the highly dynamic, nonlinear nearshore behavior, characterized by wave breaking and currents that difficult to capture with classic grid- or mesh-based numerical methods, such as finite difference methods (FDM), finite volume methods (FVM), and finite element methods (FEM). Recently, there has been growing interest in mesh-free methods, particularly SPH (Smoothed Particle Hydrodynamics). Discretizing the fluid with a set of particles that are free to move with respect to each other, SPH can implicitly and automatically handle a continuously evolving free surface, moving interfaces, large deformations and fragmentations. This method can be used to model several important aspects of the coastal dynamics involved in plastic waste dispersion, such as breaking waves and fluid/structure interaction (FSI), as shown by recent studies on the subject.
We present here our preliminary results in the development and application of an SPH model based on GPUSPH (https://gpusph.org) to simulate the transport, beaching and dispersion of plastic waste in coastal areas. Based on data from laboratory experiments conducted at the University of Messina (Italy), we analyze several SPH formulations to identify those most suitable for the case study. The choice is guided by a compromise between numerical accuracy, consistency with the experimental data, and computational performance. The preferred formulation is then used to investigate some aspects of plastic transport related to waste mass, shape and their interaction with wave motion. We observe a good match between SPH simulations and lab experiments in macroscopic parameters such as the surface velocity profile, wave height and plastic waste arrival times, supporting the choice of this method for the investigation of nearshore plastic transport.
This research work has been funded by the PRIN project “PLAstic Transport due to waves and currents ON Emerged and submerged beaches” (PLATONE) CUP: D53D23004590006.