CFD Analysis of Microplastic Transport over the Slopes

Microplastics, ubiquitous in our environment, are significantly impacted by the hydrodynamic conditions around them. This study utilizes CFD to explore how various breaker types influence the dispersion and accumulation of microplastics in nearshore areas. A special focus is given to the impact of wave dynamics and particle size, particularly on buoyant microplastics in spilling breakers. It was discovered that spilling breakers, common on gently sloping seabeds, encourage broad dispersion of microplastics, notably for smaller-sized particles. Plunging breakers exhibit a similar pattern but with less dispersion and an initial forward movement of neutral and heavy particles. Surging breakers feature minimal dispersion and a distinct oscillatory motion. It has been observed that medium-sized particles with a 1 mm diameter in this work exhibit the most substantial forward movement, likely due to an optimal balance between inertia and viscosity, enabling an effective response to wave momentum. Larger particles, influenced mainly by inertia, tend to show less dispersion and advection. Meanwhile, smaller particles, more affected by viscosity, demonstrate greater dispersion, interacting extensively with wave-induced turbulence. This study reveals the significance of inertia in the behavior of microplastics over slopes, emphasizing the importance of considering inertial effects for precise modeling of microplastic movement in nearshore areas.