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Settling processes of cylindrical microplastics in quiescent water: A fully resolved numerical simulation study
Summary
Using a lattice Boltzmann numerical model, this study simulated how cylindrical microplastic fibers sink through still water and identified a critical shape ratio (aspect ratio ~0.93–0.94) at which settling behavior shifts dramatically. Understanding how fiber shape governs sinking speed is key to predicting where MP fibers accumulate in aquatic environments and how long they remain suspended.
The settling process of marine microplastics (MPs) is crucial research concerning the transport and movement of MPs. The settling processes of MP fibers that possess a cylindrical geometry are affected by environmental factors and properties. In this study, a three-dimensional numerical model for the still water settling of MPs with complex shapes was constructed using the lattice Boltzmann method (LBM) and the immersed boundary method (IBM). The fully resolved settling simulation of cylindrical MPs was achieved, and the model results demonstrated good agreement with the semi-empirical settling velocity formulas. Based on the simulation results, the critical aspect ratio of the cylindrical MP was found to be between 0.93 and 0.94. Near this critical aspect ratio, there is a decline in the drag force. Additionally, it was found that the angular displacement and aspect ratio influence horizontal movement but not the vertical settling velocity, while the density only affects vertical movement.
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