Eksperimentalno-numerička analiza pronosa čestica mikroplastike u vodi : Doktorska disertacija

Plastic pollution poses a growing threat to aquatic environments, with microplastic (MP) particles representing a significant challenge due to their endurance and potential ecological impact. This dissertation focuses on the experimental and numerical analysis of MP particle transport in water to complement our understanding of their behavior under varying hydrodynamic conditions. This study combines experimental methods with numerical modeling to analyze the drag coefficients and transport mechanisms of MP particles of various shapes and sizes. Experiments were conducted using an experimental hydraulic channel to simulate steady and uniform water flow conditions. This setup enabled controlled conditions over hydrodynamic parameters, ensuring reproducibility of MP transport analysis. MP particles were fabricated using a high accuracy 3D printer to ensure consistent geometry, while their trajectories were recorded using high-resolution video equipment. Custom Python scripts were used to process the captured video material, enabling detailed analysis of particle motion, velocity, and acceleration. Bézier curves were used to approximate MP trajectories, providing a mathematical method for smoothing and analyzing paths based on control points. This method offers high precision in representing complex motion patterns and accurate characterization of particle behavior. A new shape parameterization method was also proposed, utilizing geometric factors such as sphericity and circularity to characterize MP particles. Based on these findings, a new drag coefficient model was developed, presenting improved accuracy in quantifying the resistance of MP particles in a fluid stream under varying Reynolds numbers. The experimental results were used for validation of numerical model that was created in OpenFOAM software. Numerical model was developed to match experimental conditions, specifically hydraulic channel geometry, flow characteristics, and particle motion recorded during experiments. Boundary conditions, including inlet velocity and outlet pressure, were defined to ensure consistency with experimental parameters, and a structured numerical mesh was created to optimize computational efficiency. Particle motion was simulated in the numerical model and compared with experimental results. A correction to the numerical model was proposed, which accounted for deviations observed in initial simulations in comparison with recorded data. Key scientific contributions include the development of a calibrated drag coefficient model, a hybrid experimental-numerical methodology for analyzing MP transport, and advancements in the use of photogrammetry, Python-based algorithms, and numerical model corrections for capturing and analyzing particle trajectories. This research presents new findings and methods in MP transport dynamics and behavior in aquatic systems. Final results aim to support mitigation strategies for MP pollution and contribute to the broader effort to preserve aquatic ecosystems.