Abstract:
The Ocean Cleanup is introducing a Digital Twin (DT) describing the cleanup systems made with netted screens to concentrate marine litters and extract them from our oceans. Our DT aims at: i) avoiding over- or under-designing the system; ii) extrapolating from one system to a fleet of systems; and iii) estimating the costs of our offshore operations. These costs are evaluated as cost per kilogram of extracted plastic which is our Key Performance Indicator (KPI). One of the main contributing parameters to the KPI is the hydrodynamic load of our "U-shape" device that spans up to 630 meters and operates at a Speed Through Water (STW or ustw) up to 1.5 m/s equivalent to a twine Reynolds number of Ret∗ = 1600. The DT is built with OrcaFlex (OF) using lines and links, the Naumov’s drag correlation and on a no-wave assumption. Data collected from the Great Pacific Garbage Patch (GPGP) are utilised to increase the accuracy of our DT for estimating the loads and the system’s dynamic deformation. The DT is built using a three-cycle validation: i) initial guess applying the Naumov’s semi-empirical drag correlation to define OF drag coefficients which is excluding the influence of the local angles of attack (AoAs); ii) calibration of the OF drag coefficients using AquaSim (AS) with its twine-by-twine drag correlation for various AoAs; iii) recalibration of the OF drag coefficients from two-dimensional CFD simulations using Direct Numerical Simulation (DNS) for a twine-by-twine establishment of a drag correlation on a one meter segment plane net to account for shielding effects at AoA < 24◦. By doing so, we decrease the discrepancy of our OF model, on large spans, with an error less than 15% compared to the GPGP data. For a narrow span, mostly exhibiting very low AoAs, the first cycle shows a 300% discrepancy whereas at the end of the third cycle it shows a 50% discrepancy. Copyright © 2023 by ASME.
