On the Digital Twin of The Ocean Cleanup Systems?Part I: Calibration of the Drag Coefficients of a Netted Screen in OrcaFlex Using CFD and Full-Scale Experiments

Resumen

The Ocean Cleanup introduces a Digital Twin (DT) describing the cleanup systems made of netting to extract marine litter from our oceans. It consists of two wings forming a ?U-shape? and a retention zone. During operation, the system is towed and drag-driven with a span-to-length ratio of 0.6 &#x2264;SR*&#x2264;" role="presentation">=????*==SR*= = S R * = 0.8. The twine Reynolds number is Ret*&#x2208;[800:1600]" role="presentation">R??*???[800:1600]Ret*?[800:1600] R e t * ? [ 800 : 1600 ] , making it experience various local drag coefficients. The DT was built with OrcaFlex (OF) aiming at: (i) avoiding over- or under-designing the system; (ii) supporting the scale-up of the system; and (iii) estimating the costs and/or the impact of our offshore operations. Therefore, we present an attempt to build an accurate DT using data from the Great Pacific Garbage Patch (GPGP). We developed a three-cycle validation: (i) initial guess applying Naumov?s semi-empirical drag coefficient to define the OF drag coefficients without the influence of the angles of attack &#x3B8;" role="presentation">??? ? of the wings; (ii) adjustment of the OF drag coefficients using AquaSim (AS) with its twine-by-twine drag correlation for various &#x3B8;" role="presentation">??? ? ; (iii) re-adjustment 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 1 m plane net, highlighting the shielding effects for &#x3B8;&lt;24&#xB0;" role="presentation">??<24°?<24° ? < 24 ° . Consequently, an initial underestimation of -3% in the combined towline tension, for a nominal span (SR*=0.6" role="presentation">????*=0.6SR*=0.6 S R * = 0.6 ), was corrected to a slight overestimation of +7% compared to the GPGP data. For a wide span (SR*=0.8" role="presentation">????*=0.8SR*=0.8 S R * = 0.8 ), the deviation remained between +1% and +15% throughout the validation process. For a narrow span (SR*&#x223C;" role="presentation">????*~SR*~ S R * ~ 0.02), mostly exhibiting low &#x3B8;" role="presentation">??? ? , the first cycle showed a +276% deviation, whereas at the end of the third cycle, it showed a +43% deviation.