## 1 Introduction
That means that the netting, ropes, and floaters of the cleanup system are exposed to cyclic wave-induced forces for longer time periods than fishing rigs. In turn, that leads to increased wear and tear, as has been verified during the System 002 test campaign. * The cleanup system netting of System 002 has a mesh size of 10 mm to catch also mesoplastics, which are plastics with sizes between 0.5 cm and 5 cm. The netting used in the trawling has normally a mesh size larger than 10 mm. That means that the drag force on a 800 m-long system (System 002) or 2 km-long system (System 03) is considerably larger than from travelling. As a consequence, understanding this force and the variables influencing it is particularly important for the cleanup application. * The wingspan of System 002 adopts a \"U-shape\" during operation, and the netting draft is 3 m. That means that the bottom of the system is completely open, allowing fish to easily escape. Additionally, in the retention zone's bottom, there are openings to allow marine life to escape. This emphasizes that the purpose is to capture plastics, not fish. Therefore, since the netting configuration is different from fishing nets, it is valuable to understand how this new application of netting performs in water, how it interacts with marine life, and how the offshore operation around it must be efficient to make it work. All these points were thoroughly studied and monitored within The Ocean Cleanup, and the present work is part of it. * An important difference between catching plastic and fishing is how dispersed the plastic is at the ocean's surface, in comparison to a dense school of fish. There is a large amount of plastic floating in the GPGP, but it circulates on a massive area of the North Pacific Ocean. That means that the area density of the catch that the cleanup system encounters is much lower than in the fishing case. As a consequence, the cleanup system needs to sweep a much larger area to match a fish catch with a plastic catch. Additionally, The Ocean Cleanup objective is to get rid of 90% of the floating plastic in the GPGP by 2040, but it is not the objective of the fisheries to deplete fish to that level. Therefore, the energy invested in cleaning is larger than in fishing, making the efficiency and the hydrodynamic performance of the cleanup system even more relevant. In Part I of our work, we aimed to shed light on three unknowns. First, we aimed to compare the estimated hydrodynamic force obtained from the cleanup system model or Digital Twin with real-world data. Second, we investigated how various angles of attack along the system's length impact the overall drag force. In other words, what the impact of the shielding effect is (cf. Section 2.3 for a description of this effect) for different system spans. Third, we explored methods to integrate this effect into the Digital Twin to refine the estimation of the hydrodynamic forces. We addressed these unknowns by intending to improve the accuracy of the hydrodynamic load estimation of our DT, which is built in OF [29], for various spans. To accomplish that, we focused on calibrating and validating the net's drag coefficients of our System 002 Digital Twin. The validation was based on data directly measured during our GPGP offshore operations with System 002. The method can be summarized as a three-stage validation process, where the following three numerical models were involved:  
* **OrcAlex** is used for the dynamic analysis of offshore marine systems, including floating structures, moorings, and risers. We used it for simulating the behavior of our complex ocean cleanup system under different environmental conditions such as waves, currents, and winds. It provides a comprehensive set of features for modeling the geometric structures of the system and its dynamic response, as well as that of the lines to tow the system. It is based on Morison's equation [30] and potential flow to model the forces on a structure generated by the fluid flow, such as the forces on a mooring line due to waves.