Mesoscale hydromechanics of a mobile plastic catching system

Mesoscale hydromechanics of a mobile plastic catching system

de Feijter, T.S.J.

Huijsmans, R.H.M. (mentor)

Mechanical, Maritime and Materials Engineering

Offshore & Dredging Engineering

Floating Structures

2017-01-10

The Ocean Cleanup’s goal is to extract, prevent and intercept plastic pollution by initiating the largest clean-up in history. It aims to achieve this by installing a large moored floating barrier, which passively concentrates the plastic debris using the ocean currents. In this thesis an alternative to this concept is developed and evaluated. By focussing on mobile solutions the need for complex mooring systems is avoided. First, different mobile cleaning concepts are generated. In a following multi criteria analysis an unmanned passive system was found to be the most promising solution. This concept is not actively propelled and will drift along with the ocean current. A sea anchor is deployed at deeper water layers to generate a braking force, slowing the system down in order to capture plastic. Several risks are identified for this concept of which three are related to the mesoscale movements of the system through the ocean. In the second part a hydro–elastic model, using the lumped mass approach, has been developed to simulate the hydrodynamic behaviour of this concept in the horizontal plane. This model will provide insight into the mesoscale movement of the system through the North Pacific. For a first estimation the scope is limited to current induced forces, since wave forces are expected to be small due to the relative size of the system. These current forces are calculated using the Morison equation. In addition, a constant draft of the flexible screen is assumed. It is proven that this is a reasonable assumption for the velocities under consideration. The developed model is validated using the results from a performed 3D test at MARIN. From the results of this validation it seems that model simulates the behaviour very well. With the validated model different simulations have been performed using the oceanic circulation model HYCOM as input. The results consist of the travelled trajectory of the system over a full year and insight into the hydrodynamic behaviour on a system scale. From these results it was found that the system tends to show unstable behaviour in low current velocities. A solution to this problem was found in increasing the weight of the sea anchor.

lumped mass approach
mesoscale hydromechanics
Morison equation
hydro-elasticity
plastic pollution
hydrodynamics

http://resolver.tudelft.nl/uuid:f1004d60-ea71-4a96-bfb3-3bf34a789092

2018-01-10

Student theses

master thesis

(c) 2017 de Feijter, T.S.J.