Mission to Metrics
The mission of The Ocean Cleanup is to develop advanced technologies to rid the world’s oceans of plastic. To do so, we must design our systems to create a difference of velocity between them and the plastics, the so-called delta-V. Therefore, it is important to know the Lagrangian trajectories and velocities of the plastics across different scales (particle to global). This internship will give you the opportunity to address how plastic particles are transported on a scale of a few hundred meters up to a kilometer.
“The best part of working at The Ocean Cleanup is that I get to use my computational modeling skills to tackle real-life problems.” - Andriarimina Daniel Rakotonirina, Computational Modeler
For a pure wave motion, the Stokes drift velocity is the average velocity when following a specific fluid parcel as it travels with the fluid flow. A particle floating on the free surface of water waves experiences a net Stokes drift velocity in the direction of wave propagation. The Stokes drift is important for the transport of plastics by a wave field. A background in nonlinear and regular waves on the Stokes drift can be seen in [1, 2] but incorporating irregular nonlinear waves  in such studies is still a challenge. Since the Stokes drift velocity decays exponentially with depth, it is important to include the latter. In general, understanding the Stokes drift of plastic particles in random wave fields and their directional spreading on a scale of a few hundred meters would help our mission to scale up on the full scale.
Several methods exist to derive the Stokes drift of Lagrangian positively buoyant particles via perturbation theory or numerical model, assuming the linear wave theory. However, these theories are not suited to capture the intrinsic features of the waves in terms of the velocity field, especially higher-order terms and breaking waves. In this internship, a CFD approach is considered which solves the two-phase Navier-Stokes equations and the motion of Lagrangian particles. This approach is implemented in the code Basilisk  which is a versatile Free Software program for the solution of partial differential equations on adaptive Cartesian meshes. With Basilisk, a high-resolution simulation of 3D waves will offer an insight on the Stokes drift using different types of boundary conditions especially those that can replicate irregular nonlinear waves and directional spreading. One of the interests of this thesis is that we will simulate experiments conducted at MARIN (Dutch Maritime Institute) earlier in 2020.
Your responsibilities include:
Work permit needed:
The Ocean Cleanup develops advanced technology to extract, prevent, and intercept plastic pollution. Our goal is to initiate the largest cleanup in history by mid-2018.