Centre of Mathematics of the University of Porto

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Exploring Controlled Passive Particle Motion Driven by Point Vortices on a Sphere

Publication . Balsa, Carlos; Otero-Espinar, M. Victoria; Gama, Sílvio M.A.

This work focuses on optimizing the displacement of a passive particle interacting with vortices located on the surface of a sphere. The goal is to minimize the energy expended during the displacement within a fixed time. The modeling of particle dynamics, whether in Cartesian or spherical coordinates, gives rise to alternative formulations of the identical problem. Thanks to these two versions of the same problem, we can assert that the algorithm, employed to transform the optimal control problem into an optimization problem, is effective, as evidenced by the obtained controls. The numerical resolution of these formulations through a direct approach consistently produces optimal solutions, regardless of the selected coordinate system.

2024Journal article

Open access

A simple mathematical model to steering oceanic debris to a targeted region

Publication . Balsa, Carlos; Otero-Espinar, M. Victoria; Gama, Sílvio M.A.

In this article, a simplified mathematical model is presented to depict the process of collecting ocean debris. The responsible autonomous vehicles for transporting the trash are represented as passive particles, while the ocean current is simulated by the movement of point vortices on a sphere. To ensure the autonomy of the vehicles, a system of piecewise constant controls is employed, using a limited number of predetermined switching points that determine their trajectories. Each control incurs an energy cost that is aimed to be minimized. This minimization is achieved by solving a nonlinear optimization problem on the spherical surface. The initial findings indicate the existence of multiple possible trajectories for autonomous vehicles.

2024Conference paper

Restricted access

Optimization of vortex dynamics on a sphere

Publication . Balsa, Carlos; Monville-Letu, Raphaelle; Gama, Sílvio M.A.

Vortex points on a sphere can be considered as simplified models of atmospheric circulation. The use of these models allows the simulation of displacements of passive particles advected by vortex flow. In this study, a strategy is proposed to determine the optimal trajectory between two given points on the sphere, taking into account that the displacement occurs due to a vortex flow. It is an alternative numerical strategy to the methods proposed by the theory of optimal control. The original problem is discretized into a constrained optimization problem. The solution of this problem by two alternative numerical optimization methods shows that the strategy is feasible and leads to optimal or quasi-optimal solutions.

2023Conference paper

Restricted access

A numerical algorithm for optimal control problems with a viscous point vortex

Publication . Balsa, Carlos; Gama, Sílvio M.A.

The dynamics of passive tracers in flows dominated by perfect or viscous point vortices is a broad area of research that continues to attract the attention of numerous studies. Recently, there has been a particular interest in the application of control theory to these issues. Viscous point vortices are singular solutions of the two-dimensional incompressible Navier-Stokes equations in which the vorticity is concentrated at a finite number of points in the flow domain, each of which carries a certain amount of time-invariant circulation. By definition, a passive tracer is a point vortex with zero circulation. This paper describes some numerical investigations of passive tracers performed by viscous point vortices to find the energy-optimal displacement of a passive particle. The numerical results show the existence of near/quasi-optimal controls.

2022Conference paper

Open access