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Cooperative Multi-Vehicle Circumnavigation and Tracking of a Mobile Target

Time: Fri 2020-03-13 10.00

Location: F3, Lindstedtsvägen 26, Stockholm (English)

Subject area: Electrical Engineering

Doctoral student: Joana Filipa Gouveia Fonseca , Reglerteknik, NetCon

Opponent: Professor Yongcan Cao, University of Texas at San Antonio

Supervisor: Professor Karl Johansson, KTH - Reglerteknik

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A multi-vehicle system is composed of interconnected vehicles coordinated to complete a certain task. When controlling such systems, the aim is to obtain a coordinated behaviour through local interactions among vehicles and the surrounding environment.One motivating application is the monitoring of algal blooms; this phenomenon occurs frequently and has a substantial negative effect on the environment such as large-scale mortality of fish. In this thesis, we investigate control of multiple unmanned surface vehicles (USVs) for mobile target circumnavigation and tracking, where the target can be an algal bloom area.A protocol based on local measurements provided by the vehicles is developed to estimate the target's location and shape.Then a control strategy is derived that brings the vehicle system to the target while forming a regular polygon.

More precisely, we first consider the problem of tracking a mobile target while circumnavigating it with multiple USVs. A satellite image indicates the initial location of the target, which is supposed to have an irregular dynamic shape well approximated by a circle with moving center and varying radius. Each USV is capable of measuring its distance to the boundary of the target and to its center. We design an adaptive protocol to estimate the circle's parameters based on the local measurements. A control protocol then brings the vehicles towards the target boundary as well as spreads them equidistantly along the boundary. The protocols are proved to converge to the desired state. Simulated examples illustrate the performance of the closed-loop system.

Secondly, we assume that the vehicles can only measure the distance to the boundary of the target and not to its center. We propose a decentralised least-squares method for target estimation suitable for circular targets. Convergence proofs are given for also this case. An example using simulated algal bloom data shows that the method works well under realistic settings.

Finally, we investigate how to extend our protocols to a quite general irregular mobile target. In this case, each vehicle communicates only with its two nearest neighbors and estimates the curvature of the target boundary using their collective measurements. We validate the performance of the protocol under various settings and target shapes through a numerical study.