2019
Authors
Cruz, NA;
Publication
2019 IEEE UNDERWATER TECHNOLOGY (UT)
Abstract
The maximum mission duration and range of an Autonomous Underwater Vehicle are governed by the amount of energy carried on board and the way it is spent during the mission. While an increase in battery capacity and a decrease in electronics demand yield a direct increase in vehicle range, the impact of velocity variation is not so obvious. With slower velocities, most of the energy will be spent in electronics, not in motion, while for faster velocities a lot of energy will be needed to balance drag. Flying-type AUVs have a minimum velocity for the control surfaces to be effective, reducing the range of values for optimization. Hovering type AUVs, on the other hand, are typically slower moving platforms, able to travel at arbitrarily slow velocities. This paper addresses the analysis of the power consumption of hovering type AUVs, providing guidelines and analytical expressions to compute the optimal velocity when the vehicle travels in a single direction, and also when the trajectory is a combination of horizontal and vertical motion.
2019
Authors
Djapic, V; Curtin, TB; Kirkwood, WJ; Potter, JR; Cruz, NA;
Publication
IEEE JOURNAL OF OCEANIC ENGINEERING
Abstract
2019
Authors
Carneiro, JF; Pinto, JB; Cruz, NA; de Almeida, FG;
Publication
INFORMATION
Abstract
The growing needs in exploring ocean resources have been pushing the length and complexity of autonomous underwater vehicle (AUV) missions, leading to more stringent energy requirements. A promising approach to reduce the energy consumption of AUVs is to use variable buoyancy systems (VBSs) as a replacement or complement to thruster action, since VBSs only require energy consumption during limited periods of time to control the vehicle's floatation. This paper presents the development of an electrohydraulic VBS to be included in an existing AUV for shallow depths of up to 100 m. The device's preliminary mechanical design is presented, and a mathematical model of the device's power consumption is developed, based on data provided by the manufacturer. Taking a standard mission profile as an example, a comparison between the energy consumed using thrusters and the designed VBS is presented and compared.
2019
Authors
Oliveira, PL; Ferreira, BM; Cruz, NA;
Publication
OCEANS 2019 MTS/IEEE SEATTLE
Abstract
Corners usually appear very distinct from the rest of the scene in a mechanical scanning imaging sonar (MSIS) image, generally characterized by sharp intensities. The detection of corners is particularly useful in human-structured environments such as tanks because the knowledge on their location provides a way to compute the vehicle position. The combination of some basic operations typically used for image segmentation have great potential to detect and localize corners in sonar images automatically. This article proposes and evaluates with experimental data a set of image segmentation algorithms for corner detection in sonar scans. The developed algorithms are evaluated with ground truth, and their performance is analyzed following a few relevant metrics for autonomous navigation.
2019
Authors
Pessoa L.M.; Duarte C.; Salgado H.M.; Correia V.; Ferreira B.; Cruz N.A.; Matos A.;
Publication
OCEANS 2019 - Marseille, OCEANS Marseille 2019
Abstract
In this paper we evaluate the long-term deployment feasibility of a large-scale network of abandoned underwater sensors, where power is provided by autonomous underwater vehicles (AUVs) in periodic visits.
2019
Authors
Antunes, HM; Cruz, NA;
Publication
OCEANS 2019 MTS/IEEE SEATTLE
Abstract
The thermocline is a relatively narrow vertical region that separates the mixed layer at the surface from the deep-water layer. In this region, the gradient of temperature with respect to depth is higher than in the rest of the water column. The characteristics of the thermocline have strong impact in marine biology, since it may trap high-nutrient organisms, and it also affects sound propagation, with direct impact on underwater acoustic communications and military operations. Under adaptive sampling, Autonomous Underwater Vehicles are practical tools for efficient ocean observation. In this work, we describe an implementation of an Extremum Seeking Controller that performs identification and tracking of thermoclines at its point of highest temperature gradient in a completely autonomous way. The vehicle chosen to perform this tracking was an autonomous vertical profiler, and the algorithms were validated using both real and simulated data.
The access to the final selection minute is only available to applicants.
Please check the confirmation e-mail of your application to obtain the access code.