Đula Nađ

Navigation, guidance and control of an overactuated marine surface vehicle

Abstract This article presents navigation, guidance and control (NGC) experimental results obtained on an innovative overactuated unmanned surface marine vessel (USV) capable of omnidirectional motion. The results were obtained during sea trials in real environmental conditions where external disturbances and sensor characteristics have significant influence on the vehicle behavior. While performing the NGC experiments, the following set of behaviors is demonstrated: (1) successful heading control even in cases when the USV is performing simultaneous omnidirectional motion; (2) dynamic positioning algorithm performance with the navigation filter that uses only GPS measurement and a simple uncoupled dynamic model of an overactuated USV; (3) two line following algorithms (one using full actuation capabilities, and the other emulating underactuated line following) and comparing them by using quality metrics; and (4) online modification of mission parameters within the mission control architecture that is based on three layers (primitives, high-level and low-level control). Finally, we use results from multiple days of experiments to show how GPS update frequency influences (i) the quality of DP performance and (ii) the quality of the commanded control signal.

Underwater Object Tracking Using Sonar and USBL Measurements

In the scenario where an underwater vehicle tracks an underwater target, reliable estimation of the target position is required. While USBL measurements provide target position measurements at low but regular update rate, multibeam sonar imagery gives high precision measurements but in a limited field of view. This paper describes the development of the tracking filter that fuses USBL and processed sonar image measurements for tracking underwater targets for the purpose of obtaining reliable tracking estimates at steady rate, even in cases when either sonar or USBL measurements are not available or are faulty. The proposed algorithms significantly increase safety in scenarios where underwater vehicle has to maneuver in close vicinity to human diver who emits air bubbles that can deteriorate tracking performance. In addition to the tracking filter development, special attention is devoted to adaptation of the region of interest within the sonar image by using tracking filter covariance transformation for the purpose of improving detection and avoiding false sonar measurements. Developed algorithms are tested on real experimental data obtained in field conditions. Statistical analysis shows superior performance of the proposed filter compared to conventional tracking using pure USBL or sonar measurements.

Multibeam Sonar-Based Navigation of Small UUVs for MCM Purposes

Abstract Autonomous vehicles (AxV), surface (ASV) and underwater (AUV), are being considered for the following maritime security missions: Mine Countermeasures (MCM) and Harbor Protection (HP). Applicable threats include attack swimmers/divers, bottom and moored mines, mines or improvised explosive devices placed on pilings, quays, or hulls of ships at anchor or in port. This article focuses on solutions for mine reacquisition and neutralization (RN). One concept for an overall RN system is two collaborating vehicles, an AxV and a unmanned underwater vehicle (UUV). The main task of the RN AxV is to reacquire a bottom target with multibeam imaging sonar, maintain distance while pointing at the target, and perform circular inspection around a target while varying the circle diameter. The main task of the RN UUV is to converge towards the desired line once deployed from the AxV. UUV guiding is accomplished by automatically processing sonar imagery onboard of the AxV and passing sonar position, and UUV range and bearing information to the UUV which processes this information to drive itself to the desired location.

Dynamic positioning of a diver tracking surface platform

Abstract This paper presents experimental results obtained on an autonomous omnidirectional surface marine platform, developed at the University of Zagreb, during two-week field trials in Murter, Croatia. We focus on results that are a part of the second phase of research on the platform that is intended to be used as a diver tracking platform. This phase includes experimental verification of the control and dynamic positioning (DP) algorithms performed in real environmental conditions, where external disturbances and sensor characteristics have significant influence on the vehicle behaviour. Specifically, we demonstrate 1) experimental results showing successful heading control of the overactuated marine platform even in cases when the platform is performing simultaneous omnidirectional motion; 2) experimental results demonstrating the quality of the DP algorithm performance, and 3) how GPS update frequency influences the quality of DP performance and the quality of the commanded control signal with the navigation filter that uses only GPS measurement and an uncoupled dynamic model of the omnidirectional marine platform.

Application of Heterogeneous Robotic System for Underwater Oil Spill Scenario

The tragic Deepwater Horizon accident in the Gulf of Mexico in 2010 as well as the increase in deepwater offshore activity have increased public interest in counter-measures available for subsurface releases of hydrocarbons. To arrive at proper contingency planning, response managers urge for a system for instant detection and characterization of accidental releases. Along these lines, this paper describes the application of a heterogeneous robotic system of unmanned vehicles: autonomous underwater vehicle (AUV), unmanned surface vehicle (USV) and unmanned aerial vehicle (UAV) extended with the oil spill numerical modeling, visualisation and decision support capabilities. A first set of field experiments simulating oil spill scenarios with Rhodamine WT was held in Croatia during the early autumn 2014. and the second set of experiments were held in Spain during the summer 2015. The objectives of this experiment were to test: effectiveness of the system for underwater detection of hydrocarbons, heterogeneous multi- vehicle collaborative navigation and communication as well as decision support system, visualisation of the system components and detected spill.

Application of an ASV for coastal underwater archaeology

Coastal underwater archaeological sites are by nature dynamic, and often subject to disturbance from the action of waves, currents, sediment, and human activity. The need to document such sites comprehensively, accurately, and quickly has been the driving force behind technological advances in predisturbance site mapping since the 1960s. Certain challenges remain constant: the need for technology to be affordable and robust, with efficient post-processing as well as data acquisition times. Non-engineers must be able to interpret the results and publish them according to archaeological conventions. Large ancient shallow water port sites, submerged settlements, and landscape surveys present additional difficulties because of the volume of data generated. In this paper the authors present results of two expeditions to map the submerged Herodian structures at Caesarea Maritima, Israel, using a robotic vehicle, the Autonomous Surface Vehicle (ASV) Pladypos, which was developed to address these challenges. This vehicle carries high-resolution imaging and remote-sensing tools to produce photomosaics and microbathymetry maps of the seafloor, as well as performing precise geo-referencing. The results were later integrated into a GIS.