1,721,000 research outputs found
COLREG-Compliant Optimal Path Planning for Real-Time Guidance and Control of Autonomous Ships
No full textWhile collisions and groundings still represent the most important source of accidents involving ships, autonomous vessels are a central topic in current research. When dealing with autonomous ships, collision avoidance and compliance with COLREG regulations are major vital points. However, most state-of-the-art literature focuses on offline path optimisation while neglecting many crucial aspects of dealing with real-time applications on vessels. In the framework of the proposed motion-planning, navigation and control architecture, this paper mainly focused on optimal path planning for marine vessels in the perspective of real-time applications. An RRT*-based optimal path-planning algorithm was proposed, and collision avoidance, compliance with COLREG regulations, path feasibility and optimality were discussed in detail. The proposed approach was then implemented and integrated with a guidance and control system. Tests on a high-fidelity simulation platform were carried out to assess the potential benefits brought to autonomous navigation. The tests featured real-time simulation, restricted and open-water navigation and dynamic scenarios with both moving and fixed obstacles
Interaction between COLREG-compliant collision avoidance systems in a multiple MASS scenario
No full textThe transportation systems are heading towards increasing autonomy in all domains, and the maritime field makes no exception. The International Maritime Organization has been working on releasing a regulatory framework for Maritime Autonomous Surface Ships (MASS) to keep pace with the technological developments in the field. Autonomous shipping forces the researcher and the designers to face a wide range of scientific challenges, such as
navigation decision support systems, collision avoidance algorithms, path planning, navigation and control, sensor data processing and fusion, remote control, and communication, with the final intent of achieving a fully integrated and autonomous worldwide maritime transportation system, where a human-less collaborative conflict resolution could potentially retire the COLREGs. However, the maritime sector will first face a transition period where traditional
ships will share the seas and interact with heterogeneous MASS with various autonomous capabilities featuring different and probably incompatible communication protocols. In such a scenario, the COLREGs will still play a primary role in helping the collision avoidance systems resolve conflicts and limiting the degrees of freedom. This paper aims to study the interaction among multiple vessels with autonomous collision avoidance capabilities operating in a close
navigation scenario. The ships operate according to a COLREG-compliant collision avoidance algorithm. The paper relies on numerical simulation to systematically investigate different scenarios in which autonomous vessels operate and interact in the presence of fixed obstacles. Results are presented and critically discussed
An environmentally sustainable energy management strategy for marine hybrid propulsion
No full textIntegrating electric technologies, such as battery energy storage systems and electric propulsion, has become an appealing option for reducing fuel consumption and emissions in the transportation sector, making these technologies increasingly popular for research and industrial application in the maritime sector. In addition, hydrogen is a promising technology for reducing emissions, although hydrogen production technologies significantly influence the overall impact of hydrogen-powered systems. This paper proposes an optimization-based strategy to minimize the environmental impact of a hybrid propulsion system over a given load profile, while furthermore considering the environmental impact resulting from the hydrogen production chain. The propulsion system includes diesel generators, hydrogen-powered fuel cells, batteries, and electric motors; mathematical models and assumptions are discussed in detail. The paper applies the proposed strategy, and compares different hybrid solutions considering equivalent CO2 emissions, discussing a test case applied to a short-range ferry operating in a marine protected area, an area particularly sensitive to the problem of atmospheric emissions. The results demonstrate that the proposed strategy can reduce greenhouse gas emissions by up to 73% compared to a conventional mechanical propulsion system
A collision avoidance algorithm for ship guidance applications
No full textThe paper presents a collision avoidance algorithm for ship open sea navigation, based on an ad hoc modified version of the Rapidly-exploring Random Tree (RRT*) algorithm. The proposed approach is designed to act as the high level layer of the navigation control structure for an autonomous ship. Collision and grounding still represent the primary source of sea accidents, thus an automatic system able to detect static and moving obstacles and plan an evasive route could significantly improve safety during navigation, especially in crowded areas. Focusing on the maritime field, a review of the scientific literature dealing with collision avoidance is presented, showing potential benefits and weaknesses of the different approaches. Among the several methods, details about the RRT and RRT* algorithms are given. The ship path planning problem is introduced and discussed, formulating suitable cost functions and taking into account both topological and kinematic constraints. The algorithm is able to manage multiple moving obstacles with variable speed and course. Eventually, a time-domain ship simulator is used to test the effectiveness of the proposed algorithm over a number of realistic operation scenarios. The obtained results are presented and critically discussed
LiDAR target detection and classification for ship situational awareness: A hybrid learning approach
No full textIn recent years, LiDARs have been used to enhance situational awareness of autonomous vehicles, including in the marine domain, driven by the need for reliable detections in Marine Autonomous Surface Ships and Unmanned Surface Vehicles. Detecting obstacles and targets within point clouds is generally handled by a fully unsupervised learning framework. While effective and simple, this approach cannot classify targets. This paper presents a combined unsupervised/supervised approach for detecting and classifying marine targets and obstacles. The unsupervised detection framework is maintained by incorporating a lightweight supervised module capable of classifying detection outputs without disrupting the workflow. Rather than training on the entire point cloud, the proposed method focuses on selected target features, reducing model size and information exchange. Specifically, a Random Forest Classifier is trained on features extracted from the point-cloud dataset. The acquisition of an ad-hoc training dataset and its statistical analysis are presented to identify key features. The selection, training, and validation processes are outlined. Finally, the supervised model is integrated into a state-of-the-art unsupervised LiDAR detection pipeline and tested in a real scenario. The results demonstrate the hybrid framework's effectiveness and compliance with real-time constraints
A structured metric approach to compare marine collision avoidance algorithms
No full textThe rapid advancement of technologies enabling autonomous ship capabilities has outpaced the development of corresponding legislative and regulatory frameworks, creating a bottleneck in the global application of autonomous ships as defined by the four MASS degrees of autonomy. A significant issue is the absence of a well-defined process for certifying new algorithms and systems to be installed on board. Recently, a reliable, open-access structured set of scenarios, including several challenging COLREG encounter situations, has been published, intended for testing the numerous path-planning algorithms developed over the years. When connected to the testing framework, the modules must accomplish two primary tasks: determining the applicable COLREG rules (COLREG classification) and computing an evasive route. This paper focuses on defining an approach to evaluate the performance of collision avoidance algorithms through dedicated metrics. These metrics are formulated to quantitatively compare escape manoeuvres according to relevant performance indexes, helping a human-based compliance evaluation assess COLREG adherence. The operation of the comparison metrics is demonstrated by testing an existing collision avoidance algorithm developed by the authors. This demonstration underscores the effectiveness of the analyzed algorithms in efficiently managing the challenging scenarios proposed in the literature. Finally, the paper provides valuable suggestions for modifying and improving the testing scenarios to enhance the robustness of the comparison metrics
Dynamic Simulation of a Waypoint-Based Decision Support System for the Collision Avoidance of Marine Vessels
No full textCollision avoidance is a critical concern in marine navigation, where safe and efficient vessel operation is based on accurate and timely decision making. This paper presents a Decision Support System (DSS) for maritime collision avoidance that combines a waypoint-based trajectory planning algorithm with speed adjustment strategies. The proposed algorithm generates an optimized route by calculating waypoints that safely guide a vessel around other ships while adjusting speed to prevent imminent collisions. The DSS integrates input on vessel maneuvering capabilities, standard seamanship, and maritime traffic behavior to produce a flexible and responsive collision avoidance strategy that can maintain safe distances in complex navigational environments. A dynamic simulation model is used to evaluate the effectiveness of suggested routes, simulating real-world navigation scenarios, and the response of the vessel when actuating the calculated trajectory. Simulation experiments demonstrate the ability of the system to adapt to various collision scenarios, ensuring vessel safety while minimizing deviations from the intended course. The results indicate that the proposed DSS can significantly enhance navigational safety, reducing the risk of collision
A comparison among innovative hybrid propulsion systems to reduce the environmental impact of a small passenger ship
No full textFossil fuels contribute to GHG emissions into the atmosphere. The need to solve this critical global problem has driven the search for alternative energy options to pave the way towards a more sustainable future. This paper analyzes the environmental and economic performance of a small cruise ship operating in the North Atlantic Ocean. The paper compares natural gas-electric and hybrid propulsive configurations, considering LNG and E-LNG produced using renewable electricity. The carbon footprint analysis is based on equivalent CO2 emissions according to a Well-to-Wake approach and includes emissions of the on-shore power for battery charging. A novel index for the energetic classification of ships is proposed, considering their equivalent CO2 emissions using a Well-to-Wake approach. The hybrid propulsive systems show a fair fuel-saving potential, ranging from 3.5% to 5.3%. The E-LNG-powered propulsion is three times more expensive than LNG, while GHG emissions produced using E-LNG are 4.5 to 6 times lower. The battery pack is a major cost item in hybrid systems. Moreover, GHG evaluation through the novel index penalizes hybrid propulsion systems compared to traditional carbon dioxide emission assessment since the former includes ground connection used for battery charging
An Innovative variable layout steam plant for waste heat recovery from marine dual-fuel engines
No full textThe paper describes an original Waste Heat Recovery (WHR) variable layout plant to produce steam from the exhaustgases of marine dual-fuel engines. A large part of the steam feeds an electric turbogenerator to improve the ship's energy efficiency.The layout of the proposed steam plant is conceived in a double configuration to satisfy both the stack temperature constraints of theengine exhaust gas, due to the use of diesel oil (no less than 160°C as outlet gas temperature) or natural gas (there are no particularstack temperature limits). The comparison with a traditional WHR single pressure steam plant shows the potential benefits of thevariable configuration. Indeed, the proposed solution allows a better exploitation of the potential thermal energy of the natural gas,without precluding a proper performance even in diesel mode, with a moderate weight increase compared to a single pressure WHR system
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