1,720,958 research outputs found
Unmanned Surface Vehicle Chase a Moving Target Remotely Controlled
No full textShortly, it is expected to have hybrid marine scenarios in which manned and unmanned vehicles navigate in the same environment. The study of the interactions between autonomous and human-controlled vessels becomes essential to improve and make the control systems more resilient. For such a reason, this paper shows a simulation architecture to test the effectiveness of a guidance law in a target tracking scenario for surface navigation. The guidance logic is based on the idea of reaching and following a target when the future motion is unknown and only the instantaneous position and speed are available. The adopted guidance law can handle both the chasing and the following phases minimising the time needed to reach the chased vehicles. The actuators’ set-point generation is ensured by speed and heading controls, properly developed for this aim. A cyber-physical testing scenario has been developed and can run in real-time. Both target and interceptor dynamics are based on detailed mathematical models in which the parameters have been validated by dedicated tank experiments. An operator remotely controls the target through a human-machine interface and tries to leave behind the autonomously controlled interceptor to make the simulation’s results more realistic. At the end of the paper, the results are reported for investigation and the conclusions are drawn
Dynamic target chasing: parameters and performance indicators assessment
No full textThis paper aims to present a systematic approach to evaluate the parameters affecting the vessel’s performances in the target tracking motion control scenario and, for this reason, three guidance laws have been formalised. Such scenario consists of reaching and following a target of which it is only possible to know the instantaneous position and velocity, hence when the future motion is unknown. The standard Line-Of-Sight, Pure Pursuit, and Constant Bearing have been modified and deeply tested. The target tracking scenario has been divided into two parts: the target approach and following strategies. The increase in system complexity needs advanced tools to predict the vehicle response in both standard and non-standard conditions. Simulation can support the designer’s effort for the transition from a traditional to an autonomous ship in the whole ship design; hence, all the guidance laws have been virtually tested and a sensitivity analysis is carried out to understand each parameter effect. Several manoeuvres have been performed and the results are shown to highlight benefits and drawbacks for each law. Eventually, key performance indicators are outlined and some suggestions are given to the proper settings of the guidance law parameters in the function of the specific mission
Real-time critical marine infrastructure multi-sensor surveillance via a constrained stochastic coverage algorithm
No full textIn recent years, monitoring and protecting marine infrastructure have become increasingly critical. Surface
marine vessels can provide valuable support in monitoring structures such as offshore wind farms, data cables,
and pipelines. Employing surface vessels with ever-increasing autonomous capabilities allows for increased op-
eration efficiency and strategic advantages. In critical infrastructure monitoring, the area of interest is known in
advance, and the aim is to detect anomalies. This paper focuses on developing a guidance, navigation, and control
framework suitable for a MASS and tailored for critical infrastructure monitoring missions. The primary goals are
developing a stochastic-based coverage algorithm to ensure the surveillance of an area of interest and a real-time
compliant shadow vessels monitoring system that provides situational awareness of the above-water surrounding
environment, detecting threats and unexpected targets over time. The navigation in the operational environment
is ensured by an appropriate proprioceptive sensing layer. The hypotheses and the methodologies are shown and
explained in detail, together with the preliminary results reporting the first integration. The results are obtained
via computer simulations applied to a wind farm critical infrastructure scenario; additional experimental tests are
carried out in indoor and outdoor controlled environments to assess the proposed navigation and control systems
capability, involving a marine autonomous surface ships test platform available in the university laboratory. The
preliminary results demonstrate the ability of the systems to cooperate in the proposed architecture, monitor an
Area Of Interest, detect threats, effectively manoeuvre the vessel in real-time, and estimate its state. Such a
framework can be further enhanced by extending the perception capabilities for the underwater domain, integrat-
ing multiple control logic to allow for more efficient surveillance strategies, or extending the vessel capabilities
beyond surveillance missions, adding capabilities like target chasin
Model-Based Motion Control Design for the Milliampere1 Prototype Ferry
No full textFollowing the recent upgrade of the propulsion
plant configuration for the milliAmpere1 passenger ferry prototype,
a model-based controller pipeline suitable for all the
milliAmpere1 speed ranges is proposed and evaluated. Some
well-known methods for force allocation and reference model
systems are implemented together with a nonlinear modelbased
motion controller, and a comparison study for different
combinations is carried out to define the best solution for this
application. Considering low-speed operations, the efficiency
of three force allocation solutions and three reference models
with two possible thruster configurations are investigated.
The resulting controllers are evaluated with five performance
metrics. For higher-speed operations, a solution with a reference
model and a force allocation is presented and investigated.
The controllers have been tested via numerical simulations,
and based on the performance metrics, indications for the best
design options are provided
From anomaly detection to root cause analysis: a novel maritime maintenance framework using digital twin synthetic dataset
No full textThis paper presents a novel approach in the context of condition-based maintenance (CBM) in the maritime sector, leveraging unsupervised learning through Long Short-Term Memory (LSTM) networks. As ships transition toward unmanned operations, the traditional approach of scheduled maintenance becomes inadequate. CBM leverages advanced sensor networks, real-time monitoring systems, and predictive analytics to enable proactive maintenance strategies without human presence onboard. The research carried out in this paper aims to develop a methodology that combines anomaly detection with feature contribution analysis to identify the presence of anomalies and determine which system parameter signals are most responsible for anomalous behaviour. The approach is validated using a marine gearbox digital twin that generates synthetic operational data. In particular, the adopted model focuses on kinematic parameters such as torque and temperature. Moreover, the digital twin enables the simulation of both step changes and continuous degradation patterns to emulate an anomaly. A key innovation lies in the integration of contribution analysis within the LSTM framework, providing deeper insights into fault progression. Moreover, by using synthetic data with known anomaly patterns, the methodology demonstrates the ability to correctly identify the features most responsible for reconstruction error. This capability is particularly significant for real-world maritime applications, where the critical parameters driving system degradation are typically unknown beforehand and must be discovered through analysis. The framework addresses the common challenge of scarce run-to-failure data in maritime maintenance by adopting a fully data-driven, unsupervised approach where failure characteristics are not pre-defined. The methodology encompasses data generation through digital twin simulation, data processing, Health Index (HI) construction, and predictive analysis. The results validate the effectiveness of this integrated approach in both identifying potential failures and their root causes, enabling more informed maintenance planning in maritime applications. Indeed, the validation approach utilizes synthetic data generated through a digital twin to address the scarcity of real-world run-to-failure data in maritime applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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