1,721,018 research outputs found
An investigation into a method for determining the stability of small craft without reference to hydrostatic data
No full textThe assessment of the stability of small craft can be difficult in the absence of hydrostatic data when it is not possible to use the normal inclining experiment. This paper provides a thorough numerical and experimental investigation in to a stability assessment method, previously proposed as a possible alternative to the inclining experiment (Birmingham, 1995; 2000). The method uses the relationship between changes in the natural roll period of vessels given changes in roll mass moment of inertia. The numerical investigation indicates that the method will be sensitive to small experimental errors although not necessarily impossible. However, the conclusions of the experimental implementation of the proposed method were that it does not ultimately provide a sufficiently accurate stability assessment as to be practically viable. Nevertheless, the work provides a comprehensive follow-up to the earlier published proposition and provides further insight in the dynamics of a rolling vessel under experimental conditions with fastidious attention to experimental accuracy.</p
A cost benefit analysis for autonomous underwater vehicles for marine search and rescue operations
No full textThis paper extends the work of the authors, Murphy et al, 2008 [1], in which the technical feasibility of using Autonomous Underwater Vehicles (AUVs) for search capabilities in marine SAR scenarios is demonstrated. This paper examines previous SAR operations and assesses the potential contribution the addition of AUVs in a search capability could offer. The analysis is based on guidelines published in the International Aeronautical and Maritime Search and Rescue Manual. Commercially available AUV specifications are assumed in the study, covering a range of systems exhibiting varying levels of technical sophistication. In addition the associated costs of AUVs are examined together with the costs of conventional search assets. A comparison between the identified benefits and associated costs is therefore made. In addition, issues relating to the introduction of novel and autonomous systems into safety critical roles are examined by the use of standard business analysis techniques such as market forces and segmentation, SWOT, and PESTLE analyses.</p
The role of autonomous underwater vehicles for marine search and rescue operations
No full textThere is an ever-increasing adoption of new technologies to improve safety of life, and autonomous technology is no exception. The use of robotic machines for assisting in search and rescue (SAR) operations is evident in land and air based scenarios, and European calls for research into the use of remotely operated or autonomous systems specifically address this requirement for marine based search and rescue. This paper addresses the current state of autonomy in the search and rescue field, as well as the current technologies available for marine applications. A concept for using autonomous underwater vehicles (AUVs) in marine search roles for SAR scenarios is provided, and the feasibility of such a system is demonstrated. Existing commercially available AUVs are shown to be capable of providing a viable search area coverage rate, and sensor technology is sufficiently mature to enable detection of survivors from the proposed autonomous platform. The technical challenges for further development of the concept are also addressed
Reducing fuel usage and CO2 emissions from tug boat fleets: sea trials and theoretical modelling
No full textSea trials on a harbour tug have been conducted and are explained. The experimental results for fuel consumption per unit transport effort, under free-running (transiting) conditions, are presented and engine speed-propulsor pitch combinations for improved fuel economy are identified. A simplified analytical approach to predict fuel consumption, including the coupled engine-propulsor-hull system, is described. This rationale is combined with experimental observations and, consequently, performance maps present the complete operating envelopes of the harbour tug under both free-running and towing conditions. This combined approach proved to be effective and can be applied to the study of other tug vessels. As a consequence of this research, the engine control system on the harbour tug was modified to permit it to operate fully within the region of best fuel economy during free-running. The results from the bollard-pull predictions provide insight for the design and operation of harbour tugs in the future.</p
A deep water beach for laboratory generation of abnormal waves
No full textThe design of ships, as well as other marine structures, requires evaluation of wave-induced loads for their operational life. Ships often encounter abnormal waves in the open ocean during normal operational conditions. Research into how abnormal waves affect a ship is important, as they may cause severe damage or even loss of a ship. The experimental method developed during this study uses an adjustable sloping beach, termed a "deep-water beach", installed upstream of the target region in a wave tank to generate steep and breaking waves from a regular wave train. The deep-water beach was found to provide a means of readily generating different types of abnormal wave either singularly or reoccurring periodically, and in both deep and shallow water. Preliminary tests were carried out placing a model yacht hull in the target region and measuring longitudinal force. Comparisons between forces measured in regular and abnormal waves (generated from the regular wave) indicate that steep waves induce longitudinal loads significantly larger than regular or breaking waves
Thermodynamic simulation for the investigation of marine Diesel engines
No full textAbstractEmissions in the shipping industry are a major environmental concern and IMO regulations are increasingly stringent. Existing methods to assess marine exhaust gas emissions require large and specialised input data-sets. There is therefore a requirement for a methodology which can resolve the dilemma of estimating time-varying gas properties with sufficient accuracy to, for example, predict NOX emissions, whilst also being applicable across the variety of engine types and operational modes that prevail in the marine context, for which there is often sparse input data.In this paper, the influence upon thermal efficiency and the prediction of gas temperature time-histories of differing levels of sophistication in modelled gas properties and composition models is therefore evaluated, as is the effect of modelling engine losses. Using the results of this study, a coupled dynamic-thermodynamic engine simulation in the time-domain is developed, capable of modelling engine performance across the full range of operational conditions (speed and load), including part-load and transient conditions. The simulation is validated against the Otto cycle and through simulations of experimental engine data, the model is shown to successfully predict actual engine performance across a range of engine load conditions
Fuel usage data analysis for efficient shipping operations
No full textAbstractThere are incentives from maritime regulatory bodies to operate ships more efficiently, driven by the need to reduce CO2 budget.In order to establish more efficient ship operations, fuel consumption across the full operational profile of a vessel is needed. This could be accomplished through a complete characterisation through extensive sea-trials, or interpretation of data from monitoring systems. Results from repeated testing under controlled sea-trial conditions provides high-fidelity data, however, this approach is prohibitively expensive and requires repeating as the condition of the vessel changes with time. Conversely, data monitoring devices are relatively inexpensive, however, the process of analysing data can be complex, particularly when a ship׳s activities are diverse.This paper describes a methodology for associating ship activity with corresponding segments of a data-stream from a commercially available monitoring system. Further analysis is then performed to determine the fuel efficient performance of the ship. The case-study used is a harbour tug, although the approach used is applicable to other ship types, its success on this basis indicates the methodology is robust. To validate the methodology, results from the data analysis are compared to fuel consumption data measured under sea-trial conditions, and are found to be in close agreement
A new active gyrostabiliser system for ride control of marine vehicles
No full textA new gyroscopic method of active ride control on marine vehicles is presented. Gyroscopic stabilisation is selected because it acts entirely within the hull of the vessel while not requiring sufficient movable weight to generate control moments. The new approach is capable of generating greater stabilising moments than existing gyroscopic systems. Physical experiments, using a modulation theory approach, on a ship model practically demonstrate that the specified system is capable of providing levels of ride control comparable with existing systems. Theoretical estimates of the system on full-scale vessels demonstrate its practical feasibility for application on small and medium sized vessels
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
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