167 research outputs found
Design of retrofit devices using CFD, validated with wind tunnel tests
No full textThe energy efficiency design index (EEDI) currently under development will lead to high emission ships being taxed heavily in the future. As a result, many possible design solutions to increase the efficiency of high powered ships are currently being investigated. However, existing ships must rely on engine room systems upgrade or the use of retro-fit devices. The aim was to seek a low cost approach to solve the challenge of how to improve the energy efficiency of existing ships. To demonstrate this approach a specific oil tanker hull form was studied and future novel methods of achieving a gain in propulsive efficiency were considered.Wind tunnel and towing tank testing are used, in conjunction with opensource computational fluid dynamics modelling, to analyse the wake field changes caused by the devices. Changes in efficiency are assessed using the propeller efficiency modelled with a blade element momentum code. A testing procedure, explained in terms of methodology with objective justification for improvements has been developed. This procedure successfully detects changes in propeller efficiency at model scale due to devices, and thus provides a route to evaluate a wide variety of devices. Preliminary results suggest that gains in efficiency of at least 3% could be obtained with simple vanes and 2% for pre-swirl ducts. These values could be greatly increased through further optimisation of device size, geometry, position and angle of attack
The use of computational fluid dynamics to assess the hull resistance of concept autonomous underwater vehicles
No full textAutonomous Underwater Vehicles (AUV’s) provide an important tool for collecting detailed scientific information from the oceans depths. The hull resistance of an AUV is an important factor in determining the powering requirements and range of the vehicle. This paper discusses the use of Computational Fluid Dynamics (CFD) to determine the hull resistance of three existing AUV’s, of differing shape and size. The predictions are compared with available experimental data and good agreement found. This work has demonstrated that with use of suitable shape parameterisation it is possible to carry out concept design evaluation using a RANS flow solver
A RANS Modelling Approach for Predicting Powering Performance of Ships in Waves
No full textIn this paper, a modelling technique for simulating selfpropelled ships in waves is presented. The flow is modelledusing a RANS solver coupled with an actuator diskmodel for the propeller. The motion of the ship is takeninto consideration in the definition of the actuator disk region as well as the advance ratio of the propeller. TheRPM of the propeller is controlled using a PID-controllerwith constraints added on the maximum permissible RPMincrease rate. Results are presented for a freely surgingmodel in regular waves with different constraints put onthe PID-controller. The described method shows promisingresults and allows for the studying of several factorsrelating to self propulsion. However, more validation datais needed to judge the accuracy of the model
Grid-based GA path planning with improved cost function for an over-actuated hover-capable AUV
No full textFor an AUV to perform a long-range mission with its maximum endurance, its energy consumption during transit must be kept to a minimum. This paper presents an improved cost function for a grid-based genetic algorithm (GA) path planning in 2D static environments. The proposed function consists of energy consumption terms that are estimated according to dynamics of a hover-capable AUV - notably Delphin2 AUV. It seeks for a path that requires least effort for the vehicle to move along. A simulation was written in Matlab and the outcomes of the GA with the improved cost function are compared with the ones of a GA with an optimal distance approach as well as an A* approach. It is found that outcomes of an improved cost function require less energy compared with the other technique
Concepts for a modular nuclear powered containership
No full textWith the amendments to the MARPOL Annex VI regulations to control NOx and SOx emissions, fuel prices will increase considerably by 2020. Coupled with depleting fossil fuel reserves and owners’ perceptions on their environmental impact, fossil fuel alternatives are being actively sought. The IMarEST reports that nuclear power is the only emissions free energy which can replace fossil fuels entirely (Jenkins, 2011).Two critical drawbacks for a nuclear powered ship are route restrictions and accidents. The goal of the research underway is to ensure that a concept nuclear containership can sustain an accident without catastrophic consequences as well as operate freely at sea without intervention from port states due to the mode of propulsion.The paper will present the work to date on the concept analysis and how the issue with route restrictions is being addressed by designing a modular vessel consisting of a propulsion module and a cargo module which can decouple outside of territorial waters. A service factor analysis with hydroelasticity models will provide the long term bending moments and the modular coupling concept assessment in open waters for unrestricted service. Accidents will be addressed using risk based design focussing on grounding and collisions in restricted waters using probabilistic model
Tribological design constraints of marine renewable energy systems
No full textAgainst the backdrop of increasing energy demands, the threat of climate change and dwindling fuel reserves, finding reliable, diverse, sustainable/renewable, affordable energy resources has become a priority for many countries. Marine energy conversion systems are at the forefront of providing such a resource. Most marine renewable energy conversion systems require tribological components to covert wind or tidal streams to rotational motion for generating electricity while wave machines typically use oscillating hinge or piston within cylinder geometries to promote reciprocating linear motion. This paper looks at the tribology of three green marine energy systems, offshore wind, tidal and wave machines. Areas covered include lubrication and contamination, bearing and gearbox issues, biofouling, cavitation erosion, tribocorrosion, condition monitoring as well as design trends and loading conditions associated with tribological components. Current research thrusts are highlighted along with areas needing research as well as addressing present day issues related to the tribology of offshore energy conversion technologies
Lifting line method for modelling covering and blanketing effects for yacht fleet race simulation
No full textAn approach is presented that can be used to enhance the realism of yacht fleet race simulations. The wake of an upwind sailing yacht is represented as a single heeled horseshoe vortex (and image) system. At each time step changes in vortex strength are convected into the wake as a pair of vortex line elements. These subsequently move in accordance with the local wind, self-induced velocity and velocity induced by the presence of the wakes of other yachts. An empirical based decay factor is used to eventually remove the far wake. A synthesis of sail yacht wake representations based on detailed 3D Reynolds Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) calculations with wind tunnel test results are used to capture the initial strength of the combined main-jib vortex system and its vertical height. These were based on a typical upwind sail arrangement for a range of heel angles and in-line calculations for a pair of yachts separated by three boat lengths. This paper details the basis of the validated CFD results for a yacht at heel and the analysis of the CFD results to provide an approximate single line vortex method for the yacht. The developed algorithm will eventually run within the Robo-Race which is a real-time yacht race strategy analysis tool based on MATLAB®-Simulink® developed at the University of Southampton
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