1,720,973 research outputs found
Characterizing influence of transition to turbulence on the propulsive performance of underwater gliders
No full textTwo models of underwater
gliders were tested in a wind tunnel, one corresponding to a legacy shape
commonly used in contemporary vehicles, the other being a scaled-down
version of a new design. Performance of the two vehicles was
characterised over a range of speeds and angles of attack. Particular
attention was paid to the effect of sharp features along the hulls of
the two vehicles and how they affect the observed flow regime. It has
been shown that the new design, which employs a bow shaped to encourage
natural laminar flow, benefits from a 10% reduction of parasitic drag
and 13%
increase in L/D when the hull surface is smooth. The legacy
glider, made up of a faired bow and a cylindrical hull, suffers from
laminar separation and up to 100% increase in induced drag if the flow
over its bow is prevented from transitioning to a turbulent state before
encountering adverse pressure gradient at lower Reynolds numbers. This
results in lowering of attainable speed at shallow glide path angles
while the associated parasitic drag reduction is demonstrated to
increase the maximum velocity of the glider when moving at glide slopes
above approximately 30
Hydrodynamic Design of Underwater Gliders Using k-k(L)-omega Reynolds Averaged Navier-Stokes Transition Model
No full textHydrodynamic design of an underwater glider is an act of balancing the requirement for a streamlined, hydrodynamically effective shape and the consideration of the practical aspects of the intended operational envelope of the vehicle, such as its ability to deploy a wide range of sensors across the water column. Key challenges in arriving at a successful glider design are discussed and put them in the context of existing autonomous underwater vehicles (AUV) of this type. The design cycle of a new vehicle shape is then described. The discussed AUV will operate both as an buoyancy-propelled glider and a flight-style, propellerdriven submersible, utilising its large size to deliver substantial scientific payloads to remote locations to perform environmental monitoring, seabed survey, and exploration for sub-sea oil, gas and material deposits. Emphasis is put on using computational fluid dynamic (CFD) methods capable of predicting laminar-turbulent transition of the flow in order to estimate the performance of candidate designs and thus inform and guide the evolution of the vehicle. A range of considered shapes are therefore described and their hydrodynamic characteristics predicted using CFD are summarised. A final shape for the new glider is then proposed. This is then subject to an in-depth flow-field analysis which points out how natural laminar flow may be used as a means of drag reduction without compromising the practical aspects of the design, such as its ability to carry sufficient payload. Finally, the obtained data are used to project the expected glide paths, as well as give preliminary estimates of its range. These show the benefits of minimising the vehicle drag, as well as highlight the possible trade offs between maximising speed and endurance ofthe AUV
Naval Architecture and Ship Design Education in Singapore and Newcastle: Under-graduate Learning and Teaching through to Initial Professional Development
No full text
Data-set supporting the article entitled "Hydrodynamic Design of Underwater Gliders Using k-kl-omega RANS Transition Model"
No full textThis dataset provides information necessary to reproduce the figures inside the manuscript accepted for publication in IEEE journal of Oceanic Engineering special issue on Cutting Edge AUV Technologies.</span
A comparison of numerical methods to predict the progressive collapse of lightweight aluminium vessels
No full textThis article presents a comparison of several methods to predict the primary longitudinal bending moment-curvature relationship for a series of box beams with dimensions equivalent to a large, lightweight aluminium ship. The comparative study includes the application of an extended progressive collapse methodology, which has been developed specifically to predict the strength behavior of lightweight hull structures under primary bending moment and accounts for compartment-level, gross panel buckling effects of the orthogonally stiffened structure. The approach is based on the principles of the Smith progressive collapse method, which has been shown to be a capable measure of ultimate strength when applied to steel ships. However, a fundamental premise of the Smith method is that buckling forms an interframe. The extended method discards this assumption and includes overall gross panel buckling effects in the determination of girder strength. For the case study, both the interframe and compartment behavior of the case study box girders are compared. The results are also compared with nonlinear finite element analyses of the box girders. The nonlinear finite element method is being increasingly applied to predict hull girder progressive collapse and, provided computation time is acceptable, will predict collapse modes over an entire compartment. The extended progressive collapse method is shown to compare favorably to the equivalent finite element analysis when overall buckling modes dominate.</p
A comparison of numerical methods to predict the progressive collapse of lightweight aluminium vessels
No full textThis article presents a comparison of several methods to predict the primary longitudinal bending moment?curvature relationship for a series of box beams with dimensions equivalent to a large, lightweight aluminium ship. The comparative study includes the application of an extended progressive collapse methodology, which has been developed specifically to predict the strength behavior of lightweight hull structures under primary bending moment and accounts for compartment-level, gross panel buckling effects of the orthogonally stiffened structure. The approach is based on the principles of the Smith progressive collapse method, which has been shown to be a capable measure of ultimate strength when applied to steel ships. However, a fundamental premise of the Smith method is that buckling forms an interframe. The extended method discards this assumption and includes overall gross panel buckling effects in the determination of girder strength. For the case study, both the interframe and compartment behavior of the case study box girders are compared. The results are also compared with nonlinear finite element analyses of the box girders. The nonlinear finite element method is being increasingly applied to predict hull girder progressive collapse and, provided computation time is acceptable, will predict collapse modes over an entire compartment. The extended progressive collapse method is shown to compare favorably to the equivalent finite element analysis when overall buckling modes dominat
Load shortening characteristics of marine grade aluminium alloy plates in longitudinal compression
No full textThis study presents detailed and rigorous numerical analysis for a parametric series of unstiffened aluminium plates typical of those used in lightweight ships and equivalent thin walled stiffened structures. The study is undertaken with a nonlinear finite element analysis procedure using ABAQUS. The strength behaviour of the plates under a progressively increasing longitudinal in-plane load are shown to be affected by a number of parameters including the alloy, geometric imperfection shape, heat affected zone distribution, level of heat softening and residual stress distribution. The comparative influences of these various factors, some of which are specific to welded aluminium structure, are explored to determine which must be accounted for in the development of a parametric series of design curve
Scaling capabilities in maritime robotics
No full textThe oceans are vast: they cover 71% of the Earth’s surface and play a key role in regulating our climate. They form 99%of the Earth’s liveable space, are home to 244,000 confirmed species, with scientists predicting that there are likely more than 2 million species in the oceans. The oceans hold significant resources of oil, gas and minerals, absorb 25% of atmospheric CO2 and with 50% of the global population living in coastal regions, fish supplying 16% of global protein intake and 90% of world trade handled by sea, the oceans and ocean processes influence all of us.Even though our very existence is coupled with the oceans and their functions, we have seen a 30% increase in ocean acidity since the industrial revolution, and increasing concerns of over fishing and stock depletion for the 3.5 billion people that depend on the ocean as their primary source of food. Yet despite the potential resources – and need for better understanding– less than 5% of the ocean floor has been explored. This is because the physics and chemistry of the ocean limits the reach of our sensors and the range and endurance of our platforms,making it one of the most challenging and unforgiving environments on our planet. When subject to such limitations,the only way to scale our capabilities is through the increased number, and autonomy of the platforms and sensors we putout to sea. Here, Maritime Robotic Systems provide unrivalled opportunities to explore and work in the oceans, improving both safety and reducing costs. They can act as our eyes and ears in places that are too dangerous or remote for humans to go, and can automate repetitive, or ‘boring’ tasks. The Maritime Robotics Laboratory (MRL) at the University of Southampton UK, is developing new technology and approaches to scale capabilities in marine robotics, by orders of magnitude. Our priority is to identify and remove the bottlenecks in the technology, enabling systems that can 1) go longer, 2) are smarter and 3) work together
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