The Mid-Cayman spreading centre is an ultraslow-spreading ridge in the Caribbean Sea. Its extreme depth and geographic isolation from other mid-ocean ridges offer insights into the effects of pressure on hydrothermal venting, and the biogeography of vent fauna. Here we report the discovery of two hydrothermal vent fields on the Mid-Cayman spreading centre. The Von Damm Vent Field is located on the upper slopes of an oceanic core complex at a depth of 2,300 m. High-temperature venting in this off-axis setting suggests that the global incidence of vent fields may be underestimated. At a depth of 4,960 m on the Mid-Cayman spreading centre axis, the Beebe Vent Field emits copper-enriched fluids and a buoyant plume that rises 1,100 m, consistent with >400 °C venting from the world's deepest known hydrothermal system. At both sites, a new morphospecies of alvinocaridid shrimp dominates faunal assemblages, which exhibit similarities to those of Mid-Atlantic vents.

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Abstract-Autonomous 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. I. INTRODUCTION The applications of Autonomous Underwater Vehicles (AUVs) are diverse, [1] ranging from :-• scientific research (e.g. ocean sampling and environmental monitoring); • commercial uses including pipeline inspection and cable surveys; • military applications such as mine hunting. Since the AUV must carry its power source, a good understanding of both the propulsion and hotel loads is required at the early design stage. Evaluating the hydrodynamic drag of a prototype AUV hull form is expensive and time consuming if carried out using either experimental facilities (towing tanks, circulating water channels, wind tunnels) or computational fluid dynamics (CFD), which requires an experienced and skilled user for reliable results. The eventual aim of the program of work under way is to develop specific AUV hull concept design techniques that are robust and reliable. To this end, CFD analysis methods are being investigated which combine automated meshing and parametric hull shape definitions to reduce overheads when evaluating the design of a concept AUV hull.As part of the design process computational studies of the fluid flow around three AUV's (see Figure 1) have been performed to determine the hydrodynamic drag experienced by existing vehicles for validation against existing model test and full scale experimental data. The objectives of this study are:(1) to demonstrate the application of CFD to determine the hull resistance of AUV's; (2) benchmark the computational results against existing experimental results; (3) demonstrate the application of geometry parametrisation suitable for design optimisation.

Abstract:The missions being proposed for autonomous underwater vehicles (AUVs), by both marine scientists and industry, are becoming increasingly complex and challenging. In order to meet these demands the next generation of AUVs will need to be faster, to operate for longer durations, and to be more manoeuvrable than existing vehicles. It is therefore vital that the hydrodynamic forces and moments acting on a self-propelled manoeuvring AUV can be predicted accurately at the initial design stage. In order to achieve this, the use of a computational-fluiddynamics-based analysis is suggested. The approaches developed are predominantly steady state and suitable for running on a workstation personal computer using a commercial software licence. It is estimated that the proposed simulations would take a competent user less than 1 month for a new concept design. The total cost of these simulations is significantly lower than the cost of building a model and having it commercially tested to capture the same level of detail for the resistance, propulsion, and manoeuvring performance. Based on the validation studies presented, it is estimated that on a 2610 6 element structured mesh a competent user should be able to predict hydrodynamic forces to within at least 10 per cent and moments to within 20 per cent of in-service performance.

In this work model predictive control is used to provide transit and hover capabilities for an autonomous underwater vehicle where the description of the system dynamics used include terms measured experimentally. The resulting controller manoeuvres the vehicle in the presence of constraints on the actuators and results obtained from the deployment of the vehicle in an inland lake for the study of the Zebra mussel, an invasive species, are also given.

This paper will concentrate on the technical aspects of the Autosub3 vehicle and its missions under the PIG, and seek to answer a number of questions: How did the AUV successfully dead reckon navigate for over 24 hours, and return accurately to the rendezvous point? How did we cope with the possibility of ice bergs or sea ice drifting over the recovery position ? How did Autosub3 (almost always) avoid collision with the jagged ice shelf above, or the unknown depths of the seabed? How did we communicate with the vehicle at the start and the end of missions? How did we manage risk, and prior to the cruise, what modifications and testing did we apply to the AUV to improve the overall reliability? What measures did we take during the cruise to further improve our chances of a successful outcome ?The paper will outline the history of the use of AUVs for polar science. Results from the recent cruise will be presented showing the actual mission tracks, with the echo sounder isonified ice draft and seabed. Not all went completely to plan: the paper will also describe the events of Autosub's close scrape on its 4 th mission under the PIG.

The use of an unsteady Computational Fluid Dynamic analysis of the manoeuvring performance of a self-propelled ship requires a large computational resource that restricts its use as part of a ship design process. A method is presented that propeller and rudder to be captured. Results are presented for the fully appended model scale self propelled KVLCC2 hull form under going static rudder and static drift tests at a Reynolds number of 4.6x10 6 acting at the ship self propulsion point. All computations were carried out on a typical workstation using a hybrid finite volume mesh size of 2.1x10 6 elements. The computational uncertainty is typically 2-3% for side force and yaw moment.

An autonomous underwater vehicle (AUV), Autosub6000, has been shown to operate safely at altitudes as low as 3 m above rugged and complex sea floor environments. This capability is essential for future AUV missions in such environments, e.g. high-resolution surveys using colour photography or multi-beam sonar bathymetry. This was achieved through the development of an obstacle avoidance system for the AUV, incorporating relatively low-cost off-the-shelf components and simple algorithms. This paper details the specification, design, and testing at sea of Autosub6000's obstacle avoidance system. It describes how the specification of the system was influenced by the need to retrofit it into the existing control architecture, together with the pragmatic need to minimize overall complexity. The sensor used in the obstacle avoidance system is a mechanically scanned forward-looking sonar, and the control algorithm is based upon the detection of the range and elevation of the horizon relative to the AUV. The avoidance behaviour is by default to fly over obstacles but, if this is not possible, a turn-around and retry collision avoidance algorithm is invoked. Results are presented of the system's performance during recent deep-water trials of the AUV over the Casablanca Seamount region of the Atlantic Ocean.