Our Research
The current research in our lab focuses on novel submersibles, propulsion and maneuvering for underwater vehicles including the development of trajectory simulations and unique underwater directional thrusters, novel oil compensated actuators for deep-sea operation, pressure vessels and sealing methods. Some of the current research topics include: motion of planning crafts in a seaway, dynamic modeling of hovering AUVs, autonomous floaters, deep sea propulsion components and pressure vessels. In the lab we perform also research in tribology where the lubricant is sea water.
01.
Development of Autonomous Underwater Vehicles Launch and Recovery System (LARS)
The objective of this study is to develop a noble system and guidance method for launch and recovery of AUVs to improve the operability in a seaway.
Currently, a typical AUV operation requires the use of relatively large surface support platforms equipped with lifting cranes and operated by multiple crew members, this is even the case in the operation of small (two men portable) AUVs.
A major reason for the need to perform AUVs operations from these relatively large surface platforms is the sea state which has a major influence on the capability to achieve a successful Launch and Recovery (L&R) operation of the AUV. In adverse weather conditions and high sea state, relatively small surface platforms present high and unpredictable movements and difficulties to remain stable and maintain a position to allow the L&R operation and avoid damage to the AUV. Under the influence of wind and waves, surface platform roll, pitch, and heave which cause unpredictable movement between AUV and surface platform. Quite often, L&R operations are delayed or canceled while waiting for the weather to calm down. Developing LARS that can better handle varying sea states and extend the operability of small size AUVs may present a significant and much required improvement. Moreover, a compact small sized LARS which can be easily fitted to small boats without significant modifications and adaptations to the existing boat, and reduced operational crew will extend the use of AUVs in scientific and commercial applications.
An innovative data fusion between acoustic, visual, and electromagnetic sensors will facilitate the detection and the navigation toward the system and guarantee a continuous and robust localization from a distance of up to 100 meters and until the terminal docking maneuver. In addition, the sensor fusion will allow the detection of potential obstacles and trigger an avoidance maneuver to avoid collision.
The LARS system
Docking Sequence
.png)
The LARS buoy, FLC and FLS
Alice AUV at Sea
02.
The objective of this research is to develop a complete framework to enhance the operational efficiency and sea keeping of Autonomous high-speed Planing Crafts (APCs).
APCs when operating at high speed in a seaway will encounter very high vertical accelerations which pose a hazard to payload and crafts' structural integrity. Currently, the existing autonomous navigation systems cannot address the seaworthiness challenges posed to APCs when operating in real sea conditions. While in manned operation the skipper can, to some degree, limit the accelerations by adjusting the craft’s speed and course in response to its behaviour as he feels and expects, in an unmanned/autonomous mode the speed and course are predefined in the mission plan and adjustment as a response to the craft’s behaviour to incoming waves is typically not provided. In this research, we considered that the prediction and estimation, in real-time, of expected vertical acceleration and angular velocity in a seaway the APC might develop to the incoming sea waves, and control algorithms embedded in the crafts’ autonomous navigation systems to limit those by automatically adjusting the APC forward speed are an essential need to ensure safe operation of APCs.
The general configuration of the proposed framework mainly consists of modules/mechanisms as staged in the figure below:
Vision aided Speed Modulation in a Seaway (VSMS) *MAPCS-Motion Assessment of Planing Craft in a Seaway
Upcoming waves reconstruction
Vertical acceleration without VSMS engaged, the speed is constant.
The abscissa is time in seconds, the ordinate is the acceleration in m/sec^2
The red line indicates speed, the green line is the wave levation, the blue line is the vertical acceleration
Vertical acceleration with VSMS engaged, the speed is modulated.
The abscissa is time in seconds, the ordinate is the acceleration in m/sec^2
The red line indicates speed, the green line is the wave levation, the blue line is the vertical acceleration
The figure below shows a comparison of vertical acceleration encountered by the APC with and without an active VSMS system for the same wave elevation time history. It can be observed from (c) that when the VSMS in engaged, the speed is modulated (in blue) as dictated by the speed setting algorithm.
Comparing the vertical acceleration (in green) in (b) and (c), when no VSMS system is employed (b), the vertical acceleration peaks cross the threshold acceleration limit very often with a very high magnitude. In contrast, when the VSMS system is engaged (c), the speed modulation causes a drastic reduction in encountered vertical acceleration peaks (in green) and the vertical acceleration peaks rarely crossed the threshold acceleration limit.
Comparison of the APC vertical acceleration responses with and without the VSMS system for the same sea state
03.
The development of a novel autonomous Lagrangian float
Lagrangain float is a current following, autonomous underwater vehicle. Such a vehicle is perfectly suited for various oceanographic scientific missions such as studying the ocean currents, temperature and salinity profile of the water column, dissolved oxygen concentration and many other oceanographic and biological parameters. These floats have been in use since 1955 and their numbers in oceanographic research is constantly growing due to their high scientific effectiveness and relative engineering simplicity. Yet, there is still much room for improvements in the performance and design of these vehicles. The subject of our research is the development of a novel autonomous Lagrangian float capable of silent operation at depths of up to 300m. Our float possesses two modes of operation; (1) Lagrangian mode where it follows the water velocity in all directions and (2) profiling mode where its depth and heave velocity are controlled by a dedicated, novel extremely silent propulsion system. The emphasis in this work is twofold; the design of a nearly Lagrangiand float hull and the development of a novel silent buoyancy propulsion system to actively control the float vertical location in the water column.gn of a nearly Lagrangiand float hull and the development of a novel silent buoyancy propulsion system to actively control the float vertical location in the water column.
Lagrangian Float
Lagrangian Float at sea
Path Planning for the SPARUS AUV
04.
Autonomous underwater vehicles (AUV) are prevalent in different industries and science. As part of the operation of these vehicles a launch and recovery(L&R) process needs to be performed either for each mission or periodically. As this process is significantly affected by sea state, the Marine Technologies department is developing a L&R concept that will enable operation in higher sea states than currently possible. As part of this project a path planning algorithm will be researched that will allow an AUV to rendezvous with the recovery apparatus whilst avoiding obstacles along its way. The algorithm will be able to plan a safe, optimal path within the vehicle and operational constraints so that the AUV can reach the rendezvous site as quickly and safely as possible.
The AUV will receive data about it's surroundings from a forward looking sonar, that data will then be converted into a map of obstacles. The path planner will then use that map to calculate an optimal path using a sampling based path planning algorithm. Optimisation parameters for the path planner include path length and distance from obstacles.
05.
Network Camera Oceanic Drifting-Free
The ocean has huge impact on our life. However, compared to observations over land, sensing of the oceanic environment is currently very sparse, for example of atmospheric phenomena (clouds, fog, dust) that propagate from sea to land. We propose a dense network of cameras to fill some of this major data gap, and also serve as a case study for other potential dense oceanic sensor networks.
06.
Subsea Tribology – Water Lubricated Journal Bearing
Sliding lubricated bearings operating in the full-hydrodynamic lubrication regime exhibit low friction coefficient and extended life. In recent years, with the increase in environmental awareness and pollution prevention, attention is directed to oil spills which pollute the environment. This is extremely prominent in ships and submarines where their propellers shafts are typically supported by oil lubricated sliding bearings. To reduce pollution risk and also to obtain a simpler and low in maintenance system, the propeller shafts of numerous modern marine crafts are supported by water lubricated bearings.
An experimental investigation on the lubrication regime of a water lubricated bearing installed in the propulsion train of a marine craft is studied. A test rig designed to allow testing of a scaled water lubricated, polymer made bearing which supports a marine craft propeller shaft has been designed and built. Experimental results quantifying the effect of the load and the rotational velocity on the operating eccentricity, the friction coefficient and on the bearing's lubrication regimes are studied. A first and preliminary attempt to observe the effect of the different lubrication regimes on the bearing's acoustic emission into the water is also studied.
Rig stand
