vol 5 issue 7

AUV

10 May 2010
By Mark Langdon
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Talisman AUV

Huge growth for AUV technology.

The Autonomous Underwater Vehicle (AUV) market is estimated to be worth $2.3bn over the next decade and it is forecast that around 1,400 new AUVs will be built. There have been at least 630 vehicles built of all shapes and sizes depending on their application with uses in the military, scientific and oil and gas sectors already well established.

'Unmanned vehicles are now used for a variety of missions in the marine environment, either as an alternative to a manned vessel, or as a 'force multiplier' for existing vessels or research campaigns,' says Paul Newman, Offshore Industry consultant and trainer and co-author of a number of major reports for Douglas Westwood on various aspects of subsea and unmanned technology.

The main driving forces for these new vehicles include the expense and problems of trying to find vessel time, the increasing need for long duration measurements and observations, the growing acceptance and maturity of unmanned technology and the need to remove personnel from risk.

With global warming high on the agenda, there is a greater need for data about the world's oceans. The collection of water quality data such as pH, turbidity, temperature and salinity remains a priority as does oceanographic, meteorological, climatic and biological observations and fisheries research.

The military is also increasingly interested in autonomous vehicles to solve problems such as threats from mines, which can be floating or buried, and threats to assets from IED on surface craft. AUVs are also ideal for covert operations because detection is difficult.

There is also interest in unmanned vehicle use for security applications in vessels, ports and harbours where they can be used to deploy mine countermeasures (MCM) or carry out anti-submarine warfare (ASW).

When it comes to MCM, the AUV has several advantages, which include increasing the distance from the threat and removing the need for divers or mammals to identify and neutralise the mines.

'The AUV can also increase the speed and tempo of operations, is deployable from a wide range of platforms and is able to work in very shallow water and surf,' explains Newman.

Design a compromise

'Every vehicle design is a compromise between cost, endurance, speed, size, depth rating, weight, sensors, autonomy and fitness for purpose,' says Newman.

Large vehicles can be up to 6m long, are usually optimised for operation in deep waters of 1,000m and deeper, and can weigh up to 5,000kg. They can support large (physically and electrically) payloads with high specification sensors and have long ranges of 150-300 line km to minimise non-productive returns. The batteries on these vehicles can be recharged in-situ or swapped. They are generally supervised via acoustic modem and are equipped with high specification positioning and navigation systems. Their size and high level of sophistication means they don't come cheap at $1m to $5m.

The main players in this area are Kongsberg with its Hugin 1000, 3000 and 4500 vehicles, Hydroid with its REMUS 6000/SAMS vehicle, ISE with its Explorer and Bluefin Robotics with its Bluefin 21.

Other players include Saab, E F Atlas, Lockheed Martin, Boeing and BAE Systems.

At the other end of the scale is the smaller AUV designed for operation in shallower waters of less than 100m. These vehicles usually remain unsupervised during operation and have a low payload capacity and a short range of 20-40 line km.

They are equipped with basic navigation and positioning systems and can operate at or near the surface as well as at depth. They can be up to 2m in length and weigh up to 50kg.

Their lower specification and capability and smaller size also makes them a lot cheaper at about $50,000 to $250,000.

The main players in this area are Hydroid with its REMUS 100 and iRobot with its Ranger and OceanServer with Iver2. Other players include Oceanscan-MST, Virginia Institute, Univ. of Porto, Kongsberg and YSI.

Battery technology

While Remotely Operated Vehicles (ROVs) use power fed from a surface vessel or from shore via an umbilical, AUVs rely solely on their batteries or other onboard systems to provide the power for their propulsion. 'The battery technology is moving forward and the power density of batteries is vastly superior to what it was even five years ago,' says Newman. 'Some of the larger vehicles have been trailed with semi fuel cells, such as the Kongsberg Hugin, which uses a hydrogen peroxide semi fuel cell and a number of the other larger vehicles have done the same.

'However, there are limitations to the use of fuel cells, particularly with the chemicals used such as hydrogen peroxide,' he explains.

Biomimetics

The majority of underwater vehicles are powered by propellers but there is a small number that use what is known as biomimetics, which is a mechanical form of biological function. These include a robotic manta ray, a robotic tuna and robotic fish for example.

'These robotic biomimetic vehicles haven't had much focused application but a number of them, such as the Manta Ray, are designed to be low power as they are of a very efficient hydrodynamic design so they can potentially perform long duration surveys and surveillance duties and environmental monitoring,' states Newman. 'It can carry a substantial payload such as sensors or whatever the end-user requires.

'All of these vehicles are, in essence, platforms for whatever purpose the end-user wants to use them for and the same base vehicle can be used for a very wide variety of applications, making them very flexible vehicles.'

Unmanned Surface Vehicles

There is increasing interest in the use of Unmanned Surface Vehicles (USVs) for military/security applications. These vessels while unmanned are usually not totally autonomous and are supervised by radio or microwave link with a single supervisor responsible for multiple USVs. Also, unlike with AUVs, positioning is simple as they can use GPS.

'USVs are not remotely-operated 'drones',' explains Newman. 'They have auto-pilots and station-keeping and can act as deployment platforms.' One of their main advantages is they can put distance between the threat and the operator. However, their role is usually limited to areas with little other marine traffic.

'While these vessels have predominantly diesel or diesel-electric propulsion, alternatives now include wind (sails), wave and solar power,' says Newman.

These vehicles can be used to patrol stretches of coastline or waterways and can be equipped with day and night vision equipment, surface radar and gunfire detection and it may even have weapons of a lethal or non-lethal variety such as sonic or water cannon.

'It can identify, approach and potentially 'detain' a suspect vessel without risk,' he explains. 'Or it can extend the radar, visual or acoustic sensor range of a command vessel and provide 'over-watch'. It can also act as equipment shuttles or for covert work.'

An incident in the Yemen in 2000 involving the USS Cole highlighted the vulnerability of ships to fast-moving, small attack craft. A speedboat carrying 1,000lbs of explosives rammed into the ship's side while rules of engagement kept guards from firing without first obtaining permission from officers. The resulting explosion killed 17 and injured a further 37. A USV could have been used to intercept the speed boat before it reached its destination, potentially avoiding the tragedy.

Surface vehicle technologies

The US Defense Advanced Research Projects Agency (DARPA) has recently announced that it will fund a programme to develop an unmanned vessel capable of carrying out Anti-Submarine Warfare (ASW). The Continuous Trail Unmanned Vessel (ACTUV), as it is called, will be 'a first of its kind unmanned naval vessel that is designed and sized for theater or global independent deployment'.

The aim of the programme, which will be in four parts, is to develop an unmanned surface vessel optimised to overtly continuously trail threat submarines.

As the vessel will be completely unmanned it opens up new possibilities for vessel design in terms of stability and sea-keeping, allowing a clean sheet design approach and enabling what DARPA describes as 'beyond state-of-the-art platform performance characteristics'.

It is envisioned that ACTUV will operate under a sparse remote supervisory command and control model, with a shore-based supervisor providing high level mission objectives and monitoring autonomous performance through an intermittent beyond-line-of-sight communications link.

A key part of the programme will be to provide the vessel with the capability to safely navigate at sea within the framework of maritime law and the International Regulations for Avoiding Collisions at Sea.

Wave Glider

Oceanology 2010 saw the European debut of the Wave Glider, a unique and innovative unmanned marine vehicle (UMV) from Liquid Robotics.

Wave Glider offers a step forward in unmanned surface vehicle technology because it harvests abundant natural wave energy. A unique two-part architecture and wing system directly converts wave motion into thrust while solar panels provide electricity for sensor payloads.

The wave energy propulsion mechanism is purely mechanical; no electrical power is generated.

'Underneath the float is another component, which we call the glider, attached by a flexible umbilical,' explains Justin Manley, director of scientific and commercial business for Liquid Robotics.

'As the float pulls up a wave, so does the glider. The glider has wings on it, and those wings change their angle of attack as they are pulled up to generate thrust. As the float comes down a wave the glider sinks and the wings change their angle again to continue to generate forward thrust.

'It is the seesaw motion back and forth between these two bodies attached by this flexible cable that enables us to convert vertical wave motion into horizontal thrust,' he explains.

Just as an airplane's forward motion through the air allows its wings to create an upward lifting force, the submerged glider's vertical motion through the calm waters at the glider's depth allows its wings to convert a portion of the upward motion into a forward force. As waves pass on the surface, the submerged glider acts as a tug pulling the surface float along a desired course, controlled by a rudder on the glider.

Wave Glider is able to maintain an average forward speed of 1.5 knots in typical seas with one to three foot waves. However, in Sea State 0 has been observed to yield speeds of 0.25 to 0.5 knots while Sea State 3 and higher can result in speeds of over two knots.

Over the past two-and- a-half years, Liquid Robotics has undertaken a vigorous series of sea trials and the current generation of Wave Gliders is the beneficiary of nearly six years of combined sea time and an estimated 60,000 cumulative nautical miles 'sailed'.

'We are working on an exciting problem,' says Manley. 'We would like to take the Wave Glider and challenge our technology and perhaps enter a hurricane. Our experience base suggests we can do that.'

The Wave Glider would then be able to send back data from inside of the hurricane, something that is extremely difficult to obtain.

The vehicle is very versatile with modular mechanical, electrical, and software interfaces to accept a wide variety of payloads, which makes it suitable for a wide range of applications from physical oceanography and intelligence surveillance to reconnaissance and many other missions. 

Further information
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Unmanned vehicle types

AUV: Autonomous underwater vehicle

ROV: Remotely operated vehicle

ROTV: Remotely operated towed vehicle

UGV: Unmanned ground vehicle

USV: Unmanned surface vehicle

UAV: Unmanned aerial vehicle

At a glance

Large AUV features

Price $250,000 to $1m

Length 2-3m, weight 50-500kg

High-specification positioning and navigation including tracking

Range 40-150km

Battery module for fast swap

Depth rated to 500-3,000m

Can support high-specification sensors

Small AUV features

Designed for shallow (100m) waters

Unsupervised during operation

Low payload capacity

Short ranges (20-40 line km)

Basic navigation and positioning

Batteries recharged in-situ or swapped in workshop (5-8 hours)

Can operate at or near the water surface as well as at depth

Up to 2m in length, weight up to 50kg

Low logistical requirements and price ($50-250,000)

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