Autonomous underwater vehicle

The oil and gas industry uses AUVs to make detailed maps of the seafloor before they start building subsea infrastructure; pipelines and sub sea completions can be installed in the most cost effective manner with minimum disruption to the environment. The AUV allows survey companies to conduct precise surveys of areas where traditional bathymetric surveys would be less effective or too costly. Also, post-lay pipe surveys are now possible, which includes pipeline inspection. The use of AUVs for pipeline inspection and inspection of underwater man-made structures is becoming more common. There also is development of AUVs for potential seabed mining and/or harvesting of polymetallic nodule rocks.[3]

A University of South Florida researcher deploys Tavros02, a solar-powered "tweeting" AUV (SAUV)

Scientists use AUVs to study lakes, the ocean, and the ocean floor. A variety of sensors can be affixed to AUVs to measure the concentration of various elements or compounds, the absorption or reflection of light, and the presence of microscopic life. Examples include conductivity-temperature-depth sensors (CTDs), fluorometers, and pH sensors. Additionally, AUVs can be configured as tow-vehicles to deliver customized sensor packages to specific locations.

The Applied Physics Lab at the University of Washington has been creating iterations of its Seaglider AUV platform since the 1950s. Though the Seaglider was originally designed for oceanographic research, in recent years it has seen much interest from organizations such as the U.S. Navy or the oil and gas industry. The fact that these autonomous gliders are relatively inexpensive to manufacture and operate is indicative of most AUV platforms that will see success in myriad applications.[4]

An example of an AUV interacting directly with its environment is the Crown-Of-Thorns Starfish Robot (COTSBot) created by the Queensland University of Technology (QUT). The COTSBot finds and eradicates crown-of-thorns starfish (Acanthaster planci), a species that damages the Great Barrier Reef. It uses a neural network to identify the starfish and injects bile salts to kill it.[5]

Many roboticists construct AUVs as a hobby. Several competitions exist which allow these homemade AUVs to compete against each other while accomplishing objectives.[6][7][8] Like their commercial brethren, these AUVs can be fitted with cameras, lights, or sonar. As a consequence of limited resources and inexperience, hobbyist AUVs can rarely compete with commercial models on operational depth, durability, or sophistication. Finally, these hobby AUVs are usually not oceangoing, being operated most of the time in pools or lake beds. A simple AUV can be constructed from a microcontroller, PVC pressure housing, automatic door lock actuator, syringes, and a DPDT relay.[9] Some participants in competitions create designs that rely on open-source software.[10]

Submarines that travel autonomously to a destination by means of GPS navigation have been made by illegal drug traffickers.[11][12][13][14]

Autonomous underwater vehicles, for example AUV ABYSS, have been used to find wreckage of missing airplanes, e.g. Air France Flight 447,[15] and the Bluefin-21 AUV was used in the search for Malaysia Airlines Flight 370.[16]

MK 18 MOD 1 Swordfish UUV

Mk 18 Mod 2 Kingfish UUV

Kingfish UUV launch

The U.S. Navy Unmanned Undersea Vehicle (UUV) Master Plan[17] identified the following UUV's missions:

• Intelligence, surveillance, and reconnaissance
• Mine countermeasures
• Anti-submarine warfare
• Inspection/identification
• Oceanography
• Communication/navigation network nodes
• Payload delivery
• Information operations
• Time-critical strikes

The Navy Master Plan divided all UUVs into four classes:[18]

• Man-portable vehicle class: 25–100 lb displacement; 10–20 hours endurance; launched from small water craft manually (i.e., Mk 18 Mod 1 Swordfish UUV)
• Lightweight vehicle class: up to 500 lb displacement, 20–40 hours endurance; launched from RHIB using launch-retriever system or by cranes from surface ships (i.e., Mk 18 Mod 2 Kingfish UUV)
• Heavyweight vehicle class: up to 3,000 lb displacement, 40–80 hours endurance, launched from submarines
• Large vehicle class: up to 10 long tons displacement; launched from surface ships and submarines

In 2019, the Navy ordered five Orca UUVs, its first acquisition of unmanned submarines with combat capability.[19]

AUVs carry sensors to navigate autonomously and map features of the ocean. Typical sensors include compasses, depth sensors, sidescan and other sonars, magnetometers, thermistors and conductivity probes. Some AUVs are outfitted with biological sensors including fluorometers (also known as chlorophyll sensors), turbidity sensors, and sensors to measure pH, and amounts of dissolved oxygen.

A demonstration at Monterey Bay, in California, in September 2006, showed that a 21-inch (530 mm) diameter AUV can tow a 400 feet (120 m)-long hydrophone array while maintaining a 6-knot (11 km/h) cruising speed.

Radio waves cannot penetrate water very far, so as soon as an AUV dives it loses its GPS signal. Therefore, a standard way for AUVs to navigate underwater is through dead reckoning. Navigation can however be improved by using an underwater acoustic positioning system. When operating within a net of sea floor deployed baseline transponders this is known as LBL navigation. When a surface reference such as a support ship is available, ultra-short baseline (USBL) or short-baseline (SBL) positioning is used to calculate where the sub-sea vehicle is relative to the known (GPS) position of the surface craft by means of acoustic range and bearing measurements. To improve estimation of its position, and reduce errors in dead reckoning (which grow over time), the AUV can also surface and take its own GPS fix. Between position fixes and for precise maneuvering, an Inertial Navigation System on board the AUV calculates through dead reckoning the AUV position, acceleration, and velocity. Estimates can be made using data from an Inertial Measurement Unit, and can be improved by adding a Doppler Velocity Log (DVL), which measures the rate of travel over the sea/lake floor. Typically, a pressure sensor measures the vertical position (vehicle depth), although depth and altitude can also be obtained from DVL measurements. These observations are filtered to determine a final navigation solution.

There are a couple of propulsion techniques for AUVs. Some of them use a brushed or brush-less electric motor, gearbox, Lip seal, and a propeller which may be surrounded by a nozzle or not. All of these parts embedded in the AUV construction are involved in propulsion. Other vehicles use a thruster unit to maintain the modularity. Depending on the need, the thruster may be equipped with a nozzle for propeller collision protection or to reduce noise submission, or it may be equipped with a direct drive thruster to keep the efficiency at the highest level and the noises at the lowest level.[27] Advanced AUV thrusters have a redundant shaft sealing system to guarantee a proper seal of the robot even if one of the seals fails during the mission.

Underwater gliders do not directly propel themselves. By changing their buoyancy and trim, they repeatedly sink and ascend; airfoil "wings" convert this up-and-down motion to forward motion. The change of buoyancy is typically done through the use of a pump that can take in or push out water. The vehicle's pitch can be controlled by moving the center of mass of the vehicle. For Slocum gliders this is done internally by moving the batteries, which are mounted on a screw.[28] Because of their low speed and low-power electronics, the energy required to cycle trim states is far less than for regular AUVs, and gliders can have endurances of months and transoceanic ranges.

Since radio waves do not propagate well under water, many AUV's incorporate acoustic modems to enable remote command and control. These modems typically utilize proprietary communications techniques and modulation schemes. In 2017 NATO ratified the ANEP-87 JANUS standard for subsea communications. This standard allows for 80 BPS communications links with flexible and extensible message formatting. Alternative communication techniques are being explored, including optical, inductive and RF based techniques, which may be combined in a multi-modal solutions.[29] Evaluations are also being conducted on novel communication techniques which are able to utilize the infrastructure as a communication path to provide alternative communication paths and opportunities from the vehicles.[30]

Most AUVs in use today are powered by rechargeable batteries (lithium ion, lithium polymer, nickel metal hydride etc.), and are implemented with some form of battery management system. Some vehicles use primary batteries which provide perhaps twice the endurance—at a substantial extra cost per mission. Previously some systems used aluminum based semi-fuel cells, but these require substantial maintenance, require expensive refills and produce waste product that must be handled safely. An emerging trend is to combine different battery and power systems with supercapacitors.

• Technology and Applications of Autonomous Underwater Vehicles Gwyn Griffiths ISBN 978-0-415-30154-1
• Review of Autonomous Underwater Vehicle (AUV) Developments doi:10.5962/bhl.title.39207 OCLC 227209412
• Masterclass in AUV Technology for Polar Science ISBN 978-0-906940-48-8
• The Operation of Autonomous Underwater Vehicles2 ISBN 978-0-906940-40-2
• 1996 Symposium on Autonomous Underwater Vehicle Technology ISBN 978-0-7803-3185-3
• Development of an Autonomous Underwater Vehicle ISBN 978-3-639-09644-6
• Optimal Control System for A Semi-Autonomous Underwater Vehicle ISBN 978-3-639-24545-5
• Autonomous Underwater Vehicles ISBN 978-1-4398-1831-2
• Recommended Code of Practice for the Operation of Autonomous Marine Vehicles ISBN 978-0-906940-51-8
• Autonomer Mobiler Roboter ISBN 978-1-158-80510-5
• Remotely operated underwater vehicle ISBN 978-613-0-30144-6
• Underwater Robots ISBN 978-3-540-31752-4
• The World AUV Market Report 2010-2019 ISBN 978-1-905183-48-7
• Autonomous Underwater Vehicles: Design and practice ISBN 978-1-78561-703-4