Underwater robots on 24-hour duty protect pipelines and cables

Why do we need underwater robots?

Increased economic activity in the ocean requires more regular monitoring and inspection of subsea infrastructure and its surroundings. Autonomous underwater vehicles capable of monitoring pipelines, cables and subsea installations are becoming increasingly important in an uncertain global security environment. In addition, we need to know more about the seabed and the ocean itself.

Monitoring and inspections are now carried out by large vessels with wide surface scanning sonars, or by submersibles that accompany the ships and are controlled from control rooms on the mother ship or on shore. Both systems require large, expensive surface vessels and many people. Renting a ship with a crew is very expensive and the CO2 emissions are significant.

“Dear Home” at a depth of 90 meters

One alternative currently being developed is autonomous underwater robots that can operate on the seabed for months or years without being brought to the surface or shore.

The autonomous underwater robot project was implemented by (from left to right) Grimsrud Waldum, Leonard Güntzel, Gabriele Kasparaviciute, Ai-Nhi Hoang, Jenny Krokstad, Md Shamin Yesher Yusha, Dana Erbolat and Abubakar Aliyu Badawi. Not pictured are Martin Ludvigsen, Selil Yilmaz, Mahmoud Hussein Abdelrazik. Researchers give an idea of ​​the scale. Photo: NTNU

Professor Martin Ludvigsen from NTNU's Department of Marine Technology says underwater robots, operating from fixed bases on the seabed and independent of expensive surface vessels, will play a key role in monitoring, inspecting and protecting the growing underwater infrastructure around the world.

Researchers from NTNU have successfully tested an autonomous underwater vehicle (AUV) and docking station at a depth of 90 meters (295 feet). Without human intervention, the robot inspected the infrastructure, found its way back to the station, connected to it to charge its batteries and upload the collected data.

“These tests are important steps towards fully autonomous operation over a long period of time,” says Leonard Florian Tom Günzel, doctoral student at the Department of Marine Technology at NTNU. He explains: The motivation for developing resident underwater vehicles is to reduce costs and make the technology available to a wider range of users. Another important reason is the safety of seafarers and environmental protection.

Schematic representation of the software and control system of the underwater robot. Photo: Leonard Guentzel, NTNU

Easier and cheaper

For years there has been talk of deploying AUVs for a near-constant presence around oil and gas installations. There are already several large, advanced systems. The recent wave of sabotage of infrastructure, communication lines, power cables and pipelines will only increase the demand for simpler and more affordable solutions.

More research and development is needed to achieve reliable and low-cost solutions. “The foundation has been laid and the first steps have been taken towards the creation and deployment of fully-fledged autonomous underwater robots with a docking station for charging and data transfer,” says Ludvigsen.

The most important tasks are the development of strong and durable docking systems. In addition, there are problems with autonomy, navigation, docking, communication and maintaining position, course and direction under water.

The Blueye robot created this 3D image of a docking station at a depth of 90 meters. Photo: NTNU

Robot Blueye

For testing, NTNU used the Blueye X3 submersible. It weighs about 10 kilograms (22 pounds) and has been specially modified for specific applications. In particular, the robot was equipped with a camera, sonar, sensors, communication equipment, an inductive charger and a magnetic “mooring” system.

Ludvigsen and Günzel emphasize that this test robot gives NTNU a platform that can be used by undergraduates, graduate students and companies.

“We have created a tool to further develop, test and refine technologies that can ultimately be commercialized,” says Günzel.

Tests in Trondheimsfjord

The tests were carried out on the existing NTNU infrastructure in Trondheimsfjord. A specially designed docking station was installed at a depth of 90 meters (295 feet).

The underwater robot uses a combination of acoustic (1) and visual navigation (2) before docking to charge (3,4) and upload collected data. Source: NTNU

To enable the robot to find the docking station and dock correctly, a variety of technologies were used: low-speed acoustic communication, navigation, including ultra-short-baseline positioning (USBL), and visual markers. Machine vision cameras read and interpreted these markers, guiding the vehicle toward the dock.

At short distances, the robot can be controlled remotely and exchange data via an optical modem. The docking station is connected to the shore equipment by a cable - it carries power and communication.

As soon as the device is in place, data is transmitted via high-frequency broadband, and the device itself is charged inductively. Such equipment has already been developed in Norway.

So far, the device has gone to sea twice, having worked for a total of four weeks. The system has completed inspection missions and achieved a 90% successful autonomous docking rate. But we need to achieve a 100% result, so new outputs are planned this spring.

“Docking is a critical moment. Without an operator, the consequences of errors are much more serious. If the device doesn’t find its way back to the station, it can’t be returned,” explains Ludvigsen.

Tethered tests

On land or sea, navigation is simple: GPS and other satellite systems provide access to location data. This won't work underwater.

Therefore, to calculate position and heading, a combination of several methods is used: gyroscopes and accelerometers (inertial navigation system, INS), as well as an acoustic system (Doppler log, DVL). Navigation systems require a lot of computing power, which means they consume a lot of electricity.

Tests of Blueye X3 were carried out on a leash - for insurance. Future exploration launches will also use tethers until a reliable autonomous solution becomes available. The process may take some more time, although artificial intelligence is helping researchers find effective solutions faster.

One of the main unresolved tasks is to make the robot completely autonomous. So that he can “understand” and “think,” that is, make his own decisions based on observations of the environment. Tests have shown that fish swimming in front of the camera confuse the program that processes the images.

“We are working on this problem,” says Günzel.

Commerce is still a long way off

Ludvigsen believes a commercial solution is still a long way off, but is optimistic about the future.

“Tests have shown that this solution works and the operations are repeatable. Fixed submersibles are a scalable and cost-effective solution for underwater monitoring,” concludes Ludvigsen