HEXATERRA

The development of a modular ‘stepping locomotion’ system for installation on subsea trenching machines used for subsea energy cable burial

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 Obiettivo del progetto (Objective)

Offshore wind and tidal energy generation is becoming an increasingly important component of the world’s energy mix with Europe at the forefront of this technological revolution. Continued strong growth is predicted. However, a growing problem is manifesting itself within the industry.

The submarine cables that are an essential infrastructural component of offshore energy now account for 80% of insurance claims related offshore renewables. Unfortunately, current practice is to simply lay these cables on top of the seabed without burial or protection, as the traditional tracked trenching machines originally developed for deep sea oil and gas applications are inadequate for the harsh coastal terrain. Cables are therefore exposed to numerous risks such as tidal forces, rock abrasion, snagging from fishing nets etc. Furthermore, unburied HV cables present serious environmental concerns related to local habitat & water temperature.

Existing technologies cannot address this growing problem. HexaTerra will develop a novel solution to the problem that builds upon recent advances made in ‘stepping’ locomotion systems for traversing undulated harsh terrain. This system will provide a robust solution for its environment, by achieving the following objectives: modular design suited to existing trenching machines; mechanical movement subsystem with <5% error in desired motion tracking & <1cm in actual tracking error; control subsystem capable of negotiating /-0.5m 90° step in terrain & turn on-the-spot; complete simulated locomotion cycle in under 5mins, with <5% desired motion tracking error.

Using this solution the project expects to comprehensively address the problem of damage to subsea energy cables, thereby maximising offshore energy reliability, maintain renewable energy affordability, & minimise the marine environmental impact of cables. In turn, we will deliver a profit of €10.95m & 100 new high skill jobs to the SME partners after 5 years.

Introduzione (Teaser)

High-voltage submarine cables are necessary to transmit offshore wind energy. An EU-funded project is developing an innovative system that traverses the seabed to prevent their damage.

Descrizione progetto (Article)

Offshore wind energy and tidal energy are becoming increasingly important parts of the world clean energy mix, with Europe being at the forefront of energy market reform. However, submarine cables are the main cause of the most frequent insurance claims against offshore wind developments. Given that the conventional trenching machines originally developed for oil and gas applications cannot penetrate the seabed, current practice involves leaving submarine cables above it.

The EU-funded project http://www.hexaterra.eu/ (HEXATERRA) is designing a modular system suited to existing trenching machines that prevents failure of unburied submarine cables. Possible threats include tidal forces, rock abrasion or snagging from fishing nets.

HEXATERRA's system is a bolt-on locomotion system for an underwater trenching machine that can move in all directions. The system automatically adapts to the terrain, keeping the trench cutting tool stable. Responding to sensor inputs, the machine distributes its weight evenly over the ground and seeks a support base for each of its six legs. Depending on ground irregularity, the machine operator can adjust both the machine ground clearance and the height of each step. It has exact step positioning and spot contact with the ground, with the ability to step over obstacles.

The user requirement and functional design specifications have been fundamental to the consortium understanding the needs of the underwater locomotion system and the human interface design.

Significant developments have taken place concerning the human-machine interface and the video overlay. Scientists focused on the relationship between the sensors on the remotely operated vehicle, the stepping platform and the user interface. This should help combine visual and sonar data, and develop a haptic feedback joystick.

Other project tasks have been to perform simulations for investigating the system's dynamic behaviour and developing various operation scenarios.

With its activities, HEXATERRA is helping maximise the reliability of renewable energy networks. Furthermore, it minimises the adverse impact of high-voltage cables on the surrounding marine environment and prevents a rise in water temperature.