Description of ENDURUNS approach
The ENDURUNS project aims to address existing operational limitations and overcome the technological barriers associated with prolonged underwater operation through the development of a hybrid AUV powered using a hydrogen fuel cell. Hydrogen as a fuel has a much higher energy density in comparison with batteries whilst various storage options can be employed, which can be selected according to the exact mission parameters. This permits a much higher amount of energy to be stored onboard, resulting in extremely higher endurance when compared with conventional commercially available AUVs and gliders. A Li-ion battery will be employed in order to provide supplementary power, particularly in case of failure or emergency, and for managing energy distribution to propulsion and sensors according the actual consumption requirements. The hybrid AUV will be capable of performing multiple types of operation, including high-resolution seabed mapping, inspection of underwater assets, surveillance, etc. The ENDURUNS AUV design will be based on modularity, enabling the integration of existing systems and sensor packages as required by the mission profile. The ENDURUNS AUV will conserve energy by gliding when it travels to the site of interest in order to minimize energy consumption. During performance of seabed surveying and inspection tasks, it will switch to propelled mode, since gliders cannot perform such tasks due to their inability to cruise steadily at a certain height and speed from the seabed or infrastructure. Moreover, gliders always move in a sinusoidal or saw-tooth like pattern (Figure 2). Control algorithms for smart energy management will be developed in order to optimize mission endurance based on actual propulsion, navigation, sensor and communication usage. The consortium will develop algorithms for effective automated data processing onboard the AUV. Data will be categorized and stored wirelessly on SD cards contained in special pencil-like bubbles which can be ejected to the surface when required or in the event of an emergency. To execute control and data processing algorithms onboard, the AUV will be equipped with a low-consumption computing system based on solid-state hardware. A suitable set of I/O ports will be used to connect the different sensors selected for each mission. When dealing with acoustic data acquired for example from sidescan sonars used for seabed mapping the embedded computing system will perform the necessary filtering, remapping and compression operations in order to reduce as much as possible the amount of stored data. During data processing of imaging data the embedded computer will regulate the frame rate of the vision system in order to obtain optimal sampling of the observed sequences whilst applying image restoration and compression. A specific set of pre-processing functions will be defined for each sensor in order to reduce the amount of data to be managed without affecting data resolution and actual content. The AUV will be accompanied by an USV (Unmanned Surface Vehicle), which will fulfil multiple roles in support of the AUV’s mission. More specifically, the USV will follow the AUV from the surface and transmit data from the AUV to RMCC onshore. When crucial data or mission parameters change the relevant data will be transmitted directly to the AUV through the USV equipped with a satellite link. The USV will provide the required high-resolution geotagging data, mission maps and mission locations. The USV will receive, store and when necessary transmit relevant data to and from the RMCC. It will also be responsible for retrieving the data from data bubbles (capsules) that are ejected from the AUV. The USV will use integrated electrical power provided through a combination of hydrogen fuel cell, Li-ion battery and thin film solar cells. The USV will have docking capability to aid re-charging the AUV battery when the hydrogen onboard has been exhausted but some additional operations are required to complete the mission as well as for LAR to port activities.
The USV will be equipped with suitable data processing hardware in order to supplement more in-depth data processing when required. An optimal allocation of required functions between AUV and USV will ensure efficient data flow throughout the system architecture, respecting the constraints on storage and energy consumption set for each mission. The complete ENDURUNS system including the AUV and USV will be designed to have prolonged operational autonomy in deep ocean conditions lasting up to 8 months, be capable of accomplishing complex missions, including seabed mapping, habitat assessment, geophysical surveys, inspection of underwater infrastructure assets and surveillance. The ENDURUNS system will provide the necessary capability required for performing a wide range of versatile missions. The control and communication technologies implemented in the project will aid in dynamically adapting operation while underway when this is deemed necessary.