Unmanned Systems Technology 036

56 Report | Oceanology International 2020 capacity used by fish living in muddy and obstructed tropical waters, the Elwave sensors – which are mounted on underwater vehicles – generate a weak electromagnetic field, then measure any interferences in the vicinity. “Algorithmic and AI processing of these interferences then enable us to create a 3D and real-time 360 º ‘electric image’ of the environment, even in degraded situations such as turbid water, very constrained environments, or when trying to detect objects buried in sediment. Cameras and sonars tend to reach the limits of their usefulness in these situations.” The system works using a sensor- processor core (housed in a waterproof pod about 40 cm long and with a total weight of 5 kg) and up to 24 electrodes distributed on the hull of the host vehicle. This enables sensing ranges of up to five times the length of the vehicle, which can penetrate up to 2 m into sediments. This enables precise localisation and characterisation of the size, shape and composition of nearby objects, opening up possibilities in underwater research, inspection of sub-sea bed assets such as cables or pipelines, and autonomous sense & avoid capabilities. Elwave’s system consumes less than 30 W and can output its data over RS- 232, RS-422, RS-485 or Ethernet. Lapasset added that companies in the commercial maritime sector, such as Total, Saipem and Subsea7 – as well as players in the defence sector – are now working with Elwave to equip their underwater vehicles with the electric sense systems. The aim is to give ROVs and AUVs greater safety and speed of navigation in close approaches, docking, target tracking, buried object detection and other functions. Prevco Subsea spoke to us about its latest product, the High-Flow Pressure Relief Valve (HFPRV), which may be critical in the event of large AUVs’ pressure housings – carrying batteries, cameras or electronics, for example – experiencing sudden pressure build-ups and needing quick release. “The new valve is based on the engineering principles of our current range of pressure relief valves, with the exception that the flow rate is very much higher,” explained Stephen Ashley. “It can reach a flow rate of 7 standard cubic feet per minute at 36 psi – or 11.89 m 3 /hour at 2.48 bar – and units can be customised to a higher or lower flow rate, according to customer need.” The HFPRV can be built from a range of materials including stainless steel, titanium or Inconel 625 and others by request. The choice would be determined largely by the depth rating required, the length of time at depth (for reasons of corrosion resistance) resistance to bio- fouling, cost and other factors. It can operate at depths down to 6000 m (or potentially deeper), and in temperatures from -26 C to +130 C (-15 F to +266 F). “Several hundred of these valves are now in use as annulus vent valves for flexible risers in the oil & gas industry, but there are of course many other applications where pressure vessels may need to be brought to the surface quickly, while off-gassing any potentially dangerous internal pressure,” Ashley noted. “Owing to the highly customisable nature of the high-flow valves, they are not sold as standard stock products. However, we are happy to engage with anyone to explore options, in order to customise the valves to their specific needs.” AML Oceanographic told us about three new sondes it has launched in its X2change series of ocean sensing instruments: the AML-1, AML-3 and AML-6 (each named for the number of sensors each sonde can accommodate). Each sensor port on all three use the same style of plug-and-play connectors to provide maximum flexibility in meeting various measurement requirements regardless of the type of project or survey. With more than 15 different X2change sensors in its line-up, AML can accommodate most requested sensor configurations on the end cap itself. “The AML-1 is a real-time single-port instrument with a 6000 m depth rating, and it can accommodate any of our X2change sensors,” said Chris Malzone. “It weighs 270 g in air and is ideal for measuring sound velocity using multi-beam sonar. “The AML-3 is a three-port instrument with 500 and 6000 m depth ratings, and is designed for outputting data in real time or autonomous logging or, if desired, both. Its users can combine any three X2change sensors, with typical configurations including sound velocity profiling [SVP], sound velocity February/March 2021 | Unmanned Systems Technology Prevco Subsea’s new HFPRV under test