Nature in Engineering for Monitoring the Oceans (NEMO): An isopycnal soft bodied approach for deep diving autonomous underwater vehicles

Abstract

Taking inspiration from nature the NEMOdeep vehicle described in this paper is being developed as a laboratory demonstrator to showcase potential technologies to achieve small deep diving autonomous underwater vehicles. The design of the vehicle is a hybrid of conventional AUV components with engineered analogues of marine animal organs. The internal structure is comprised of a spine, ribs and sternum, which support a hydrodynamic fairing or 'skin'. The 'brain' and actuators are developed using pressure tolerant electronics, negating the need for pressure vessels. The pressure tolerant electronics are surrounded by light mineral oil which transmits the hydrostatic pressure uniformly to the components while also providing buoyancy. The internal fluid is more compressible than seawater and the batteries and internal structure are less compressible than seawater: a 'Buoyancy/Compressibility' organ is being developed to passively maintain neutral buoyancy over the 0 to 6000m depth range.

Depth control for an over-actuated, hover-capable autonomous underwater vehicle with experimental verification

“…The power consumption, P tot , of a neutrally buoyant flight style AUV can be assumed to be split between hotel load, P H , which is invariant to forward speed, and propulsion power, P P , which is related to propulsion speed raised to the power 3 [40,41]. For a positively buoyant over-actuated vehicle, additional power is required to maintain depth, P B :…”

Preliminary design and fast prototyping of an Autonomous Underwater Vehicle propulsion system

“…For a more precise customization of the static balance of the vehicle, three drop-weights placed according to the scheme of Figure 8 should be easily adjusted. This way, in normal operating conditions (vehicle ballasted by drop-weights), the vehicle is neutral with a slight additional buoyancy of about 1%−2%, with respect to the one calculated from vehicle volume, to compensate compressibility of the hull at maximum depth 19 and to make the return to surface easier when state of charge of batteries could be lower; in the case of severe failure, the drop-weights (which are usually hold through a solenoid system) are released assuring an additional buoyancy of about 3%−4% with respect to vehicle volume. In this way, in case of failure, a rapid return to surface is assured.…”

Numerical investigation of a pair of self-propelled AUVs operating in tandem

“…Since the range and endurance are limited by the cruise speed (Bingham et al, 2002;Furlong et al, 2007;McPhail, 2009;Stevenson et al, 2007;Tripp, 2006), the options to extend an endurance are: minimising drag (Huggins and Packwood, 1994;Parsons, 1972;Parsons et al, 1974), enhancing propulsive efficiency (Ageev, 2000(Ageev, , 1995Stevenson et al, 2007), increasing specific energy of power sources (Ageev, 2000;Alers, 1981), and reducing hotel load Phillips et al, 2012).…”