Because our work is open-source, anyone is able to download it and benefit from our designs. During test runs, the device has to accurately respond to both visual and acoustic-based tasks, and their ThinkPad makes it easy to collect and respond to this data in real-time. Will it need repair? Demers-Morin is not alone in her preferred choice of technology. There is no time to worry if your technology is going to work. The day can start as early as 6 a. Over cups of coffee and fresh pastries, they will decide what they need to examine that day. It could be the hydrophones, the thrusters, torpedoes or the droppers.
Demers-Morin might sneak in some last-minute soldering, triple-checking that the batteries are in order. Once at the pool, they have two tables of coders working on ThinkPads while the submarine is in the water. In addition, divers are in the pool to provide any hands-on assistance. By the time they finish testing, making adjustments and return everything to the university, it can be as late as midnight.
Observing the synergy of team S. A series of synchronised sonar and position data sets were collected, at varying speeds and approach angles Figure 1. However, there remain many interesting and practical combinations of simulated and real systems. Its key successes are its flexible and extendable architecture; the interface design that allows easy migration from simulation to real hardware; its modified approach to time-slicing that allows the real hardware to be run in longer, more realistic sections of logical time; and its synchronisation strategy that helps reduce thrashing where the simulations continually rollback back, unable to make any progress.
Until recently, the choice of practical power sources for most applications was limited to lead-acid and silver-zinc batteries. Lead-acid batteries are a well-established technology and are available at low cost. There is, in practice, no all-purpose, ideal choice of power source for an autonomous underwater vehicle AUV.
Developers have sought to use a variety of battery types including nickelcadmium, nickel-metal hydride, lithium ion and primary manganese alkaline and lithium cells, often using stacks of cells developed for the consumer or industrial markets. In recent years considerable research and development work has been done on advanced power sources for road electric and hybrid vehicles. This on-going work is motivated by environmentally driven legislation aimed at reducing the harmful emissions of conventional internal combustion engine vehicles e.
IEA, Many in the AUV community have an expectation that breakthroughs and or cost reduction in electric power for road vehicles may deliver the ideal AUV power source. However, this potentially advantageous spin-off may prove difficult to achieve in practice. Electric cars need sources capable of delivering 5—50 kW at a capital cost per kW not too dissimilar from that of an internal combustion engine. In contrast, most AUVs have a power consumption an order of magnitude less, typically 0.
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- The technology and applications of autonomous underwater vehicles.
- 1. Introduction.
Furthermore, the AUV user would be willing to pay a higher price per kW than the car owner would. Much research and development effort is also directed at providing high energy density sources for low power consumption devices. For example, micro-fuel cells are becoming available for portable electronic equipment such as cellular telephones and laptop computers requiring 5—50 W.
For these, the consumer is prepared to pay an even higher price per kW than the AUV user. The ideal power source for an AUV should have a high energy density, high power density higher charge and discharge rates , low cost, long life, low maintenance, high efficiency and wide operating temperature range.
It should be safe and recyclable. Ideally, the power source should be non-gassing and in the case of batteries, the electrolyte should be spill-proof. The operation of the power source should also be independent of depth. This chapter begins by reviewing the state of development of different types of rechargeable power sources that look promising for use in AUVs, and then briefly reviews the recent development of flywheel electromechanical batteries and supercapacitor energy storage systems. Although these latter technologies may not see service as the primary power source in AUVs, they may well have applications in particular circumstances.
Section 2. The difficulties of estimating the energy remaining in the battery pack are explored and a simple fuelgauge algorithm is derived based on electrochemical equations and laboratory performance data.
Technology and Applications of Autonomous Underwater Vehicles
The practicality of this fuel-gauge algorithm is demonstrated using data from a series of Autosub missions. Primary batteries are considered in Section 2. Sealed lead-acid cells have been used as the power source in many AUVs, especially for engineering trials and short-duration missions. This was sufficient energy for up to 10 h operation giving a range of 70 km Millard et al.
Silver-zinc cells have been used extensively in AUVs.
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However, batteries formed from silver-zinc cells require very careful maintenance and record keeping on the state of charge to ensure safe operation. Standard silver—zinc cells also have a limited number of charge-discharge cycles, a limited life once the electrolyte has been added to the cell and a high capital cost. These limitations have led several AUV manufacturers to seek alternative rechargeable power sources. Nevertheless, significant research and development effort has been directed towards augmenting the silver-zinc chemistry in order to improve the energy density and the number of charge-discharge cycles.
These efforts have involved modified anodes, for example adding bismuth, cadmium or lead oxide to the zinc oxide and using new electropermeable membranes to almost double the cycle life Smith et al. Nickel-cadmium presents one commercially available proven alternative to lead-acid and silver-zinc. The higher energy density and longer life of nickel-cadmium cells, however, comes at a price that is ten times that of lead-acid for the same capacity. Table 2.
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During charging, the process is exothermic; in large packs the heat generated must be dissipated to avoid an excessive temperature rise that will reduce the charging efficiency. Disposal of used nickel-cadmium cells requires special considerations due to the significant amount of toxic heavy metals present. Notwithstanding these complications, nickel-cadmium cells have been used in several AUVs, including those from Florida Atlantic University Smith et al.
Nickel-metal hydride batteries are under active development e. Cornu, In Urashima, the power source comprises three V Ah batteries in parallel, giving a total capacity of 39 kWh, sufficient for the vehicle to travel km Aoki, Improvements in the materials used within these cells, such as increasing the amount of lithium at the cathode, will lead to an increase in energy density but the cell chemistry limits will be reached at about Wh kg-1 Green and Wilson, Lithium-solid polymer cells look promising for underwater vehicle applications because their solid-state construction allows their use at ambient pressure without the need for a pressure case Huang et al.
Their solid-state construction also means that they are resistant to shock and vibration and, in principle, need not be restricted to cylindrical form factors. Experiments have been successfully carried out on small ca. As the technology matures, and higher capacity cells that operate at ambient temperature become available, lithium-polymer will become a feasible and cost-effective power source for AUVs.
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However, the support systems that needed to be installed in the vehicle to manage the cells led to a substantial decrease in the effective energy density. Nevertheless, except in Japan, sodium-sulphur battery development has ceased Dell, Zebra batteries are a recent development—a class of cells that use liquid sodium metal as the anode and chlorides of various transition metals as the cathode.
The nickel chloride cell, for example, has an open circuit voltage of 2. Extensive trials of these batteries with capacities in the region 13—17 kWh have taken place in electric road vehicles. Metal seawater secondary batteries based on magnesium or aluminium anodes and silver chloride, lead chloride or manganese dioxide can produce high energy densities, but at low power densities Lee et al.
Open circuit voltages of 1. Alupower developed aluminium-oxygen semi-fuel cell prototypes for AUVs Scamans et al. This has been followed by the installation of a 35 kWh unit into the larger HUGIN vehicle as the standard power source see Chapter 11 , giving the vehicle an endurance of 40—50 h.
Each charging cycle involves exchanging the hydrogen peroxide and each alternate charge requires the aluminium anode to be replaced.
While these batteries have a high energy density, they are, to some degree, still under development and require very careful handling, servicing and maintenance. The invention of proton exchange membranes PEM has been an important factor in the development of fuel cells capable of operating efficiently at low temperatures. Using suitable noble metal catalysts bonded to the membrane, areal current densities of 0. Despite the very small volume of the fuel cell reactor, storage of the reactants remains a problem and it is not surprising that very few true fuel cells have been incorporated within an AUV to date.
This hydrogen-oxygen cell used cryogenic gas storage. Cryogenic storage of hydrogen within an AUV is not an attractive option for most users. Fuel cells are under development that use room-temperature liquids such as methanol. The direct methanol fuel cell consumes a dilute solution of methanol in water and oxygen and generates carbon dioxide and water as the reaction products. It has the additional advantages of operating at low temperature 2. Energy is coupled into and out of the rotor via a highly efficient electric motor-generator and associated electronics. While the concept of a flywheel is old, its realisation as a viable battery with an energy density that compares well with the best of secondary batteries has been possible only recently.
The main factor in the rebirth of the flywheel as an electromechanical battery is the improvement of carbon fibre technology. The energy density of a flywheel is proportional to the ratio of the tensile strength to mass density of the rotor material. In other words, for high energy density, the rotor material should be strong and light, which are properties of carbon fibre.
Currently, there are at least five development programmes of flywheel batteries for EV applications Abacus Technology Corporation, The most notable of these is that by Trinity Flywheel Batteries Inc. The Trinity development programme is expected to deliver a power flywheel having a rated capacity of kW discharged over a period of 30s. Flywheel Energy Systems Inc. Prototype flywheels have been developed and the units are available for evaluation by potential customers.
A schematic diagram of the IES flywheel is shown in Figure 2. The focus of most flywheel manufacturers including Trinity and Urenco is mainly on power quality and aerospace applications. The Urenco flywheel is designed for stationary applications and would not be suitable for use in a moving vehicle, nevertheless all the enabling technologies for the development of a flywheel for AUV applications are available, although considerable work is still needed. Figure 2. Capacitors with power densities up to W kg-1 and energy densities of 15 Wh kg-1 are claimed to be possible Eureka, Capacitors with power densities of 9 Wh kg-1 have been made, but the technology is still maturing and the costs remain high.
While the low energy density of supercapacitors may exclude them from being used in most AUVs, they could be attractive for some applications including untethered shortrange UUVs or seabed vehicles operating from underwater rapid-charging stations. They may also be used in parallel with batteries to provide high power impulses.
This could easily be the case for AUVs engaged in scientific research or on missions for the military. The main advantage of primary over secondary cells is their high energy density.
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