The three-meter diamond-shaped Wave Glider is somewhat like a surfboard, partly a kayak. It floats on the surface of the ocean and uses the energy of the waves and the sun for its hybrid power supply system and movement, while during long journeys the device collects and processes data
For a long history Seafaring mankind has found several ways to extract energy from the environment and replenish its scarce reserves on board in order to increase the navigation range and discover new lands, although sometimes with a tragic outcome.
For millennia sails, oars and muscular strength remained vital navigation technologies, and only relatively recently came steam to help, an internal combustion engine appeared, followed by nuclear energy, which radically changed the nature of navigation. However, modern unmanned underwater and surface gliders (glider), use the change in buoyancy and wave energy, respectively, in order to move at low speeds for many months. This allows humanity to solve many pressing problems, obtaining information and data using previously inaccessible tools. Although the technologies of driving motion due to wave energy and changes in buoyancy have been used for many years, they are still little known and rather unusual for the general public, so it’s worthwhile to give a brief description of the principles of their work before embarking on the study of individual platforms and the tasks they perform.
Buoyancy for movement
The float glider is an autonomous underwater vehicle (AUV) that moves under the action of alternating changes in residual buoyancy using the so-called module of changes in residual buoyancy - the analogue of a fish bubble. The change in buoyancy causes the apparatus to rise or fall in the water column, while the wing lift vector causes the apparatus to slowly and economically (the rule of thumb is half a watt per half node [0,9 km / h]) to move forward along the “sawtooth” path. Although some of them are equipped with hydrodynamic steering rudders, often steering is performed simply by moving a heavy battery compartment: from side to side to create the desired roll angle, and back and forth to change the inclination of the vehicle in the longitudinal plane.
The payload typically includes sensors CTD (Conductivity, Temperature and Depth; water salinity, temperature and depth), whose output data is sent to the so-called sound speed profiles SSP (Sound Speed Profile), which are graphs that build local sound speed relative depth. This allows you to get very valuable information for calculating the parameters of sonars used by other platforms to combat submarines and mines. Underwater gliders using lift floats are mainly limited to low data rate communication systems, including acoustic modems and satellite channels. At regular intervals, they rise to the surface in order to download data for the task, service data and receive new instructions using their satellite communications antenna.
Liquid Robotics' Wave Glider devices are ready for deployment. These reliable wave gliders perform various tasks, including working as a gateway between underwater systems and the rest of the world, using acoustic modems and satellite communications.
All power from the waves
A remotely controlled surface apparatus using wave energy, or a wave glider, is a special device for converting wave energy into energy of forward translation due to freely rotating fin movers (wings). The Wings use the energy of the oncoming wave and move the underwater part forward, which pulls the surface part behind it.
For example, the wave glider Wave Glider from the company Boeing / Liquid Robotics has a two-section structure. The surfboard, similar to a surfboard, with lithium-ion batteries and solar panels is connected to the underwater steering module with a 8 meter-long cable. The wings (set of planes) of the module, freely rotating around the horizontal axis, using the energy of the waves, make oscillatory movements and give the surface part a speed of the order of 2 km / h. In addition, the Wave Glider can use the Thrudder device, which is a combination of a jet engine and a rudder, which creates additional controlled thrust at very low seas, both in the equatorial calm zone and at very strong currents. If necessary, Thrudder adds about half a node to the velocity of the Wave Glider glider.
The Seaglider machine is immersed and begins its mission. The sensor kit includes the Sea Bird oxygen profiler and the WET Labs fluorimeter-optical backscatter reflectometer. The sampling rate may vary by sensor and depth.
The origin of float gliders
According to Gerald Dispeyn of the University of San Diego, active development of float gliders began in the early 90s, when the US Marine Research Administration allocated funds for this. He added that these platforms, for example, the Spray glider from the Scripps Institute of Oceanography, Seaglider from the Applied Physics Laboratory of the University of Washington, and the Slocum glider, originally developed by the Woods Hole Oceanographic Institute, can be manually deployed by two people. Over the past decade, they have become common data collection systems for US federal and local organizations, such as the National Oceanographic and Atmospheric Administration, as well as the oil and gas industry. Currently, they are equipped with a variety of small-sized sensors and sensors with low power consumption, as well as small computers using independent algorithms that can make independent decisions based on information gathered by on-board sensors.
According to the representative of the Office of Naval Meteorology and Oceanography, the main marine application of float gliders is primarily oceanography. The growth in popularity of such devices over the past decade has been facilitated by progress in data transmission systems in real time, the miniaturization and expansion of the sensor range and an increase in the duration of the task. The US Navy has at its disposal the largest fleet of gliders in the world, more than 100 vehicles, mostly produced by Teledyne Marine.
In addition to ocean monitoring with CTD (salinity-temperature-depth) sensors that provide hydroacoustic stations (GAS), the US Naval Meteorology and Oceanography Department uses gliders to collect environmental data and improve its modeling in order to better understand the structure of the oceans and ensure marine operations. A representative of the Office noted: “We are open to research any use of gliders or onboard sensors that could help improve the quality of task performance.” Gliders must be very energy efficient in order to maintain performance for a long time, this also applies to propulsion systems and to onboard equipment. “Modern onboard sensors consume very little energy. The system of displacement, which changes buoyancy, being the main consumer of energy in the glider, limits the number of dives of the apparatus, which it is capable of performing in one exit, he continued. “The sensory systems for gliders Slocum, which we use in military oceanography, are quite effective. Such high efficiency in energy management allows for the analysis of samples taken at significantly lower costs compared to traditional methods of sampling from the vessel. " Dyspein pointed out that reduced glider energy consumption is, by and large, a consequence of their slowness. He noted that for any mobile platform, the amount of energy expended per unit of time increases with the speed cube, taking into account the environment in which this platform moves. In other words, doubling the speed of the underwater vehicle entails an increase in energy consumption of eight times. “The movement of the glider under water is so efficient, given the energy consumption per unit of time, because it moves rather slowly in this environment.”
A more relevant measure of propulsion efficiency is the energy expended per unit of distance traveled, the amount of which directly depends on the hydrodynamic coefficient. "The concept of a flying wing maximizes this factor, so gliders based on it consume less energy per horizontal distance than any other glider of comparable size, moving at a comparable speed." A new type of glider, which uses these principles, was tested in real conditions. The glider “flying wing” is larger and faster than the previous versions, it is optimized for longer distances and longer tasks. "Its much larger dimensions (the span of the 6,1 wing of the meter) also make it possible to increase hydrodynamic efficiency, increase speed, target load and payload."
The Seaglider glider, developed by the Laboratory of Applied Physics and its Oceanographic School, has a streamlined shape and tail wings, which increase the cruising range, and a satellite antenna and a CTD sensor are installed in the tail section
“As in the case of other autonomous underwater vehicles, the progress in the accumulation and consumption of energy promises to increase the duration and range and provide more energy for the onboard sensors, although there is still a lot of work to be done before they are ready for actual operation,” said Dan Radnik, a professor at the University of California at San Diego, who developed the Spray glider. - Of course, systems are being developed that use alternative energy sources, for example, ocean temperature drops and water-activated batteries. I would not classify already developed technologists. ” In turn, Dispeyn gave an example of paraffin waxes with variable phase states, which were successfully used to demonstrate the ability of platforms with variable buoyancy under certain conditions to use temperature varying with depth for movement.
He recalled the joint work of Scripps and the Jet Propulsion Laboratory to demonstrate the work of the submersible buoy-meter, which sailed in the sea for over a year. It implemented a variable buoyancy system powered by a heat engine, the technology for which was developed by the founder of Webb Research (now part of Teledyne Marine) Doug Webb while he was still working at Woods Hole. "The maturity of this technology can demonstrate the availability of such a glider with a heat engine on the market." One important point to note is the phase transition materials, which extract energy from temperature differences, such as paraffin waxes, which is that they decrease in volume during solidification and expand when melted, which is the wrong direction for their direct use as float propulsion. “The engine should increase the volume of the glider when it goes down in its dive cycle and reduce it at the top. Therefore, the thermal glider should have an energy storage system that could ensure the availability of energy extracted from the phase transition for the next half cycle. For example, this phase transition energy could be used as additional energy when charging onboard batteries. ”
Radnick explained that, depending on the set of sensors onboard, the movement usually goes from 60 to 70 percent of the energy balance of gliders developed by the University of California. "That is, our sensors consume less electricity (usually from 20 to 30 percent), but often they determine the duration of the voyage, since we change them more often, while the energy for movement remains constant." The remaining approximately 10 percent goes to other systems, including computer, communications and navigation. The University is studying the ways of accumulating more energy in the gliders, including the easiest way. “The easiest way to increase energy capacity is to make the gliders bigger, which we study. Another way is to improve batteries, ”added Professor Radnik.
The layout of the Spray glider shows the placement of the main internal modules. Two battery packs change the center of gravity, and the cylinders and pump in the tail section change the buoyancy
Interest in gliders has always been wider than scientific oceanography and, as Dispane noted, with the beginning of their transition to combat fleets, this market segment is expected to grow. In November 2016, the U.S. Navy announced that it was ready to deploy gliders from its destroyers in order to give the fleet new opportunities. After successful trials in the Pacific, the US Navy Command approved the arming of Arly Burke class destroyers with one or two gliders. APA will provide GAS operators on destroyers with real-time data. Most likely, the data will come from CTD sensors and will be used to update the “sound speed-depth” diagrams for calibrating HAS on the surface and on air platforms.
While their direct use for detecting submarines, for example, using passive sonars, is obvious, this is not what the fleet is talking about openly. However, they are willing to discuss activities for the detection, tracking and study of other underwater entities. As Dispeyn explained, “The US Navy is interested in a better understanding of the distribution and behavior of marine mammals, endangered species and other marine life in order to minimize the consequences of their activities on the oceanic environment.” This is a challenge for newer, larger gliders with acoustic sensors. Autonomous flying wing gliders are equipped with multi-element sonar receiving antennas installed along the leading edge of the wing, as well as additional underwater acoustic sensors to quietly listen and determine the direction to the sources of sounds in the ocean. That is, these gliders are well suited for detecting, localizing and tracking individual animals that make sounds. ”
When tracking one glider of individual marine mammals, it is necessary for the animal to make sounds quite often, that is, a certain sequence of sounds that could be associated with it. Only then will the glider be able to determine the direction from which each cry is coming, and draw up the route of movement for the desired animal. “If, for example, propulsion systems with propellers generate sound continuously, then some species of marine mammals often do not make sounds so often that they can create a route. Other species congregate in tight groups and make sounds so often (for example, dolphin groups) that it’s almost impossible to track individuals in a group. ” Dispeyn noted that flying wing gliders may be the only platform with sufficient payload capable of carrying large antenna arrays on board. As an alternative, you can tow such an antenna, but there are additional difficulties. "Tracking the populations of marine mammals that emit screams can be implemented by a group of gliders distributed in space, in which each glider" listens "and determines the presence or absence of specific individuals of interest."
Automatic surface vehicles using wave energy, for example, Wave Glider, provide a longer service life, since they can recharge their batteries from solar batteries and, as it floats on the surface, they can stay connected constantly and receive updated coordinates from global navigation satellite Global Positioning System. Liquid Robotics calls its Wave Glider a “transformational technology that can help build a digital ocean,” implying that it is ideally suited to work as a communication gateway from the seabed to outer space, allowing submersible devices, including float gliders, equipped with acoustic modems, communicate anywhere in the oceans without the need for ascent. As noted in the company, “We are part of a larger system of systems connecting habitable and uninhabited platforms. This important infrastructure is needed to help open up the 95 percent of the ocean, which has not yet been studied, and help solve some of the world's most complex problems. ”
Wave Glider gliders, as reported by the company, passed more than 1,1 million nautical miles (2,1 million kilometers) into the sea. Despite the fact that these devices are already well established, the company is actively engaged in their improvement. This applies to power and energy, sensor kits and communications, durability and software, with particular emphasis on autonomy. The company Liquid Robotics argue that Wave Glider can remain at sea from several months to a year depending on the task to be performed. The limiting factors are fouling by marine organisms or shells of the apparatus itself and its sensors, the waves of the sea and the amount of available solar energy. These factors largely depend on the time of year in which the glider is deployed, its location and types of sensors. The rapid growth of seashells in the summer in the Gulf of Mexico, for example, affects the operation of sensors to such an extent that gliders need to be cleaned regularly. This problem is solved by the operators with the help of a special fluid, in which the gliders replacing them are washed; overgrown gliders go home for cleaning.
Anti-submarine warfare, whether situational awareness or long-term observation, consists mainly of sea tasks, which determines the installation of basic meteorological and acoustic sensors. Like other APA developers, Liquid Robotics and Boeing regularly participate in exercises and combat experiments, for example, in the UNMANNED WARRIOR experiment, which took place off the British coast in the fall of 2016, during which Wave Glider gliders demonstrated their capabilities in anti-submarine warfare — collecting and geospatial intelligence data distribution.
Under an agreement with CoMotion, the University of Washington Innovation Center, Kongsberg develops Seaglider, the Oculus glider for shallow water, and the Seaglider M-6 variant
These vehicles also took part in several exercises on the development of geospatial intelligence MASSMO (Marine Autonomous Systems in Support of Marine Observations), led by the British National Oceanographic Center. When performing MASSMO exercises, they collected what the company describes as valuable and consistent information about water temperature, currents and other phenomena in difficult sea conditions. "We also demonstrated how data from several Wave Glider can be integrated into third-party systems, for example, those offered by Boeing to simplify operational decisions."
Looking to the foreseeable future, in the Naval Meteorology and Oceanography Department of the US Navy expect that the main direction of development should be a further increase in the duration of the gliders and the expansion of the range of sensors. “The information collected is very useful for the fleet, these data help in building models of the ocean. Prospects for gliders in the fleet are obvious, - said his representative. “I believe that the most important direction will be simplification of work with gliders, their accessibility for non-specialists, which is important for increasing the number of gliders on the ocean expanses.” Float and wave autonomous devices represent a young technology with great potential for research. Technology, to which submariners in the future will be taken very seriously.