Other vehicles

WaveGlider

Another vehicle that will soon come to market is Liquid Robotics' entirely new autonomous ocean vehicle "WaveGlider" that harvests all of its energy from waves and sun. The concept is a shallow water vehicle that uses the ocean waves as its primary energy source to propel it through the water. During the spring and summer of 2008 the WaveGlider underwent extended periods of field testing in the Pacific Ocean.

The design consists of a surface float (similar to a surfboard) that is tethered to a sub-surface glider about 7 meters below the surface. This subsurface glider looks similar to the Slocum glider (i.e., a torpedo hull with a simple rudder), except instead of one pair of wings there are six sets of wings down the vehicle's side. The wings have a mechanism that "ratchet" in such a way that when a wave at the surface lifts the float, the entire system (float and glider) rises while the wings stay horizontal. As the wave passes by, the glider sinks and the wings pivot to create a downward pitch which causes the glider to fly forward and slide downward at an angle. Because the float and glider are tethered together the glider will stop at the end of the line's reach causing the surface float to move forward. Consequently, the whole system moves forward in a "saw-tooth" pattern corresponding to the waves. The surface-float shoots forward in small bursts across the water controlled by the rudder. The vehicle requires at least seven (7) meters of water and a minimum wave height to operate. It has high-endurance, is able to station-keep and the method of movement allows it to move in any direction regardless of wave direction. The vehicle does not "surf" the wave, consequently, it can traverse up a wave. All it needs is the up and down motion that translates into forward motion of the vehicle. The vehicle moves quite slowly3 and high currents are a problem.

The WaveGlider's surface float houses most of the electronics (i.e., navigation and communication equipment) along with solar cells to recharge the electronic battery packs. Only wave motion is used for propulsion. The vehicle is quite remarkable and Harbor Branch Oceanographic Institute is expected to develop a mobile observatory, in other words, a distributed sensor network for surface sensing using these vehicles. Additionally, they are hoping to demonstrate the swarming technologies that the engineering division at Harbor Branch has been working on with these vehicles (Frey, 2008). ALBAC

One of the first gliders, the ALBAC conducted sea trials at the Suruga Bay of Japan in 1992. The vehicle, developed at the University of Tokyo in the lab of Tamaki Ura, does not have an active buoyancy control system, but a simple drop weight system with only one glide cycle.

The "ALBAC has fixed wings and a vertical and horizontal tail. It is 1.4 m long," 120 cm in wide, "weighs 45 kg, and can dive to depths of 300 m at speeds of one to two knots (.5 to 1.0 m/s). It has horizontal tail fins which change angle at inflection from downwards to upwards gliding, a feature not present in other gliders. The wings and tail are larger in comparison to the body than on Slocum, Spray or Seaglider. ALBAC moves a battery pack internally to control pitch and yaw in the same manner as Seaglider. Because it has no ballast pump, ALBAC carries batteries to power only its instruments and actuators.

ALBAC carries flight sensors including compass, depth, pitch, roll, and a propeller-type velocity meter. Note, that Slocum, Spray and Seaglider do not carry velocity meters in order to conserve power and because of the difficulty of accurately sensing velocity at glider operating speeds" (Graver, 2005). The vehicle glides horizontally by up to 20 degrees down from the horizontal plane and controls its trajectory by changing pitch angle and roll angle by displacing the center of gravity. To accomplish this, an internal actuator system changes the location of the center of gravity longitudinally and laterally by moving a weight. The vehicle has no external communication ability. It has a 3-liter dry pay load space for scientific measurement devices. It consists of a 1/2 ellipse shaped front cap, a cylindrical pressure hull, a corn shape tail cap

3 No technical data of this vehicle has been released at printing.

with a vertical stabilizing fin, a pair of wings, tail wings and various electronic devices, i.e., a depth sensor, a gravity sensor, a magnetic sensor, two CPUs, interface boards and two actuators to trim and roll. A ranging sensor, a velocity sensor, a drop ballast system, a tail angle trigger and a transponder are fitted in the front and the tail caps (Kawaguchi et al., 1993).

Fig. 12. ALBAC Glider (Kawaguchi et al., 1993)

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