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Using the same method deployed for the University of Washington's Seaglider, the pressure-tight housing is depressurized so that the oil in the bladder fows into the reservoir when the two-way valve is open at the sea surface. This BE realizes high energy effciency of more than 40 percent at pressure higher than 30 megapascals. A rolling diaphragm is used for the oil reservoir. The volume of the oil reservoir is monitored using a linear potentiometer. The GCC moves and rotates built-in batteries and weights to change the pitching and the rolling angles. The controllable range of the statistical pitching and roll angles are, respectively, ±40 and ±45 degrees. The GCC can hold up to 49 lithium-sulfuryl chloride Electrochem (Clarence, New York) 3B0036 cells, which enables operation of more than one year. When approaching the seafoor, Tsukuyomi will measure the altitude with a built-in acoustic altimeter and adjust its pitching angle for a soft landing. When descending to the seafoor, the front of the vehicle pulls up slightly, allowing Tsukuyomi to land on the seafoor. JAMSTEC is now developing an acoustic altimeter with broad directivity. The glider is expected to move only slightly and stay at an essentially fxed point in deeper waters, because the velocity of ocean currents and tides there is commonly low. After sleeping for a specifed period, it will wake up and ascend to the sea surface operating the BE and the GCC. When foating at the surface, Tsukuyomi locates its position with GPS and communicates via Iridium. It will be able to change its observation scheme according to received commands and glide back to the designated waters if it drifts away. Tank and Sea Tests As described above, Tsukuyomi is expected to descend and ascend with a steep pitching angle. Stable gliding and turning performance are also required. To fulfll these requirements, the team produced a halfsized model and measured its hydrodynamic characteristics in the Ocean and Engineering Tank at Kyushu University's Research Institute for Applied Mechanics. Three main wings and two vertical tail wings were also produced and compared. The team also conducted computer simulations of their performance. A steep pitching angle can be realized by adopting large horizontal wings because the lift force acting on the horizontal wings generates a momentum that makes the pitching angle larger. These wings also secure the vertical stability. Two vertical wings attached at the end of the horizontal wing secure horizontal stability. The team conducted gliding tests in the ocean and in an engineering tank. Pitch, roll and yaw were measured using an attitude measurement unit, consisting of an AMU Light from Sumitomo Precision Products Co. Ltd. (Amagasaki, Japan) and an OS5000 from OceanServer Technology Inc. (Fall River, Massachusetts), mounted in Tsukuyomi. The data were recorded using a built-in Linux-based computer. The engineering tank was equipped with a 7-meter-long and 6-meter-wide electrically driven towing device. By manually controlling the velocity of the towing device to make it almost equal to that of Tsukuyomi, the team estimated Tsukuyomi's horizontal velocity. The maximum recorded horizontal velocity in the tests was 0.59 meters per second. Because of the limited tank depth, only gliding tests with OSIL Salinity Measurement – The complete solution for high quality salinity data • IAPSO Standard Seawater • High precision salinometers • Operator training courses • Salinometer service and repair • Worldwide distribution & support T: +44 (0)2392 488240 / E: osil@osil.co.uk / www.osil.co.uk www.sea-technology.com DECEMBER 2012 / st 19