日本財団 図書館


OCEAN SCIENCE AND TECHNOLOGY (OST)
Coordinator: Norman Estabrook (USA)
Co-Coordinator: Kenzo Takano (Japan)
 
OST-1A: Advanced Ships
COMPUTATIONAL ELECTROMAGNETICS PROOF OF FEASIBILITY FOR THE AMPLIFIED MAGNETOHYDRODYNAMIC DRIVE
Rodolfo E. Diaz
 
Arizona State University, Dept. of Electrical Engineering
Laboratory for Material Wave Interactions
Tempe, Arizona, USA
rudydiaz@asu.edu
 
High efficiency propulsion mechanisms not based on a water-screw are needed to maximize the speed of surface transports, undersea vehicles, and undersea missiles.
Magnetohydrodynamic (MHD) propulsion has the potential for meeting these needs. Its performance is not bounded by the cavitation limit of propellers and because it involves no moving engine components in contact with the water it does not contaminate the waterways with petroleum products. However, MHD has never seen large-scale deployment because the poor conductivity of seawater precludes the use of highly efficient AC induction pumping. Thus, the less efficient DC mode with cryogenically cooled superconductors has been the baseline until now.
 
A new version of MHD has been proposed that functions in the induction pumping mode. One of its key components is the magnetic field amplifier. In this paper we demonstrate by a computational simulation that the amplifier is capable of multiplying a source magnetic field by up to two orders of magnitude. By using the Finite Difference Time Domain (FDTD) solution of Maxwell's equations the performance of an amplified propulsor is studied. The amplification of the magnetic field as well as the Lorentz force distribution across the propulsor's aperture has been calculated for realistic material parameters. The relative performance in the presence of conventional seawater and in the presence of an induced water plasma are compared, showing that the plasma has a 104 advantage over seawater. The beneficial role of the thermal energy dissipation in this propulsor is emphasized.
 
OST-1A: Advanced Ships
ONBOARD WAVE MONITORING SYSTEM BY VIDEO IMAGE PROCESSING
Shigesuke Ishida1, Yoshifumi Takaishi1, Nobuo Kiriya1, Iwao Watanabe1, Tsuyoshi Miyazaki2, Kohichi Masuda3, Kohei Ohtsu4 and Kiyokazu Minami4
 
1National Maritime Research Institute, Maritime Safety Department Mitaka, Tokyo, JAPAN
ishida@nmri.go.jp
 
2Japan Marine Science and Technology Center Yokosnka, Kanagawa, JAPAN
 
3Nihon University, Funabashi Chiba, JAPAN
 
4Tokyo University of Mercantile Marine Koto-ku, Tokyo, JAPAN
 
Information of ocean waves is important not only for safe and economical operation of ships but also for ocean environment survey. Recently altimeters loaded on artificial satellites are measuring global wave information, but only of wave height. Observation from merchant ships is still useful because it gives wave height, period and direction. However the problem of accuracy and dispersion, caused by visual observation, should be overcome. In this background a monitoring system of ocean waves was developed, supported by the Program for Promoting Fundamental Transport Technology Research from the Corporation for Advanced Transport & Technology (CATT).
 
The major information of the onboard wave monitoring system is relative wave elevation in some positions along ship hull. The elevation is measured by processing video image taken by CCD cameras. The image processing is based on brightness in the analysis window, however, for removing the effect of flicker on sea surface, painting of the hull and so on, an ingenious algorithm is developed. For the measurement at night near infrared ray is used.
 
The relative wave elevation is converted to the absolute elevation in combination with vertical acceleration of the same location. And the wave field around the ship, i.e., wave height, period and direction, is estimated from the elevation of at least three points. The performance of the wave monitoring system was examined by experiments in laboratory and in real sea.
 
OST-1A: Advanced Ships
STUDY ON AUTOMATIC BERTHING SYSTEM FOR MINIMUM TIME CONTROL
Tadatsugi Okazaki1 and Kohei Ohtsu2
 
1National Maritime Research Institute Mitaka, Tokyo, JAPAN
okaza@nmri.go.jp
 
2Tokyo University of Mercantile Marine Koto-ku, Tokyo, JAPAN
 
Recently, minimum time berthing problems have been numerically solved, however, there are some problems to use the numerical solution for actual ship's berthing. First, it takes several hours to obtain a meaning optimal solution even by using a high-speed workstation. Secondly, it is difficult to obtain same result, if feed forward the numerical solution to ship's control, because of error of maneuvering model and disturbance on sea. Therefore, it is necessary to have some servomechanism.
 
This paper describes the development and application of tracking controller for automatic minimum time ship's berthing. In order to follow the result of minimum time berthing problem, waypoints are chosen from numerical solution appropriately. Then the controller guides a ship to berth point automatically in minimum time. Using a small training ship, actual sea tests are carried out validity of proposed controller.
 
OST-1A: Advanced Ships
THE KITE TOWING SYSTEM (ANTI-SYMMETRICAL TOWING SYSTEM)
Yutaka Terao1 and Takeo Nikko2
 
1Department of Marine Design and Engineering, School of Marine Science and Technology, Tokai University Shimizu, Shizuoka, JAPAN
Seagull1@scc.u-tokai.ac.jp
 
2Imabari Shipbuilding Co., Ltd.
 
It is well known that the fishtailing instability or whirling motion occurs when the ship is moored by single point mooring (SPM) system or towed with a single line. This motion causes not only an excessive snap tension of the mooring or towed line but also the problem of course stability of the towing ship. Whirling motion is mainly introduced by the instability of the SPM or single line towing system itself, and worsens due to the slack motion. Strong hawser which is one of devices, commonly used in the oil loading system and suppresses the whirling motion, shows how much penalty one must pay for the harmful slack motion.
 
We propose a new towing method, named Kite Towing System, which needs no additional special equipment. In mooring, no extra energy is needed. Well-designed and good tuned kites are stable in the high sky even in the wind. Kite Towing System is a simple method of towing a ship or floating structure by the principle of the kite stability, that is using the hydrodynamic forces, which are generated by the moored or towed hull, and suppressing the whirling motion itself. This paper shows the analysis of this basic principle and results of the self-running model test in a water tank and numerical results using the newly developed simulation program.
 
From this model and numerical examinations, the stability of the towed hull motion by the Kite Towing System is proved.







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