• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.57-63
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• 2002

This paper describes a control algorithm for the buffer of a deep-sea mining system, in which the buffer is connected to a long slender pipe and then to a surface ship on one end, and to a collector on sea floor through a flexible hose on the other end. A mathematical modeling is established for designing the controller for buffer thrusters, in which the dynamic response of the long pipe is taken into account based on the mode superposition method. The fluid loading acting on the pipe is estimated by using Morison's formula. For simplicity, the surface ship is assumed to be kept stationary, the reaction from the flexible hose is ignored and only the lateral motions are considered. In order to guide the buffer to react only to the low-frequency motion of the surface vessel, the FIR digital filter is introduced to a PID-based controller It can be shown numerically that the high frequency component of the ship's motion can be effectively filtered out by using the FIR low pass filter.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.1
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• pp.34-44
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• 1998

Analysis of gravity, magnetic, and seismic reflection data from the Ulleung Basin, East Sea has provided some insights into the opening mechanism and crustal type of the basin. Free-air gravity anomaly data show positive anomalies of about 40~60 mgal near the Korea Plateau and Oki Bank and of about -20~20 mgal in the central basin. Bouguer gravity anomaly data exhibit NE-SW trending positive anomalies of about 150 mgal in the central basin which is interpreted to be related to high-density crustal material. Abrupt changes in both Free-air and Bouguer gravity anomaly profiles across the basin margins may be due to transition between continental and oceanic crusts. Magnetic anomalies in the basin are generally less than -400 nT. No stripe pattern is evident in the magnetic anomaly map but a NW-SE trending symmetric pattern is seen in some magnetic profiles. The symmetric pattern is probably associated with the high-density crustal material in the central basin suggested by Bouguer gravity anomaly. The acoustic basement in the deep part of the basin has only a small amount of local relief. No graben or half-graben structures are seen in the acoustic basement from which mechanical extension might be inferred. The lack of high-relief structures in the acoustic basement may suggest that the basin is underlain by oceanic crust or that the basement is overlain by thick volcanic layer which obscures the structures and relief of the basement. High-density crust in the central basin inferred from gravity data, abrupt changes in gravity anomalies across the basin margins, symmetric pattern seen in some magnetic anomaly profiles, and lack of relief in the acoustic basement may suggest sea-floor spreading origin of the Ulleung Basin.