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홍사영(Sa Y. Hong),이판묵(Pan M. Lee),김용철(Yong C. Kim),홍도천(Do C. Hong) 한국해양공학회 1988 韓國海洋工學會誌 Vol.2 No.1
This paper presents the results of motion tests of a moored semi-submersible platform in regular waves. To investigate the effects of mooring system on the motion characteristics, the tests were performed under the various mooring conditions in regular head and beam waves. Two types of mooring system were employed: one is composed of soft springs and the other is of chains. In the case of chains the pretensions were varied to investigate the dynamic effects of mooring forces as well as the motion responses of the semi-submersible.<br/> The motion responses and mooring tensions were measured and analyzed by the double amplitude method. The measured motion responses were also compared with the results of calculation from three-dimensional potential theory. Finally, the dynamic behaviors of mooring chains were studied.
김용철(Yong C. Kim),이판묵(Pan M. Lee),홍사영(Sa Y. Hong) 한국해양공학회 1988 韓國海洋工學會誌 Vol.2 No.1
The experimental investigations on the motion characteristics of a marine riser both in air and water were performed. The static deflections and natural frequencies of the riser in air including the effect of static offset, were obtained from the experiment. These results were compared with those of theoretical prediction by using a simple asymptotic formula. In order to investigate the nonlinear motion characteristics of the riser subject to nonlinear viscous drag and large displacement, the forced oscillation tests both in air and water were performed. In the forced oscillation tests in air, it was found that the transverse motion due to geometrical nonlinearity grows when the amplitude of in-line oscillation exceeds a certain critical value, say, order of 1-2 diameters. The planar motions of the riser in water due to vortex shedding and the geometrical nonlinearity were described. Some of these results were also compared with those of theoretical analysis, which uses a numerical perturbation technique based on the derived linear asymptotic solutions, and found to be generally in good agreement.
이판묵(Pan M. Lee),이상무(Sang M. Lee),홍사영(Sa Y. Hong) 한국해양공학회 1988 韓國海洋工學會誌 Vol.2 No.2
A dynamically positioned vessel must be capable of maintaining a specified position and direction by controlling the thruster devices. The motions of a vessel are often assumed to the sum of low frequency(LF) motions and high frequency(HF) motions. The former is mainly due to wind, current and second order wave forces, while the latter is mainly due to first order wave forces. In order to avoid the high frequency thruster modulation, the control system must include filters to estimate the low frequency motions from the measured motion signals. This paper presents a control system based on Kalman filtering technique and optimal control theory. Using the combined Kalman filter, LF motion estimates and HF ones are achieved from the motion measurement of the vessel. The estimated low frequency motions are used as inputs to the dynamic positioning system. The thruster modulation is minimized using the optimal control theory; Linear Quadratic Gaussian(LQG) controller. The performances of the Kalman filter and the dynamic positioned vessel are investigated by computer simulation.