• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.60-65
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• 1992

The roll response of a ship to random beam seas is investigated in terms of the threshold crossing process. The non-white excitation process is modeled as an equivalent white-noise one based on the assumption that the upcrossing properties of the response can be approximately replaced by the excitation with a white noise process with a suitable intensity. Then the non-linear damping is reinstated. The reinstated equation of motion with the equivalent white-noise intensity is solved using the equivalent non-linear method to get the desired probability density function. The proposed scheme is tested extensively with varing coefficients.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.6
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• pp.805-814
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• 1999

In this paper, elliptic function bandpass filters using ceramic coaxial resonators are designed. Since elliptic function filters have better performance of frequency selectivity than those based on Butterworth or Chebyshev, therefore it is possible to make better use of limited frequency resources. Elliptic function bandpass filters using ceramic coaxial resonators are designed for reducing it's size, weight, cost and for easy manufacturing and tuning. From measurements, an accurate resonator model is obtained and the coupling coefficient values are extracted. Based on these results, elliptic function bandpass filters are designed. The experimental results have shown that the 8th order elliptic function filter of 959 MHz center frequency with 28 MHz bandwidth using coaxial ceramic resonators have about more tan 17 dB return loss, 5 dB insertion loss, more than 20 dB attenuation at $f_c\pm$5 MHz.

• Journal of Ocean Engineering and Technology
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• v.11 no.1
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• pp.65-73
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• 1997

The floating body discussed in this study is a 2-D rectangular floating unit supported by four vertical piles at its corners. Structures of this type are frequently seen as floating piers for the crafts in a small harbour. The movement in some modes of motion of such a flating body is fully or partially restrincted by the piles. The authors(Kim et al. 1994) carried out a series of model tests on its wave control function, its motion and the loads on piles. The experimental results showed that a certain degree of intial constriction force which clamps the floating unit in the horizontal direction can effectively reduce the body motion and wave energy without increasing mooring forces. This may be due to the friction forces occuring between the piles and the rollers installed in the mooring equipments on the floating unit. In this paper, we develop a numerical model for the prediction of wave transformation and floating body motions, where the friction force is idealized as the Coulomb friction and linearized into a damping force using the equivalent damping cofficient. This linearization is verified by comparing the results of motions between the linear and nonlinear analysis of the ezuations of motion. We further compare the caculation results by the linear model with the experimental results and discuss the effect of the friction force or the constriction force on body motions and wave energy dissipation.