• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.202-207
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• 2001

The added resistance of a ship advancing in waves can be split into the resistance due to the radiation wave and the resistance due to the diffraction wave. In this study, the former has been calculated by a method based on Maruo's formula. The latter must be calculated by other methods. Ship motion is calculated by the usual strip method. The amplitude of two dimensional far-field waves is calculated using the improved Green integral equation. The present numerical method can be used for the estimation of the added resistance due to the radiation wave since the present numerical result is much smaller than other existing numerical results considered to be overestimated.

• Journal of Ocean Engineering and Technology
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• v.16 no.3
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• pp.8-18
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• 2002

Formulation of the far-field method for the prediction of time-mean hydrodynamic force and moment acting on a 3-D surface-piercing body in waves is reviewed. It is found that the inequality between the weight of the floating body and its buoyancy force permits the replacement of the fluid particles inside the control surface by the fluid particles outside the control surface. Under such circumstances, momentum exchanges across the control surface make the time-mean value of the time rate of the momentum of the fluid inside the control surface non-vanishing. It is a second-order quantity which is hard to calculate by the far-field method. The drift forces and moments on half-immersed ellipsoids are calculated by both the far-field method and the near-field method. The discrepancy between two numerical results is presented and discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.4
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• pp.216-230
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• 1999

A Galerkin finite element model for the analysis of harbor oscillation has been developed based on the extended mild-slope equation. Infinite elements are used to accomodate the radiation condition at infinity and joint elements to treat the matching conditions at the harbor entrance which include the energy loss due to flow separation. The numerical tests for rectangular harbors with fully or partially open entrances show that the energy loss at the harbor entrance considerably reduces the the amplification ratios at the innermost parts of the harbors and that the amplification ratios decrease considerably with increasing incident wave heights and jet lengths at the harbor entrance. Application of the model to the Gamcheon harbor show that when the incident wave amplitude is small the amplification ratios rather increase when the entrance energy loss is included than when ignored because of the shift of the resonance periods. Even though the entrance energy loss was insignificant for the measured long-period incident waves, it would be of great importance if the incident waves were large as in the attack of tsunamis. The resonance period of the Helmholtz mode at the Gamcheon Harbor was calculated to be 31 minutes, which agrees well with the measured one between 27 and 33.3 minutes. The measured resonance periods between 9.4 and 12.1 minutes and 5.2 and 6.2 minutes were also calculated by the numerical model as 10.4 minutes and 6.6 or 5.6 minutes, indicating good performance of the model. On the other hand, it was shown that a variety of oscillation modes exists in the Gamcheon Harbor and lateral resonances of considerable amplification ratios also exist at the periods of 3.6 and 1.6 minutes as in the Young-II Bay.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.114-131
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• 1992

In the present work, a two-dimensional boundary-value problem for a large amplitude motion is treated as an initial-value problem by satisfying the exact body-boundary and nonlinear free-surface boundary conditions. The present nonlinear numerical scheme is similar to that described by Vinje and Brevig(1981) who utilized the Cauchy's theorem and assumed the periodicity in the horizontal coordinate. In the present thesis, however, the periodicity in the horizontal coordinate is not assumed. Thus the present method can treat more realistic problems, which allow radiating waves to infinities. In the present method of solution, the original infinite fluid domain, is divided into two subdomains ; ie the inner and outer subdomains which are a local nonlinear subdomain and the truncated infinite linear subdomain, respectively. By imposing an appropriate matching condition, the computation is carried out only in the inner domain which includes the body. Here we adopt the nonlinear scheme of Vinje & Brevig only in the inner domain and respresent the solution in the truncated infinite subdomains by distributing the time-dependent Green function on the matching boundaries. The matching condition is that the velocity potential and stream function are required to be continuous across the matching boundary. In the computations we used, if necessary, a regriding algorithm on the free surface which could give converged stable solutions successfully even for the breaking waves. In harmonic oscillation problem, each harmonic component and time-mean force are obtained by the Fourier transform of the computed forces in the time domain. The numerical calculations are made for the following problems. $\cdot$ Forced harmonic large-amplitude oscillation(${\omega}{\neq}0,\;U=0$) $\cdot$ Translation with a uniform speed(${\omega}=0,\;U{\neq}0$) The computed results are compared with available experimental data and other analytical results.