• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.6
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• pp.275-286
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• 2021

In this study, the analytical solution for diffraction near a vertical detached breakwater was suggested by superposing the solutions of diffraction near a semi-infinite breakwater suggested previously using linear wave theory. The solutions of wave forces acting on front, lee and composed wave forces on both side were also derived. Relative wave amplitude changed periodically in space owing to the interactions between diffracting waves and standing waves on front side and the interactions between diffracting waves from both tips of a detached breakwater on lee side. The wave forces on a vertical detached breakwater were investigated with monochromatic, uni-directional random and multi-directional random waves. The maximum composed wave force considering the forces on front and lee side reached maximum 1.6 times of wave forces which doesn't consider diffraction. This value is larger than the maximum composed wave force of semi-infinite breakwater considering diffraction, 1.34 times, which was suggested by Jung et al. (2021). The maximum composed wave forces were calculated in the order of monochromatic, uni-directional random and multi-directional random waves in terms of intensity. It was also found that the maximum wave force of obliquely incident waves was sometimes larger than that of normally incident waves. It can be known that the considerations of diffraction, the composed wave force on both front and lee side and incident wave angle are important from this study.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.1
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• pp.28-33
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• 2013

Multidirectional random waves that obliquely approach the shore were found to become directionally asymmetric due to refraction. The directional asymmetry was expressed in terms of the asymmetry parameter which is related to the maximum spreading parameter ($s_{max}$). In this study, we calculate variation of both the asymmetry and maximum spreading parameters at different water depths for various cases of incident wave angles and maximum spreading parameters in deep water. These values are different from Goda and Suzuki (1975) who neglected directional asymmetry of waves. In calculating directional asymmetry and maximum spreading parameters, we use the JONSWAP spectrum (Hasselmann et al., 1973) and Lee et al.'s (2010) directional distribution function. The processes and results are nondimensionalized with significant wave height, peak frequency and peak wave length in deep water.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1997.10a
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• pp.53-57
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• 1997

해양파는 해양구조물에 작용하는 주된 외력이고, 쇄파와 물질의 확산등 해양의 역학적 현상을 유발하며, 표사와 누유의 이동등 물질유동의 원인이 된다. 이러한 이유 때문에 정확한 해양파의 역학적 특성 및 재현기법에 대한 연구가 활발히 이루어져 왔다. Longet-Hggins(1975)와 Barber(1963)가 파의 방향분산성을 나타내는 방향스텍트럼 해석법을 제안한 이래 Mtsuyasu(1970)는 실해역 측정을 통해 Mitsuyasu형 방향분포함수 및 주파수 스펙트럼을 얻는 등 많은 심해역 파랑의 해석기법에 대한 연구가 꾸준히 진행되고 있다. (중략)

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.5
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• pp.429-438
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• 2008

The present study is to predict the multidiretional random wave height at the front face and concave corner of a refracted breakwater which is not straight. The numerical simulation on wave height at the front face of an insular breakwater is performed by using the boundary element method, and obtained results have been compared with those of exact- and analytical solutions of the eigenfunction presented by Goda et al. (1971) and the other existing numerical solution. Also, the results of wave-height distribution due to the refracted breakwater have been validated through comparisons with previous results of analytical solution. Based on the validation through these comparisons, several wave-height distributions at the interested region have been illustrated for various conditions related with concave corner angles and the wave incidence, and then the prediction of wave height are simulated at the front face and concave corner of a refracted breakwater under construction currently. Excellent agreements have been obtained in all cases, and this study can effectively be utilized for predicting random waves for various breakwater system.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.2
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• pp.90-103
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• 1997

A numerical procedure is described for predicting the motion and structural responses of the very large floating offshore structures supported by multiple 3-D floating bodies of arbitrary shape in multi-directional irregular waves. The developed numerical approach taking into account of the hydrodynamic interactions among the multiple floating bodies is based on a combination of the 3-D source distribution method, the wave interaction theory, the finite element method and the spectral analysis method to get the significant values of the dynamic responses in the multi-directional irregular waves. The effects of wave interactions and directionality on the dynamic responses of a very large offshore structure, which is semisubmersible ring type, are numerically examined.

• Journal of Ocean Engineering and Technology
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• v.8 no.1
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• pp.23-32
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• 1994

A numerical procedure is described for simultaneously predicting the motion and structural responses of tension leg platforms (TLPs) in multi-directional irregular waves. The developed numerical approach is based on a combination of a three dimensional source distribution method, the finite element method for structurally treating the space frame elements and a spectral analysis technique of directional waves. The spectral description for the linear responses of a structure in the frequency domain is sufficient to completely define the responses. This is because both the wave inputs and the responses are stationary Gaussian ran dom process of which the statistical properties in the amplitude domain are well known. The hydrodynamic interactions among TLP members, such as columns and pontoons, are included in the motion and structural analysis. The effect of wave directionality has been pointed out on the first order motion, tether forces and structural responses of a TLP in multi-directional irregular waves.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.2
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• pp.153-159
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• 2012

This study gives the vertical motion analysis in multi-directional irregular waves using a commercial code(MAXSURF v.16) based on linear strip theory for a training ship. To verify the commercial code prior to the analysis, we guarantees the reliability of this paper's results using the commercial code by comparing with the results(Flokstra, 1974) of same hull and experimental conditions on a Panamax container. The analysis conditions are Beaufort wind scale No. 5($\bar{T}=5.46$, $H_{1/3}=2m$) based on ITTC wave spectrum, encounter angle Head & bow seas($150^{\circ}$) and Froude number Fn=0.257. Finally, we calculates heave RAO, pitch RAO and obtains the result of ship's response spectra for heave and pitch motions. In the motion response spectrum under the multi-directional irregular waves, heave motion reacts slightly high in short-crested waves and pitch motion reacts high in long-crested waves.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.705-712
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• 2001

It is of great importance to represent the directional ocean waves in a laboratory basin for hydraulic model tests. The directional ocean waves can be expressed as a linear superposition of a large number of component waves with different frequencies and propagating directions. The aim of the study is to check the wave generating characteristics by serpent-type wave generating system in PKNU (Pukyong National University) which is composed of 10 piston-type wave generators. In the experiment, spatial variation of irregular wave heights and propagating angles are measured in the multi-directional wave maker basin. Target wave directional spectrum is reproduced in the area of multi-directional wave maker basin. The directional spreading of the generated waves varied spacially in the basin. They differed from target spectrum as the measurement point becomes far from the center line normal to the generator face, The effective generation area where that target can be reproduced is limited to the triangular area attached the generator face. According to the results, it is emphasized that the effective experiment area in the basin considered wave generator characteristics should be determined in consideration of experimental conditions including structural shapes, water depth, wave directionality etc.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.2
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• pp.121-127
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• 2017

The actual wave is multi-direction irregular wave. In the case of a long structure, a reduction effect of the wave occurs. In this study, in order to grasp the extent to which these influences contribute to the failure probability and compare the existing modular breakwaters to the stability, we used existing modular breakwaters and long caisson breakwaters using wave force reduction parameter to analysis the reliability. As a result, the reliability index of the long caisson breakwater was higher than that of the existing modular caisson breakwater, and it was confirmed that the significant wave height of the design variables had the highest influence. In addition, the reliability analysis was performed according to the change of the mean value of the variables used in the calculation of the wave force reduction parameter. It is confirmed that the relationship between each variable value and the wave force reduction parameter appears in the analysis results.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.4
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• pp.276-284
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• 2011

The rip current occurred at Haeundae beach was numerically investigated under directional random wave environment. The numerical simulation was performed using a fully nonlinear Boussinesq equation model, FUNWAVE which is capable of simulating nearshore circulation since it includes the effect of wave-induced momentum flux and horizontal turbulent mixing. The results of numerical simulation show the time-dependent evolution of the wave-induced nearshore circulation system (including rip current) that are caused by nonlinear transformation of directional irregular waves due to unique topography of Haeundae. From the results, it was found that rip current is well generated and developed where relatively lower wave height and relatively deeper water depth along the longshore direction, and sudden and strong events of rip current were observed.