• Proceedings of the KSRS Conference
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• v.1
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• pp.364-367
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• 2006

Nonlinear internal waves (NLIWs) are usually generated by nonlinear process on linear internal waves (IW). Near HengChun Ridge that links Taiwan and Luzon Islands, we found that there are linear internal waves following NLIW and they travel westward at different speed, about 1.5 m/s for IW and 2.9 m/s for NLIW. This phenomenon was observed on site with ship radar and echo sounders, and later verified with thermistor chain. West of Luzon Strait, the separation of NLIW are 5 km or more, while linear internal waves are lines of wave crests at nearly equal distance that is only a few hundred meters apart. The current hypothesis is that most of the energy of internal tide forms a beam that propagates upward from the eastern shoulder of ocean ridge and later interacts with sea surface and thermocline. The interaction with thermocline generates linear internal wave that propagate along the pycnocline at about 1.5 m/s. The interaction with sea surface scatters internal wave energy downward, ensonifies the water column and generates large nonlinear waves that propagate westward at 2.9 m/s as mode 1 in a waveguide.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.2
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• pp.61-67
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• 2009

In this paper time series wave data which contain a freak wave is investigated. Various wave characteristics are compared between wave data with a freak wave and without. Among 24 hour wave data measured in the Yura Sea, two adjacent 30 min wave data with and without a freak wave are examined intensively. It is seen that the highest waves do not have the longest wave period. The wave period of the longest period waves is a little longer than the average wave period and much shorter than the significant wave period. Although the sea state is quite high, the Rayleigh distribution fits well to the probability of wave height. The characteristics of the wave spectra do not change much, but the nonlinearity increases for the wave data with a freak wave. The significant wave height without a freak wave is larger than that with a freak wave. Hence, the higher significant wave height does not always increase the probability of the occurrence of the freak waves.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.244-254
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• 2013

In this study, a method has been developed for estimating the change of nearshore random waves in response to sea-level rise, by extending the method proposed for regular waves by Townend in 1994. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height for random waves are presented as functions of relative change in water depth. The changes in wavelength and refraction coefficient are calculated by using the significant wave period and principal wave direction in the regular-wave formulas. On the other hand, the changes in shoaling coefficient and wave height are calculated by using the formulas proposed for shoaling and transformation of random waves in the nearshore area including surf zone. The results are proposed in the form of both formulas and graphs. In particular, the relative change in wave height is compared with the result for regular waves.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.15 no.2
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• pp.62-67
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• 2010

Swells occurred on the coast of the East Sea on February 24, 2008 caused a loss of three lives and also damaged several west coasts of Japan. The recent increase of swell intensity with number of accidents demands more accurate forecasting of swells in terms of time and location. The swells occurred in February 2008 are hindcasted using SWAN model to examine the accuracy of the model for future forecasting. The model results are compared with ReWW3 data as well as measurement wave data and specially, wave spectrum is analysed by comparing with observed spectrum at two wave stations located in the east coast of Korea. The SWAN model shows similar results with observation data in terms of significant wave heights and swell arrival time but the shapes of wave spectrum are different between model and in-situ measurement data. For further improvement of swell forecasting, more comparison and analysis with observed wave spectrum is necessary and wave directional spectrum data are required to study on the characteristics of swells in the East Sea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.335-343
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• 2019

Overtopping discharge for sea dike having low mound and high wave wall (LMHW sea dike) is investigated with hydraulic experiments in this study. Vertical, Flare and Bullnose type wave walls are selected and Tetrapods (double layer) and Accropode (one layer) are adopted for armour layers of the front slope. The results of the hydraulic experiments are compared to the overtopping formulas for armoured rubble slopes and vertical sea dikes suggested by EurOtop Manual. Predicted overtopping discharges are underestimated as the roughness efficiency factors (γ_f) of armour blocks suggested by EurOtop are adopted when the overtopping formula for armoured rubble slopes sea dike is used. Meanwhile the predicted overtopping discharges agree well with the hydraulic experiments when the modified roughness efficiency factors redefined by multiplying efficiency factor of the heights of armoured crest berm and wave wall (γ_AR) are adopted. Return wall effects on a vertical wall (Kortenhaus et al., 2003; Pearson et al., 2004a) and the effects on a smooth dike slope (Van Doorslaer et al., 2015) in EurOtop Manual are investigated for Flare and Bullnose type wave walls. As a results of the comparison between experimental results and 2 formulas, return wall effect on a smooth dike was more valid for LMHW sea dike.

• Journal of the Korean earth science society
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• v.44 no.4
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• pp.264-274
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• 2023

The Korea Strait comprises a continental shelf in a shallow sea that experienced glacio-eustastic sea-level changes during the Quaternary period. A long core of 76.6 m in length was acquired at the South Sea Drilling Project site (SSDP-101; 34°19.666'E and 128°16.335'N) with a 60 m water deep. The uppermost massive sand beds were interpreted as sandy sediments of the nearshore marine sand ridge in the shallow sea during the transgression of sea level, whereas the lower parts of alternating sandy and muddy beds were interpreted as deposits in marsh, estuary, and tidal flat environments. A three-layered geoacoustic model was reconstructed for the sedimentary succession in the high-resolution seismic profile based on a 140-grain size and sediment type of core SSDP-101. For the actual underwater simulation and experiments, the in-situ P-wave speeds were calculated using the sound speed ratio of the Hamilton method.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.175-180
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• 2006

This study is carried out the investigation of nonlinear characteristics of the ocean based on the field wave observation data acquired the western sea area in Jeju island during one year. It is aimed to offer the fundamental data for Freak wave forecasting in real sea. For this, the nonlinearity parameters of ocean waves, which are Skewness, Atiltness, Kurtosis and Spectrum band width parameter, are introduced, and the parameters are compared and discussed with some characteristic wave components, ie, significant wave height, maximum wave height, and so on.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.6
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• pp.800-809
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• 2014

The gridded environmental data is usually provided by the numerical simulation coupled with a data assimilation technique and various inter- or extrapolation algorithms, both of which are based on the observation spanning from simple equipments to satellites. But it is difficult to represent the natural phenomenon such as sea mount, internal-wave, warm eddy in modeling or observation because of increase in the complexity of model. This paper introduces the algorithm artificially representing the natural phenomenon and the techniques applying it to the gridded volume data and smoothing for natural effects. Moreover, the inserted results are analyzed by use of graphical tool. The results can be used for the battle simulation or acoustic model.

• Journal of Ocean Engineering and Technology
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• v.7 no.1
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• pp.56-61
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• 1993

Standard values in graphic porms are presented for the ratio of added wave resistance to the sun of added wave and wind resistances in head sea for three ship types, tanker, container ship and passenger ship. The effect of ship length on the ratio defined above is investigated for the three ship types. Obique sea added resistance is determined using wave direction reduction factor. The factor is obtained from model test results and cubic spline interpolation technique.

• Journal of Ocean Engineering and Technology
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• v.16 no.2
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• pp.27-31
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• 2002

The purpose of this study is to investigate the variation of resonance that is possible caused by construction of new port in a practical sea area between the existing port and the new one. The research of amplification that of the sea area was accomplished for the variation of resonance. In this study, long period wave that is observed continuously in the practical sea area was analyzed, and then secondary undulation was reproduced by numerical analysis. As a result of numerical analysis, the first mode resonant periods in the existing port is 640sec, and in the new one is 500sec. On the other hand, we know there is long period wave of 500sec from analyzation of field datas. Because that period this period is the resonant period in the new port. There is also the possibility of secondary undulation cause of resonant.