• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.263-269
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• 2018

Changes in water depth caused by underwater earthquakes and landslides cause sea surface undulations, which in turn propagate to the coast and result in significant damage as wave heights normally increase due to the wave shoaling process. Various types of numerical models have been developed to simulate the generation and propagation of tsunami waves. Most of tsunami models determine the initial surface of the water based on the assumption that the movement of the seabed is immediately and identically transmitted to the sea surface. However, this approach does not take into account the characteristics of underwater earthquakes that occur with time history and spatial variation. Thus, such an incomplete description on the initial generation of tsunami waves is totally reflected in the error during the simulation. In this study, the analytical solution proposed by Hammack (1973) was applied in the tsunami model in order to simulate the generation of initial water surface elevation by the change of water depth with time history and its propagation. The developed solution is expected to identify the relationship among various type of seabed motions, initial surface undulations, and wave speeds of elevated water surfaces.

• Geophysics and Geophysical Exploration
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• v.14 no.3
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• pp.254-260
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• 2011

We studied magnitude determination method using high-frequency energy radiation duration to calculate rapidly magnitude of large earthquakes that occurred around Japan. Fourteen earthquakes were analyzed using Korea Meteorological Administration (KMA) data. We calculated duration of high-frequency energy radiation with 2~4 Hz band pass filter at each data and estimated magnitude. As a result, duration becomes longer as magnitude becomes larger and the magnitude estimated using regional earthquake data are similar to that using teleseismic data. Therefore when an earthquake occurs around Japan we will be able to estimate the magnitude in a relatively short time using KMA data and it may be possible to determine if the earthquake is large enough to produce tsunami.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.1
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• pp.38-49
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• 2015

Past study of tsunami heavily relied on the numerical modelling using 2D Boussinesq Eq. and Solitary wave. Lately, based on the fact that numerically simulated run up heights based on solitary wave are somewhat smaller than the measured one, Leading Depression N (LDN) Wave has been elaborated, which can account the advancement of a shore line before tsunami strikes a shore. Thereafter it is reported that more accurate simulation can be possible once LDN is deployed. On the other hand, there were numerous reports indicating that stable LDN wave can't be sustained in the hydraulic model test. These conflicts between the hydraulic model tests and numerical results have their roots on the assumption made in the derivation of Boussinesq type wave model such as that wave nonlinearity is equally balanced with wave dispersiveness. Hence, in the numerical simulation based on the Boussinesq type wave model, wave dispersiveness is inevitably underestimated, especially in deep water. Based on this rationale, we developed the modified methodology for the generation of stable LDN wave in the 3D numerical wave flume, and proceeded to numerically analyze the depression effect of Hybrid Breaker on the run up height due to tsunami using the Navier Stoke Equation. The verification of newly proposed wave model in this study was carried out using the run up height from the hydraulic model test. It was shown that Hybrid Breaker consisting of three water chamber and slope at its front can reduce 13% of run up height for H = 5m, and 10% of run up height for H = 6m.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.31-31
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• 2016

국내 해안선을 따라 발생되는 침식 및 퇴적현상으로 인하여 해안구조물의 안정성과 같은 안전 문제가 발생되고 있다. 이러한 자연현상을 대비하여 연안지역 특성에 맞는 침식 저감 대책 마련에 대한 연구가 되고 있다. 침식현상은 다양한 외력조건과 지리적 특성을 함께 고려해야 한다. 고립파로 인한 침식 발생 현상에 대한 국외 연구들이 다수 수행되어 왔으며, 국내에는 이와 관련된 연구가 상대적으로 부족하다. 고립파는 파고의 특성에 따라 파형이 결정되는 특징을 가지고 있어, 침식현상과 지진해일의 실험적 연구에 있어 입사파로 주로 활용되고 있다. 기존의 방법과 동일하게 sluice gate를 순간적으로 개방하여 고립파를 재현하는 방식으로 파랑을 재현하였다. 본 연구에서는 폭 0.80 m, 높이 0.75 m, 수로연장 12.00 m의 강화유리로 설계된 직사각형 단면 수로에서 실험을 수행하였다. 측면에 두 대의 카메라(Model No. : Sony, HDR-XR550)를 고정설치하여 경사면 하상변화를 촬영하였고, 영상분석을 통하여 하상변동을 측정하였다. 유사특성에 따른 하상변동을 연구하기 위하여 경사면에 포설된 유사로는 주문진 표준사($d_{50}=0.6268mm$, $c_u=1.68$)와 안트라사이트($d_{50}=1.547mm$, $c_u=1.387$)를 동일한 실험조건에서 함께 사용하였다. 경사면에서 고립파의 처오름, 처내림을 추적하여 그 경향을 분석하였다. 하상의 침식 및 퇴적구간 길이, 침식, 퇴적의 높이 및 깊이와 같은 형상분석을 통한 영향인자를 함께 무차원화 하여 실험결과를 제시하였다. 본 연구의 결과를 바탕으로 Sluice gate를 이용한 고립파 수리실험으로 경사면 하상의 침식 및 퇴적 현상에 관한 기초적인 실험자료로 활용될 것이다.