• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.4
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• pp.342-354
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• 2008

Some statistical characteristics of deepwater waves along the Korean coast have been investigated using various sources of wave measurement and hindcasting data. For very large waves comparable to design waves, it is recommended to use the average value of the empirical formulas proposed by Shore Protection Manual in 1977 and by Goda in 2003 for the relation between significant wave height and period. The standard deviation of significant wave periods non-dimensionalized with respect to the mean value for a certain significant wave height varies between 0.04 and 0.21 with a typical value of 0.1 depending upon different regions and different ranges of significant wave heights. The mean and standard deviation of the principal deepwater wave direction are presented at the 106 coastal grid points along the Korean coast. For relatively large waves, the probability density function of the directional spreading parameter $s_{max}$ is expressed as a lognormal distribution. The most suitable frequency spectrum in the Korean coast is the TMA spectrum. The probability density function of the peak enhancement factor $\gamma$ is also expressed as a lognormal distribution, with its mean value of 2.94, which is close to the value in the North Sea.

• Journal of Ocean Engineering and Technology
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• v.21 no.6
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• pp.34-41
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• 2007

The present study investigates numerically damping characteristics of irregular waves passing over a permeable seabeds. At first, the numerical model, which is able to consider the flow through a porous medium with inertial, laminar and turbulent resistance terms and determine the eddy viscosity with LES turbulent model, is validated by comparing with existing experimental data. And then, the numerical test on irregular wave damping over a permeable seabeds is performed in case that wave and flume conditions are changed. It is revealed from the numerical results that the more porosity and mean grain are increased, the more wave damping is increased. Also, the effect of wave period on damping of irregular waves over a permeable seabed is discussed.

• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.100-105
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• 2013

This paper presents a sea surface reconstruction method that uses measured radar images by applying filtering techniques and identifying wave characteristics of the surrounding the Ieodo ocean research station using WaveFinder (X-band wave measurement radar), which is installed in the station. In addition, the results obtained from real radar images are used to verify the reconstructed sea surface. WaveFinder is a marine system that was developed to measure wave information in real time. The WaveFinder installed in the station could acquire sequent images for the sea surface at constant time intervals to obtain real time information (Wave height, mean wave period, wave directionality, etc.) for the wave by getting a three-dimensional spectrum by applying an FFT algorithm to the acquired sequent images and wave dispersion relation. In particular, we found the wave height using the SNR (Signal to noise ratio) of the acquired images. The wave information measured by WaveFinder could be verified by comparing and analyzing the results measured using the wave measurement instrument (Sea level monitor) in the station. Additionally, the wave field around the station could be reconstructed through the three-dimensional spectrum and the inverse FFT filtering from the analyzed results for the measured radar images. We verified the applicability of the sea surface reconstruction method by comparing the measured and simulated sea surfaces.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.562-571
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• 2006

Mean shear wave velocity of the upper 30m $(V_s30)$ used as the current site classification criterion for determining seismic design ground motions in Korea was established based on the typical depth of site investigations in western US, in which the depth to bedrock is much deeper than that in Korea. In this study, to establish appropriate site classification system for site conditions of Korea, site investigations including in-situ seismic tests to determine shear wave velocity $(V_s)$ were carried out at total 72 sites in Korean peninsula. The mean $V_s's$ to the depths of 5m, 10m, 15m, 20m and 25m together with the $V_s30$ at the testing sites were determined, and the correlation between the mean $V_s$ to a depth shallower than 30m and the $V_s30$ was drawn and suggested for the efficient seismic site classification in Korea. The proposed correlation could be utilized for the seismic design in case of the $V_s$ profiles shallower than 30 m in depth. The correlation in this study, nevertheless, requires further modification by means of the accumulation of various site data in Korea.

• Journal of Navigation and Port Research
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• v.28 no.5
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• pp.353-358
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• 2004

A transient irregular wave was designed based on ISSC spectrum The designed wave was generated in the towing tank and ,the roll motion of a model was measured A method to predict the maximum roll motion, expected in the short-term sea state, was investigated with comparison of the theoretical and experimental results.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.1
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• pp.34-39
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• 2013

In this study, the quantitative analysis and pattern analysis of the error bounds with respect to recording period were carried out using the wave climate data from coastal areas. Arbitrary recording periods were randomly sampled from one month to six years using the bootstrap method. Based on the analysis, for recording periods less than one year, it was found that the error bounds decreased rapidly as the recording period increased. Meanwhile, the error bounds were found to decrease more slowly for recording periods longer than one year. Assuming the absolute estimate error to be around 10% (${\pm}0.1m$) for an one meter significant wave height condition, the minimum recording period for reaching the estimate error for Sokcho and Geoje-Hongdo stations satisfied this condition with over two years of data, while Anmado station was found to satisfy this condition when using observational data of over three years. The confidence intervals of the significant wave height clearly show an increasing pattern when the percentile value of the wave height increases. Whereas, the confidence intervals of the mean wave period are nearly constant, at around 0.5 seconds except for the tail regions, i.e., 2.5- and 97.5-percentile values. The error bounds for 97.5-percentile values of the wave height necessary for harbor tranquility analysis were found to be 0.75 m, 0.5 m, and 1.2 m in Sokcho, Geoje-Hongdo, and Anmado, respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.2
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• pp.96-102
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• 2016

In order to establish the basic data for the active use of the LED light source in the aquaculture industry, the experiment about the behavior of rockfish (Sebastes inermis) corresponding to the LED light was conducted by image analysis. LED lights for the experiment were one red light (wave length: 622 nm; light power: 811 mW) and two green lights (wave length: 518 nm; light power: 648 mW, wave length: 518 nm; light power: 810 mW). Behavior of the rockfish was analyzed using a moving distance (MD5) for 5 minutes where MD5s during the period of feeding were 20.0 m, 19.6 m, 16.3 m and 20.5 m in the ch1, ch2, ch3 and ch4. At the sunrise, mean MD5 of the entire channel about right before and right after were 6.3 m and 8.2 m. At the sunrise, mean MD5s of the entire channel about right before and right after were 13.6 m and 12.0 m. In the ch1, ch2 and ch3, mean MD5s during the period of 24 hours were 13.2 m, 9.6 m and 6.8 m at experiment 1and 5.2 m, 3.8 m and 2.9 m in the experiment 2.

• Journal of Ocean Engineering and Technology
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• v.37 no.6
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• pp.225-237
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• 2023

In this study, numerical simulations for a single fixed truncated circular cylinder in regular waves were conducted to investigate the nonlinear wave run-up under various dampers and wave period conditions. The present study used the volume of fluid (VOF) technique to capture the air-water interface. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation with the k- 𝜖 turbulence model was solved using the commercial computational fluid dynamics (CFD) software STAR-CCM+. First, a systematic spatial convergence study was conducted to assess the performance and precision of the present numerical wave tank. The numerical scheme was validated by comparing the numerical results of wave run-up on a bare truncated cylinder with the experimental results, and a good agreement was achieved. Then, a series of parametric studies were carried out to examine the wave run-up time series around the truncated cylinder with single and dual dampers in terms of the first- and second-order harmonic and mean set-up components. Additionally, the local wave field and the flow velocity vectors adjacent to the cylinder were evaluated. It was confirmed that under short wave conditions, the high position of the damper led to a noticeable increase in the wave run-ups with significant changes in the first- and second-order harmonic components.

• Journal of Ocean Engineering and Technology
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• v.33 no.6
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• pp.526-534
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• 2019

The average coastline and the erosion control line introduced as the management coastline, and the average shoreline (MSL) was established from the observed coastline. Also, the median grain size and the wave height of 30-years return period were applied. The erosion control line (ECL) was established through the model, HaeSaBeeN. These two lines set the coastline for evaluation. Based on the observed monitoring data along the coastline, the 1-day variation according to the normal distribution was used to estimate the regional variation, and the width of the erosion was calculated by applying the median grain size (D₅₀) and the wave height of 30-years return period through the high-wave coastal erosion width model, i.e., HaeSaBeeN.

• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.327-338
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• 2007

We estimate the momentum fluxes of short-period gravity waves which are observed in the OI 557.7 nm nightglow emission with all-sky camera at Mt. Bohyun ($36.2^{\circ}\;N,\;128.9^{\circ}\;E$) in Korea. The intrinsic phase speed ($C_{int}$), the intrinsic period (${\tau}_{int}$), and vertical wavelength (${\lambda}_z$) are also deduced from the horizontal wavelength (${\lambda}_h$), observed period (${\tau}_{ob}$), propagation direction (${\phi}_{ob}$), observe phase speed (${\upsilon}_{ob}$) of the gravity wave on the all-sky images. The neutral winds to deduce intrinsic wave parameters are measured with Fabry-Perot interferometer on Shigaraki ($34.8^{\circ}\;N,\;13.1^{\circ}\;E$) in Japan. We selected 5-nights of observations during the period between July 2002 and December 2006 considering of the weather and instrument conditions in two observation sites. The mean values of intrinsic parameter of gravity waves are $({\tau}_{int})\;=\;12.9\;{\pm}\;6.1\;m/s,\;({\lambda}_z)\;=\;12.9\;{\pm}\;6.5,\;and\;(C_{int})\;=\;40.6\;{\pm}\;11.6\;min$. The mean value of calculated momentum fluxes for four nights besides of ${\lambda}_z\;<\;6\;km$ is $12.0\;{\pm}\;15.2\;m^2/s^2$. It is needed the long-term coherent observation to obtain typical values of momentum fluxes of the mesospheric gravity waves using all-sky camera and the neutral wind measurements.