• Journal of Ocean Engineering and Technology
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• v.33 no.3
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• pp.252-258
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• 2019

In this paper, the time history of the surface elevation measured at the Draupner platform in the North Sea in 1995 is used to examine the statistical characteristics of the wave data. The wave statistics for 48 surface measurements, which contain three freak wave occurrences, are summarized. The quartiles, boxplots, correlations, and pair plots of 15 variables, along with the abnormality index, are presented. The kurtosis and skewness of the surface elevation are two variables that are highly correlated with the abnormality index, which defines freak waves. Principal coordinate analysis showed that the direction of the changes in the abnormality index agreed with the changes in the kurtosis and skewness. In addition, various wave heights, except the maximum wave height, showed a similar direction for the height changes, and various wave periods showed a similar direction for the period changes. Based on the correlations and PCA analysis, the kurtosis and skewness of the surface profiles are the two most important variables to predict the abnormality index.

• Journal of Coastal Disaster Prevention
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• v.4 no.4
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• pp.189-196
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• 2017

Ocean Research Stations (ORSs) is the ocean platform type observation towers and measured oceanic, atmospheric and environmental data. These station located on the offshore area far from the coast, so they can produce the data without land effect. This study focused to improve the wave data quality of ORS station. The wave observations at ORSs are used by the C-band (5.8 GHz, 5.17 cm) MIROS Wave and Current Radar (MWR). MWR is convenient to maintenance and produce reliability wave data under bad weather conditions. MWR measured significant wave height, peak wave period, peak wave direction and 2D wave spectrum, so it's can provide wave information for researchers and engineers. In order to improve the reliability of MWR wave data, Datawell Waverider Buoy was installed near the one ORS (Socheoncho station) during 7 months and validate the wave data of MWR. This study found that the wave radar tend to be overestimate the low wave height under wind condition. Firstly, this study carried out the wave Quality Control (QC) using wind data, however the quality of wave data was limited. So, this study applied the four filters (Correlation Check, Direction Filter, Reduce White Noise and Phillips Check) of MWR operating software and find that the filters effectively improve the wave data quality. After applying 3 effective filters in combination, the RMSE of significant wave height decreased from 0.81m to 0.23m, by 0.58m and Correlation increased from 0.66 to 0.96, by 0.32, so the reliability of MWR significant wave height was significantly improved.

• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.2
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• pp.112-120
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• 2010

In this paper time series wave data measured continuously for 24 hours during a storm in Yura Sea Area are used to investigate statistical characteristics of nonlinear waves. The exceedance probability of wave height is compared using the Rayleigh distribution and the Edgeworth-Rayleigh (ER) distribution. Wave data which show stationary state for 10 hours contain 4600 waves approximately. The Gram-Chalier distribution fits the probability of wave elevation better than the Gaussian distribution. The Rayleigh ($H_{rms}$) distribution follows the exceedance probability of wave height in general and predicts the probability of freak waves well. The ER distribution overpredicts the exceedance probability of wave heights and the occurrence of freak waves. If wave data measured for 30 minute period which contains 250 waves are used, the ER distribution can predict the occurrence probability of freak waves well. But it overpredicts the probability of overall wave height If no freak wave occurs, the Rayleigh ($H_{rms}$) distribution agrees well with wave height distribution for the most of wave height ranges. The wave height distribution of freak waves of which height are less than 10 m shows similar tendency compared with freak waves greater than 10 m. The value of $H_{max}/H_{1/3}$ is related to the kurtosis of wave elevation. It seems that there exists threshold value of the kurtosis for the occurrence of freak waves.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.3
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• pp.137-145
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• 2004

Long-term wave distribution at Jeju sea is investigated by a numerical simulation based on the thirdgeneration wave model SWAN (Simulating WAves Nearshore). The Jeju sea which retains relatively high wave energy density among Korean coastal regions is considered to be a suitable site for wave power generation and the efficiency of wave power generation is closely related to local wave characteristics. The monthly mean of a large-scale long-term wave data from 1979 to 2002, which is provided by Korea Ocean Research & Development Institute. is used as the boundary condition of SWAN model simulation with 1km grid. An analysis of wave distribution concentrates on the seasonal variation and spatial distribution of significant wave heights, mean wave directions and mean wave periods. Significant wave heights are higher in winter and summer and the west sea of Jeju appears relatively higher than east's. The highest significant wave height occurs at the northeast sea in winter and the second highest significant wave height appears at the southeast sea in summer, while the significant wave heights in spring and autumn are relatively low but homogeneous. The distribution of wave directions reveals that except the rear region influenced by wave refraction, the northwest wave direction is dominant in summer and the southeast in winter. Wave periods are longer in summer and winter and the west sea of Jeju appears relatively longer than east's. The longest wave period occurs at the west sea in winter, and in summer it appears relatively homogeneous with a little longer period at the south sea.

• 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 the Korean Society of Industry Convergence
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• v.24 no.6_2
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• pp.841-848
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• 2021

This study investigated the acceleration characteristics of rock slopes when earthquakes, which have not been studied much in Korea, occur. The rock slope was modeled with a similar raw of 1/20 in consideration of the height(10m), roughness, strength, and the joint dips(20°). After the completion of the model, a shaking table tests was conducted according to the magnitude of the acceleration and the type of seismic wave. The maximum acceleration was greater in the short-period seismic wave than in the long-period seismic wave, and the maximum acceleration was larger in the small acceleration. The rock slope was close to a rigid block and a structure more vulnerable to the long period wave than to the short period wave. In the event of an earthquake smaller than the domestic earthquake-resistant maximum design acceleration(0.154g), safety management of the rock slope was required.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.2
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• pp.73-87
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• 2019

Ocean waves are the driving force for the sediment transport and the beach process. However, wave actions are nonlinear and non-stationary, and the response of the beach is inconsistent in terms of reaction rate and magnitude. Therefore, the beach process is difficult to predict accurately. The purpose of this study is to identify the correlations between the shoreline change and ocean waves observed in the east coast of Korea. The relation of the beach width obtained from video monitoring at five sandy beaches and the wave data obtained from nearby wave monitoring at three points was analyzed. Although the correlations estimated over the whole data sets was not significant, the correlations estimated based on the seasonal period or wave conditions provided more noteworthy information. When the non-exceedance probability of the wave height was greater than 0.99, the wave period and beach width showed strong negative correlations. In case the non-exceedance probability of the wave period was greater than 0.99, the wave height and beach width showed strong negative correlations as well. Furthermore, the erosion rate of the beach width increased when the primary wave direction was close to normal to the coastline. Little significant seasonal or monthly change was found between the beach width and the wave, but it was greatly affected by intensive events such as typhoons. Thus, it is necessary to analyze in detail the wave height or period level explaining the change of beach width for more relevant and practical information.

• Journal of Korea Water Resources Association
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• v.37 no.6
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• pp.461-466
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• 2004

This study presents a combined experimental and numerical effort to investigate wave breaking of sinusoidal waves in a surf zone. Numerical predictions are verified by comparing to laboratory measurements. The model solves the Reynolds equations and$textsc{k}$-$\varepsilon$ models for the turbulence analysis. To track the free surface displacement, the volume of fluid method is employed. As the height of incident wave increases, the wave breaking occurs at a closer point of the slope in the numerical model and laboratory experiments with the same depth and period. When a wave breaking occurs, the ratio of wave height becomes larger, with the same wave height and depth, as the period increases.

• Journal of Ocean Engineering and Technology
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• v.34 no.1
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• pp.26-36
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• 2020

An extreme value analysis of metocean data which include wave, wind, and current data is a prerequisite for the operation and survival of offshore structures. The purpose of this study was to provide information about the return wave, wind, and current values for the Barents Sea using extreme value analysis. Hindcast datasets of the Global Reanalysis of Ocean Waves 2012 (GROW2012) for a waves, winds and currents were obtained from the Oceanweather Inc. The Gumbel distribution, 2 and 3 parameters Weibull distributions and log-normal distribution were used for the extreme value analysis. The least square method was used to estimate the parameters for the extreme value distribution. The return values, including the significant wave height, spectral peak wave period, wind speed and current speed at surface, were calculated and it will be utilized to design offshore structures to be operated in the Barents Sea.

• Journal of Ocean Engineering and Technology
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• v.37 no.3
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• pp.89-98
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• 2023

Analyzing the interactions of free surface waves caused by a submerged-body movement is important as a fundamental study of submerged-body motion. In this study, a two-dimensional mini-towing tank was used to tow an underwater body for analyzing the generation and propagation characteristics of free surface waves. The magnitude of the maximum wave height generated by the underwater body motion increased with the body velocity at shallow submerged depths but did not increase further when the generated wave steepness corresponded to a breaking wave condition. Long-period waves were generated in the forward direction as the body moved initially, and then short-period waves were measured when the body moved at a constant velocity. In numerical simulations based on potential flow, the fluid pressure changes caused by the submerged-body motion were implemented, and the maximum wave height was accurately predicted; however, the complex physical phenomena caused by fluid viscosity and wave breaking in the downstream direction were difficult to implement. This research provides a fundamental understanding of the changes in the free surface caused by a moving underwater body.