• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.1
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• pp.79-90
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• 2009

This paper presents the development of dynamically combined Typhoon generated surge-tide-wave numerical model which is applicable from deep to shallow water. The dynamically coupled model consists of hydrodynamic module and wind wave module. The hydrodynamic module is modified from POM and wind wave module is modified from WAM to be applicable from deep to shallow water. Hydrodynamic module computes tidal currents, sea surface elevations and storm surges and provide these information to wind wave module. Wind wave mudule computes wind waves and provides computed information such as radiation stress, sea surface roughness and shear stress due to winds. The newly developed model was applied to compute the surge, tide and wave fields by typhoon Maemi. Verification of model performance was made by comparison of measured waves and tide data with simulated results.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.51-60
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• 2010

In this study, the performance evaluation of a conventional wave resonator at the entrance of a port or a pier against secondary undulation has been performed using 2D hydrodynamic modeling within port. A wave resonator has been designed for the attenuation of the secondary undulation induced by the long-periodic waves. The controlled performance of the wave resonator has been numerically investigated for CGWAVE MODULE of finite-element model of SMS (Surface water Modeling System) based on the elliptic mild-slope wave equation. SMS was verified though the comparisons with analytical solution performed by Ippen and Goda (1963). Also, It was confirmed that a wave resonator of a rectangular model harbor is effective enough to control the secondary undulation when it compares variation of water level with the case of no resonance system. From the above results, amplification phenomenon induced by long-period waves transferred from 1900 sec to 2100 sec when it applied a wave resonator in Busan Gamcheon Port which is a deep-sea. And it was confirmed that a wave resonator of Pohang New Port attenuates largely long-period waves which are within the range of 300 sec induced by long-period motion of the moored ship.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.50 no.3
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• pp.233-243
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• 2014

The difference of mooring tension by type of buoy was investigated in the circulating water channel and the wave tank for deducting the most stable buoy from the current and the wave condition. 5 types of buoy made up of short cylinder laid vertically (CL-V), short cylinder laid horizontally (CL-H), capsule (CS), sphere (SP) and long cylinder (CL-L) were used for experiments. A mooring line and a weight were connected with each buoy. A tensile gauge was installed between a mooring line and a weight. All buoy's mooring tension was measured at the same time for the wave test with periods of 1.5~3.0 sec and wave heights of 0.1~0.3 m, and the current test with flow speeds of 0.2~1.0 m/sec. As a result, the order of tension value in the wave test was CL-H > CL-V > SP > CS > CL-L. In the current test CL-V and CL-H were recorded in the largest tension value, whereas SP has the smallest tension value. So it seems that SP buoy is the most effective in the location affected by fast current. CS is predicted to be suitable for a location that influence of wave is important more than that of current if practical use in the field is considered. And it was found that the difference of mooring tension among buoys in wave is related to the product of the cross sectional area and the drag coefficient for the buoy's bottom side in high wave height. The factor for the current condition was not found. But it was supposed to be related to complex factors like a dimension and a shape by buoy's posture to flow.

• Journal of Ocean Engineering and Technology
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• v.27 no.1
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• pp.102-108
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• 2013

In this paper time series wave data, which were measured at the Draupner platform in the North Sea on 1995, are used to investigate statistical characteristics of nonlinear wave. Various statistical properties based on time and frequency domain are examined. The Gram-Chalier distribution fits the probability of wave elevation better than the Gaussian distribution. The skewness of wave profile is 0.393 and the kurtosis is 4.037 when the freak wave is occurred. The nonlinearity of D1520 data is higher than two adjacent wave data. AI index of the New Year Wave is 2.11 and the wave height is 25.6m. The zero crossing wave period of the New Year Wave is 12.5s which is compared to the average zero up-crossing period 11.3s. The significant steepness of wave data is 0.077 when the freak wave was occurred. H1/3/${\eta}_s$ does not increases as the kurtosis increases and the values is close to 4. The New Year Wave belongs to highly nonlinear wave data packet but the AI index is within linear focusing range.

• Ocean and Polar Research
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• v.30 no.4
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• pp.453-466
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• 2008

In order to examine the generation mechanism of long ocean waves along the west coast of Korea and to understand the amplification process of the long ocean waves, sea level, atmospheric pressure and wind data observed every minute from 2007 March 29 to 2007 April 1 were analyzed and onedimensional numerical ocean model experiments were performed. An atmospheric pressure jump propagated southeastward from Backryungdo to Yeonggwang along the west coast of Korea with speed of $13{\sim}27\;m/s$ between 2007 March 30 23:00 and 2007 April 1 1:30. Average magnitude of pressure jump was 4.2 hPa. As a moving atmospheric jump propagated from north to south along the coast, long ocean waves were generated and the sea level abnormally rose or fell at Anheung, Kunsan, Wido and Yeonggwang. Average amplitude of sea level rise (or fall) was about 113.6 cm. In a one-dimensional numerical ocean model, nonlinear shallow water equations were numerically integrated and a moving atmospheric pressure jump with traveling speed of 24 m/s was used as an external force. While the atmospheric pressure jump travels over 60 m depth ocean, a long ocean wave is generated. Because the propagation speed of the atmospheric jump is almost equal to that of the long ocean wave, Proudman resonance occurs and the long ocean wave amplifies. As the atmospheric pressure jump moves into the coastal area shallower than 60 m, the speed of the long ocean wave decreases and Proudman resonance effect decreases. However, the amplitude of the long ocean wave increases and wave length becomes shorter because of shoaling effect. When the long ocean wave hits the land boundary, amplitude of the long ocean wave drastically amplifies due to reflection. Data analysis and numerical experiments suggest that the southeastward propagation of an atmospheric pressure jump over the shallow ocean, which is a necessary condition for Proudaman resonance, generated the long ocean waves along the west coast of Korea on 2007 March 31 and the ocean waves amplified due to shoaling effect in the coastal area and reflection at the shore.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.25-32
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• 2017

We present a 3D SH-wave velocity model of the crust and uppermost mantle and seismic radial anisotropy beneath East Asia. The SH-wave velocity structure model was built using Love-wave group-velocity dispersion data from earthquake data recorded at broadband seismic networks of Korea, Japan, and China. Love-wave group-velocity dispersion curves were obtained by using the multiple filtering technique in the period range of 3 to 150 s for 3,369 event-station pairs. The inverted model using these data sets provides a crust and upper mantle SH-wave velocity structure down to 100 km depth. At 10 ~ 40 km depths SH-wave velocity beneath the East Sea is higher than beneath the Japanese island region. We estimated the Moho beneath the East Sea to be between 10 ~ 20 km depth, while Moho beneath the Korean Peninsula at around 35 km based on the depth where high-velocity anomalies are detected. We estimated the lithosphere-asthenosphere boundary beneath the East Sea to be at around 50 km based on the depth where strong low-velocity anomalies are observed. Widespread low-velocity anomalies are found between 50 ~ 100 km depth in the study region. Positive radial anisotropy ($V_{SV}$ > $V _{SH}$) is observed down to 35 km depth, while negative radial anisotropy ($V_{SV}$ > $V _{SH}$) is observed for deeper depth.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.2
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• pp.109-119
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• 2012

Long-term wave observation was carried out near Busan New Port and the major wave characteristics were analyzed. At Busan New Port, waves from south direction were predominant throughout the year, while waves from the west, developed at the north sea of Geoje island, appeared almost the same frequency in winter season, showing apparent seasonal variation. During the observation period, the significant wave height was mostly less than 1 m, but it reached its maximum of 8.0 m when typhoon Maemi passed on September 2003. Also, the seasonal variation was hardly observed except July. In contrast, seasonal variation was apparent for the significant wave period, whose peak ranges 4~5 s in summer whereas about 3 s in winter. The largest significant wave period was 15.56 s, observed on June 2003. Meanwhile, the annual variation was negligible for mean wave direction as well as significant wave height and period. Further analysis of the wave data acquired for 5 years at 4.5 km south, in the south sea of Daejuk island, confirmed high correlation between the two observation points in summer and vice versa in winter.

• Korean Journal of Remote Sensing
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• v.34 no.2_2
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• pp.419-429
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• 2018

An unmanned autonomous maritime surface system can move the vehicle to the areas for observing the ocean accidents, disasters, and severe weather conditions. Detection and monitoring technologies have been developed by the converging of the regional and local surveillance system. Wave Glider, one of the autonomous maritime surface systems, is ocean-wave propelled autonomous surface vehicle and controlled using Iridium satellite communication. In this study, we carried out two-time Wave Glider observations for 2016 and 2017 summer in the East China Sea that the area was influenced by low-salinity water. We observed the sea surface warming effect due to the low-salinity water using the regional (satellite) and local (Wave Glider) surveillance system. We also monitored the effect of the typhoon and understood the change of the ocean-atmosphere environments in real-time. New unmanned surface system with autonomous system and high endurance structure can measure comprehensively and usefully a long observation in complicated ocean environments because of connecting with other surveillance systems.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.3
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• pp.101-109
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• 2021

Wave observations using a marine X-band radar are conducted by analyzing the backscattered radar signal from sea surfaces. Wave parameters are extracted using Modulation Transfer Function obtained from 3D wave number and frequency spectra which are calculated by 3D FFT of time series of sea surface images (42 images per minute). The accuracy of estimation of the significant wave height is, therefore, critically dependent on the quality of radar images. Wave observations during Typhoon Maysak and Haishen in the summer of 2020 show large errors in the estimation of the significant wave heights. It is because of the deteriorated radar images due to raindrops falling on the sea surface. This paper presents the algorithm developed to increase the accuracy of wave heights estimation from radar images by adopting convolution neural network(CNN) which automatically classify radar images into rain and non-rain cases. Then, an algorithm for deriving the Hs is proposed by creating different ANN models and selectively applying them according to the rain or non-rain cases. The developed algorithm applied to heavy rain cases during typhoons and showed critically improved results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.168-177
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• 2020

Many coastal engineering designs utilize empirical formulas containing the Equivalent Deep-water Wave Height (EDWH), which is normally given a priori. However, no studies have explicitly discussed a method for determining the EDWH and the resulting design wave heights (DEWH) under irregular wave conditions. Unfortunately, it has been the case in many design practices that the EDWH is incorrectly estimated by dividing the Shallow-water Wave Height (SWH) at the structural position with its corresponding shoaling coefficient of regular wave. The present study reexamines the relationship between the Shallow-water Wave Height (SWH) at the structural position and its corresponding EDWH. Then, a new procedure is proposed to facilitate the correct estimation of EDWH. In this procedure, the EDWH and DEWH are determined differently according to the wave propagation model used to estimate the SWH. For this, Goda's original method for nonlinear irregular wave deformation is extended to produce values for linear shoaling. Finally, exemplary calculations are performed to assess the possible errors caused by a misuse of the wave height calculation procedure. The relative errors with respect to the correct values could exceed 20%, potentially leading to a significant under-design of coastal or harbor structures in some cases.