• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2013.10a
• /
• pp.609-611
• /
• 2013

There's little to obstacles obstructing communication in the sky. There are nearly fixed obstacles obstructing communication on the ground. But communication disruption can be occur frequently and unexpectedly on the sea surface. Especially, it is difficult for a small station which can be greatly affected by waves and low antenna height to secure the LOS for radio communication. In this paper, LOS and minimum antenna height is calculated due to changing wave height and Tx/Rx antenna height on the sea surface.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.4
• /
• pp.252-261
• /
• 2020

Numerical simulations of the storm surge and waves induced by the Typhoon Kong-Rey incident on the south coast of Korea in 2018 are conducted using the JMA-MSM weather field provided by the Japan Meteorological Agency, and the calculated surge heights are compared with the time history observed at harbours along the south-east coast. For the waves occurring coincidentally with the storm surges the calculated significant wave heights are compared with the data measured using the wave buoys operated by the KHOA (Korea Hydrographic and Oceanographic Agency) and the KMA (Korea Meteorological Administration), and the data observed at AWAC stations of the KIOST (Korea Institute of Ocean Science and Technology). Additional simulations are also performed based on the pressure and wind fields obtained using the best track information provided by the JTWC (Joint Typhoon Warning Center) of the United States, and the results are compared and analyzed. Based on the results of this study it is found that the reliable weather fields are essential for the accurate simulation of storm surges and waves.

• Bulletin of the Korean Space Science Society
• /
• 2010.04a
• /
• pp.37.5-38
• /
• 2010

경희대학교 우주탐사학과에서는 우주공간 탐사를 위해 Trio(TRiplet Ionospheric Observatory)-CINEMA(Cubesat for Ions, Neutrals, Electrons and MAgnetic fields)로 명명된 초소형 위성을 개발하고 있다. 과학임무는 지구 저궤도에서 고에너지 입자를 관측하는 것이며, 이를 위해 고에너지 (2~300keV) 입자 검출기와 자기장 측정기가 탑재된다. 저에너지 입자 검출기 시스템인 STEIN(SupraThermal Electrons, Ions, Neutrals)은 $1\times4$ Array의 개선된 실리콘 검출기와 이온, 전자, 중성입자를 분리할 수 있는 정전장 편향기, 그리고 신호를 처리하는 전자회로로 구성되어있다. 설계된 전자회로는 매우 작은 검출기 기판, 아날로그 기판과 디지털 기판으로 이루어져 있고, 475mW 이하의 저 전력으로 동작한다. 또한 2~100keV의 에너지를 1keV이하의 해상도로 30,000event/sec/pixel 까지 관측 할 수 있도록 회로를 설계하였다. 센서로 들어온 입자로 인해 발생한 펄스의 신호는 4개의 아날로그 회로가 담당하게 되는데, Folded cascode amplifier를 배치하여 증폭률을 높인 Charge sensitive amplifier를 통해 신호를 증폭하고, $2{\mu}s$ unipolar gaussian shaping amplifier를 통해 읽기 쉽게 처리된 신호를 상한파고선별기와 하한파고 선별기를 통해 유효 값 여부를 판단하고, 피크 검출기를 통해 피크의 타이밍을 측정한 뒤 신호를 아날로그-디지털 변환 회로를 통하여 8bit의 값으로 나타내어, 입자들의 Spectrum을 측정하게 된다. 크기와 소비전력이 적음에도 검출성능이 우수하기 때문에 이 시스템은 향후 우주탐사 시스템에 있어 매우 중요한 역할을 수행 할 것으로 생각한다.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.6
• /
• pp.465-480
• /
• 2020

Numerical simulations of the storm surge and the wave induced by the Typhoon Sanba incident on the south coast of Korea in 2012 are conducted using the JMA-MSM forecast weather field, NCEP-CFSR reanalysis weather field, ECMWF-ERA5 reanalysis weather field, and the pressure and wind fields obtained using the best track information provided by JTWC. The calculated surge heights are compared with the time history observed at harbors along the coasts of Korea. For the waves the calculated significant wave heights are compared with the data measured using the wave buoys and the underwater pressure type wave gauge. As a result the JMA-MSM and the NCEP-CFSR weather fields give the highest reliability. The ECMWF-ERA5 gives in general surge and wave heights weaker than the measured. The ECMWF-ERA5, however, reproduces the best convergence belt formed in front of the typhoon. The weather field obtained using JTWC best track information gives the worst agreement.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.14 no.2
• /
• pp.138-145
• /
• 2011

In this paper time series wave data are simulated by the Monte Calo method using random numbers to generate random phases of the wave signal. The simulated wave signasl are used to study the characteristics of freak waves. Various sea states are represented by combinations of the significant wave height $H_s$ defined in the spectrum method and the significant wave steepness $S_s$. For a fixed value of $S_s$, the probability of the occurrence of the freak wave is decreased as $H_s$ increases. For a fixed value of $H_s$ the probability of the occurrence of the freak wave increases as $S_s$ increases. The average value of the maximum wave height increase as $S_s$ increases, but the average height of freak wave remains the same and the value approaches two times of $H_s$. For the fixed value of $S_s$, average kurtosis of wave elevation increases as $H_s$ increases, but for a fixed $H_s$, the average kurtosis decreases as $S_s$ increases. The average of abnormality index(AI) is around 2.11 irregardless of $H_s$ and $S_s$. The maximum value of AI lies between 2.5 - 3.0. Therefore it is conjectured that AI maximum due to linear focusing is 3.0.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.27 no.5
• /
• pp.281-294
• /
• 2015

In order to quantitatively estimate the nonlinear destructive interaction of wave load with wind load, which is very vital for the optimal design of offshore wind energy converter, we carried out a hydraulic model test and wind tunnel test. As a substructure of offshore wind energy converter, we would deploy the monopile, which is popular due to its easiness in construction. Based on the simulation using Monte Carlo simulation using Kaimal spectrum and cross spectrum, the instantaneous maximum wind velocity is adjusted to 10 m/s. And, considering the wave conditions of the Western Sea where a pilot wind farm is planned to be constructed, $H_s=0.1m$, 0.15 m, 0.2 m is carefully chosen. It turns out that the nonlinear destructive interaction between the wind and wave loads acting on the offshore wind energy converter is more clearly visible at rough seas rather than at mild seas, which strongly support our deduction that a Large eddy, a swirling vortex developed near the bumpy water surface in the opposite direction of the wind, is the driving mechanism underlying nonlinear destructive interaction between the wind and wave loads.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.33 no.4
• /
• pp.139-147
• /
• 2021

In this study, waves were defined using the water surface elevation data observed from the HeMOSU-1 and 2 marine meteorological observation towers installed on the west coast of Korea, and correlation analysis was performed between wave parameters. The wave height and wave period were determined using the wave-train analysis method and the wave spectrum analysis method, and the relationship between the wave parameters was calculated and compared with the previous study. In the relation between representative wave heights, most of the correlation coefficients between waves showed a difference of less than 0.1% in error rate compared to the previous study, and the maximum wave height showed a difference of up to 29%. In addition, as a result of the correlation analysis between the wave periods, the peak period was estimated to be abnormally large at rates of 2.5% and 1.3% in HeMOSU-1&2, respectively, due to the effect of the bimodal spectrum that occurs when the spectral energy density is small.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.7 no.3
• /
• pp.95-99
• /
• 2002

3.5KHz subbottom profiling systems are useful for delineating of shallow (up to 10~100m below the sea bottom) geological structure. These systems are generally used to image geological structures with less than 1m of vertical resolution. However swell in the sea is quite often higher than 1m, causing degradation in the quality of the 3.5KHz subbottom profiles. In this paper, we show the quality of digitally recorded data can be enhanced by the suppression of swell effect. Prior to suppression of swell effect, sea bottom detection procedure was applied using the characteristics that the amplitude of sea bottom reflection is high. To suppress the swell effect, we applied moving average method and high-cut filtering method using the extracted water depth of adjacent traces. Acceptable results were obtained from both methods. In the case of bad quality data or shallow data interfered with direct wave, the suppression of swell effect is difficult due to incorrect sea bottom detection.

• The Journal of Korean Institute of Information Technology
• /
• v.16 no.12
• /
• pp.41-47
• /
• 2018

The buoy-enabled underwater surveillance system is a device that is installed in a particular sea area and operated for a certain period of tine and moved to another sea area after recovery. In this paper, a mooring method which is applied for a buoy-enabled underwater surveillance system was selected to maintain installation and enure stable operation. Also, the structure of the mooring line was designed. Two-point mooring method was selected considering interference with the communication cable of array-assembly. The composite structure of buoy chain, nylon rope, and anchor chain is designed as the basic component of mooring line. For the verification of design, a numerical simulation and wave tank experiment were performed. Their results were confirmed similarity in test condition. Finally, the mooring lines were designed for the environment of the sea trial location. The mooring line produced by the final design confirmed the stability above the significant wave height considered in the design on the sea trial.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.35 no.5
• /
• pp.95-101
• /
• 2023

Recent persistent coastal developments have expanded recreational areas and enhanced accessibility. However, this growth has also led to a rise in safety incidents. These accident factors can be divided into human-made and natural types. The latter is comprised of dynamic factors like waves, tides, sea fogs, and winds. While institutions like the Korea Meteorological Administration and the Korea Hydrographic and Oceanographic Agency already offer data on these dynamic factors, the resolution is often insufficient for a precise assessment of localized risks. In this study, to overcome these limitations, we utilized the dynamic information from existing open systems to construct a high-resolution numerical simulation. Through this, we developed an automated module to predict dynamic factors in localized coastal activity areas. Particularly during the module's construction, we compared and reviewed the numerical prediction results for waves with observed wave heights.