• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.5
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• pp.333-342
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• 2012

We studied the characteristics of spatial distribution of global wave height and carried out the modelsensitivity test by changing the input field, model resolution and physical factor (effective wind factor) since the spatial and temporal resolution in wind wave forecasting is one of most important factors. Comparisons among the different cases, and also between model, buoy and satellite data have been made. As a results of the wind-wave model run using the high resolution wind field, the bias of significant wave height showed the positive tendency and the Root-Mean Square Error(RMSE) was a bit decreased based on the comparison with buoy data. When the model resolution was changed to higher, the bias and RMSE was increased, and as the effective wind factor was smaller than default value(= 1.4) the bias and RMSE showed also decreasing pattern.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.5
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• pp.571-576
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• 2015

This paper presents a comparative study of wave height estimation method that was used for signal to noise ratio and shadowing ratio based on X-band marine radar. If the signal to noise ratio, and is widely used as a method for estimating an wave height, a new method is presented for shadowing ratio. In the case of radar images used in this study it is measuring the data from the coast of Ulsan Jujeon, compared with marine meteorological information from the Meteorological Agency measured a light beacon. We compared the measured data for about 34 days, the typhoon was measured, incluidng a period in the East Sea, and verify the results for various distribution of wave height. For estimate wave height using a shadowing ratio analysis, it does not require calibration and real-time advantages of this part, coming confirmed the possibility of the measurement, the cause detection error for radar image was caused due to determine.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.125.1-125.1
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• 2012

The wave number 4 (wave-4) and wave number 3 (wave-3) longitudinal structures in the thermospheric neutral mass density are understood as tidal structures driven by diurnal eastward-propagating zonal wave number 3 (DE3) and wave number 2 (DE2) tides, respectively. However, those structures have been identified using data from limited time periods, and the consistency and recurrence of those structures have not yet been examined using long-term observation data. We examine the persistence of those structures by analyzing the neutral mass density data for the years 2001-2008 taken by the CHAllenging Minisatellite Payload (CHAMP) satellite. During years of low solar activity, the amplitude of the wave-4 structure is pronounced during August and September, and the wave-4 phase shows a consistent eastward phase progression of $90^{\circ}$ within 24 h local time in different months and years. During years of high solar activity, the wave-4 amplitude is small and does not show a distinctive annual pattern, but the tendency of the eastward phase shift at a rate of $90^{\circ}$/24 h exists. Thus the DE3 signature in the wave-4 structure is considered as a persistent feature. The wave-3 structure is a weak feature in most months and years. The amplitude and phase of the wave-3 structure do not show a notable solar cycle dependence. Among the contributing tidal modes to the wave-3 structure, the DE2 amplitude is most pronounced. This result may suggest that the DE2 signature, although it is a weak signature, is a perceivable persistent feature in the thermosphere.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.1
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• pp.36-45
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• 2017

In the present study, the storm waves at the Korean Straits of April, 2016 have been reproduced by the wave hindcasting, and then their characteristics were investigated. Before the wave hindcasting, the wave measurements at the Korean Straits were analyzed. The analysis showed that the waves at the Korean Straits were dominated by the Northeastern waves, same as those in the East Sea. Accordingly, the wave hindcasting was been carried out with the same condition in Ahn et al. (2016). In the numerical results, the maximum significant wave height at the Korean Straits was 5.06 m, and the corresponding significant wave period was 9.2 s. The computed significant wave heights and wave periods were overestimated by 4 cm and 0.8 s, respectively. After the wave hindcasting, the computed significant wave heights and peak periods were compared with the JONSWAP relationship. This comparison showed that the storm waves at the Korean Straits were close to wind waves, not swell.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.4
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• pp.291-297
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• 2015

The wave spectrum was generated from wave data measured at the Chagwi-do site in Jeju, where a 10MW class floating wave-offshore wind hybrid power generation system will be installed. The latching control technology (Sheng et al.[2015]) was applied in order to improve the extracted power from WEC (Wave Energy Converter), which is heaving in corresponding irregular waves. The peak period as a representative value of irregular waves was used when we determined the latching duration. From the numerical results in the time-domain analysis, the latching control technology can significantly improve the extracted power about 50%.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.23-27
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• 2004

Developing of electromagnetic wave absorbers for GHz frequency, we used cast Alnico magnets. It is the first research paper to show that electromagnetic wave absorbers with Alnico magnets have good reflectivity in the GHz frequencies. Especially in this study, we used recycled cast Alnico magnets for natural resources problems and natural environment problems. New electromagnetic wave absorbers developed in this study are useful for X-band and C-band.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.4
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• pp.254-262
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• 2015

Parametric study on submerged body shape of an oscillating hemisphere point absorber was conducted to predict the optimal relation between radius and draft of the body. As an additional damping due to power takeoff system, the optimal damping same as wave radiation damping was applied to the PTO system to produce the maximum wave power. Body response spectrum and power spectrum were obtained for various peak frequencies on wave spectra. It was found that the maximum power can be generated when the peak frequency of available wave power was 20% greater than that of wave spectrum.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.3
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• pp.165-172
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• 2009

A set of equations for description of transformation of harmonic waves is proposed here. Velocity potential function and separation of variables are introduced for the derivation. The continuity equation is in a vertical plane is integrated through the water so that a horizontal one-dimensional wave equation is produced. The new equation composed of the complex velocity potential function, further be modified into. A set up of equations composed of the wave amplitude and wave phase gradient. The horizontally one-dimensional equations on the wave amplitude and wave phase gradient are the first and second-order ordinary differential equations. They are solved in a one-way marching manner starting from a side where boundary values are supplied, i.e. the wave amplitude, the wave amplitude gradient, and the wave phase gradient. Simple spatially-centered finite difference schemes are adopted for the present set of equations. The equations set is applied to three test cases, Booij's inclined plane slope profile, Massel's smooth bed profile, and Bragg's wavy bed profile. The present equations set is satisfactorily verified against existing theories including Massel's modified mild-slope equation, Berkhoff's mild-slope equation, and the full linear equation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.293-300
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• 2013

This study used a water tank and wave maker to generate conditions similar to the real ocean environment. Given that the waves were properly generated in the water tank, a precise analysis indicated the quantitative value of the wave force acting on a body. A high-speed camera and wave-level gauge were used to measure the temporal wave motion and period. A series of artificial water waves were successfully generated using three different wave periods and amplitudes. Each of the waves captured by a high-speed camera was sinusoidal and did not maintain its shape properly without a wave absorber, but it was substantially improved and well shaped when the wave absorber was installed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.5
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• pp.1069-1076
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• 2017

C-ITS(Cooperative-Intelligent Transportation System) provides services that require strict real-time such as forward collision warning, road safety service and emergency stop. WAVE(Wireless Access in Vehicular Environments), a core technology of C-ITS, is a technology designed for high-speed driving. However, in order to provide stable communication service by applying to real road environment, various performance tests of real vehicular environment are required. In the real road environment, WAVE communication performance is influenced by the surrounding environment such as moving vehicle, road shape and topography. Especially, when the vehicle is moving at high speed, the traveling position according to the speed of the vehicle, The surrounding environment changes rapidly. Such changes are factors affecting the communication performance, therefore a system and methods for analyzing them are needed. In this paper, we propose the configuration and test method of an effective performance evaluation system under high-speed driving and describe the results of analyzing the communication performance based on the data measured through the actual vehicle test.