• 한국방재학회:학술대회논문집
• /
• 2010.02a
• /
• pp.66.2-66.2
• /
• 2010

장대 케이슨 방파제에 작용하는 다방향 불규칙파랑의 파력 평활화 계수를 계산하였다. 다방향 불규칙파랑의 주파수 스펙트럼으로는 Bretschneider-Mitsuyasu 스펙트럼을 사용하였고, 방향 스펙트럼은 Mitsuyasyu 타입의 스펙트럼을 적용하였다. 계산 결과 단일 케이슨의 길이가 길수록, 주파향의 입사각이 클수록 평활화 계수는 감소하였다. 다양한 에 대해서도 계산하였으며, 가 클수록 평활화계수는 규칙파와 비슷한 경향을 보였다.

• Proceedings of the Korea Contents Association Conference
• /
• 2016.05a
• /
• pp.437-438
• /
• 2016

3차원 수치모형을 이용하여 이안류 흐름을 재현하였다. 이안류 흐름이란 지형의 변화 또는 다방향 입사파의 영향으로 연안지역에서 외해방향으로 흐르는 흐름을 의미한다. 이러한 흐름은 그 발생원인이 다양하여 정교한 수치모의를 수행하여야 하나 지금까지는 주로 수심적분된 이차원 모형을 이용하여 연구가 수행되었다. 본 연구에서는 N-S방정식을 직접 수치모의하는 3차원 모형을 이용하여 이안류를 재현하고 그 현상을 분석해보았다.

• Proceedings of the Optical Society of Korea Conference
• /
• 2008.07a
• /
• pp.217-218
• /
• 2008

In this paper, we investigate the optical and structural properties of linear and circular polarization-discriminatory inverters. Circular polarization-discriminatory handedness inverter is realized as a combination of half-wave plate and Bragg reflector and that of linear polarization in verter is realized as a combination of quarter-wave plate, Bragg reflector and quarter-wave plate.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.15 no.3
• /
• pp.177-185
• /
• 2012

Wave field measurements were made over a period of 18 days to study the spatial distribution of incident wave on seaweed tarm field around Gumil-up Sea, Wando, Korea. These measured data were compared with data from the Geomun-do ocean weather/wave observation buoy. A numerical simulation model that combined the offshore design wave with the seasonal normal incoming wave was used to study the incident wave distribution surrounding a seaweed farm. The results are summarized as follows. (1) On-site wave measurements showed that the major relationship between maximum and significant wave height was $H_{max}=1.6H_{1/3}$. (2) Offshore incident wave energy reaching the coast was greatly influenced by the wind direction. A north wind reduced the incident wave energy and a south wind increased it. (3) The calculated maximum wave height under the design wave boundany conditions was in the range of 4~5 m and the reduction in the incident wave height ratio ranged from approximately 38.1% to 47.6% at Gumil-up Sea. Under normal wave conditions, the maximum wave heights were 3.6~4.0 m in summer and 2.3~2.7 m in winter while the reduction in the incident wave height ratio was about 41.8% to 49.1%. (4) The sea state in the southern area of Gumil-up was the most affected by ocean waves, whereas the sea state in the northern area was very stable. The significant wave ratio in the south was about six times that in the north.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.17 no.3
• /
• pp.182-188
• /
• 2014

In an oscillating water column (OWC)-type wave energy conversion system, the performance of the OWC chamber depends on the chamber shape, as well as the incident wave direction and pressure drop produced by the turbine. Although the previous studies on OWC chambers have focused on wave absorbing performance in ideal operating conditions, incident waves do not always arrive normally to the OWC chamber in real sea conditions, especially in fixed devices. The present study deals with experiments and numerical calculations to investigate the effects of wave direction on the performance of the OWC chamber. The experiments were carried out in a three-dimensional wave basin for five different wave directions, including the effect of turbine using the corresponding orifice. The wave elevation inside the chamber was measured at the center point under various incident wave conditions. The numerical study was conducted by using a numerical wave tank-based volume-of-fluid model to compare the results with experimental data and to reveal the detailed flows around the chamber.

• Korean Journal of Remote Sensing
• /
• v.14 no.4
• /
• pp.325-342
• /
• 1998

Two RADARSAT SAR images with different modes acquired by Canadian Space Agency to test the effectiveness of geological lineament extraction and spring water detection over the Cheju Island. Geological lineaments are poorly developed this basalt dominant volcanic island, but more linear features can be extracted when SAR and TM images are simultaneously analyzed than when TM image alone is used. This results mainly owe to the facts that RADARSAT SAR systems are able to provide data with different frequencies, azimuth, and incidence angles. Distribution of spring water along coast is poorly correlated with geological lineaments or drainage pattern, but those in middle range of mountain region are developed along geological lineaments. Detection of spring water using remotely sensed images are turned out to be very difficult to achieve. Radial shaped sea surface temperature anomaly derived from TM thermal band should be the best candidate for spring water, but the resolution is not high enough. We also investigate the normalized radar cross section (or sigma naught) converted from RADARSAT and ERS-1 SAR data but to discriminate the spring water effectively except where relatively large water mass is observed on land side. Speckle noise and irregularity in physical sea surface condition are the serious obstacles for this application. ERS-1 SAR image acquired in low incidence angle was more useful for geological lineament estimation and water body study than RADARSAT SAR images with high incidence angles. Therefore the selection of incidence angle is critical in geological and spring water applications of SAR images, and low incidence angles less than about 30$^{\circ}$ are recommended to monitor the Cheju volcanic island.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.1
• /
• pp.155-162
• /
• 2020

In this paper, we present a radiation compensation method and experiment method for two-dimensional direction finding by elevation and azimuth angles of broadband GPS signal, and then produce experimental results. Previous studies have performed direction finding by only using the azimuth angle of the detected signal. So, the compensation table utilizes compensation data by azimuth angles only. However, the presented method in this study has compensation data by azimuth and elevation angles for two-dimensional direction finding. Because of direction finding systems and applications are diversified, recently. So, we present a two-dimensional radiation compensation method. For evaluation of the presented compensation method, we calculate the ideal phase differences on the antenna for two-dimensional direction finding and simulate phase differences using a FEKO EM simulator. Subsequently, we analyze experimental data by radiation compensation experiments using the presented compensation method in an anechoic chamber.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.53 no.8
• /
• pp.95-104
• /
• 2016

Subspace-based direction-of-arrival (DOA) estimation algorithms have a difficulty in dealing with coherent signals caused by multi-path environment. As one of attempts to solve this problem, a spatial differencing method is known to be useful for not only estimating DOAs of the coherent signals but also improving the number of resolvable wavefronts even more than the number of antenna elements. However, since the conventional spatial differencing method uses only the partial statistics of the observed data, this method suffers from the performance degradation in estimation accuracy caused by the residual correlation between the uncorrelated signals. To cope with this problem, in this paper, a generalized spatial differencing method is proposed. Unlike the conventional method, the proposed method utilizes the entire statistics of the received signals. Therefore, the additional performance enhancement in both estimation accuracy and the number of resolvable wavefronts can be achieved. The performance analyses with computer simulations show that the proposed method outperforms the conventional method in terms of the estimation accuracy and the number of resolvable wavefronts.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.8
• /
• pp.917-920
• /
• 2016

SpSF algorithm is direction-of-arrival estimation algorithm based on sparse representation of incident signlas. Cost function to be optimized for DOA estimation is multi-dimensional nonlinear function, which is hard to handle for optimization. After some manipulation, the problem can be cast into convex optimiztion problem. Convex optimization problem tuns out to be constrained optimization problem, where the parameter in the constraint has to be determined. The solution of the convex optimization problem is dependent on the specific parameter value in the constraint. In this paper, we propose a rule-of-thumb for determining the parameter value in the constraint. Based on the fact that the noise in the array elements is complex Gaussian distributed with zero mean, the average of the Frobenius norm of the matrix in the constraint can be rigorously derived. The parameter in the constrint is set to be two times the average of the Frobenius norm of the matrix in the constraint. It is shown that the SpSF algorithm actually works with the parameter value set by the method proposed in this paper.

• Progress in Medical Physics
• /
• v.7 no.2
• /
• pp.29-40
• /
• 1996

We had designed and made the cylindrical ionization chamber which operated above 5 mR/h. Using commercial electrometer, we investigated the characterictic of charge collection in the ion chamber. The active volume was 190.4㎤ and overall length and diameter in the chamber was 15.5cm, 5.22cm, respectively. The chamber had three electrodes(inner, central, wall electrode). And background current was 8.39${\times}$10$\^$-14/${\pm}$1.5${\times}$10$\^$-15/A to arrange the electrodes which were coaxial in chamber axis. The collection efficiency of chamber for Cs$\^$137/ was 99.7％ when the opreating voltage was applied 400V. Comparing with the commertial dosimetry system, the exposure calibration constant was 4.531${\times}$19$\^$7/R/C. By normalizing to CS$\_$137/ the relative energy response of the chamber was 1.30 for Am$\_$24/, 1.05 for C0$\_$60/, respectively. When the irrarition tranversed to the chamber axis, the isotropic effect of the chamber was not considerable.