• Title, Summary, Keyword: Incident wave

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An Experimental Study of Sediment Transport Patterns behind Offshore Structure (외해 구조물 배후의 표사이동에 관한 실험적 연구)

  • Shin Seung-Ho;Hong Keyyong
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.7 no.4
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    • pp.207-215
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    • 2004
  • Recently, securing a vast land in the land region becomes more difficult and efforts to seek its alternation in the sea area have been increased. As a consequence, the coastal region has been faced to extensive beach erosion problems. In planning offshore structures such as artificial islands, it is necessary to forecast the influence of the structure construction exerting on the beach erosion of the adjacent coast. In the present study, the sediment movement pattern behind offshore structure was examined through a series of three dimensional movable bed experiments, so as to develop the numerical model which forecasts morphological change including beach erosions. The experimental results reveal that the sediment movement patterns of the beach line side and the depth region are separated at a certain boundary line. In details, at the beach side including swash zone the sediment movement becomes dominant, which is governed by a relation between depth contours and incident wave directions, while at the depth region the bed load and suspended load due to the orbit motion of waves are carried by nearshore currents, and both movements are clearly separated at a specified boundary that is related to partial standing wave from the beach. It is expected that these results can be effectively used for verification of a numerical model on morphological change of the coast.

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Characteristics of Erosion Variation at Haeundae Beach due to Multiple Typhoons (복수의 태풍내습에 의한 해운대 해수욕장 침식변화특성)

  • Kang, Tae-Soon;Lee, Jong-Sup;Kim, Jong-Beom;Kim, Jong-Kyu
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.25 no.7
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    • pp.920-926
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    • 2019
  • In this study, we analyzed the erosion variation of beach area at Haeundae Beach after coastal improvement project using video monitoring system operated by the Coastal Erosion Monitoring (Ministry of Oceans and Fisheries). Haeundae Beach was well maintained and stabilized following large scale nourishment through coastal improvement project despite of seasonal fluctuations. However, multiple typhoons over the last two years caused beach stabilization patterns and seasonal fluctuations to lost equilibrium, resulting in rapid erosion. In particular, the sandy beach was eroded by typhoon Solic and Kongray in 2018 and failed to recover beach area in winter by seasonal fluctuations. And due to multiple typhoons in 2019, the beach area was reduced 9.5 % (12,607 ㎡) year-on-year. According to analyze the observed wave and beach area data in Haeundae, the tendency of erosion and sedimentation was influenced by seasonal incident wave direction for each section(west, center and east part). Therefore, to identify the causes of decreasing seasonal fluctuation characteristics and continuous erosion, hereafter, more precise monitoring of different factors are needed, such as the crest heights of submerged breakwater and its loss of function, and sand leakage to the outside around submerged breakwater.

Seismic Properties Study of Gas Hydrate in Deep Sea using Numerical Modeling Technique (수치 모델링 기술을 이용한 심해 가스 하이드레이트의 탄성파 특성 연구)

  • Shin, Sung-Ryul;Yeo, Eun-Min;Kim, Chan-Su;Park, Keun-Pil;Lee, Ho-Young;Kim, Young-Jun
    • Geophysics and Geophysical Exploration
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    • v.9 no.2
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    • pp.139-147
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    • 2006
  • We had conducted a numerical modeling to investigate seismic properties of gas hydrate with field parameters acquired over the East sea in 1998. We used a 2-D staggered grid finite difference method to generate synthetic elastic seismograms for multi-channel seismic survey, OBC (Ocean Bottom Cable) survey and VCS (Vertical Cable Seismic) survey. The results of this study showed that the method using staggered grid yielded stable results and could be used to seismic imaging. We could find out the high amplitude anomaly and the phase reversal phenomenon of reflection wave at interface between the gas hydrate layer and free gas layer such a BSR (Bottom Simulating Reflector) which is the evidence for existence of gas hydrate in seismic reflection data. And we computed the reflection coefficients at the incident angles corresponding to offset distance with the synthetic seismograms. The reflection coefficients acquired from the numerical modeling were nearly consistent with the reflection coefficient computed by Shuey's equation.

Cu(In,Ga)Se2 Thin Films Annealed Using a Continuous Wave Nd:YAG Laser (λ0 = 532 nm): Effects of Laser-Annealing Time

  • Yoo, Myoung Han;Ko, Pil Ju;Kim, Nam-Hoon;Lee, Hyun-Yong
    • Journal of the Korean Physical Society
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    • v.71 no.12
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    • pp.1038-1047
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    • 2017
  • Preparation of $Cu(In,Ga)Se_2$ (CIGS) thin films has continued to face problems related to the selenization of sputtered Cu-In-Ga precursors when using $H_2Se$ vapor in that the materials are highly toxic and the facilities extremely costly. Another obstacle facing the production of CIGS thin films has been the required annealing temperature, as it relates to the decomposition temperature of a typical flexible polymer substrate. A novel laser-annealing process for CIGS thin films, which does not involve the selenization process and which can be performed at a lower temperature, has been proposed. Following sputtering with a $Cu_{0.9}In_{0.7}Ga_{0.3}Se_2$ target, the laser-annealing of the CIGS thin film was performed using a continuous 532-nm Nd:YAG laser with an annealing time of 200 - 1000 s at a laser optical power of 2.75 W. CIGS chalcopyrite (112), (220/204), and (312/116) phases, with some weak diffraction peaks corresponding to the Cu-Se- or the In-Se-related phases, were successfully obtained for all the CIGS thin films that had been laser-annealed at 2.75 W. The lattice parameters, the d-spacing, the tetragonal distortion parameter, and the strain led to the crystallinity being worse and grain size being smaller at 600 s while better crystallinity was obtained at 200 and 800 s, which was closely related to the deviations from molecularity and stoichiometry, which were greatest at 600 s while the values exhibited near-stoichiometric compositions at 200 and 800 s. The band gaps of the laser-annealed CIGS thin films were within a range of 1.765 - 1.977 eV and depended on the internal stress. The mean absorbance of the laser-annealed CIGS thin films was within a range of 1.598 - 1.900, suggesting that approximately 97.47 - 98.74% of the incident photons in the visible spectral region were absorbed by this 400-nm film. The conductivity types exhibited the same deviations (${\Delta}m$ > 0 and ${\Delta}s$ < 0) in all the laser-annealed CIGS thin films. After laser-annealing, the resistivity fell abruptly to a range of $3.551{\times}10^{-2}-1.022{\times}10^{-1}{\Omega}{\cdot}cm$. The carrier concentration was on the order of $10^{19}-10^{21}cm^{-3}$, and the carrier mobility was $5.7{\times}10^{-2}-5.7{\times}10^0cm^2/V{\cdot}s$.

Preventive Congestion Management Algorithm for Ubiquitous Freeway System (유비쿼터스 교통환경을 위한 연속류 정체예방관리 알고리즘)

  • Park, Eun-Mi
    • Journal of Korean Society of Transportation
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    • v.27 no.3
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    • pp.161-168
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    • 2009
  • The ubiquitous transportation system environments make it possible to collect each vehicle's position and velocity data and to perform more sophisticated traffic flow management at individual vehicle or platoon level through V2V and V2I communication. It is necessary to develop a new traffic management paradigm to take advantage of the ubiquitous transportation system environments. This paper proposed a preventive congestion management algorithm for uninterrupted flow, whose goal is to minimize the incident potential and maximize the productivity by maintaining traffic flow stability. The algorithm includes the following steps: Processing the raw data to produce the 3-dimension speed/flow/density profile and to produce the platoon profile and the shock wave profile, Determining the traffic state and the flow stability based on the processed data, Deciding the desirable speed the according the traffic flow state, and finally Providing the desirable speed information. It remains as further work to perform field experiments and calibrate the algorithm parameters.

Study on the limitation of AVO responses shown in the seismic data from East-sea gas reservoir (동해 가스전 탄성파 자료에서 나타나는 AVO 반응의 한계점에 대한 고찰)

  • Shin, Seung-Il;Byun, Joong-Moo;Choi, Hyung-Wook;Kim, Geon-Deuk;Ko, Seung-Won;Seo, Young-Tak;Cha, Young-Ho
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.107-112
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    • 2008
  • In the case of the deep reservoirs like the gas reservoirs in the East-sea, it is often difficult to observe AVO responses in CMP gathers. Because the reservoir becomes more consolidated as its depth deepens, P-wave velocity does not decrease significantly when the pore fluid is replaced by the gas. In this study, we analyzed the effects of Poisson's ratio difference on AVO response with a variety of Poisson's ratios for the upper and lower layers. The results show that, as the difference in Poisson's ratio between the upper and lower layers decreases, the change in the reflection amplitude with incidence angle decreases. To consider the limitation of AVO responses shown in the gas reservoir in East-sea, the velocity model was made by simulation Gorae V structure with seismic data and well logs. The results of comparing AVO responses observed from the synthetic data with theoretical AVO responses calculated by using material properties show that the amount of the change in reflection amplitude with increasing incident angle is very small when the difference in Poisson's ratio between the upper and lower layers is small. In addition, the characteristics of AVO responses were concealed by noise or amplitude distortion arisen during preprocessing. To overcome such limitations of AVO analysis of the data from deep reservoirs, we need to acquire precisely reflection amplitudes in data acquisition stage and use processing tools which preserve reflection amplitude in data processing stage.

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A Compact 3-Layer EBG Structure with Square Ring Stripline (사각 링 스트립선로를 결합시킨 소형 3층 EBG 구조)

  • An Sung-Nam;Shin Dong-Gu;Kim Sang-ln;Choo Ho-Sung;Kim Moon-Il;Park Ikmo;Lim H.
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.16 no.3
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    • pp.300-310
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    • 2005
  • In this paper we propose the compact three-layer EBG structure. The unit cell of the proposed EBG structure is composed of a square patch in the upper layer and a square ring stripline in the lower layer that are connected to the ground plane through conducting vias. Reflection phase analysis method and tangential transmission method were considered to accomplish effective EM simulation and measurement. EM simulation results indicate that bandgap characteristics of the EBG structure using both methods is nearly identical. Parametric studies have been performed with the EM simulator to analyze the properties of the EBG structure by investigating the phase shift of the normally incident plane wave, and the transmission measurements between simple monopole antennas positioned near the EBGstructure have been done. The operating fiefuency bandgap of the proposed EBG structure is about 34 $\%$ lower than the conventional EBG structure with the same size. Measured results show bandgap from 0.930 GHz to 0.945 GHz.

Performance Analysis of the Array Shape Estimation Methods Based on the Nearfield Signal Modeling (근거리 신호 모델링을 기반으로 한 어레이 형상 추정 기법들의 성능 분석)

  • Park, Hee-Young;Lee, Chung-Yong
    • The Journal of the Acoustical Society of Korea
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    • v.27 no.5
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    • pp.221-228
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    • 2008
  • To estimate array shape with reference sources in SONAR systems, nearfield signal modeling is required for the reference sources near a towed array. Array shape estimation method based on the nearfield signal modeling generally exploits the spatial covariance matrix of the received reference sources. Among those method, nearfield eigenvector method uses the eigenvector corresponding to the maximum eigenvalue as a steering vector of the reference source. In this paper, we propose a simplified subspace fitting method based on the nearfield signal modeling with spherical wave modeling. Furthermore, we analyze performance of the array shape estimation methods based on the nearfield signal modeling for various environments. The results of the numerical experiments indicate that the simplified subspace fitting method and the nearfield eigenvector method with single reference source shows almost similar performance. Furthermore, the simplified subspace fitting method with 2 reference sources consistently estimates the shape of the array regardless of the incident angle of the reference sources, whereas the nearfield eigenvector method cannot apply for the case of 2 reference sources.

Socialist Pop After Cultural Revolution (문화혁명기 이후의 중국의 사회주의 팝아트)

  • Park, Se-Youn
    • The Journal of Art Theory & Practice
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    • no.6
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    • pp.27-50
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    • 2008
  • This thesis examines contemporary Chinese painting after the Cultural Revolution(1966~76), focusing upon so-called "Chinese Pop art", which I termed as "Socialist Pop art". I considered the art of this period within the broader context of social changes especially after the Tienanmen incident of 1989. After the Cultural Revolution during which idolization of Chairman Mao was at its peak, one of the major changes in communist China was that an anti-Mao wave was generated in almost every social class. For example, novels that revealed the hardships during the Cultural Revolution were published. Posters that openly criticized the Maoism were also produced and displayed on the walls, and demand for democracy spurred widespread activist movements among young generations. These broad social changes were also reflected in art. A variety of art movements were introduced from the West to China, and after a period of experimentation with the new imported styles, artists began to apply the new artistic idiom to their works in order to visualize their own social and political realities they lived in. It was a shift from earlier Socialist Realism to a new expression either directly or indirectly, "Socialist Pop", an amalgam of Socialist Realism and Pop art tradition. After the 1989 crackdown of Tienanmen Square protest, when communist government quelled with brutal measures the students, workers, and ordinary people who rose for democracy, greater urge to protest the Deng Xiaoping regime emerged. This time coincided with the gradual emergence of art using Pop art vocabulary to satirize the social reality, the Socialist Pop art, along with many other art forms all with avant-garde spirit. One of the most frequent subjects of Chinese Pop art was visual images of Chairman Mao and his Cultural Revolution, and new China that was saturated with capitalism, which tainted the Chinese way of life with a Western way of consumerism and commercialism. The reason for the popularity of Mao's image was spurred by the "Mao Craze" in the early 1990's. People suddenly began to fall in a kind of nostalgia for the past, and once again, Mao Zedong was idolized as an entity who can heal the problems of modern China who had been marching towards their ultimate destination, the economic development. But this time Chairman Mao was no more an idol but just a popular, commercial product. He is no more an object of worship of almost religious nature but he has become an iconography symbolizing the complex nature of present Chinese society. During this process of depicting the social reality, Chinese artists are making the authority and sanctity of Maoism ineffective. Dealing with this new trend of contemporary Chinese art in view of "Socialist Pop art" two manners of re-creating Pop art can be illustrated: one that incorporates the propaganda posters of the Cultural Revolution; the other borrows from Chinese traditional popular imagery or mass media, such as photos taken during Mao era. What is worth mentioning is that these posters and photos of the Cultural Revolution can be identified as 'popular' media, as they were directed to educate the popular mass, thus combination of this ingenuous pop media with Western Pop art can be fully justified as a genre unique to China. Through this genre, we can discover a new chapter of the Chinese contemporary painting and its society, as their Pop art can be considered as self-portraits true to their present appearances.

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Effect of Wall Thickness of Perforated Wall with Vertical Slits on Wave Reflection and Transmission (연직 슬릿 유공벽의 벽두께가 파랑 반사 및 전달에 미치는 영향)

  • Kwon, Kab Keun;Lee, Jong In;Yoon, Sung Bum
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.26 no.6
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    • pp.343-351
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    • 2014
  • The reflection and transmission coefficients of waves due to perforated wall are mainly determined by both the porosity and wall thickness of the perforated wall and the period and nonlinearity of incident waves. Among them the wall thickness is very important because it affects the head loss coefficient and the inertia length of the wall. However, by employing the head loss coefficient derived for sharp crested orifice, the previous researches have neglected, or incorrectly considered the effect of wall thickness on the head loss coefficient. Even though it is considered, the effect of the inertia length is neglected in some empirical formulae. Thus, the effect of wall thickness on the reflection and transmission coefficients of waves is not properly considered. In this study comprehensive experiments are conducted for the perforated walls with various thicknesses, and the results are compared with those predicted by the empirical formulae. As a result it is found that the existing formulae can not properly consider the effect of wall thickness, and it is confirmed that a new formula which can correctly consider the effect of wall thickness on the head loss coefficient is necessary.