• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.51-56
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• 2008

The waveform inversion for isotropic media has ever been studied since the 1980s, but there has been few studies for anisotropic media. We present a seismic waveform inversion algorithm for 2-D heterogeneous transversely isotropic structures. A cell-based finite difference algorithm for anisotropic media in time domain is adopted. The steepest descent during the non-linear iterative inversion approach is obtained by backpropagating residual errors using a reverse time migration technique. For scaling the gradient of a misfit function, we use the pseudo Hessian matrix which is assumed to neglect the zero-lag auto-correlation terms of impulse responses in the approximate Hessian matrix of the Gauss-Newton method. We demonstrate the use of these waveform inversion algorithm by applying them to a two layer model and the anisotropic Marmousi model data. With numerical examples, we show that it's difficult to converge to the true model when we assumed that anisotropic media are isotropic. Therefore, it is expected that our waveform inversion algorithm for anisotropic media is adequate to interpret real seismic exploration data.

• Korean Journal of Remote Sensing
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• v.25 no.5
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• pp.445-454
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• 2009

Localized unprecedented torrential rain and heavy rainfall cause repeated damages and make it difficult to detect and predict the landslide caused by heavy rainfall. To analyze the landslide characteristics of Inje area this study used satellite images photographed after the occurrence of landslide caused by the typhoon Ewiniar occurred in July, 2006, and for GIS analysis purpose, interpreted the satellite images (SPOT5) visually to digitize into developing parts, water traveling parts and sediment parts. For analysis of spatial characteristics, landslide areas obtained from visual interpretation of digital map, 3rd & 4th forest vegetation maps and detailed soil map and grids were overlaid and analyzed. As a result, in regard to topographic features, landslide occurred at places, of which average slope is $26.34^{\circ}$, had south, south-east, south-west aspects and average altitude of 627m. From hydrological analysis, it was found out that water traveling area rapidly spread approaching water traveling area and sediment area. From forest type analysis, it was found out that landslide occurrence was high in pine woods, and in terms of girth class attribute, landslide occurred in small-sized woods, in which the crown occupancy of trees that have the diameter at breast height, 6~16cm, was greater than 50%. From the analysis of soil series, landslide areas constitute 37.85% of OdF and 37.35% of SmF, which had sandy loam soil and excellent drainage capacity. Through this study, landslides in Inje area were characterized and SPOT5 images of 2.5m resolution could be used. But there was a difficulty in determining water traveling parts adjacent to urban area.

• Journal of the Korean Society for Railway
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• v.17 no.3
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• pp.171-177
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• 2014

PWM converter trains exhibit excellent load characteristics in comparison with conventional phase-controlled trains with low power factors, as they can be operated at power factors which are close to unity by means of a voltage vector control method. However, in the case of a high track density or extended feeding, significant line losses and voltage drops can occur. Instead of operating these trains at a fixed unity power factor, this paper suggests a continuous optimal power factor control scheme for each train in an effort to minimize line losses and improve voltage drops according to varying load conditions. The proposed method utilizes the steepest descent algorithm targeting each car in the same feeding section to establish the optimized reactive power compensation levels that can minimize the reactive power loss of the feeder. The results from a simulation of a sample system show that voltage drops can be improved and line losses decreased.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.15 no.1
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• pp.1-7
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• 1997

In the digital mapping for data base contruction, the positional information is used as an important tool in LIS/GIS(Land Information System/Geographic Information System) that is used for a facility management, urban/cadastral management as well as in spatial analysis. In this paper, for an error analysis of X, Y coordinates data on digital map, test area was classified by topography, density, and slope. The coordinates on topographic map were assumed as true values and they were compared with the coordinates on digital map. A result of the numerical test show that a vector data of line type had more gross error than vector data of polygon type. And, SME(stanadrd mean error) of urban or intermountain area had small values compared to that of suburban area in topography analysis. The SME of dense and middle zone had small values compared to that of loose zone in density analysis. In another slope analysis. the SME of steep of gentle slope had small values compared to that of flatland.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.3
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• pp.67-73
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• 1991

To define a small river in Korea. hydrologic- and geographic-characteristics. such as watershed area, channel slope, channel length and time of concentration are investigated and their limits are presented. The current equations of design-width-determination of the small rivers are examined and two equations for the design-width-determination of the small rivers have been suggested in this paper. A small river in Korea can be defined that watershed area is less than $10km^2$, channel length less than 6 km, channel slope over 0.02. time of concentration less than 30 minutes. As Band Q are defined as a design width and a design flood, respectively, the suggested equation to determine the design width is $B=1.235Q^{064}$ for less than $300m^3/sec$ of design flood. and when B and A are defined as a design width and a watershed area, respectively. the recommended equation is $B=8.794A^{0.56}$ for less than $10km^2$ of watershed area.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.1077-1086
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• 2013

Recent huge losses of both life and property have occurred by unexpected natural disasters. We studied snow damages, an important natural disaster issue because it happens more frequently in recent years. This study tries to select vulnerable areas of snowfall in advance and then establish climate change adaptation policy for minimizing unexpected snowfall damage. Busan, where is our study area, has hilly in downtown areas so that topography characteristics of the roads such as slope, elevation and aspect are vulnerable to snowfall. The sudden snowfall in Busan causes traffic jam and causes some schools in hilly to close some schools. At this moment, the adaptation policy has to be established for infrastructure (such as roads) in advance, because prediction of anomaly climate due to global warming is so difficult beside the damage of natural disaster is huge. Therefore, the purpose of this study is contribute to selecting and assessing vulnerable zones of snow damage focusing topography characteristics of the roads and then evaluating the degree of risk of vulnerable zones.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.373-377
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• 2007

본 연구는 하천수를 직접 취수하는 기존 취수장의 취수장애 문제를 해결하기 위한 대안을 개발하는데 목적이 있다. 이를 위해 지금까지 취수장 문제해결 방법으로 검토되지 않았던 유로(流路) 및 하천의 지형변동을 GIS 및 항공사진을 이용하여 정량적으로 파악하였으며, 유사영역 구분 및 하도특성 분석, 하천 특성 해석에 적합한 이동경계 좌표계를 이용한 수치모형을 적용하여 2차원 하상 및 지형변동 예측을 검토하였다. 저수로의 이동 및 하상저하로 인하여 취수문제가 발생하고 있는 경상북도 구미시에 위치한 해평취수장 주변에 대하여 항공사진 분석 및 GIS 기법을 이용하여, 시간 경과에 따른 하천 형태 변화 저수로의 이동 특성을 조사하고 분석하였다. 저수로는 좌안에서 우안으로 이동해 가고 있으며, 이는 하천의 경사가 급하고 하폭이 증가하면서 발생하는 현상으로 저수로의 불안정성이 크게 증가 하는 특성을 보여주었다. 시간의 증가에 따라 저수로 하폭의 증가율이 감소하고 있으며, 수로의 측방 이동을 보여주고 있으며, 시간이 증가함에 따라 측방향 이동율이 감소하였다. 만재유량을 이용하여 유사의 영역구분을 수행한 결과, 망상하천으로서, 모래하천으로 부유사가 지배적인 하천으로 판단되었다. 2차원 수치모형을 이용하여 하상변동을 모의한 결과, 유량이 $2,000\;m^3/s$일 경우에는, 해평 취수장 측의 하천 하상은 상승하였으며, 구미정수장 측에서는 하상이 저하되었다. 홍수유량 $8,000\;m^3/s$일 경우에는 해평 취수장 측에서는 약간 저하하였고, 구미정수장 측에서는 하상이 상승하나, 직하류에서는 하상이 세굴되고, 하천 가운데 자리하고 있는 하중도는 커지는 현상을 보여 주었다. 또한 하중도 직하류에서는 하중도를 중심으로 좌안인 해평 취수장과 우안인 구미정수장 쪽으로 분류된 흐름이 합류되면서 하상에서는 퇴적과 세굴이 반복되며, 복렬 사주가 발생하는 것으로 나타났다. 이는 두 흐름에 의해 와(vortex)가 크게 형성되어 하상의 세굴에 영향을 미치기 때문으로 판단되었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.9
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• pp.700-707
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• 2013

Experimental analyses on a supersonic plasma wind tunnel of CBNU (Chonbuk National University) were carried out. In these experiments, a segmented arc heater was employed as a plasma source and operated at the gas flow rates of 16.3 g/s and the total currents of 300 A. The input power reached ~350 kW with the torch efficiency of 51.4 %, which is defined as the ratio of total exit enthalpy to the input power. The pressure of plasma gas in the arc heater was measured up to 4 bar while it was down to ~45 mbar in a vacuum chamber through a Laval nozzle. During this conversion process, the generated supersonic plasma was expected to have a total enthalpy of ~11 MJ/kg from the measured input power and torch efficiency. In addition to the measurement of total enthalpy, a cone type probe was inserted into the supersonic plasma flow in order to estimate the angle between shock layer and surface of the probe. From these measurements, the temperature and the Mach number of the supersonic plasma were predicted as ~2,950 K and ~3.7, respectively.

• Journal of Korean Society of Forest Science
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• v.13 no.1
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• pp.67-78
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• 1971

The measures of contour-terracing with sod has been executed as a major measures for hillside erosion control works for a long time in Korea. It is, however, recognized that pair terracings make a new slope-face having the more steeper degree of slope between the upper and the lower terraces on hillsides and it also does not contribute for establishing the natural vegetation-cover by penetration of pioneer seeds on the slope faces or cut-faces of hillsides. The study was therefore conducted in connection with the above problems on the cut-face having slope of $40^{\circ}$ and 1.6 meter in slope length with clay soils. Plot allocation for the experiment consists of 3 kinds of 3 replica plots having each $1.6m^2$ of slope area, i. e., the control plot with direct seeding on slopes only ($T_1$), the covering plot with the straw-mats after seeding on slopes ($T_2$) and the seeding plot after covering with the straw-mats. ($T_3$). The main results obtained may be summarized as follows : 1. Effects of the straw-mat mulchings on surface soil loss control:-The total amount of soil losses from each treatments are measured as 4,651 gr from $T_1$, 163 gr. from $T_2$ and 2,891 gr. from $T_3$ treatment respectively. (Refer to table No. 2, 3 and 4). In short, it is recognized that effect of $T_2$ treatment is compared as 28.5 times than that of $T_1$ treatment and 17.7 times than that of $T_3$ treatment respectively. Effect of $T_3$ treatment compared with $T_1$ treatment is also such recognizable as 1.6 times in control of surface soil losses on a slope face. 2. Effect of the straw-mat mulchings on soil moisture content on slopes; -Average per cent of surface soil moisture content by treatments show as 21.60 at the $T_1$, 23.04 at the $T_2$ and 22.21 at the $T_3$ treatment respectively and that of subsurface soil moisture content by treatment show as 23.81 at the $T_1$, 26.16 at the $T_2$ and 24.81 at the $T_3$ treatment respectively. The variance of soil moisture content by treatments was highly significant (Refer table No. 7, 8 and 9). 3. Effect of the straw-mat mulchings on vegetation establishment;-Average numbers of germination by treatments are counted as 237 Nos. at the $T_1$, 246 Nos. at the $T_2$ and 262 Nos. at the $T_3$ treatment plots and the vegetation coverage on ground was almost same as about 90% of covers in all treatments. This effect is more or less lower than that of surface soil erosion control. 4. Regarding the effect on surface soil erosion control, the straw-mat mulchings would be effective as a new measures for control of soil erosion on erosion susceptible lands such slope-faced bare-lands as cut-fill faces, mass-movement faces and bare hillsides.

• Korean Journal of Ecology and Environment
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• v.46 no.4
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• pp.561-569
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• 2013

This study examines locational environment factors that may affect the vegetation structure in the forests of Naejang National Park. To that end, we selected LAI (Leaf Area Index), diameter at breast height, and tree height as structural variables as well as altitude above sea level, gradient, slope direction, soil moisture, topographic location, and amount of solar radiation as locational environment factors, using the method of canonical correlation analysis in order to find out correlation between them. As to the simple correlation between the locational environment factors and structural variables, the correlation coefficient was relatively low (0.6). The values of LAI, measured along the ridge with higher altitudes, decreased as the soil moisture and solar radiation increased. However, LAI increased as the gradient increased and the slope direction faced the north (farther from the east). In respect of the diameter at breast height, the diameter decreased as the altitude and gradient increased. But the diameter increased as the moisture and solar radiation increased. The tree height decreased as the moisture increased and the site was closer to the ridge. These various correlations show a variety of locational environment factors in the national park, implying that the structural variables are affected by complex locational environment factors. This study conducted a canonical correlation analysis on locational environment factors which may affect the vegetation structure, and the result showed that LAI increased and tree height & diameter at breast height decreased as the solar radiation & moisture decreased and altitude increased. Although more factors that may affect vegetation structure (e.g. climate) should be taken into account, this study is significant in that the vegetation structure, which can adapt to more unfavorable conditions in terms of solar radiation, moisture, and higher altitudes, could be inferred in a statistical way. The results of this study, especially the locational environment factors based on DEM, can be used for assessing diversity of vegetation structure in a forest and for monitoring the structure in a national park on a regular basis so as to establish more effective maintenance plans of a park.