• Geomechanics and Engineering
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• 제23권6호
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• pp.575-585
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• 2020

In this numerical study, the 2D dynamic behavior of a clayey basin and its effect on damage pattern over basin edge are investigated. To attain this goal, a fully nonlinear time domain analysis method has been applied. Then, the fragility curves of the considered two typical industrial structures for that certain point are estimated using the acceleration time histories recorded at each surface point. The results show that the use of the damage related parameters in site effect analyses, instead of amplification curves, can yield more realistic estimation of the basin dynamic response. In a distance about 150 m from outcrop at the basin edge, the differences between fragility curves increase when increasing the distance from outcrop with respect to the reference rock site. Outside this region and towards the basin center, they tend to occur in rather single curves. Furthermore, to connect the structural damage to the basin edge effect, the earthquake demand value at different points for two typical structures was evaluated. It was seen that the probability of occurrence of damage increases over 250 m from outcrop, while the effect of the basin edge was limited to 150 m in case of the basin edge evaluation by using fragility curves.

• IUGG한국위원회:학술대회논문집
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• IUGG한국위원회 2003년도 정기총회 및 학술발표회
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• pp.18-18
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• 2003

Three-dimensional finite-difference simulation of earthquake ground motion is performed using a locally variable time-step (LVTS) scheme matching with discontinuous grids. Discontinuous grids in three directions and extension of the discontinuous grids' boundary to the free-surface in the LVTS scheme minimize the cost of both the computational memory and the CPU time for models like the localized sedimentary basin. A simplified model of sedimentary basin is dealt to show the feasibility and efficiency of the LVTS scheme. The basin parameters are examined to understand the main characteristics on ground-motion response in the basin. The results show that the seismic energy is concentrated on a marginal area of the basin far from the source. This focusing effect is mainly due to the constructive interference of the direct S-wave with the basin-edge induced surface waves. The ground-motion amplification over the deepest part of the basin is relatively lower than that above the shallow basin edge. Therefore the ground-motion amplification may be more related to the source azimuth or the direction of the incident waves into the basin rather than the depth of it.

• Geomechanics and Engineering
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• 제36권4호
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• pp.367-380
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• 2024

Investigations has shown that the correct estimation of the effective amplification period is as important as the amplification value itself. It gets more important in 2D basins. This study presents a quantitative coefficient for consideration of the nonlinearity effect in terms of amplification value and the shift in its period which is missing or ineffectively considered in the previous studies. To attain this goal, by the application of a time domain fully nonlinear method, the deviation of the more common equivalent linear results from the basin nonlinear behavior under strong ground motions is investigated quantitatively. Also, despite the increase in the damping ratio, the possibility of the increase in the amplification due to the increase in motion strength is shown. To make the results useful in engineering practice, by introducing nonlinearity ratio, the effect of the nonlinearity is quantitatively estimated for two soft and stiff clayey basins with three different depths under a set of motions scaled to two target spectrum. Results show that at the 100 m depth soft clayey basin, while the nonlinearity ratio shows a 35% deviation at the basin edge part under DD1 motion level, its effect moves to the central part with 20% effect under DD3 motion level. By the increase in depth to 150 m, the results show a decrease in the overall effect of the nonlinear behavior for both clay types. At this depth, the nonlinearity ratio gives a 30% and 17% difference on a limited distance from outcrop at the soft clayey basin under DD1 and DD3 motion levels, respectively. At the 30 m depth basins, the nonlinearity ratio shows up to 25% difference for different cases. The presented ratio would be introduced as nonlinearity coefficients for consideration of the nonlinearity effects in the codes. The presented quantitative margins will help the designer to have a better understanding of the amplification period change because of nonlinearity over 2D basin surface.

• 대한원격탐사학회지
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• 제37권3호
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• pp.419-430
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• 2021

신속하게 면단위(2-Dimension)로 하천의 녹조 우심지역을 관측하기 위해 드론 다중분광영상을 이용한 분석기법을 연구하였다. 드론은 항공기나 위성에 비해 관측 면적이 작지만 높은 공간해상도와 현장접근 및 데이터 획득 용이성, 대기에 의한 간섭 저감, 다중분광센서를 이용한 신속한 자료처리로 녹조 모니터링 효율성을 향상시킬 수 있을 것으로 보고 있다. 이러한 드론의 다중분광센서 영상으로 하천의 녹조발생 현황을 모니터링하기 위해 광합성 색소에 의한 분광특성을 반영하는 분광지수들을 비교 분석하고 Chlorophyll-a(Chl-a) 농도 추정식에 적용 가능성을 평가하였다. 주로 Red-edge 밴드를 포함하는 분광지수가 Chl-a 농도와 높은 상관성을 보였는데, 그 중에서도 3-Band Model(3BM), Normalized Difference Chlorophyll Index(NDCI)가 각각 비슷한 수준으로 가장 높은 통계적 유의성(R²=0.86, RMSE=7.5)을 나타내었다. NDCI의 경우에는 두 개의 분광밴드만 적용되는 간결한 수식과 정규화된(Normalizing) 결과값으로 신속하고 표준화된 프로세싱이 가능할 것으로 보이며 드론 녹조 모니터링에서 적용성이 높을 것으로 기대된다. 3BM의 경우에는 Red-edge 영역에서 두 개의 파장대를 적용해야 하나 본 연구에서 사용한 드론 센서에는 한 개의 Red-edge 밴드만 포함되어서 근적외선으로 대체하여 수식을 적용하였는데 Red-edge 파장영역이 세밀한 분광센서를 활용할 경우에 NDCI 보다 높은 정확도를 나타낼 수 있을 것으로 보인다.

• 지구물리와물리탐사
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• 제15권2호
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• pp.92-101
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• 2012

평탄한 자유표면을 갖는 소규모 반구형 분지에서 임의의 전단변형 점진원에 대한 3차원 유한차분 모의를 수행하였다. 자유표면 경계조건을 다루기 위한 새로운 방법을 고안하였다. 분지에서 지반운동 응답에 대한 주요한 특징들을 파악하기 위하여 분지특성 변수를 조사하였다. 분지에서 지반운동의 주파수 함량을 분석하기 위하여, 각 주파수에 대한 진폭을 분지 주변 4개의 위치에서 계산하고 서로 비교하였다. 또한 어떤 종류의 파가 이들 각 지점에서의 지반운동 응답에 우세한 역할을 하는지 보기 위하여 입자운동을 분석하였다. 계산 결과, 지진파 에너지가 진원으로부터 먼 쪽의 분지 경계부에서 집중되는 것을 알 수 있었다. 이러한 집중 효과는 주로 직접 S-파와 분지 경계에서 생성된 표면파의 보강간섭으로 인한 것이다. 또한, 분지의 가장 깊은 곳 상부에서의 지반운동 증폭은 얕은 깊이의 분지 경계 부에 비하여 상대적으로 작게 나타났다. 이러한 결과로부터, 상대적으로 단순한 기반암 경계를 갖는 소규모 분지에서의 지반운동 증폭은 분지의 깊이 보다는 진원의 방위 또는 분지 내부로 입사하는 파의 진행방향에 더 많은 관계가 있다는 것을 추정할 수 있다.

• Geomechanics and Engineering
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• 제31권2호
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• pp.183-195
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• 2022

Under the effects of the near-field earthquakes, the incident angle of the incoming wave could be different. In this study, the influences of some parameters such as incident angle, basin edge, peak ground acceleration level of the bedrock motion as well as different clay types with different consistency on the amplification behavior of the shallow basins are investigated. To attain this goal, the numerical analyses of the basins filled with three different clay types are performed using a fully nonlinear method. The two dimensional models of the basins are subjected to a set of strong ground motions with different peak ground acceleration levels and three different incident angles of 30◦, 45◦ and 90◦ with respect to the horizontal axes. The results show the dominant effect of the obliquely subjected waves at most cases. The higher effect of the 45◦ incident angle on the basin response was concluded. In the other part of this study, the spectral amplification curves of the surface points were compared. It was seen that the maximum spectral amplification of different surface points occurs at different periods. Also, it is affected by the increase in the peak acceleration level of the incoming motions.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1999년도 Proceedings of the 1999 Annual Conference The Korean Society of Agricutural Engineers
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• pp.465-472
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• 1999

Hydraulic model tests are performed to find economical and hdrqulically stable design of cooling water intake channel of steam power plant. The result of tests show that the standard distributiion of y-components in the chamber of CWP(circulating Water Pump) are recommended below 3.5 to maintain hydraulic stability, so that this value is considered as the design criteria. Common basin is necessary to improve the hydraulic stability of inflow, however the longer basin does not always improve the hydraulic stability , and the optimal length of basin can be found in some range. From the results the flow stability maintained the best condition when the length of basin is 7.2m. Beside the standard tests the auxiliary tests like edge , baffle, trapezoidal section and increase of pump capacity are carried out based on the optimal condition foudn in the standard tests. From the series of tests the economical and hydraulically stable design of intake channel was proposed.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제25권1호
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• pp.57-81
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• 1997

Numerical prediction of nocturnal thermal high in summer of the 1995 near Taegu city located in a basin has been carried out by a non-hydrostatic numerical model over complex terrain through one-way double nesting technique in the Z following coordinate system. Under the prevailing westerly winds, vertical turbulent fluxes of momentum and heat over mountains for daytime hours are quite strong with a large magnitude of more than $120W/\textrm{m}^2$, but a small one of $5W/\textrm{m}^2$ at the surface of the basin. Convective boundary layer (CBL) is developed with a thickness of about 600m over the ground in the lee side of Mt. Hyungje, and extends to the edge of inland at the interface of land sea in the east. Sensible heat flux near the surface of the top of the mountain is $50W/\textrm{m}^2$, but its flux in the basin is almost zero. Convergence of sensible heat flux occurs from the ground surface toward the atmosphere in the lower layer, causing the layer over the mountain to be warmed up, but no convergance of the flux over the basin results from the significant mixing of air within the CBL. As horizontal transport of sensible heat flux from the top of the mountain toward over the basin results in the continuous accumulation of heat with time, enhancing air temperature at the surface of the basin, especially Taegu city to be higher than $39.3^{\circ}C$. Since latent heat fluxes are $270W/\textrm{m}^2$ near the top of the mountain and $300W/\textrm{m}^2$ along the slope of the mountain and the basin, evaporation of water vapor from the surface of the basin is much higher than one from the mountain and then, horizontal transport of latent heat flux is from the basin toward the mountain, showing relative humidity of 65 to 75% over the mountain to be much greater than 50% to 55% in the basin. At night, sensible heat fluxes have negative values of $-120W/\textrm{m}^2$ along the slope near the top of the mountain and $-50W/\textrm{m}^2$ at the surface of the basin, which indicate gain of heat from the lower atmosphere. Nighttime radiative cooling produces a shallow nocturnal surface inversion layer with a thickness of about 100m, which is much lower than common surface inversion layer, and lifts extremely heated air masses for daytime hours, namely, a warm pool of $34^{\circ}C$ to be isolated over the ground surface in the basin. As heat transfer from the warm pool in the lower atmosphere toward the ground of the basin occurs, the air near the surface of the basin does not much cool down, resulting in the persistence of high temperature at night, called nocturnal thermal high or tropical night. High relative humidity of 75% is found at the surface of the basin under the moderate wind, while slightly low relative humidity of 60% is along the eastern slope of the high mountain, due to adiabatic heating by the srong downslope wind. Air temperature near the surface of the basin with high moisture in the evening does not get lower than that during the day and the high temperature produces nocturnal warming situation.

• Journal of the korean society of oceanography
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• 제31권4호
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• pp.207-216
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• 1996

A geochemical study of three piston cores (ST.4, ST.6 and ST.20) taken from the Northwest Pacific (eastern edge of Shikoku Basin) provides information about changes in surface water paleoproductivity and sedimentation during the last 127 kys. Paleoproductivity variations were estimated on the basis of total organic carbon content and carbonate mass accumulation rate. The paleoproductivity based on total organic carbon shows significant spatial variations between glacial and interglacial periods. During the last glacial maximum (LGM) paleoproductivity increased about 1.5 times with deglaciation decrease compared with those of the Holocene at inner side of the Shikoku Basin (ST.4 and ST.6). On the other hand, paleoproductivity at outer side of Shikoku Basin (ST.20) indicating not distinctive increase but deglaciation increase. The C/N ratios fall below 10 for cores ST.4 and ST.6, but C/N ratios between 100 ka and 80 ka in ST.20 which show around 10 or larger values suggest a predominance of marine organic carbon with some admixture of terrigenous materials. The carbonate mass accumulation rate of three cores show different patterns of calcareous record with respect to organic carbon based paleoproductivity variation. In the inner side of Shikoku Basin (ST.4 and ST.6) the carbonate mass accumulation rate decreased during last glacial maximum, and significant increase of carbonate mass accumulation rate is recognized at outer side of Shikoku Basin (ST.20). Thus, this set of data reveals that spatial paleoproductivity variations between inner and outer side of Shikoku Basin during the glacial and interglacial periods.

• 지구물리
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• 제2권1호
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• pp.27-38
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• 1999

최근 공개된 위성중력을 이용하는 오차 최소화 기법을 적용하여 선상중력내 존재하는 구간 측선간 오차나 교차점 오차를 성공적으로 보정하였으며, 보정된 선상중력을 위성중력과 결합하여 고해상 중력분포를 도출하였다. 오차 최소화 과정에서 울릉분지의 선상중력은 위성중력보다 장주기 성분에서 상대적으로 크게 보정되었으나 단주기 성분은 그대로 보존되었다. 이것은 선상중력이 갖는 단주기의 중력 성분이 훼손되지 않은 채 안정되고 연속성을 갖는 장주기의 인공위성 중력분포에 잘 접합될 수 있다는 것을 보여 준다. 통합된 후리에어이상도는 위성중력의 장주기 성분과 선상중력의 단주기 성분을 모두 표현하므로 해저지형 및 지질분포의 해석에서 보다 상세하고 신뢰성 있는 정보를 제공한다. 후리에어이상은 수심이 깊은 분지 중앙 지역이 해저산이나 대지 등 높은 지형으로 이루어진 분지 주변부 보다 상대적으로 낮게 분포하는 등 전반적으로 해저지형의 분포 경향에 부합되어 변화한다. 그러나 대륙사면을 이루고 있는 분지의 서쪽 및 동쪽 주변부를 따라서는 지역적으로 함몰된 퇴적기반과 두꺼운 퇴적층 및 대륙 주변부에서 특징적인 가장자리 효과로 인한 저이상대가 발달하고 있다. 울릉도 북동부에 위치한 한국대지 및 울릉대지에서 북동-남서방향의 선형분포를 갖는 중력이상은 동해가 열개되는 동안 균열된 지각 사이를 따라 일어난 화산활동의 결과로 형성된 해산이나 관입암체가 선형으로 배열함으로서 기인한 것으로 해석된다. 선형으로 배열된 고중력분포는 울릉대지 서쪽 경계부에서 급구배를 보이는 북북서-남남동 방향의 직선적인 중력분포에 의해 절단되고 있는 데 이 급구배의 중력이상은 울릉대지 서부 경계를 이루는 단층선애에 기인한다. 울릉대지가 서쪽으로 뚜렷한 단층 접촉을 나타내고 있으나 지형적인 형태에 있어서 대비되지 않는 것은 울릉대지가 단층을 경계로 분리되어 이동되어 왔을 가능성을 시사한다. 분지의 중앙 북동부에서는 수심이 깊어지는 데 비해 중력치는 오히려 높아지는 경향을 나타내고 있는 것은 맨틀이 주변부에 비해서 상대적으로 천부에 존재하고 있는 것이 가장 큰 요인이며, 해저지각의 두께가 얇은 대신 지각의 밀도가 주변 대륙보다 높은 데도 기인한다.