• The Journal of Engineering Geology
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• v.6 no.2
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• pp.83-93
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• 1996

A method is proposed to estimate aquifer parameters in a heterogeneous and anisotropic aquifer under steady-state groundwater flow conditions on the basis of maximum likelihood concept. Zonation method is adopted for parameterization, and estimation errors are analyzed by examining the estimation error covariance matrix in the eigenspace. This study demonstrates the ability of the proposed model to estimate parameters and helps to understand the characteristics of the inverse problem. This study also explores various features of the inverse methodology by applying it to a set of field data of the Taegu area. In the field example, transmissivities were estimated under three different zonation patterns. Recharge rates in the Taegu area were also estimated using MODINV which is an inverse model compatible with MODFLOW.The estimation results indicate that anisotropy of aquifer parameters should be considered for the crystalline rock aquifer which is the dominant aquifer system in Korea.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.91-91
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• 2018

해안 및 도서지역의 경우 다양한 목적으로 지하수를 개발하게 된다. 이러한 지역은 내륙의 담수와 해안의 바닷물이 대수층에서 만나게 되는데, 비중차이에 의해 섞이지 않고 해수-담수 경계면을 가지는 일정한 형태를 유지하게 된다. 하지만, 담수영역에 위치한 지하수개발관정의 과잉양수와 해수면 상승 등으로 인해 해수침투 길이가 길어지게 되어 기존 해안지역 지하수개발관정이 해수로 오염되는 경우가 발생한다. 해수침투로 오염된 대수층의 경우 회복까지는 오랜 시간이 소요되어 취수원으로 사용이 어렵게 된다. 국내외에서는 해수침투저감 방법에 대한 다양한 연구가 진행되고 있다. 대표적 해수침투 저감방법으로는 해수양수로 내륙으로 침투하는 해수를 제거하거나 담수 주입으로 침투 하는 해수를 밀어내게 된다. 또는 지하 차수벽 설치로 해수침투를 조절하기도 한다. 이러한 해수침투 저감방법들은 장단점을 가지고 있어, 적용지역에 적절한 해수침투 방법을 선정하는 것이 중요하다. 하지만 기존 해수침투 저감 방법의 경우 공통적으로 해수양수, 담수 주입을 위한 동력조달 혹은 차수벽 설치비용과 같이 경제적인 측면에 대한 고려가 부족하였다. 본 연구에서는 조위를 이용한 무동력 해수침투 저감 방법을 실험을 통해 연구하였다. 본 연구에서 제안한 방법은 기존 해수침투 저감방법과 비교해서 설치 및 운영비측면에서 장점이 있을 것으로 예상된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.265-265
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• 2021

해수면 상승과 연안지역의 무분별한 지하수의 이용으로 해수침투는 가속화되고 있다. 해수면 상승과 지하수의 과잉 양수로 인한 연안지역의 대수층은 사용 가능한 담수 지하수자원이 줄어들고 있다. 연안지역의 대수층을 대상으로 해수 침투 영역에 미치는 영향에 대한 연구는 활발하게 진행되고 있다. GALDIT은 index & ranking 방법을 이용한 지하수자원의 해수침투에 대한 취약성 평가 방법으로 Geographic Information System (GIS)을 통해 주제도에 대한 중첩으로 평가 지수를 산정한다. 한국의 해수침투 취약성 평가에 대한 선행 연구 중 상당수는 제주도를 대상으로 많은 연구가 수행되었으며, GALDIT을 이용하여 해수침투에 대한 취약성 평가가 수행되었다. 본 연구에서는 내륙의 연안지역을 대상으로 GALDIT을 적용하였다. 한국의 서해안 지역 중 도심지가 밀집되어 있는 북쪽으로 선택하였다. 연구지역은 인천, 아산, 안산, 김포, 화성, 시흥, 평택, 당진, 오산으로 9개의 행정구역으로 구성되어 있다. 9개의 지역은 모두 제조업이 발달되어 도시화가 가속화되고 있으며, 지속적인 인구의 유입이 진행되고 있다. GALDIT은 지속가능한 해안지하수를 위한 수자원 계획을 뒷받침하는 평가 자료로 사용될 수 있으며, 국내 기후 및 공간 특성 매개변수를 고려한 가중치 및 평가 기준의 확대 등이 필요할 것으로 생각된다.

• Journal of Korea Spatial Information System Society
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• v.7 no.1 s.13
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• pp.13-24
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• 2005

Objects, which change their positions over time such as cars, are called moving objects. Trajectories of a moving object have large volumes because trajectories are accumulated. Efficient indexing techniques for searching these large volumes of trajectories are needed in the moving object databases. Especially the TB-tree which supports bundling trajectories is suitable for processing combined queries which have 2 steps: first step is selecting trajectories (range search), next is selecting the parts of each trajectory (trajectory search). But the TB-tree has unnecessary disk accesses cause of lack of spatial discrimination in range queries. In this paper, we propose and implement the splitting polity which can reduce dead spaces of non-leaf node in order to process range queries efficiently. The policy has better performance about range queries than the TB-tree as well as the advantages of the TB-tree, such as highly space utilization and efficient trajectory extraction. This paper shows that the newly proposed split policy has better performance in processing the range queries than that of the TB-tree by experimental evaluation.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.37 no.3
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• pp.31-40
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• 2000

A robust scheme of locating and counting the number of vehicles m urban traffic scenes, a core component of vision-based traffic monitoring systems, is presented The method is based on the evidential reasoning, where vehicle evidences m the background subtraction Image are obtained by a new locally optimum thresholding, and the evidences are merged by three heuristic rules using the geometric constraints The locally optimum thresholding guarantees the separation of bright and dark evidences of vehicles even when the vehicles are overlapped or when the vehicles have similar color to the background Experimental results on diverse traffic scenes show that the detection performance is very robust to the operating conditions such as the camera location and the weather The method may be applied even when vehicle movement is not observed since a static Image IS processed without the use of frame difference.

• Journal of KIISE:Databases
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• v.31 no.2
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• pp.150-162
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• 2004

Moving objects have characteristics that they change continuously their positions over time. The movement of moving objects should be stored on trajectories for processing past queries. Moving objects databases need to provide spatio-temporal index for handling moving objects queries like combined queries. Combined queries consist of a range query selecting trajectories within a specific range and a trajectory query extracting to parts of the whole trajectory. Access methods showing good performance in range queries have a shortcoming that the cost of processing trajectory Queries is high. On the other hand, trajectory-based index schemes like the TB-tree are not suitable for range queries because of high overlaps between index nodes. This paper proposes new TR(Trajectory Riving)-tree which is revised for efficiently processing the combined queries. This index scheme has several features like the trajectory preservation, the increase of the capacity of leaf nodes, and the logical trajectory riving in order to reduce dead space and high overlap between bounding boxes of nodes. In our Performance study, the number of node access for combined queries in TR-tree is about 25% less than the STR-tree and the TB-tree.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.1
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• pp.41-55
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• 2003

A dynamically-interfaced multi-grid finite difference model for simulation of tsunamis in the East Sea(Choi et al.) was established and further applied to produce detailed feature of coastal inundations along the whole eastern coast of Korea. The computational domain is composed of several sub-regions with different grid sizes connected in parallel of inclined directions with 16 innermost nested models. The innermost sub-region represents the coastal alignment reasonably well and has a grid size of about 30 meters. Numerical simulations have been performed in the framework of shallow-water equations(linear, as well as nonlinear) over the plane or spherical coordinate system, depending on the dimensions of the sub-region. Results of simulations show the general agreements with the observed data of run-up height for both tsunamis. The evolution of the distribution function of tsunami heights is studied numerically and it is shown that it tends to the log-normal curve for long distance from the source.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.157-162
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• 2011

In this paper, we propose enhanced methods of path finding based on an abstract graph with extension of search space to improve the quality of path. The proposed methods that are called simple buffering method, velocity constrained method and distance constrained method are to extract buffering-cells for using search space with valid-cells. The simple buffering method is to extract adjacent cells of valid-cells as buffering-cells. velocity constrained method and distance constrained method are based on simple buffering method, these eliminate buffering-cells through each of threshold. In experiment, proposed methods can improve the quality of path. The proposed methods are applicable to develop various kinds of telematics application, such as path finding and logistics.

• Education of Primary School Mathematics
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• v.19 no.1
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• pp.1-18
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• 2016

Patterns are of great significance to develop algebraic thinking of elementary students. This study analyzed teaching methods of patterns in current elementary mathematics textbook series in terms of three main activities related to pattern generalization (i.e., analyzing the structure of patterns, investigating the relationship between two variables, and reasoning and representing the generalized rules). The results of this study showed that such activities to analyze the structure of patterns are not explicitly considered in the textbooks, whereas those to explore the relationship between two variables in a pattern are emphasized throughout all grade levels using function table. The activities to reason and represent the generalized rules of patterns are dealt in a way both for lower grade students to use informal representations and for upper grade students to employ formal representations with expressions or symbols. The results of this study also illustrated that patterns in the textbooks are treated rather as a separate strand than as something connected to other content strands. This paper closes with several implications to teach patterns in a way to foster early algebraic thinking of elementary school students.

• Journal of Korea Water Resources Association
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• v.53 no.1
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• pp.1-13
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• 2020

The most common approach for computing engineering flow problems at high Reynolds number is still the Reynolds-averaged Navier-Stokes (RANS) computations based on turbulence models with wall functions. The recently developed generalized wall functions blending between the wall-limiting viscous and the outer logarithmic relations ensure a smooth transition of flow quantities across two regions. The performances and convergence properties of widely used turbulence models with wall functions that are applicable for turbulence kinetic energy (TKE), turbulent and specific dissipation rates, and eddy viscosity are presented through a series of near wall flow simulations. The present results show that RNG k-𝜖 model should be carefully applied with small tolerance to get the stable solution when the first grid lies in the buffer layer. The standard k-𝜖 and RNG k-𝜖 models are not sensitive to the selection of wall functions for both TKE and eddy viscosity, while the k-ω SST model should be applied together with kL-wall function for TKE and nutUB-wall functions for eddy viscosity to ensure accurate and stable boundary conditions. The applications to a backward-facing step flow at Re=155,000 reveal that the reattachment length is reasonably well predicted on appropriately refined mesh by all turbulence models, except the standard k-𝜖 model which about 13% underestimates the reattachment length regardless of the grid refinement.