• Journal of Soil and Groundwater Environment
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• v.11 no.1
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• pp.37-44
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• 2006

This study summarizes advantages and disadvantages of numerical methods and compares ELLAM and LEZOOMPC to develop an efficient numerical modeling technique on contaminant transport. Eulerian-Lagrangian method and Eulerian method are commonly used numerical techniques. However Eulerian-Lagrangian method does not conserve mass globally and fails to treat boundary in a straightforward manner. Also, Eulerian method has restrictions on the size of Courant number and mesh Peclet number because of time truncation error. ELLAM (Eulerian Lagrangian Localized Adjoint Method) which has been popularly used for past 10 years in numerical modeling, is known for overcoming these numerical problems of Eulerian-Lagrangian method and Eulerian method. However, this study investigates advantages and disadvantages of ELLAM and suggests a change for the better. To figure out the disadvantages of ELLAM, the results of ELLAM, LEZOOMPC (Lagrangian-Eulerian ZOOMing Peak and valley Capturing), and visual MODFLOW are compared for four examples having different mesh Peclet numbers. The result of ELLAM generates numerical oscillation at infinite of mesh Peclet number, but that of LEZOOMPC yields accurate simulations. The simulation results suggest that the numerical error of ELLAM could be alleviated by adopting some schemes in LEZOOMPC. In other words, the numerical model which combines ELLAM with backward particle tracking, forward particle tracking, adaptively local zooming, and peak/valley capturing of LEZOOMPC can be developed for not only overcoming the numerical error of ELLAM, but also keeping the numerical advantage of ELLAM.

• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.212-224
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• 1994

A numerical method has been developed for studying the dynamics of a flexible cylinder in a coaxial cylindrical duct, immersed in inviscid flow. The unsteady inviscid fluid-dynamic force acting on the oscillating cylinder has been estimated more rigorously by means of a spectral collocation method without simplification of governing equations. This numerical approach is applicable to the system haying wider annular gap and/or shorter length of cylinder as compared to existing potential theory. The governing equation of the unsteady flow was obtained from Laplace equation. The equation of cylinder motion coupled with the fluid motion was discretized by Galerkin's method, from which the dynamic behaviour of the system has been evaluated. The effect of the length of the cylinder and the annular gap on the critical flour velocity, where the system loses stability by buckling, was investigated. To validate the numerical method, the potential flow theory developed by Hobson based on thin film approximation has been improved. Typical results of the present numerical theory on the dynamics and stability of the system are compared with those of available existing theory and the present approximate results. Good agreement was found between the results. It was also found that a nondimensional critical flow velocity becomes larger as increasing the annular gap and decreasing the length of cylinder.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.2
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• pp.281-288
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• 2009

In the paper, we try to develop the methodology for updating road networks of large-scale digital maps by using construction drawing data. For the purpose, it is pre-requite step to merge road networks detached in CAD drawing data. As such, tie points are identified in neighboring drawings and used for solving the parameters of 2D conformal transformation between drawings. Then, the merged road network in CAD data is transformed to the coordinate system of digital maps. In the process, IPs in the drawings are considered as control information and 2D affine transformation is selected for coordinate transformation. Through the experiments with real dataset, we can identify that the developed method is valid and generally applicable.

• Journal for History of Mathematics
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• v.18 no.4
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• pp.49-66
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• 2005

Finite element Methods(FEM) have been the primary computational methodologies in science and engineering computations for more than half centuries. One of the main limitations of the finite element approximations is that they need mesh which is an artificial constraint, and they need remeshing to solve in some special problems. The advantages in meshfree Methods is to develop meshfree interpolant schemes that only depends on particles, so they relieve the burden of remeshing and successive mesh generation. In this paper we describe the development of meshfree particle Methods and introduce the numerical schemes for Smoothed Particle hydrodynamics, meshfree Galerkin Methods and meshfree point collocation mehtods. We discusse the advantages and the shortcomings of these Methods, also we verify the applicability and efficiency of Meshfree Particle Methods.

• Journal of the Korean Geotechnical Society
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• v.38 no.8
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• pp.67-74
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• 2022

The setting of the target area for ground stability evaluation during ground excavation is categorized into theoretical and empirical estimation methods and numerical analysis methods. Generally, the applied theoretical and empirical estimation methods include those by Peck (1969), Caspe (1966), and Clough et al. (1990). The numerical analysis method comprehensively considered the current status of the task section (maximum excavation depth section, ground condition vulnerable section, etc.). It reflected the results of performing two and three-dimensional numerical analyses on the weakest section. Therefore, this study shows an example of setting the scope of influence when excavating the vertical and tunnel sections of a 000-line double-track private investment project through the above theoretical, empirical, and numerical analysis methods.

• Korean Journal of Remote Sensing
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• v.14 no.3
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• pp.250-261
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• 1998

The purpose of this paper is to extract fast DEM (Digital Elevation Model) using satellite images. DEM extraction consists of three parts. First part is the modeling of satellite position and attitude, second part is the matching of two images to find corresponding points of them and third part is to calculate the elevation of each point by using the results of the first and second part. The position and attitude modeling of satellite is processed by using GCPs. A area based matching method is used to find corresponding points between the stereo satellite images. The elevation of each point is calculated using the exterior orientation parameters obtained from modeling and conjugate points from matching. In the DEM generation system, matching procedure holds most of a processing time, therefore to reduce the time for matching, a new fast matching algorithm using gradient correlation and fast similarity measure calculation method is proposed. In this paper, the SPOT satellite images, level 1A 6000$\times$6000 panchromatic images are used to extract DEM. The experiment result shows the possibility of fast DEM extraction with the satellite images.

• Journal of Korean Society for Geospatial Information Science
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• v.18 no.2
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• pp.131-138
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• 2010

To manage the architecture information of Seoul, aerial photographs have been taken and Photographic Interpretation Status Maps(PISP) have been produced through interpretation process. However PISP of SEOUL has a number of errors and difficulties to update maps, owing to its analogue formation by hand skill. In this study, some digitizing methods are tested to make Digital Photographic Interpretation Status Maps(DPISP). The digitizing methods by scanning maps, using ortho-images and true ortho-images, digital correction plotting process, and LiDAR techniques were used for comparative analysis of PISP. As a result of this study, the author suggest DPISP by the digital correction plotting method is proper for economical efficiency and its accuracy of the architecture information.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.2
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• pp.141-147
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• 1995

Various numerical models for predicting wave deformation have been proposed. Among them a time-dependent mild-slope equation based on the line discharges and surface-elevation changes has been widely used in the wave fields with reflective waves. If applying this model to the case of obliquely-incident waves, not only the open-sea boundary but also one of the lateral boundaries should be treated as incident boundaries. In this study, Maruyama and Kajima (1985), Copeland (1985) and Ohnaka and Watanabe (1987)'s method are reviewed and the characteristics of these methods are analyzed using e normalized wave heights, wave angels and phases obtained from the numerical experiments. It is shown that Ohnaka and Watanabe(1987)'s method provides the most adequate driving boundary is the most suitable in e wave field with a general bottom slope.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.1
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• pp.75-82
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• 1999

일반 해양 구조물이나 해저면에 설치되는 해저 관로는 외력에 의한 변형이 발생된다. 구조물 형상이 복잡하거나, 구성 요소의 개수가 많을 경우 응력해석 시 많은 초기값이 필요하고 해석 시간 또는 장 시간 소요된다. 해양 구조물에 작용하는 대표적인 외력은 파도, 조류, 바람이고 이런 외력은 구조물의 사용 기간(operation life)동안 계속적으로 작용하기 때문에 구조물의 변형율은 항상 허용치 안에서 발생되도록 설계되어야 한다. 허용 변형은 탄성범위 내에 존재해야 하며, 비교적 큰 변형을 일으키는 구조물이나 해저파이프라인의 응력해석을 수치적으로 접근하는 방법을 고찰하였다. 평행상태의 하중 벡터값만 직각 좌표계에서 인트린직(intrinsic) 좌료로 변환시킬 때 변형이 발생함으로, 본 논문에서 소개하는 이차 요소(quadratic element)방법을 사용할 경우 수치해석 시 많은 장점이 있다는 것을 보여준다. 본 방법을 도입함으로써 비교적 큰 변형이 발생되는 구조물 해석 시 일반 수치해석 방법과 그 결과는 같으나 해석 시간을 단축시킬 수 있다는 장점이 있다. 응력 해석 시 국부 강도 행열(element stiffness matrix)은 방향과 무관하며 이차요소 방법을 사용하여 각 요소 벡터를 발생시켰다. 해저관로 일점 상승 시 관로에 작용하는 변형과 상승력에 따른 휨 모멘트를 산출하여 일반적으로 사용되는 선형이론과 비교하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.187-190
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• 2010

기초세굴에 따른 교각에서의 1차 모드 고유진동수 변화를 이용하여 교량 세굴 건전성을 정량적으로 평가하기 위하여 공용중인 광탄1교의 T형 교각 1기에 대하여 충격진동실험을 수행하였으며, 교축직각방향의 1차 모드 고유진동수를 수치해석결과와 비교하였다. 교량 상부구조물의 모델링 방법에 따라 상부구조물을 전체 모델링한 방법과 교각만을 모델링하고 상부구조물의 영향범위를 가정하여 교량받침 위치에 질점질량으로 변환하여 적용한 방법으로 구분하여 수치해석을 수행하였다. 상부구조물을 전체 모델링한 경우와 집중하중 형태로 상부구조물을 모델링한 경우 모두 고유진동수는 충격진동실험결과와 큰 차이를 보였다. 충격진동실험을 통해 얻은 고유진동수는 교각의 국부적인 진동수로 사료되는 반면, 수치해석을 통해 구한 결과는 교량 상부와 하부의 Coupling 효과가 반영된 시스템 전체의 고유진동수이기 때문에 결과의 큰 편차가 생기는 것으로 판단된다. 따라서 충격진동실험에서 구한 고유치 양상을 올바로 구현하기 위한 모델링을 찾기 위해서는 새로운 접근 방법이 필요할 것으로 사료된다.