• Title/Summary/Keyword: Curved boundaries

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Extraction and Modeling of Curved Building Boundaries from Airborne Lidar Data (항공라이다 데이터의 건물 곡선경계 추출 및 모델링)

  • Lee, Jeong Ho;Kim, Yong Il
    • Journal of Korean Society for Geospatial Information Science
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    • v.20 no.4
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    • pp.117-125
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    • 2012
  • Although many studies have been conducted to extract buildings from airborne lidar data, most of them assume that all the boundaries of a building are straight line segments. This makes it difficult to model building boundaries containing curved segments correctly. This paper aims to model buildings containing curved segments as combination of straight lines and arcs. First, two sets of boundary points are extracted by adaptive convex hull algorithm and local convex hull algorithm with a larger radius. Then, arc segments are determined by average spacing of boundary points and intersection ratio of perpendicular lines. Finally, building boundary is modeled through regularization of least squares line or circle fitting. The experimental results showed that the proposed method can model the curved building boundaries as arc segments correctly by completeness of 69% and correctness of 100%. The approach will be utilized effectively to create automatically digital map that meets the conditions of the Korean digital mapping.

탄성학 문제의 경계적분방정식에서 초특이해 커널의 해법

  • 윤승원
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.04a
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    • pp.573-577
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    • 1995
  • An integration method for the hypersingular kernels, in the boundary integralequations used for the solution of crack-like problems in elasticity, has been developed. To isolate the stronger singularities, the actual boundaries are replaced by the smoothly curved auxiliary boundaries which provide the detoured, non-singular integration paths. The auxiliary boundary can be interpreted as a contracted form of the actual boundaries except for the singular element where the collocating point is located. For an optimal integration path for every singular collocation point, the auxiliary boundary may have different shape depending on the position of the collocation point on the singular element.

Generalized curved beam on elastic foundation solved by transfer matrix method

  • Arici, Marcello;Granata, Michele Fabio
    • Structural Engineering and Mechanics
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    • v.40 no.2
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    • pp.279-295
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    • 2011
  • A solution of space curved bars with generalized Winkler soil found by means of Transfer Matrix Method is presented. Distributed, concentrated loads and imposed strains are applied to the beam as well as rigid or elastic boundaries are considered at the ends. The proposed approach gives the analytical and numerical exact solution for circular beams and rings, loaded in the plane or perpendicular to it. A well-approximated solution can be found for general space curved bars with complex geometry. Elastic foundation is characterized by six parameters of stiffness in different directions: three for rectilinear springs and three for rotational springs. The beam has axial, shear, bending and torsional stiffness. Numerical examples are given in order to solve practical cases of straight and curved foundations. The presented method can be applied to a wide range of problems, including the study of tanks, shells and complex foundation systems. The particular case of box girder distortion can also be studied through the beam on elastic foundation (BEF) analogy.

A Study on the Two-Dimensional Automatic Mesh Generation Programming (2차원 자동요소분할 프로그램 개발에 관한 연구)

  • Jo, Myeong-Cheol;Yu, Hyeong-Seon
    • Journal of the Korean Society for Precision Engineering
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    • v.9 no.2
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    • pp.44-51
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    • 1992
  • This paper is concerned with the propram of the automatic mesh generation for 2-dimensional domain which contains the curved boundaries and holes. This program treats a new vertical-line drawing method. This method starts with 4-subdivisions of problem domain and the classification of the cross points of grid lines and boundaries. The new node is generated by the vertical line to the line connecting the two intersections of a boundary and two grid lines in gereral. And the node very close to the boundary is moved to the boundary. The automatic mesh generation composed of only rectangular elements is achieved by this procedure. The boundaries are piecewise-curves composed of lines, circles, arcs, and free curves. The free curves are generated by B-Spline form. Although there were some bad elements for the complex boundary, it was possible to obtain the acceptible rectangular elements for the given boundaries.

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A study on the two-dimensional automatic mesh generation programming (2차원 자동요소분할 프로그램 개발에 관한 연구)

  • 조명철;유형선
    • 제어로봇시스템학회:학술대회논문집
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    • 1991.10a
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    • pp.720-725
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    • 1991
  • This paper is concerned with the program of the automatic mesh generation for 2-dimensional domain which contains the curved boundaries and holes. This program treats a new vertical - line drawing method. This method starts with 4-subdivisions of problem domain and the classification of the cross points of grid lines and boundaries. And the new node is generated by the vertical line to the line connecting the two intersections of a boundary and two grid lines in general. The boundaries are piecewise-curves composed of lines, circles, arcs, and free curves. The free curves are generated by B-Spline form. Although there were some bad elements for the complex boundary, it was possible to obtain the acceptable elements for the given boundaries. The results of automatic mesh generation can be verified directly by drawing on the computer monitor in executing the program. And it is possible to add the processes - that is, editing, hard copying, etc - using the script file in Auto-CAD.

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Numerical Simulation of Stress Waves in Plates with Material Interfaces (물질경계면을 갖는 판에서의 응력파에 대한 수치해석)

  • Kyung-Su Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.32 no.4
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    • pp.114-122
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    • 1995
  • In this paper a computational method is presented to solve the plane problem of wave propagation in linear-elastic plate with zones of different materials. An existing numerical scheme of bicharacteristics for rectangular plate is extended to plates with curvilinear boundaries. In order to show the validity of the employed concept, it is necessary to examine the numerical results whether they reproduce the well-known physical phenomena of stress waves. It seems also desirable to make a comparison between the numerical results and appropriate experimental results for plates with curvilinear boundaries. Also studied are the focusing phenomena induced by reflection and refraction at curved outer boundaries and material interfaces.

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Preparation of Yttria-stabilized Zirconia with Irregular Grain Shapes by Ceria Doping (CeO$_2$ 도핑에 의한 불규칙 입자형상의 이트리아 안정화 지르코니아 제조)

  • Lee, Jong-Kook;Kang, Hyun-Hee;Kim, Young-J.;Kim, Hwan
    • Journal of the Korean Ceramic Society
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    • v.35 no.12
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    • pp.1294-1300
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    • 1998
  • Yttria-stabilized zirconia ceramics with irregular grain shapes and curved grain boundaries was prepared by ceria doping. The amount of ceria doped into zirconia compacts by a dipping method were at range of 2 to 20 mol% Irregular grain shapes and curved grain boundaries were formed only inspecimens doped with more than 8mol% cerial. Ceria-doped specimens showed large grain size and low sintered density compared with pure yttria-stabilized zirconia which was due to the increase in the contents of stabilizer and cubic phase. The amount of doped ceria was larger on the surface than the inside regions and therefore mi-crostructure and phase on the surface were different from those in the inside regions. Transgranular frac-ture mode was observed ion ceria doped specimens due to irregular large grain sizes.

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2D Finite Element Modeling of Bed Elevation Change in a Curved Channel (유한요소법을 이용한 만곡수로에서의 2차원 하상변동 수치모형)

  • Kim Tae Beom;Choi Sung-Uk;Min Kyung Duck
    • Proceedings of the Korea Water Resources Association Conference
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    • 2005.05b
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    • pp.414-418
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    • 2005
  • A finite element model is developed for the numerical simulation of bed elevation change in a curved channel. The SU/PG (Streamline-Upwind/Petrov-Galerkin) method is used to solve 2D shallow water equations and the BG (Bubnov-Galerkin) method is used for the Exner equation. For the time derivative terms, the Crank-Nicolson scheme is used. The developed model is a decoupled model in a sense that the bed elevation does not change simultaneously with the flow during the computational time step. The total load formula with is used for the sediment transport model. The slip conditions are described along the lateral boundaries. The effects of gravity force due to geometry change and the secondary flows in a curved channel are considered in the model. For the verification, the model is applied to two laboratory experiments. The first is $140^{\circ}$ bended channel data at Delft Hydraulics Laboratory and the second is $140^{\circ}$ bended channel data at Laboratory of Fluid Mechanics of the Delft University of Technology. The finite element grid is constructed with linear quadrilateral elements. It is found that the computed results are in good agreement with measured data, showing a point bar at the inner bank and a pool at the outer bank.

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PRECONDITIONED SPECTRAL COLLOCATION METHOD ON CURVED ELEMENT DOMAINS USING THE GORDON-HALL TRANSFORMATION

  • Kim, Sang Dong;Hessari, Peyman;Shin, Byeong-Chun
    • Bulletin of the Korean Mathematical Society
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    • v.51 no.2
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    • pp.595-612
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    • 2014
  • The spectral collocation method for a second order elliptic boundary value problem on a domain ${\Omega}$ with curved boundaries is studied using the Gordon and Hall transformation which enables us to have a transformed elliptic problem and a square domain S = [0, h] ${\times}$ [0, h], h > 0. The preconditioned system of the spectral collocation approximation based on Legendre-Gauss-Lobatto points by the matrix based on piecewise bilinear finite element discretizations is shown to have the high order accuracy of convergence and the efficiency of the finite element preconditioner.

Depth contours appeared on SAR images by interactions between tidal current and bottom topography

  • Kim, Tae-Rim
    • Proceedings of the KSRS Conference
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    • v.2
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    • pp.692-694
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    • 2006
  • X-SAR images taken on the coastal waters of Hwanghe province in Korea during SIR-C/X-SAR campaign in April and October 1994 are analysed. The SAR images show the peculiar signatures like nail marks, curved long string, and vortex streets patterns and they all seem to be produced by strong interactions between the topography in the coastal waters and tidal currents. The nail mark signatures are located at the same position of small scaled sand banks and the curved line patterns are almost identical to the outer boundary of large sand banks. Based on the tidal record, all the three images are taken at the almost same phase of tidal cycles, which are close to the low tide. It seems that bottom shapes are more strongly appeared on the SAR images when the tidal currents are slow. The front between two different current velocities caused by the flows along the steep boundaries of sandbanks is also the main factors imprinting the bottom features to the sea surface SAR images

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