• Title/Summary/Keyword: approximate model

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Road Detection in the Spaceborne Synthetic Aperture Radar Images (위성 탑재 합성개구 레이더 영상에서의 도로 검출)

  • Chun, Sung-Min;Hong, Ki-Sang
    • Journal of the Korean Institute of Telematics and Electronics S
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    • v.35S no.11
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    • pp.123-132
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    • 1998
  • This paper presents a road detection technique for spaceborne synthetic aperture radar (SAR) images. Roads are important cartographic features. We incorporate an active contour model called snake as a model for the road and define a new external energy for snake which is appropriate for the road. Detecting roads in spaceborne SAR images is very difficult without other information. In this paper, digital maps are utilized to obtain the initial position and shape for snake. Only approximate geodetic location of roads appearing in SAR images can be known through geocoding process and usual digital maps also have location errors. Therefore, there exist large location offsets between the two data. By introducing initial matching procedure, the errors are reduced significantly. Then we initialize the snake's shape using the roads extracted from digital map and minimize the energies of all snake points to detect roads. We outline two problems in detection and propose a method that mitigates them.

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Face Tracking and Recognition on the arbitrary person using Nonliner Manifolds (비선형적 매니폴드를 이용한 임의 얼굴에 대한 얼굴 추적 및 인식)

  • Ju, Myung-Ho;Kang, Hang-Bong
    • 한국HCI학회:학술대회논문집
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    • 2008.02a
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    • pp.342-347
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    • 2008
  • Face tracking and recognition are difficult problems because the face is a non-rigid object. If the system tries to track or recognize the unknown face continuously, it can be more hard problems. In this paper, we propose the method to track and to recognize the face of the unknown person on video sequences using linear combination of nonlinear manifold models that is constructed in the system. The arbitrary input face has different similarities with different persons in system according to its shape or pose. Do we can approximate the new nonlinear manifold model for the input face by estimating the similarities with other faces statistically. The approximated model is updated at each frame for the input face. Our experimental results show that the proposed method is efficient to track and recognize for the arbitrary person.

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Nonlinear Fracture Analysis of Concrete Structures Based on Stress-Strain Relation (응력(應力)-변형도관계(變形度關係)를 이용(利用)한 콘크리트 구조(構造)의 비선형파괴해석(非線型破壞解析))

  • Oh, Byung Hwan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.4 no.4
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    • pp.1-11
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    • 1984
  • Developed is a nonlinear fracture theory which can model the complex fracture behavior of concrete. This theory is based on the nonlinear behavior due to progressive microcracking and strain-softening in the fracture process zone of concrete cracks. The simplified realistic fracture model which preserves the same fracture energy for the different fracture process zone widths is also derived. By modeling fracture through stress-strain behavior, the effect of compressive stresses parallel to the crack plane can be easily taken into account. The comparisons of the present theory with valuable fracture test data available in the literature show good agreements, and the existing linear theory exhibits in many cases large deviations from the actual test results. A simple approximate formula for the fracture energy of concrete which should, be necessary for the fracture analysis of concrete structures is derived. Finally, the application of fracture theory to reinforced concrete and the necessity of further research are discussed.

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Flow Visualization and Unstructured Grid Computation of Flow over a High-Speed Projectile (고속탄자 유동의 가시화 실험 및 비정렬격자 계산)

  • 이상길;최서원;강준구;임홍규;백영호;김두연;강호철
    • Transactions of the Korean Society of Automotive Engineers
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    • v.6 no.2
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    • pp.12-20
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    • 1998
  • Exter ballistics of a typical high-speed projectile is studied through a flow-visualization experiment and an unstructured grid Navier-Srokes computation. Experiment produced a schlieren photograph that adequately shows the characteristic features of this complex flow, namely two kinds of oblique cone shocks and turbulent wake developing into the downstream. A hybrid scheme of finite volume-element method is used to simulate the compressible Reynolds-Averaged Navier-Stok- es solution on unstructured grids. Osher's approximate Riemann solver is used to discretize the cinvection term. Higher-order spatial accuracy is obtained by MUSCL extension and van Albada ty- pe flux limiter is used to stabilize the numerical oscillation near the solution discontinuity. Accurate Gakerkin method is used to discretize the viscous term. Explict fourth-order Runge-Kutta method is used for the time-stepping, which simplifies the application of MUSCL extension. A two-layer k-$\varepsilon$ turbulence model is used to simulate the turbulent wakes accurately. Axisymmetric folw and two-dimensional flow with an angle of attack have been computed. Grid-dependency is also checked by carrying out the computation with doubled meshes. 2-D calculation shows that effect of angle of attack on the flow field is negligible. Axi-symmetric results of the computation agrees well with the flow visualization. Primary oblique shock is represented within 2-3 meshes in numerical results, and the varicose mode of the vortex shedding is clearly captured in the turbulent wake region.

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Analysis of 1D and 2D Flows in Open-Channel with FDM and FVM (유한차분법과 유한체적법을 이용한 1차원과 2차원 개수로 흐름해석)

  • Kim, Man Sik;Lee, Jin Hee;Jeong, Chan;Park, Roh Hyuk
    • Journal of Wetlands Research
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    • v.10 no.2
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    • pp.67-79
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    • 2008
  • The one-dimensional (1D) finite-difference method (FDM) with Abbott-Ionescu scheme and the two-dimensional (2D) finite-volume method (FVM) with an approximate Riemann solver (Osher scheme) for unsteady flow calculation in river are described. The two models have been applied to several problems including flow in a straight channel, flow in a slightly meandering channel and a flow in a meandering channel. The uniform rectangular channel was employed for the purpose of comparing results. A comparison is made between the results of computation on 1D and 2D flows including straight channel, slightly meandering channel and meandering channel application. The implementation of the finite-volume method allows complex boundary geometry represented. Agreement between FVM and FDM results regarding the discharge and stage is considered very satisfactory in straight channel application. It was concluded that a 1D analysis is sufficient if the channel is prismatic and remains straight. For curved (meandering) channels, a 2D or 3D model must be used in order to model the flow accurately.

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Analysis for Breakdown Voltage of Double Gate MOSFET according to Device Parameters (소자파라미터에 따른 DGMOSFET의 항복전압분석)

  • Jung, Hakkee
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.17 no.2
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    • pp.372-377
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    • 2013
  • This paper have presented the breakdown voltage for double gate(DG) MOSFET. The analytical solution of Poisson's equation and Fulop's breakdown condition have been used to analyze for breakdown voltage. The double gate(DG) MOSFET has the advantage to reduce the short channel effects as improving the current controllability of gate. But we need the study for the breakdown voltage of DGMOSFET since the decrease of the breakdown voltage is unavoidable. To approximate with experimental values, we have used the Gaussian function as charge distribution for Poisson's equation, and the change of breakdown voltage has been observed for device geometry. Since this potential model has been verified in the previous papers, we have used this model to analyze the breakdown voltage. As a result to observe the breakdown voltage, the smaller channel length and the higher doping concentration become, the smaller the breakdown voltage becomes. Also we have observed the change of the breakdown voltage for gate oxide thickness and channel thickness.

Comparison of Seepage Quantity Calculated by Experiments and Finite Element Method (실험(實驗)과 FEM기법(技法)을 사용(使用)하여 구(求)한 침투유량(浸透流量)의 비교(比較))

  • Jin, Byung Ik;Kim, Jae Hong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.5 no.2
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    • pp.83-90
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    • 1985
  • The thesis is established on the basis of model tests on the central core dam. With variations in the upstream water level, the quantity of seepage in the downstream boundaries were obtained for each specific water level. Seepage alignment and equipotential lines to these occasions were also researched and measured. By making use of the resulting data from the experiment, the flow velocities and seepage quantity computed to the flow rate of each element of flownets by the Finite Element Method was compared with the values produced by experiments and approximate theoretical formula. Further to this, transitions of water level related thereto was also examined in the thesis. During the high water level, seepages shown by the experiment were larger than that of the F.E.M. Meanwhile, the in-between differences were found to be quite small during the low water level. In the flow rate of each element with which the flow-nets are constructed, flow velocities of the X and Z axis were faster on account of the variations in water level. Flow velocities of the Y axis were extremely small enough to be disregarded.

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Generation Method of the Rectangular Grid Information for Finite Difference Model (유한차분모형을 위한 직사각형 격자정보 생성기법)

  • 정신택;조범준;김정대
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.15 no.3
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    • pp.190-195
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    • 2003
  • For many coastal problems, such as wave transformation, tidal circulation, sediment transports and diffusion phenomena, we resort to numerical techniques. The representative numerical techniques are the method of finite differences and finite elements. The approximate algebraic equations, referred to as finite difference equations(FDEs), are subsequently solved at discrete grid points within the domain of interests. Therefore, a set of grid points within the domain, as well as the boundaries of the domain, must be specified. The generation of grids for FDEs, with uniform spacing, is very simple compared to that of finite elements. However, within a very complex domain, there are few grid generation tools we can use conveniently. Unfortunately, most of the commercial grid generation programs are developed only for finite element method. In this paper, grid generation method using digitizer, with uniform rectangular spacing, are introduced in detail. Didger and Surfer programs by Golden Software are necessary to produce comparatively accurate and simple depth data.

Weighted Averaged Flux Method for Computation of Shallow Water Equations (WAF 기법을 이용한 천수방정식 해석)

  • Kim, Woo-Gu;Jung, Kwan-Sue;Kim, Jae-Han
    • Journal of Korea Water Resources Association
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    • v.36 no.5
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    • pp.777-785
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    • 2003
  • A numerical model for the solution of two-dimensional free surface flow is developed on unstructured grid. By using fractional step method, the two-dimensional shallow water equations (SWE) are treated as two one-dimensional problems. Thus, it is possible to simulate computational hydraulic problems with higher computational efficiency. The one-dimensional problems are solved using upwind TVD version of second-order Weighted Averaged Flux (WAF) scheme with HLLC approximate Riemann solver. The numerical oscillations which are common with second-order numerical scheme are controlled by exploiting WAF flux limiter, Some idealized test problems are solved using this model and very accurate and stable solutions are obtained. It can be concluded as an efficient implement for the computation of SWE including dam break problems that concerning discontinuities, subcritical and supercritical flows and complex domain.

Optimization Technique using Ideal Target Model and Database in SRS

  • Oh, Seung-Jong;Suh, Tae-Suk;Song, Ju-Young;Choe, Bo-Young;Lee, Hyoung-Koo
    • Proceedings of the Korean Society of Medical Physics Conference
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    • 2002.09a
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    • pp.146-149
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    • 2002
  • The aim of stereotactic radiosurgery(SRS) is to deliver a high dose to a target region and a low dose to critical organ through only one or a few irradiation. To satisfy this aim, optimized irradiating conditions must be searched in the planning. Thus, many mathematical methods such as gradient method, simulated annealing and genetic algorithm had been proposed to find out the conditions automatically. There were some limitations using these methods: the long calculation time, and the difficulty of unique solution due to the different shape of tumor. In this study, optimization protocol using ideal models and data base was proposed. Proposed optimization protocol constitutes two steps. First step was a preliminary work. Some possible ideal geometry shapes, such as sphere, cylinder, cone shape or the combination, were assumed to approximate the real tumor shapes. Optimum variables such as isocenter position or collimator size, were determined so that the high dose region could be shaped to fit ideal models with the arrangement of multiple isocenter. Data base were formed with those results. Second, any shaped real targets were approximated to these models using geometry comparison. Then, optimum variables for ideal geometry were chosen from the data base predetermined, and final parameters were obtained by adjusting these data. Although the results of applying the data base to patients were not superior to the result of optimization in each case, it can be acceptable as a starting point of plan.

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