• Journal of Power Electronics
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• 제11권5호
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• pp.688-696
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• 2011

This paper proposes a simple space vector PWM (SVPWM) scheme including overmodulation operation for 3-level NPC (Neutral Point Clamped) Inverters. The proposed scheme features a simple decision and calculation procedure for determining switching times in the overmodulation range by utilizing the duty calculation method used in 2-level inverters and the minimum phase error projection method widely employed in motor drive systems. The proposed scheme does not need to detect the angle of the reference vector or calculate trigonometric functions to determine the magnitude of the voltage vector. The magnitude of the angle of the new reference voltage vector is decided in advance with the help of the Fourier Series Expansion to extend the linearity of the output voltage of 3-level inverters in the overmodulation region. Experimental results demonstrate the validity of the proposed SVPWM scheme including overmodulation operation for 3-level NPC inverters.

• 한국지능시스템학회논문지
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• 제19권5호
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• pp.648-654
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• 2009

본 논문에서는 얼굴을 인식하기 위한 쌍대각 2차원 LDA를 제안하였다. 기존의 Dia2DPCA와 Dia2DLDA가 대각 방향 영상들의 행 변화량과 열 변화량 사이의 상관을 제한하기 위하여 제안되어지고 있다. 그러나 이러한 방법들은 영상들의 행방향으로 동작한다. 제한 방법에 있어서 행방향의 투영 행렬은 기존 방법과 전혀 다르게 대각 방향 얼굴 영상들의 열 변화량을 고려한 클래스 간의 공분산 행렬과 클래스 내의 공분산 행렬을 이용함으로써 얻어진다. 그리고 열방향의 투영 행렬은 대각방향 얼굴 영상들의 행 변화량을 고려한 클래스 간의 공분산 행렬과 클래스 내의 공분산 행렬을 이용함으로써 얻어진다. 좌우 양측의 투영 방법은 투영 행렬들을 좌우로 곱함으로써 적용된다. 그 결과로 특징 행렬의 차원과 계산 시간이 감소된다. ORL 얼굴 데이터베이스에서 수행된 실험들은 Frobenius, Yang, AMD와 같은 3가지 거리 척도를 사용하여 2DPCA, B2DPCA, 2DLDA 등과 같은 다른 얼굴 인식 방법들보다 제안된 방법의 인식률이 높음을 보여준다.

• 한국산업융합학회 논문집
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• 제17권2호
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• pp.54-60
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• 2014

The equipment of SCARA robot in processing and assembly lines has rapidly increased. In order to achieve high productivity and flexibility, it becomes very important to develop the visual feedback control system with Off-Line Programming System(OLPS). We can save much efforts and time in adjusting robots to newly defined workcells by using OLPS. A proposed visual calibration scheme is based on position-based visual feedback. The calibration program firstly generates predicted images of objects in an assumed end-effector position. The process to generate predicted images consists of projection to screen-coordinates, visible range test, and construction of simple silhouette figures. Then, camera images acquired are compared with predicted ones for updating position and orientation data. Computation of error is very simple because the scheme is based on perspective projection, which can be also expanded to experimental results. Computation time can be extremely reduced because the proposed method does not requirethe precise calculation of tree-dimensional object data and image Jacobian.

• Wind and Structures
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• 제12권1호
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• pp.1-19
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• 2009

In this paper, the airflow around an ideal thin plate (hereafter referred to as ITP) with various ratios of central slot is simulated by using the finite-difference-method (FDM)-based Arbitrary-Lagrangian-Eulerian descriptions for the rigid oscillating body. The numerical procedure employs the second-order projection scheme to decouple the governing equations, and the multigrid algorithm with three levels to improve the computational efficiency in evaluating of the pressure equation. The present CFD method is validated through comparing the computed flutter derivatives of the ITP without slot to Theodorsen analytical solutions. Then, the unsteady aerodynamics of the ITP with and without central slot is investigated. It is found that even a smaller ratio of central slot of the ITP has notable effects on pressure distributions of the downstream section, and the pressure distributions on the downstream section will further be significantly affected by the slot ratio and the reduced wind speeds. Continuous increase of $A_2^*$ with the increase of central slot may be the key feature of the slotted ITP. Finally, flutter analyses based on the flutter derivatives of the slotted ITP are performed, and moreover, flutter instabilities of a scaled sectional model of a twin-deck bridge with various ratios of deck slot are investigated. The results confirm that the central slot is effective to improve bridge flutter stabilities, and that the flutter critical wind speeds increase with the increase of slot ratio.

• 대한기계학회논문집A
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• 제23권7호
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• pp.1129-1138
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• 1999

[$Moir\acute{e}$] technique is now being extensively investigated as a fast non-contact means of three-dimensional profile measurement especially for reverse engineering. One problem with $moir\acute{e}$ technique is so called $2\pi$-ambiguity problem that limits the maximum step height difference between two neighboring sampling points to be less than half the equivalent wavelength of $moir\acute{e}$ fringes. In this investigation, a new two-wavelength scheme of projection $moir\acute{e}$ topography is proposed and tested to cope with the $2\pi$-ambiguity problem. Experimental results are discussed to assess the new method in measuring large objects with high step discontinuities.

• 전기학회논문지P
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• 제66권3호
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• pp.129-134
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• 2017

We investigated theoretically the quantum optical transition properties of Si, in quasi 2-Dimensinal Landau splitting system, based on quantum transport theory. We apply the quantum transport theory (QTR) to the system in the confinement of electrons by square well confinement potential under linearly polarized oscillating field. We use the projected Liouville equation method with Equilibrium Average Projection Scheme (EAPS). In order to analyze the quantum transition, we compare the temperature and the magnetic field dependencies of the QTLW and the QTLS on four transition processes, namely, the intra-leval transition process, the inter-leval transition process, the phonon emission transition process and the phonon absorption transition process.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제9권2호
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• pp.55-64
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• 2005

In this paper, generalized difference methods(GDM) for one-dimensional viscoelastic problems are proposed and analyzed. The new initial values are given in the generalized difference scheme, so we obtain optimal error estimates in $L^p$ and $W^{1,p}(2\;{\leq}\;p\;{\leq}\;{\infty})$ as well as some superconvergence estimates in $W^{1,p}(2\;{\leq}\;p\;{\leq}\;{\infty})$ between the GDM solution and the generalized Ritz-Volterra projection of the exact solution.

• 한국멀티미디어학회논문지
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• 제16권9호
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• pp.1044-1056
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• 2013

본 논문에서는 피부 색소 침착 영역을 검출하고 침착 정도를 측정하는 알고리즘을 제안한다. 제안한 알고리즘에서는 먼저 훈련 영상(training image)의 통계적 분석을 통해 피부 영역에 대한 GMM-EM 클러스터링 기반 컬러 모델을 구축하고 이를 통해 피부 영역을 추출한 후, 형태학적 처리(morphological processing)를 통해 피부 영역에 존재하는 잡음을 제거한다. 이후 ICA (independent component analysis) 알고리즘을 통해 피부 영역을 헤모글로빈 및 멜라닌 성분으로 분리하고, 각 성분에 대한 투영 변환 블록 계수에 의하여 색소 침착 영역 및 크기를 결정한다. 성능 평가를 위한 모의실험으로부터 제안한 색소 침착 검출 알고리즘은 피부 색소 침착 영역의 크기 및 침착 정도를 정확하게 검출할 수 있음을 확인하였다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제15권3호
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• pp.233-251
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• 2011

The Gauge-Uzawa method [GUM] in [9] which is a projection type algorithm to solve evolution Navier-Stokes equations has many advantages and superior performance. But this method has been studied for backward Euler time discrete scheme which is the first order technique, because the classical second order GUM requests rather strong stability condition. Recently, the second order time discrete GUM was modified to be unconditionally stable and estimated errors in [12]. In this paper, we contemplate several GUMs which can be derived by the same manner within [12], and we dig out properties of them for both stability and accuracy. In addition, we evaluate an stability condition for the classical GUM to construct an adaptive GUM for time to make free from strong stability condition of the classical GUM.

• 한국CDE학회논문집
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• 제4권2호
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• pp.153-161
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• 1999

An atomatic mesh generation scheme with unstructured quadrilateral elements on trimmed surfaces has been developed. Trimmed surfaces are often encountered in modeling of structures with complex shapes such as aircrafts, automobile structures, pressure vessels and etc. For unstructured mesh generation with quadrilateral elements, a domain decomposition algorithm employing loop operators has been used. Mesh generation on trimmed surface is performed in three steps. First, trimmed surfaces with holes or cuts are transformed to th largest projection planes in which the meshes are constructed. The constructed meshes are transformed to the u-v parametric plane and then finally to the original 3D surfaces. Th exact locations of holes or cuts in projection planes are determined by the Newton-Raphson method. Sample meshes are constructed to demonstrate the effectiveness of the proposed algorithm.