• 한국멀티미디어학회논문지
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• 제7권4호
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• pp.579-591
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• 2004

본 논문에서는 직선과 곡선으로 구성된 단순한 도면으로부터 곡선을 검출한 다음에 곡선을 원형 아크로 분할하는 방법을 제안한다. 본 논문의 방법에서는 먼저 선의 중심점을 찾은 다음에 연결된 중심점을 추적하여 선분을 검출한다. 그 다음에는 선분의 양 끝에서 선분의 방향을 이용하여 이웃한 선분을 검출하여 선분을 확장해 나간다. 선분을 확장한 다음에는 직선을 제거하고 곡선만 남긴 다음에 재귀적 분할 방법을 이용하여 곡선을 아크들의 집합으로 분할한다. 본 논문에서는 기존의 벡터화 소프트웨어와 벡터 기반 아크 분할 방법과 비교 실험을 수행하였다. 실험 결과에 의하면 본 논문에서 제안된 방법이 기존의 방법에 비하여 교차점을 가지는 곡선에 대하여 보다 정확하게 아크로 분할하였다.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1613-1623
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• 1996

In this paper, two discretization methods, hybrid and QUICK, are tested for the Navier-Stokes equations written in general nonorthogonal body fitted coordinates. Comparison is made by calculating two laminar flows at low Reynolds numbers of 10 - 100. One is a two-dimensional channel of gradually expanding cross section and the other is an axisymmetric flow through a circular tube having a circular constriction. Results show that the QUICK scheme results in a numerical solution more accurate than that of hybrid. The QUICK scheme also shows faster convergence for both test cases. As the number of grid points increases, all numerical solutions converge with more oscillation. The number of grid points in the y-direction(cross stream direction) is also shown to play a significant role in the approximation of convection term within separated flow zone.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1355-1364
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• 2001

Characteristics of secondary vortices is topologically investigated in the near-wake region of a circular cylinder, where the Taylor's hypothesis does nut hold. The three-dimensional flow fields in the wake-transition regime were measured by a time-resolved PIV for various planes of view. The convection velocities of the Karman and secondary vortices are evaluated from the trajectory of the vortex center. Then, saddle points are determined by applying the critical point theory. It is shown that the inclination angle of the secondary vortices agrees well with the previous experimental data. The flow fields in a moving frame of reference have several critical points and the mushroom-like structure appears in the streamline patterns of the secondary vortices. Since the distributions of fluctuating Reynolds stresses defined by triple decomposition are closely related with the existence of secondary vortices, the physical meaning of them is explained in conjunction with the vortex center and saddle point trajectories.

• 한국산학기술학회논문지
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• 제7권5호
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• pp.793-800
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• 2006

곡선보(curved beam)의 회전관성(rotatory inertia) 및 전단변형(shear deformation)을 고려한 평면내(in-plane) 자유진동을 해석하는데 미분구적법(DQM)을 이용하여 고정-고정 경계조건(boundary conditions)과 다양한 굽힘각(opening angles)에 따른 진동수(frequencies)를 계산하였다. DQM의 결과는 엄밀해(exact solution) 또는 다른 수치해석(Rayleigh-Ritz, Galerkin 또는 FEM) 결과와 비교하였으며, DQM은 적은 요소(grid points)를 사용하여 정회한 해석결과를 보여주었다.

• 한국정밀공학회지
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• 제20권11호
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• pp.166-170
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• 2003

Contouring errors are important especially for high speed and precision machining. In this study, contouring errors along contours having inflection points are studied. When a table of a machine tool moves along a circular path, acceleration acts toward the center of the circle. Thus, at inflection points, acceleration as well as inertia force changes its direction abruptly. The effect of inertia force on the contouring error is investigated in this study. It is found that the contouring error at an inflection point is proportional to the acceleration. This result can be useful in determining contouring errors along general paths.

• 한국CDE학회논문집
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• 제8권4호
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• pp.278-288
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• 2003

Presented in this paper is a numerical method for calculating the intersection points between Z-map vectors and the tool swept surface for circularly moving filleted-end mills. In numerically controlled(NC) machining simulation for large moulds and dies, a workpiece is frequently approximated as a set of z-axis aligned vectors, called Z-map vectors, and then the machining processes can be simulated through updating the Z-map with the intersection points. Circular motions are typically used for machining the free-form surfaces. For fast computation, we express each of intersection points with a single-variable non-linear equation and calculate the candidate interval in which the unique solution exists. Then, we prove the existence of a solution and its uniqueness in this candidate interval. Based on these properties, we can effectively apply numerical methods to finally calculate the solution of the nonlinear equation within a given precision. Experimental results are given for the case of a TV monitor and the hood of a car.

• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.116-122
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• 2009

In this paper, a robust method is developed to locate the irises of both eyes. The method doesn't put any restrictions on the background. The method is based on the AdaBoost algorithm for face and eye candidate points detection. Candidate points are tuned such that two candidate points are exactly in the centers of the irises. Mean crossing function and convolution template are proposed to filter out candidate points and select the iris pair. The advantage of using this kind of hybrid method is that AdaBoost is robust to different illumination conditions and backgrounds. The tuning step improves the precision of iris localization while the convolution filter and mean crossing function reliably filter out candidate points and select the iris pair. The proposed structure is evaluated on three public databases, Bern, Yale and BioID. Extensive experimental results verified the robustness and accuracy of the proposed method. Using the Bern database, the performance of the proposed algorithm is also compared with some of the existing methods.

• 한국정보통신학회논문지
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• 제20권10호
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• pp.1845-1851
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• 2016

본 논문에서는 DTV용 광대역 정사각형 루프 안테나에 대한 설계 방법에 대하여 연구하였다. 제안된 루프 안테나는 정사각형 루프 안테나와 중앙 급전점을 연결하는 원형 섹터가 결합된 형태이다. 안테나의 크기를 소형화하기 위해 원형 루프 대신에 사각형 루프를 사용하였다. DTV응용을 위해 75옴 포트 임피던스와 정합하도록 입력 반사계수와 이득 특성을 분석하였다. 원형 섹터 사이의 간격과 정사각형 루프의 길이 변화에 따른 입력 반사계수와 이득 특성을 분석하여 최적의 설계 변수를 도출하였다. 최적화된 안테나를 FR4 기판에 제작하고 특성을 실험한 결과, 전압 정재파비(VSWR; voltage standing wave) < 2인 대역이 468-1,268 MHz으로 DTV 대역(470-806 MHz)에서 동작하는 것을 확인하였다.

• 한국전산유체공학회지
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• 제10권1호
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• pp.8-15
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• 2005

Aerodynamic sounds generated by a uniform flow around a two-dimensional circular cylinder at Re=150 are simulated by applying the finite difference lattice Boltzmann method. Thethird-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives, and the second-order-accurate Runge-Kutta scheme is applied for the time marching. We have succeed in capturing very small pressure fluctuations with the same frequency of the Karman vortex street compared with the pressure fluctuation around a circular cylinder. The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow. For the downstream, on the other hand, it is faster. It is also apparent that the amplitude of sound pressure is proportional to r /sup -1/2/,r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence, furthermore, 2D computations of the tone noises radiated by a square cylinder and NACA0012 with a blunt trailing edge at high incidence and low Reynolds number are also investigate.

• 한국방재학회 논문집
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• 제3권1호
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• pp.123-131
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• 2003

파형강관을 삽입하여 보강된 중공원형단면의 역학적 거동을 연구하기 위하여 직경 50cm, 길이 340cm의 시험체를 제작하였고, 3점 휨시험을 수행하였다. 하중재하는 파괴 또는 최대한변형이 발생할 때까지 느리게 증가시켰다. 시험하는 동안에 시험체 중앙의 휨방향 변위와 인장측과 압축측의 종방향 변위를 측정하였다. 측정데이타를 분석한 결과를 파형강관이 삽입되지 않은 등가단면에 대한 해석결과와 비교하였다. 비교결과, 중공 철근콘크리트 부재의 휨강성과 연성이 파형강관을 내부에 삽입함으로써 크게 향상시킬 수 있는 것으로 나타났다.