• 한국전산유체공학회지
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• 제5권1호
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• pp.1-7
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• 2000

In general, FDM(finite difference method) and FVM(finite volume method) are used for analyzing the fluid flow numerically. However it is difficult to apply them to problems involving complex geometries, multi-connected domains, and complex boundary conditions. On the contrary, FEM(finite element method) with coordinates transformation for the unstructured grid is effective for the complex geometries. Most of previous studies have used commercial codes such as KIVA or STAR-CD for the flow analyses in the engine cylinder, and these codes are mostly based on the FVM. In the present study, using the FEM for three-dimensional, unsteady, and incompressible Navier-Stokes equation, the velocity and pressure fields in the engine cylinder have been numerically analyzed. As a numerical algorithm, 4-step time-splitting method is used and ALE(arbitrary Lagrangian Eulerian) method is adopted for moving grids. In the Piston-Cylinder, the calculated results show good agreement in comparison with those by the FVM and the experimental results by the LDA.

• 대기
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• 제21권3호
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• pp.243-256
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• 2011

This paper presents the development of new algorithm for identifying and tracking the convective cells in three dimensional reflectivity fields in Cartesian coordinates. First, the radar volume data in spherical coordinate system has been converted into Cartesian coordinate system by the bilinear interpolation. The three-dimensional convective cell has then been identified as a group of spatially consecutive grid points using reflectivity and volume thresholds. The tracking algorithm utilizes a fuzzy logic with four membership functions and their weights. The four fuzzy parameters of speed, area change ratio, reflectivity change ratio, and axis transformation ratio have been newly defined. In order to make their membership functions, the normalized frequency distributions are calculated using the pairs of manually matched cells in the consecutive radar reflectivity fields. The algorithms have been verified for two convective events in summer season. Results show that the algorithms have properly identified storm cells and tracked the same cells successively. The developed algorithms may provide useful short-term forecasting or nowcasting capability of convective storm cells and provide the statistical characteristics of severe weather.

• 한국콘텐츠학회논문지
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• 제7권12호
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• pp.322-332
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• 2007

프랙탈의 특성에 알맞은 변형 방법을 고려하였다. IFS 프랙탈에서 점의 위치 특성은 공간적 좌표뿐만 아니라 코드에 의해서도 표현된다. 코드는 프랙탈 내에서의 점의 주소로 볼 수 있는데, 코드값을 바꾸어 생기는 점의 이동에 프랙탈적 특성이 있으므로, 코드의 정보를 이용한 세 가지 변형 방법을 제안하였다. 즉, 한점의 이동에 사용될 벡터로서 1) 코드 변환을 통해 얻어지는 다른 점에서의 벡터장 값을 이용하는 방법과 2) 코드 정보를 활용하여 변위 벡터를 정하는 방법을 구현하여 본 결과, 연속적 변형의 특징과 프랙탈적 특징을 모두 갖는 변형을 얻을 수 있었다. 또한 3) 변형이 가해질 영역을 코드를 활용하여 제한함으로써, 고사리의 경우, 보다 자연물에 적합한 변형을 얻을 수 있었다.

• 대한기계학회논문집
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• 제17권6호
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• pp.1509-1517
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• 1993

본 연구에서는 3차원 운동을 하는 다물체 기구가 물체 수와 조인트 연결상태 만 주어진 상태에서 구성상태에 따라 절점 좌표계를 이용하여 모델링하고 MACSYMA를 써서 복잡단조로운 대수 계산을 하여 모든 운동학적 정보를 얻어내며 수치계산이 필요 하면 별도의 프로그램을 이용 수치해석을 하는 과정을 밟는다.

• 한국운동역학회지
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• 제17권4호
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• pp.157-167
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• 2007

The purpose of this study was to analyze kinematic techniques in the woman's 100m hurdle. In order to find the kinematic parameters, a 3-D video system for kinematic analysis-kwon3d 3.1(Kwon3D Motion Analysis Program Version 3.1)-was used. Eight JVC video cameras(GR-HD1KR) were used to film the performance of Lee Yeon-Kyoung at a frame rate of 60fields/s. The kinematic characteristics from the first hurdle to last hurdle were analyzed at the clearing hurdle spots such as distance, velocities, heights and angles. The real-life three-dimensional coordinates of 20 body landmarks during each phases were collected using a Direct Linear Transformation procedure. After analyzing the kinematic variables in the 100m hurdle run, the following conclusion were obtained; Lee Yeon-Kyoung had to maintain constant stride lengths between hurdles and increase takeoff distance before clearance and shorter landing distance after clearance. She also had to hit the correct takeoff point in front of the hurdle and extend the lead leg at the moment of landing in order to minimize the loss of velocity. She had to sprint between hurdles as fast as possible over 8m/s and run powerful first stride and shortened third stride preparing for the following hurdle clearances.

• 한국측량학회지
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• 제9권2호
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• pp.103-113
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• 1991

SPOT 수치영상자료를 이용한 지상좌표 계산 과정에서 지상기준점 및 검사점 입럭좌표의 정확도는 계산 결과의 신빙성에 커다란 영향을 준다. CRT 모니터상에 직접 나타난 SPOT 원초 영상은 일반적으로 지상물체의 판별과 점위치 결정에 적합하지 않으므로 전체영상의 대비개선, 영상소보간, 경계선강조, 공간필터처리 등 적절한 영상처리 기병의 적용이 필요하다. 본 연구에서는 대상지역의 3차원 위치 결정과 파장대특성분석에 이용되는 SPOT 위성영상의 시각분석에 필요한 수치영상처리기법의 원리를 고찰하고, 그 적용을 위한 알고리즘을 개발하여 프로그래밍 하였으며, 실제 P-mode 및 XS-mode의 SPOT 영상을 이용하여 고해상도 천연색영상인 SPOT P＋XS 영상으로 합성하였다.

• 한국측량학회지
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• 제32권6호
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• pp.563-570
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• 2014

This paper purposes on stimulating the dynamic behavior of a floating structure model with the image processing and the close-range photogrammetry, instead of the contact sensors. Previously, the movement of structures was presented by the exterior orientation estimation from a single camera following the space resection. The inverse resection yields to 6 orientation parameters of the floating structure, with respect to the camera coordinates system. The single camera solution of interest in applications is characterized by the restriction in terms of costs, unfavorable observation conditions, or synchronization demands when using multiple cameras. This paper discusses the theoretical determinations of camera exterior orientation by using the least squares adjustment, applied of the values from the DLT (Direct Linear Transformation) and the photogrammetric resection. This proposed method is applied to monitor motions of a floating model. The results of 6DOF (Six Degrees of Freedom) from the inverse resection were signified that applying appropriate initial values from DLT in the least square adjustment is effective in obtaining precise exterior orientation parameters. Therefore, the proposed method can be concluded as an efficient solution to simulate movements of the floating structure.

• 한국운동역학회지
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• 제16권2호
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• pp.135-144
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• 2006

This study was to investigate the kinematic analysis to score of the Yurchenko stretch skill according to phases in a horse vaulting. For this study, 8 male national gymnasts were participated in acquiring three dimensional kinematical imagining data with four Sony PD-150 video cameras After digitizing motion, the Direct Linear Transformation(DLT) technique was employed to obtain 3-D position coordinates. The kinematic factors of the distance, velocity and angle variable were calculated for Kwon3D 3.1. The following conclusions were drawn; 1) The COG resultant velocity of the less skilled group decreased in PRF phase because the less skilled group had a larger flexion-knee angle than the skilled group in BC phase, Because the less skilled group had larger flexion-shoulder angle than the skilled group in HTO phase, At blocking movement, the body inclined a moving direction. By means of it, COG lowered 2) The skilled group had a more rapid COG's vertical velocity than the less skilled group at HTD and HTO event in HC phase, because this was performed the blocking movement with body angle and contacted on a horse vaulting small and its time short by means of contacting hands on a horse vaulting quickly. Such blocking movement made the vertical up-flight movement easy at POF phase bringing out rapid COG's vertical velocity after take off a horse vaulting.

• 한국운동역학회지
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• 제15권4호
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• pp.75-83
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• 2005

The purpose of this study was to determine the kinematic characteristics of the ankle joint and RPM(repetition per minutes) during the supra maximal training in cycling. For this study, 8 national representative cyclists, distance cyclists in track and road, were selected. During the super-maximum pedalling, kinematic data were collected using a six-camera(240Hz) Qualisys system. the room coordinate system was right-handed and fixed in the back of a roller for cycle, with right-handed orthogonal segment coordinate systems defined for the leg and foot. Lateral kinematic data were recorded at least for 3 minutes while the participants pedal on a roller. Two-dimensional Cartesian coordinates for each marker were determined at the time of recording using a nonlinear transformation technique. Coordinate data were low-pass filtered using a fourth-order Butterworth recursive filter with cutoff frequency of 15Hz. Variables analyzed in this study were compared using a one factor(time) ANOVA with repeated measures. The results of investigation suggest that the number of rotating pedal was decreased with time phase during the super-maximum pedaling. Maximum angle of the ankle joint showed little in change with time phase compared with minimum angle of that.

• KEPCO Journal on Electric Power and Energy
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• 제2권2호
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• pp.253-257
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• 2016

This paper analyzes voltage control method in order to supply high-quality power for stand-alone microgrid. Stand-alone microgrid is composed of battery bank, stand-alone PCS and controllable loads. The main role of stand-alone PCS is to supply high-quality power to loads as main source by using stable voltage method regardless of load conditions. In particularly, output voltage of stand-alone PCS gets severely unbalanced voltage under unbalanced loads. Fundamental positive and negative sequences are transformed by two coordinates transformation which are rotated in each opposite direction, respectively. Each fundamental d-q voltage is regulated by each fundamental PI control. In addition, low-order harmonics are compensated through resonant controllers. Performance of stand-alone microgrid is tested for feasibility, and it is verified that output voltage of THD is improved to 1% from 2.2% under 50 kW balanced load, and is improved to 1.1% from 2.6% under 50 kW unbalanced load.