• 대한기계학회논문집A
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• 제27권8호
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• pp.1303-1308
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• 2003

This research proposes an implementation method of linearized equations of motion for multibody systems with closed loops. The null space of the constraint Jacobian is first pre-multiplied to the equations of motion to eliminate the Lagrange multiplier and the equations of motion are reduced down to a minimum set of ordinary differential equations. The resulting differential equations are functions of ail relative coordinates, velocities, and accelerations. Since the coordinates, velocities, and accelerations are tightly coupled by the position, velocity, and acceleration level constraints, direct substitution of the relationships among these variables yields very complicated equations to be implemented. As a consequence, the reduced equations of motion are perturbed with respect to the variations of all coordinates, velocities, and accelerations, which are coupled by the constraints. The position, velocity and acceleration level constraints are also perturbed to obtain the relationships between the variations of all relative coordinates, velocities, and accelerations and variations of the independent ones. The perturbed constraint equations are then simultaneously solved for variations of all coordinates, velocities, and accelerations only in terms of the variations of the independent coordinates, velocities, and accelerations. Finally, the relationships between the variations of all coordinates, velocities, accelerations and these of the independent ones are substituted into the variational equations of motion to obtain the linearized equations of motion only in terms of the independent coordinate, velocity, and acceleration variations.

• 한국컴퓨터정보학회논문지
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• 제13권1호
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• pp.125-133
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• 2008

모션 블러란 카메라나 촬영대상의 움직임에 의해서 화소가 혼합되어 이미지의 경계가 흐려지는 현상을 말한다. 촬영 순간 카메라와 촬영 대상간의 상대적 움직임에 의해 촬영된 이미지에는 움직인 방향으로 모션 블러가 발생할 수 있다. 촬영 대상들이 서로 다른 속도로 이동하면 지역적으로 다양한 크기의 모션 블러가 발생할 수 있다. 이러한 지역적으로 다양한 모션 블러가 발생한 이미지를 복원하기 위해서는 지역적으로 다양한 블러의 크기를 추출해야만 한다. 본 논문에서는 지역적으로 다양한 모션 블러가 발생된 이미지로부터 RATS(Robust Automatic Threshold Selection)를 이용하여 지역적으로 다양한 블러의 크기를 각 지역별로 추출하는 새로운 방법을 제안한다. 또한 이전 방법과의 비교 실험을 통해 성능을 검증한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.893-898
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• 2004

This research proposes an implementation method of linearized equations of motion for multibody systems with closed loops. The null space of the constraint Jacobian is first pre multiplied to the equations of motion to eliminate the Lagrange multiplier and the equations of motion are reduced down to a minimum set of ordinary differential equations. The resulting differential equations are functions of all relative coordinates, velocities, and accelerations. Since the coordinates, velocities, and accelerations are tightly coupled by the position, velocity, and acceleration level constraints, direct substitution of the relationships among these variables yields very complicated equations to be implemented. As a consequence, the reduced equations of motion are perturbed with respect to the variations of all coordinates, velocities, and accelerations, which are coupled by the constraints. The position, velocity and acceleration level constraints are also perturbed to obtain the relationships between the variations of all relative coordinates, velocities, and accelerations and variations of the independent ones. The perturbed constraint equations are then simultaneously solved for variations of all coordinates, velocities, and accelerations only in terms of the variations of the independent coordinates, velocities, and accelerations. Finally, the relationships between the variations of all coordinates, velocities, accelerations and these of the independent ones are substituted into the variational equations of motion to obtain the linearized equations of motion only in terms of the independent coordinate, velocity, and acceleration variations.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 1995년도 학술대회
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• pp.125-129
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• 1995

Motion blur, which occurs when relative motion between a camera and an object exits, is inevitable in moving pictures. By this reason there have been many research results for reducing such motion blur, especially for spatially variant case. Int he present paper, an adaptive iterative restoration method is applied to reduce the irregular motion blur in the image.

• International Journal of Ocean System Engineering
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• 제4권1호
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• pp.1-18
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• 2014

Heave plates have been widely used to enhance viscous damping and thus reduces the heave response of Spar platforms. Single heave plate attached to the keel of the Spar has been reported in literature (Tao and Cai 2004). The effect of double heave plates on hydrodynamic response in random waves has been investigated in this study. The influence of relative spacing $L_d/D_d$ ($D_d$-the diameter of the heave plate) on the hydrodynamic response in random waves has been simulated in wave basin experiments and numerical model. The experimental investigation has been carried out using 1:100 scale model of Spar with double heave plates in random waves for different relative spacing and varying wave period. The influence of relative spacing between the heave plates on the motion responses of Spar are evaluated and presented. Numerical investigation has been carried out to investigate effect of relative spacing on hydrodynamic characteristics such as heave added mass and hydrodynamic responses. The measured results were compared with those obtained from numerical simulation and found to be in good agreement. Experimental and numerical simulation shows that the damping coefficient and added mass does not increase for relative spacing of 0.4 and the effect greater than relative spacing on significant heave response is insignificant.

• 한국항공우주학회지
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• 제33권2호
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• pp.1-10
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• 2005

비정상 유동의 모사를 위한 병렬화된 비정렬 중첩격자기법을 개발하였다. 비정렬 격자계에서 효율적이고 강건하게 쓰일 수 있는 탐색방법과 병렬경계에서 유동적으로 변하는 데이터의 수를 처리할 수 있는 자료구조를 제안하였다. 격자계간의 정보전달을 위한 삽간경계면을 정의하였고, 공간상의 이차정확도를 유지하기 위한 삽간방법 및 물체내부에 위치하는 삽간점에 대한 처리방법을 제안하였다. 개발된 해석코드의 검증을 위해 Eglin/Pylon 형상에서 분리되는 스토어의 궤적을 해석하여 실험치와 비교하였고, 다 물체간의 상대운동이 있는 비정상유동의 적용을 위해 세 개의 스토어 분리에 대한 해석을 수행하였다.

• 한국정밀공학회지
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• 제19권8호
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• pp.47-54
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• 2002

A barrel cam is used as a very important part of an index drive unit. The index drive unit must have an intermittent-rotational motion. The barrel typed cam and roller gear mechanism has the advantages of high reliability to perform a prescribed motion of a follower. This paper proposes a new method for the shape design of the barrel cam and also a CAD program is developed by using the proposed method. As defined in this paper, the relative velocity method for the shape design calculates the relative velocity of the follower versus cam at a center of roller, and then determines a contact point by using the geometric relationships and the kinematic constraints, where the direction of the relative velocity must be parallel to a common tangential line at the contact point of two independent bodies, i.e. the cam and the follower Then, the shape of the cam is defined by the coordinate transformation of the trace of the contact points. This paper presents two examples for the shape design of the barrel cam in order to prove the accuracy of the proposed methods.

• 한국컴퓨터정보학회논문지
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• 제15권4호
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• pp.65-74
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• 2010

본 논문에서는 기존의 광학식 모션 캡처에서 생길 수 있는 마커들 간의 간섭이나 복잡한 시스템 구성으로 인한 시스템 설치의 복잡성 문제들을 해결하기 위해, 2차원 위치정보를 제공하는 단일 카메라와 특정부위의 방향정보를 제공하는 가속도센서와 자이로 센서로 구성된 동작센서를 융합하여 간편한 모션 캡처를 실현하는 새로운 기법을 제안한다. 본 논문의 동작 인식은 크게 영상기반 위치 정보와 동작센서기반 방향 정보의 융합을 통해 이루어진다. 영상은 보이는 부위에 장착된 컬러마커의 위치를 기준점으로 제공하고, 동작센서들은 각 패지의 이동방향과 속도를 측정하여 영상에서 제공하는 마커들의 3차원 포즈정보를 알아 낼 수 있다. 제안하는 시스템은 사람동작의 측정에 필요한 최소한의 센서정보를 사용함으로써 시스템의 구성과 센서의 설치가 매우 간단하며 경제적이라는 장점을 갖는다. 이러한 장점은 다양한 실험을 통해 검증하였다.

• Wind and Structures
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• 제26권3호
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• pp.179-190
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• 2018

Translation of tornadoes is an important feature in replicating the near-ground tornado flow field which has been simulated in previous studies based on Ward-type tornado simulators using relative motion of the ground plane. In this laboratory investigation, effects of translation on the near-ground tornado flow field were studied using the ISU Tornado Simulator that can physically translate over a ground plane. Two translation speeds, 0.15 m/s and 0.50 m/s, that scale up to those corresponding to slowly-moving tornadoes in the field were selected for this study. Compared with the flow field of a stationary tornado, the simulated tornado with translation had an influence on the spatial distribution and magnitude of the horizontal velocities, early reversal of the radial inflow, and expansion of the core radius. Maximum horizontal velocities were observed to occur behind the center of the translating tornado and on the right side of its mean path. An increase in translation speed, resulted in reduction of maximum horizontal velocities at all heights. Comparison of the results with previous studies that used relative motion of the ground plane for simulating translating tornadoes, showed that translation has similar effects on the flow field at smaller radial distances (~2 core radius), but different effects at larger radial distances (~4 core radius). Further, it showed that the effect of translation on velocity profiles is noticeable at and above an elevation of ~0.6 core radius, unlike those in studies based on the relative motion of the ground plane.

• International Journal of Aeronautical and Space Sciences
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• 제11권3호
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• pp.206-220
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• 2010

This paper proposes optimal control techniques for determining translational and rotational maneuvers that facilitate proximity operations and docking. Two candidate controllers that provide translational motion are compared. A state-dependent Riccati equation controller is formulated from nonlinear relative motion dynamics, and a linear quadratic tracking controller is formulated from linearized relative motion. A linear quadratic Gaussian controller using star trackers to provide quaternion measurements is designed for precision attitude maneuvering. The attitude maneuvers are evaluated for different final axis alignment geometries that depend on the approach distance. A six degrees-of-freedom simulation demonstrates that the controllers successfully perform proximity operations that meet the conditions for docking.