• 한국유체기계학회 논문집
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• 제5권1호
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• pp.7-12
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• 2002

As the first step to investigate the fundamental mechanism of a dispersed two-phase flow, we studied the detailed interactions between bubble or particle motion and flow around it. Experiments were carried out with a rising bubble or particle in stagnant water in a vertical pipe. Particles with different densities, and/or different shapes were used for comparison with a bubble. We adopted 3D-PTV (Three-Dimensional Particle Tracking Velocimetry) for measuring the bubble or particle motions, and PIV (Particle Image Velocimetry) for measuring the water flow simultaneously (Hybrid PIV). The experimental results showed that the oblate spheroidal solid particle rose along the longer axis direction at the point that the inclination of the longer axis reached the maximum, and the inclination direction changed after moving. The bubble moved to the direction that the spheroid's projected width grew up to the largest, and the minor axis of the oblate spheroidal body of the bubble was parallel to the moving direction. The trajectory of the center of the particle/bubble which was measured with 3D-PTV, was marked on the section (x-y) of the pipe. It exhibited the pattern of the particle/bubble motion.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 1999년도 학술대회
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• pp.109-114
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• 1999

Due to the temporal correlation of the image sequence, the motion vector of a block is highly related to the motion vector of the same coordinate block in the previous image frame. If we can obtain useful and enough information from the motion vector of the same coordinate block of the previous image frames, the total number of search points used to find the motion vector of the current block may be reduced significantly. Using that idea, an efficient new predicted direction search algorithm (PDSA) for block matching motion estimation is proposed in this paper.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.265-268
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• 2008

The safety of a tunnel under seismic motion is most often evaluated by ovalling deformation of tunnel. This paper research about tunnel's longitudinal deformation. Because of spatial variation of seismic ground motion, the longitudinal structures like tunnel are likely to experience relative displacements along longitudinal direction. The spatially variable ground motion can be estimated by coherency function obtained empirically, and can be considered from different arrival times of ground motion. As a result of estimating tunnel's relative displacements at maximum curvature of tunnel, the displacements and curvatures estimated by coherency function affect the tunnel's safety more than different arrival times. However, if tunnel's displacements by coherency function superpose on displacements by different arrival times, the relative displacements and curvatures of tunnel will be more severe. Therefore, to estimate accurately tunnel's deformation in longitudinal direction has to consider both coherency and wave passage effects.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2000년도 하계종합학술대회논문집
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• pp.309-312
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• 2000

In this work, a new algorithm for canceling MRI artifact due to translational motion in image plane is described. In the previous approach, the motions in the x direction and the y direction are estimated simultaneously. By analyzing their features, each x and y directional motion is canceled by different algorithms in two steps. First, it is noticed that the x directional motion corresponds to a shift of the x directional spectrum of the MRI signal. Next, the y directional motion is canceled by using a new constraint condition. This algorithm is shown to be effective by using a phantom image with simulated motion.

• 한국정보과학회논문지:소프트웨어및응용
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• 제27권4호
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• pp.432-440
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• 2000

본 연구에서는 촬상단면 내의 평행이동에 기인한 MRI 아티팩트를 제거하는 새로운 알고리즘으로서, 수렴에 대한 보증이 없는 기존의 반복적인 위상탐색에 의한 알고리즘과는 달리, MRI 촬상원리에 근거한 체동량을 탐색하기 위한 직접적인 방법이 제안된다. 기존의 접근방법에는 x(read out) 방향과 y(phase encoding) 방향의 체동이 동시에 탐색되었다. 하지만 x 방향과 y 방향에 대한 각각의 체동특성이 서로 다르기 때문에 본 방법에서는 이들의 체동특성의 해석에 기초해서 두 단계의 서로 다른 알고리즘을 적용함으로써 x 방향과 y 방향의 각 체동이 제거된다. 우선, x 방향의 체동은 MRI 신호의 x 방향 스펙트럼 변위에 해당하고, 그 스펙트럼의 비제로 영역(non-zero area)은 밀도함수의 x축 투영영역과 일치함에 주목한다. 따라서 체동은 스펙트럼의 비제로 영역과 제로영역(zero area)의 경계를 검출함으로써 추정되며, x 방향의 체동은 역방향으로 스펙트럼을 변위시킴으로써 제거된다. 그 다음으로, y 방향의 체동은 그 체동성분과 실제의 화상성분을 분리할 수 있는 구속조건을 적용함으로써 제거된다. 최종적으로 phantom 화상을 사용한 시뮬레이션을 통해서 본 방법의 유효성을 확인하였으며, 그 결과 제안한 방법이 기존의 방법에 비해 포괄적으로 사용할 수 있음을 알 수 있었다.

• 한국소음진동공학회논문집
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• 제21권3호
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• pp.258-263
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• 2011

The direction of the cutting tool plays a critical role in elliptical vibration cutting(EVC) where the cutting tool cuts workpiece in a trochoidal motion. In this study, EVC cutting device was developed using two parallel piezoelectric materials and it was observed that the rotation direction of the tool reverses as the EVC device undergoes resonance at which either flexural(cutting direction) or longitudinal( thrust direction) mode shapes occurs. To analytically explain reversal of the rotation direction, kinematic motion analysis of the tool was modified to incorporate amplification of the vibration amplitude and phase introduced by resonance. It successfully demonstrated, through Matlab simulation, reversal of the rotation direction of the cutting tool as the excitation frequency increases beyond resonance frequencies at which either flexural or longitudinal vibration occurs.

• 대한기계학회논문집A
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• 제31권6호
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• pp.686-693
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• 2007

To perceive body movement, the nervous system uses multi-sensory cues such as vision, vestibular signals, and somatosensation. Among the multi-sensory modality, the previous researchers reported that the lower limb somatosensation plays an important role on maintaining postural balance. In this study, we examined the contribution of somatosensory cues to linear motion perception by measuring the detection threshold of the direction of linear motion with and without lower limb somatosensory constraints. Six healthy male volunteers participated in randomly ordered 33 single sinusoidal acceleration trials with the stimulus at 0.25Hz with peak magnitude ranged from 0 to 8mG. After each stimulus, subjects reported their perceived direction of motion by button press. Results showed that the reduced lower limb somatosensation significantly increased perception threshold. Without constraints, mean threshold was $0.82{\pm}0.23mG$, while it was $1.23{\pm}0.35mG$ with reduced lower limb somatosensation. The results suggest that without visual cues, perception of the movement direction strongly depends on the lower limb somatosensory information.

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.879-888
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• 2013

This paper addresses the vision based local path planning system for obstacle avoidance. To handle the obstacles which exist beyond the field of view (FOV), we propose a Panoramic Environment Map (PEM) using the MDGHM-SIFT algorithm. Moreover, we propose a Complexity Measure (CM) and Fuzzy logic-based Avoidance Motion Selection (FAMS) system to enable a humanoid robot to automatically decide its own direction and walking motion when avoiding an obstacle. The CM provides automation in deciding the direction of avoidance, whereas the FAMS system chooses the avoidance path and walking motion, based on environment conditions such as the size of the obstacle and the available space around it. The proposed system was applied to a humanoid robot that we designed. The results of the experiment show that the proposed method can be effectively applied to decide the avoidance direction and the walking motion of a humanoid robot.

• Journal of Theoretical and Applied Mechanics
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• 제2권1호
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• pp.51-70
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• 1996

This study is generalization of the study of Miles[Physica 11D, 1984, pp.309-323]on the resonant motion of a spherical pendulum, which is equivalent to a particle on a spherical container subject to a linear, horizontal excitation. This study covers an arbitrary shape of container and a more general excitation (horizontal but elliptic motion). The averaging method is applied to reduce the governing equations to an autonomous system with cubic nonlinear terms, under the assumption of small amplitude of the container motion. It is shown that both the container shape and the excitation pattern affect the particle dynamics. Under the linear excitation, the anharmonic motion of the particle is possible only for a certain finite range of the parameter a controling the container shape. Stability of the particle's harmonic motion is also influenced by the excitation pattern; as the excitation trajectory becomes closer to a circle, the particle's motion has a stronger tendency to become stable and to follow the rotational direction of the excitation. Under a circular excitation, the motion is always stable and circular with the same rotational direction as the excitation. Analogy between the present model and that of the surface wave inside a circular is studied quantitatively.

• 대한방사선기술학회지:방사선기술과학
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• 제16권2호
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• pp.19-26
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• 1993

Magnetic Resonance Image represents three-dimensional diagnostic imaging technique using both nuclear magnetic resonance phenomenon and computer. Compared with computed tomography (CT), MRI have advantages harmless to patient's body, three-dimensional image with high resolution and disadvantages long data acquisition time because of long T1 relaxation time, relatively low signal to noise ratio, high cost of setting, also. As physiologic motion of tissue results in motion ghost in MRI, high 2.0Tesla make improve low signal to noise ratio. This study have aim to improve image quality with controling motion ghost of tissue. Supposing a moving pixel in constant frequency, one pixel make two ghosts which are same size and different anti-phase. So, this study will show adjust parameter on locational control of motion ghost. Author made moving phantom replaced by respiratory movement of human, researched change of motion frequency, FOV by location shift, and them decided optimal FOV (field of view). The results are as follows: 1. The frequency content of the motion determines how far the image always appear in phase-encoding direction, the morphology of the ghost image is characteristic of the direction of the motion and its amplitude. 2. Double FOV of fixed signal object for locational control of motion ghost is recommended. Decreasement of spatial resolution by increasing FOV can compensate on increasing of matrix in spite of scan time increasement.