• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.384.2-384.2
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• 2016

Recent publications reported the self-propelled jumping of coalescing dew droplets on superhydrophobic surfaces [1-2]. We further investigated the initial growth, coalescence, and removal by self-propelled ejection of nano and microscopic water droplets on the superhydrophobic surface of lotus leaves under condensing conditions. By using a high-speed digital camera mounted on an optical microscope, we have found: (1) sub-micrometer droplets form and grow on nanoscale waxy hairs; (2) growing droplets coalesce rapidly upon contact, but never jump off the surface unless the diameter of merged droplets exceeds ${\sim}15{\mu}m$; (3) the diameter and direction of jumping droplets are very narrowly distributed, centered at $20-30{\mu}m$ and ${\sim}20$ degrees from the surface normal, respectively. We present a rationale for these observations on the basis of: (a) the hierarchically rough surface structure on nano- and micro-scales; (b) its chemical composition; and (c) the balance among competing forces of cohesion (surface tension), adhesion and gravity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.232-239
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• 2000

The paper describes the parametric instability of free-free beams subjected to a controlled pulsating follower force. The beam has a tip rigid body not a mass point, and the direction of pulsating follower force is controlled by the direction control sensor. Equations of motion are derived by Hamilton's principle and the instability regions are obtained by finite element formulation. The effects of magnitude, rotary inertia, the distance between free end of the beam and the center of gravity of the rigid body on the instability types and regions are investigated by the change of the constant and periodic part of the follower force.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.9-11
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• 2003

A homogeneous flow field including more than 2000 spherical particles was directly simulated. Particles are settling by gravity with the Reynolds number ranging from 50 to 300, based on diameter and slip velocity. Particular attention was focused on the distribution of particles. The Reynolds-number dependence, influences of particle rotation and loading ratio, and the dynamics of particle clusters are discussed. In the higher Reynolds number case, the wake attraction causes particle clusters and the average drag coefficient decreases significantly. Non-rotating particles maintain cluster structure and rotating ones moves randomly in the horizontal direction. It is because of the difference in the direction of the lift force.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.66.1-66.1
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• 2010

Using two-dimensional numerical hydrodynamic simulations, we investigate the star formation rate (SFR) in turbulent, multiphase, galactic gaseous disks. Our simulation domain is axisymmetric, and local in the radial direction and global in the vertical direction. Our models include galactic rotation, vertical density stratification, self-gravity, radiative heating and cooling, and thermal conduction, but do not include spiral-arm features. Turbulence in our models is driven by momentum feedback from supernova explosion events occurring in localized dense regions formed by thermal and gravitational instabilities. Self-consistent radiative heating, representing enhanced/reduced FUV photons from the star formation, is also taken into account. By controlling three parameters (the gas surface density, the stellar disk density, and the angular rotation rate) that characterize local galactic disks, we explore how the SFR depends on the background environmental state. We also discuss the relation between the SFR and the gas surface density found in our numerical models in comparison with observations.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10c
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• pp.263-266
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• 2007

We introduce a vision-based hand gesture recognition fer understanding musical time and patterns without extra special devices. We suggest a simple and reliable vision-based hand gesture recognition having two features First, the motion-direction code is proposed, which is a quantized code for motion directions. Second, the conducting feature point (CFP) where the point of sudden motion changes is also proposed. The proposed hand gesture recognition system extracts the human hand region by segmenting the depth information generated by stereo matching of image sequences. And then, it follows the motion of the center of the gravity(COG) of the extracted hand region and generates the gesture features such as CFP and the direction-code finally, we obtain the current timing pattern of beat and tempo of the playing music. The experimental results on the test data set show that the musical time pattern and tempo recognition rate is over 86.42% for the motion histogram matching, and 79.75% fer the CFP tracking only.

• Proceedings of the Korea Information Processing Society Conference
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• 2016.04a
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• pp.758-761
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• 2016

본 논문에서는 손목형 가속도계를 이용하여 운동 가속도가 없는 행동들을 인식하기 위한 방법을 제안한다. 중력 가속도 값과 손목 방향의 가속도 값 간의 각도를 구하고, 이를 통해 흡연과 식사의 손목 행동을 모델링하여 흡연 시간과 식사 시간을 추론한다. 대학원생 1명으로부터 수집한 약 7시간 데이터를 통해 흡연 시간을 추론 결과 98.96%의 정확도를 보이고, 대학원생 2명으로부터 수집한 약 9시간 데이터로부터 식사 시간을 추론한 결과 99.36%의 정확도를 보인다.

• Journal of the Korea Computer Graphics Society
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• v.19 no.4
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• pp.13-22
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• 2013

A motion capture system is widely used in movies, computer game, and computer animation industries because it allows for creating realistic human motions efficiently. The inertial motion capture system has several advantages over more popular vision-based systems in terms of the required space and cost. However, it suffers from low accuracy due to the relatively high noise levels of the inertial sensors. In particular, the accelerometer used for measuring gravity direction loses the accuracy when the sensor is moving with non-zero linear acceleration. In this paper, we propose a method to remove the linear acceleration component from the accelerometer data in order to improve the accuracy of measuring gravity direction. In addition, we develop a simple method to calibrate the joint axis of a link to which an inertial sensor belongs as well as the position of a sensor with respect to the link. The calibration enables attaching inertial sensors in an arbitrary position and orientation with respect to a link.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.683-693
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• 2010

In this paper, we propose a new parallel mechanism for the legs of biped robots and the control of the robot's locomotion. A leg consists of two 3-DOF parallel platforms linked serially: one is an orientation platform for a thigh and the other is the 3-DOF asymmetric parallel platform for the shank. The desired locomotion trajectory is generated on the basis of the Gravity-Compensated Inverted Pendulum Mode (GCIPM) in the sagittal direction and the Linear Inverted Pendulum Mode (LIPM) in the lateral direction, respectively. In order to simulate the ground reaction force, a 6-DOF elastic pad model is used underneath each of the soles. The performance and effectiveness of the proposed parallel mechanism and locomotion control are shown by the results of computer simulations of a 12-DOF parallel biped robot using $SimMechanics^{(R)}$.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.490-493
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• 2003

This paper describes the development of a small 6-axis force/moment sensor for robot's finger, which measures forces Fx. Fy, Fz, and moments Mx, My, Mz simultaneously. In order to safely grasp an unknown object using the robot's gripper, and accurately perceive the position of it in the gripper, it should measure the force in the gripping direction, the force in the gravity direction and the moments each direction. and perform the control using the measured forces and moments. Thus, the robot's gripper should be composed of 6-axis force/moment sensor that can measure forces Fx, Fy, Fz, and moments Mx, My. Mz simultaneously. In this paper, the small 6-axis force/moment sensor for measuring forces Fx, Fy, Fz, and moments Mx, My, Mz simultaneously was newly modeled using several parallel-plate beams, designed, and fabricated. The characteristic test of made sensor was performed, and the result shows that interference errors or the developed sensor are less than 3%. Thus, the developed small 6-axis force/moment sensor may be used for robot's gripper.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.421-426
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• 2006

To examine the behaviors of traditional wooden structural frame in Korea in direction of beam, an experimental study was performed. The interior frame of Daewoongjeon of Bongjeongsa was selected as a model, which has two short exterior columns and one high inside column. The experimental frame has 1/2 scale and lateral forces are applied at high inside column by using drift control. The vertical gravity loads are applied on the frame. From the results of experiment it was shown that the stiffness and lateral capacity of the frame was increased when vertical loads are applied and the force-drift relationship in positive load direction was not same as in negative load direction. And push-over analysis are performed by using macro model in which the rotational and shear springs which were derived from the another experiments of subassemblies were used. The numerical analysis with macro model showed a good correspondence with the experiment within 2% story drift.