• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.36-41
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• 2002

In this study we produced 1-dimensional p wave velocity structure of the crust using 449 P arrivals of 35 stations and we analysed hypocenters of the southeastern Korean peninsula area. A initial velocity model was selected from the priori studies and 30 different initial models were generated using random number generation from it. Using the veriest program 30 different velocity structures were calculated and the result show that velocities are 5.8 - 6.4 km/sec within 6 - 16 km depth and 7 $\pm$ 0.2 km/sec within 20 - 30 km with resonable resolution. Hypocenters were relocated by using resulted 1-dimensional velocity model as a initial model. Recalculated hypocenters'depth are shallower than initial data and epicenters show a little better lineality around study area but more much earthquake information are needed fur the determination of relation between epicenter distribution and geological tectonic structures.

• Proceedings of the IEEK Conference
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• 2003.07c
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• pp.2713-2716
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• 2003

This paper presents a dynamic manipulability analysis method of the limb moving in viscous fluid. The key idea of the presented method is that the boundary of joint velocity can be converted to the velocity-dependant dynamic manipulability polytope through the coriolis, centrifugal and drag terms in dynamic equation. The velocity-dependant dynamic manipulability polytope is added to the inertial and restoring force manipulability polytope to get overall manipulability polytope of the limb moving in the fluid Each of the torque and velocity bounds arc considered in the infinite norm sense in joint space, and the drag force of a limb moving in fluid viscous is modeled as a quadratic form An analysis example with proposed analysis scheme is presented to validate the method.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.10
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• pp.9-15
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• 2002

We propose a new transit time device to extend the operating frequency to submillimeter-wave(extreme infrared) ranges by utilizing velocity overshoot effects in the drift region. We name it a velocity overshoot transit time (OVTT) diode. This device adopts fast heterostructure tunneling as injection mechanism and a short drift region to optimize the velocity overshoot effects. To enhance dc-to-RF conversion efficiencym the drift region is designed with a bandgap grading method. Simulation results demonstrate that a VOTT diode can be operated at THz ranges.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.563-570
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• 2004

Turbulence is a crucial component of dynamics of astrophysical fluids dynamics, including those of ISM, clusters of galaxies and circumstellar regions. Doppler shifted spectral lines provide a unique source of information on turbulent velocities. We discuss Velocity-Channel Analysis (VCA) and its offspring Velocity Coordinate Spectrum (VCS) that are based on the analytical description of the spectral line statistics. Those techniques are well suited for studies of supersonic turbulence. We stress that a great advantage of VCS is that it does not necessary require good spatial resolution. Addressing the studies of mildly supersonic and subsonic turbulence we discuss the criterion that allows to determine whether Velocity Centroids are dominated by density or velocity. We briefly discuss ways of going beyond power spectra by using of higher order correlations as well as genus analysis. We outline the relation between Spectral Correlation Functions and the statistics available through VCA and VCS.

• Journal of the Korean Society of Visualization
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• v.5 no.1
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• pp.43-48
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• 2007

Micro-PIV(particle image velocimetry) has been widely used to measure the velocity of micro flow. Although this micro-PIV method can give accurate 2D instantaneous velocity information of mea-surement plane, it cannot resolve the out of plane component of velocity vectors. Lots of the micro fluidic devices generate three-dimensional flow and 3D measurement of velocity is useful to understand the physics of micro flow phenomena. In this study, we constructed stereoscopic micro-PIV(SMPIV) system and applied this method to the impinging micro jet flow. The results show that this method can produce accu-rate 3D reconstruction of micro jet flow.

• Journal of Environmental Science International
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• v.11 no.9
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• pp.925-931
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• 2002

Land-use types should be included in air pollutant diffusion model because a complex mixture of various land-use patterns with computational grid can make errors in calculation of several parameters. However, the air pollutant diffusion model has generally been treated with a uniform component with land-use type in each mesh because of the complexity of the simulation. This study presents a numerical simulation of the horizontal distribution of $O_3$dry deposition velocity during summertime in Busan metropolitan city. The calculation of the meteorological field was conducted using the land cover data. Simulation has been performed by the following two scenarios : (1) one with current land cover data, and (2) the other with only land and sea for the surface characteristics. The results from each scenario reveals considerable differences on the meteorological fields and these differences can cause changes in the calculation values of $O_3$deposition velocity.

• Journal of Ocean Engineering and Technology
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• v.16 no.6
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• pp.55-59
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• 2002

Delamination means that cracking occurs on the interface layer between composite laminates. In this paper, to predict the delamination growth in composite laminates subjected to low-velocity impact, the unit load method was introduced, and an eighteen-node 3-D finite element analysis, based on assumed strain mixed formulation, was conducted. Strain energy release rate, necessary to determine the delamination growth, was calculated by using the virtual crack closure technique. The unit load method saves the computation time more than the re-meshing method. The virtual crack closure technique enables the strain energy release rate to be easily calculated, because information of the singular stress field near the crack tip is not required. Hence, the delamination growth in composite laminates that are subjected to low-velocity impact can be efficiently predicted using the above-mentioned methods.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2234-2244
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• 1994

A process sequence of multi-operation cold forging for actual application in industry is designed with the rigid-plastic finite element method to form a constant velocity joint housing(CVJ housing). The material flow during the CVJ housing forming is axisymmetric until the final forging process for forming of ball grooves. This study treats the deformation as an axisymmetric case. The main objective of the process sequence design is to obtain preforms which satisfy the design criteria of near-net-shape product requiring less machining after forming. The process sequence design also investigates velocity distributions, effective strain distributions and forging loads, which are useful information in the real process design.

• Journal of the Korean Society of Visualization
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• v.3 no.1
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• pp.71-77
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• 2005

Information on temporal evolution of whole velocity fields are essential for physical understanding of a complicated turbulent flow. Due to advances of high-speed imaging technique, laser and electronics, high-speed digital cameras and high-repetition pulse lasers are commercially available in nowadays. A dynamic PIV system that can measure consecutive instantaneous velocity field with 1K$\times$ 1K pixels resolution at 1 fps was developed. It consists of a high-speed CMOS camera and a high-repetition Nd:YLF pulse laser. Theoretically, it can capture velocity fields at 20 fps with a reduced spatial resolution. In order to validate its performance, the dynamic PIV system was applied to a turbulent jet of which Reynolds number is about 3000. The particle images of 1024$\times$512 pixels were captured at a sampling rate of 4 KHz. The dynamic PIV system measured successfully the temporal evolution of instantaneous velocity fields of the turbulent jet, from which spectral analysis of turbulent structure was also feasible.

• Proceedings of the IEEK Conference
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• 2002.06c
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• pp.5-8
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• 2002

In this paper, we propose the self-autonomous algorithm for mobile robot system. The proposed mobile robot system controlled by Personal Digital Assistant(PDA) can follow the target at regular intervals. The mobile robot can evaluate the distance between robot and target with ultrasonic sensors, transmits the distance to the PDA. The velocity and direction decided in PDA are transmitted to the mobile robot with wireless LAN communication. Considering the state, velocity-changing and distance-maintenance, of the mobile robot, driving velocity and direction are applied. For safety, the velocity of the mobile robot is changed step by step. As a result, we confirm the ability of following the target with proposed mobile robot.