• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.66.2-66.2
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• 2010

We have studied the properties of interstellar turbulence as observed by Boston University-Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS). This observation uses 13CO J=$1{\rightarrow}0$ emission with high spectral resolution of 0.21 kms-1 and covers wide galactic plane regions ($18^{\circ}$ < 1 < $55.7^{\circ}$ and -1 < b < $1^{\circ}$). Firstly, we measured the one dimensional power spectrum of 13CO intensity along the galactic longitude and along the galactic latitude. We found the slope of the power spectrum changes around the molecular ring structure and the center of the galactic plane. Secondly, we explored how the power spectral slope is related with the velocity dispersion of supersonic giant molecular clouds in the GRS. Finally, we suggest the turbulent nature of the interstellar medium is connected with star formation activities in spiral arms.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.445-455
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• 2013

A new linearization model for MR dampers is analyzed. The nonlinear hysteretic damping force model of MR damper can be modeled as a hyperbolic tangent function of currents, positions, and velicities, which is an algebraic function with constant parameters. Model parameters can be identified with numerical method using experimental force-velocity-position data obtained from various operating conditions. The nonlinear hysteretic damping force can be linearized with a given slope of damping coefficient if there exist corresponding currents to compensate for the nonlinearity. The corresponding currents can be calculated from the inverse model when the given linear damping force is set equal to the nonlinear hysteretic damping force. The linearization controller is realized in a DSP controller such that the corresponding currents to satisfy a given damping coefficient should be calculated. Experiments show that the current inputs to the MR damper produce linearized damping force with a given slope of the damping coefficient.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.7
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• pp.597-604
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• 2001

Recently, the study of the moving sliding mode in the variable structure control is in progress ac-tively. The conventional time-invariant sliding model control can\`t guarantee the sliding mode in the reaching phase, which is robust against the uncertainty. But with the time-varying method, the controller makes the states track the desired trajectories and keeps the sliding mode. Nevertheless, the piecewise continuous method of the past still has the reaching mode. Thus we propose the continuously moving sliding surface by the fuzzy algorithm. The proposed algorithm is made of the fuzzy rule considering both the error and the error velocity, and may apply to the entire phase plane without sacrificing sliding mode. Especially the proposed scheme can rotate tot he slope-decreasing direction, needless to say rotating to the slope-increasing direction. For showing that the proposed controller guarantees the sliding model and ensures the robustness, we apply the proposed method to the two-link robot manipulator simulation.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.581-584
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• 2008

This study analyzed activity of rockfall and its effect factor by the shape and mass. We performed research on the kinetic energy distribution, velocity and bounce height according to the rockfall characteristics using rockfall simulation program in cut-slope. In addition, this study discussed how to utilize kinetic energy and bounce height of rockfall for efficient establishment of rockfall prevention fence which is a countermeasure to cut-slope.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.496-503
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• 2016

To analyze an infinite slope that is reinforced with stabilizing piles, the forces on the stabilizing pile were estimated by the theory of plastic deformation and the theory of plastic flow and the effects of diverse factors on the factor of safety of an infinite slope were investigated. According to the results of the analyses, the factor of the safety of the slope reinforced with stabilized piles were increased tremendously and the factor of safety decreased as the center to center distance of the stabilizing pile increased. The effect of the existence of seepage of the infinite slope with stabilizing piles on the factor of safety appears to be insignificant. Considering the formulated factor of safety of an infinite slope with stabilizing piles, the width and length of the element of the infinite slope and force on the stabilizing pile influence the factor of safety of the infinite slope with a stabilizing pile including the soil strength parameter, inclination of the slope and depth of the slope, which are important for calculating the factor of safety of a non-reinforced infinite slope. The factor of safety of an infinite slope with stabilizing piles derived from the theory of plastic deformation were increased significantly with the internal friction angle of the soil, and the minimum and the maximum factor of safety under the conditions considered in this study were 13.7 and 65.6, respectively. As the diameter of the stabilizing pile increased, the forces on the stabilizing pile also increased but the factor of safety of the infinite slope with stabilizing piles decreased due to the effects of the width and the length of the element of the infinite slope. The factor of safety of the infinite slope with stabilizing piles derived from plastic flow were much larger than that of the non-reinforced infinite slope and the factor safety of the infinite slope with a stabilizing pile increased with increasing product of the flow velocity and plastic viscosity ( ) and the factor of safety of the infinite slope with stabilizing piles decreased with increasing center to center distance of the pile.

• The Journal of the Korea Contents Association
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• v.16 no.4
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• pp.614-623
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• 2016

Grid(pipe network) design is an important element of Smart Water Grid, which essential to estimate hydraulic parameters such as the pressure, friction factor, friction velocity, head loss and energy slope. Especially, friction velocity in a grid is an important factor in conjunction with energy gradient, friction coefficient, pressure and head loss. However, accurate estimation friction head loss, friction velocity and friction factor are very difficult. The empirical friction factor is still estimated by using theory and equation which were developed one hundred years ago. Therefore, in this paper, new equation from maximum velocity and friction velocity is developed by using integration relationship between Darcy-Weisbach's friction head loss equation and Schlichting equation and regression analysis. To prove the developed equation, smooth pipe data areis used. Proposed equation shows high accuracy compared to observed data. Study results are expected to be used in stability improvements and design in a grid.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.1
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• pp.10-15
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• 2012

Wave characteristics in the presence of energy damping are investigated using the linear shallow water equations. To get the phase and energy velocities, geometric optics approach is used and then these values are validated through numerical experiments. Energy damping affects wave height, phase and energy velocities which result in wave transformation. When the complex wavenumber is used by the Eulerian approach, it is found that the phase velocity decreases as the damping increases while the energy velocity increases showing higher values than the phase velocity. When the complex angular frequency is used by the Lagrangian approach, the energy-damping wave group is found to propagate in the energy velocity. The energy velocity is found to affect shoaling and refraction coefficient which is verified through numerical experiments for waves on a plane slope.

• Journal of Korean Society of Forest Science
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• v.107 no.1
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• pp.25-34
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• 2018

This study was performed to discover the comparison of the understory species composition and the growth velocity of the regeneration seedlings in Pinus densiflora forests being managed by the seed-tree method from 2008 year. The investigation site located in Bonghwa, Gyeongsangbuk-do province was established by eighteen quadrats such as six control ones, six slope ones and 6 concave ones, in which we carried out the vegetation survey and measured annual height growth of each seedlings. As a result of vegetation analysis, the understory vegetation of the seed-tree forest area was mainly composed of shrub plants such as Lespedeza bicolor, Zanthoxylum schinifolium, Securinega suffruticosa, Lespedeza maximowiczii and Stephanandra incisa, herb plants such as Miscanthus sinensis var. purpurascens, Carex humilis var. nana, Spodiopogon sibiricus and Artemisia keiskeana, and vine plants such as Pueraria lobata, Smilax sieboldii, Dioscorea batatas, Actinidia arguta, Vitis amurensis and Rubus crataegifolius. Especially, the vine plants were relatively more imported to the concave site than the control site and the slope site. As a result of measurement of growth velocity, the seedlings of the Pinus densiflora appeared to be 3,175 trees/ha for the non-suppressed trees and 7,842 trees/ha for the suppressed trees. In cases of the concave site, individuals of seedlings were much lower than those on the slope site, probably due to the competition effects of vine plants. Consideringly, silvicultural practices for clearing the vine plants should be inevitably accompanied. Also, the growth velocity of the suppressed and non-suppressed trees has been constantly increasing, those of the non-suppressed trees much higher than the suppressed trees. This represents that the seedlings grow rapidly after the suppressed period with competition to the surrounding plants. Therefore, specific practices such as blush control and vine clear should be carried out at the beginning stage of regeneration in the seed-tree stand.

• Journal of Conservation Science
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• v.28 no.2
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• pp.153-164
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• 2012

The major petroglyphs of Bangudae site were composed mainly of hornfelsed shale. Surface of the rock was formed weathering layer (average porosity 25%) that discriminated mineral and chemical composition against fresh rock (average porosity 0.4%). The lost area of major petroglyphs in the past up images carved to the present was calculated about 23.8%. And occurrence area of exfoliation indicated 1.2% of the whole petroglyphs. As a result of the chromaticity analysis, color of the major petroglyphs was changed brighter and yellower than fresh rock by chemical and biological weathering factors. Average ultrasonic velocity of petroglyphs was measured 2,865m/s. This result indicated that ultrasonic velocity decreased especially bottom of petroglyphs than measured result in 2003 year. The results of the evaluation for slope stability, it identified the possibility of toppling, planar and wedge failure in host rock. The 3D image analysis and modeling data of the cavern obtained for structural reinforcement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.1500-1506
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• 2015

The headcut erosion at the confluence section of a mainstream and tributary can migrate up the tributary streams, and rapid degradation can threaten the stability of hydraulic structures installed in the channel. Therefore, quantitative analysis for the development and mechanism of headcut erosion is needed to prevent damage due to the headcut. In this study, hydraulic experiments for headcut erosion in the channel with noncohesive materials were performed and the knickpoint movement and final bed slope change were analyzed based on the different hydraulic conditions. As a result, the knickpoint movement was 1.5 times faster when the difference in velocity between the upstream and downstream sections was 2.5 times greater and the central part of the cross-section was eroded and collapsed earlier than the left and right sides. The movement length of headcut erosion was longer and the final bed slope was milder as the velocity difference between the upstream and downstream sections was increased. This study showed that a correlation between the knickpoint movement and bed slope change by headcut erosion and the water level difference of upstream and downstream sections was not constant compared to the velocity difference.