• 한국대기환경학회지
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• 제19권3호
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• pp.249-261
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• 2003

A three-dimensional mesoscale atmospheric dispersion modeling system consisting of the Lagrangian particle dispersion model (LPDM) and the meteorological mesoscale model (MM5) was employed to simulate the transport and dispersion of non-reactive pollutant during the nuclear spill event occurred from Sep. 31 to Oct. 3, 1999 in Tokaimura city, Japan. For the comparative analysis of numerical experiment, two more sets of foreign mesoscale modeling system; NCEP (National Centers for Environmental Prediction) and DWD (Deutscher Wetter Dienst) were also applied to address the applicability of air pollution dispersion predictions. We noticed that the simulated results of horizontal wind direction and wind velocity from three meteorological modeling showed remarkably different spatial variations, mainly due to the different horizontal resolutions. How-ever, the dispersion process by LPDM was well characterized by meteorological wind fields, and the time-dependent dilution factors ($\chi$/Q) were found to be qualitatively simulated in accordance with each mesocale meteorogical wind field, suggesting that LPDM has the potential for the use of the real time control at optimization of the urban air pollution provided detailed meteorological wind fields. This paper mainly pertains to the mesoscale modeling approaches, but the results imply that the resolution of meteorological model and the implementation of the relevant scale of air quality model lead to better prediction capabilities in local or urban scale air pollution modeling.

• Smart Structures and Systems
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• 제21권2호
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• pp.195-205
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• 2018

Research on Lamb wave-based damage identification in plate-like structures depends on precise knowledge of dispersive wave velocity. However, boundary reflections with the same frequency of interest and greater amplitude contaminate direct waves and thus compromise measurement of Lamb wave dispersion in different materials. In this study, non-reflecting boundaries were proposed in both numerical and experimental cases to facilitate time-frequency characterization of Lamb wave dispersion. First, the Lamb wave equations in isotropic and laminated materials were analytically solved. Second, the non-reflecting boundaries were used as a series of frames with gradually increased damping coefficients in finite element models to absorb waves at boundaries while avoiding wave reflections due to abrupt property changes of each frame. Third, damping clay was sealed at plate edges to reduce the boundary reflection in experimental test. Finally, the direct waves were subjected to the slant-stack and short-time Fourier transformations to calculate the dispersion curves of phase and group velocities, respectively. Both the numerical and experimental results suggest that the boundary reflections are effectively alleviated, and the dispersion curves generated by the time-frequency analysis are consistent with the analytical solutions, demonstrating that the combination of non-reflecting boundary and time-frequency analysis is a feasible and reliable scheme for characterizing Lamb wave dispersion in plate-like structures.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2000년도 학술발표회 발표논문집
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• pp.346-351
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• 2000

The study was carried out to investigate the characteristics of vertical velocity distribution measured by current meter at Kangkyung station in Keum river during the period of 1995 to 1997. It suggests the quadratic parabola equation to estimate the vertical velocity profile only from the measurement data of surface velocity. The equation was found to be statistically very stable and showed high significance to express the surface velocity and bottom velocity. The vertical velocity profile was determined by the relationships to the surface velocity, and a coefficient of the quadratic parabola equation. The vertical velocity profile can be applied to calculating the mean velocity and discharge, and to and to analyse the dispersion of pollutant materials in the streamflow.

• 한국환경과학회지
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• 제12권3호
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• pp.265-274
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• 2003

The Pasquill-Gifford stability category is a very important scheme of the Gaussian type dispersion model defined the complex turbulence state of the atmosphere by A grade(very unstable) to F grade(very stable). But there has been made a point out that this stability category might decrease the predictability of the model because it was each covers a broad range of stability conditions, and that they were very site specific. The APSM (Air Pollution Simulation Model) was composed of the turbulent parameters, i.e. friction velocity(${\mu}$$\_$*/), convective velocity scale($\omega$$\_$*/) and Monin-Obukhov length scale(Ｌ) for the purpose of the performance increasing on the case of the unstable atmospheric conditions. And the PDF (Probability Density Function)model was used to express the vertical dispersion characteristics and the profile method was used to calculate the turbulent characteristics. And the performance assessment was validated between APSM and EPA regulatory models(TEM, ISCST), tracer experiment results. There were very good performance results simulated by APSM than that of TEM, ISCST in the short distance (<1415 m) from the source, but increase the simulation error(%) to stand off the source in others. And there were differences in comparison with the lateral dispersion coefficient($\sigma$$\_$y/) which was represent the horizontal dispersion characteristics of a air pollutant in the atmosphere. So the different calculation method of $\sigma$$\_$y/ which was extrapolated from a different tracer experiment data might decrease the simulation performance capability. In conclusion, the air pollution simulation model showed a good capability of predict the air pollution which was composed of the turbulent parameters compared with the results of TEM and ISCST for the unstable atmospheric conditions.

• 한국통신학회논문지
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• 제33권1A호
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• pp.7-15
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• 2008

본 논문에서는 광섬유에서 발생하는 그룹 속도 분산과 비선형 효과에 의한 왜곡을 보상하기 위해 적용하는 MSSI(Mid-Span Spectral Inversion)에서 광 위상 공액기(OPC; optical phase conjugator)를 중심으로 광 전력의 비대칭화 때문에 나타나는 기술적 한계를 부가적으로 집중형 분산 제어(DM; dispersion management) 기술을 결합시켜 극복할 수 있다는 것을 고찰하였다. 본 연구에서 고려한 집중형 DM은 송신단 바로 다음과 수신단 바로 앞에만 분산 보상 광섬유(DCF; dispersion compensating fiber)를 두는 구조(구조 A)와 전체 전송 링크 중간에 위치한 OPC의 바로 전후에 DCF를 두는 구조(구조 B)로 나누어 각 경우에 대해 전송 성능 개선 정도를 비교하였다. 분석 결과 MSSI에 구조 A의 집중형 DM이 결합된 경우가 구조 B가 결합된 경우에 비해 전송 성능을 크게 개선하는 것을 확인하였다. 본 논문에서 고려한 2가지 구조 모두 비선형 현상 중 자기 위상 변조(SPM; self phase modulation)에 의해 성능이 제한되는 WDM 시스템에서 총 전송 링크의 전체 잉여 분산량(NRD; net residual dispersion)이 양의 값으로 결정되어야 모든 채널에 대해 최상의 성능을 얻을 수 있다는 것을 확인하였다.

• 지구물리
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• 제6권2호
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• pp.99-105
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• 2003

Rayleigh waves which has more than 70% of the total seismic energy is the principal component of ground roll. Frequency component of a surface wave has a different propagation velocity, that is, phase velocity, which results in a different wavelength called dispersion. Rayleigh wave is one of the most common ways to use the dispersive properties of surface waves. MASW is a seismic method to evaluate shear-wave velocity information of the ground.

• 천문학회지
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• 제39권4호
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• pp.107-114
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• 2006

We conducted an analysis of a selected region from the FCRAO $^{12}CO$ Outer Galaxy Survey. The selected region is located between galactic longitude $117^{\circ}$ and $124^{\circ}$ with the velocity of -23 km $s^{-1}. Molecular clouds in this region show a peculiar velocity field, protruding from the Local Arm population. The selected region is divided into 7 clouds by spatial location. Though we were not able to identify the direct driving source for peculiar velocity of our target region, we find that there are several internal YSOs or star forming activities; there are many associated sources like an outflows, a high-mass protostellar candidate and $H_2O$ maser sources. We attribute the driving energy source to older generation of episodic star formation. Masses of main clouds(cloud 1-4) estimated using a conversion factor from $^{12}CO$ luminosity are larger than $10^4M_{\odot}$. Other components have a small mass as about $10^3M_{\odot}$. Among main clouds, cloud 2 and 4 seem to be marginally gravitational bound systems as their ratio of $M_{CO}$ to $M_{VIR}$ is about $2{\sim}3$, and the internal velocity dispersion is larger than the centroid velocity dispersion. Total mass estimated using a conversion factor from $^{12}CO$ luminosity is $7.9{\times}10^4M_{\odot}$.

• 한국안전학회지
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• 제16권4호
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• pp.22-28
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• 2001

Heat transfer and pressure distribution for heat exchanger type of domestic gas boiler are different from shape, pitch, thickness of fin and array of pipe respectively. In order to measure the pressure distribution across the heat exchanger, a suction type wind tunnel was constructed and velocity distribution was measured for pilot tube(4 point) of rack type. The experiments were performed for 5 different air flow mass, rpm=3,6,9,12,15 and transverse axis of heat exchanger(x-length) is 5cm respectively. Results showed that above 9.5m/s, pressure distribution dispersion for wet type of heat exchanger is on the increase and above 5.5m/s, pressure distribution dispersion for dry type of heat exchanger is on the increase. Also, pressure distribution dispersion by comparing two different types heat exchanger, dry type of heat exchanger showed a higher augmentation than wet type of heat exchanger.

• 반도체디스플레이기술학회지
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• 제19권2호
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• pp.37-44
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• 2020

In improving laser cutting of optical plastic films for mass production of optoelectronics display units, it is important to understand particle contamination over optical film surface due to fume particle generation and dispersion. This numerical study investigates the effects of downward and upward air flow motions on fume particle dispersion around laser cut line. The simulations employ random particle sampling of up to one million fume particles by probabilistic distributions of particle size, ejection velocity and angle, and fume particle dispersion and surface landing are predicted using Basset-Boussinesq-Oseen model of low Reynolds number flows. The numerical results show that downward air flow scatters fume particles of a certain size range farther away from laser cut line and aggravate surface contamination. However, upward air flow pushes fume particles of this size range back toward laser cut line or sucks them up with rising air motion, thus significantly alleviating surface contamination.

• Composites Research
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• 제18권1호
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• pp.38-44
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• 2005

본 연구에서는 단일방향 탄소섬유강화복합재료 판에서 $S_o$ 대칭모드의 군속도 분선곡선을 전파 방향을 변화시키먼서 계산하였다. 그리고 속노 분산 곡선에서 첫 번째 단절주파수 이하인 0.2 MHz-mm에 해당하는 $S_o$ 대칭모드 군속도를 가지고서 위상속도 곡선을 얻고 slowness 곡선을 도입하여 군속도 곡선으로 교정하였다. 단일방향 섬유강화복합재료 판에서 $S_o$ 대칭모드의 속도를 전파 방향을 변화시키면서 측정하였고 교정된 군속도 곡선과 비교하였다. 측정된 속도는 섬유 방향 근처의 cusp 영역을 제외하고는 교정된 군속도 곡선과 잘 일치하였다. 이것은 단일방향 탄소섬유강화복합재료 판에서 속도가 빠른 방향으로 에너지를 더 잘 전파하기 때문에 전파 방향이 주축방향과 일치하지 않을 때 군속도 방향은 섬유 방향 쪽으로 기울어지는 결과로 나타난 것이다.