• Title/Summary/Keyword: Dispersion Radius

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A Study on the Kinetic Energy and Dispersion Behavior of High-velocity Impact-induced Debris Using SPH Technique (SPH 기법을 이용한 고속충돌 파편의 운동에너지와 분산거동 연구)

  • Sakong, Jae;Woo, Sung-Choong;Kim, Tae-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.5
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    • pp.457-467
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    • 2016
  • In this study, we investigate the dispersion behavior of debris and debris cloud generated by high-velocity impacts using the smoothed particle hydrodynamics (SPH) technique. The projectile and target plate were made of aluminum, and we confirm the validity of the SPH technique by comparing the measured major and minor axis lengths of the debris cloud in the reference with the predicted values obtained through the SPH analysis. We perform high-velocity impact and fracture analysis based on the verified SPH technique within the velocity ranges of 1.5~4 km/s, and we evaluate the dispersion behavior of debris induced by the impact in terms of its kinetic energy. The maximum dispersion radius of the debris on the witness plates located behind the target plate was increased with increasing impact velocity. We derive an empirical equation that is capable of predicting the dispersion radius, and we found that 95% of the total kinetic energy of the debris was concentrated within 50% of the maximum dispersion radius.

An experimental study on the correlation of hydraulic mean radius and hydrodispersive parameters in rockfill porous media (자갈 다공성매질에서 수리평균반경과 수리분산 매개변수의 상관성에 관한 실험적 연구)

  • Han, Ilyeong;Lee, Jaejoung;Kim, Gyoo Bum
    • Journal of Korea Water Resources Association
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    • v.54 no.11
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    • pp.863-873
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    • 2021
  • The mechanical dispersion which dominates solute transport in porous media is caused by the difference in flow velocity within pores. Longitudinal dispersion coefficient and longitudinal dispersivity that are hydro-dispersive parameters of advection-dispersion equation can only be obtained by experiment. Hydraulic mean radius that represents the amount and intensity of flowing water within pores can be obtained by the formula using the factors for physical properties. A slug injection test was conducted and a power type empirical formula for obtaining a longitudinal dispersivity using a hydraulic mean radius in rockfill porous media was derived. It is possible to obtain the longitudinal dispersivity depending on transport distance because it contains a formula for a scale constant, and expected to be applicable to waterways filled with homogeneous gravel and small flow rate.

A Simple Mlodel for Dispersion in the Stable Boundary Layer

  • Sung-Dae Kang;Fuj
    • Journal of Environmental Science International
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    • v.1 no.1
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    • pp.35-43
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    • 1992
  • Handling the emergency problems such as Chemobyl accident require real time prediction of pollutants dispersion. One-point real time sounding at pollutant source and simple model including turbulent-radiation process are very important to predict dispersion at real time. The stability categories obtained by one-dimensional numerical model (including PBL dynamics and radiative process) are good agreement with observational data (Golder, 1972). Therefore, the meteorological parameters (thermal, moisture and momentum fluxes; sensible and latent heat; Monin-Obukhov length and bulk Richardson number; vertical diffusion coefficient and TKE; mixing height) calculated by this model will be useful to understand the structure of stable boundary layer and to handling the emergency problems such as dangerous gasses accident. Especially, this simple model has strong merit for practical dispersion models which require turbulence process but does not takes long time to real predictions. According to the results of this model, the urban area has stronger vertical dispersion and weaker horizontal dispersion than rural area during daytime in summer season. The maximum stability class of urban area and rural area are "A" and "B" at 14 LST, respectively. After 20 LST, both urban and rural area have weak vertical dispersion, but they have strong horizontal dispersion. Generally, the urban area have larger radius of horizontal dispersion than rural area. Considering the resolution and time consuming problems of three dimensional grid model, one-dimensional model with one-point real sounding have strong merit for practical dispersion model.al dispersion model.

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TURBULENCE IN THE OUTSKIRTS OF THE MILKY WAY

  • Sanchez-Salcedo, F.J.;Santillan, A.;Franco, Jose
    • Journal of The Korean Astronomical Society
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    • v.40 no.4
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    • pp.171-177
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    • 2007
  • In external galaxies, the velocity dispersion of the atomic hydrogen gas shows a remarkably flat distribution with the galactocentric radius. This has been a long-standing puzzle because if the gas velocity dispersion is due to turbulence caused by supernova explosions, it should decline with radius. After a discussion on the role of spiral arms and ram pressure in driving interstellar turbulence in the outer parts of galactic disks, we argue that the constant bombardment by tiny high-velocity halo clouds can be a significant source of random motions in the outer disk gas. Recent observations of the flaring of H I in the Galaxy are difficult to explain if the dark halo is nearly spherical as the survival of the streams of tidal debris of Sagittarius dwarf spheroidal galaxy suggests. The radial enhancement of the gas velocity dispersion (at R > 25 kpc) due to accretion of cloudy gas might naturally explain the observed flaring in the Milky Way. Other motivations and implications of this scenario have been highlighted.

Spectroscopic observation of the massive high-z (z=1.48) galaxy cluster SPT-CL J2040-4451 using Gemini Multi-Object Spectrographs

  • Kim, Jinhyub;Jee, Myungkook J.;Kim, Seojin F.;Ko, Jongwan
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.1
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    • pp.74.2-74.2
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    • 2019
  • Mass measurement of high-redshift galaxy clusters with high accuracy is important in constraining cosmological parameters. Extremely massive clusters at high redshift may impose a serious tension with the current ΛCDM paradigm. SPT-CL J2040-4451 at z=1.48 is considered one such case given its redshift and mass estimate inferred from the SZ data. The system has also been confirmed to be indeed massive from a recent weak-lensing (WL) analysis. Comparison of the WL mass with the spectroscopic result may provide invaluable information on the dynamical stage of the system. However, the existing spectroscopic coverage of the cluster is extremely poor; only 6 blue star-forming galaxies have been found within the virial radius, which results in highly inflated and biased velocity dispersion. In this work, we present a spectroscopic analysis of the member candidates using Gemini Multi-Object Spectrographs (GMOS) observation in Gemini South. The observation was designed to find early-type member galaxies within the virial radius and to obtain reliable velocity dispersion. We explain our selection scheme and preliminary results of the spectra. We also compare the dynamical mass estimate inferred from the velocity dispersion with the WL mass.

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A Study of Microwave Output Experiment of Slow Wave Waveguide (지파 도파관을 이용한 마이크로파 출력 실험 연구)

  • Kim, Won-Sop
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.58 no.4
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    • pp.465-468
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    • 2009
  • The dispersion relation and the characteristic of propagation are measured. The measurements of the dispersion relation are observed by a plunger method employed in slow plasma density by pumping microwaves on the axis are observed in plasma loaded slow wave structure. In case of small incident microwave powers the well known plasma density cavity are observed. At the axial positions of minimal radius in the waveguides, the maxima og the electron density, the plasma potential and the RF electric field are observed in cases of high-power microwaves.

Kelvin Equation and Its Role in Nano Systems (켈빈 식과 이의 나노 계에서의 구실)

  • Lim, Kyung-Hee
    • Journal of the Korean Applied Science and Technology
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    • v.23 no.1
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    • pp.54-62
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    • 2006
  • Kelvin equation is revisited, which accounts for important phenomena observed frequently in nano-dispersion systems. They include vapor pressure increase for curved interfaces, nucleation, capillary condensation, Ostwald ripening and so on. The smaller the radius of curvature is, the more significant Kelvin equation becomes. Therefore, its meaning, curvature effect, and importance are examined and discussed.

Modeling and Evaluation on the Dispersion of Air Pollutants in the Large Scale Thermal Power Plant (대단위발전소의 대기오염물질 확산에 관한 모델링 및 평가에 관한 연구)

  • Chun, Sang-Ki;Lee, Sung-Chul
    • Journal of Environmental Impact Assessment
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    • v.6 no.2
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    • pp.81-92
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    • 1997
  • This paper presents the results from the comparison analysis and evaluation between the air pollutant dispersion modeling results and the observation data in the area within a 10 km radius from the Boryong thermal power plants. The observation data used in this study were the air pollutant concentrations which had been continuously measured from 8 locations around the Boryong power plants by TMS(tele-monitoring system) for 3 months from September to November, 1996. The short-term and long-term predictions were carried out using ISC3 model and LPDM(Lagrangian Panicle Dispersion Model). The results of ISC3 modeling in a short-term showed highly as 0.7 in a correlation coefficient, but in a long-term showed just 0.54. On the other hand, LPDM showed 0.78 in a correlation coefficient for a long-term, but in a short-term showed highly value than the observation concentrations.

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A comparative study of borehole size and tool effect on dispersion curves (시추공경과 공내검층기가 분산곡선에 미치는 영향에 대한 비교 연구)

  • Zhao, Weijun;Kim, Jong-Man;Kim, Yeong-Hwa
    • Geophysics and Geophysical Exploration
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    • v.12 no.1
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    • pp.154-162
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    • 2009
  • Sonic wave dispersion characteristics are one of the most important targets of study, particularly in estimating shear wave velocity from borehole sonic logging. We have tested dispersion characteristics using monopole and dipole sources. Theoretical dispersion curves were computed for tool-absent and tool-included models having the same physical properties but different diameters (including ${\Phi}520mm$, ${\Phi}150mm$, and ${\Phi}76mm$). Comparisons were made between boreholes of different sizes and between tool-absent and tool-included models. Between the tool-included and the tool-absent boreholes, a close similarity in dispersion curve shape was revealed for the monopole source, and a significant difference was shown for the dipole source. However, for the cut-off frequency, particularly in the engineering boreholes (${\Phi}76mm$ and ${\Phi}50mm$), a significant difference was observed for signals from the monopole source, but approximately the same cut-off frequencies were found with the dipole source. This indicates the need of careful choice of source frequency in monopole-source sonic logging, particularly in an engineering borehole. The results of numerical experiments show that cut-off frequency is exponentially proportional to the inverse of borehole radius, irrespective of the mode type and the presence of a tool, and that the cut-off frequencies for each borehole environment could be expressed as an exponential function, rather than the inversely proportional relationship between the cut-off frequency and the borehole radius that was previously generally recognised. From the direct comparison of dispersion curves, the effects on the dispersion characteristics of borehole size and the presence of the tool can be revealed more clearly than in previous studies, which presented the dispersion curve and/or characteristics for each borehole environment separately.

A Simple Model for Dispersion in the Stable Boundary Layer

  • Kang Sung-Dae;Kimura Fujio;Lee Hwa-Woon;Kim Yoo-Keun
    • Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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    • v.1 no.1
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    • pp.35-43
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    • 1997
  • Handling the emergency problems such as Chemobyl accident require real time prediction of pollutants dispersion. One-point real time sounding at pollutant source and simple model including turbulent-radiation process are very important to predict dispersion at real time. The stability categories obtained by one-dimensional numerical model (including PBL dynamics and radiative process) are good agreement with observational data (Golder, 1972). Therefore, the meteorological parameters (thermal, moisture and momentum fluxes; sensible and latent heat; Monin-Obukhov length and bulk Richardson number; vertical diffusion coefficient and TKE; mixing height) calculated by this model will be useful to understand the structure of stable boundary layer and to handling the emergency problems such as dangerous gasses accident. Especially, this simple model has strong merit for practical dispersion models which require turbulence process but does not takes long time to real predictions. According to the results of this model, the urban area has stronger vertical dispersion and weaker horizontal dispersion than rural area during daytime in summer season. The maximum stability class of urban area and rural area are 'A' and 'B' at 14 LST, respectively. After 20 LST, both urban and rural area have weak vertical dispersion, but they have strong horizontal dispersion. Generally, the urban area have larger radius of horizontal dispersion than rural area. Considering the resolution and time consuming problems of three dimensional grid model, one-dimensional model with one-point real sounding have strong merit for practical dispersion model.

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