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RISS 인기검색어
- 검색키워드
- 주제어 : conditional ensemble average (검색결과 6 건)
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Sangkyun Koo 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.8
A numerical method based on fast multipole summation scheme is used to calculate hydrodynamic interactions in random suspensions of non-colloidal hard-sphere particles. The calculation is carried out for suspensions of 1,024 particles randomly placed in periodic unit cell to determine hydrodynamic transport properties such as permeability of a viscous flow through porous medium, effective viscosity of suspension, and sedimentation velocity of the suspended particles. The particle volume fraction φ ranges from 0.01 to 0.25. Effect of particle number N on the transport properties was examined through the numerical calculations with N=64-1,024. It is shown that sedimentation velocity increases with N approaching an estimate for infinite N, and the finite N effect is negligible in effective viscosity and permeability problems. The present scheme is quite useful for obtaining a statistically-averaged quantity for random suspensions. As an example, ensemble-averaged velocity when position of one particle is fixed is numerically obtained in sedimentation problem. The numerical results are shown to be in excellent agreement with theoretical prediction.
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An investigation of the structure of ensemble averaged extreme wind events
Scarabino, A.,Sterling, M.,Richards, P.J.,Baker, C.J.,Hoxey, R.P. Techno-Press 2007 Wind and Structures, An International Journal (WAS Vol.10 No.2
This paper examines the extreme gust profiles obtained by conditionally sampling full-scale velocity data obtained in the lower part of the atmospheric boundary layer. It is demonstrated that three different types of behaviour can be observed in the streamwise component of velocity. In all cases the corresponding vertical velocity component illustrates similar behaviour. An idealised horseshoe vortex model and a downburst model are investigated to examine if such structures can explain the behaviour observed. In addition, an empirical model is developed for an isolated gust corresponding to each of the three types of behaviour observed. It is possible that the division of the gust profile into three different types may lead to an improvement in the correlation of extreme gust events with respect to type.
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Sedimentation velocity of bidisperse suspensions
구상균 한국공업화학회 2008 Journal of Industrial and Engineering Chemistry Vol.14 No.5
The present study deals with a simple method to predict the sedimentation velocity of suspensions with bidisperse size distribution of particles. The method is developed by modifying the effective-medium theory for monodisperse suspensions. The predictions by the method of the present study are compared with the previous experimental results and the theoretical estimations by Batchelor and Wen [G.K. Batchelor, C.S. Wen, J. Fluid Mech. 124 (1982) 495]. It is shown that the estimations by the effective-medium model of the present study agree well with the experimental results for wider range of concentrations of the suspensions than do those by Batchelor and Wen [G.K. Batchelor, C.S. Wen, J. Fluid Mech. 124 (1982) 495]. However, it is also found that an effective-medium region intrudes the space for the small particle at origin at high total volume fractions near 0.3 when the size ratio of small to large particle is 0.52 and both the volume fractions of the large and small particles are equal. This behavior may be attributed to the segregation of the particles, which has been observed in earlier experiments at the high volume fractions.
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Effective viscosity of bidisperse suspensions
송광호,Sangkyun Koo 한국유변학회 2005 Korea-Australia rheology journal Vol.17 No.1
We determine the effective viscosity of suspensions with bidisperse particle size distribution by modifying an effective-medium theory that was proposed by Acrivos and Chang (1987) for monodisperse suspensions. The modified theory uses a simple model that captures some important effects of multi-particle hydrodynamic interactions. The modifications are described in detail in the present study. Estimations of effective viscosity by the modified theory are compared with the results of prior work for monodisperse and bidisperse suspensions. It is shown that the estimations agree very well with experimental or other calculated results up to approximately 0.45 of normalized particle volume fraction which is the ratio of volume faction to the maximum volume fraction of particles for bidisperse suspensions.
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Effective viscosity of bidisperse suspensions
Koo Sangkyun,Song Kwang Ho The Korean Society of Rheology 2005 Korea-Australia rheology journal Vol.17 No.1
We determine the effective viscosity of suspensions with bidisperse particle size distribution by modifying an effective-medium theory that was proposed by Acrivos and Chang (1987) for monodisperse suspensions. The modified theory uses a simple model that captures some important effects of multi-particle hydrodynamic interactions. The modifications are described in detail in the present study. Estimations of effective viscosity by the modified theory are compared with the results of prior work for monodisperse and bidisperse suspensions. It is shown that the estimations agree very well with experimental or other calculated results up to approximately 0.45 of normalized particle volume fraction which is the ratio of volume faction to the maximum volume fraction of particles for bidisperse suspensions.
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