• 천문학회보
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• 제41권1호
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• pp.47.2-47.2
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• 2016

The protons and helium ions in the solar wind are observed to possess anisotropic temperature profiles. The anisotropy appears to be limited by various marginal instability conditions. One of the efficient methods to investigate the global dynamics and distribution of various temperature anisotropies in the large-scale solar wind models may be that based upon the macroscopic quasi-linear approach. The present paper investigates the proton and helium ion anisotropy instabilities on the basis of comparison between the quasi-linear theory versus particle-in-cell simulation. It is found that the overall dynamical development of the particle temperatures is quite accurately reproduced by the macroscopic quasi-linear scheme. The wave energy development in time, however, shows somewhat less restrictive comparisons, indicating that while the quasi-linear method is acceptable for the particle dynamics, the wave analysis probably requires higher-order physics, such as wave-wave coupling or nonlinear wave-particle interaction. We carried out comparative studies of proton firehose instability, aperiodic ordinary mode instability, and helium ion anisotropy instability. It was found that the agreement between QL theory and PIC simulation is rather good. It means that the quasilinear approximation enjoys only a limited range of validity, especially for the wave dynamics and for the relatively high-beta regime.

• 대한기계학회논문집B
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• 제33권10호
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• pp.811-819
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• 2009

In the present study, deposition of discrete and small particles on a filter fiber was simulated by stochastic method. Trajectory of each particle was numerically solved by Langevin equation. And Lattice Boltzmann method (LBM) was used to solve flow field around the filter collector for considering complex shape of deposit layer. Interaction between the flow field and the deposit layer was obtained from a converged solution from an inner-loop calculation. Simulation method is properly validated with filtration theory and collection efficiency due to different filtration parameters are examined and discussed. Morphology of deposit layer and its evolution was visualized in terms of the particle size. The particle loaded effect on collection efficiency was also discussed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.571-572
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• 2012

• Structural Engineering and Mechanics
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• 제62권2호
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• pp.163-170
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• 2017

This study presents a particle-wall filtration model for predicting the particle motion behavior in a typical rotational flow field-filtration in blower system of cooker hood. Based on computational fluid dynamics model, air flow and particles has been simulated by Lagrangian-particle/ Eulerian-gas approaches and get verified by experiment data from a manufacturer. Airflow volume, particle diameter and local structure, which are related to the particle filtration has been studied. Results indicates that: (1) there exists an optimal airflow volume of $1243m^3/h$ related to the most appropriate filtration rate; (2) Diameter of particle is the significant property related to the filtration rate. Big size particles can represent the filtration performance of blower; (3) More than 86% grease particles are caught by impeller blades firstly, and then splashed onto the corresponding location of worm box internal wall. These results would help to study the micro-particle motion behavior and evaluate the filtration rate and structure design of blower.

• 한국토양비료학회지
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• 제40권4호
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• pp.326-329
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• 2007

Quantifying soil organic carbon (SOC) has long been considered to improve our understanding of soil productivity, soil carbon dynamics, and soil quality. And also SOC could contribute as a major soil management factor for prescribing fertilizers and controlling of soil erosion and runoff. Reducing tillage intensity has been recommended to sequester SOC into soil. On the other hand, determination of traditional SOC could barely identify the tillage practices effect. Physical soil fractionation has been reported to improve interpretation of soil tillage practices impact on SOC dynamics. However, most of these researches were focused onupland soils and few researches were conducted on paddy soils. Therefore, the objective of this research was to evaluate paddy soil tillage impact on SOC by physical soil fractionation. Soils were sampled in conventional-tillage (CT), partial-tillage (PT), no-tillage (NT), and shallow-tillage (ST)plots at the National Institute of Crop Science research farm. Samples were obtained at the three sampling depth with 7.5-cm increment from the surface and were sieved with 0.25- and 0.053-mm screen. Soil organic carbon was determined by wet combustion method. Significant difference of SOC contentwas found among sampling soil depth and soil particle size. SOC content tended to increase at the ST plot with increasing size of soil particle fraction. We conclude that quantifying soil organic carbon by physical soil particle fractionation could improve understanding of SOC dynamics by soil tillage practices.

• 대한기계학회논문집B
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• 제40권1호
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• pp.9-19
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• 2016

본 연구는 테일러 반응기내 각속도와 유입속도 변화에 따른 테일러 유동의 변화와 입자의 체류시간 변화를 전산수치해석 기법을 이용하여 알아보았다. 반응기내 유동은 각속도가 증가함에 따라 점점 불안정해지는 경향을 보였다. 유동은 레이놀즈 수의 증가에 따라 CCF, TVF, WVF, MWVF 영역으로 이동하게 되고 각 영역에서 상이한 유동특성을 보였다. 유입속도의 변화가 테일러 유동에 영향을 주는 것을 확인하였다. 각속도가 빠를수록, 그리고 유입속도가 느릴수록 입자의 체류시간과 표준편차는 증가하였다.

• Bulletin of the Korean Chemical Society
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• 제31권4호
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• pp.959-964
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• 2010

In this work, equilibrium molecular dynamics (MD) simulations in a microcanonical ensemble are performed to evaluate the friction coefficient of a Brownian particle (BP) in a Lennard-Jones (LJ) solvent. The friction coefficients are determined from the time dependent friction coefficients and the momentum autocorrelation functions of the BP with its infinite mass at various ratios of LJ size parameters of the BP and solvent, ${\sigma}_B/{\sigma}_s$. The determination of the friction coefficients from the decay rates of the momentum autocorrelation functions and from the slopes of the time dependent friction coefficients is difficult due to the fast decay rates of the correlation functions in the momentum-conserved MD simulation and due to the scaling of the slope as 1/N (N: the number of the solvent particle), respectively. On the other hand, the friction coefficient can be determined correctly from the time dependent friction coefficient by measuring the extrapolation of its long time decay to t=0 and also from the decay rate of the momentum autocorrelation function, which is obtained by time integration of the time dependent friction coefficient. It is found that while the friction coefficient increases quadratically with the ratio of ${\sigma}_B/{\sigma}_s$ for all ${\sigma}_B$, for a given ${\sigma}_s$ the friction coefficient increases linearly with ${\sigma}_B$.

• 한국정보과학회논문지:시스템및이론
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• 제32권1호
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• pp.29-38
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• 2005

유체 애니메이션은 물리적 시뮬레이션과 시각적 렌더링으로 구성된다. 물리적 시뮬레이션은 입자 동역학을 이용한 해석 방법과 나비어-스토크스(Navier-Stokes) 방정식을 이용한 연속체 유동해석 방법이 많이 사용된다. 입자 동역학을 이용한 시뮬레이션은 연산 속도는 빠르나 유체의 움직임이 경우에 따라 부자연스러우며, 나비어-스토크스 방정식을 이용한 방법은 적절한 조건 하에서 사실적인 유체의 움직임을 표현할 수 있으나 방대한 연산량과 계산의 복잡성으로 인하여 실시간 응용이 어렵다. 우수한 품질의 렌더링 영상은 주로 전역적 조명 방법을 사용하여 얻을 수 있는데, 이 역시 실시간 응용에 적합한 속도론 내기에는 부적합하다. 본 논문에서는 개선된 입자 동역학 시뮬레이션과 선적분 볼륨 렌더링을 이용한 고속유체 애니메이션 방법을 제안한다 레나드-존스(Lennard-Jones) 모턴을 이용한 입자동역학 해석기법을 이용하여 유체의 움직임을 고속으로 시뮬레이션 하였으며, 적은 수의 입자만으로도 충분한 유체의 부피를 표현할 수 있도록 연산효율을 개선하였다. 또한 실시간 렌더링을 위하여 적은 수의 슬라이스로도 우수한 품질의 영상을 빠르게 얻을 수 있는 선적분 볼륨 렌더링 방식을 사용하였다. 본 제안 방법을 사용하여 실시간 응용에 적절한 속도와 화질을 보여주는 유체 애니메이션이 가능하다.

• Journal of Theoretical and Applied Mechanics
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• 제2권1호
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• pp.51-70
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• 1996

This study is generalization of the study of Miles[Physica 11D, 1984, pp.309-323]on the resonant motion of a spherical pendulum, which is equivalent to a particle on a spherical container subject to a linear, horizontal excitation. This study covers an arbitrary shape of container and a more general excitation (horizontal but elliptic motion). The averaging method is applied to reduce the governing equations to an autonomous system with cubic nonlinear terms, under the assumption of small amplitude of the container motion. It is shown that both the container shape and the excitation pattern affect the particle dynamics. Under the linear excitation, the anharmonic motion of the particle is possible only for a certain finite range of the parameter a controling the container shape. Stability of the particle's harmonic motion is also influenced by the excitation pattern; as the excitation trajectory becomes closer to a circle, the particle's motion has a stronger tendency to become stable and to follow the rotational direction of the excitation. Under a circular excitation, the motion is always stable and circular with the same rotational direction as the excitation. Analogy between the present model and that of the surface wave inside a circular is studied quantitatively.

• Korean Journal of Chemical Engineering
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• 제35권12호
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• pp.2355-2364
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• 2018

We evaluated the effect of particle size and associated dynamics on a hydrocyclone separation process in order to understand the movement of the particle trajectories inside the hydrocyclone via numerical analysis, with particles of acid hydrolysis residues discharged in $TiO_2$ production via the sulfate method as a case study. The values obtained from the numerical simulation were successfully compared with those from experimental tests in the literature, allowing a description of the dynamics of the particles, their acting forces, and their relevant properties together with separation efficiency. The results showed that particle motion is jointly controlled by the drag force, the pressure gradient force and the centrifugal force. With increasing particle size, the influence of the drag force is weakened, whereas that of the centrifugal force and pressure gradient is strengthened. Factors including particle density, slurry viscosity, and inlet slurry flow rate also contribute to a clear and useful understanding of particle motion behavior in the hydrocyclone as a method for improving the separation efficiency.