• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.11-19
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• 2005

First, methods of numerical analysis of gas-particle flows is classified into micro, meso and macro scale approaches based on the concept of multi-scale mechanics. Next, the explanation moves on to discrete particle simulation where motion of individual particles is calculated numerically using the Newtonian equations of motion. The author focuses on the cases where particle-to-particle interaction has significant effects on the phenomena. Concerning the particle-to-particle interaction, two cases are considered: the one is collision-dominated flows and the other is the contact-dominated flows. To treat this interaction mathematically, techniques named DEM(Distinct Element Method) or DSMC (Direct Simulation Monte Carlo) have been developed DEM, which has been developed in the field of soil mechanics, is useful for the contact -dominated flows and DSMC method, developed in molecular gas flows, is for the collision-dominated flows. Combining DEM or DSMC with CFD (computer fluid dynamics), the discrete particle simulation becomes a more practical tool for industrial flows because not only the particle-particle interaction but particle-fluid interaction can be handled. As examples of simulations, various results are shown, such as hopper flows, particle segregation phenomena, particle mixing in a rotating drum, dense phase pneumatic conveying, spouted bed, dense phase fluidized bed, fast circulating fluidized bed and so on.

• Bulletin of the Korean Chemical Society
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• 제25권12호
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• pp.1893-1897
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• 2004

Hydrodynamic simulations of mesoscopic solvent have been performed by multi-particle collision algorithm in a real dimensional system without and with the random shifting of the grid. A systematic conversion of the dimensionless units to a real dimensional system was confirmed by jump rates of solvent particles. Speed distributions of solvent particles obtained from the simulations agreed very well with the Maxwell-Boltzmann distributions. Solvent viscosities obtained from the simulations and from the conversion of units are exactly the same which confirmed the correct conversion of the units once again. The calculation of the friction coefficient of a massive Brownian particle in a mesoscopic solvent as a function of Brownian particle diameter was examined as an example.

• Journal of Advanced Marine Engineering and Technology
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• 제34권7호
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• pp.981-990
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• 2010

The main objective of this study is to investigate the fluid flow and the heat transfer characteristics of nanofluids using multi-phase thermal LBM and to realize theenhancement of heat transfer characteristics considered in the Brownian motion. In multi-phase, fluid component($H_2O$) is driven by Boussinesq approximation, and nanoparticles component by the external force gravity and buoyancy. The effect of Brownian motion as a random movement is modified to the internal velocity of nanoparticles(Cu). Simultaneously, the particles of both the phases assume the local equilibrium temperature after each collision. It has been observed that when simulating $H_2O$-Cu nanoparticles, the heat transfer is the highest, at the particle volume fraction 0.5% of the particle diameter 10 nm. The average Nusselt number is increased approximately by 33% at the particle volume fraction 0.5% of the particle diameter 10 nm when compared with pure water.

• Advances in robotics research
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• 제2권2호
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• pp.161-182
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• 2018

This paper proposes a novel receding horizon control (RHC) algorithm for formation control of a swarm of unmanned surface vehicles (USVs) using particle swarm optimization (PSO). The proposed control algorithm provides the coordinated path tracking of multi-agent USVs while preventing collisions and considering external disturbances such as ocean currents. A three degrees-of-freedom kinematic model of the USV is used for the RHC with guaranteed stability and convergence by incorporating a sequential Monte Carlo (SMC)-based particle initialization. An ocean current model-based estimator is designed to compensate for the effect of ocean currents on the USVs. This method is compared with the PSO-based RHC algorithms to demonstrate the performance of the formation control and the collision avoidance in the presence of ocean currents through numerical simulations.

• 한국산업정보학회논문지
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• 제24권5호
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• pp.115-120
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• 2019

본 논문에서는 이동 구간 입자 군집 최적화 (Receding horizon particle swarm optimization; RHPSO) 알고리즘 기반 다개체 로봇 편대 제어 알고리즘의 통계적 성능 분석 결과를 제시한다. 다개체 로봇의 편대 제어 문제는 로봇 간 충돌 회피를 고려할 경우, 구속 조건이 있는 비선형 최적화 문제로 정의될 수 있다. 일반적으로 구속 조건이 있는 비선형 최적화 문제는 최적해를 찾는데 많은 시간이 걸리는 문제점이 있다. 이동 구간 입자 군집 최적화 알고리즘은 로봇 편대 제어의 최적화 문제에 대한 준최적해를 빠르게 찾기 위해 제안된 알고리즘이다. 이동 구간 입자 군집 최적화 알고리즘은 알고리즘에 사용되는 후보해의 개수와 세대 수가 증가함에 따라 계산 복잡도가 증가한다. 따라서 최소의 후보해와 세대 수만으로 실시간 제어에 사용될 수 있는 준최적해를 찾는 것이 중요하다. 본 논문에서는 이동 구간 입자 군집 최적화 알고리즘의 후보해의 수와 세대 수에 따른 제어 오차를 비교하였다. 다양한 조건의 시뮬레이션 실험을 통해서 통계적으로 결과를 분석하고, 허용 가능한 편대 오차 범위 내에서 이동 구간 입자 군집 최적화 알고리즘의 최소 후보해의 수와 세대 수를 도출한다.

• 한국기계가공학회지
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• 제18권3호
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• pp.59-65
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• 2019

In many industries, particle packing is adopted quite frequently. In the particle packing process, the Discrete Element Method (DEM) can analyze the multi-collision of particles efficiently. Two types of contact models are frequently used for the DEM. One is the linear spring model, which has the fastest calculation time, and the other is the Hertz-Mindlin model, which is the most frequently used contact model employing the DEM. Meanwhile, very tiny particles in the micrometer order are used in modern industries. In the micro length order, surface force is important to decreased particle size. To consider the effect of surface force in this study, we performed a simulation with the Hertz-Mindlin model and added the Johnson-Kendall-Roberts (JKR) theory depicting surface force with surface energy. In addition, three contact models were compared with several parameters. As a result, it was found that the JKR model has larger residual stress than the general contact models because of the pull-off force. We also validated that surface force can influence particle behavior if the particles are small.

• 한국가시화정보학회지
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• 제20권3호
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• pp.74-85
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• 2022

We propose a Cubic-Interpolated Pseudo-Particle Lattice Boltzmann method (CIP-LBM) for the convection-diffusion equation (CDE) based on the Bhatnagar-Gross-Krook (BGK) scheme equation. The CIP-LBM relies on an accurate numerical lattice equilibrium particle distribution function on the advection term and the use of a splitting technique to solve the Lattice Boltzmann equation. Different schemes of lattice spaces such as D1Q3, D2Q5, and D2Q9 have been used for simulating a variety of problems described by the CDE. All simulations were carried out using the BGK model, although another LB scheme based on a collision term like two-relation time or multi-relaxation time can be easily applied. To show quantitative agreement, the results of the proposed model are compared with an analytical solution.

• 로봇학회논문지
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• 제15권1호
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• pp.55-61
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• 2020

Getting on and off an elevator is one of the most important parts for multi-floor navigation of a mobile robot. In this study, we proposed the method for the pose recognition of elevator doors, safe path planning, and motion estimation of a robot using RGB-D sensors in order to safely get on and off the elevator. The accurate pose of the elevator doors is recognized using a particle filter algorithm. After the elevator door is open, the robot builds an occupancy grid map including the internal environments of the elevator to generate a safe path. The safe path prevents collision with obstacles in the elevator. While the robot gets on and off the elevator, the robot uses the optical flow algorithm of the floor image to detect the state that the robot cannot move due to an elevator door sill. The experimental results in various experiments show that the proposed method enables the robot to get on and off the elevator safely.

• Bulletin of the Korean Chemical Society
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• 제24권6호
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• pp.771-776
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• 2003

The structural and dynamic properties of small n-alkane clusters embedded in a mesoscopic solvent are investigated. The solvent interactions are taken into account through a multi-particle collision operator that conserves mass, momentum and energy and the solvent dynamics is updated at discrete time intervals. The cluster molecules interact among themselves and with the solvent molecules through intermolecular forces. The properties of n-heptane and n-decane clusters interacting with the mesoscopic solvent molecules through repulsive Lennard-Jones interactions are studied as a function of the number of the mesoscopic solvent molecules. Modifications of both the cluster and solvent structure as a result of cluster-solvent interactions are considered. The cluster-solvent interactions also affect the dynamics of the small n-alkane clusters.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.574-578
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• 2013

In this work, the friction and diffusion coefficients of a tracer in a mesoscopic solvent are evaluated as a function of the tracer size by a hybrid molecular dynamics simulation where solute molecules evolve by Newton's equations of motion but the solvent evolves through the multi-particle collision dynamics. The friction coefficient is shown to scale linearly with the tracer size for larger tracers in accord with predictions of hydrodynamic theories. The diffusion coefficient of tracer is found to be inversely proportional to tracer size. The behavior of Stokes-Einstein formula is validated as a function of tracer size.