• Journal of the Korea Society for Simulation
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• v.28 no.4
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• pp.21-32
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• 2019

Inspired by the social behavior models of a bird flock or fish school, particle swarm optimization (PSO) is a popular metaheuristic optimization algorithm and has been widely used from solving a complex optimization problem to learning a artificial neural network. However, PSO is difficult to apply to many real-life optimization problems involving stochastic noise, since it is originated in a deterministic environment. To resolve this problem, this paper incorporates a resampling method called the uncertainty evaluation (UE) method into PSO. The UE method allows the particles to converge on the accurate optimal solution quickly in a noisy environment by selecting the particles' global best position correctly, one of the significant factors in the performance of PSO. The results of comparative experiments on several benchmark problems demonstrated the improved performance of the propose algorithm compared to the existing studies. In addition, the results of the case study emphasize the necessity of this work. The proposed algorithm is expected to be effectively applied to optimize complex systems through digital twins in the fourth industrial revolution.

• Resources Recycling
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• v.23 no.6
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• pp.30-39
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• 2014

The trajectories of PCB(Printed Circuit Board) particles in the corona discharge electrostatic separation was simulated. The PCB particles are prepared by crushing bare board, which disassembled from electronic components, consist mostly of copper and FR-4(Flame Retardant Level-4) Firstly, a model was established for calculating of detachment points of PCB particles from the rotating electrode in separator. The model of detachment points was derived from equilibrium of force such as gravity force, centrifugal force, electrostatic force. The trajectories of particles after detachment was calculated by acceleration derived from time-integrating method of motion equation. In this simulation, particle size, supplied voltage, rotation speed of rotating roll electrode and angle of induction electrode were adopted as variables. While the trajectories of FR-4 particles were affected by all variables, rotation speed of rotating roll electrode was dominant variables affecting trajectories of copper particles.

• Journal of the Korea Computer Graphics Society
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• v.24 no.2
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• pp.11-20
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• 2018

We propose a new method particle-based method that explicitly preserves thin liquid sheets for animating liquids on CPU-GPU heterogeneous computing framework. Our primary contribution is a particle-based framework that splits at thin points and collapses at dense points to prevent the breakup of liquid on GPU. In contrast to existing surface tracking methods, the our method does not suffer from numerical diffusion or tangles, and robustly handles topology changes on CPU-GPU framework. The thin features are detected by examining stretches of distributions of neighboring particles by performing PCA(Principle component analysis), which is used to reconstruct thin surfaces with anisotropic kernels. The efficiency of the candidate position extraction process to calculate the position of the fluid particle was rapidly improved based on the CPU-GPU heterogeneous computing techniques. Proposed algorithm is intuitively implemented, easy to parallelize and capable of producing quickly detailed thin liquid animations.

• Journal of the Korea Society for Simulation
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• v.32 no.1
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• pp.23-34
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• 2023

The purpose of this paper is to review global stochastic optimization algorithms(GSOA) in case binary response experimentation is used and to compare the performances of them. GSOAs utilise estimator of probability of success $\^p$ instead of population probability of success p, since p is unknown and only known by its estimator which has stochastic characteristics. Hill climbing algorithm algorithm, simple random search, random search with random restart, random optimization, simulated annealing and particle swarm algorithm as a population based algorithm are considered as global stochastic optimization algorithms. For the purpose of comparing the algorithms, two types of test functions(one is simple uni-modal the other is complex multi-modal) are proposed and Monte Carlo simulation study is done to measure the performances of the algorithms. All algorithms show similar performances for simple test function. Less greedy algorithms such as Random optimization with Random Restart and Simulated Annealing, Particle Swarm Optimization(PSO) based on population show much better performances for complex multi-modal function.

• Journal of Ocean Engineering and Technology
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• v.31 no.6
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• pp.388-396
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• 2017

A Lagrangian approach based computational fluid dynamics (CFD) was used to simulate large and/or sharp deformations and fragmentations of interfaces, including free surfaces, through tracing each particle with physical quantities. According to the concept of the particle-based CFD method, it is possible to apply it to both fluid particles and solid particles such as sand, gravel, and rock. However, the presence of more than two different phases in the same domain can make it complicated to calculate the interaction between different phases. In order to solve multiphase problems, particle interaction models for multiphase problems, including surface tension, buoyancy-correction, and interface boundary condition models, were newly adopted into the moving particle semi-implicit (MPS) method. The newly developed MPS method was used to simulate a typical validation problem involving dam breaking. Because the soil and other particles, excluding the water, may have different viscosities, various viscosity coefficients were applied in the simulations for validation. The newly developed and validated MPS method was used to simulate the mobile beds induced by broken dam flows. The effects of the viscosity on soil particles were also investigated.

• Journal of the Korea Society for Simulation
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• v.22 no.4
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• pp.21-28
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• 2013

This paper describes the method to solve the optimization problems for stochastic simulation which is represented by military simulations. For this reason, the test fitness function reflecting the characteristics of military simulations, complex and stochastic results, is defined and PSO is used to solve the test fitness function. To control the known weak point of PSO for stochastic simulations, this paper proposes a technique which reevaluates the value of global optimum. By using the technique, the result shows notable improvements. From the simulation results, interactions among the calculation conditions which affect the accuracy and speed of optimization are analyzed. And the strategy for the optimization of stochastic simulations is proposed.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.456-466
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• 2017

This work investigated the particle morphology change to difference in milling media in a metal based composite fabrication process using a stirred ball mill with ball behavior of DEM simulation. A simulation of the three dimensional motion of grinding media in the stirred ball mill for the research of grinding mechanism to clarify the force, kinetic energy, and medium velocity of grinding media were calculated. In addition, the rotational speed of the stirred ball mill was changed to the experimental conditions for the composite fabrication, and change of the input energy was also calculated while changing the ball material, the flow velocity, and the friction coefficient under the same conditions. As the rotating speed of the stirred ball mill increased, the impact energy between the grinding media to media, media to wall, and media and the stirrer increased quantitatively. Also, we could clearly analyze the change of the particle morphology under the same experimental conditions, and it was found that the ball behavior greatly influences in the particle morphology changes.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.1
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• pp.23-34
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• 2020

This paper covers the development of prediction techniques for ice load on ice-breakers operating in continuous ice-breaking under level ice conditions using particle-based continuum mechanics. Ice is assumed to be a linear elastic material until the fracture occurs. The maximum normal stress theory is used for the criterion of fracture. The location of the crack can be expressed using a local scalar function consisting of the gradient of the first principal stress and the corresponding eigen-vector. This expression is used to determine the relative position of particle pair to the new crack. The Hertz contact model is introduced to consider the collisions between ice fragments and the collisions between hull and ice fragments. In order to verify the developed technique, the simulation results for the three-point bending problems of ice-specimen and the continuous ice-breaking problem around a wedge-type model ship with bow angle of 20° are compared with the experimental results carrying out at Korea Research Institute of Ships and Ocean Engineering (KRISO).

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.251.2-251.2
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• 2014

현재 의료 및 표면처리 분야에 많이 이용되고 있는 상온 대기압 플라즈마 중에서 유전체 격벽 방전(DBD) 장치는 비교적 간단한 구조를 가지며 sub-millimeters 사이즈에서도 매우 높은 플라즈마 밀도의 발생 및 유지가 가능하다. 그러나, 현재로선 이러한 Micro DBD의 특성을 실험적으로 분석하는 것은 장비의 한계가 있으므로, Particle-In-Cell 시뮬레이션을 이용하여 중요 플라즈마 변수들을 관찰하였다. 여기서 사용된 중요변수로는 13.56 MHz~600 MHz사이의 인가 주파수를 두었으며, 유전체 표면에서 양이온에 대한 이차전자 방출계수를 고려하였다, 또한 중성기체는 헬륨가스와 아르곤가스의 2가지 중성기체인 경우를 살펴보았다. 이러한 시뮬레이션을 통해 인가전압의 주기 대비 Ion transit time의 비율이 달라짐에 따라 플라즈마 쉬스의 특성변화와 함께 전자 에너지 확률함수(EEPF)의 특성이 달라진다는 것을 확인하고, 이러한 전자 가열 양상의 변화 원리에 대해서 분석하였다. 또한 주파수 비율 조정을 통한 전자온도, 파워, 효율 등을 조절하는 방법의 공학적 가치에 대해 의견을 제시하였다.

• Proceedings of the Korean Society of Computer Information Conference
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• 2022.01a
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• pp.357-360
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• 2022

본 논문에서는 대용량 데이터에서 빠르게 주변 데이터를 접근하기 위한 자료구조인 최근접 이웃 탐색(Nearest neighbor search, NNS) 문제를 빠르게 풀 수 있는 바이토닉 정렬(Bitonic sort) 기반 해시 테이블을 GPU기반에서 설계하는 방법과 이를 통해 입자 기반 물리 시뮬레이션을 고속화할 수 있는 방법에 대해 살펴본다. 본 논문에서는 CUDA 아키텍처를 이용하여 해시 테이블을 설계하였으며, 계산양이 가장 큰 데이터 정렬부분을 최적화함으로써 NVIDIA에서 제공하는 CUDA 해시 테이블보다 빠른 결과를 얻을 수 있으며, 이 자료구조를 입자 기반 시뮬레이션에 통합함으로써 고성능 시뮬레이션을 쉽게 제작할 수 있다.