Simulation of solid-liquid flows using a two-way coupled smoothed particle hydrodynamics-discrete element method model

권지회,Heechan Cho 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.10

We introduce a coupled smoothed particle hydrodynamics-discrete element method (SPH-DEM) to describe the two-way interaction between the two phases of a solid-liquid flow. To validate the model, we simulated two test problems: a solid-liquid counter-flow in a periodic box and particle settlement. The simulations correctly predicted the dynamics, and the results showed good agreement with the theory. The developed model was then applied to simulate the slurry coagulation process to examine the coagulation efficiency. When the rotational speed exceeded the normal range, the coagulation rate decreased with time, even though the rate was high during the early stage due to the size separation effect of the particles. Given this result, overly fast stirring appears to have an adverse effect on the coagulation efficiency. The model is applicable to the design of various types of solid-liquid flows.

이산요소법의 파분쇄 분야 적용: 현황 및 전망

권지회 한국자원공학회 2020 한국자원공학회지 Vol.57 No.5

For several decades, the discrete element method (DEM) has been broadly applied to problems that are difficult to solve using the conventional continuum approach. In the field of mineral processing, DEM has played a key role in understanding the crushing and grinding processes for the past two decades. DEM, which has been mainly utilized for obtaining detailed energy spectra inside mills in the early age, has been broadening its application to fracture analysis, crushing, and wearing in mills. Furthermore, the reliability of process scale analysis can be enhanced by combining DEM with the population balance model. This study provides a general overview of research trends, applications, prospects, and challenges of DEM in the field of comminution. 최근 수십년간 이산요소법(discrete element method, DEM)은 전통적인 연속체 접근법으로 해석이 어려운 다양한 문제에그 활용성이 날로 증가하고 있으며, 선광 분야 중 파분쇄 분야에서 20여년 전부터 적극적으로 활용되고 있다. 초기 장비 내 에너지 스펙트럼 분석 중심으로 활용되던 DEM은 입자내 균열의 발생 및 전파, 파쇄, 장비 마모에 이르기까지 다양한 현상을 입자 스케일의 정보를 활용하여 분석하는 도구로 활용되어 왔으며, 물질수지모델과의 연계 해석을 통해 공정 스케일 연구의 폭을 확장시키는 데도 기여해 왔다. 본 연구에서는 최근 DEM을 이용한 분쇄 연구 동향의 변화, 활용 사례, 추후 전망 및 해결 과제 등에 대해 세부적으로 살펴보았다.

Large-scale SPH simulation for three-dimensional flow

권지회,조희찬,Cheolho Song,Daeyang Lee 한국자원공학회 2012 Geosystem engineering Vol.15 No.3

Computational load and numerical instability are two of the most challenging problems in enlarging the scale of smoothed particle hydrodynamics (SPH) simulation and applying SPH to a 3D problem. In this work, a study on advanced algorithm is conducted for large-scale SPH simulation in 3D. To reduce computational cost, the concept of a grid-based, linked-list algorithm was adopted and tested by being applied to solve a rotating cylinder problem. The result shows that the size of the search grid should be above or equal to the size of the support domain to obtain a stable and accurate solution. A zero order filtering algorithm is applied for reduction of noise signal in density and pressure for every 50 steps. Consequently, noise signal in density and pressure is apparently decreased and potential instability of computation has decreased. The improved SPH algorithm was applied to simulate 3D water discharge and the result shows that the algorithm satisfies Bernulli’s theorem with acceptable degree of errors.

3D DISCRETE ELEMENT METHOD SIMULATION TO VARIOUS TYPES OF MILL

권지회,이훈,조희찬 한국자원공학회 2008 Geosystem engineering Vol.11 No.1

A model based on the Discrete Element Method (DEM) was used to simulate various types of mill (ball mill, centrifugal mill and vibration mill). The model is capable of describing the motion of balls and predicting the types of force between ball and ball, and ball and wall. In the case of ball mill, it was found that the movement of balls was mostly cascading type at the low speed, and at the speed beyond the critical value, the movement of balls was mostly centrifugal. Also, it was found that the movement of balls mainly depends on the lifter design of the mill. In the case of centrifugal mill, the operation characteristics of the mill were observed with the change of G/D (gyration diameter to mill diameter). The result of the simulation showed that the ball movement was similar to that of vibration mill at a low G/D ratio, and that of planetary mill at a high G/D ratio. In the case of vibration mill, different patterns of ball movements to the various ball filling conditions were observed and there was a linear relationship between impact energy and specific rate of breakage. The developed 3-dimensional DEM model can provide the ways of improving the energy efficiency and the operating at the optimum milling conditions. A model based on the Discrete Element Method (DEM) was used to simulate various types of mill (ball mill, centrifugal mill and vibration mill). The model is capable of describing the motion of balls and predicting the types of force between ball and ball, and ball and wall. In the case of ball mill, it was found that the movement of balls was mostly cascading type at the low speed, and at the speed beyond the critical value, the movement of balls was mostly centrifugal. Also, it was found that the movement of balls mainly depends on the lifter design of the mill. In the case of centrifugal mill, the operation characteristics of the mill were observed with the change of G/D (gyration diameter to mill diameter). The result of the simulation showed that the ball movement was similar to that of vibration mill at a low G/D ratio, and that of planetary mill at a high G/D ratio. In the case of vibration mill, different patterns of ball movements to the various ball filling conditions were observed and there was a linear relationship between impact energy and specific rate of breakage. The developed 3-dimensional DEM model can provide the ways of improving the energy efficiency and the operating at the optimum milling conditions.

완화 입자 유체 동역학을 이용한 유동 해석 및 고체-유체 연성 해석

권지회 대한기계학회 2020 기계저널 Vol.60 No.9

시각지능 및 동적 시뮬레이션 기반의 사용자 맞춤형 가상 지진 실감화

권지회,류동우,이상호 한국자원공학회 2018 한국자원공학회지 Vol.55 No.6

The recent occurrence of consecutive large earthquakes in the southeastern part of the Korean peninsula has brought significant attention to the prevention of earthquake damage in Korea. This article aims to explore a technology-based approach for earthquake drills using state-of-the-art visual intelligence and virtual reality technologies. The technical process consists of several stages, including acquisition of image information in living spaces using a camera, recognition of objects from the acquired image information, extraction of three dimensional geometric information, simulation of virtual earthquakes using dynamic modelling techniques such as the discrete element method, and realization of the simulated earthquake in a virtual reality environment. This article provides a comprehensive analysis of the individual processes at each stage of the technical process, a survey on the current status of related technologies, and discussion of the technical challenges in its execution. 최근 한반도 남동부에서 발생한 연이은 강진들로 인해 국내에서도 지진 방재에 대한 관심도가 높아지고 있 다. 본 연구에서는 최근 들어 급격히 진보하고 있는 시각지능과 가상현실 분야 기술들을 기반으로 하는, 맞춤형 지진 재해 대응을 위한 기술적 방법론에 대해 살펴보고자 한다. 해당 기술은 카메라를 이용한 생활공간 영상 정보의 취득, 개별 객체의 영상 기반 인식, 3차원 공간 정보의 추출, 이산요소법 등을 활용한 가상 지진의 동역학적 모의, 가상현실 환경에서의 모의 지진 실감화 등의 단계를 통해 구성된다. 본 연구에서는 이러한 전체 기술 프로세스를 구성하기 위한 각 단계의 프로세스, 해당 이슈와 관련한 현재 기술 동향, 실시를 위한 기술적 해결 과제 등을 분석하였다.

SPH-DEM 결합모델에 의한 고/액시스템 내 2상간 상호작용의 전산적 모델링

권지회,조희찬 한국자원공학회 2010 한국자원공학회지 Vol.47 No.2

Base studies on the modeling of liquid-solid flows using an SPH-DEM combined model were conducted in microscale and macroscale views. In the microscale model, flows around a cylindrical solid particle were simulated at three different values of Reynolds numbers, Re=1, 10, and 1000 using SPH. Drag forces acting on the cylinder were determined using the velocity distribution of neighboring fluid particles on the surface of the cylinder. The drag coefficient from the simulation showed good agreement with that obtained from experimental data under the condition of Re=1. As the Reynolds number of the flow increased, error in the drag coefficient increased accordingly, because the boundary layer thickness became much smaller than the space between fluid particles and the cylinder. In the macroscale model, the process of size separation of 100 solid particles was simulated in an elutriation separator using an SPH-DEM combined model. The motions of fluids and solid particles were solved by DEM and SPH algorithms. The size-based separation of solid particles can be observed clearly from the results. Different flow properties, and also the different movements of solids in various regions in the elutriator, showed good agreement with the corresponding physical phenomena. DEM와 SPH를 이용한 고체-액체 유동 모사를 위한 기반 연구가 미시적, 거시적 관점에서 각각 시행되었다. 미시적 모델에서는 실린더 주변을 흐르는 유동을 Re=1, 10, 1,000의 세 가지 다른 레이놀즈수 영역에서 모사하고 얻어진 속도 분포를 통해 입자에 작용하는 항력을 계산하였다. 시뮬레이션 결과 Re=1의 영역에서는 실험적으로 알려진 해와 비교적 근접한 drag coefficient 값을 얻을 수 있었다. Re가 증가할수록 결과는 알려진 값과 차이를 보였는데, 이는 경계층의 두께가 줄어들면서 입자간 간격이 경계층을 표현할 만큼 충분히 작지 않게 되는 데서 기인하는 것으로 판단된다. 거시적 모델에서는 100개의 고체 입자의 침강분리기 내에서의 입도 분리 공정을 SPH-DEM 결합모델에 의해 모사하였다. 시뮬레이션 결과, 고체입자의 입도에 따른 분리 현상은 시뮬레이션에서 명확히 관찰되었으며, 침강분리기 내부의 영역별 유동 특성과 이에 의한 고체 입자의 각 영역에서의 운동 특성은 일반적으로 알려진 물리적 현상을 정성적으로 잘 표현하였다.

신예미 광산 철광석의 볼밀 분쇄 및 단체분리 특성 연구

이돈우,권지회,김관호,조희찬,Lee, Donwoo,Kwon, Jihoe,Kim, Kwanho,Cho, Heechan 한국자원리싸이클링학회 2020 資源 리싸이클링 Vol.29 No.3

This study aims to investigate breakage and liberation characteristics of iron ore from Shinyemi mine, Jeongseon by ball mill. Parameters of breakage functions for three grade samples of iron ore were obtained using single-sized-feed breakage test and back-calculation based on nonlinear programming. The results showed that with the increase in the grade of iron ore, the breakage rate factor decrease whereas the particle size sensitivity decreases. This results from retardation of microcrack-propagation by magnetite grain in the ore. Breakage distribution analysis showed that the breakage mechanism appear to be impact fracture dominant with the increase of grade owing to the stress distribution effect by magnetite grain. Degree of liberation (DOL) increased with the increase in grade and decrease in particle size, respectively. Using the breakage function and size-DOL relationship, a model that can predict time-dependent-DOL is established. When scale-up factors from operating condition are available, the model is expected to be capable of predicting size and DOL with time in actual mining process.

Increased Thrombogenicity in Chronic Renal Failure in a Rat Model Induced by 5/6 Ablation/Infarction

송태진,권일,Honglim Piao,이지은,한겨레,장윤경,오형중,최현정,이경열,김용재,한기환,허지회 연세대학교의과대학 2018 Yonsei medical journal Vol.59 No.6

Purpose: Abnormalities in hemostasis and coagulation have been suggested in chronic renal failure (CRF). In this study, we comparedprocesses of thrombus formation between rats with CRF and those with normal kidney function. Materials and Methods: CRF was induced by 5/6 ablation/infarction of the kidneys in Sprague-Dawley rats, and surviving rats after4 weeks were used. Ferric chloride (FeCl3)-induced thrombosis in the carotid artery was induced to assess thrombus formation. Whole blood clot formation was evaluated using rotational thromboelastometry (ROTEM). Platelet aggregation was assessedwith impedance platelet aggregometry. Results: FeCl3-induced thrombus formation was initiated faster in the CRF group than in the control group (13.2±1.1 sec vs. 17.8±1.0 sec, p=0.027). On histological examination, the maximal diameters of thrombi were larger in the CRF group than in the controlgroup (394.2±201.1 μm vs. 114.0±145.1 μm, p=0.039). In extrinsic pathway ROTEM, the CRF group showed faster clot initiation(clotting time, 59.0±7.3 sec vs. 72.8±5.0 sec, p=0.032) and increased clot growth kinetics (α angle, 84.8±0.2° vs. 82.0±0.6°, p=0.008),compared to the control group. Maximal platelet aggregation rate was higher in the CRF group than in the control group(58.2±0.2% vs. 44.6±1.2%, p=0.006). Conclusion: Our study demonstrated that thrombogenicity is increased in rats with CRF. An activated extrinsic coagulation pathwaymay play an important role in increasing thrombogenicity in CRF.

Characterization of Ferric Chloride-Induced Arterial Thrombosis Model of Mice and the Role of Red Blood Cells in Thrombosis Acceleration

심예슬,권일,박영선,이효원,김자영,김영대,남효석,박성하,허지회 연세대학교의과대학 2021 Yonsei medical journal Vol.62 No.11

Purpose: The ferric chloride (FeCl3)-induced thrombosis model is widely used for thrombosis research. However, it lacks standardization with uncertainty in the exact mechanism of thrombosis. This study aimed to characterize thrombus formation in a mouse model. Materials and Methods: We investigated thrombus formation and stability using various FeCl3 concentrations (10%, 20%, 30%, 40%, and 50%, w/v) in carotid arteries of the Institute of Cancer Research (ICR) and C57BL/6N mice using the FeCl3-induced thrombosis model. We also investigated thrombus histopathology using immunohistochemistry and electron microscopy. Results: Higher FeCl3 concentrations induced dose-dependent, faster, larger, and more stable thrombus formation in both strains of mice. However, the ICR mice showed better dose-responses in thrombus formation and stability compared to the C57BL/6N mice. Thrombi were fibrin- and platelet-rich without significant changes across FeCl3 concentrations. However, the content of red blood cells (RBCs) increased with increasing FeCl3 concentrations (p for trend <0.001) and inversely correlated with time to occlusion (r=-0.65, p<0.001). While platelets and fibrin were evenly distributed over the thrombus, RBCs were predominantly located near the FeCl3 treatment area. Transmission electron microscopy showed that RBCs attached to and were surrounded by aggregates of degranulated platelets, suggesting their potential role in platelet activation. Conclusion: Faster and larger thrombus formation is induced in a dose-dependent manner by a wide range of FeCl3 concentrations, but the stable thrombus formation requires higher FeCl3 concentrations. Mouse strain affects thrombus formation and stability. RBCs and their interaction with platelets play a key role in the acceleration of FeCl3-induced thrombosis.