• Agricultural and Biosystems Engineering
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• 제1권1호
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• pp.1-6
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• 2000

Using the modified DEM (Distinct Element Model), which we proposed, the effect of cross section of tire lug on the tire performance was simulated. Though the DEM has an advantage over the FEM when it is applied to simulate the behavior of discrete assembly of particles such as soil, there was still a problem in the case of conventional DEM, that the simulated movement of particles was too free. We constructed a new mechanical model (modified DEM) which can take account of the effect of adhesion between particles. It is shown that the soil deformation is simulated by the modified DEM better than the conventional DEM. Comparing the simulated soil reaction to the tire lug with the experimental results, the adequate DEM parameters were found. It is also indicated possible to find the effect of lug cross section shape on the tractive performance of tire by the DEM simulation.

• 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.

• 한국재료학회지
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• 제26권11호
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• pp.611-622
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• 2016

Particle morphology change and different experimental condition analysis during composite fabrication process by traditional ball milling with discrete element method (DEM) simulation were investigated. A simulation of the three dimensional motion of balls in a traditional ball mill for research on the grinding mechanism was carried out by DEM simulation. We studied the motion of the balls, the ball behavior energy and velocity; the forces acting on the balls were calculated using traditional ball milling as simulated by DEM. The effect of the operational variables such as the rotational speed, ball material and size on the flow velocity, collision force and total impact energy were analyzed. The results showed that increased rotation speed with interaction impact energy between balls and balls, balls and pots and walls and balls. The rotation speed increases with an increase of the impact energy. Experiments were conducted to quantify the grinding performance under the same conditions. Furthermore, the results showed that ball motion affects the particle morphology, which changed from irregular type to plate type with increasing rotation speed. The evolution was also found to depend on the impact energy increase of the grinding media. These findings are useful to understand and optimize the particle motion and grinding behavior of traditional ball mills.

• Geomechanics and Engineering
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• 제10권4호
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• pp.455-470
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• 2016

In ballasted railway tracks, ballast fouling due to finer material intrusion has been identified as a challenging issue in track maintenance works. In this research, deformation characteristics of crushed stone-sand mixtures, simulating fresh and fouled ballasts were studied from laboratory and a 3-D discrete element method (DEM) triaxial compression tests. The DEM simulation was performed using a recently developed DEM approach, named, Yet Another Dynamic Engine (YADE). First, void ratio characteristics of crushed stone-sand mixtures were studied. Then, triaxial compression tests were conducted on specimens with 80 and 50% of relative densities simulating dense and loose states respectively. Initial DEM simulations were conducted using sphere particles. As stress-strain behaviour of crushed stone-sand mixtures evaluated by sphere particles were different from laboratory specimens, in next DEM simulations, the particles were modeled by a clump particle. The clump shape was selected using shape indexes of the actual particles evaluated by an image analysis. It was observed that the packing behaviour of laboratory crushed stone-sand mixtures were matched well with the DEM simulation with clump particles. The results also showed that the strength properties of crushed stone deteriorate when they are mixed by 30% or more of sand, specially under dense state. The results also showed that clump particles give closer stress-strain behaviour to laboratory specimens than sphere particles.

• 한국대기환경학회지
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• 제19권5호
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• pp.583-594
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• 2003

Ozone is an important atmospheric pollutant that is occurred in tropospheric chemical process and it also affects the human health and plants. For a correct application of abatement strategies for ozone, it is necessary to understand the factors that control atmospheric ozone removal by dry deposition processes. The present study investigates the numerical simulation of the dry deposition velocity (V$^{d}$ ) obtained from PNU/DEM (Pusan National University Deposition Model). PNU/DEM includes seasonal categories, meteorological factors, surface properties and land-use types and proposes for an accurate numerical computation. And, this study examines the ability of the PNU/DEM to compute V$_{d}$ of ozone over water surfaces and evaluates PNU/DEM by comparing its estimated V$_{d}$ to past observed V$_{d}$ over water. The parametrization was found to yield V$_{d}$ values generally in good agreement with the observations for the deciduous forest and the coniferous forest. Ozone is removed slowly at wet surface or water due to its low water solubility. Therefore V$_{d}$ values over water were lower than Vd values over the other surfaces. Comparison of PNU/DEM simulated V d values to observations of ozone V$_{d}$ that have been reported in the literature implies that PNU/DEM produces realistic results.

• Korean Chemical Engineering Research
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• 제57권6호
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• pp.804-811
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• 2019

본 연구는 매체형 전동밀(전동 볼 밀)에서 매체선정에 관한 공정조건 최적화를 위하여, 직경과 재질이 각각 다른 3가지 종류의 분쇄매체를 이용, 매체의 움직임을 실제 촬영하고 DEM 시뮬레이션을 병행하여 비교 연구하였다. 시뮬레이션에서는 밀의 회전속도, 매체의 재질, 매체의 운동속도, 매체와 포트 벽면과의 마찰계수 등을 실제 실험조건과 동일하게 조건을 맞추었다. 다양한 종류의 분쇄매체의 움직임을 실제 촬영된 사진 및 시뮬레이션에서 해석된 스냅샷 사진 위에, 본 연구에서 정의한 분쇄장을 설정하여 해석함으로써 그 값을 정량적으로 측정하였다. 또한, 정량적으로 측정된 값과 분쇄시료의 변화된 모습을 관찰하여 그 상관관계를 검토하였다. 따라서 특정 실험조건에서 분쇄장에 가장 큰 영향을 주는 분쇄매체의 최적화를 제언 하고자 하였다.

• 지구물리와물리탐사
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• 제8권1호
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• pp.1-6
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• 2005

조립질 물질을 이용한 축소모형실험(예를 들어 모래상자실험)을 다양한 크기의 많은 지질학적 문제에 성공적으로 적용되어왔다. 이러한 물리적 실험은 개별요소법(DEM)을 이용하여 수치적으로도 수행될수 있다. 이연구에서는 현재 지구상에서 가장 중요한 지구조적 과정 중의 하나인 인도판과 유라시아판의 충돌문제를 시뮬레이션하기 위해 개별요소법을 적용하였다. 개별요소 시뮬레이션은 구조지질학뿐만 아니라 토질역학, 암석역학 등의 다양한 동역학적 분야에 적용되어왔다. 조사대상이 많은 작은 입자들의 조합으로 가정되기 때문에 개별요소 시뮬레이션은 거대하고 불연속적인 변형이 일어나는 대상을 다룰 수 있다. 그러나 DEM 시뮬레이션에서는 개개 입자에 대한 입력변수들과 전체 물성의 관계에 대해 거의 알려져 있지 않기 때문에 입력 변수들의 타당성을 검증하기 어려운 경우가 자주 있다. 그러므로 이전의 연구들에서는 시행착오에 의해 입력변수를 조정하여만 하였다. 이러한 어려움을 극복하기 위하여, 이 연구에서는 개별요소 시뮬레이션에 수치적인 이축 시험을 도입하였으며, 이러한 수치 시험 결과를 이용하여 충돌 모델에 사용되는 입력변수의 타당성을 검토하였다. 결과적인 층돌 모델은 동 아시아에서 관측되는 실제 변형과 매우 비슷하며, GPS 자료 및 동 아시아의 원위치 응력자료와 잘 대비된다.

• Advances in Computational Design
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• 제5권3호
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• pp.261-276
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• 2020

The reasonable layout of vacuum cleaner can effectively improve the collection efficiency of iron filings generated in the process of steel production. Therefore, in this study, the CFD-DEM coupling model and two-fluid model are used to calculate the iron filings collection efficiency of vacuum cleaner with different inclination/cross-sectional area, pressure drop and inlet angle. The results are as follows: The CFD-DEM coupling method can truly reflect the motion mode of iron filings in pneumatic conveying. Considering the instability and the decline of the growth rate of iron filings collection efficiency caused by high pressure drop, the layout of 75° inclination is suggested, and the optimal pressure drop is 100Pa. The optimal simulation results based on two-fluid model show that when the inlet angle and pressure drop are in the range of 45°~65° and 70Pa~100Pa, larger mass flow rate of iron filings can be obtained. It is hoped that the simulation results can offer some suggestion to the layout of vacuum cleaner in the rolling mill.

• 한국통신학회논문지
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• 제32권7C호
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• pp.635-643
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• 2007

본 논문에서는 OFDM(Orthogonal Frequency Division Multiplexing) 기반 셀룰라 시스템에서 채널추정 성능을 향상시키기 위한 DEM(Decision-directed Expectation Maximization) 알고리듬을 제안한다. DEM 알고리듬은 다중안테나를 사용하는 단말이 셀 경계지역에 위치하는 경우 데이터 신호를 이용하여 주파수 효율의 감소 없이 채널추정 성능을 향상시킬 수 있으며, 한 그룹 내 채널변화 성분을 고려하여 채널갱신을 함으로써 고속 이동환경에도 큰 열화 없이 채널추정 성능을 향상시킬 수 있다. 모의실험을 통하여 제안된 DEM 알고리듬이 EM(Expectation Maximization) 기법과 비교하여 고속이동 환경에서 채널추정 성능을 향상 시키면서 연산 복잡도를 크게 감소시킬 수 있음을 확인한다.

• 한국지리정보학회지
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• 제11권3호
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• pp.151-165
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• 2008

지형경사와 사면방향은 BROOK90 Model과 같은 물리 결정 물수지 모델에서 증발산과 융설, 순복사 등을 계산하기 위해서 사용하는 중요한 매개변수가 된다. 본 연구에서는 수치표고모형(DEM)을 제작하고, DEM의 해상도가 달라짐에 따라서 유역 평균 지형경사와 유역 평균 사면방향이 어떻게 달라지는지, 그리고 이 차이는 물리 결정 일괄 매개변수 물수지 모델인 BROOK90의 물수지 모의 결과에 어떤 영향을 미치는지를 평가하였다. 충청도 병천천 유역을 대상으로, DEM은 1:25,000 수치지형도를 이용하여 TIN과 Topo To Raster 방법으로 제작하였다. 각각의 방법으로 10m~100m 해상도의 DEM을 10m 간격으로 10개씩 총 20개의 DEM을 제작하였다. DEM의 해상도가 높아지면 병천천 유역의 평균 지형경사가 커져서 이는 병천천 유역의 증산량을 증가시키고 하천유출량을 감소시켰다. 이것은 평지보다 경사지가 직달복사량을 많이 받는 물리적 특성이 모델에 반영되어 있기 때문이다. 한편, DEM의 해상도가 낮아지면 병천천 유역에서는 평균 사면방향이 남동방향에서 남향으로 이동하는 경향이 있었다. 이에 따라 증발산량이 증가하고 하천유출량은 감소하는 것으로 나타났다.