Effective mixing of different-sized aggregates in mobile asphalt plant dryers is crucial for ensuring high-quality, consistent asphalt production. This study explores the application of spatial analysis techniques, particularly the Discrete Element Method (DEM), to understand and optimize the mixing process of aggregates in drum dryers. The research emphasizes the importance of proper mixing to achieve uniform moisture removal and heating across various aggregate sizes. Larger aggregates heat more slowly, while finer particles risk overheating or being carried away by air currents, necessitating careful management of the mixing process. Using LIGGGHTS, an open-source simulation framework, we conducted DEM simulations to analyze the spatial distribution and behavior of aggregates within a 3D model of a drum dryer. The study considered multiple factors affecting mixing efficiency, including drum inclination, rotational speed, and aggregate feeding frequency. Results indicate that the rotational speed of the drum dryer has the most significant impact on mixing effectiveness. The DEM simulations provided valuable insights into particle movement, heat transfer, and potential segregation issues within the dryer. Further investigations into additional factors that may influence aggregate mixing in drum dryers is recommended, paving the way for improved efficiency and quality in asphalt manufacturing.

식용 옥수수 수확기는 수확 시 옥수수 이삭의 손상율을 결정하는 탈과 시스템이 중요하다. 탈과 시스템을 개발하기 위해서는 탈과 시스템의 손상율에 영향을 미치는 주요 설계 변수를 구명해야 하고, 설계 변수의 영향 분석에는 시뮬레이션 기법이 많이 사용되고 있다. 본 연구의 목적은 탈과 시스템의 시뮬레이션 해석에 사용할 옥수수 줄기에 대한 이산요소 모델을 개발하는 것이다. 식용 옥수수의 특성을 고려하기 위하여 옥수수 줄기의 물리적 특성을 분석하였으며, 만능재료시험기를 이용한 압축 시험과 3점 굽힘 시험을 통하여 역학적 특성을 확인하였다. 또한, 옥수수 줄기의 이산요소 모델은 접촉 모델과 결합 모델로 구현하였고, 매개변수 연구를 통해 이산요소 모델의 주요 파라미터를 도출하였으며, 시험 결과와 비교하여 개발된 이산요소 모델을 검증하였다. 본 연구로부터 개발된 옥수수 줄기 모델은 탈과 시스템의 시뮬레이션에 활용된다.

Accurate and effective powder compaction analyses are performed for brittle materials such as graphite, utilized as a solid lubricant, by using the discrete element method (DEM). The reliability of the DEM analysis is confirmed by comparing the results of graphite powder compaction analyses using the DEM particle bonding contact model and particle non-bonding contact model with those from the powder compaction experiment under the same conditions. To improve the characteristics, the parameters influencing the compaction properties of the metal-graphite mixtures are explored. The compressibility increases as the size distribution of the graphite powder increases, where the shape of the graphite particles is uniform. The improved compaction characteristics of the metal-graphite (bonding model) mixtures are further verified by the stress transmission and compressive force distribution between the top and bottom punches. It is confirmed that the application of graphite (bonding model) powders resulted in improved stress transmission and compressive force distribution of 24% and 85%, respectively.

덤프 트럭 데크의 경량화를 통한 연료 소비를 줄이고 에코 친화적인 설계를 위해서는 정확한 구조 분석이 필요하다. 지금까지 데크의 하중은 정수압 또는 토압 이론을 기반으로 계산되었다. 이 방법으로 데크의 하중 불균일을 계산할 수 없다. 하중 분포는 골재 입자의 크기 분포 및 상호 작용에 따라 달라진다. 이산요소법은 유한요소법보다 효과적으로 골재의 거동을 시뮬레이션할 수 있다. 본 논문에 서는 벌크 밀도와 안식각을 측정하여 주요 특성을 얻었다. 15톤 덤프 트럭 데크는 범핑, 브레이킹 및 회전 시의 운동 조건을 적용하여 얻은 하중을 사용했다. 시뮬레이션은 이산요소해석 소프트웨어인 EDEM을 사용했다. 데크의 응력 및 변형 분포는 NASTRAN에 의해 계산되었다. 측정된 값과 비교하였고, 이를 통해 DEM 시뮬레이션의 결과는 수학적 가정에 의한 결과보다 정확함을 확인하였다.

PURPOSES : The feasibilities of cohesive elastoplastic contact model and discrete element method (DEM) for asphalt concrete mixture compaction process were evaluated. METHODS : The contact models that were used to simulate the dynamic behavior of construction materials were reviewed. The characteristics of cohesive elastoplastic models were discussed from the perspective of integration with existing contact models. Two asphalt mixtures that were fabricated with specific aggregate gradations and binder contents were compacted according to the Superpave gyratory compaction specification. The parameters for the model were determined via trial-and-error method. The heights of the specimens were plotted with respect to number of gyrations. The results of the laboratory tests were compared to those of numerical simulations. The displacement of particles in asphalt mixture specimen was also visualized to understand the effect of gyratory compaction on asphalt mixture specimen. RESULTS : The DEM model exhibited a significant friction coefficient dependency on compaction degree and slop. The DEM model with parameters determined through trial and error demonstrated reasonable simulation results in terms of specimen height at a gyration number. CONCLUSIONS: Even though a little discrepancy was observed between the results of the experimental test and numerical simulation, a combination of DEM with cohesive elastoplastic contact model seems to be applicable for the simulation of asphalt mixture compaction in laboratory. However, the model needs to be enhanced to be used for more realistic compaction processes, including heat transfer, phase change, and vibratory loading.

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.

PURPOSES: Implementation and verification of the simple linear cohesive viscoelastic contact model that can be used to simulate dynamic behavior of sticky aggregates. METHODS: The differential equations were derived and the initial conditions were determined to simulate a free falling ball with a sticky surface from a ground. To describe this behavior, a combination of linear contact model and a cohesive contact model was used. The general solution for the differential equation was used to verify the implemented linear cohesive viscoelastic API model in the DEM. Sensitivity analysis was also performed using the derived analytical solutions for several combinations of damping coefficients and cohesive coefficients. RESULTS : The numerical solution obtained using the DEM showed good agreement with the analytical solution for two extreme conditions. It was observed that the linear cohesive model can be successfully implemented with a linear spring in the DEM API for dynamic analysis of the aggregates. CONCLUSIONS: It can be concluded that the derived closed form solutions are applicable for the analysis of the rebounding behavior of sticky particles, and for verification of the implemented API model in the DEM. The assumption of underdamped condition for the viscous behavior of the particles seems to be reasonable. Several factors have to be additionally identified in order to develop an enhanced contact model for an asphalt mixture.