Development of accurate and efficient numerical methods for bubble-particle interaction

DoctorAccurate and efficient numerical methods have been developed to simulate flow including bubble-particle interaction. First, to achieve high scalability for large computation, the Navier-Stokes equations are solved by an alternating-directional- implicit (ADI) method parallelized by a parallel diagonal dominant (PDD) algorithm. Second, the phase interface is tracked by a conservative volume-of-fluid (VOF) method. The developed numerical methods have been further improved by modeling bubble-particle interaction. New algorithms are proposed to predict that particles are attached or slide away on the bubble surface in a VOF framework. Fluid motions are predicted in an Eulerian frame, while particle motions are predicted in a Lagrangian framework. To consider bubble-particle interaction, numerical models connecting phase interfaces and solid particles are required. In this study, algorithms that are used to detect collision and determine the sliding or attachment of the particle are developed. An effective bubble is also introduced to model the bubble-particle interaction in a VOF framework. The proposed numerical method is validated through experimental cases that entail the rising of a single bubble with particles. Collision and attachment probabilities obtained from the simulation are compared to theoretical and experimental results based on bubble diameters, particle diameters, and contact angles. The particle trajectories near the bubble are presented to show differences with and without the proposed bubble-particle interaction model. The sliding and attachment of the colliding particle are observed using this model

A Case study of sport education curriculum model in teaching physical education at a selected secondary school

학위논문(박사)--서울대학교 대학원 :체육교육과,1998.Docto

Effect of Zr on Liquid-Liquid Phase Separation in Microstructure of Cu-Fe alloys

Master동철합금의 혼합 엔탈피는 양의 값을 갖으며 대표적인 상분리 합금으로 알려져 있으며, 은 온도 구간의 고액 공존 영역이 존재하여 하나의 액상이 두 개의 액상 으로 나누어지는 액상분리 거동이 발생한다. 이 거동을 제어하기 위한 많은 시도가 있었지만 뚜렷한 결과는 지금까지 발견되지 않았다. Zr을 동철합금에 첨가함으로 서 달라지는 것은 첫 번째, 혼합 엔탈피 값을 낮추고 동시에 혼합 엔트로피를 증가시 킴으로써 혼합 깁스 자유 에너지 값이 크게 낮아지게 되는 것이다. 두 번째는 실험 과정 중에 Zr이 산소와 반응하여 ZrO2가 되면 이는 γ-Fe과 적은 lattice mismatch 로 인해서 균일 핵생성을 돕는 역할을 하게 된다. 마지막으로는 금속간 화합물이 형성되지만 이는 액상분리 거동에는 영향을 미치지 않음을 확인하였다. 기존 동철 합금의 응고 순서는 액상분리가 일어난 후 큰 과냉도와 함께 Binodal curve 내에서 γ-Fe의 핵생성이 시작되는 반면에, Zr이 첨가된 동철합금은 액상선과 Binodal curve 사이에서 액상분리가 일어나지 않고 적은 과냉으로 γ-Fe의 핵생성이 시작하는 것을 시차 주사 열량계 (DSC)를 통해서 밝혀냈다. 또한, Zr 첨가의 영향으로 변하는 DSC 의 발열 그래프를 통해 결정화도를 계산함으로써 수지상정은 비교적 적지만 조대한 것을 알 수 있다. ZrO2의 직접적인 존재와 역할을 발견하진 못하였으나 고전 핵생성 이론을 통해 핵생성 속도를 계산하는 것으로 Zr이 첨가된 동철합금에서 균일 핵생성을 촉진 된다는 증거를 통해 ZrO2가 존재할 수 밖에 없음을 간접적으로 증명하였다. 결과적으로, 동철합금의 액상분리 거동은 Zr이 첨가됨으로서 명백히 제어됨을 보인다.In the Cu-Fe binary phase diagram, the metastable miscibility gap exists in the liquid-solid coexisting zone. Assuming that γ-Fe nucleation has occurred between the liquidus line and the binodal curve with low supercooling, it could be obtained fully dendritic microstructure and there is no liquid-liquid phase separation (LLPS) behavior throughout the specimens. But, γ-Fe nucleation started under binodal curve with high supercooling, LLPS behavior was investigated and minority phase droplets were obtained in the microstructure of CFA. The LLPS behavior was possible to control by promoting γ-Fe nucleation that happened above the binodal curve. For a combination of classical nucleation theory and thermal instrumental analysis, Zr is added to CFA to decrease the Gibbs free energy of mixing and form ZrO2 that accelerates heterogeneous nucleation by acting as a nucleation site for γ-Fe. Furthermore, to observe clear evidence of LLPS behavior and γ-Fe crystallization by adding 1wt％Zr to Cu-40wt％Fe and Cu-20wt％Fe respectivel

Numerical Simulation of an Air Jet in Cross Water Flow with Application to Air-Layer Drag Reduction

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Computational Analysis of an Air Jet in Cross Water Flow

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Computational Analysis of Heat Transfer In Stacked Heat Exchangers Using Multi-Level Resolution

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Numerical simulation of liquid-layer breakup on a moving wall due to an impinging jet

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Prediction of the Thermal Performance of Stacked Heat Exchangers in an SOFC System

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Numerical simulation of liquid-layer breakup on a moving wall due to an impinging jet

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