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Simulation of Self-Assembled Nanostructures Induced by Electrostatic Field
김동철(Dongchoul Kim),Wei Lu 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
Experimentally it has been observed that a thin polymer film may self-assemble uniform pillars emerging out of the film surface by an applied electrostatic field. In order to account for this behavior, a three dimensional dynamic model is developed and the interplay of the thermodynamic forces and the kinetic processes is studied. The model incorporates the coupled diffusion, viscous flow, and dielectric effect based on a phase field framework. The semi-implicit Fourier spectral method and the preconditioned biconjugategradient method are applied in the simulations for high efficiency and numerical stability. Numerical simulations reveal rich dynamics of the pattern formation process.
The Phase Field Model for Nano/Microstructure evolution
Dongchoul Kim(김동철) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
This study reports on the way of control the self-assembly process of nano- or micro-structures with various externally applied fields based on the phase field model that incorporates the multiple energetics and kinetics of the system. The nanoscale self-assembly process of a two-phase monolayer on an elastic substrate is simulated and revealed that the self-assembly process can be guided by tuning the surface chemistry of a substrate and applying an elastic field to the substrate. A three dimensional model of polymer thin film is presented to account for the uniform self-organized pillars emerging out of the film surface. The phase field model is also adopted to develop a three dimensional electromigration model for studying the reliability of various MEMS devices. Recently, it has been employed to develop a three-dimensional chemotaxis model for cell migrations and presented its efficiency and effectiveness.
김하성(Hasung Kim),김민수(Minsoo Kim),이형일(Hyungyil Lee),김낙수(Naksoo Kim),김동철(Dongchoul Kim) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
In this study, a 2-step stamping model with additional 1st stamping tool is proposed to reduce stamping flaws in the curved parts of dimple in nuclear fuel spacer grid. A reference 2D FE model of 1-step stamping is then established, and corresponding maximum strain is obtained. By varying the values of process variables of 1st stamping tool in 2-step stamping model, FE solutions are obtained to express the strain as a function of process variables, which provides the optimum values of process variables. Finally, applying these optimum values to a 3D FE model, we show the enhanced formability of the proposed 2-step stamping model.
김하성(Hasung Kim),김민수(Minsoo Kim),이형일(Hyungyil Lee),김낙수(Naksoo Kim),김동철(Dongchoul Kim) 대한기계학회 2013 大韓機械學會論文集A Vol.37 No.7
본 연구에서는, 핵연료 지지격자 딤플 굴곡부에 성형결함을 줄이고자, 1차 스탬핑 금형이 추가된 2-step 스탬핑모델을 제시한다. 우선 순수굽힘 변형률과의 비교로, 딤플 굴곡부 변형률의 특성을 조사한다. 이어 2 차원 1-step 기준 스탬핑 유한요소모델을 정하고 이에 상응하는 최대변형률을 구한다. 1차 스탬핑 금형의 설계변수들을 각각 변화시켜 변형률에 대한 목적함수를 구하고, 반응표면법을 이용해 1차 스탬핑 금형의 최적 변수값을 선정한다. 다음으로 이를 3차원 모델에 적용해 2-step 스탬핑 모델의 향상된 성형성을 확인한다. In this study, a 2-step stamping model with an additional 1st stamping tool is proposed to reduce stamping flaws in the curved parts of a dimple in a nuclear fuel spacer grid. First, the strains of curved part of dimple are characterized via a comparison with strain solutions in pure bending. A reference 2D finite element (FE) model of 1-step stamping is then established, and the corresponding maximum strain is obtained. By varying the values of design variables of the 1st stamping tool in the 2-step stamping model, FE solutions are obtained to express the strain as a function of process variables, which provides the optimum values of process variables. Finally, applying these optimum values to a 3D FE model, we demonstrate the enhanced formability of the proposed 2-step stamping model.
리튬 이차전지 양극재 Li<sub>x</sub>V<sub>2</sub>O<sub>5</sub>의 효율적인 방전을 위한 구조 설계
박준규,김수일,김동철,Park, Jun Kyu,Kim, Soo Il,Kim, Dongchoul 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.7
전기자동차와 하이브리드 자동차의 상용화에 따라 전기용량과 에너지 밀도가 향상된 리튬 이온 전지의 개발이 필요하다. 본 논문에서는 상장 모델을 이용하여 5산화 바나듐으로 구성된 다공성 구조물로의 리튬 이온 삽입현상을 분석하였다. 다공성 5산화 바나듐 구조물은 구멍을 갖는 구체의 구조물로 정의하였으며, 이때 구멍의 형상은 원통형이다. 원통형 구멍의 반지름, 깊이 및 개수를 조절하여 다양한 다공성 5산화 바나듐의 미세조직 형상을 고려하였으며, 각 미세조직의 형상인자와 구조물에 삽입되는 리튬 이온의 개수 사이의 관계를 분석하였다. 마지막으로 최적화 작업을 통하여 가장 많은 수의 리튬 이온이 삽입될 수 있는 다공성 5산화 바나듐의 구조체 형상을 찾아내었다. Recently, higher capacity and energy density of lithium ion batteries are increasingly demanded for enhancing their performance in view of the rise in the commercial distribution of electric and hybrid vehicles. Computational analysis of a porous structure of vanadium pentoxide cathode was performed, employing a phase field model. The incipient model was designed as a spherical structure with cylindrical-shaped pores. Modifying the diameters and lengths of the pore cylinder and the number of pores, we considered different conditions for the porous vanadium pentoxide cathodes for analyzing their effect on the amount of lithium ion intercalated to them. Subsequently, we optimized the porous structure to contain the largest amount of intercalated lithium ion during discharge.