• 한국결정성장학회지
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• 제13권3호
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• pp.145-151
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• 2003

전산유체역학을 이용하여 전형적인 구조를 갖는 사이클론 분리기 시스템 내에서의 주입 가스 유동 및 입자 거 동해석을 통해 가스 주입 유속에 따른 입자 거동 양상을 3차원적으로 해석하였다. 해석 결과는 Navier-stokes 방정식을 이용한 유체 유동 현상과 Lagrangian 접근법을 이용한 입자 거동 경로 추적을 결합시켜 도출되었다. 주입 유속이 증가함에 따라 내부 압력 손실이 증가하였고 이런 내부 압력 변화는 분리기 내의 유체의 유동 양상에 영향을 미쳤다. 입자의 거동은 유체의 유동에 의해 결정되었으며 일정 유속에 대해서는 입자의 크기에 크게 의존하였다. 그리고 주입 유속의 증가는 입자의 경로를 증가시키면서 분리기의 하부 영역으로 이동시켰다. 이로 인해 분리기내에 존재하는 입자의 최소 크기가 작아지며 일정 크기의 입자의 경우 분리율이 증가하였다. 결론적으로 가스 유입 유속의 변화는 내부의 유체 유동 변화와 입자 거동 양상에 중요한 요인이 된다.

• 콘크리트학회논문집
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• 제20권3호
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• pp.317-323
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• 2008

본 연구에서는 굳지 않은 콘크리트 및 유동 콘크리트의 흐름 거동에 관한 해석 시뮬레이션 모델의 개발에 관한 것으로, 입자법의 일종인 MPS법 (moving particle semi-implicit method)을 적용하였다. 콘크리트의 유동 현상을 점소성의 흐름 문제로 고려하였으며, 콘크리트 입자의 운동에 관한 지배방정식은 라그랑지 정식화의 Navier-Stokes 방정식과 질량보존의 법칙에 기초하도록 하였다. 굳지 않은 콘크리트의 점소성 흐름 구성관계의 정식화를 위하여 콘크리트는 부동 상태인 경우 고점성체의 유체로, 유동상태인 경우 항복응력 이후 점소성체의 유체로 모델링하였다. 개발된 모델을 이용하여 L-형 박스의 콘크리트 유동 시험에 대해 시뮬레이션 하였으며, 그 결과 예측된 흐름량은 실험의 흐름량과 잘 일치하는 것으로 나타났다. 개발된 입자법의 해석 모델은 점소성 유체의 운동현상에 기초하여 정식화 되어 콘크리트 입자의 유동 및 운동 현상을 잘 묘사해 주는 것으로 평가된다.

• 제어로봇시스템학회논문지
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• 제7권1호
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• pp.1162-1170
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• 2001

This paper proposes a practical gain-scheduling control law considering robust stability and performance of Linear Parameter Varying(LPV) systems in the presence of nonlinearities and uncertainties. The proposed method introduces LMI-based pole placement synthesis and also associates with a recently developed fuzzy control system based on Takagei-Sugenos fuzzy model. The sufficient conditions for robust controller design of linearized local dynamics and robust stabilization of fuzzy control systems are reduced to a finite set of Linear Matrix inequalities(LMIs) and solved by using co-evolutionary algorithms. The proposed method is applied to the longitudinal acceleration control of high performance aircraft with linear and nonlinear simulations.

• 대한기계학회논문집
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• 제15권1호
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• pp.1-10
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• 1991

본 연구에서는 고속 대변형 탄소성 변형 과정을 해석할 수 있는 프로그램(NET )을 개발하고 이것을 실린더 및 링 성형 문제에 적용하여 마찰 및 관성 효과가 변형 거동에 미치는 영향을 규명하여 보았다.

• 한국해양공학회지
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• 제31권6호
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• pp.388-396
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• 2017

A Lagrangian approach based computational fluid dynamics (CFD) was used to simulate large and/or sharp deformations and fragmentations of interfaces, including free surfaces, through tracing each particle with physical quantities. According to the concept of the particle-based CFD method, it is possible to apply it to both fluid particles and solid particles such as sand, gravel, and rock. However, the presence of more than two different phases in the same domain can make it complicated to calculate the interaction between different phases. In order to solve multiphase problems, particle interaction models for multiphase problems, including surface tension, buoyancy-correction, and interface boundary condition models, were newly adopted into the moving particle semi-implicit (MPS) method. The newly developed MPS method was used to simulate a typical validation problem involving dam breaking. Because the soil and other particles, excluding the water, may have different viscosities, various viscosity coefficients were applied in the simulations for validation. The newly developed and validated MPS method was used to simulate the mobile beds induced by broken dam flows. The effects of the viscosity on soil particles were also investigated.

• 한국대기환경학회지
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• 제23권4호
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• pp.478-486
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• 2007

Numerical analysis had been performed to understand flow characteristics of the flue gas and slurry in the absorber of a flue gas desulphurization (FGD) system using computational fluid dynamics (CFD) technique. Two-fluid(Euler-Lagrangian) model had been employed to simulate physical phenomenon, which slurry particles injected through slurry spray nozzles fall down and bump into the flue gas inflowing through inlet duct. It was not necessary to adopt pre-defined pressure drop inside the absorber because interaction between flue gas and slurry particles was considered. Hundreds of slurry spray nozzles were considered with the spray velocity at the nozzles, swirl velocity and spreading angle. The results note that the flow disturbance of flue gas is found at the bottom of the absorber, and the current rising with high speed stream is observed in the opposite region of the inflow duct. The high speed stream is reduced as the flue gas goes up, because the high speed stream of flue gas dumps falling slurry particles due to momentum exchange between flue gas and slurry particles. In spite of some disproportion in slurry distribution inside the absorber, escape of slurry particles from the absorber facility is not observed. The pressure drop inside the absorber is mainly occurred at the bottom section.

• 대한수학회지
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• 제53권4호
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• pp.795-834
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• 2016

The main purpose of this paper is to propose a scheme of a proof of the nonsimpleness of the group $Homeo^{\Omega}$ ($D^2$, ${\partial}D^2$) of area preserving homeomorphisms of the 2-disc $D^2$. We first establish the existence of Alexander isotopy in the category of Hamiltonian homeomorphisms. This reduces the question of extendability of the well-known Calabi homomorphism Cal : $Diff^{\Omega}$ ($D^1$, ${\partial}D^2$)${\rightarrow}{\mathbb{R}}$ to a homomorphism ${\bar{Cal}}$ : Hameo($D^2$, ${\partial}D^2$)${\rightarrow}{\mathbb{R}}$ to that of the vanishing of the basic phase function $f_{\underline{F}}$, a Floer theoretic graph selector constructed in [9], that is associated to the graph of the topological Hamiltonian loop and its normalized Hamiltonian ${\underline{F}}$ on $S^2$ that is obtained via the natural embedding $D^2{\hookrightarrow}S^2$. Here Hameo($D^2$, ${\partial}D^2$) is the group of Hamiltonian homeomorphisms introduced by $M{\ddot{u}}ller$ and the author [18]. We then provide an evidence of this vanishing conjecture by proving the conjecture for the special class of weakly graphical topological Hamiltonian loops on $D^2$ via a study of the associated Hamiton-Jacobi equation.

• 한국대기환경학회지
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• 제23권2호
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• pp.203-213
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• 2007

Numerical analysis has been performed to understand flow characteristics in the reactor with bag filters in an integrated adsorption/catalytic process which can treat dioxin and $NO_{x}$ together. Computational fluid dynamics technique was employed with Euler-Lagrangian model to consider flue gas and activated carbon particles simultaneously, so that residence time of flue gas and activated carbon particle could be obtained from the numerical analysis directly. The numerical analysis has been performed with different three particle sizes and compared each flow characteristics with particle's size. Fundamental flow patterns of flue gas and activated carbon particles, pressure distribution, residence time of flue gas and activated carbon particles, and distribution of activated carbon have been obtained from the numerical analysis. Flow patterns of flue gas and activated carbon particles in the reactor were very complicated and they moved along very various paths. Therefore, their residence time in the reactor was also various. The results obtained would be effectively used to estimate the removal efficiency in the reactor once the residence time is combined with the reaction equation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.626-630
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• 2005

This paper presents a novel Intelligent-Welding-Carriage (IWC) for automation of curved block in shipbuilding. The curved block is usually used in both front and back side of the ship. In curved block root gap is big, $1{\sim}7$ [mm] and inclination, $0{\sim}30$ [deg]. Since available conventional carriage type is limited to use below root gap of 3 [mm], only manual welding is employed in curved block. To adopt an IWC in curved block, it requires control of the welding conditions, i.e., voltage, current and travel speed, with respect to root gap and inclination to achieve good welding quality. In this paper, an IWC is developed for automization of welding operation to accommodate gap and inclination. Kinematics model and dynamics using Lagrangian formulation of the manipulator is introduced. IWC utilizes a database to perform accurate welding. The database is programmed based on numerous experimental test results with respect to gap, inclination, material, travel speed, weaving condition, voltage, and current. Finally, experimental result using PID control is addressed for verify the trajectory tracking accuracy of end-effector.

• Journal of Mechanical Science and Technology
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• 제15권8호
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• pp.1090-1096
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• 2001

In this paper, new methods for efficiently solving linear acceleration equations of multibody dynamic simulation exploiting sparsity for real-time simulation are presented. The coefficient matrix of the equations tends to have a large number of zero entries according to the relative joint coordinate numbering. By adequate joint coordinate numbering, the matrix has minimum off-diagonal terms and a block pattern of non-zero entries and can be solved efficiently. The proposed methods, using sparse Cholesky method and recursive block mass matrix method, take advantages of both the special structure and the sparsity of the coefficient matrix to reduce computation time. The first method solves the η$\times$η sparse coefficient matrix for the accelerations, where η denotes the number of relative coordinates. In the second method, for vehicle dynamic simulation, simple manipulations bring the original problem of dimension η$\times$η to an equivalent problem of dimension 6$\times$6 to be solved for the accelerations of a vehicle chassis. For vehicle dynamic simulation, the proposed solution methods are proved to be more efficient than the classical approaches using reduced Lagrangian multiplier method. With the methods computation time for real-time vehicle dynamic simulation can be reduced up to 14 per cent compared to the classical approach.