• Journal of Mechanical Science and Technology
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• 제19권spc1호
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• pp.364-370
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• 2005

A stable walking pattern generation method for a biped robot is presented in this paper. In general, the ZMP (zero moment point) equations, which are expressed as differential equations, are solved to obtain a stable walking pattern. However, the number of differential equations is less than that of unknown coordinates in the ZMP equations. It is impossible to integrate the ZMP equations directly since one or more constraint equations are involved in the ZMP equations. To overcome this difficulty, DAE (differential and algebraic equation) solution method is employed. The proposed method has enough flexibility for various kinematic structures. Walking simulation for a virtual biped robot is performed to demonstrate the effectiveness and validity of the proposed method. The method can be applied to the biped robot for stable walking pattern generation.

• Journal of applied mathematics & informatics
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• 제19권1_2호
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• pp.215-229
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• 2005

In this paper, constraint aggregation is combined with the adjoint and multiple shooting strategies for optimal control of differential algebraic equations (DAE) systems. The approach retains the inherent parallelism of the conventional multiple shooting method, while also being much more efficient for large scale problems. Constraint aggregation is employed to reduce the number of nonlinear continuity constraints in each multiple shooting interval, and its derivatives are computed by the adjoint DAE solver DASPKADJOINT together with ADIFOR and TAMC, the automatic differentiation software for forward and reverse mode, respectively. Numerical experiments demonstrate the effectiveness of the approach.

• 대한기계학회논문집
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• 제18권9호
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• pp.2339-2348
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• 1994

The objective of this paper is to develop a solution method for the differential-algebraic equation(DAE) derived from constrained muti-body dynamic systems. Mechanical systems are often modeled as bodies and joints. Differential equations of motion are formulated for bodies. Since the bodies are connected by joint, the differential variables must satisfy the kinematic constraint equations that come from the joints. Difficulties are arised due to drift of the differential variables off the constraint equations. An optimization method is adopted to correct the drift of the differential variables. To demonstrate the efficiency of the proposed method a slider-crank mechanism is analyzed dynamically. Identical results are obtained as these from the commercial program DADS. Dynamic analysis of a High Mobility Multi-purpose Wheeled. Vehicle(HMMWV) is carried out to show the practicalism of the proposed method.

• 한국항공우주학회지
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• 제30권3호
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• pp.8-16
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• 2002

헬리콥터 비행 시뮬레이션을 위한 로터 운동방정식을 implicit formulation 형태로 유도하였다. 좌표계 사이의 상대운동을 고려한 일반화된 벡터 kinematics 를 유도하고 이를 적용하여 브레이드 임의 위치 에서 관성속도 및 관성가속도를 구하였다. 유도된 속도 및 가속도 벡터를 이용하여 플래핑, 리드래그 및 토오크 방정식 등을 implicit form으로 유도하였다. 브레이드 스팬에 따른 공간 적분 방법을 살펴보고, 다양한 힌지형상 및 힌지배열 순서에 관계없이 응용영역을 확장할 수 있음을 밝혔다. DAE(Differential Algebraic Equation) 형태를 갖는 본 연구의 결과식을 이용하여 동특성 계산을 위한 시간적분법을 검토하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1841-1844
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• 2004

'Mixing Index($D_I$)'s generally used to measure the degree of mixing. A new method to calculate $D_I$ was proposed, when insoluble solution flows in micromixer. 'Vortex Index (${\Omega}_I$)'which indicate the degree of chaotic advection, is defined and formulated. A lots of arbitrary shaped microchannels were tested to calculate the $D_I$ and ${\Omega}_I$. And then a simple algebraic equation, $D_I=A{\Omega}_I+B$, was obtained. This equation may be used instead of partial differential equation, concentration equation.

• 대한기계학회논문집B
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• 제29권2호
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• pp.232-238
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• 2005

The 'Mixing Index($D_I$)' is used as a conventional guidance measuring the degree of mixing for multiphase flows. For the case when insoluble solutions flow in a passive micromixer, a new method to calculate $D_I$ is proposed. The 'Vortex Index(${\Omega}_I$)' is suggested and formulated. We infer that ${\Omega}_I$ relates to the degree of chaotic advection. Various arbitrary shaped microchannels were tested to calculate the $D_I\;and\;{\Omega}_I$, and then a simple algebraic equation, $D_I=Aexp(B{\Omega}_I)$, is obtained. This equation may be used instead of the conventional partial differential equation, concentration equation, to estimate the degree of mixing.

• International Journal of Automotive Technology
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• 제2권3호
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• pp.117-122
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• 2001

For a dynamic analysis of a constrained multibody system, it is necessary to have a routine for satisfying kinematic constraints. LU decomposition scheme, which is used to divide coordinates into dependent and independent coordinates, is efficient but has great difficulty near the singular configuration. Other method such as the projection matrix, which is more stable near a singular configuration, takes longer simulation time due to the large amount of calculation for decomposition. In this paper, the row space and the null space of the Jacobian matrix are proposed by using the pseudo-inverse method and the projection matrix. The equations of the motion of a system are replaced with independent acceleration components using the null space of the Jacobian matrix. Also a new hybrid method is proposed, combining the LU decomposition and the projection matrix. The proposed hybrid method has following advantages. (1) The simulation efficiency is preserved by the LU method during the simulation. (2) The accuracy of the solution is also achieved by the projection method near the singular configuration.

• 멤브레인
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• 제20권1호
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• pp.29-39
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• 2010

본 연구는 차세대 에너지원으로 주목 받고 있는 직접메탄올연료전지(Direct Methanol Fuel Cell, DMFC)에 대해 mutiscale 기법을 사용하여 DMFC의 MEA부분에 대한 상세 모델링 및 전산모사를 통한 이론적 고찰을 시도하였다. 본 연구에서 이용한 multiscale 모델링 방법은 공정시스템 공학의 kinetic 중심의 모델링 방법과 전산유체역학(Computational Fluid Dynamics, CFD)의 유동중심의 모델링 방법을 유기적으로 결합하여 모사 중간에 필요한 데이터 교환을 함으로써 정확한 모델링 및 전산모사 결과를 얻었다. CFD 모델링으로 유체 이동현상을 3차원으로 해석하였고, 동시에 복잡한 비선형 대수방정식으로 표현되는 반응속도, 전기화학반응을 DAE (Differential & Algebraic Equation) solver로 계산하였다. 모델은 메탄올의 산화반응과 산소의 환원반응을 중심으로 MEA (Membrane Electorde Assembly)부분에서 물리화학적, 전기적 현상 현상을 규명하고, 반응 메커니즘을 구성하였다. MEA 모델은 3차원 공간에서 변위를 가지는 3차원 모델로 구성하였으며, 정상상태 및 등온공정의 조건하에 수립되었다. 이를 통해 channel을 포함한 MEA 부분에서 발생되는 물리적, 화학적, 전기적 현상을 정확히 예측 할 수 있다. 본 연구를 통해 수행된 결과는 DMFC의 실험계획 및 운전조건을 도출함에 있어 매우 유용한 역할을 할 수 있을 것으로 사료되며, 추가적인 연구를 통해 DMFC의 상용화에 크게 이바지 할 수 있을 것으로 사료된다.