• 대한화장품학회지
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• 제25권3호
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• pp.67-86
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• 1999

기능성 물질로서 다양한 생리적 기능을 가진 ascorbic acid는 구조적으로 불안정하여 쉽게 산화되는데 이러한 ascorbic acid의 산화를 억제하기 위해 리포좀에 순수한 ascorbic acid를 봉입시켜 안정한 리포좀을 제조하였다. 안정한 리포좀의 제조를 위해 cholesterol이나 $\beta$-sitosterol 이 리포좀의 안정화에 미치는 영향을 측정하였으며 ascorbic acid의 산화방지를 위해 항산화제로 butylated hydroxytoluene(BHT), tertiary butylhydroquinone(TBHQ)와 $\alpha$-glycosyl rutin, natural concentrated tocopherol을 사용하였다. 리포좀 제조시 cholesterol이나 $\beta$-sitosterol을 사용한 경우 ascorbic acid의 산화가 감소하였는데 이는 cholesterol이나 $\beta$-sitosterol이 리포좀의 이중막을 강화하여 봉입한 ascorbic acid의 방출을 감소시켜 산화를 방지하는 것으로 생각된다 또한 cholesterol의 농도가 0.3%인 경우 가장 안정한 리포좀이 생성됨을 알 수 있었다. 사용된 항산화제는 ascorbic acid에 대하여 모두 산화억제효과를 나타내었으며 tertiary butylhydroquinone, $\alpha$-glycosyl rutin, butylated hydroxytoluene, natura] concentrated tocopherol 순으로 우수함을 보였다. 그러나 제약 및 화장붐에 사용되는 ascorbic acid의 산화억제에는 효과가 가장 좋은 합성 항산화제인 tertiary butylhydroquinone보다 천연물질에서 추출한 항산화제인 $\alpha$-glycosyl rutin이 더 적합할 것으로 생각된다.

• 한국위성정보통신학회논문지
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• 제6권2호
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• pp.136-140
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• 2011

위성은 효용성 증가로 지속적인 발전를 거치며 여러 종류의 위성이 개발 및 계획이 진행되고 있으며, 여러 가지 필수적인 시스템을 포함하고 있다. 이중 전력 공급 시스템은 위성의 수명에 직접적인 영향을 가지고 있으며, 다양한 요구에 맞게 설계가 이루어 져야 하는 특성을 지니고 있다. 따라서 위성의 설계 요구조건에 부합하는 전압 변압기의 설계 및 안정한 제어가 요구된다. 일반적으로 저궤도 위성의 전력 변환은 각 모듈 및 부하에 따라 여러 단계를 거쳐 전달하게 된다. 이러한 다양한 단계의 전력 변환에 대한 분석 및 이를 반영한 설계는 복잡성으로 인해 쉽게 파악하기 힘든 특성을 가지게 된다. 본 논문에서는 간결 화된 일반화 모델링을 통한 대신호, 소신호분석으로 정 전압 변압기 설계 및 안정화 제어를 위한 방안을 제시한다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.216-221
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• 2004

In two dimensional incompressible flaws, a preconditioning technique called Hierarchical Iterative Procedure(HIP) has been implemented on a SUPG finite element formulation. By using the SUPG formulation, one can escape from the LBB constraint and hence achieve an equal order formulation. In this paper, we increased the order of interpolation up to cubic. The conjugate gradient squared(CGS) method is used for the outer iteration, and the HIP for the preconditioning for the incompressible Navier-Stokes equation. The hierarchical elements has been used to achieve a higher order accuracy in fluid flaw analyses, but a proper efficient iterative procedure for higher order finite element formulation has not been available so far. The numerical results by the present HIP for the lid driven cavity flaw showed the present procedure to be stable, very efficient and useful in flaw analyses in conjunction with hierarchical elements.

• 제어로봇시스템학회논문지
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• 제11권9호
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• pp.750-754
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• 2005

This paper deals with the design problem of multivariable PID controllers guaranteeing the closed-loop system stability and a prescribed $H_\infty$ norm bound constraint. We reduce the problem to the static output feedback stabilization problem. We derive a necessary and sufficient condition f3r the existence of PID controllers and we give an explicit formula of PID controllers. We also give an existence condition of PID controllers guaranteeing a prescribed decay rate. Finally, we give an LMI-based design algorithm, together with a numerical design example.

• 제어로봇시스템학회논문지
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• 제19권3호
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• pp.183-189
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• 2013

This paper presents a stabilization method for NCS (Networked Control Systems) with two additive time-varying delays. Each time delay component between the plant and the controller has different characteristics depending on communication network, and has the upper and lower bounds. The time delay occurring from the controller to the plant has an effect on the time delay occurring from the plant to the controller, and the relationship between two delays is taken into account on the stability analysis. Based on the two additive delay components and the bound conditions, the appropriate Lyapunov-Krasovskii functional and the LMI (Linear Matrix Inequality) method derive the stability condition and the $H_{\infty}$ norm constraint for time-varying delayed NCS. Simulation results are finally given to demonstrate the effectiveness of the proposed method.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.1993-1998
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• 2004

This paper proposes a new framework for control system design, called the data-based control approach or data space approach, in which the input and output data of a dynamical system is directly and solely used to analyze or design a control system without the employment of any mathematical models like transfer functions, state space equations, and kernel representations. Since, in this approach, most of the analysis and design processes are carried out in the domain of the data space, we introduce some notions of geometrical objects, e.g., the openloop and closed-loop data spaces, which serve as the system representations in the data space. In addition, we establish a relationship between the open-loop and closed-loop data spaces that the closed-loop data space is contained in the open-loop data space as one of its subspaces. By using this relationship, we can derive the data-based stabilization condition for a linear time-invariant discrete-time system, which leads to a linear matrix inequality with a rank constraint.

• 한국해양공학회지
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• 제17권5호
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• pp.11-18
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• 2003

In two-dimensional incompressible flows, a preconditioning technique called Hierarchical Iterative Procedure (HIP) has been implemented on a SUPG finite element formulation. By using the SUPG formulation, one can escape from the LBB constraint hence, achieving an equal order formulation. In this paper, we increased the order of interpolation up to cubic. The conjugate gradient squared (CGS) method is used for the outer iteration, and the HIP for the preconditioning for the incompressible Navier-Stokes equation. The hierarchical elements have been used to achieve a higher order accuracy in fluid flow analyses, but a proper and efficient iterative procedure for higher order finite element formulation has not been available, thus far. The numerical results by the present HIP for the lid driven cavity flow showed the present procedure to be stable, very efficient, and useful in flow analyses, in conjunction with hierarchical elements.

• 한국정밀공학회지
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• 제24권12호
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• pp.65-73
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• 2007

In this paper, the gain scheduled state feedback and disturbance feedforward control design proposed in the previous paper has been applied to a simple matching system and a turret stabilization system. In such systems, it is needed to attenuate disturbance response effectively as long as control input satisfies the given constraint on its magnitude. The scheduled control gains are derived in the framework of linear matrix inequality(LMI) optimization by means of the MatLab toolbox. Its effectiveness is verified along with the simulation results compared with the conventional optimum constant gain control and the scheduled state feedback control cases.

• Journal of Advanced Marine Engineering and Technology
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• 제34권7호
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• pp.943-950
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• 2010

An efficient meshfree method based on a stabilized conforming nodal integration method is developed for elastoplastic contact analysis of metal forming processes. In this approach, strain smoothing stabilization is introduced to eliminate spatial instability in Galerkin meshfree methods when the weak form is integrated by a nodal integration. The gradient matrix associated with strain smoothing satisfies the integration constraint for linear exactness in the Galerkin approximation. Strain smoothing formulation and numerical procedures for path-dependent problems are introduced. Applications of metal forming analysis are presented, from which the computational efficiency has been improved significantly without loss of accuracy.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전력기술부문
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• pp.268-270
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• 2002

본 논문에서는 댐핑이 고려된 전력계통에서 동요시 안정도를 향상시킬 수 있는 확장된 PI제어를 이용한 조속기 제어기를 제안하였다. 전력계통에서의 동요는 대부분 고장기간 동안에 발전기에 저장된 과잉운동에너지에 의해 발생한다. 계통이 안정하도록 하기 위해서 과잉에너지를 효과적으로 다루려면 보통 직접법을 사용된다. 과잉에너지를 제어하기 위한 직접적인 방법으로는 LFC(Load Frequency Control)의 궤한이 활용된다. 확장된 PI제어 방식이 적용된 제어기는 지역내에서와 지역사이에서의 동요를 감쇄시키기 위한 조속기에 적용될 수 있다 또한 제안된 제어기는 조속기에 스팀밸브 제한 조건이나 발전율 제약조건(Generation Rate Constraint; GRC)과 같은 특이점이 존재할 때에도 우수한 성능을 보여주었다. 시뮬레이션은 두지역의 다기계통에서 부하를 변화시켜가며 실시하였다. 시뮬레이션 결과는 제안된 PI 제어기를 기존의 PI 제어기와 비교하여 매우 향상된 성능을 보여주었다.