• 한국생물정보학회:학술대회논문집
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• 한국생물정보시스템생물학회 2004년도 The 3rd Annual Conference for The Korean Society for Bioinformatics Association of Asian Societies for Bioinformatics 2004 Symposium
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• pp.265-271
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• 2004

The interaction network of protein -protein plays an important role to understand the various biological functions of cells. Currently, the high -throughput experimental techniques (two -dimensional gel electrophoresis, mass spectroscopy, yeast two -hybrid assay) provide us with the vast amount of data for protein-protein interaction at the proteome scale. In order to recognize the role of each protein in their network, the efficient bioinformatical and computational analysis methods are required. We propose a systematic and mathematical method which can analyze the protein -protein interaction network rigorously and enable us to capture the biological and physical essence of a topological character and stability of protein -protein network, and sensitivity of each protein along the biological pathway of their network. We set up a Laplacian matrix of spectral graph theory based on the protein-protein network of yeast proteome, and perform an eigenvalue analysis and apply a perturbation method on a Laplacian matrix, which result in recognizing the center of protein cluster, the identity of hub proteins around it and their relative sensitivities. Identifying the topology of protein -protein network via a Laplacian matrix, we can recognize the important relation between the biological pathway of yeast proteome and the formalism of master equation. The results of our systematic and mathematical analysis agree well with the experimental findings of yeast proteome. The biological function and meaning of each protein cluster can be explained easily. Our rigorous analysis method is robust for understanding various kinds of networks whether they are biological, social, economical...etc

• 대한토목학회논문집
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• 제13권4호
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• pp.15-25
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• 1993

복합재료를 효과적으로 사용하기 위하여 복합재료 구조물의 설계기준 개발을 위한 연구가 진행되고 있다. 금속 셀의 좌굴에 대한 설계시에는 초기 결함의 영향과 탄성임계좌굴응력을 근거로 한 녹다운계수(Knock-down factor)를 정의하는 것이 중요한 과정이나 복합재료 쉘의 좌굴에 대한 설계시에는 초기 결함에 대한 민감도가 거의 연구되어 있지 않은 실정이다. 복합재료 쉘의 좌굴거동에 영향을 주는 설계변수는 많기 때문에, 쉘의 설계시 이 변수들로 인한 초기 결함 민감도를 분석하기 위하여 많은 실험을 필요로 하고 있으며 실험 이외의 다른 방법으로서는 이미 검증된 수치모델을 사용하는 것이다. 본 논문에서는 복합재료 쉘요소를 개발하는데 사용된 이론을 요약, 정리 하였으며 수치예제를 통하여 본 연구에서 제안한 쉘요소의 정확성을 검증하였다. 그리고 축방향으로 압축을 받는 GFRP 곡선형 판넬의 설계시 고려해야 하는 각 변수들을 다양하게 변화시키면서 좌굴거동에 미치는 영향을 유한요소 모델링에 의해 고찰하였다. 방법으로서 초기 결합 및 두께의 진폭을 고려한 비선형 해석과 고유치 해석을 수행하였으며 이 결과를 이용하여 녹다운 계수를 산출하였다.

• Transactions on Electrical and Electronic Materials
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• 제18권5호
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• pp.287-297
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• 2017

Novel power system stabilizers (PSSs) have been proposed to effectively dampen low frequency oscillations (LFOs) in multi-machine power systems and have attracted increasing research interest in recent years. Due to this attention, recently, fractional order controllers (FOCs) have found new applications in power system stability issues. Here, a tilt-integral-derivative power system stabilizer (TID-PSS) is proposed to enhance the dynamic stability of a multi-machine power system by providing additional damping to the LFOs. The TID is an extended version of the classical proportional-integral-derivative (PID) applying fractional calculus. The design of the proposed three-parameter tunable TID-PSS is systematized as a nonlinear time domain optimization problem in which the tunable parameters are adjusted concurrently using a modified group search optimization (MGSO) algorithm. An integral of the time multiplied squared error (ITSE) performance index is considered as the objective function. The proposed stabilizer is simulated in the MATLAB/SIMULINK environment using the FOMCON toolbox and the dynamic performance is evaluated on a 3-machine 6-bus power system. The TID-PSS is compared with both classical PID-PSS (PID-PSS) and conventional PSS (CPSS) using eigenvalue analysis and time domain simulations. Sensitivity analyses are performed to assess the robustness of the proposed controller against large changes in system loading conditions and parameters. The results indicate that the proposed TID-PSS provides the better dynamic performance and robustness compared with the PID-PSS and CPSS.

• 한국전산구조공학회논문집
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• 제28권5호
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• pp.441-449
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• 2015

본 논문에서는 커코프 판이론과 폰-칼만 비선형 변형율-변위 관계를 이용하여 서형화된 좌굴해석을 수행하였다. 평면응력과 좌굴문제에서 영률과 두께에 관한 설계민감도식을 유도하였고, 고유치를 최대화하면서 컴플라이언스를 최소화하는 위상최적설계 기법을 정식화하였다. 좌굴해석에서의 프리스트레스를 이용하여 판 좌굴문제에 적용할 수 있는 위상최적설계 기법을 개발하였다. 폰-칼만 비선형 변형률을 사용하여 좌굴문제의 응력행렬을 구성하는데 프리스트레스가 필요하므로 면외로의 운동을 도입하였다. 위상최적설계를 위하여 정규재료밀도를 설계변수로 하고, 목적함수는 최소 컴플라이언스와 최대 고유진동수로 하였으며 제한조건은 허용되는 재료량이다. 여러 수치예제를 통하여 개발된 설계민감도 해석법은 유한차분 민감도와 비교하여 매우 정확한 값을 가지고, 위상최적설계는 물리적으로 의미있는 결과를 제공함을 확인하였다.

• Progress in Superconductivity
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• 제14권1호
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• pp.52-59
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• 2012

In this paper, the robust superconductor flywheel energy storage system(SFESS) controller using $H_{\infty}$ control theory was designed to damp low frequency oscillation of power system. The main advantage of the $H_{\infty}$ controller is that uncertainties of power system can be included at the stage of controller design. Both disturbance attenuation and robust stability for the power system were treated simultaneously by using mixed sensitivity $H_{\infty}$ problem. The robust stability and the performance for uncertainties of power system were represented by frequency weighted transfer function. To verify control performance of proposed SFESS controller using $H_{\infty}$ control, the closed loop eigenvalue and the damping ratio in dominant oscillation mode of power system were analyzed and nonlinear simulation for one-machine infinite bus system was performed under disturbance for various operating conditions. The results showed that the proposed $H_{\infty}$ SFESS controller was more robust than conventional power system stabilizer (PSS).

• Advances in aircraft and spacecraft science
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• 제4권2호
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• pp.169-184
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• 2017

The optimum design of structures with frequency constraints is of great importance in the aeronautical industry. In order to avoid severe vibration, it is necessary to shift the fundamental frequency of the structure away from the frequency range of the dynamic loading. This paper develops a novel topology optimisation method for optimising the fundamental frequencies of structures. The finite element dynamic eigenvalue problem is solved to derive the sensitivity function used for the optimisation criteria. An alternative material interpolation scheme is developed and applied to the optimisation problem. A novel level-set criteria and updating routine for the weighting factors is presented to determine the optimal topology. The optimisation algorithm is applied to a simple two-dimensional plane stress plate to verify the method. Optimisation for maximising a chosen frequency and maximising the gap between two frequencies are presented. This has the application of stiffness maximisation and flutter suppression. The results of the optimisation algorithm are compared with the state of the art in frequency topology optimisation. Test cases have shown that the algorithm produces similar topologies to the state of the art, verifying that the novel technique is suitable for frequency optimisation.

• Steel and Composite Structures
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• 제44권5호
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• pp.651-676
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• 2022

Most of the experimental, theoretical, and numerical studies on the stability of functionally graded composites are deterministic, while there are full of complex interactions of variables with an inherently probabilistic nature, this paper presents a non-intrusive framework to investigate the stochastic nonlinear buckling behaviors of porous functionally graded cylindrical shells exposed to inevitable source-uncertainties. Euler-Lagrange equations are theoretically derived based on the three variable refined shear deformation theory. Closed-form solutions for the shell buckling loads are achieved by solving the deterministic eigenvalue problems. The analytical results are verified with numerical results obtained from finite element analyses that are conducted in the commercial software ABAQUS. The non-intrusive framework is completed by integrating the Monte Carlo simulation with the verified closed-form solutions. The convergence studies are performed to determine the effective pseudorandom draws of the simulation. The accuracy and efficiency of the framework are verified with statistical results that are obtained from the first and second-order perturbation techniques. Eleven cases of individual and compound uncertainties are investigated. Sensitivity analyses are conducted to figure out the five cases that have profound perturbative effects on the shell buckling loads. Complete probability distributions of the first three critical buckling loads are completely presented for each profound uncertainty case. The effects of the shell thickness, volume fraction index, and stochasticity degree on the shell buckling load under compound uncertainties are studied. There is a high probability that the shell has non-unique buckling modes in stochastic environments, which should be known for reliable analysis and design of engineering structures.

• Journal of the Optical Society of Korea
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• 제18권4호
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• pp.317-329
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• 2014

In vision measurement systems based on structured light, the key point of detection precision is to determine accurately the central position of the projected laser line in the image. The purpose of this research is to extract laser line centers based on a decision function generated to distinguish the real centers from candidate points with a high recognition rate. First, preprocessing of an image adopting a difference image method is conducted to realize image segmentation of the laser line. Second, the feature points in an integral pixel level are selected as the initiating light line centers by the eigenvalues of the Hessian matrix. Third, according to the light intensity distribution of a laser line obeying a Gaussian distribution in transverse section and a constant distribution in longitudinal section, a normalized model of Hessian matrix eigenvalues for the candidate centers of the laser line is presented to balance reasonably the two eigenvalues that indicate the variation tendencies of the second-order partial derivatives of the Gaussian function and constant function, respectively. The proposed model integrates a Gaussian recognition function and a sinusoidal recognition function. The Gaussian recognition function estimates the characteristic that one eigenvalue approaches zero, and enhances the sensitivity of the decision function to that characteristic, which corresponds to the longitudinal direction of the laser line. The sinusoidal recognition function evaluates the feature that the other eigenvalue is negative with a large absolute value, making the decision function more sensitive to that feature, which is related to the transverse direction of the laser line. In the proposed model the decision function is weighted for higher values to the real centers synthetically, considering the properties in the longitudinal and transverse directions of the laser line. Moreover, this method provides a decision value from 0 to 1 for arbitrary candidate centers, which yields a normalized measure for different laser lines in different images. The normalized results of pixels close to 1 are determined to be the real centers by progressive scanning of the image columns. Finally, the zero point of a second-order Taylor expansion in the eigenvector's direction is employed to refine further the extraction results of the central points at the subpixel level. The experimental results show that the method based on this normalization model accurately extracts the coordinates of laser line centers and obtains a higher recognition rate in two group experiments.

• 대한기계학회논문집A
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• 제40권4호
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• pp.363-372
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• 2016

강체와 유연체가 혼합된 다종 구조 시스템의 동특성을 개선을 위한 최적화를 수행하는 경우, 일반적으로 그 시스템의 고유 진동수를 높이게 된다. 강체와 유연체의 시스템을 동시에 다루는 위상 최적화 정식화가 있으나, 그 시스템의 고유 진동수를 다룬 연구는 드물며, 특히 목적하는 진동수가 중복 고유 진동수 의 하나로 되는 경우를 다룬 연구는 보고된 바 없다. 본 연구에서는 중복 고유 진동수를 다루어야 하는 경우에 나타나는 수치적 문제를 해결하였으며 그 방법을 활용한 위상최적설계 정식화와 민감도 해석을 제시하였다. 그 다음, 몇 가지 수치 예제를 통해 제안된 정식화의 타당성을 검증해 보았다.

• 비파괴검사학회지
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• 제28권2호
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• pp.211-216
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• 2008

이 연구에서 다층구조물에서 각 모드에 대한 위상속도, 군속도, 감쇠 그리고 파형구조를 구하는 프로그램을 개발하였다. 판의 수와 재료 물성치를 변화시키면서 각 모드의 파형구조를 얻었다. 유체가 닿아 있는 구조물에서 유도파를 이용한 비파괴 검사의 성공여부는 에너지 손실을 최소화하는 모드선정의 최적화이다. 이 연구에서는 자유표면판재의 표면에서 정규화된 두께방향의 변위가 감쇠의 변화를 예측하기 위해서 사용되었으며 감쇠와 파형구조의 관계를 밝혔다. 이것은 유도파의 감쇠를 물이 닿아 있는 경우 복소수근을 찾는 수학적 어려움을 경감하면서 자유표면에서 두께방향 변위의 변화로부터 손쉽게 얻을 수 있다. 이 연구를 통하여 다층구조물에서 보다 민감하고 효율적인 비파괴 검사를 위한 유도파의 모드선정의 최적화 개념을 완성했다.