• 대한전자공학회논문지SD
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• 제37권2호
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• pp.28-37
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• 2000

수정된 Airy 함수들과 WKB 시도해를 조합하여 언덕형 굴절율 분포를 가지는 광섬유에 대한 매우 정확한 고유방정식을 수학적으로 유도하였다. 적절한 경계조건을 적용하여 일반적인 WKB 방법이 가지는 고유한 오차 문제를 개선하도록 위상 천이 보정항 δ를 이끌어냈다. 모의 전산을 통하여, 유도된 고유방정식의 결과가 유한차분법에 의한 결과와 잘 일치함을 보였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.641-646
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• 2008

Long and slender body with or without flexible supports under severe operating condition can be unstabilized even by the small cross flow. Turbulent flow mixer, which actually increases thermal-hydraulic performance of the nuclear fuel by boosting turbulence, disturbs the flow field around the fuel rod and affects dynamic behavior of the nuclear fuel rods. Few studies on this problem can be found in the literature because these effects depend on the specific natures of the support and the design of the system. This work shows how the dynamics of a multi-span fuel rod can be affected by the turbulent flow, which is discretely activated by a flow mixer. By solving a state-space form of the eigenvalue equation for a multi-span fuel rod system, the critical velocity at which a fuel rod becomes unstable was established. Based on the simulation results, we evaluated how stability of a multi-spanned nuclear fuel rod with mixing vanes can be affected by the coolant flow in an operating reactor core.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.155-160
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• 2001

Actual engineering structure is frequently very complex, and parts of structure are designed independently by different engineers. Also each structure contains so many degree of freedom. For these reason, methods have been developed which permits the structure to be divided into components or substructures, with analysis being done on a small substructure in order to obtain a full structural system. In such case, because of different mesh size among finite element model (FEM) or different matching points among FEM models and experimentally obtained models, their interfacing points may be non-matching. Solving this non-matching problem is useful to other application such as structural dynamic modification or model updating. In this work, virtual node concept is introduced. Lagrange multipliers are used to enforce the interface compatibility constraint, and interface displacement is approximated by polynomial presentation. The governing equation of whole structure is derived using hybrid variational principle. The eigenvalue of whole structure are calculated using the determinant search method. The number of degree of freedom in the eigenvalue problem can be drastically reduced to just the number of interface degree of freedom. Some numerical simulation is performed to show usefulness of synthesis method.

• 생명과학회지
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• 제10권2호
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• pp.169-176
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• 2000

At Koppl area, undamaged natural habitat of sundew, I have analysed interspecific affinities and community composition through mathematical method and important environmental factors. Interspecific affinities of the species with frequency of more than 5% in vegetation table were analysed through chi-square test and showed obvious group of Drosera rotundifolia, Vaccinium uliginosum, Calluna vulgaris, Eriophorum angustifolium and 21 species. The result of ordination anlysis using DECORANA of VESPAN II showed eigenvalue of 0.6047 for axis I, 0.2024 for axis II and 0.0763 for axis Ⅲ. And it divided into 4 groups of quadrat number 1-5 for Sphagnum squarrosum-community, 6-10 for Crepis paludosa-community. 11-25 for Carex panicea-community and 26-35 for Scorpidium scorpioides-community. By the classification using TWINSPAN, the 7 areas divided into 2 groups of 1-10 and 11-35 at first level of division with high eigenvalue of 0.588 and indicator was Sphagnum squarrosum. At second level of division it divided into 4 groups as the results of DECORANA with eigenvalues of 0.268 and 0.423 and indicators were Pinguicula vulgaris and Scorpidium scorpioides. Microclimatic environment of studied area was low in temperature and high in humidity and soil environment showed high in field moisture capacity, acid, high organic matter content, low NO3 and K2O content, compare to normal soil, and high ground water level.

• Steel and Composite Structures
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• 제22권6호
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• pp.1281-1299
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• 2016

This paper deals with the analysis of vibration of antisymmetric angle-ply plates using spline method for higher order shear theory. Free vibration of laminated plates is addressed to show the capability of the present method in the vicinity of higher order shear deformation theory and simply supported edges of plates. The coupled differential equations are obtained in terms displacement and rotational functions. These displacement and rotational functions are approximated using cubic and quantic spline. A generalized eigenvalue problem is obtained and solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The antisymmetric angle-ply fiber orientation are taken as design variables. Numerical results enable us to examine the frequencies for various geometric and material parameters and accuracy and effectiveness of the proposed method is also verified by comparative study.

• 한국소음진동공학회논문집
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• 제20권3호
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• pp.215-222
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• 2010

Long and slender body, like a fuel rod, oscillating in axial flow can be unstabilized even by the small cross flow which can be activated by the flow mixer or turbulent generator. It is important to include these effects of flow disturbance in dynamic stability analysis of nuclear fuel rod. This work shows how eigen frequency of a multi-span fuel rod can be changed by the swirl flow, which is discretely generated by a flow mixer. By solving a state-space form of the eigenvalue equation for a multi-span fuel rod system, the critical velocity at which a fuel rod becomes unstable was calculated. Based on the simulation results, we evaluated how stability of a multi-spanned nuclear fuel rod with mixing vanes can be affected by the coolant flow in an operating reactor core.

• 한국수산과학회지
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• 제27권6호
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• pp.782-786
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• 1994

Dey and Morrison (1979)이 육상의 전기탐사문제의 해결에 성공적으로 적용한 적분차분법(integral finite different method)의 해양에서의 응용성을 연구해보기 위해, 해석해가 존재하는 연안역의 해수고유진동 문제를 도출하여 기존의 고유진동문제에 적용하여 보았다. 그 응용성의 평가는 기존 해양에 널리 적용되는 기존차분법(conventional finite different method)으로 구한 수치결과와 적분차분법으로 구한 결과를 해석해와의 비교검증을 통하여 실시되었다. 그 결과 적분차분법으로 구한 고유치와 고유함수값이 기존차분법으로 구한 결과보다 좋은것으로 나타났다. 이러한 결과는 적분차분법의 경우 원래의 기본방정식에 Green's theorem을 적용함으로써, 기본방정식에 존재하는 2계 미분연산자가 1계 미분연산자로 해석적으로 처리되었기 때문으로 사료된다. 따라서 적분차분법을 이용하여 해수고유진동문제를 비롯한 다른 유사문제를 풀 경우 기본차분법보다 좋은 결과가 나을 것으로 사료된다. 또한 미분방정식의 수치해를 구할 경우 적분법이 차분법보다 좋은해를 줄 수 있다는 것을 증명한 것으로 사료된다.

• 한국자동차공학회논문집
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• 제15권2호
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• pp.126-134
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• 2007

Although there has been substantial research on the squeal noise for the automotive brake system, robust design issues with respect to control factors equivalent to design variables in optimization, noise factors due to system uncertainties, and signal factors designed to accommodate a user-adjustable setting still need to be addressed. For the purpose, the robust design applied to the disk brake system has been investigated by DOE (Design of Experiments) based Taguchi analysis with dynamic characteristics. The specific goal of this methodology is to identify a design with linear signal-response relationship, and variability minimization. The finite element models of the disk brake assembly have been constructed, and the squeal noise problems have been solved by complex eigenvalue analysis. As the practical robust design to reduce the brake squeal noise, material properties of pad, disk, and backplate, thickness and geometry of pad are selected as control factors, material properties of pad and disk, and the contact stiffness have been considered as noise factors, and friction coefficient between pad and disk is chosen as a signal factor. Through the DOE based robust design, the signal-to-noise ratio and the sensitivity for each orthogonal array experiment have been analyzed. Also, it has been proved that the proposed robust design is effective and adequate to reduce the brake squeal noise.

• 한국전산구조공학회논문집
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• 제18권2호
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• pp.151-158
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• 2005

본 연구에서는 유한요소법을 이용하여 Pasternak 지반 위에 놓인 보강판의 고유치해석을 수행하였다. 보강판 해석은 Mindlin 판 이론과 Timoshenko 보-기둥 이론을 적용하여 해석하였으며, 유한요소법 적용시 판요소는 8절점 Serendipity 요소계를, 보요소는 3절점 유한요소를 적용하였다. 탄성지반은 지반의 연속성을 고려한 Pasternak 지반으로 모형화하였다. 본 연구의 타당성을 검증하기 위하여 이 연구의 결과를 문헌, 실험 및 SAP 2000의 결과와 비교하였다. 이 연구의 결과로 문헌 해가 존재하지 않는 Pasternak 지반 위에 놓인 보강판의 지반 변수의 변화 및 보강재 크기에 따른 고유진동수를 산정하였다.

• 대한기계학회논문집A
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• 제38권12호
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• pp.1351-1358
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• 2014

본 논문은 차량 제동 시 발생하는 소음의 원인을 해석적으로 예측하고, 본 실험실에서 제작한 브레이크 다이나모 메터를 이용하여 실험적으로 검증하였다. 압력 변화에 따른 브레이크 시스템에 대한 주파수 응답 시험 및 유한 요소 해석(FEM)을 실시하여 캘리퍼 및 디스크의 수직 모드(Out-of-plane)의 시스템 주파수를 추적하였다. 이를 제동 시 발생한 스퀼 소음의 주파수와 비교해본 결과 스퀼 주파수는 캘리퍼 및 패드의 변위를 갖는 시스템 모드임을 확인하였다. 또한 유한 요소 해석을 이용한 복소수 고유치 해석 결과 패드의 회전변위를 발생시키는 캘리퍼 모드가 음의 마찰곡선 기울기와 연동하여 불안정하게 됨을 확인하였다.