• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2011.04a
• /
• pp.635-638
• /
• 2011

유한요소법은 편미분방정식(Partial Differential Equation)의 수치적 근사 해를 구하기 위한 가장 일반적이고 효율적인 방법으로 다양한 공학 분야에서 널리 사용되어지고 있다. 유한요소법의 해석은 연속적인 범위를 가지는 문제를 여러 개의 요소로 나누어 다항식의 형상함수를 만들게 되며 결과적으로 근사 해를 구하게 된다. 이때 해석의 정확성을 높이기 위하여 형상함수의 차수를 높이고 요소의 개수를 늘리게 되면, 이에 따른 수치 계산량의 급격한 증가로 인해 수치해석의 효율성은 떨어지게 된다. 이를 보완하기 위해 유한요소법에 영역분할기법을 적용하여 병렬해석을 수행하면 해의 정확성과 효율성을 동시에 높인다. 병렬해석을 수행하는데 있어서 클러스터의 구조적 특성은 해석의 효율성에 영향을 미치게 된다. 따라서 본 논문에서는 일반적인 모델에 대하여 병렬해석의 수행을 통하여 클러스터의 구조적 특성이 병렬해석의 효율성에 미치는 영향에 대해 확인한다.

• Journal of the Korean Institute of Telematics and Electronics B
• /
• v.33B no.8
• /
• pp.50-59
• /
• 1996

In this paper, a new hierarchical motion estiamtion scheme using the wavelet transformed multi-resolution image layers is proposed. Compared with the full search motion estimation method, the existing hierarchical methods remarkably reduce the amount of the computation but their efficiencies are depreciated by the local minima problem. In order to solve the local minima problem, the multi-resolution image layers are composed using the wavelet transform and the number of layers participated in the motion estimation for a block is determined by considering of its low band energy and higher band energy on the first wavelet transformed layer. The ratio between higher band energy and low band energy of each block is evaluated and in the case of the blocks which include relatively large higher band energy, the motion estimation is carried out in the high resolution layer. Otherwise, all layers are used. The final motion vectors are obtained in the first wavelet transformed layer. So less bits for motion vectors are transmitted, and the decomposition of received image using inverse wavelet transform decreases the blocking effect.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 2001.05a
• /
• pp.109-112
• /
• 2001

Recently, the subject of \"wavelet analysis\" has drawn much attention from both mathematical and engineering application fields such as Signal Processing, Compression/Decomposition, Statistics and ets. Analogous to Fourier analysis, wavelets is a versatile tool with very rich mathematical content and great potential for applications. Specially, wavelet transform uses localizable various mother wavelet functions in time-frequency domain. In this paper, discrimination analyses of acquired electrical current signals for each and mixed loads were tried by using Morlet wavelet transform. Their representative loads were classified as TV, DRY(Dryer), REF(Refrigerate), and FL(Fluorescent Lamp).

• Proceedings of the KIEE Conference
• /
• 2000.07d
• /
• pp.3050-3052
• /
• 2000

Recently. the subject of "wavelet analysis" has drawn much attention from both mathematical and engineering application fields such as Signal Processing, Compression/ Decomposition, Statistics and etc. Analogous to Fourier analysis, wavelets is a versatile tool with very rich mathematical content and great potential for applications. Specially, wavelet transform uses localizable various mother wavelet functions in time-frequency domain. In this paper, discrimination analyses of acquired electrical current signals for each and mixed loads were tried by using Morlet wavelet transform. Their representative loads were classified as TV, DRY, REF, and FL.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1999.05a
• /
• pp.235-239
• /
• 1999

This thesis is concerned with the development of useful engineering techniques to detect and analyze nonlinearities in mechanical systems. The methods developed are based on the concepts of higher order spectra, in particular the bispectrum. The study of higher order statistics has been dominated by work on the bispectrum. The bispectrum can be viewed as a decomposition of the third moment(skewness) of a signal over frequency and as such is blind to symmetric nonlinearities. Initially auto higher order spectra are studied in detail with particular attention being paid to normalization method. Traditional method based on the bicoherence are studied. Under certain conditions, notably narrow band signals, the above normalization method is shown to fail and so a new technique based on prewhitening the signal in the time domain is developed.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2010.04a
• /
• pp.60-63
• /
• 2010

일반적인 포화된 다공질 매체의 수치해석에서는 거시적 관점의 고체변형과 유체이동을 동시에 고려한 혼합유한요소방법(Mixed Finite Element Method)이 쓰인다. 그러나 고체변형이 거의 없는 상태에서 유체가 이동할 경우, 또는 고체변형과 유체유동이 거의 없고 외력에 의한 간극압만 존재할 경우 이를 혼합유한 요소방법으로 해석하기에는 요소 잠김(Element Locking)현상 때문에 매우 불안정하다. 본 논문에서 Park과 Tak(2010)이 제안한 비압축성, 비투과성 포화 다공질 매체의 해석기법인 Staggered Method를 소개하고 수치적 효율성을 높이기 위해 요소분할기술 중 하나인 FETI(Finite Element Tearing and Interconnecting) 기법의 접목을 제안하고자 한다.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2010.04a
• /
• pp.72-75
• /
• 2010

본 논문에서는 열탄점소성 손상과 접촉 문제의 효율적인 해석을 위하여 적응성 영역/경계 분할법을 제안하였다. 적응성 영역/경계 분할법은 시간 증분 또는 반복 기법 단계에서 열탄점소성 손상과 같은 재료 비선형성을 감안하여 부영역을 재설정하며, 접촉에 따른 경계 비선형성은 경계면을 통하여 부영역으로부터 독립적으로 분할한다. 분할된 각각의 부영역과 경계면을 기준으로 유한요소 정식화를 수행하며, 공유면 및 접촉 공유면의 연속 구속 조건을 처리하기 위하여 벌칙 함수 기법을 적용하였다. 결과적으로 재료 및 경계 비선형성은 일부 부영역과 접촉 경계면에서 계산되는 유한요소 행렬에 국한된다. 수치 실험을 통하여 적응성 해석 알고리듬의 기본적인 특성과 효율성 향상에 대하여 분석하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2010.04a
• /
• pp.68-71
• /
• 2010

극심한 고온 및 고압 환경에 노출되기 쉬운 항공우주 구조물에서 발생하는 기계적 삭마 현상을 해석하기 위하여 영역/경계 분할법을 적용한 삭마 해석 모델을 제안하였다. 영역 및 경계는 상변화 현상에 의한 비선형 거동을 하는 삭마 부영역과 선형 거동을 하는 선형 열탄성 부영역, 공유면, 경계 공유면으로 분할하였다. 삭마 재료 내부의 열분해 반응은 엔탈피 방법을 이용하였으며, 표면 침식 반응은 공기역학적 전단 응력과 삭마 재료의 전단 강도를 기반으로 매칭 기법을 이용하였다. 화학적 및 열적 삭마는 고려하지 않았으며, 간단한 수치 해석을 통해서 기본적인 기계적 삭마 특성을 분석하였다.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.05a
• /
• pp.324-329
• /
• 2003

Spectral analysis is an important signal processing tool for time series data. The transformation of a time series into the frequency domain is the basis for a significant number of processing algorithms and interpretive methods. Recently developed transforms based on the new mathematical field of wavelet analysis bypass the resolution limitation and offer superior spectral decomposition. The discrete wavelet transform of Sonar data provides spectral localization of noises, hence noises can be filtered out successfully.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.264.1-264.1
• /
• 2013

Graphene is a two-dimensional carbon material whose structure is one-atom-thick planar sheet of sp2-bonded carbon atoms densely packed in a honeycomb crystal lattice. It has drawn significant attention with its distinguished structural and electrical properties. Extremely high mobility and a tunable band gap make graphene potentially useful for innovative approaches to electronics. Although mechanical exfoliation of graphite and decomposition of SiC surfaces upon thermal treatment have been the main method for graphene, they have some limitations in quality and scalability of as-produced graphene films. Solutionphase and solvothermal syntheses of graphene achieved a major improvement for processing, however for device fabrication, a reproducible method such as chemical vapor deposition (CVD) growth yielding high quality films of controlled thickness is required. In this research, we synthesized hexagonal graphene flakes on Cu foils by CVD method and controlled its coverage, density and the size of graphene domains by changing reaction parameters. It is important to control these parameters of graphene growth during synthesis in order to achieve tunable properties and optimized device performance.