• 한국해양공학회지
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• 제25권2호
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• pp.1-6
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• 2011

Vibration-based Structural Health Monitoring (SHM) systems use field measurements of operational signals, which are distorted by noise from many sources. Reducing this noise allows a more accurate assessment of the original "clean" signal and improves analysis results. The implementation of a noise reduction methodology for the Modal Distribution Method (MDM) is reported here. The spectral subtraction method is a popular broadband noise reduction technique used in speech signal processing. Its basic principle is to subtract the magnitude of the noise from the total noisy signal in the frequency domain. The underlying assumption of the method is that noise is additive and uncorrelated with the signal. In speech signal processing, noise can be measured when there is no signal. In the MDM, however, the magnitude of the noise profile can be estimated only from the magnitude of the Power Spectral Density (PSD) at higher frequencies than the frequency range of the true signal associated with structural vibrations under the additional assumption of white noise. The implementation of the spectral subtraction method to MDM may decrease the energy of the individual mode. In this work, a modification of the spectral subtraction method is introduced that enables the conservation of the energies of individual modes. The main difference is that any (negative) bars with a height below zero after subtraction are set to the absolute value of their height. Both noise reduction methods are implemented in the MDM, and an application example is presented that demonstrates its effectiveness when used with a signal corrupted by noise.

• 한국소음진동공학회논문집
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• 제19권11호
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• pp.1192-1201
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• 2009

Analysis of the vibration characteristic for cylindrical shell is more complex than plates since the coupling effects are considered on three dimensions. Based on Love's equation, spectral finite element method(SFEM) is introduced to predict frequency response function of finite circular cylindrical shell in the air with simply supported - free boundary condition without simplifying the equation of motion. And for the radiated noise analysis of cylindrical shell, indirect boundary element method(BEM) is applied using out-of-plane displacements as an input from structural vibration analysis. Comparisons of the structural vibration results by the spectral finite element method and commercial code, NASTRAN(FEM based) are carried out. Likewise, for verification of radiated noise analysis results, commercial code, SYSNOISE(BEM based) are used.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 가을 학술발표회 논문집
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• pp.103-112
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• 1994

Various kinds of fatigue failures of ocean structures were reported and the importance of fatigue life estimation at the design state is significantly recognized and various kinds of analysis approaches have been discussed. In this paper characteristics of the simplified method proposed here and the spectral method are studied and the elements of the approach are discussed. The merits and demerits of the forementioned analysis schemes are studied and the relating parameters such as SCF and S-N curves are also investigated. The simplified fatigue analysis approach and tile spectral fatigue analysis technique is applied for the analysis of bracing members of typical semi-submersible drilling rig structure for the verification of the usage of two methods and the sensitivity study has been performed using the simplified method. The result from the spectral analysis give a more realistic picture of the fatigue life of the offshore structure considered here.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2006년도 춘계학술발표회 논문집
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• pp.211-216
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• 2006

The Constrained Linear Spectral Unmixing(CLSU) is investigated for sub-pixel image processing, Its result is the abundance map which mean fractions of endmember existing in a mixed pixel. Compared to the Linear Spectral Unmixing using least square method, CLSU uses the NNLS (Non-Negative Least Square) algorithm to guarantee that the estimated fractions are constrained. But, CLSU gets Into difficulty in image processing due to select endmember at a user's disposition. In this study, endmember selection optimization method using entropy in the error-image analysis is proposed. In experiments which is used hyperion image, it is shown that our method can select endmember number than CLSU based on unsupervised endemeber selection.

• 대한수학회보
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• 제51권2호
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• pp.595-612
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• 2014

The spectral collocation method for a second order elliptic boundary value problem on a domain ${\Omega}$ with curved boundaries is studied using the Gordon and Hall transformation which enables us to have a transformed elliptic problem and a square domain S = [0, h] ${\times}$ [0, h], h > 0. The preconditioned system of the spectral collocation approximation based on Legendre-Gauss-Lobatto points by the matrix based on piecewise bilinear finite element discretizations is shown to have the high order accuracy of convergence and the efficiency of the finite element preconditioner.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1993년도 학술논문발표회 논문집 제12권 1호
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• pp.238-241
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• 1993

We present a new method to normalize spectral variations of different speakers based on physiological studies of hearing. The proposed method uses the cochlear frequency map to warp the input speech spectra by interpolation or decimation. Using this normalization method, we can obtain much improved recognition results for speaker independent speech recognition.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 1995년도 춘계공동학술대회논문집; 전남대학교; 28-29 Apr. 1995
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• pp.587-599
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• 1995

This paper proposes a method for pattern recognition using spectral analysis and a hybrid genetic-neural-fuzzy networks. The feature vectors using spectral analysis on contour sequences of 2-D images are extracted, and the vectors are not effected by translation, rotation and scale variance. A combined model using the advantages of conventional method is proposed, those are supervised learning BP, global searching genetic algorithm, and unsupervised learning fuzzy c-method. The proposed method is applied to 10 aircraft recognition to confirm the performance of the method. The experimental results show that the proposed method is better accuracy than conventional method using BP or fuzzy c-method, and learning speed is enhanced.

• 호남수학학술지
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• 제37권3호
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• pp.299-315
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• 2015

In this paper, we study the first-order system least-squares (FOSLS) spectral method for parabolic partial differential equations. There were lots of least-squares approaches to solve elliptic partial differential equations using finite element approximation. Also, some approaches using spectral methods have been studied in recent. In order to solve the parabolic partial differential equations in parallel, we consider a parallel numerical method based on a hybrid method of the frequency-domain method and first-order system least-squares method. First, we transform the parabolic problem in the space-time domain to the elliptic problems in the space-frequency domain. Second, we solve each elliptic problem in parallel for some frequencies using the first-order system least-squares method. And then we take the discrete inverse Fourier transforms in order to obtain the approximate solution in the space-time domain. We will introduce such a hybrid method and then present a numerical experiment.

• 분석과학
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• 제8권4호
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• pp.477-480
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• 1995

Isotopic-spectral method [I] was applicated for determination of carbon in silicate materials (pure silica, guartz glasses, geological probs etc.). Isotopic heterogeneous balancing of carbon in gaseous phase and solid samples was carried out at the temperature of $1500-1900^{\circ}K$. Spectroscopic measuring of isotope concentration in a balanced gas was made using the electron-vibrational band heads of CO molecules excited in HF discharge. Limits of detection of carbon concentrations appear to be $n^*10^{-6}$.

• 한국멀티미디어학회논문지
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• 제4권4호
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• pp.306-315
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• 2001

잡음환경에서의 음성인식을 위하여 음성에 부가된 잡음을 제거하는 방법에 있어, 기존의 스펙트럼 차감법은 잡음과 음성을 정확히 구별하기 힘들고 정확한 잡음의 특성을 추정할 수 없는 단점이 있다. 또한 웨이브렛 변환영역에서의 잡음제거 방법은 임계값 적용시 저주파 영역보다는 고주파영역에 상대적으로 더 큰 영향을 미쳐 고주파영역에서 신호의 손실이 발생하는 단점이 있다. 본 논문에서는 스펙트럼 차감법 및 웨이브렛 변환을 이용한 잡음제거 방법의 단점을 개선하기 위하여 연속 웨이브렛 변환 영역에서 웨이브렛 계수의 스케일별 표준편차로 묵음구간과 음성 구간을 판별하여 끝점을 검출 후, 잡음이 섞인 음성신호를 이산 웨이브렛 변화에 의해 3개의 대역으로 분리하여 각각의 대역 내에서 스펙트럼 차감법을 적용시키는 방법을 제안한다. 끝점을 검출하고 대역을 나눔으로써 스펙트럼 차감을 적응할 잡음 신호의 특성을 정확히 추출할 수 있다. 실험을 통하여 제안한 방법이 기존의 스펙트럼 차감법 및 웨이브렛 변환을 이용한 잡음제거 방법보다 신호대 잡음비 및 Itakura-Saito거리 측면에서 향상됨을 확인할 수 있었다.