• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.777-789
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• 1990

본 연구에서는 비교적 저가인 소형 컴퓨터(IBM-AT급) 및 주변 장치를 이용하 는 다점가진 모우드해석 시스템의 개발과 관련된 신호 수집, 다차원 스펙트럼 해석법 에 의한 주파수 응답함수 행렬의 계산, 곡선 피팅에 의한 후처리 문제등을 소개하고, 모의실험(simulation) 및 실제 가진실험을 통하여 개발된 시스템의 실용화 가능성을 검토하였다.

• Composites Research
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• v.13 no.6
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• pp.47-54
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• 2000

One promising method for impact detection of composite structures is based on the use of piezopolymer thin fim (PVDf) sensor. In this paper, the relationship between the contact force and the signals of the attached strain gage and PVDF sensor to the composite plate subjected to low-velocity impact were derived. The relation for the open circuit and short circuit voltage of PVDF sensor was derived based on the equivalent circuit model of the piezoelectric sensor. The work was then extended to include experimental investigation into the use of short circuit voltage of PVDF sensor without using charge amplifier to detect low-velocity impact. The natural frequencies and damping ratio of the composite plate obtained from the vibration test were used to modify the analytical model and therefore the differences between measured and simulated signal of the modified analytical model in both forward and backward problem were considerably reduced. The reconstructed contact force and simulated sensor signals agreed well with the measured contact force, strain gage signal, and PVDF sensor singanl.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.37 no.6
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• pp.22-31
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• 2000

In this paper, we propose a method for removing noise components in the feature extraction process for robust speech recognition. This method is based on blind separation using independent component analysis (ICA). Given two noisy speech recordings the algorithm linearly separates speech from the unwanted noise signal. To apply ICA as closely as possible to the feature level for recognition, a new spectral analysis is presented. It modifies the computation of band energies by previously averaging out fast Fourier transform (FFT) points in several divided ranges within one met-scaled band. The simple analysis using sample variances of band energies of speech and noise, and recognition experiments showed its noise robustness. For noisy speech signals recorded in real environments, the proposed method which applies ICA to the new spectral analysis improved the recognition performances to a considerable extent, and was particularly effective for low signal-to-noise ratios (SNRs). This method gives some insights into applying ICA to feature levels and appears useful for robust speech recognition.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.3
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• pp.191-199
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• 2000

In this paper, a numerical analysis using the finite element method (FEM) is presented which models the eddy current testing (ECT) of tubes with 3-dimensional defects. For the description of 3-dimensional eddy current problems, the governing equation is derived from the Maxwell's equations. The 3-dimensional FEM formulation with hexahedral elements is carried out using the Galerkin weighted residual method. The INCONEL 600 steam generator tube with inner and outer diameter defects is adopted for the numerical analysis, and the ECT signal, which is the trajectory of the probe impedance, is calculated. For the verification of the numerical analysis method, results of numerical calculations and experiments are compared and they show good agreements. Based on this verification, several defect signals are predicted and their characteristics are investigated with the variation in the defect depth and the circumferential angle of the defect.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.161-171
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• 1999

Impact resonance testing was carried out on small and large concrete blocks containing several types of artificial flaws respectively. Quantitative analysis of the observed peak frequencies in the impact resonance tests identifies the possible normal modes of concrete blocks containing flaws. and enables to determine the depth and size of the flaws in concrete blocks. In this study, concrete can be treated as a homogeneous and isotropic material. The flaw size and location at each section of artificial flaw series in small and large concrete blocks, determined through two-dimensional scanning of impact point and real-time fast Fourier transform, are in good agreement with real size location, respectively. Consequently, quantitative analysis method of vibration modes in the impact resonance tests, which can be applied for homogeneous and isotropic material, can be useful for the detection of flaws in any case of small and large concrete blocks in this study.

• The Journal of the Acoustical Society of Korea
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• v.19 no.1
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• pp.32-39
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• 2000

In this paper, we have introduced the feature extraction for the ultrasonic signal analysis of the undamaged and damaged concrete specimens. Since the concrete has the heterogeneous nature by itself, it has been difficult to classify the feature with using ultrasonic signal which is acquired from the undamaged and damaged concrete specimens. Therefore, in this paper, we proposed the combinational analysis which is using both the damage coefficient and the number of zerocrossing for the feature extraction. And the pulse velocity method and the damage coefficient, which was proposed by Suaris, were reviewed. In this experiment, two types of concrete specimen have been considered: 180kg/㎠ and 240kg/㎠. The ultrasonic signals were acquired in normal direction. As a result, it has been that combinational analysis method, which is proposed in this paper, shows the better performance than the traditional ultrasonic pulse velocity method and the damage coefficient using maximum amplitude of the ultrasonic signal in the feature extraction.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.451-454
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• 2005

Recently, many methods to analyze signal have been proposed and representative methods are the Fourier transform and wavelet transform. In these methods, the Fourier transform represents signal with combination cosine and sine at all locations in the frequency domain. However, it doesn't provide time information that particular frequency occurs in signal and depends on only the global feature of the signal. So, to improve these points the wavelet transform which is capable of multiresolution analysis has been applied to many fields such as speech processing, image processing and computer vision. And the wavelet transform, which uses changing window according to scale parameter, presents time-frequency localization. In this paper, we proposed a new approach using a wavelet of cosine and sine type and analyzed features of signal in a limited point of frequency-time plane.

• Journal of Korean Society of Transportation
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• v.31 no.1
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• pp.77-86
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• 2013

This paper focuses on the development of analytical models for estimating the changes in saturation flow rates (SFR) at the stop-lines of a signalized intersection due to the existence of nearby work-zones, and thereby calculating the prevailing capacity values for specific lane groups. Major changes were incorporated in the logics of previous models and significant revisions have been made to secure the accuracy and simplicity. Furthermore, much attention was paid to model validation by making comparisons to both extensive simulation results and empirical data from various sites. It was found that SFRs are highly sensitive to the location of work-zones, the distance to each work-zone from the stop-line of a concerned approach, the number of lanes open and closed, and the effective green time. Using such geometric and operating conditions that constitute work-zone environment, the proposed models successfully estimated SFR values with a miniscule margin of error.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.4
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• pp.639-644
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• 2001

Sequence Code Division Multiple Access) and TDMA(Time Division Multiple Access) system. In this system, the narrowband TDMA signals can cause intolerant interferences to CDMA signals. In this paper, DS-CDMA/TDMA frequency sharing system have been analyzed in AWGN(Additive white Gaussian Noise), MAI (Multi Access Interference) and NI(Narrowband Interference) environment. Also, performance improvement has been obtained by adopting an adaptive notch filtering scheme using complex filter bank and CCI canceller.

• Journal of the Korean Institute of Telematics and Electronics
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• v.2 no.1
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• pp.10-13
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• 1965

본논문은 단종된 전송선과 개방된 전송선 및 2개의 결합저항기로 구성된 초광대역전송선형 FM변별기의 동적인 해석(dynamic analysis)을 취급하였다. 변별기의 출력파형의 Harmonic Distortion과 입력신호의 최대허용주파수변위와의 제관계를 Fourier transfrom으로 상세하게 해석하였다. 결합저항계수r(Fig 1 참조)는 변별기의 감도와 입력신호의 전주파수변위에 걸쳐 입력 Impedance가 일정하다는 견지에서 일로 놓아야 된다는 것이 판명되었다. 이론상으로는 100%의 주파수변위를 가진 FM신호라도 본변별기로 불과 2.6% Harmonic distortion으로 검파할 수 있으며 또한 검파시에 변별기의 입력 Impedance는 전종선의 특성 Impedance Z0로 일정하게 유지된다. 이론적인 결과를 뒷받침하기 위하여 실험결과를 첨부하였다. 본실험에서는 변별기의 특성곡선이 중심주파수 85.5Mc를 중심으로 40%의 주파수변위에 대하여 Linear하며, 또한 이때의 변별기의 입력 Impedance의 변화율은 이상치 Z0의 ±14% 이내이다.