• 한국소음진동공학회논문집
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• 제20권12호
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• pp.1153-1160
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• 2010

A circular plate is the main part of a circular saw blade, which is widely used in industrial cutting tools. In experiments using a circular saw containing slots, we observed that a number of natural frequencies are simultaneously emerged in specific frequency regions. The interesting phenomenon is called the frequency convergence. Effects of design parameters such as the number, the length and the width of slots, on the frequency-convergence phenomenon are analyzed by FEM simulations using ALGOR. The frequency-convergence phenomenon will be intensified when the number, length and width of slots increase.

• 대한기계학회논문집
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• 제19권8호
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• pp.1901-1906
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• 1995

The frequency response functions of systems incorporating a non-linear cubic stiffness subject to sinusoidal excitation are derived using the Volterra series and the convergence characteristics investigated. It is shown that the series representation of the frequency response functions converges only when the sinewave input amplitude is within a certain range. Within the range of convergence the frequency response function based on the Volterra series approaches the analytical one as more higher order frequency response function terms are included. Proposed is a criterion for the studies systems to predict approximately the range of sinewave input amplitude for which the series representation of the frequency response functions converges.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2000년도 하계종합학술대회논문집
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• pp.45-48
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• 2000

In this paper algorithms of frequency hopping sequences generation such as Lempel-Greenberger, optimum Lempel-Greenberger and Kumar sequences for spread spectrum communications are described. Using the scalogram based on wavelet transform, time-frequency characteristics of frequency hopped signals corresponding to the considered hopping sequences are analyzed.

• 한국지능시스템학회논문지
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• 제13권2호
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• pp.175-179
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• 2003

반복 학습 제어에서 수렴 조건은 수렴 속도와 잔존 오차와 같은 성능을 결정한다. 따라서, 덜 신중한 수렴 조건을 구할 수 있다면, 그 성능은 향상될 것이고 사용 적합한 학습 제어기의 수는 증가된다. 주파수 영역에서, 연속적인 오차들간의 전달 함수의 $H_{\infty}$ 놈(norm)을 학습 시스템의 수렴성을 조사하기 위해 사용해왔다. 그러나, $H_{\infty}$ 놈을 바탕으로 한 수렴 조건이 단조 수렴성에 대하여 명확한 특성을 가진다하더라도, 특히, 다중 입출력 시스템에서 몇 가지 단점을 가진다. 본 논문에서 는 수렴 조건과 수렴의 단조성간의 관계를 밝힌다. 또한 주파수 영역에서 기존의 수렴 조건을 대신할 수 있는 수정된 수렴 조건을 주파수 영역 리아프노프(Lyapunov) 방정식을 이용하여 구한다.

• 비파괴검사학회지
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• 제31권5호
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• pp.516-521
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• 2011

청각기관인 달팽이관에 존재하는 기저막의 중요한 기능은 등자뼈로부터 전달되는 진동에너지를 주파수별로 분리하는 것이다. 본 연구에서는 인간 기저막의 형상을 모사하여 설계한 매크로 스케일의 폴리머 박막을 사용하여 주파수 분리 특성을 연구하였다. 각각의 폴리머 박막상의 위치에 따른 변위 분포는 LDV (laser Doppler vibrometer) 스캐닝 기법을 이용하여 측정하였고, 측정된 결과는 후처리 과정을 거쳐 주파수별로 분리하였다. 인가된 주파수에 따른 최대 변위 발생 위치를 추출하여 각 박막에 대한 주파수-최대 변위 발생 위치 관계를 도식화하였다. 아울러 박막 두께 및 물성치가 주파수-최대 변위 발생 위치 관계에 미치는 영향에 대해서도 논하였다.

• 한국산업융합학회 논문집
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• 제25권5호
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• pp.783-789
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• 2022

In this study, STS316L rolled at five rolling degrees were treated with two types of subzero temperatures for 10, 30, and 60 minutes, respectively, and the dominant frequencies of elastic waves was investigated. The dominant frequency was higher as the subzero temperature was lower and the subzero treatment time was longer at each rolling degree. On the other hand, the dominant frequency was higher as the elongation decreased. In the time-frequency analysis for subzero temperature and time of the specimen with a rolling degree of 33%, the dominant frequency was higher at a subzero temperature of -196℃ than -50℃ regardless of subzero treatment time.

• 한국음향학회지
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• 제12권1호
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• pp.37-46
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• 1993

The adaptive algorithm for the Volterra filter is considered. Owing to its simplicity, the LMS algorithm for adaptive Volterra filter(AVF) is widely used as in linear adaptive filters. However, the convergence speed is unsatisfactory. For improving the convergence speed, the frequency domain LMS second order adaptive Volterra filter(FLMS-AVF) is proposed and analyzed. We show that the time and frequency domain LMS AVF's have the same steady state performance under approprate conditons. Moreover, it can be shown that this algorithm can improve the convergence speed significantly by applying self-orthogonalizing method.

• Journal of electromagnetic engineering and science
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• 제16권1호
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• pp.13-18
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• 2016

This paper presents a design of an impedance transformer (IT) with high frequency selectivity characteristics. The frequency selectivity can be controlled by even- and odd-mode impedance of a shunt coupled transmission line (TL). For experimental validation, a 50- to $20-{\Omega}$ IT was implemented at a center frequency ($f_0$) of 2.6 GHz for the long-term evolution signal. The measured results were in good agreement with the simulations, showing a return loss higher than 19 dB over a passband bandwidth of 0.63 GHz (2.28-2.91 GHz) and good sharp frequency selectivity characteristic near to the passband. The series coupled TL provides a transmission zero at 5.75 GHz, whereas the shunt coupled TL provides three transmission zeros located at 2 GHz, 3.1 GHz, and 7.14 GHz.

• 한국산업융합학회 논문집
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• 제25권3호
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• pp.325-331
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• 2022

In this study, austenitic 316L stainless steel was rolled at three different temperatures (100℃, -50℃, -196℃) at five rolling degree (0, 16, 33, 50, 66 and 80%). The rolled specimen was examined for micro structure, and the volume fraction and mechanical properties were evaluated. In particular, the rolling specimen detected the elastic wave generated in tensile and investigated the relationship between the rolling degree and the dominant frequency. As the rolling degree increased, austenite decreased and martensite increased. The volume fraction of martensite more increased at lower temperatures, but increased rapidly at the rolling degree of 50% of all rolling temperature. Tensile strength increased rapidly with the increase of the rolling degree, and was larger at lower temperatures. The elongation decreased sharply to the rolling degree of 33%, but decreased gently thereafter. The dominant frequency highly appeared as the volume fraction of martensite increased, but the dominant frequency was higher at the low temperature rolling temperature. A similar trend was also observed in the relationship between tensile strength and dominant frequency.

• 정보처리학회논문지A
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• 제11A권2호
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• pp.203-206
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• 2004

저자는 등각사상을 구하기 위한 기존의 여러 Theodorsen 방정식의 해법 중 가장 유효한 해법으로 알려져 있는 Wegmann의 방법을 다룬바 있다. Wegmann의 방법으로 수치실험을 한 결과 난이도가 높다고 예상되는 문제에 있어 수렴했다가 발산을 하는 불안정현상이 나타났으며 수렵하지 않는 불안정현상의 원인을 분석하여 저주파필터를 적용한 새로운 반복법을 제안하였다. 원래의 Wegmann 반복법으로는 발산하는 모튼 문제에 있어서 새로 제안한 방법에 의해서 수렴하는 수치실험 결과를 얻었는데 본 논문에서는 저주파필터를 적용한 Wegmann해법에 의해 실험적으로 수렴한 결과를 Fourier 분석기법에 의해 이론적으로 증명한다.