• Earthquakes and Structures
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• 제3권6호
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• pp.839-852
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• 2012

Earthquake records are often analyzed in various earthquake engineering problems, making time-frequency analysis for such records of primary concern. The best tool for such analysis appears to be based on wavelet functions; selection of which is not an easy task and is commonly carried through trial and error process. Furthermore, often a particular wavelet is adopted for analysis of various earthquakes irrespective of record's prime characteristics, e.g. wave's magnitude. A wavelet constructed based on records' characteristics may yield a more accurate solution and more efficient solution procedure in time-frequency analysis. In this study, a low-pass reconstruction filter is obtained for each earthquake record based on multi-resolution decomposition technique; the filter is then assigned to be the normalized version of the last approximation component with respect to its magnitude. The scaling and wavelet functions are computed using two-scale relations. The calculated wavelets are highly efficient in decomposing the original records as compared to other commonly used wavelets such as Daubechies2 wavelet. The method is further advantageous since it enables one to decompose the original record in such a way that a clear time-frequency resolution is obtained.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.763-766
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• 2004

Recently, various acoustic artifacts that contains speaker have been produced such as cellular phone. Speaker consists of diaphragm generating sound and coil vibrating diaphragm. Generally, good speaker means that it has a wide frequency range, high output power rate to input power and flat sound pressure level in specified frequency range. Acoustic characteristic was estimated through the experiment and computer simulation, or sound power was controlled with acoustic sensitivity in a natural frequency range fer last decade. However, the flatness of sound pressure level has not been considered to enhance the sound quality of a speaker. Tn this study, a method for speaker design is proposed for a good acoustic characteristic, which is flatness of SPL(sound pressure level) and wideness between the first and second natural frequency. SYSNOISE is used fer acoustic analysis and ANSYS is used for harmonic response analysis and modal analysis. Optimization for acoustic characteristics of a speaker diaphragm is performed using ModelCenter. All analyses are done within a frequency domain. And we confirm that the experimental and computational simulations have similar trend.

• 대한방사선기술학회지:방사선기술과학
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• 제41권5호
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• pp.463-469
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• 2018

Morphological information such as shape and margin of micro lesion is important information for diagnosis of disease in clinical imaging. In this study, we investigated the morphological changes of the micro lesions by comparing the contrast and area in grid suppressed DR images according to grid frequency. In the profile analysis of the image, the mass showed an average intensity variation of 8.6 ~ 72.4 after suppression, The higher the grid frequency, the more the contrast was increased. However, in the images obtained using 103 lp / inch, which is a grid frequency less than the sampling frequency, the contrast of the mass in the vertical direction decreased after suppression. In the binary image, the area change of the mass was also large. As a result, the shape, size, and margin of the mass changed. In the case of very small calcification, the higher the grid frequency is the larger the change in contrast, so that a clear image can be obtained in the post-suppression image. However, we could confirm that the margin of the lesion was blurred and the lesion was lost in some of the images using the 103 lp / inch grid. The higher the frequency of the grid, The change of the contrast of fiber occurred largely and clear boundary was confirmed. The decrease of the number of pixels was small and morphological change was small. In conclusion, when using a grid frequency that is not suitable for the sample frequency, morphological changes or lesion loss of micro lesions in the post- suppression image may give the possibility of misdiagnosis in diagnosis and differentiation of the image.

• 한국공작기계학회논문집
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• 제13권6호
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• pp.94-101
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• 2004

The purpose of this raper is to assess the benefits of frequency domain fatigue analysis and compare it with more conventional time domain techniques. The multi-body dynamic analysis, FE analysis and fatigue life prediction technique are applied for the frequency domain fatigue analysis. To obtain the dynamic load history used in the frequency domain fatigue analysis, the computer simulations running over typical road Profiles are carried out by utilizing vehicle dynamic model. The fatigue life estimation for the rear suspension system of small-sized passenger car is performed by using resonance durability analysis technique, and the estimation results are compared with the conventional quasi-static durability analysis results. For the pothole simulation, the percent changes, of the fatigue life between the two durability analysis techniques don't exceed 10%. But for the Belgian road simulation because of the resonance effect, the fatigue life using the resonance durability analysis technique are much smaller estimated than the quasi-static durability analysis results.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.139-142
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• 2004

The object of the present work is the acoustic emission energy analysis of subambient pressure tri-pad slider. Head/disk interaction during start/stop and constant speed were detected by using acoustic emission (AE) test system The frequency spectrum analysis is performed using the AE signal obtained during the head/disk interaction Natural frequency analysis was performed using Ansys program. Acoustic emission energy was calculated for the slider modes.

• 한국전산구조공학회논문집
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• 제28권5호
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• pp.467-475
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• 2015

본 논문에서는 구조물에 작용하는 하중의 크기와 진동수에 따른 거동의 비선형성을 확인하고 정확한 예측을 위한 방법을 모색하기 위하여 외팔보의 정적 및 동적해석의 수행에서 선형, 비선형 해석의 결과를 비교하는 연구를 진행하였다. 우선 보의 자유단에 수직방향의 정적 및 동적 하중을 가한 상황을 예측하였다. 선형 해석방법으로 고전 외팔보 이론을 적용하였고, co-rotational dynamic 유한요소해석 기법을 개발하여 비선형 해석방법으로 사용하였다. 먼저 정적해석에서 외력의 크기가 달라질 때 선형 및 비선형 해석 예측이 어떠한 차이를 보이는지 비교하였다. 그리고 동적해석을 통해 가진 진동수의 변화에 따른 보 끝단의 무차원화된 변위의 양상을 연구하였고, 공진진동수 근방에서의 상당한 변위가 발생함을 보였다. 마지막으로 주파수 지연현상을 조사하기 위해 특정 진동수에서의 시간 경과에 따른 보의 변위를 확인하였다.

• 한국수자원학회논문집
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• 제44권11호
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• pp.889-902
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• 2011

본 연구에서는 한반도에서 발생했던 과거 가뭄사상의 정량적 평가를 위한 가뭄심도-지속기간-생기빈도(Severity-Duration-Frequency, SDF) 곡선을 유도하기 위해서 가뭄지수를 이용한 빈도해석을 실시하였다. 분석지점으로는 4대강 유역을 중심으로 하는 기상청 산하의 서울, 대전, 대구, 광주, 부산관측소를 선정하였으며 강수자료는 1974~2010년(37년)의 강수 자료를 이용하였다. 가뭄빈도해석에는 기상학적 가뭄지수인 SPI (Standardized Precipitation Index)를 선정하였으며 확률분포형에 대한 적합도 검정에서는 일반극치분포(GEV, Generalized Extreme Value)가 최적의 확률분포형으로 선정되었다. 가뭄지수의 빈도해석 통하여 유도된 주요 관측소별 SDF (Severity-Duration-Frequency) 곡선을 이용하여 과거의 주요 가뭄사상에 대한 재현기간을 제시하였으며 1994~1995년 가뭄의 경우 남부지방을 중심으로 하는 극심한 가뭄으로서 광주관측소에서는 50~100년, 부산관측소에서는 100~200년의 높은 재현기간을 나타내었다. 그밖에 1988~1989년 가뭄의 경우 서울관측소에서는 300년의 재현기간을 나타내었다.

• Current Optics and Photonics
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• 제2권3호
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• pp.250-260
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• 2018

A pressure wave created by the photoacoustic effect is affected by the medium and by laser parameters. The effect of these parameters on the generated pressure wave can be seen by solving the photoacoustic wave equation. These solutions which are examined in the time domain and the frequency domain should be considered by researchers in acoustic sensor design. In particular, frequency domain analysis contains significant information for designing the sensor. The most important part of this information is the determination of the operating frequency of the sensor. In this work, the laser parameters to excite the medium, and the acoustic signal parameters created by the medium are analyzed. For the first time, we have obtained solutions for situations which have no frequency domain solutions in the literature. The main focal point in this work is that the frequency domain solutions of the acoustic wave equation are performed and the effects of the frequency analysis of the related parameters are shown comparatively from the viewpoint of using them in acoustic sensor designs.

• 한국전자파학회논문지
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• 제14권11호
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• pp.1156-1160
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• 2003

많은 시간-주파수 영역 해석법들이 레이다 영상의 이동보상기법에 적용되어져 오고 있다. 이 논문에서는 새로운 시간-주파수 영역 해석법으로서 진화 프로그래밍을 이용한 적응 웨이브릿 변환과 적응 시간-주파수 영역 해석법을 제안하고 이들을 움직이는 표적물에 대한 2차원 레이다 영상의 이동보상기법에 적용해 본다. 제안하는 알고리즘의 타당성을 증명하기 위해서, 우리는 MIG-25와 B-727 데이터를 이용하였다. 진화 프로그래밍을 이용한 적응 웨이브릿 변환과 적응 시간-주파수 영역 해석법을 이용한 레이다 영상은 다른 시간-주파수 영역 해석법과 마찬가지로 퍼짐 현상이 제거된 깨끗한 영상을 얻을 수 있음을 보여 준다.

• 한국농공학회지
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• 제45권5호
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• pp.97-109
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• 2003

This study is mainly conducted to derive the design drought rainfall by the consecutive duration using probability weighted moments with rainfall in the regional drought frequency analysis. It is anticipated to suggest optimal design drought rainfall of hydraulic structures for the water requirement and drought frequency of occurrence for the safety of water utilization through this study. Preferentially, this study was conducted to derive the optimal regionalization of the precipitation data that can be classified by the climatologically and geographically homogeneous regions all over the regions except Cheju and Ulreung islands in Korea. Five homogeneous regions in view of topographical and climatological aspects were accomplished by K-means clustering method. Using the L-moment ratio diagram and Kolmogorov-Smirnov test, generalized extreme value distribution was confirmed as the best fitting one among applied distributions. At-site and regional parameters of the generalized extreme value distribution were estimated by the method of L-moments. Design drought rainfalls using L-moments following the consecutive duration were derived by the at-site and regional analysis using the observed and simulated data resulted from Monte Carlo techniques. Relative root-mean-square error (RRMSE), relative bias (RBIAS) and relative reduction (RR) in RRMSE for the design drought rainfall derived by at-site and regional analysis in the observed an simulated data were computed and compared. In has shown that the regional frequency analysis procedure can substantially more reduce the RRMSE. RBIAS and RR in RRMSE than those of at-site analysis in the prediction of design drought rainfall. Consequently, optimal design drought rainfalls following the regions and consecutive durations were derived by the regional frequency analysis.