• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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• pp.49-56
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• 1999

This paper present a study on the application of sound pressure and vibration signals to detect the presence of defects in a rolling element bearing using a statistical analysis method. The well established statistical parameters such as the crest factor and the distribution of moments including kurtosis and skewless are utilized in this study. In addition, other statistical parameters derived from the beta distribution function are also used. A comparison study on the performance of the different types of parameter used is also performed. The statistical analysis is used because of its simplicity and quick computation. Under ideal conditions, the statistical method can be used to identify the different types of defect present in the bearing. In addition, the results also reveal that there is no significant advantages in using the beta function parameters when compared to using kurtosis and the crest factor for detecting and identifying defects in rolling element bearings from both sound and vibration signals.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.208-211
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• 2001

This paper presents the considerations of the high frequency modulation method for the metal halide lamp electronic ballast. The acousitc resonance phenomenon is occurred, if the metal halide lamp is driven at constant high frequency. The frequency modulation method therefore, is used to avoid the acoustic resonance phenomenon, but the crest factor of lamp current is increased. In this paper, the driving characteristic of the metal halide lamp according to the waveshape and frequency variations of modulating signal is considered with a viewpoint of crest factor.

• Steel and Composite Structures
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• 제30권6호
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• pp.577-589
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• 2019

In this study, on-site testing was carried out to investigate the vibration performance of a composite steel-bar truss slab with steel girder system. Ambient vibration was performed to capture the primary vibration parameters (natural frequencies, damping ratios, and mode shapes). The composite floor possesses low frequency (< 10 Hz) and damping (< 2%). Based on experimental, theoretical, and numerical analyses on natural frequencies and mode shapes, the boundary condition of SCSC (i.e., two opposite edges simply-supported and the other two edges clamped) is deemed more reasonable for the composite floor. Walking excitations by one person (single excitation), two persons (dual excitation), and three persons (triple excitation) were considered to evaluate the vibration serviceability of the composite floor. The measured acceleration results show a satisfactory vibration perceptibility. For design convenience and safety, a crest factor ${\beta}_{rp}$ describing the ratio of peak acceleration to root-mean-square acceleration induced from the walking excitations is proposed. The comparisons of the modal parameters determined by ambient vibration and walking tests reveal the interaction effect between the human excitation and the composite floor.

• 한국통신학회논문지
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• 제32권12C호
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• pp.1175-1187
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• 2007

이동통신 기지국 시스템에서 송신 신호의 PAR 성능을 (peak-to-average power ratio) 개선함으로써 범용 전력 증폭기의 사용이 가능하게 되며, 이로 인해 전체적인 기지국 비용의 절감을 기대할 수 있다. 일반적으로 PAR 값을 줄임으로 인해 기지국 송신신호의 인근 대역 간섭 제한 성능을 나타내는 ACLR이나 (adjacent channel leakage ratio) 품질을 나타내는 EVM이나 (error vector magnitude) PCDE 성능의 (peak code domain error) 열화를 발생시킨다. 본 논문에서 이러한 문제점을 해결하기 위하여 필터링 기반의 CFR 방식인 (crest factor reduction) FDCFR 알고리즘을 (filter-dependent CFR) 소개하며, 히스토그램 기반 코드 영역 보상(HBWCDC; histogram based waterfilling code domain compensation)기법을 제안한다. 본 논문에서 제안한 CFR 알고리즘은 PAR 감소뿐만 아니라 앞서 언급한 ACLR, EVM 및 PCDE등의 성능 열화를 방지한다.

• 한국해안·해양공학회논문집
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• 제23권6호
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• pp.414-421
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• 2011

경사입사파 내습시 직립구조물의 마루높이 산정을 위해 기존 연구의 대부분은 입사각에 따른 월파량 저감계수를 제시하였다. 그러나 기존 연구에서 파랑증폭과 월파의 공간적 분포는 고려하지 않았다. 본 연구에서는 직립구조물을 따른 파랑 증폭현상에 의한 월파의 공간적분포를 실험적으로 검토하였다. 실험결과에 의하면, 직립구조물 시점으로부터 유의파 파장 기준 3파장까지 구간은 직각입사와 동일한 방법으로 마루높이를 산정하고, 그 이후 구간에 대해서는 파랑의 증폭과 월파의 공간적 분포를 고려한 월파량 저감계수를 사용하는 것이 합리적인 것으로 검토되었다.

• 대한전자공학회논문지TC
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• 제44권6호
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• pp.31-39
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• 2007

본 논문에서는 코드분할다중접속방식을 사용하는 이동통신 시스템에서 기지국의 순방향 송신전력 및 파일롯 전력 등 RF 파라미터를 실시가 또는 주기적으로 측정하여 분석함으로써 시스템의 장애를 미연에 방지하고 셀커버리지 확대, 가입자 수용용량 증가 등 최적의 서비스 품질을 확보하고 투자효율을 극대화하기 위한 방안을 제시하였다. 순방향 전력 측정에서는 디텍터 내의 국부발진기 주파수를 가변함으로써 모든 채널의 송신출력을 측정할 수 있도록 하였다. 채널전력의 측정에 의하여 통화량 증가에 따른 송신출력의 변화를 관찰할 수 있으며, 순방향 $E_c/I_o$ 와의 비교를 통하여 파일롯 채널의 전력을 유추함으로써 대전력증폭기 등 송신부 모듈의 열화를 판독할 수 있도록 하였다. 일련의 모든 측정에는 CDMA 레벨디텍터에 의한 정밀 계측에 이은 정확한 분석이 이루어져야 하므로 변조방식 차이에서 오는 Crest factor 가 상이함으로 인한 측정상의 오차를 극복할 수 있도록 설계하였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 전력전자학술대회 논문집
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• pp.228-232
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• 2002

In this paper, In order to solve the problem is proposed using a new type of electronic ballast that the traditional magnetic ballasts operated at 50-60Hz have been suffered from noticeable flicker, high loss, large crest factor and heavy weight which is composed of rectifier, active power corrector, series resonant half bridge inverter, micro-controller and piezoelectric transformer for driving for driving T5 fluorescent lamp were manufactured. The proposed electronic ballast operated at high frequency (about 75kHz) shows a input power factor of more than 0.995, total harmonic distortion of less than $12\%$ and lamp current crest factor of less than 1.5, respectively. Output power and efficiency showed 28w and $85\%$, respectively. Accordingly, it is considered that the ballast using piezoelectric transformer can replace the typical electronic ballast.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 F
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• pp.2789-2791
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• 1999

This paper deals with the design of the HPS electronic ballast, which consists of the ignitor for turning-up and the resonant converter for driving the lamp. Also it contains Power Factor Controller to improve the electronic efficiencies such as power factor, crest factor, low distortion, etc. To make this circuit, it is necessary to simulate it on the computer before we implement it actually. In this paper, we try to modelize the HPS lamp and ballast, and have experiments with 150 watt-HPS lamp from Kwangjunsa.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.585-590
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• 2004

Many machine failures are not detected well in advance due to the masking of background noise and attenuation of the source signal through the transmission mediums. Advanced signal processing techniques using adaptive filters and higher order statistics have been attempted to extract the source signal from the measured data at the machine surface. In this paper, blind deconvolution using the eigenvector algorithm (EVA) technique is used to recover a damaged bearing signal using only the measured signal at the machine surface. A damaged bearing signal corrupted by noise with varying signal-to-noise (s/n) was used to determine the effectiveness of the technique in detecting an incipient signal and the optimum choice of filter length. The results show that the technique is effective in detecting the source signal with an s/n ratio as low as 0.21, but requires a relatively large filter length.

• Steel and Composite Structures
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• 제21권3호
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• pp.573-588
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• 2016

Carbon Fiber Reinforced Plastic (CFRP) and Titanium Alloy (Ti6Al4V) stack, extensively used in aerospace structural components are assembled by fasteners and the holes are made using drilling process. Drilling of stack in one shot is a complicated process due to dissimilarity in the material properties. It is vital to have optimal machining condition and tool geometry for better hole quality and tool life. In this study the tool wear and hole quality were analysed by experimental analysis using three modified twist drills and online tool condition monitoring using Acoustics Emission (AE) sensor. Helix angle and point angle influence tool performance and cutting force. It was found that a tool geometry (TG1) with high helix angle of $35^{\circ}$ with low point angle $130^{\circ}$ results in reduction in thrust force of 150-500 N range but the TG2 also perform almost similar to TG1, but when compared with the AErms voltage generated during drilling it was found that progressive rise in voltage in TG1 is less with respect to TG2 which can be attributed to tool life. In process wear monitoring was done using crest factor as monitoring index. AErms voltage were measured and correlated with the performance of the drills.