• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1183-1186
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• 2007

The low frequency noise, including infra-sound is known to affect human physiology and psychology. Guidelines and measurement method of low frequency noise has been introduced in several countries in order to evaluate low frequency noise. In this work, low frequency noise characteristics of dump truck was investigated in terms of the noise level and spectrum. The interior sound pressure level of the dump truck was between 60 and 105 dB in the frequency range of $1{\sim}250$ Hz.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.887-890
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• 2007

The low frequency noise, including infra-sound is known to affect human physiology and psychology. Guidelines and measurement method of low frequency noise has been introduced in several countries in order to evaluate low frequency noise. In this work, low frequency characteristics of Daejeon subway was investigated in terms of the noise level and spectrum in the interior of running subway car and the subway station. The interior sound pressure level of the passenger car was between 60 and 102 dB in the frequency range of $1{\sim}250$ Hz.

• Interaction and multiscale mechanics
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• 제3권4호
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• pp.373-387
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• 2010

This study is intended to assess low frequency sound radiated from a viaduct under normal traffic. The bridge comprises steel box girders and wide cantilever decks on which vehicles pass. The low frequency sound and the acceleration response of the bridge under normal traffic are measured to investigate how bridge vibrations affect the low frequency sound observed near the bridge. Observations demonstrate that strong relationships exist between frequency characteristic of bridge's acceleration response and the sound pressure level of low frequency sound. A noteworthy point is that the dynamic feature of the sound pressure level is mostly affected by dynamic feature of the span locating near the observation point.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3361-3379
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• 2022

A nuclear power plant (NPP) piping is designed against low-frequency earthquakes. However, earthquakes that can occur at NPP sites in the eastern part of the United States, northern Europe, and Korea are high-frequency earthquakes. Therefore, this study conducts bi-directional shaking table tests on actual-scale NPP piping and studies the response characteristics of low- and high-frequency earthquake motions. Such response characteristics are analyzed by comparing several responses that occur in the piping. Also, based on the test results, a piping numerical analysis model is developed and validated. The piping seismic performance under high-frequency earthquakes is derived. Consequently, the high-frequency excitation caused a large amplification in the measured peak acceleration responses compared to the low-frequency excitation. Conversely, concerning relative displacements, strains, and normal stresses, low-frequency excitation responses were larger than high-frequency excitation responses. Main peak relative displacements and peak normal stresses were 60%-69% and 24%-49% smaller in the high-frequency earthquake response than the low-frequency earthquake response. This phenomenon was noticeable when the earthquake motion intensity was large. The piping numerical model simulated the main natural frequencies and relative displacement responses well. Finally, for the stress limit state, the seismic performance for high-frequency earthquakes was about 2.7 times greater than for low-frequency earthquakes.

• 전산구조공학
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• 제10권4호
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• pp.185-193
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• 1997

대형 건축물의 진동과 같은 초저주파 진동특성의 해석을 수행하기 위해서는 측정대상 및 측정조건, 그리고 목적으로 하는 측정요소에 적합한 측정시스템이 구축되어야 하며, 구축된 측정시스템으로부터 얻어진 극히 제한된 유한량의 데이터로부터 목적하는 특성요소를 추출하기 위한 정밀한 데이터분석기술이 요구된다. 따라서, 본 연구에서는 고신뢰성을 저주파진동 특성의 분석을 위한 효과적인 데이터처리기법의 개발을 목표로, 측정조건에 따른 저주파진동 해석의 문제점을 분석하고, FFT법과 MEM법의 저주파응답 특성을 비교하였으며, 비교결과를 토대로 저주파진동 해석에 적합한 알고리즘을 결정하였다. 또한, 결정된 분석 알고리즘의 성능을 명확히 하여 정밀분석을 위한 측정데이터의 최적조건을 제시하였다.

• 한국소음진동공학회논문집
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• 제13권4호
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• pp.274-280
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• 2003

If a sinusoidal excitation force moves back and forth along a structure with a certain frequency, the structure will be excited with the difference frequency of these two frequencies. A low frequency vibration shaker has been developed using this force frequency shifting without actually moving a shaker The shaker consists of an ordinary eccentric mass shaker, a plate, constant springs, and time varying dampers. The dampers are turned on and off in a sequential manner to simulate a traveling slide of an excitation force. The operation of the shaker is simulated by solving the equations of motion of the shaker. Characteristics of the shaker have been found and they can be utilized to design efficient low frequency shakers.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1597-1609
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• 2015

This paper introduces the fundamentals of the conventional LC low-pass filter circuit in the fractional domain. First, we study the new fundamentals of fractional-order LC low-pass filter circuit including the pure real angular frequency, the pure imaginary angular frequency and the short circuit angular frequency. Moreover, sensitivity analysis of the impedance characteristics and phase characteristics of the LC low-pass filter circuit with respect to the system variables is studied in detail, which shows the greater flexibility of the fractional-order filter circuit in designs. Furthermore, from the filtering property perspective, we systematically investigate the effects of the system variables (LC, frequency f and fractional orders) on the amplitude-frequency characteristics and phase-frequency characteristics. In addition, the detailed analyses of the cut-off frequency and filter factor are presented. Numerical experimental results are presented to verify the theoretical results introduced in this paper.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.147-147
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• 2012

Cutoff probe has been used for measuring a plasma density using the cutoff peak which is located at the plasma frequency in the low pressure plasma. However, research on analysis of low frequency region of transmission microwave frequency (TMF) spectrum does not performed even though important plasma parameters are located in the low frequency region, i.e., ion plasma frequency and collision frequency. In this research, we analyzed the low frequency region of the TMF spectrum. Experimental results reveal the effect of plasma parameters on the low frequency region on the TMF spectrum. Based on the response of TMF spectrum from changing of plasma parameters, deduction of the plasma parameters was tried. This comprehensive analysis of TMF spectrum expands applicable area of cutoff probe.

• 대한물리의학회지
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• 제6권3호
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• pp.353-360
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• 2011

Purpose : The purpose of this study was to compare the effect of muscle strength by stimulation of russian current and low frequency. Methods : The subjects were thirty young healthy volunteers who were divided into two groups including russian current group(n=15) and low frequency group(n=15). The intervention was applied totally 12 times (1 time, 10 minute) for 4weeks in each group. The peak torque and average power were measured and analysed using Biodex system 4 before the treatment, after 2 weeks, 4 weeks. Results : As a result, russians currents and low frequency stimulation increased significantly average power and peak torque with the lapse of time. However, there were not significant differences of the average power and peak torque between the groups in all periods. Conclusion : In conclusion, russians currents and low frequency stimulation had no differences in the increase of muscle strength.

• Ocean and Polar Research
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• 제29권4호
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• pp.311-316
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• 2007

Ocean noise may be used for monitoring wind speed and rainfall rate on the sea surface, as well as for tracking whales' migration routes. In particular, low-frequency ocean noise has recently been of concern with relation to the behavior of marine mammals. Low-frequency ocean noise has been increasing over the past few decades due to increase of ship traffic and offshore oil industry activities. Mechanical noise such as flow noise and cable strumming noise may be induced if low-frequency ocean noise is measured by cabled traditional hydrophone in high current areas. To successfully measure low-frequency ocean noise in a shallow water environment with strong current, we developed a self-recording hydrophone. This paper describes the main configurations of the self-recording hydrophone and presents some results on measured data.