• Journal of Biosystems Engineering
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• 제26권4호
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• pp.315-322
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• 2001

Agricultural products can be damaged due to the vibration of transporting trailer on the off-road. So, this study was conducted to identify the vibration characteristics of the agricultural products transporting trailer by measuring the vertical acceleration according to positions on the trailer loaded with agricultural products. The results of this study can be summarized as follows: 1. At non-operating state of engine, the larger vertical acceleration was occurred at rear side compared with front side in the case of 4.5Hz of vibration frequency. But, in the case of 53.5Hz of frequency, the maximum vertical acceleration at front side of trailer was higher than value at rear side. So, the maximum acceleration at front side of the trailer was increased with the increase in frequency. 2. At operating state of engine, the maximum vertical acceleration at front side of the trailer was increased with the increase in frequency. 2 At operating state of engine, the maximum vertical acceleration delivered through the hitch from the engine was occurred at front side of the trailer as $3.0\times10^{-3}m/s^2$, in the case of 8.75Hz of frequency. But, in the case of 102.5Hz of high frequency, the maximum vertical acceleration was occurred at rear side of the trailer. 3. When the power tiller loaded with pear of 325kg was travelling on the artificial uneven road of 3cm height, the maximum acceleration was occurred at rear side of the trailer as $4.7\times10^{-3}m/s^2$at 3.75Hz of frequency. But, that was occurred at diagonal of the trailer 43.5Hz and 91.25Hz, which meant that there was rolling and pitching on the trailer. 4. At operating state of engine, the mean acceleration of the trailer delivered through the hitch according to the increase in frequencies was showed the maximum value at range of 40-90Hz. At rear side of traiㅣer, the maximum value was occurred at about 40Hz, and that was reduced according to the increase in frequencies and diminished at about 100Hz. 5. When the power tiller loaded with pear of 32.5kg was travelling on the artificial uneven road of 3cm height, the mean acceleration by the increase in frequencies was showed lower level at rear side than front side of the trailer. This was opposite configuration to the Hinsch’s results tested with air-conditioned truck. This means that the shorter length of the trailer, the more effect of engine vibration is transferred to the front side of trailer.

• 한국통신학회논문지
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• 제30권7A호
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• pp.628-638
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• 2005

The analysis of maximum diversity order and coding gain for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over time-and frequency-selective (or doubly-selective) channels is addressed in this paper. A novel channel time-space correlation function is developed given the spatially correlated doubly-selective Rayleigh fading channel model. Based on this channel-model assumption, the upper-bound of pairwise error probability (PEP) for MIMO-OFDM systems is derived under the maximum likelihood (ML) detection. For a certain space-frequency code, we quantify the maximum diversity order and deduce the expression of coding gain. In this wort the impact of channel time selectivity is especially studied and a new definition of time diversity is illustrated correspondingly

• 한국생산제조학회지
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• 제21권5호
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• pp.733-740
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• 2012

This paper studies with structural and vibration analysis to evaluate the structural safety according to the types of steering wheels. This study models are two, three and four spoke types. As the number of spokes increases, the maximum equivalent stress becomes smaller but the maximum total deformation becomes a little higher. The natural frequency at three models are shown from 180 to 230Hz as the maximum deformation. The frequency responses as maximum amplitude displacement are happened at 200Hz, 500Hz and 500Hz respectively. In this study, the steering wheel with three spoke type is shown to become suitable at durability and production.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.38-42
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• 1999

We prepared hish T$_c$ Josephson junctions that have different I$_c\;'s$ and R$_n\;'s$ and studied their microwave properties. We measured the current-voltage characteristics of the junctions under the irradiation of 22 GHz electromagnetic wave at various temperatures. from the Shapiro steps, we calculated the maximum detectable frequency and the microwave received power of the junctions. Increasing critical current values increase both maximum detectable frequency and sensitivity. However, increasing temperature increase sensitivity but decrease maximum detectable frequency.

• 한국공작기계학회논문집
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• 제13권1호
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• pp.81-87
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• 2004

A 3-D FEM (Finite Element Method) analysis of the turbo-blower shaft attached to a fuel cell was performed using Lanczos algorithm. The modal analysis was analyzed in order to investigate natural frequency and maximum displacement for 10 times. It was found that the first mode of natural frequency is 109.1Hz with the maximum displacement of 0.16mm while the tenth mode of natural frequency is 2464Hz with the maximum displacement of 0.25mm. Consequently, the results of modal analysis of the turbo-blower for a fuel cell system show good dynamic responses.

• 반도체디스플레이기술학회지
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• 제13권4호
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• pp.55-58
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• 2014

The next-generation AlGaN/GaN HEMT power devices need higher power at higher frequencies. To know the device characteristics, the simulation of those devices are made. This paper presents a simulation study on the DC and RF characteristics of AlGaN/GaN HEMT power devices. According to the reduction of gate length from $2.0{\mu}m$ to $0.1{\mu}m$, the simulation results show that the drain current at zero gate voltage increases, the gate capacitance decreases, and the maximum transconductance increases, and thus the cutoff frequency and the maximum oscillation frequency increase. The maximum oscillation frequency maintains higher than the cutoff frequency, which means that the devices are useful for power devices at very high frequencies.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2004년도 학술발표회
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• pp.479-483
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• 2004

A new calculation method of expected overtopping probability of rubble mound breakwater considering real tide occurrence has been proposed. A calculation method of expected overtopping probability of rubble mound breakwater was proposed by Kweon and Suh (2003). In their calculation, the fluctuation of tidal elevation was expressed by the sinusoidal change that yields the uniform distribution of occurrence frequency. However, the realistic distribution of tidal elevation should influence on the overtopping chance. In this study, the occurrence frequency of tidal elevation obtained from the real sea is included. The tidal elevation used in this study is collected from the east coastal part of Korean peninsular. Analyzing the annual data of the tidal fluctuation measured hourly during 355 days, the distribution of occurrence frequency is formulated utilizing by the normal distribution with one peak. Among the calculation procedures of annual maximum wave height, wave height-period joint distribution, wave run-up height and occurrence frequency of tide, only the annual maximum wave height is again chosen randomly from normal distribution to consider the uncertainty. The others are treated by utilizing the distribution function or relationship itself, It is found that the inclusion of the variability of tidal elevation has great influence on the computation of the expected overtopping probability of rubble mound breakwater. The bigger standard deviation of occurrence frequency is, the lower the overtopping probability of rubble mound breakwater is.

• 전기학회논문지P
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• 제62권1호
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• pp.1-5
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• 2013

The aim of this study is to research maximum harvesting energy by the optimal input wave condition. The voltage characteristics of the PZT bimorph were investigated in terms of the sine wave, triangle wave and square wave according to frequency range 0~70Hz. It was found that the square wave compared with a triangular wave or square wave was showed the higher output energy. PZT bimorph was mechanically vibrated by solenoid coil experiments, which revealed two voltage peak mode according to frequency. Maximum voltage at second vibration frequency 28Hz demonstrated that the generated DC voltage was proportional to the tip displacement of the bimorph and the phase difference between the input frequency and bimorph vibration frequency was 90 degree. It was expected that optimized design to harvest a much higher energy level from lower frequency vibrations.

• 터널과지하공간
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• 제15권5호
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• pp.352-358
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• 2005

콘크리트 비파괴 검사를 위하여 배면공동모형과 교량공동모형에 대하여 시간영역 탐사와 주파수영역 탐사를 실시하였다. 시간영역 탐사는 초동주시 역산법을 이용하여 토모그래피를 작성하여 공동의 여부를 해석하였다. 주파수영역 탐사는 시간영역 기록을 푸리에 변환에 의한 주파수영역에서의 최대 주파수를 분석하여 해석하였다.

• 물과 미래
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• 제19권3호
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• pp.249-258
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• 1986

본 연구는 수공구조물의 계획설계와 물관리 계획시 계획강우량의 결정기준이 되는 우리나라 전역의 최대하강수량 추정을 위한 최대하강수량 빈도계수 산정에 관한 내용이다. PMP 빈도계수 산정에 있어서는 연속기록년 20년의 자기우량기록지 보유지점을 대상으로 하였으며, 지속기간별(10분, 1,2,4,6,12,24시간) 연최대치 강우자료집단을 이용하여 연최대평균강우량에 따른 PMP 빈도계수를 결정할 수 있는 상관도를 작성하였다. 최대하강수량은 최대평균강우량과 빈도계수 및 지속기간 상관도상에서 얻어진 PMP 빈도계수와 통계치를 사용하여 통계학적 방법으로 산정하였으며, 포락선에 의해서 지점 최대하강수량과 지속기간 관계식을 유도하여 산정하였다. 산정된 지점 최대하강수량으로부터 전국에 대한 24시간 최대하강수량 분포도와 PMP·DAD 곡선을 작성하였다. ^ The purpose of this study is to estimate the PMP frequency factor for evaluation of the Probable Maximum Precipitation (PMP) in Korea. The value of PMP is the criterion of the determination of design rainfall in Planning and designing hydraulic structures, and water resources management. To obtain the object, 12 key stations were selected in which have the automatic rain0recording paper of 20 years, and the annual maximum rainfall values were calculated for each 7 durations(10 min., 1,2,4,6,12,24 hr.). The statistics(mean, standard deviation)were estimated, and diagram which shows the relationship between mean annual maximum rainfall($$) and frequency factor for each durations were drawn. PMP was estimated by statistical method using the PMP frequency factor obtained from the diagram and statistics($$, Sn). The PMP-Duration Equation was derived from the envelope curve in order to obtain the PMP for an arbitrary duration. The isohyetal map of 24 hours PMP and PMP. DAD curve for the whole of Korea were drawn in accordance with the point PMP values.