• 대한기계학회논문집B
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• 제26권3호
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• pp.432-438
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• 2002

In order to design and analyze the performance of an axial-flow pump it is necessary to know the flow deviation, deflection angle and pressure loss coefficient as a function of the angle of incidence for the hydrofoil section in use. Because such functions are unique to the particular section, however, general correlation formulae are not available for the multitude of hydrofoil profiles, and such functions must be generated by either experiment or numerical simulation for the given or selected hydrofoil section. The purpose of present study is to generate design correlations for hydrofoils with double circular arc (DCA) camber by numerical analysis using a commercial code, FLUENT. The cascade configuration is determined by a combination of the inlet blade angle, blade thickness, camber angle, and cascade solidity, and a total of 90 cascade configurations are analyzed in this study. The inlet Reynolds number based on the chord and the inlet absolute velocity is fixed at 5${\times}$10$\^$5/. Design correlations are formulated, based on the data at the incidence angle of minimum total pressure loss. The correlations obtained in this way show good agreement with the experiment data collected at NASA with DCA hydrofoils.

• 한국융합학회논문지
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• 제6권5호
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• pp.249-255
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• 2015

본 논문에서는 상관형 위상비교(correlative interferometer) 방향탐지의 방위각 오차에 대해서 기술하였다. 상관형 위상비교 방식은 잡음이 없는 이상적인 환경에서 계산한 위상과 잡음이 있는 실제 환경에서 측정한 위상을 상호 비교하여 상관계수가 가장 큰 방위각을 전파 발신기의 방향으로 추정하는 방식이다. 5개의 안테나를 원형으로 배치하는 원형 배열안테나(circular array antenna)를 이용하여 각 안테나 사이의 상관함수를 유도하여 잡음에 의한 방향탐지 오차를 유도하였다. 이 방법은 잡음에 대한 방탐오차가 매우 작고, 특히 전파 발사체와 방향탐지 장치의 고도 차이가 큰 경우에도 방향탐지 오차가 작은 것으로 나타났다.

• 한국산업정보학회:학술대회논문집
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• 한국산업정보학회 2002년도 추계공동학술대회
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• pp.407-411
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• 2002

삼치 시퀀스(ternary sequence)는 -1, 0, 1의 3가지 값으로만 구성되어 있는 디지털 코드이다. 따라서 디지털 하드웨어로 구현이 편리하다는 장점이 있다 본 시퀀스는 환형 자기상관함수(circular/periodic autocorrelation function)가 이상적으로 나타나는 특징을 가지고 있다. 하지만 본 시퀀스를 이용해 송신기와 수신기사이의 통신 채널 특성을 긴 시간 구간에 걸쳐서 파악하고자 상호상관 법을 사용하기 위해서는 환형이 아니라 선형적인 자기상관함수(linear/aperiodic autocorrelation function) 특성이 요구된다 따라서 본 고에서는 삼치 시퀀스의 비 이상적인 선형 자기상관함수를 개선시키기 위해 주파수 영역에서 역 필터링과 쓰레쉬홀딩 연산을 결합한 방법과 특이치분해(SVD)방법을 제안하며 잡음이 있는 상황에서 그 성능을 평가하고자 한다. 제안한 방법은 시뮬레이션 결과 역 필터링 방법은 신호대잡음비가 30㏈인 경우 최대 부엽 레벨이 11㏈ 감소했고 SVD 방법도 유사한 결과를 보였으나 잡음에 좀 더 약하며 특이치 값의 세밀한 조정이 필요하였다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.804-809
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• 2009

The present study measured frost pattern on a cylinder to propose empirical correlation equations for the local and average frost thickness, frost density and frost mass. The key parameters were diameter of the cylinders (7mm, 20mm), cooling surface temperature of the circular tube, absolute humidity of air, air temperature and air velocity. A 50% ethylene glycol aqueous solution was applied as a coolant. The frost thicknesses at both front and rear were larger than those at the other parts, while they were increased as diameter of the cylinder was increased. The local frost thicknesses at high air velocity were more uniform than those at low air velocity. The values predicted by Kim et al. under the freezer condition showed larger by the maximum of $30{\sim}50%$ than the measured data under heat pump condition. The empirical correlations for the local and average frost thickness and frost mass were proposed. The correlation equations for the frost thickness and frost mass under the heat pump condition in the present study might predict more accurate than the other correlation equations. The proposed correlations might be applied for the freezer condition within the maximum 15% deviation from the previous correlations under freezer condition.

• 제어로봇시스템학회논문지
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• 제17권3호
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• pp.206-210
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• 2011

Vision-based robot localization is challenging due to the vast amount of visual information available, requiring extensive storage and processing time. To deal with these challenges, we propose the use of features extracted from omni-directional panoramic images and present a method for localization of a mobile robot equipped with an omni-directional camera. The core of the proposed scheme may be summarized as follows : First, we utilize an omni-directional camera which can capture instantaneous $360^{\circ}$ panoramic images around a robot. Second, Nodes around the robot are extracted by the correlation coefficients of Circular Horizontal Line between the landmark and the current captured image. Third, the robot position is determined from the locations by the proposed correlation-based landmark image matching. To accelerate computations, we have assigned the node candidates using color information and the correlation values are calculated based on Fast Fourier Transforms. Experiments show that the proposed method is effective in global localization of mobile robots and robust to lighting variations.

• 전기학회논문지
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• 제58권5호
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• pp.1050-1056
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• 2009

Heart Rate Variability(HRV) is a parameter that represents monitoring variability of time intervals between R-peak in electrocardiography. HRV serves to various applications, such as indices of autonomic functions, prediction of cardiac sudden death, assessment of stress and emotional, etc. However, as measuring R-peak in ECG needs at least 3-electrodes, and it is inconvenient for end users. In this paper, we suggested the modified laplacian electrodes for measuring HRV at one-point, which are producted by MEMS fabrication and have the two circular electrodes on the pad. For optimal position and direction, we performed an experiment that compared with pearson correlation coefficient and the amplitude of signals, between standard lead II and proposed electrodes. We analyzed the HRV parameters, such as standard deviation of the NN interval(SDNN), high frequency(HF), low frequency(LF), LF/HF ratio. The result showed that the average correlation coefficient and amplitude are 0.967 and 0.685 mVpp at the position 2. The coeffiecient correlation between the standard HRV and proposed electrode-HRV is 0.999

• 한국정보통신학회논문지
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• 제8권2호
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• pp.232-238
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• 2004

본 논문에서는 각각 2.4㎓ 대역과 5.8㎓ 대역에서 팬빔 안테나, 원형편파 안테나 그리고 지향성 안테나를 사용하여 지하철 터널에서의 전파 특성을 실험하였다. 협대역 채널 측정의 격과, NLOS (Non-Line-Of-Sight) 경로에서 수신전력 레벨이 LOS(Line-Of-Sight)에 비하여 급격히 감소함을 보였다. 광대역채널 측정은 PN sliding correlation 방법을 사용하여 수행하였다. 2.4㎓ 대역과 5.8㎓ 대역을 포함하는 IEEE 802.11 무선랜 대역에서 다양한 지향성 빔에 대한 평균초과지연(mean access delay)과 RMS 지연확산(RMS delay spread) 등의 채널 파라미터를 비교하였다.

• 한국안전학회지
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• 제27권2호
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• pp.111-116
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• 2012

This study deals with the traffic accidents of circular intersections in Korea. The purposes are to comparatively analyze the characteristics by operational type, and to develop the models using the data of 82 intersections. In pursuing the above, this study gives particular emphasis to modeling such the accidents as the roundabout and rotary in urban area. The main results analyzed are as follows. First, the null hypotheses that the number of accidents are the same in both the urban and rural intersections, and roundabout and rotary in urban area, were analyzed to be rejected. Second, 3 accident models were developed, which were all statistically significant. The independent variables used in the above models are the ADT, number of approach lane, bus stop, parking facilities, and others. This study could be expected to give some implications to the traffic safety policy decision-making.

• Journal of Advanced Marine Engineering and Technology
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• 제25권3호
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• pp.552-562
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• 2001

Measurement of average of heat transfer and friction coefficients were obtained with air flowing through electrically heated ducts having square, rectangular(aspect ration, 5), and triangular cross section for range of surface temperature from $540^{\circ}$to $1780^{\circ}$ R and Reynolds number from 1000 to 330,000. The results indicates that the effect of heat flux on correlations of the average heat transfer and friction coefficients is similar to that obtained for circular tubes in previous investigation and was nearly eliminated by evaluating the physical properties and density of the air a film temperature halfway between the average surface and fluid bulk temperatures, With the Nusselt and Reynolds numbers on the hydraulic diameter of the ducts, the data for the noncircular ducts could be represented by the same equations obtained in the previous investigation for circular tubes. Correlation of the average difference between the surface corner and midwall temperatures for the square duct was in agreement with predicted values from a previous analysis. However, for the rectangular and triangular ducts, the measured corner temperature was greater by approximately 20 and 35 percent, respectively, than the values predicted by analysis.

• 한국전자파학회논문지
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• 제29권1호
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• pp.32-35
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• 2018

5G 이동통신시스템에서 요구되는 높은 주파수 효율을 달성하기 위해서는 대규모 다중 입출력 송수신(Massive Multiple-Input Multiple-Output: Massive MIMO) 기술의 활용이 필수적이며, 원소 수의 증가에 따라 다양한 형태의 어레이 형상이 사용될 수 있다. 본 논문에서는 균일 원형 어레이(Uniform Circular Array: UCA)를 사용하는 다중 사용자 MIMO 전송 시 활용 가능한 빔 형성 알고리듬을 제시하며, 빔 간 상관도를 활용하여 준 직교적인 빔 인덱스 쌍을 바탕으로 사용자간 간섭을 최소화하여 얻어지는 성능 이득을 평가한다.