• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.234-241
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• 1999

The flow at the impeller exit is important to validate engineering design and numerical analysis of pumps. However, it is not easy to measure the flow at the impeller exit and evaluate the impeller performance since there is usually strong interaction between the impeller and the volute casing. We installed axisymmetric collector instead of the volute casing, so there is no interaction between the impeller and casing. A 3-hole Cobra probe is used to investigate the flow at impeller exit and vaneless diffuser region for design and on design flow rate. For a single suction centrifugal pump of low specific speed, the flow field such as velocity, flow angle, and total pressure are measured by traversing the probe across the vaneless diffuser. These data can be used for performance prediction, desist and numerical analysis of pumps.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2004년도 춘계학술대회 논문집
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• pp.511-513
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• 2004

In a switched reluctance motor drive, it is important to synchronize the stator phase excitation with the rotor position, because the position of rotor is an essential information. In the high-speed region, switching angles are fluctuated back and forth out of the preset value, which is caused by the sampling period of the microprocessor. In this paper, a low cost analog encoder suitable for practical applications is proposed. The validity of the proposed analog encoder with a proper logic controller is verified from the experiments.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제4B권3호
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• pp.108-113
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• 2004

This paper presents methods to improve performance of the power supply system in a NASA deep space explorer. In the Stirling engine driven reciprocating Brushless DC (BLDC) generator, the accurate position information of the prime mover is important to diagnose the performance of the engine and prevent distortion of the output power. Since sensors to detect the position are fragile and unreliable, and conventional sensorless techniques have drawbacks in the low speed region, a novel sensorless position detection technique for the prime mover has been proposed and verified. Another major issue of the generator for the spacecraft is power density maximization. The mass of the power system is important to the mass of the satellite. Therefore, the components of the spacecraft should be lightweight. Conventional rectification methods cannot achieve the maximum power possible due to non-optimal current waveforms. The optimal current waveform for maximizing power density and minimizing machine size and weight in a nonsinusoidal power supply system has been derived, incorporated in a control system, and verified by simulation work.

• 대한의용생체공학회:의공학회지
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• 제27권1호
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• pp.6-13
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• 2006

Ultrasound visualization is a typical diagnosis method to examine organs, soft tissues and fetus data. It is difficult to visualize ultrasound data because the quality of the data might be degraded by artifact and speckle noise, and gathered with non-linear sampling. Rendering speed is too slow since we can not use additional data structures or procedures in rendering stage. In this paper, we use several visualization methods for fast rendering of ultrasound data. First method, denoted as adaptive ray sampling, is to reduce the number of samples by adjusting sampling interval in empty space. Secondly, we use early ray termination scheme with sufficiently wide sampling interval and low threshold value of opacity during color compositing. Lastly, we use bilinear interpolation instead of trilinear interpolation for sampling in transparent region. We conclude that our method reduces the rendering time without loss of image quality in comparison to the conventional methods.

• 대한조선학회논문집
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• 제31권1호
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• pp.111-120
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• 1994

본 논문은 Van & Lee[1]의 후속 연구이다. [1]에서 얻어진 결과 중 제대로 설명되지 못했던 부분에 대한 논의를 하고, Tulin[2]의 엄밀해에 대해 간략하게 살펴보았다. 다음 Tulin의 엄밀해를 2차항까지 근사한 2차이론을 사용하여 2차원 몰수체가 저속으로 운동하는 경우에 대해 Poisson 형태와 Dawson[3] 형태의 자유표면조건이 얼마나 정확한 해를 주는지 알아보고자 하였다. 결과적으로 보다 나은 결과를 줄 수 있는 자유표면조건이 필요함을 보이고, 순전히 수치적인 관점에서 새로운 자유표면조건을 유도하였으며, 이를 사용하여 만족할 만한 결과를 얻을 수 있음을 보였다.

• 한국정보과학회논문지:소프트웨어및응용
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• 제32권12호
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• pp.1247-1259
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• 2005

본 연구는 웹카메라와 같은 저해상도의 동영상으로부터 실시간 다중 얼굴 인식 시스템을 제안한다. 동영상을 이용한 얼굴 인식 시스템은 크게 얼굴 검출 단계와 얼굴 분류 단계로 나눌 수 있다. 첫째, 얼굴 검출 단계에서는 빠르고 강인한 객체 검출 성능을 가진 AdaBoost를 이용하여 얼굴 후보 영역을 검출하였고, 검출된 얼굴 후보 영역에 대한 주성분을 수행하여 데이타의 크기기 현저히 줄어든 특징 벡터를 구한 다음에 특징 벡터에 대해 SVM 기반 이진 분류를 수행하여 얼굴 후보 영역을 검증하였다. 둘째, 얼굴 분류 단계에는 주성분 분석과 멀티 SVM을 이용하여 각 얼굴들을 분류하였다. 실험 결과 본 논문에서 제안한 방법은 저해상도에서도 높은 얼굴 검출율과 동영상에서 실시간 처리가 가능한 빠른 다중 얼굴 검출과 인식 성능을 보였다. 또한 팬-틸트 기능을 가진 웹카메라를 이용한 자동 추적형 얼굴 인식 시스템을 적용하여 얼굴 검출 성능을 향상시켰고, 얼굴 인식 시스템의 응용으로 무선 On/off 얼굴인식 도어락 시스템을 구현하였다.

• 한국항공우주학회지
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• 제33권1호
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• pp.20-25
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• 2005

본 연구에서는 UH-1H 헬리콥터의 축소 로터에 대한 두께소음과 하중소음, 그리고 와류흘림에 의한 광역소음을 각각 수치계산을 통해 얻어내고, 그 크기를 비교하였다. 로터의 후류형상은 Kocurek과 Tangler의 지정후류 방법을 사용하였으며, 팁 마하수 $M_{T}$의 범위는 0.2, 0.4, 0.8로 나누어서 유동장 계산과 그에 따른 소음해석을 시도하였다. 팁 마흐 수 $M_{T}$ = 0.8에서 와류 흘림에 의한 광역 소음은 가청주파수 대역 및 A-가중함수를 고려하였을 때에 상대적으로 저주파수 특성을 갖는 두께소음이나 하중소음에 비해 작은 값을 보이는 것으로 나타났다. 특히 광역소음은 가청주파수를 벗어난 초음파 영역에서 대부분의 음압을 방사하는 것으로 나타났다. 반면 $M_{T}$를 0.4 이하로 하였을 때에는 광역소음이 저주파수 영역으로 이동하면서 이산소음에 비해 더 소음레벨을 보이는 것으로 나타났다. 즉, 저속 회전하는 헬리콥터 로터의 경우에는 광역소음의 고려가 필수적임을 알 수 있다.

• 한국환경과학회지
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• 제29권1호
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• pp.1-13
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• 2020

Recently, a heavy rainfall with high spatial variation occurred frequently in the Korean Peninsula. The meteorological event that occurred in Busan on 3 May 2016 is characterized by heavy rain in a limited area. In order to clarify the reason of large spatial variation associated with mountain height and location of low level jet, several numerical experiments were carried out using the dynamic meteorological Weather Research and Forecasting (WRF) model. In this case study, the raised topography of Mount Geumjeong increased a barrier effect and air uplifting due to topographic forcing on the windward side. As a result, wind speed reduced and precipitation increased. In contrast, on the downwind side, the wind speed was slightly faster and since the total amount of water vapor is limited, the precipitation on the downwind side reduced. Numerical experiments on shifting the location of the lower jet demonstrated that if the lower jet is close to the mountain, its core becomes higher due to the effect of friction. Additionally, the water vapor convergence around the mountain increased and eventually the precipitation also increased in the area near the mountain. Hence, the location information of the lower jet is an important factor for accurately predicting precipitation.

• 한국유체기계학회 논문집
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• 제15권1호
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• pp.58-63
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• 2012

Three dimensional unsteady numerical calculations were performed to investigate unsteadiness of the tip leakage flow in an axial compressor. The first stage of the four-stage low-speed research axial compressor was examined. Since this compressor has a relatively large tip clearance, the unsteadiness of the tip leakage flow is induced. Through the results from the unsteady calculations, the process of the induced unsteady tip leakage flow was investigated. It was shown that the leakage flow that occurred at a rotor blade tip clearance affected the pressure distribution on the pressure side near the tip of the adjacent blade, thus caused the fluctuation of the pressure difference between the pressure side and suction side. Consequently, the unsteady tip leakage flow was induced at the adjacent rotor blade. The unsteady feature of the tip leakage flow was changed as the operating point was moved. The interface between the tip leakage flow and the main flow only affected the trailing edge region at the design point whereas the interface influenced up to the leading edge at the low flow rate point. As the flow rate decreased, additionally, it was seen that the vortex size of the tip leakage flow increased and the relatively large length scale disturbance occurred. On the other hand, using frequency analysis, it was shown that the unsteadiness was not associated with the rotor speed and was about 40% of the blade passing frequency. This feature was explained in the rotor relative frame of reference, and the frequency decreased as the flow rate decreased.

• Wind and Structures
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• 제17권1호
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• pp.43-68
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• 2013

The fluctuating wind induced vibration is one of the most important factors which has been taken into account in the design of long-span bridge due to the low stiffness and low natural frequency. Field measurement characteristics of sustained wind on structure site can provide accurate wind load parameters for wind field simulation and structural wind resistance design. As a suspension bridge with 1490 m main span, the Runyang Suspension Bridge (RSB) has high sensitivity to fluctuating wind. The simultaneous and continuously wind environment field measurement both in mid-span and on tower top is executed from 2005 up to now by the structural health monitoring system installed on this bridge. Based on the recorded data, the wind characteristic parameters, including mean wind speed, wind direction, the turbulence intensity, the gust factors, the turbulence integral length, power spectrum and spatial correlation, are analyzed in detail and the coherence functions of those parameters are evaluated using statistical method in this paper. The results indicate that, the turbulence component of sustain wind is larger than extremely strong winds although its mean wind speed is smaller; the correlation between turbulence parameters is obvious; the power spectrum is special and not accord with the Simiu spectrum and von Karman spectrum. Results obtained in this study can be used to evaluate the long term reliability of the Runyang Suspension Bridge and provide reference values for wind resistant design of other structures in this region.