• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1292-1297
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• 2004

Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by adopting linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analysis are conducted in the combustors without and with acoustic resonator, which is one of combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in a good agreement with the measurement data. In this regard, the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. The acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity.

• 한국환경과학회지
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• 제23권4호
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• pp.615-623
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• 2014

The groundwater level varies according to the characteristics and composite materials of aquifer. In this study, specific yield and reaction factor which are the major two hydrogeological parameters in the WTF(Water Table Fluctuation) method were estimated and analyzed spatial characteristics. 8 groundwater level stations which have enough measuring period and high correlation with rainfall in the Hancheon watershed were used. The results showed that specific yield was randomly distributed and reaction factor showed inverse trend with altitude. If the enough data were collected, reaction factor according to altitude in ungauged points could be estimated by using these parameter characteristics.

• 상하수도학회지
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• 제26권3호
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• pp.479-486
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• 2012

Runoff characteristics of pollutant loads of the lower Han River was studied before full implementation of Total Pollution Load Management System(TPLMS). Magnitude of macroscopic(annual) fluctuation was in the order of Namhan River > Han River > Bukhan River, gross weight TP > gross weight TN > gross weight BOD, gross weight deviation > concentration deviation. Flux variation was higher than that of concentration. Microscopic(weekly) fluctuation showed similar pattern to macroscopic scale. TP showed the highest deviation resulting in the lowest reliability. 60% of annual flux passed during summer 3months resulting in 43-46% pass of gross weight at the lower Han River. Strong correlation was found between flux and gross weight especially in gross weight TN. Gross weight pollution increased as high as 400% while passing Seoul area due to the concentration. The deviation from moving average increased during summer season in the gross weight TP and BOD. Seasonal tendency was confirmed especially in gross weight TN and TP using autocorrelation function.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.633-635
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• 2007

To cope with increasing power demand in metropolitan area, the power system in Korea has equipped with unit generator of large capacity, high density and uneven distribution, and transmission line of long distance, large capacity and high voltage. As the power system growing up enormous, it has become difficult to maintain the standard voltage in case of radical fluctuation of load or severe change of voltage by power system fault for its weakness of responsive characteristics although the power condenser has been installed to solve the unstability by lack of reactive power. Consequently, we review harmonic wave production and control characteristics to solve unstability problem of voltage in northern metropolitan, to reduce transmission restriction cost and to minimize load shedding by relocation of SVC (Static Var Compensator), which is highly effective for improvement of responsive characteristics for radical voltage fluctuation.

• 한국습지학회지
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• 제17권4호
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• pp.339-347
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• 2015

저수지의 이용목적에 따라서 수력발전용, 농업용수용, 생활 공업용수용 및 홍수조절용으로 구분한 우리나라 35개 저수지의 호안에서 출현하는 관속식물 종류와 지형, 수문, 물 및 토양 환경을 조사하여 이용목적에 따른 호안 환경과 식물상 특성의 차이를 규명하고자 하였다. 호안의 식물상은 저수지의 용도에 따라서 종수, 종류 및 식물종 특성에서 차이를 나타내었다. 단계별 변수선택법 결과에 의하면 저수지 호안의 출현종수는 중앙수위에서 범람빈도가 높고 호안의 연평균노출기간이 길수록 증가하였다. 주좌표분석과 집괴분석의 결과에서 저수지 호안의 식물상은 이용목적에 따라서 크게 3가지 유형, 홍수조절용과 생활 공업용수용, 농업용 및 발전용 저수지로 구분이 되었다. 식물상의 특성에 영향을 미치는 주요한 환경 요인은 연간 수위변동폭, 중앙수위 연범람빈도, LQI 지수 및 연평균노출기간이었다. 수위가 안정적으로 유지되고 수질이 중영양으로 유지되는 발전용 저수지에서는 종풍부도가 높고 침수식물종을 비롯한 수생식물종이 풍부한 연안대가 발달하였다. 수위변동이 심하고 수질이 빈영양 혹은 중영양인 홍수조절용과 생활 공업용수용 저수지 식물상은 수위변동역에서 단명의 교란지식물이 분포하였다. 수위변동이 중간 정도이고 중영양 또는 부영양인 농업용 저수지에서는 부엽식물과 부유식물과 같은 수면을 덮는 식물종이 특징적으로 분포하였다. 결론적으로 저수지 호안의 식물상 특성은 이용목적에 따라서 수위변동, 수질 등의 환경요인이 차이가 나타나고 이에 따라서 식물상의 구조와 종풍부도가 다르게 나타났다.

• 한국자동차공학회논문집
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• 제8권4호
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• pp.1-9
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• 2000

To understand the thermal characteristics around the piston ring gap ring gap positions and piston temperatures are measured simultaneously. The locations of piston ring gap are measured by the radio-tracer method and piston temperature are measured by a K-type thermocouple and scissors type linkage system. From these experiments following facts are clarified. Piston temperatures fluctuate according to the piston ring rotation. And the temperature fluctuation is mainly affected by top ring gap position irrelevant to the second ring fop position. If the top ring gap position increases and the temperature of top ring groove shows maximum value when top rin gap position coincide with temperature measuring point. The maximum amplitude of temperature fluctuation which is proportional to the blow by gas rate is around 12-15$^{\circ}C$.

• 한국전자파학회논문지
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• 제29권8호
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• pp.640-647
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• 2018

본 논문은 전투기 레이다의 표적 추적정확도(추적오차)를 분석하는 방법에 대한 연구이다. 레이다 측정 시 발생하는 측정오차, 탐지실패, radar cross section(RCS) 요동은 측정 품질을 열화시키며, 이는 추적정확도에 영향을 미치는 요인이 될 수 있다. 따라서 정확한 추적성능분석을 위해 이러한 레이다 측정 특성을 고려하는 것이 필요하다. 본 논문에서는 측정오차, 탐지확률, RCS 요동과 같은 레이다 특성을 복합적으로 활용하여 추적정확도를 분석하는 방법에 대해서 제안한다. 제안한 분석 방법을 활용한 실험을 통해 탐지확률과 RCS 요동에 의한 추적정확도 열화를 확인할 수 있었다.

• 한국기계가공학회지
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• 제2권1호
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• pp.85-91
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• 2003

The experimental study for turning circular free fanned surface with TiN coated insert tool was conducted for different cutting conditions such as cutting speed, feed rate and depth-of-cut. For the fluctuation of 1.0mm depth-of-cut, the characteristics for machined surface and tool wear were less influenced by the feed rate and cutting speed than those of higher depth of cut. The higher surface roughness and surface precision were obtained in lower cutting speed. For the fluctuation of 1.5mm depth-of-cut, the higher surface roughness was obtained for the case of the lower feed rate of 0.05-10mm/rev and the higher cutting speed of 80m/min. For the fluctuation of 2.0mm depth-of-cut, the surface roughness and surface precision were too worse to machine the specimen And the flank wear on the tool was increased rapidly rather than the crater wear.

• 한국대기환경학회지
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• 제12권2호
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• pp.141-149
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• 1996

Lateral dispersion parameter(.sigma.$_{y}$) which is an important factor in atmospheric dispersion can be estimated byusing wind direction fluctuation(.sigma.$_{\theta}$). In this paper, we studied the characteristics of the .sigma.$_{\theta}$ in the Chunchon basin and calculated the .sig- ma.$_{y}$ by using the .sigma.$_{\theta}$. We could find some characteristics of the .sigma.$_{\theta}$ which showed small value, when the atmospheric condition was in weak unstable (C class) and neutral (D class). Moreover, when the atmospheric stability was neutral, there was no difference of .sigma.$_{\theta}$ with wind speed. On the other hand, .sigma.$_{\theta}$ showed large values at the strong unstable (A class) and strong stable (F class) condition with low wind speed. In this case, the .sigma.$_{\theta}$ increased as long as averaging time due to the long-period wind direction fluctuation by the terrain effect. In the result of calculation of .sigma.$_{y}$, it was smaller than that of pasquill-Gifford curve. Especially, when the atmospheric condition was in a neutral and stable, .sigma.$_{y}$ showed small increment as the downwind distance increased.creased.

• 대한조선학회논문집
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• 제58권1호
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• pp.10-16
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• 2021

This paper systematically investigates and correlates pressure fluctuation and nominal wake characteristics according to the angle of the vortex generators by introducing the angle adjustment method of the Vortex Generator (VG). The vortex generators are installed at the port and starboard of a model ship. The vortex generator performance test is executed on a model ship installed in the Large Cavitation Tunnel (LCT) and the angle of VG is freely controlled by a servo motor. The systematic test results for the vortex generator show that the well-designed VG is an effective appendage for reducing the pressure fluctuation level and shows the direction of VG's angular design optimization.