• 한국공간구조학회논문집
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• 제12권3호
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• pp.47-54
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• 2012

대공간 건축물의 특징 중 경량화 된 지붕 구조 및 재료의 사용으로 인해 지붕면의 손상이나 파괴 등의 피해가 많다. 대규모 경기장의 경우에는 지붕의 구조가 철골 트러스와 인장케이블을 기반으로 테프론이라는 막재료를 사용하여 구조체를 감싸거나 덮는 형태로 많이 설계가 되는데, 특히 이 막재료의 피해가 많으며 심각한 상황이다. 이러한 사례를 통해 대공간 건축물의 지붕에 대한 내풍설계 연구는 아직 미흡한 상태임을 알 수 있다. 본 논문은 쌍곡포물선 대공간구조물의 지붕의 형태에 대한 공기역학적인 특성을 알아보기 위하여 풍압실험과 유체해석을 실시하였다. 실험결과 바람이 불어오는 방향의 지붕 모서리에서 가장 큰 최소피크외압계수가 나타나지만 지붕의 길이방향으로 갈수록 최소피크풍압계수는 감소하고 있었다.

• 한국산업보건학회지
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• 제18권3호
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• pp.177-184
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• 2008

The purpose of this study was to compare the performance characteristics of Andersen and total suspended particulate (TSP) samplers in terms of particle size distribution (PSD) and mass sampling efficiency. In the present study, two Andersen and four TSP samplers were selected and tested to quantitatively estimate human exposure to fly ash representing industrial particulate matter (PM) in a carefully controlled chamber. The PSD characteristics, a mass median aerodynamic diameter and a geometric standard deviation, were found from the sampled PM of airborne samplers in the chamber. An Andersen sampler was compared with a TSP sampler quantified by a coulter counter multisizer, as a reference sampler, to describe the correlation of mass sampling efficiencies between two types of samplers. Overall results indicate that Andersen samplers overestimated small PM due to particle bounce phenomena between impaction stages. There was reasonably good correlation ($R^2$ = 0.89 and 0.91) between the mass sampling efficiencies of Andersen and TSP samplers during the two tests. However, the lower values of slope (0.71 and 0.72) in two tests showed that the Andersen sampler underestimated PM (> AD $10.1\;{\mu}m$) with sufficient inertia due to a relatively lower Andersen inlet velocity at 0.8 m/s comparing with the operating air velocity at 2.1 m/s in the sampling zone of a chamber.

• International Journal of Fluid Machinery and Systems
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• 제2권1호
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• pp.80-91
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• 2009

In this study, a prediction theory for specific noise that is the overall characteristic of the fan has been proposed. This theory is based on total pressure prediction and broadband noise prediction. The specific noises of two forward curved fans with different number of blades were predicted. The flow around the impeller having 120 blades (MF120) was more biased at a certain positions than the impeller with 40 blades (MF40). An effective domain of the energy conversion of MF40 has extended overall than MF120. The total pressure was affected by the slip factor and pressure loss caused by the vortex flow. The suppression of a major pressure drop by the vortex flow and expansion of the effective domain for energy conversion contributed to an increase in the total pressure of MF40 at the design point. The position of maximum relative velocity was different for each fan. The relative velocity of MF120 was less than that of MF40 due to the deviation angle. The specific noise of MF120 was 2.7 dB less than that of MF40 due to the difference in internal flow. It has been quantitatively estimated that the deceleration in the relative velocity contributed to the improvement in the overall performance.

• 한국전산유체공학회지
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• 제11권3호
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• pp.28-36
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• 2006

NSBT(No Slip Boundary Treatment) is a newly developed scheme for the treatment of a no slip condition on the solid wall of obstacle in a flow field. In our research, NSBT was used to perform LBM simulation of a flow over a circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of NSBT on the complex shape of the obstacle, it was first simulated for the case of the flow over a circular and square cylinder in a channel and the results were compared against the solution of Navier-Stokes equation. The simulations were performed in a moderate range of Reynolds number at each cylinder position to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical reynolds number for vortex shedding is in the range of 200$\sim$250. For the gap parameter $\gamma$ = 2 cases at Re > 240, the vortex shedding were symmetric and it resembled the Karmann vortex. As the cylinder approached to one wall, the vorticity significantly reduced in length while the vorticity on the other side elongated and the vorticity combined with the wall boundary-layer vorticity. The resultant $C_d$ by LBM concurred with the results of DNS simulation performed by previous researchers.

• Journal of Advanced Marine Engineering and Technology
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• 제35권4호
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• pp.475-482
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• 2011

본 연구는 풍력블레이드의 공력특성 향상을 위한 기초연구로서, 익형의 표면에 형성된 groove의 형상에 따른 양항비의 개선정도를 전산해석을 통해 분석하였다. 본 연구의 계산 범위에서 경계층(${\delta}$)과 groove 깊이(h)의 비는 1.1, groove 깊이(h)와 폭(d)의 비는 0.1, groove 사이의 거리(p)와 폭(d)의 비는 1.2, groove 수는 2개의 경우에서 양항비가 8.7% 향상된 결과를 보였다. Groove에 의한 양항비의 개선정도가 특정 받음각 이후에서도 지속됨을 확인하였다.

• 한국항공우주학회지
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• 제33권6호
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• pp.8-14
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• 2005

지면 근처에 존재하는 뭉뚝한 물체의 유동장 이해는 자동차 및 항공 업계에 매우 중요한 분야이다. 이를 위해 비압축성 평균 Navier-Stokes 방정식에 $\varepsilon{-SST}$ 난류 모델을 적용하여 정사각주와 이동 지면의 간극 유동을 해석하였다. 비정상 진동을 억제하기 위하여 사각주 하부에 수직/수평의 펜스 설치 효과를 연구하였다. 지면이 운동할 경우에는 지면의 박리 전단층의 강도가 약화되어 사각주 상/하부의 박리 전단층 상호 작용을 촉진시키므로 고정 지면에 비하여 더 낮은 간극에서도 와류 배출이 발생한다.

• Wind and Structures
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• 제15권6호
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• pp.509-529
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• 2012

Traditionally, a quasi steady response concerning the aerodynamic force and moment coefficients acting on a flat plate while 'flying' through the air has been assumed. Such an assumption has enabled the flight paths of windborne debris to be predicted and an indication of its potential damage to be inferred. In order to investigate this assumption in detail, a series of physical and numerical simulations relating to flat plates subject to autorotation has been undertaken. The physical experiments have been carried out using a novel pressure acquisition technique which provides a description of the pressure distribution on a square plate which was allowed to auto-rotate at different speeds by modifying the velocity of the incoming flow. The current work has for the first time, enabled characteristic pressure signals on the surface of an auto-rotating flat plate to be attributed to vortex shedding.

• 한국소음진동공학회논문집
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• 제14권11호
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• pp.1107-1114
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• 2004

Axial fans are widely used for automotive engine cooling device due to their ability to produce high flow rate to keep engine cool. At the same time, the noise generated by these fans causes one of the most serious problems. Especially, engine cooling fan noise in idle condition of a car is noticeable. Therefore. the high efficient and low-noise fan is seriously needed. When a new fan system is designed, system resistance and non-uniform inflow are the key factors to get the high performance and low noise fan system. In this study, aerodynamic and acoustic calculations are carried out on the automotive cooling fan and system. Effects of various design parameters are studied through the free wake analysis and experiments. Better performance and noise characteristic are obtained for the new design fan using the methodology. Furthermore through the modification of the fan system geometry parameters, the fan system produce more flow rate and become less noisy.

• 대한후두음성언어의학회지
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• 제15권1호
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• pp.47-51
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• 2004

Normally, as a result of increased laryngeal growth, the male voice drops about one octave in pitch level during adolescence. Failure of the voice to drop in pitch is consider to be a clinically significant voice disorder - 'mutational dysphonia'. The aim of this article is to evaluate the changes brought about by voice therapy, using the analysis of the EGG measure from Lx Speech Studio program(Laryngograph Ltd, UK) as well as acoustic, and aerodynamic studies in 18-year-old mutational dysphonia patient. The results from the Lx Speech Studio program demonstrated bimodal distribution of DFx(Hz), DQx(%), QxFx and diplophonic characteristic. After voice therapy combined with manual compression method, the distribution of DFx, DQx, QxFx was changed uniform with a dramatic reduction of higher pitch level. In addition, this finding suggests the EGG measure helps to choice treatment options, monitor the efficacy of therapy, and estimate the prognosis of diseases.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1178-1179
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• 2008

This paper describes a modeling of fixed speed wind power generation system which comprise of wind turbine, generator and grid. The wind turbine is based on MOD-2, which is IEEE standard wind turbine, and includes a component using wind turbine characteristic equation. Fixed speed induction generator is directly connected to grid, so the variation of wind speed has effects on the electrical torque and electrical output power. Therefore the power control mode pitch control system is necessary for aerodynamic control of the blades. But the power control mode does not operate at the fault condition. So it is required some methods to control the rotor speed at transient state for stabilization of wind power system. In this paper, simulation model of a fixed speed wind power generation system based on the PSCAD/EMTDC is presented and implemented under the real weather conditions. Also, a new pitch control system is proposed to stabilize the wind power system at the fault condition. The validity of the stabilization method is demonstrated with the results produced through sets of simulation.