• 한국산업정보학회논문지
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• 제28권6호
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• pp.21-27
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• 2023

현대 함정은 외부로 방사되는 적외선 신호를 낮추기 위해 폐기관에 적외선 신호저감 장치(Infra-Red Signature Suppression system, IRSS)를 설치한다. 그리고 함정은 생의 주기가 매우 긴 전략 자산으로 탑재 장비들의 성능에 대한 높은 신뢰성을 충분히 확보해야 한다. 따라서, IRSS와 같은 장비들은 설계 단계에서 모형시험을 통해 성능평가를 하고 있다. IRSS의 모형시험에서는 다양한 계측기기들이 사용된다. 그러므로, 모형시험 단계 이전에 계측기들의 신뢰성을 평가해야 한다. 본 연구에서는 IRSS 모형시험에 사용되는 계측 장비들의 신뢰성 평가에 관한 연구를 수행하였다. 시험 장비와 계측기는 열 풍동 시험기, 피토 튜브와 디지털 차압계, 열전대 센서 그리고 디지털 기록계가 사용되었다. 계측 결과 열 풍동 시험기의 풍속이 증가할수록 유동의 계측 편차가 감소하였으며, 열전대 센서의 온도는 사용 방법에 따라 반응 속도 및 민감도의 차이를 보였다.

• 한국소음진동공학회논문집
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• 제12권3호
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• pp.236-242
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• 2002

This paper presents some advanced and supplemental methods to enhance the accuracy In case of calculating geometric divergence attenuation, attenuation by multiple screening structures, ground attenuation at unflat surfaces of sound during propagation outdoors by the methods specified in ISO 9613-2. Moreover, a calculation method for considering short-term wind effect, specified in ASJ Model-1998, is also introduced. To verity the accuracy of adopted methods, we have carried out highway traffic noise prediction and measurement at tile twelve locations appearing representative road shapes and structures, such as flat, retained cut, elevated, barrier-constructed roads. From the results, we have confirmed the predicted results show good correspondence with the measured at direct, diffracted and reflected sound fields within 30 m from the center of near side lane.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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• pp.91-94
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• 2003

An experimental study has been carried out in a supersonic blow-down wind tunnel for examining the influence of streamwise vortices on normal shock-wave/boundary layer interaction. It has been reported by the earlier investigator the streamwise vortices generated by the blowing jets can significantly suppress the shock-induced separation and reduce the wave drag. The blowing jets generate the streamwise vortices with 45$^{\circ}$ angle in the spanwise direction. The shock waves are visualized by a Schlieren optical system. Appropriate measurement systems are provided for the characterization of shock wave/boundary layer interaction. The chamber pressure ratio and blowing pressure ratio are varied from 1.5 to 2.4 and 1.0 to 2.0 respectively.

• 한국건축시공학회지
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• 제16권2호
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• pp.125-131
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• 2016

도심지 건물의 증가는 친환경 공간에 대한 요구를 발생시키고, 이에 따라 옥상 및 인공지반 녹화의 보급이 급속히 증가되고 있다. 본 연구는 녹화시스템의 보급 확대를 위해 공법의 단순화, 일체화, 프리훼브화 개념을 적용, 연속 토양층 형성 박스 유닛형 녹화시스템을 개발하고, 이 시스템의 주요 성능으로 부착성, 내풍성, 단열성을 평가하여 적용 가능성을 검토하였다. 부착성 및 내풍성 시험결과, 설계 풍압 및 풍속과 비교하면 100m 높이의 건물에 설치해도 안전한 것을 확인하였고, 단열성 평가를 위해 120일간 측정한 내부 온도의 변화를 분석한 결과, 개발 시스템이 연속된 토양층을 형성하여 기존 유닛박스 시스템보다 주간은 17%, 야간은 45% 우수한 단열성능을 보여 주었다.

• 한국터널지하공간학회 논문집
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• 제16권3호
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• pp.269-285
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• 2014

터널내의 NVP(자연환기력)은 환기 및 방재시스템 설계시 중요성에도 불구하고, 측정 및 정량화의 어려움으로 인해 관련 연구가 극히 제한적이었다. 본 연구에서는 터널 환기시스템의 최적 설계를 위하여 지형 및 기상학적 자료를 이용한 국내 터널내 작용하는 NVP을 정량화함으로써 궁극적으로는 정량화 및 적용 설계지침의 마련을 목적으로 하였다. 국내 주요 노선상의 22개 터널을 분석대상으로 하였다. 기상자료에 기초한 NVP의 범위는 20~140 Pa이며, 지형자료에 기초한 경우는 20~200 Pa로 추정되었다. 터널내 제트팬의 대당 승압력이 10~15 Pa인 점을 감안하면, NVP는 제트팬 1대 이상의 영향력을 가지고 있음을 의미하므로 터널의 경제적이고 안전한 설계를 위해서는 NVP의 정량화 및 적용이 반드시 필요함을 알 수 있다. NVP의 크기 결정에 영향을 미치는 변수중, 터널 입출구 갱구사이의 기압차가 가장 중요한 변수이며 기여도는 평균 61%, 그리고 외풍에 의한 갱구면 작용 압력이 22%, 공기 밀도차에 의한 굴뚝효과가 17%의 기여도를 보인다.

• Wind and Structures
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• 제30권6호
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• pp.617-631
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• 2020

Wake-induced aerodynamics of yawed circular cylinders with smooth and grooved surfaces in a tandem arrangement was studied. This pair of cylinders represent sections of stay-cables with smooth surfaces and high-voltage power conductors with grooved surfaces that are vulnerable to flow-induced structural failure. The study provides some insight for a better understanding of wake-induced loads and galloping problem of bundled cables. All experiments in this study were conducted using a pair of stationary section models of circular cylinders in a wind tunnel subjected to uniform and smooth flow. The aerodynamic force coefficients and vortex-shedding frequency of the downstream model were extracted from the surface pressure distribution. For measurement, polished aluminum tubes were used as smooth cables; and hollow tubes with a helically grooved surface were used as power conductors. The aerodynamic properties of the downstream model were captured at wind speeds of about 6-23 m/s (Reynolds number of 5×10⁴ to 2.67×10⁵ for smooth cable and 2×10⁴ to 1.01×10⁵ for grooved cable) and yaw angles ranging from 0° to 45° while the upstream model was fixed at the various spacing between the two model cylinders. The results showed that the Strouhal number of yawed cable is less than the non-yawed case at a given Reynolds number, and its value is smaller than the Strouhal number of a single cable. Additionally, compared to the single smooth cable, it was observed that there was a reduction of drag coefficient of the downstream model, but no change in a drag coefficient of the downstream grooved case in the range of Reynolds number in this study.

• 대한기계학회논문집B
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• 제33권6호
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• pp.389-395
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• 2009

A specially designed flat plate was mounted vertically over the axial line in the wind tunnel of the Pusan National University. Strain balances were mounted in the trailing part of the plate to measure the skin friction drag over removable insertions of $0.55{\times}0.25m^2$ size. A set of the insertions was designed and manufactured: 3 mm thick polished metal surface and three compliant surfaces. The compliant surfaces were manufactured of a silicone rubber Silastic$^{(R)}$ S2 (Dow Corning company). To modify the viscoelastic properties of the rubber, its composition was varied: 90% rubber + 10% catalyst (standard), 92.5% + 7.5% (weak), 85% + 15% (strong). Modulus of elasticity and the loss factor were measured accurately for these materials in the frequency range from 40 Hz to 3 kHz. The aging of the materials (variation of their properties) for the period of one year was documented as well. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coating. The strong compliant coating achieved 5% drag reduction within a velocity range $20{\sim}40$ m/s while standard and weak coatings increased drag reduction.

• Asian Journal of Atmospheric Environment
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• 제5권2호
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• pp.105-112
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• 2011

In order to investigate the effects of local and synoptic meteorological conditions on urban scale particulate air pollutants observed over the Busan coastal area, power spectrum analysis was applied to observed particulate matter with an aerodynamic diameter $\leq10\;{\mu}m$ ($PM_{10}$) for the period from 1 October, 1993 to 31 December, 2004. Fast Fourier Transform (FFT) analysis was used to obtain the hourly mean observed $PM_{10}$ concentrations to identify different periodicity scales of $PM_{10}$ concentrations. The results showed that, aside from the typical and well-known periodicities such as diurnal and annual variations caused by anthropogenic influences, three other significant power spectral density peaks were identified: 7-day, 21-day and 2.25-year periodicities. Cospectrum analysis indicated that the seven-day variations were closely related to the synoptic meteorological conditions such as weak wind speed, which are relevant to the stagnant high pressure system slowly passing through the Korean Peninsula. The intra-seasonal 21-day variation was negatively correlated with wind speed but was consistently positively correlated with relative humidity, which is related to aerosol formation that can be achieved as a result of the hygroscopic characteristics of aerosols. However, the quasibiennial 2.25-year variation was correlated with the frequency of Asian dust occurrence, the periodicities of which have been recorded inter-annually over the Korean Peninsula.

• Wind and Structures
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• 제31권4호
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• pp.351-362
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• 2020

In this study, the impact of roof slope on the flow characteristics over low-sloped gable roofs was investigated using steady computational fluid dynamics (CFD) simulations based on a k-ω SST turbulence model. A measurement database of the flow field over a scaled model of 15° was created using particle image velocimetry (PIV). Sensitivity analyses for the grid resolutions and turbulence models were performed. Among the three common Reynolds-averaged Navier-Stokes equations (RANS) models, the k-ω SST model exhibited a better performance, followed by the RNG model and then the realizable k-ε model. Next, the flow properties over the differently sloped (0° to 25°) building models were determined. It was found that the effect of roof slope on the flow characteristics was identified by changing the position and size of the separation bubbles, 15° was found to be approximately the sensitive slope at which the distribution of the separation bubbles changed significantly. Additionally, it is suggested additional attention focused on the distributions of the negative pressure on the windward surfaces (especially 5° and 10° roofs) and the possible snow redistribution on the leeward surfaces.

• 한국대기환경학회지
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• 제24권5호
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• pp.604-612
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• 2008

The ozone concentration is one of the important environmental issue for measurement of the atmospheric condition of the country. This study focuses on applying the Autoregressive Error (ARE) model for analyzing the ozone data at middle part of the Gyeonggi-Do, Anyang monitoring site in Korea. In the ARE model, eight meteorological variables and four pollution variables are used as the explanatory variables. The eight meteorological variables are daily maximum temperature, wind speed, amount of cloud, global radiation, relative humidity, rainfall, dew point temperature, and water vapor pressure. The four air pollution variables are sulfur dioxide $(SO_2)$, nitrogen dioxide $(NO_2)$, carbon monoxide (CO), and particulate matter 10 (PM10). The result shows that ARE models both overall and monthly data are suited for describing the oBone concentration. In the ARE model for overall ozone data, ozone concentration can be explained about 71% to by the PM10, global radiation and wind speed. Also the four types of ARE models for high level of ozone data (over 80 ppb) have been analyzed. In the best ARE model for high level of ozone data, ozone can be explained about 96% by the PM10, daliy maximum temperature, and cloud amount.