• Journal of Advanced Marine Engineering and Technology
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• 제38권9호
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• pp.1075-1080
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• 2014

본 연구는 5MW급 해상풍력 하부구조물개발에 있어 설계에 필요한 다양한 해양환경 조건에 대하여 높은 안정성 확보가 요구되는 해상용 풍력발전 하부구조물과 관련, 구조물의 설계방법을 제시하고 그 안정성을 고찰하여 관련 기술 분야에 기여함을 목표로 한다. 특히, 5MW급 해상풍력발전 시스템에 대해 시험영역에서 큰 바람의 방향이 지속되고 있는 동안에 동시에 발달된 파도의 계산에 대한 정보를 제공한다. 그러므로 바람의 영역과 접근하는 파동 행열간의 관련성을 검토하여 강도, 방향 그리고 시간의 이동성을 계산할 수 있음을 확인하였다. 쇄파에서의 국부적인 압력분포를 물리적인 모델링과 수치적 모델링을 통해 조사하는 것이 가능하다. 해상 풍력 에너지 변환장치의 지지구조물들에 대해 최근 적용된 구조 및 피로에 대한 평가는 일반 설계규칙에 근거했다. 5MW 해상풍력 하부구조물은 제약조건이 많아 단일구조로 취급하는데 이는 생산에서 높은 안전계수를 고려해야함을 의미한다.

• 한국군사과학기술학회지
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• 제18권4호
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• pp.469-477
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• 2015

In this study, the characteristics of main wind direction, vertical temperature and wind speed profile near the Moseulpo airfield for HALE UAV(High Altitude Long Endurance Unmaned Aerial Vehicle) is investigated. The results are summarized as follows, main wind direction is governed by air mass according to season and local wind such as land-sea breeze. The directions of landing and take-off of HALE UAV will be selected as the south-east direction in June ~ August, north-west direction in October ~ March, and south-east direction at daytime in April ~ May, September. Annual variation of temperature at 100 hPa showed that temperature in summer season is lower than winter season. On the other hands, wind speed at 250 hPa in winter season is higher than summer season. The threshold values of temperature and wind speed for HALE UAV flight are $-75^{\circ}C$ and $90ms^{-1}$, which were determined by 5 % frequency value($1.96{\sigma}$), respectively.

• Wind and Structures
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• 제34권2호
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• pp.231-257
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• 2022

Transmission lines systems are important components of the electrical power infrastructure. However, these systems are vulnerable to damage from high wind events such as hurricanes. This study presents the results from a 1:50 scale aeroelastic model of a multi-span transmission lines system subjected to simulated hurricane winds. The transmission lines system considered in this study consists of three lattice towers, four spans of conductors and two end-frames. The aeroelastic tests were conducted at the NSF NHERI Wall of Wind Experimental Facility (WOW EF) at the Florida International University (FIU). A horizontal distortion scaling technique was used in order to fit the entire model on the WOW turntable. The system was tested at various wind speeds ranging from 35 m/s to 78 m/s (equivalent full-scale speeds) for varying wind directions. A system identification (SID) technique was used to evaluate experimental-based along-wind aerodynamic damping coefficients and compare with their theoretical counterparts. Comparisons were done for two aeroelastic models: (i) a self-supported lattice tower, and (ii) a multi-span transmission lines system. A buffeting analysis was conducted to estimate the response of the conductors and compare it to measured experimental values. The responses of the single lattice tower and the multi-span transmission lines system were compared. The coupling effects seem to drastically change the aerodynamic damping of the system, compared to the single lattice tower case. The estimation of the drag forces on the conductors are in good agreement with their experimental counterparts. The incorporation of the change in turbulence intensity along the height of the towers appears to better estimate the response of the transmission tower, in comparison with previous methods which assumed constant turbulence intensity. Dynamic amplification factors and gust effect factors were computed, and comparisons were made with code specific values. The resonance contribution is shown to reach a maximum of 18% and 30% of the peak response of the stand-alone tower and entire system, respectively.

• 한국지리정보학회지
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• 제20권2호
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• pp.75-88
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• 2017

본 연구에서는 대구시를 사례로 도시내에서의 공간지형적 특성에 따른 국지적 바람유동성을 분석하였다. 분석은 3단계로 이루어졌는데, 1단계에서는 지역풍향(종관풍)과 국지적 바람유동간의 기상학적 관계를 비교하였다. 2단계에서는 도심지역과 교외지역으로 구분하여 국지적 바람유동의 변화를 비교 분석하였다. 3단계에서는 KLAM_21을 활용하여 국지적 바람유동과 도시공간전체의 바람길 형성 및 유동과의 공간적 관계에 대하여 비교 검증하였다. 연구결과를 요약하면 다음과 같다. 첫째, 지역의 대표풍향(종관풍)과 국지적 바람유동 사이에는 기상학적으로 상관성이 낮았다. 둘째, 도심지역 5개와 교외지역 2개 측정지점에서의 국지적 바람유동에 대한 관측결과에서는 지점별로 다양한 풍향을 나타내었다. 이는 측정지점 인근에서의 공간지형적 특성이 국지적 바람유동에 영향을 미치고 있음을 보여주고 있다. 셋째, KLAM_21을 활용하여 분석한 결과를 AWS 측정자료와 비교 검증한 결과 수치모델링분석의 신뢰도를 확인할 수 있었다. 본 연구를 통해 검증한 도시의 국지적 바람유동은 도시열섬현상의 개선을 위한 공간적 기능과 역할을 할 수 있는 요소가 될것으로 판단된다. 즉, 도시계획 수립시 공간지형적 특성에 따른 국지적 바람유동을 체계적으로 파악하고 이를 도시열섬발생지역과 공간적으로 연계될 수 있는 계획적 기법을 적용한다면 도시열섬 현상을 효과적이며 지속적으로 개선할 수 있을 것으로 기대된다.

• 한국농림기상학회지
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• 제21권4호
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• pp.277-285
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• 2019

아고산 지역에서 지형은 바람과 일사, 토양수분함량 등에 영향을 주며 식물의 생장과 발달에 중요한 영향을 미친다. 아고산 지역에서 바람막이 지형이 가문비나무의 수관 생장에 미치는 영향을 알아보기 위해 서식지를 사면과 미지형에 따라 구분하고, 수고와 수관생장을 조사하였다. 아고산 지역의 가문비 나무는 서식지 내 바람의 영향과 미지형에 따라 수고 생장과 수관 생장이 다르게 나타났다. 바람맞이 사면에서 수고 생장과 수관생장률이 낮았고, 바람맞이 사면의 홀로 돋아져 바람과 같은 외부 환경에 노출된 미지형에서 자라는 나무는 바람의지 사면의 주변식생과 함께 자라는 나무보다 수관 생장이 절반 수준으로 낮았다. 바람의 영향이 강한 곳에서는 바람이 불어오는 방향으로 수관 생장이 억제되어 수관이 깃발형으로 발달하였다. 바람맞이 사면에서도 바람에 노출된 미지형 1 유형은 바람막이 역할을 하는 지피물이 존재하는 미지형 3 유형에 비해 수관의 기형이 심하였다. 본 연구는 바람이 심한 아고산 지역의 지형과 생장의 관계를 분석하여 가문비나무의 분포와 생장에서 바람막이 지형의 역할이 중요함을 보여주었다. 아고산 서식지 관리와 복원을 위해서 바람의 영향을 고려한 사면과 지형별 분포에 대한 분석이 필요하다.

• Smart Structures and Systems
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• 제17권3호
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• pp.471-489
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• 2016

Modal identification based on ambient vibration data has attracted extensive attention in the past few decades. Since the excitation for ambient vibration tests is mainly from the environmental effects such as wind and traffic loading and no artificial excitation is applied, the signal to noise (s/n) ratio of the data acquired plays an important role in mode identifiability. Under ambient vibration conditions, certain modes may not be identifiable due to a low s/n ratio. This paper presents a study on the mode identifiability of an instrumented cable-stayed bridge with the use of acceleration response data measured by a long-term structural health monitoring system. A recently developed fast Bayesian FFT method is utilized to perform output-only modal identification. In addition to identifying the most probable values (MPVs) of modal parameters, the associated posterior uncertainties can be obtained by this method. Likewise, the power spectral density of modal force can be identified, and thus it is possible to obtain the modal s/n ratio. This provides an efficient way to investigate the mode identifiability. Three groups of data are utilized in this study: the first one is 10 data sets including six collected under normal wind conditions and four collected during typhoons; the second one is three data sets with wind speeds of about 7.5 m/s; and the third one is some blind data. The first two groups of data are used to perform ambient modal identification and help to estimate a critical value of the s/n ratio above which the deficient mode is identifiable, while the third group of data is used to perform verification. A couple of fundamental modes are identified, including the ones in the vertical and transverse directions respectively and coupled in both directions. The uncertainty and s/n ratio of the deficient mode are investigated and discussed. A critical value of the modal s/n ratio is suggested to evaluate the mode identifiability of the deficient mode. The work presented in this paper could provide a base for the vibration-based condition assessment in future.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1281-1289
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• 2011

본 논문에서는 소형풍력발전시스템 블레이드 제작에 사용되는 복합재료의 피로수명 데이터에 대한 통계적 해석을 위하여 다양한 확률분포 모델의 적합성에 대한 연구를 수행하였다. 이를 위하여 삼축 유리섬유강화 복합재료를 대상으로 0$^{\circ}C$, 45$^{\circ}C$ 및 90$^{\circ}C$ 의 하중방향에 대한 인장시험을 실시하였다. 또한 상기의 하중방향에 대하여 4 수준의 피로응력준에서의 피로시험을 수행하였다. 이를 통하여 획득한 피로수명 데이터를 대상으로 1) 전체 적합성, 2) 끝단 적합성 및 3) 피로물리 일치성의 기준을 이용하여 2 모수 Weibull, 3 모수 Weibull, 정규 및 대수정규분포의 적합성을 평가하였다. 또한 피로수명의 분산에 대한 하중방향 및 피로응력의 영향 역시 검토하였다.

• 한국대기환경학회지
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• 제12권4호
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• pp.441-448
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• 1996

The cyclone/annular denuder system/filter pack sampling system (ADS) was used to collect the acidic air pollutants in Chongju city. The data set was collected on nine different days with 24 hour sampling period from July 27 through August 27, 1995. The chemical species measured were $HNO_3, HNO_2, SO_2 and NH_3$ in the gas phase, and $PM_{2.5}(d_P<2.5 \mum), SO_4^{2-}, NO_3^- and NH_4^+$ in the particulate phase. Mean concentrations measured from this study were: $0.90 \mug/m^3 for HNO_3, 1.27 \mug/m^3 for HNO_2, 10.9 \mug/m^3 for SO_2, 4.82 \mug/m^3 for NH_3, 27.5 \mug/m^3 for PM_{2.5}, 5.24 \mug/m^3 for SO_4^{2-}, 1.22 \mug/m^3 for NO_3^-, and 1.64 \mug/m^3 for NH_4^+$. The fine particle $(PM_{2.5})$ mass measured for the ADS samples was slightly higher than the fine particle mass measured for the corresponding dichotomous sampler. For the wind coming from Chongju industrial complex the concentrations of acidic air pollutants measured were higher when compared with other directions. Specially, $SO_2 and PM_{2.5}$ concentrations for the wind coming from Chongju industrial complex were 3.6 and about 2 times, respectively, higher than those of other wind directions. High correlations were observed between $PM_{2.5} and fine particle's ion components $(r=0.82 with SO_4^{2-}, r=0.76 with NO_3^- and r=0.89 with NH_4^+). NH_4^+ and SO_4^{2-}$ was also highly correlated (r=0.97).

• Wind and Structures
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• 제30권3호
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• pp.219-229
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• 2020

Net pressures on roofs and walls of buildings are dependent on the internal and external pressure fluctuations. The variation of internal and external pressures are influenced by the size and location of the openings. The correlation of external and internal pressure influences the net pressures acting on cladding on different parts of the roof and walls. The peak internal and peak external pressures do not occur simultaneously, therefore, a reduction can be applied to the peak internal and external pressures to obtain a peak net pressure for cladding design. A 1:200 scale wind tunnel model study was conducted to determine the correlations of external and internal pressures and effective reduction to net pressures (i.e., net pressure factors, F_C) for roof and wall cladding. The results show that external and internal pressures on the windward roof and wall edges are well correlated. The largest ${\mathcal{C}}_{{\check{p},net}$, highest correlation coefficient and the highest F_C are obtained for different wind directions within 90° ≤ θ ≤ 135°, where the large openings are on the windward wall. The study also gives net pressure factors F_C for areas on the roof and wall cladding for nominally sealed buildings and the buildings with a large windward wall opening. These factors indicate that a 5% to 10% reduction to the action combination factor, K_C specified in AS/NZS 1170.2(2011) is possible for some critical design scenarios.

• Wind and Structures
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• 제19권2호
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• pp.113-144
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• 2014

Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the corrected quasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.