• Wind and Structures
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• 제19권6호
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• pp.585-601
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• 2014

The effect of multiple roughness changes close to a building site was examined through three dimensional computational fluid dynamics (CFD) simulations conducted in a virtual boundary layer wind tunnel (V-BLWT). The results obtained were compared with existing wind speed models, namely ESDU-82026 and Wang and Stathopoulos (WS) model. The latter was verified by wind tunnel tests of sixty nine cases of multiple roughness patches, and also with a simplified 2D numerical model. This work extends that numerical study to three dimensions and also models roughness elements explicitly. The current numerical study shows better agreement with the WS model, that has shown better agreements with BLWT tests, than the ESDU model. This is in contrast to previous results of Wang and Stathopoulos, who concluded that CFD shows better agreement with the ESDU model. Many cases were simulated in a V-BLWT that has same dimensions as BLWT used in the original experiment and also in a reduced symmetrical version (S-BLWT) that takes advantage of regular arrangement of roughness blocks. The S-BLWT gives results almost identical to V-BLWT simulations, while achieving significant reduction on computational time and resources.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.779-782
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• 2002

We examine the problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick, open-cell foam with fabric covering and a viscoelastic painted plate of 1mm thick over an acoustic board of 4m thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber ($k_{ch}$) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

• Wind and Structures
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• 제13권5호
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• pp.413-431
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• 2010

The focus of this article is on the assessment of vertical wind vector components and their aerodynamic impact on lattice framework, specifically two distinct sections of a guyed transmission tower. Thunderstorm winds, notably very localized events such as convective downdrafts (including downbursts) and tornadoes, result in a different load on a tower's structural system in terms of magnitude and spatial distribution when compared to horizontal synoptic winds. Findings of previous model-scale experiments are outlined and their results considered for the development of a testing rig that allows for rotation about multiple body axes through a series of wind tunnel tests. Experimental results for the wind loads on two unique experimental models are presented and the difference in behaviour discussed. For a model cross arm with a solidity ratio of approximately 30%, the drag load was increased by 14% when at a pitch angle of $20^{\circ}$. Although the effects of rotation about the vertical body axis, or the traditional 'angle of attack', are recognized by design codes as being significant, provisions for vertical winds are absent from each set of wind loading specifications examined. The inclusion of a factor to relate winds with a vertical component to the horizontal speed is evaluated as a vertical wind factor applicable to load calculations. Member complexity and asymmetric geometry often complicate the use of lattice wind loading provisions, which is a challenge that extends to future studies and codification. Nevertheless, the present work is intended to establish a basis for such studies.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2005년도 추계학술대회 논문집
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• pp.229-234
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• 2005

본 연구는 75m/s의 풍하중이 컨테이너 크레인에 작용할 때, 풍하중이 50ton급 컨테이너 크레인의 안정성에 미치는 영향을 풍동실험을 통하여 분석하여 컨테이너 크레인의 내풍설계 시 필요한 자료를 제공하기 위해 수행되었다. 풍동실험에 적용된 데이터 수집조건은 상사법칙에 준하여 설정되었으며, 컨테이너 크레인 모형, 풍속 및 시간의 축척률은 각각 1/200, 1/13.3 및 1/15로 하였다. 그리고 실험은 $11.25m^2$의 측정부 단면을 갖는 개방형 대기경계층풍동을 사용하여 수행하였다. 풍향에 따른 컨테이너 크레인의 풍력계수 및 전도모멘트계수가 조사되었으며, 풍하중에 의해 각 지지점에서 발생되는 전도력이 분석되었다.

• Wind and Structures
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• 제4권4호
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• pp.279-298
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• 2001

The greatest suction on the cladding of flat roof low-rise buildings is known to occur beneath the conical vortices that form along the roof edges for cornering winds. In a companion paper, a model of the vortex flow mechanism has been developed which can be used to connect the surface pressure beneath the vortex to adjacent flow conditions. The flow model is experimentally validated in this paper using simultaneous velocity and surface pressure measurement on a 1 : 50 model of the Texas Tech University experimental building in a wind tunnel simulated atmospheric boundary layer. Flow visualization gives further insight into the nature of peak suction events. The flow model is shown to account for the increase in suction towards the roof corner as well as the presence of the highest suction at wind angles of $60^{\circ}$. It includes a parameter describing vortex suction strength, which is shown to be related to the nature of the reattachment, and also suggests how different components of upstream turbulence could influence the surface pressure.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.247-252
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• 2001

The flow around free end of a finite circular cylinder(FC) embedded in an atmospheric boundary layer has been investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with varying aspect ratio of the finite cylinder mounted vertically on a flat plate. The wake structures behind a 2-D cylinder and a finite cylinder located in a uniform flow were also measured for comparison. Reynolds number based on the cylinder diameter was about Re=20,000. A hot-wire anemometer was employed to measure the wake velocity and the mean pressure distributions on the cylinder surface were also measured. The flow past the FC free end shows a complicated three-dimensional wake structure and flow phenomenon is quite different from that of 2-D cylinder. The three-dimensional flow structure was attributed to the downwashing counter rotating vortices separated from the FC free end. As the FC aspect ratio decreases, the vortex shedding frequency is decreased and the vortex formation length is increased compared to that of 2-D cylinder. Due to the descending counter-rotating twin-vortex, in the region near the FC free end, regular vortex shedding from the cylinder is suppressed and the vortex formation region is hardly established. In the wake center region, the mean velocity for the FC located in atmospheric boundary layer has large velocity deficit, compared to that of uniform flow.

• 한국추진공학회지
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• 제5권3호
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• pp.25-32
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• 2001

본 연구에서는 2차원 압축성 Navier-Stokes 방정식을 이용하여, 약한 수직충격파와 난류 경계층의 간섭현상에 대한 피동제어 유동장을 수치계산법으로 조사하였다. 벽 내부에 공동을 가지는 다공벽을 사용하여 충격파와 난류경계층간 상호간섭을 제어하였다. 본 연구로부터 $\lambda$형 충격파의 하류쪽 가지를 중심으로 하여, 그 하류에서는 주유동이 공동내부로 또 그 상류에서는 공동내부로부터 주유동쪽으로 피이드백되는 유동을 관찰하였으며, 다공벽의 구멍을 통하는 유동은 초크하지 않는다는 것을 알았다.

• 대한토목학회논문집
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• 제40권1호
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• pp.105-110
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• 2020

태풍 등과 같은 강풍에 의한 비산물로부터 구조물과 인명의 피해를 최소화하기 위해서는 비산물의 비행 시작 풍속을 예측할 수 있어야 한다. 본 연구의 목적은 강풍 시 비산물의 비행시작 풍속을 예측하기 위한 방법과 예측에 필요한 데이터를 제공하는 것이다. 이를 위해 힘의 평형방정식으로부터 비산물의 비행 시작 풍속 예측식을 제시하였다. 또한 예측식에 필요한 공기력계수를 산출하기 위해 풍동실험을 수행하여 비산물의 길이와 높이의 비에 따른 공기력계수를 측정하고, 아울러 비율에 따른 공기력계수를 계산할 수 있는 경험식을 제시하였다. 예측 비행 시작 풍속을 검증하기 위해 풍동에서 자유비산 실험을 수행하여 비산물의 비행 시작 풍속을 측정하였다. 비산물의 길이와 두께의 비가 10 미만인 경우에는 주로 미끄러짐에 의해 비행이 시작되었고, 10 이상인 경우에는 주로 전도에 의해 비행이 시작되는 것으로 나타났다. 실제 비행 시작 풍속은 예측 풍속과 전반적으로 일치하나 약 20~30 % 낮았다. 이는 도류판 표면의 경계층 흐름 및 시험체의 변형 등이 원인으로 추정되며, 향후 예측 정확도를 높이기 위한 추가 연구가 필요하다.

• Wind and Structures
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• 제23권5호
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• pp.465-483
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• 2016

This study aims to enhance the understanding of the surface pressure distribution around rectangular bodies, by considering aspects such as the suction pressure at the leading edge on the top and side faces when the body aspect ratio and wind direction are changed. We carried out wind tunnel measurements and numerical simulations of flow around a series of rectangular bodies (a cube and two rectangular bodies) that were placed in a deep turbulent boundary layer. Based on a modern numerical platform, the Navier-Stokes equations with the typical two-equation model (i.e., the standard $k-{\varepsilon}$ model) were solved, and the results were compared with the wind tunnel measurement data. Regarding the turbulence model, the results of the $k-{\varepsilon}$ model are in overall agreement with the experimental results, including the existing data. However, because of the blockage effects in the computational domain, the pressure recovery region is underpredicted compared to the experimental data. In addition, the $k-{\varepsilon}$ model sometimes will fail to capture the exact flow features. The primary emphasis in this study is on the flow characteristics around rectangular bodies with various aspect ratios and approaching wind directions. The aspect ratio and wind direction influence the type of wake that is generated and ultimately the structural loading and pressure, and in particular, the structural excitation. The results show that the surface pressure variation is highly dependent upon the approaching wind direction, especially on the top and side faces of the cube. In addition, the transverse width has a substantial effect on the variations in surface pressure around the bodies, while the longitudinal length has less influence compared to the transverse width.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.811-816
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• 2000

It has been long suspected that the transition region may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. Experimental investigation described in this paper concerns the characteristics of pressure fluctuations at the transition. Flush-mounted microphones and hot wires are used to measure the pressure fluctuations and local flow velocities within the boudary layer in the low noise wind tunnel. From this experimental we could observe the spatial and temporal development process of T-S wave using Wigner-Ville method and found the possibility of relation between the characteristic frequency of T-S wave and free stream velocity and the boundary layer thickness based on nondimensional pressure spectra scaled on outer variables.