• Wind and Structures
• /
• 제10권2호
• /
• pp.99-119
• /
• 2007

Estimations of wind flow over terrain are often needed for applications such as pollutant dispersion, transport safety or wind farm location. Whilst field studies offer very detailed information regarding the wind potential over a small region, the cost of instrumenting a natural fetch alone is prohibitive. Wind tunnels offer one alternative although wind tunnel simulations can suffer from scale effects and high costs as well. Computational Fluid Dynamics (CFD) offers a second alternative which is increasingly seen as a viable one by wind engineers. There are two issues associated with CFD however, that of accuracy of the predictions and set-up and simulation times. This paper aims to address the two issues by demonstrating, by way of an investigation of wind potential for the Askervein Hill, that a good level of accuracy can be obtained with CFD (10% for the speed up ratio) and that it is possible to automate the simulations in order to compute a full wind rose efficiently. The paper shows how a combination of script and session files can be written to drive and automate CFD simulations based on commercial software. It proposes a general methodology for the automation of CFD applied to the computation of wind flow over a region of interest.

• 신재생에너지
• /
• 제18권3호
• /
• pp.60-71
• /
• 2022

A wind tunnel provides artificial airflow around a model throughout the test section for investigating aerodynamic loads. It has various applications, which include demonstration of aerodynamic loads in the building, automobile, wind energy, and aircraft industries. However, owing to the high equipment costs and space-requirements of wind tunnels, it is challenging for numerous studies to utilize a wind tunnel. Therefore, a digital wind tunnel can be utilized as an alternative for experimental research because it occupies a significantly smaller space and is easily operable. In this study, we performed airfoil testing based on velocity field measurements utilizing a digital wind tunnel. This wind tunnel can potentially be utilized to test the full-range aerodynamic characteristics of airfoils.

• 한국태양에너지학회 논문집
• /
• 제34권3호
• /
• pp.98-106
• /
• 2014

The effect of blockage ratio on wind tunnel testing of small vertical-axis wind turbine has been investigated in this study. Height and rotor diameter of the three blades Darrieus vertical axis wind turbine used in present test were 0.4m and 0.35m respectively. We measured the wind speeds and power coefficient at three different wind tunnels where blockage ratio were 3.5%, 13.4% and 24.7% respectively. The test results show that the measured powers have been strongly influenced by blockage ratio, generally increased as the blockage ratio increases. The maximum power at higher blockage ratio has been obtained at relatively high tip speed ratio compared with that at low blockage ratio. The measured power coefficients under high blockage ratio can be improved from proper correction using the simple correction equation based on blockage factor. In present study, the correction error for power coefficient can be less than 5%, however correction effectiveness reveals relatively poor at high blockage ratio and low wind speed.

• Wind and Structures
• /
• 제7권2호
• /
• pp.131-144
• /
• 2004

A technique for the simulation of atmospheric boundary layers in wind tunnels is developed and tested experimentally. The device consists of a grid made of seven horizontal and vertical evenly distributed bars in which air injection holes are drilled in order to influence the flow in the wind tunnel. The air flow in each bar can be controlled independently. Firstly, the device is used together with a rough carpet, which covers the test section floor, in order to simulate the boundary-layer characteristics over an open rural area. Hot-wire measurements, performed at different positions in the test-section, show the capability of the grid in generating the required boundary layer. An acceptable agreement with statistical values of mean velocity and turbulence profiles has been achieved, together with a good span-wise homogeneity. The results are also compared with those of a passive simulation technique based on the use of spires.

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

• 설비공학논문집
• /
• 제16권7호
• /
• pp.652-657
• /
• 2004

Development of underground space in urban area has a huge amount of potential to ease the limitations on the land use and the efficiency especially in urban area. Considering public transportation in urban area, subway system could be one of the most efficient and practical approaches. Subsequently this leads the public to have more chances to experience the indoor air quality (IAQ) in subway systems. In this study, it was aimed to produce useful data for the IAQ control in subway environments, Specifically the train-induced wind has been investigated by means of field survey and analysis. The recent updates including the quantified characteristics of train-induced wind are presented in this paper.

• 한국터널지하공간학회 논문집
• /
• 제20권2호
• /
• pp.405-421
• /
• 2018

현재 국내터널에 적용중인 벽면마찰계수는 단순히 외국의 연구결과를 인용하여 사용하고 있는 실정이다. 또한 기존 선행연구들에서는 속도감쇄법을 이용하여 벽면마찰계수를 추정하였으나, 터널 내 수렴풍속이 음수(-)이거나 자연풍의 변화가 있는 경우에는 벽면마찰계수에 대한 추정이 어려운 점이 있었다. 이에 따라 본 연구에서는 기존 속도감쇄법과 더불어 동적 시뮬레이션기법을 적용하여 벽면마찰계수를 추정하였다. 분석결과, 총 9개 터널(양방향 18개 튜브)에 대한 터널 내 마찰계수는 0.011~0.025 정도로 분석되었으며, 평균값은 0.020로 추정되었다. 또한, 본 연구를 통해 정량적으로 획득한 벽면마찰계수를 현재 적용중인 설계기준과 비교하였다.

• Journal of Mechanical Science and Technology
• /
• 제18권9호
• /
• pp.1614-1622
• /
• 2004

When a High Speed Train (HST) passes through a station with no stop, effects of wind pressure transients caused by this passing train have to be considered for the safety of passengers on the platform and for the possible structural safety problems as well. In Gwangmyeong and Daejeon stations of the Korean high speed railroad, tunnels inside stations for the passing train are proposed to reduce the noise and wind pressure transients to the passengers on the platform. In the present study, transient 3-D full Navier-Stokes solutions with moving mesh to implement train movement are obtained and compared with the results obtained by the towing tank experiment. Investigations on flow phenomena for various train speeds and design modifications are also performed.

• Journal of Mechanical Science and Technology
• /
• 제14권11호
• /
• pp.1267-1275
• /
• 2000

A series do wind tunnel tests were conducted for Korean high-speed train model with various shape components to assess the contributions to aerodynamic drag. In order to elucidate the ground effects, two different wind tunnels, one with a moving ground system and the other with a fixed ground, were used for the same model and the results of both were compared and analyzed in detail. The result show that a suitable ground simulation is necessary for the test of a train model with many cars and detailed underbody. But the relative difference of the drag coefficients for the modifications of shape components can be measured by a fixed ground test with high accuracy and low cost. The effects of the nose shape, the inter-cargap and the bogie-fairing on total drag were discussed and some ideas were prosed to decrease the aerodynamic resistance of high speed train.

• 대한관절경학회지
• /
• 제1권1호
• /
• pp.66-71
• /
• 1997

The all inside anterior cruciate ligament reconstruction technique places an anterior ligament substitutes within two bony sockets rather than hone tunnel. This approach is accomplished through arthroscopic three portal which avoids the surgical exposure and morbidity associated with creating traditional bone tunnel. This technique has several distinct advantages when compared with the traditional ACL reconstruction through the bone tunnels. It offers the surgeon a less morbid method for ACL reconstruction that positions an ACL substitute at the anatomic attachment sites of the original ACL with two bone sockets, obviating the need for traditional bone tunnels. Graft fixation at or near the anatomic attachment points of the original ACL minimizes creep with early range of motion and reduces the abrasive 'wind-shield wipe' motion of the graft which occur with bone plugs positioned inside bone tunnels. The sagittal posterior angle to the tibial socket increases fixation strength to pullout with anterior translation force for the tibia on the femur. This technique is not graft specific and can accomodate any graft in which graft length can be customized to the intraarticular native ACL length.