• 한국전산유체공학회지
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• 제14권3호
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• pp.9-15
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• 2009

Numerical investigation has been carried out for laminar flow past an inclined square cylinder in cross freestream. In particular, inclination of a square cylinder with respect to the main flow direction can cause sudden shift of the separation points to other edges, resulting in drastic change of flow-induced forces on the cylinder such as Strouhal number (St) of vortex shedding, drag and lift forces on the cylinder, depending upon the inclination angle. Collecting all the numerical results obtained, we propose contour diagrams of drag/lift coefficients and Strouhal number on an Re-Angle plane. This study would be the first step towards understanding flow-induced forces on cylindrical structures under a strong gust of wind from the viewpoint of wind hazards.

• 한국응용과학기술학회지
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• 제27권4호
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• pp.470-474
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• 2010

Various anti-scattering agents for suppression of dust scattering at waste depository were compared in this study. Based on the price, easy of usage, and no toxicity, 1% of $Al_2(SO_4)_3$ was selected as surface hardening agents. Only lower than 2% of total weight were flied when wind speed was monthly maximum velocity during 1 hr. These results were quite good with comparison of S anti-scattering agents which was made by C company in Korea. When $Al_2(SO_4)_3$ was spread, the surface waste became hard therefore the effect of suppression of scattering dust was long lasting. It was recommend that 2% of $Al_2(SO_4)_3$ was spread to keep suppression of scattering dust when sudden gust of wind such as natural disaster was occurred.

• 한국전산유체공학회지
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• 제14권2호
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• pp.19-24
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• 2009

A parametric study has been carried out to elucidate the characteristics of flow past a square cylinder inclined with respect to the main flow for Re$\leq$150. Reynolds number and angle of incidence are the key parameters which determine the flow characteristics. This study would be the first step towards understanding flow pattern past a cylindrical structure under a strong gust of wind from the viewpoint of wind hazards. A complete classification of flow pattern has been obtained in the laminar region.

• Wind and Structures
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• 제25권3호
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• pp.283-299
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• 2017

Two types of aerodynamic admittance function (AAF) that have been adopted in bridge aerodynamics are addressed. The first type is based on a group of supposed relations between flutter derivatives and AAFs. In so doing, the aero-elastic properties of a section could be used to determine AAFs. It is found that the supposed relations hold only for cases when the gust frequencies are within a very low range. Predominant frequencies of long-span bridges are, however, far away from this range. In this sense, the AAFs determined this way are of little practical significance. Another type of AAFs is based on the relation between the Theodorsen circulation function and the Sears function, which holds for thin airfoil theories. It is found, however, that an obvious illogicality exists in this methodology either. In this article, a viewpoint is put forward that AAFs of bluff bridge deck sections are inherently dependent on oncoming turbulent properties. This kind of dependence is investigated with a thin plate and a double-girder bluff section via computational fluid dynamics method. Two types of wind fluctuations are used for identification of AAFs. One is turbulent wind flow while the other is harmonic. The numerical results indicate that AAFs of the thin plate agree well with the Sears AAF, and show no obvious dependence on the oncoming wind fields. In contrast, for the case of bluff double-girder section, AAFs identified from the turbulent and harmonic flows of different amplitudes differ among each other, exhibiting obvious dependence on the oncoming wind field properties.

• 한국철도학회논문집
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• 제15권6호
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• pp.537-542
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• 2012

철도차량은 자연 강풍 뿐만 아니라 두 열차의 교행으로 인한 교행 풍압도 동시에 받는 경우가 종종 발생하며, 이러한 풍압에 의하여 철도차량의 주행 안정성이 저해될 뿐만아니라 전복의 원인이 되기도 한다. 또한, 해외에서는 강력한 돌풍에 의하여 철도차량이 전복되는 실제 사고 사례가 종종 보고되기도 한다. 따라서, 대부분의 국가에서는 풍속에 대한 차량 운전 규제를 통하여 안전성을 확보하고 있다. 본 연구에서는 다물체 모델에 기초한 철도차량의 전복안전성 이론식을 개발하였으며, 이를 강체모델의 결과와 비교하였다. 후자에서는 대차 및 차체를 별도의 자유도를 가진 것으로 간주하였다. 다물체 모델은 윤중 감소율을 평가하는데 사용 되어온 상용 프로그램을 이용한 기존의 방법을 대체하여 해석할 수 있음을 알 수 있다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.812-817
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• 2011

철도 차량은 자연 횡풍 뿐만 아니라 두 열차의 교행으로 인한 교행 풍압도 동시에 받는 경우가 종종 발생하며, 이러한 풍압에 의하여 철도 차량의 주행 안전성이 저해될 뿐만아니라 전복의 원인이 되기도 한다. 또한, 해외에서는 순간적인 돌풍에 의하여 철도 차량이 전복되는 사고 사례가 보고되기도 하여 이를 뒷받침하고 있다. 따라서, 대부분의 국가에서는 풍속에 대한 차량 운전 규제를 통하여 안전성을 확보하고 있다. 본 연구에서는 우리나라 국토해양부의 철도 차량 안전 기준에 관한 규정에서 정한 차량 전복 안전 기준에서의 전복 한계 기준과 차체-대차 다물체 모델로 가정하여 전복 한계에 대한 식을 유도하였으며, 두 해석 기준을 비교하였다. 후자에서는 대차 및 차체를 별도의 자유도를 가진 것으로 간주하여 각각의 중심, 중량 및 횡가속도를 변수로 추가 고려하였다. 향후에는 시험값과의 비교를 통하여 두 해석법간의 차이를 분석 검토할 필요가 있다. 다물체 해석법은 선로 중심 간격 설정시, 차량 중행 안전성 검토에 사용되어 온 전산 해석의 해석 기준인 탈선 계수, 횡압 및 윤중 감소율을 전복 안전율로 대체 평가할 수 있음을 보여준다.

• 한국환경과학회지
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• 제27권3호
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• pp.203-217
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• 2018

For this study, WRF numerical modeling was performed, using RDAPS information for input data on typhoons affecting the Korean peninsula to produce wind data of 700hPa. RAM numerical modeling was also used to calculate 3-second gusts as the extreme wind speed. After comparing wind speeds at an altitude of 10 m to evaluate the feasibility of WRF numerical modeling, modeled values were found to be similar with measured ones, reflecting change tendencies well. Therefore, the WRF numerical modeling results were verified. As a result of comparing and analyzing these wind speeds, as calculated through RAM numerical modeling, to evaluate applicability for disaster preparedness, change tendencies were observed to be similar between modeled and measured values. In particular, modeled values were slightly higher than measured ones, indicating applicability for the prevention of possible damage due to gales. Our analysis of 3-second gusts during the study period showed a high distribution of 3-second gusts in the southeast region of the Korean peninsula from 2002-2006. The frequency of 3-second gusts increased in the central north region of Korea as time progressed. Our analysis on the characteristics of 3-second gusts during years characterized by El $Ni{\tilde{n}}o$ or La Nina showed greater strength during hurricanes that affected the Korean peninsula in El $Ni{\tilde{n}}o$ years.

• 대한지리학회지
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• 제48권2호
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• pp.167-183
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• 2013

본 연구에서는 한국에 출현한 황사 발원지별로 기상 특성을 파악하였다. 이를 위하여 한국의 일별 황사자료와 발원지의 일별 기상자료를 이용하여 한국에 황사 출현 시의 발원지 기상상태를 분석하였다. 한국에 출현한 황사 중 네이멍구에서 발원한 황사의 빈도가 가장 높다. 황토고원을 제외한 발원지에서 출현한 황사 일수가 최근 증가하고 있으며, 한국의 전국에 영향을 미친 빈도가 높았다. 황토고원의 경우 1960년대의 출현빈도가 가장 높았으며, 한국의 남부지방에 영향을 미친 빈도가 높았다. 한국의 황사 발생일수와 발원지의 봄철 및 4월 기상요소와 유의한 관계가 있다. 네이멍구에서 발원한 황사 발생일과 4월 해면기압, 봄철 상대습도와 음의 관계가 있다. 고비에서 발원한 황사 발생일과 4월 돌풍일수와 양의 관계이며, 4월 해면기압과 음의 관계이다. 만주에서 발원한 황사 발생일과 4월 강수량, 해면기압과는 음의 관계이다. 황토고원에서 발원한 황사 발생일과 4월 최대풍속과는 양의 관계이며, 해면기압과는 음의 관계이다.

• Structural Engineering and Mechanics
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• 제49권5호
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• pp.619-629
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• 2014

As hyperboloidal cooling towers (HCTs) growing larger and slender, they become more sensitive to gust wind. To improve the dynamic properties of HCTs and to improve the wind resistance capability, stiffening rings have been studied and applied. Although there have been some findings, the influence mechanism of stiffening rings on the dynamic properties is still not fully understood. Based on some fundamental perceptions on the dynamic properties of HCTs and free ring structures, a concept named "participation degree" of stiffening rings was proposed and the influence mechanism on the dynamic properties was illustrated. The "participation degree" is determined by the modal deform amplitude and latitude wave number of stiffening rings. Larger modal deform amplitude and more latitude waves can both result in higher participation degree and more improvement to eigenfrequencies. Also, this concept can explain and associate the pre-existing independent findings.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.19-19
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• 2009

Dynamic Stall is a flow phenomenon which occurs on the retreating side of helicopter rotor blades during forward flight. It also occurs on blades of stall regulated wind turbines under yawing conditions as well as during gust loads. Time scales occurring during this process are comparable on both helicopter and wind turbine blades. Dynamic Stall limits the speed of the helicopter and its manoeuvrability and limits the amount of power production of wind turbines. Extensive numerical as well as experimental investigations have been carried out recently to get detailed insight into the very complex flow structures of the Dynamic Stall process. Numerical codes have to be based on the full equations, i.e. the Navier-Stokes equations to cover the scope of the problems involved: Time dependent flow, unsteady flow separation, vortex development and shedding, compressibility effects, turbulence, transition and 3D-effects, etc. have to be taken into account. In addition to the numerical treatment of the Dynamic Stall problem suitable wind tunnel experiments are inevitable. Comparisons of experimental data with calculated results show us the state of the art and validity of the CFD-codes and the necessity to further improve calculation procedures. In the present paper the phenomenon of Dynamic Stall will be discussed first. This discussion is followed by comparisons of some recently obtained experimental and numerical results for an oscillating helicopter airfoil under Dynamic Stall conditions. From the knowledge base of the Dynamic Stall Problems, the next step can be envisaged: to control Dynamic Stall. The present discussion will address two different Dynamic Stall control methodologies: the Nose-Droop concept and the application of Leading Edge Vortex Generators (LEVoG's) as examples of active and passive control devices. It will be shown that experimental results are available but CFD-data are only of limited comparison. A lot of future work has to be done in CFD-code development to fill this gap. Here mainly 3D-effects as well as improvements of both turbulence and transition modelling are of major concern.