• Wind and Structures
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• 제2권2호
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• pp.119-125
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• 1999

The ZG Bridge(preliminary design), with unfavorable aerodynamic stability characteristics, is a truss-stiffened suspension bridge, its critical wind speed of flutter instability is much lower than that of code requirement, In the present paper, based on both aerostatic and aeroelastic section model wind tunnel test, not only effects of some aerodynamic means on aerodynamic stability of its main girder are investigated, but also such effective aerodynamic means of it as flap and plate-like center stabilizer are concluded.

• Wind and Structures
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• 제13권3호
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• pp.293-307
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• 2010

This paper describes a new method for the estimation of six complex aerodynamic admittance functions. The aerodynamic admittance functions relate buffeting forces to the incoming wind turbulent components, of which the estimation accuracy affects the prediction accuracy of the buffeting response of long-span bridges. There should be two aerodynamic admittance functions corresponding to the longitudinal and vertical turbulent components, respectively, for each gust buffeting force. Therefore, there are six aerodynamic admittance functions in all for the three buffeting forces. Sears function is a complex theoretical expression for the aerodynamic admittance function for a thin airfoil. Similarly, the aerodynamic admittance functions for a bridge deck should also be complex functions. This paper presents a separated frequency-by-frequency method for estimating the six complex aerodynamic admittance functions. A new experimental methodology using an active turbulence generator is developed to measure simultaneously all the six complex aerodynamic admittance functions. Wind tunnel tests of a thin plate model and a streamlined bridge section model are conducted in turbulent flow. The six complex aerodynamic admittance functions, determined by the developed methodology are compared with the Sears functions and Davenport's formula.

• 한국철도학회논문집
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• 제19권6호
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• pp.709-716
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• 2016

고속열차의 공기저항 저감을 위해 KTX-산천의 구성요소별 공기저항을 상세하게 분석하였다. 전체 공기저항의 약 42.9%는 동력차(선두차, 후미차)에서 그리고 약 10.1%는 대차에서 유발되는 것으로 나타났다. 전두부의 공기저항 저감을 위해 Broyden-Fletcher-Goldfarb-Shanno 기법을 이용한 전두부 최적설계를 수행하였다. 그리고 차체 공기저항 저감을 위해 동력차 형상 변화 및 대차커버를 적용하였다. 공기저항 저감을 위해 최적설계된 편성열차의 공기저항은 KTX-산천 대비 약 15.0% 저감되었으며, 주행저항은 속도 350km/h에서 약 12% 감소될 것으로 예상된다.

• 한국전산유체공학회지
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• 제19권1호
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• pp.41-46
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• 2014

The aerodynamic drag of high-speed train has been calculated and the effect of bogie side fairing on the aerodynamic drag has been investigated. Computational Fluid Dynamics (CFD) simulation based on steady-state 3 dimensional Navier-Stokes equation has been conducted employing FLUENT 12 and the aerodynamic model of HEMU-430x, the Korean next generation high-speed train under development has been built using GAMBIT 2.4.6. Three types of bogie side fairing configuration, the proto-type without fairing, half-covered fairing to avoid the interference with the bogie frame and full-covered fairing have been adopted to the train model to compare the drag reduction effects of the bogie side fairing configurations and the numerical results yields that the bogie side fairing can reduce the aerodynamic drag of the 6-car trainset up to 7.8%. The aerodynamic drag coefficient of each vehicle as well as the flow structures around the bogie system have also been examined to analyze the reason and mechanism of the drag reduction by bogie side fairing.

• Wind and Structures
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• 제13권5호
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• pp.471-485
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• 2010

In comparison with the common two-tower suspension bridge, due to the lack of effective longitudinal restraint of the center tower, the three-tower suspension bridge becomes a structural system with greater flexibility, and more susceptible to the wind action. By taking a three-tower suspension bridge-the Taizhou Bridge over the Yangtze River with two main spans of 1080 m as example, effects of structural parameters including the cable sag to span ratio, the side to main span ratio, the deck's dead load, the deck's bearing system, longitudinal structural form of the center tower and the cable system on the aerodynamic stability of the bridge are investigated numerically by 3D nonlinear aerodynamic stability analysis, the favorable structural system of three-tower suspension bridge with good wind stability is discussed. The results show that good aerodynamic stability can be obtained for three-tower suspension bridge as the cable sag to span ratio is assumed ranging from 1/10 to 1/11, the central buckle are provided between main cables and the deck at midpoint of main spans, the longitudinal bending stiffness of the center tower is strengthened, and the spatial cable system or double cable system is employed.

• Wind and Structures
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• 제36권6호
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• pp.423-434
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• 2023

Aerodynamic force coefficients are generally obtained from traditional wind tunnel tests or computational fluid dynamics (CFD). Unfortunately, the techniques mentioned above can sometimes be cumbersome because of the cost involved, such as the computational cost and the use of heavy equipment, to name only two examples. This study proposed to build a deep neural network model to predict the aerodynamic force coefficients based on data collected from CFD simulations to overcome these drawbacks. Therefore, a series of CFD simulations were conducted using different geometric parameters to obtain the aerodynamic force coefficients, validated with wind tunnel tests. The results obtained from CFD simulations were used to create a dataset to train a multilayer perceptron artificial neural network (ANN) model. The models were obtained using three optimization algorithms: scaled conjugate gradient (SCG), Bayesian regularization (BR), and Levenberg-Marquardt algorithms (LM). Furthermore, the performance of each neural network was verified using two performance metrics, including the mean square error and the R-squared coefficient of determination. Finally, the ANN model proved to be highly accurate in predicting the force coefficients of similar bridge sections, thus circumventing the computational burden associated with CFD simulation and the cost of traditional wind tunnel tests.

• International Journal of Aeronautical and Space Sciences
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• 제17권1호
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• pp.132-138
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• 2016

Korea Aerospace Research Institute (KARI) is developing an electric-driven HALE UAV in order to secure system and operational technologies since 2010. Based on the flight tests and design experiences of the previously developed electric-driven UAVs, KARI has designed EAV-3, a solar-powered HALE UAV. EAV-3 weighs 53kg, the structure weight is 22kg, and features a flexible wing of 19.5m in span with the aspect ratio of 17.4. Designing the main wing and empennage of the EAV-3 the amount of the bending due to the flexible wing, 404mm at 1-G flight condition based on T-800 composite material, and side wind effects due to low cruise speed, $V_{cr}=6m/sec$, are carefully considered. Also, unlike the general aircraft there is no center of gravity shift during the flight because of the EAV-3 is the solar-electric driven UAV. Thus, static margin cuts down to 28.4% and center of gravity moves back to 31% of the Mean Aerodynamic Chord (MAC) comparing with the previously designed the EAV-2 and EAV-2H/2H+ to upgrade the flight performance of the EAV-3.

• 항공우주기술
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• 제12권1호
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• pp.73-80
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• 2013

한국형발사체 시스템설계 형상에 대해 전산유동해석(CFD) 기법을 이용하여 공력 특성 및 하중을 예측하였다. 이전 형상에 비하여 엔진 카울이 없어짐에 따라 축력과 수직력이 감소하였으며, 압력 중심이 전방으로 크게 이동하였다. 그리고 하중 해석을 위해 비행 중 및 발사대 대기 중의 공력 하중을 산출하였다. 공력 계수 및 공력 하중 해석 결과는 다음 설계 단계의 임무 설계 및 구조 해석 분야에 활용된다.

• 국제초고층학회논문집
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• 제8권4호
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• pp.303-311
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• 2019

The effectiveness of aerodynamic modification to reduce wind loadings has been widely reported. However, most of previous studies have been investigated dynamic forces and pressure distributions on tall buildings with various unconventional configurations. This study was investigated dynamic characteristics and aerodynamic instability of super-tall buildings with unconventional configurations through extensive aeroelastic model experiments. Seventeen types of supertall building models were considered such as basic and corner modification with corner cut, chamfered, oblique opening, tapered, inversely tapered, bulged, helical with twist angles of $90^{\circ}$, $180^{\circ}$, $270^{\circ}$, $360^{\circ}$ and composite with $360^{\circ}$ helical & corner cut, 4-tapered & $360^{\circ}$ helical & corner cut, setback & corner cut, setback & $45^{\circ}$ rotate. As a result, aerodynamic characteristics of helical models with single modification are superior to those of other models with single modification. However, effect of twist angle for helical model is negligible. Further, the 4-tapered & $360^{\circ}$helical & corner cut model is most effective in reducing the along- and across-wind fluctuating displacement responses in all of experimental models.

• Wind and Structures
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• 제37권1호
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• pp.57-78
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• 2023

In this study, a generalized three-degree-of-freedom (3-DoF) analytical model is formulated to predict linear aerodynamic instabilities of a prism under quasi-steady (QS) conditions. The prism is assumed to possess a generic cross-section exposed to turbulent wind flow. The 3-DoFs encompass two orthogonal horizontal directions and rotation about the prism body axis. Inertial coupling is considered to account for the non-coincidence of the mass center and the rotation center. The aerodynamic force coefficients-drag, lift, and moment-depend on the Reynolds number based on relative flow velocity, angle of attack, and the angle between the wind and the cable. Aerodynamic forces are linearized with respect to the static equilibrium configuration and mean wind velocity. Routh-Hurwitz and Liénard and Chipart criteria are used in the eigenvalue problem, yielding an analytical solution for instabilities in galloping and static divergence types. Additionally, the minimum structural damping and stiffness required to prevent these instabilities are numerically determined. The proposed 3-DoF instability model is subsequently applied to a conductor with ice accretion and a full-scale dry inclined cable. In comparison to existing models, the developed model demonstrates superior prediction accuracy for unstable regions compared with results in wind tunnel tests.