• Wind and Structures
• /
• 제14권2호
• /
• pp.133-151
• /
• 2011

For a detailed investigation of the dynamic behaviour of slender bridges under wind action especially the motion-induced fluid forces should be available not only for harmonic motions but also for more general ones. If linear transfer behaviour is assumed, the force-displacement relation for almost arbitrary motions can be handled in the frequency domain using aerodynamic transfer functions. In aerospace engineering as well as in bridge engineering, these functions are usually approximated by special kinds of complex-valued rational functions which depend on complex frequencies. The quality of this approximation is evaluated for several bridge cross sections in this article. It is shown that rational functions are for some sections scarcely suitable to realistically represent the transfer behaviour of motion-induced aerodynamic forces for arbitrarily complex frequencies.

• Wind and Structures
• /
• 제8권2호
• /
• pp.135-146
• /
• 2005

Divergent galloping-like motion of a dry inclined cable has been observed in a limited number of experimental studies, which, due to the uncertainties in its onset conditions, has induced serious concerns in the bridge stay cable design. A series of dynamic and static model wind tunnel tests have been carried out to confirm the existence of the phenomenon and clarify its excitation mechanism. The present paper focuses on exploring the spatial flow structure around an inclined cable. The pattern of resultant aerodynamic forces acting at different longitudinal locations of the model and the spatial correlation of the forces are examined. The results lead one step closer in revealing the physical nature of the phenomenon.

• 한국소음진동공학회논문집
• /
• 제19권6호
• /
• pp.575-582
• /
• 2009

This study presents the vibration excitation system to extract the aerodynamic stability derivatives which is generally called as flutter derivatives in civil engineering. The system consists of the excitation part to give a forced harmonic motion to the model and the sensing part to measure the aerodynamic forces as well as inertia forces acting on a bridge model. A data processing algorithm for extracting the flutter derivatives from the measured forces is also presented. From the wind tunnel tests, verification of present system was done by comparing the measured and analytical results for rectangular shaped model. The effects of excitation frequencies and amplitudes on flutter derivatives are discussed. Five kinds of actual bridge model were presented from the wind tunnel.

• Wind and Structures
• /
• 제7권1호
• /
• pp.29-40
• /
• 2004

This study has focused on aerodynamics for a wind-resistance design about the single and tandem box girder sections to realize a super-long span bridge in the near future. Three-dimensional static analysis of flows around the fundamental single and tandem box girder sections with fairing is carried out by means of the IBTD/FS finite element technique with LES turbulence model. As the results of the analysis, computations have verified aerodynamic characteristics of both sections by the histories of aerodynamic forces, the separation and reattachment flow patterns and the surface pressure distributions. The relationship between the section shapes and the aerodynamic characteristics is also investigated in both sections. And the mechanism about the generation of fluctuating aerodynamic forces is discussed.

• 한국수소및신에너지학회논문집
• /
• 제29권2호
• /
• pp.197-204
• /
• 2018

In the present study, unsteady flow analysis has been conducted to investigate the blade forces and wake flow around a hybrid street-lamp having a vertical-axis small wind turbine and a photovoltaic panel. Uniform velocities of 3, 5 and 7 m/s are applied as inlet boundary condition. Relatively large vortex shedding is formed at the wake region of the photovoltaic panel, which affects the increase of blade torque and wake flow downstream of the wind turbine. It is found that blade force has a good relation to the variation of the angle of attack with the rotation of turbine blades. Variations in the torque on the turbine blade over time create a cyclic fluctuation, which can be a source of turbine vibration and noise. Unsteady fluctuation of blade forces is also analyzed to understand the nature of the vibration of a small wind turbine over time. The detailed flow field inside the turbine blades is analyzed and discussed.

• KEPCO Journal on Electric Power and Energy
• /
• 제5권2호
• /
• pp.75-81
• /
• 2019

본 연구에서는 최근 정부에서 제시한 표준설계 응답스펙트럼을 이용하여 송전용량, 높이 및 구조타입 등 다양한 변수를 고려한 송전철탑 24기를 선정하여 내진성능평가를 수행하였다. 또한, 정부에서 요구한 내진기준 상향 시 철탑의 설계에 미치는 영향을 검토하기 위하여, 현 설계 풍하중 및 개정 지진하중에 의해 발생되는 응력 및 단면력의 크기를 비교해 보았다. 내진성능평가 결과 대상 철탑들은 0.31~0.91g의 내진성능을 보유하고 있는 것으로 나타나, 2,400년 재현주기의 내진특등급 수준을 만족하였으며 내진안전성을 확보하고 있는 것으로 나타났다. 또한, 철탑의 지진에 의한 단면력은 풍하중에 의한 값의 33~82.5%로 나타나, 상향된 내진기준에서도 설계 풍하중이 지진하중보다 지배적임을 확인하였다.

• Wind and Structures
• /
• 제34권5호
• /
• pp.407-419
• /
• 2022

Many factors should be considered by architects and designers for designing a tall building. Wind load is one of these important factors that govern the design of tall building structures and can become a serious challenge when buildings tend to be built very tall and slender. On the other hand, through the initial stages of a design process, choosing the design geometry greatly affects the wind-induced forces on a tall building. With this respect, geometric shapes with 3-fold rotational symmetry are one of the applied plan shapes in tall buildings. This study, therefore, aims to investigate the aerodynamic characteristics of 8 different geometrical shapes using Computational Fluid Dynamics (CFD) by measuring the drag and lift forces. A case study approach was conducted in which different building shape models have the same total gross area and the same height of 300 meters. The simulation was an incompressible transient flow that ran 1700 timesteps (85 seconds on the real-time scale). The results show a great difference between wind-induced force performance of buildings with different plan shapes. Generally, it is stated that the shapes with the same area, but with smaller perimeters, are better choices for reducing the drag force on buildings. Applying the lift force, the results show that the buildings with plan shapes that have rounded corners act better in crosswind flow while, those with sharp corners induce larger forces in the same direction. This study delivers more analytical understanding of building shapes and their behavior against the wind force through the parametric modelling.

• Wind and Structures
• /
• 제14권5호
• /
• pp.481-498
• /
• 2011

During the past decade, many electrical transmission tower structures have failed during downburst events. This study is a part of a research program aimed to understand the behaviour of transmission lines under such localized wind events. The present study focuses on assessing the behaviour of self supported transmission line towers under downburst loading. A parametric study is performed to determine the critical downburst configurations causing maximum axial forces for various members of a tower. The sensitivity of the internal forces developing in the tower's members to changes in the downburst size and location was studied. The structural behaviour associated with the critical downburst configurations is described and compared to the behaviour under 'normal' wind loads.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2004년도 한국우주과학회보 제13권2호
• /
• pp.258-261
• /
• 2004

Numerical simulations are made to predict the axial force coefficients of a two-stage launch vehicle, and the results are compared with those by wind tunnel tests. It is found that the forebody axial force is not affected by whether the base of the body is modeled or not. Modeling the sting support used in wind tunnel tests reduced the base axial force compared to the results without it. The present calculation shows that the forebody axial forces are underestimated while the base axial forces are overestimated. The total axial force, therefore, compares with the experimental data with better accuracy by cancelling out the errors of opposite signs. Modeling of the sting support in numerical simulations is found to be necessary to get a better agreement with the experiments for both base and overall axial force coefficients.

• Wind and Structures
• /
• 제20권1호
• /
• pp.95-115
• /
• 2015

Wind effects on roofs are usually considered by equivalent static wind loads based on the equivalence of displacement or internal force for structural design. However, for large-span spatial structures that are prone to dynamic instability under strong winds, such equivalent static wind loads may be inapplicable. The dynamic stability of spatial structures under unsteady wind forces is therefore studied in this paper. A new concept and its corresponding method for dynamic instability-aimed equivalent static wind loads are proposed for structural engineers. The method is applied in the dynamic stability design of an actual double-layer cylindrical reticulated shell under wind actions. An experimental-numerical method is adopted to study the dynamic stability of the shell and the dynamic instability originating from critical wind velocity. The dynamic instability-aimed equivalent static wind loads of the shell are obtained.