• Wind and Structures
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• 제13권6호
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• pp.499-517
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• 2010

Advances in structural materials and construction methods have resulted in flexible and light tall buildings, making an assessment of structural safety during strong wind and serviceability/habitability during comparable medium/weak wind important design criteria. So far, lots of studies on suppressing the wind-induced responses have been carried out for tall buildings with aerodynamic modification. Most of the studies on aerodynamic modification have forced on the corner modification, while the studies on taper and set-back are limited. Changes of sectional shape through taper and set-back can modify the flow pattern around the models, encouraging more 3-dimensionalities, which results in reducing the wind-induced excitations. This paper discusses the characteristics of overturning moments and wind-induced responses of the tall buildings with height variations. The reduction of mean along-wind and fluctuating across-wind overturning moments are apparent in the suburban area than in urban area. A series of the response analyses, the rms displacement responses of the tall buildings with height variations are reduced greatly, while the rms acceleration responses are not necessarily reduced, showing dependences on wind direction.

• 한국농공학회지
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• 제38권2호
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• pp.145-151
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• 1996

Wind force coefficients of multi-span arched greenhouses with respect to wind direction of $0^{\circ}$ and $30^{\circ}$ were estimated to give more reasonable coefficient. The conventional and subdivided division types of wind force coefficient distribution diagrams were constructed by using the wind tunnel experimental data. Bending moments on the greenhouses were determined through structural analysis using obtained wind force coefficients, and were analyzed. Because actual wind pressure values on a face of greenhouse varied with locations, the more divisions of wind force coefficient distribution were subdivided, the better distribution type was coincided with actual state. In order to calculate the more accurate section force occurred on the arched greenhouse by the wind loads, it was recommendable that the wind force coefficient distribution should take more subdivision type. The maximum bending moment at the multi-span greenhouse frame at wind direction of $30^{\circ}$ was greater than that at O。, therefore the wind force coefficient at inclined wind direction to the wall was needed to be considered for the multi-span greenhouse structural design.

• Wind and Structures
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• 제18권4호
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• pp.391-422
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• 2014

The high frequency force balance (HFFB) technique provides convenient measurements of integrated forces on rigid building models in terms of base bending moments and torque and/or base shear forces. These base moments or forces are then used to approximately estimate the generalized forces of building fundamental modes with mode shape corrections. This paper presents an analysis framework for coupled dynamic response of tall buildings with HFFB technique. The empirical mode shape corrections for generalized forces with coupled mode shapes are validated using measurements of synchronous pressures on a square building surface from a wind tunnel. An alternative approach for estimating the mean and background response components directly using HFFB measurements without mode shape corrections is introduced with a discussion on higher mode contributions. The uncertainty in the mode shape corrections and its influence on predicted responses of buildings with both uncoupled and coupled modal shapes are examined. Furthermore, this paper presents a comparison of aerodynamic base moment spectra with available data sets for various tall building configurations. Finally, e-technology aspects in conjunction with HFFB technique such as web-based on-line analysis framework for buildings with uncoupled mode shapes used in NALD (NatHaz Aerodynamic Loads Database) is discussed, which facilitates the use of HFFB data for preliminary design stages of tall buildings subject to wind loads.

• 한국항공운항학회지
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• 제24권2호
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• pp.19-24
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• 2016

Positional stability analysis based on aerodynamic forces and induced moments of formation flight using two small aircraft models is presented. The aerodynamic force and moments of the trailing aircraft are analyzed in the aspect of flight stability. The induced moments with the change of local flow direction by wing-tip vortex from the leading aircraft can affect the flight positional stability of aircraft in closed formation flight. Aerodynamic forces and moments of trailing aircraft model are measured by 6-component internal balance at the 49 locations with vertical and lateral space between two aircraft models. Results are shown that the positional stability of trailing aircraft in formation flight can be analyzed by positional stability derivatives with vertical and lateral space. It is concluded that flying positions can be important factors for aircraft position stability due to induced aerodynamic force and moments with vertical and lateral spacing by the variation of flow pattern from the leading aircraft in formation flight.

• 한국해안해양공학회지
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• 제14권2호
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• pp.161-170
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• 2002

이어도 해양과학기지의 풍력을 검토하기 위하여 50m/s의 설계풍속에 대하여 풍동실험과 수치해석을 수행하였다. 해수면위 상부구조물의 축소모형(1/80)에 대하여 풍력 및 모멘트를 계측하고 풍력계수를 산출하여 수치해석 결과와 비교한 결과, 이들 결과들이 대체적으로 잘 일치함을 확인하였다 따라서, 본 풍동실험의 결과를 상부구조물의 내풍설계자료로 충분히 활용할 수 있을 것으로 판단된다 실험결과를 이용하여 상부구조물 전체에 작용하는 풍력 및 모멘트 값들과 그리고 불투과 부속시설(주 데크, 태양광 발전판, 헬기 이 착륙장)의 외장 설계풍압과 구조설계용 풍압을 제시하였다.

• Wind and Structures
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• 제11권4호
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• pp.323-340
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• 2008

In this paper, the along-wind, across-wind as well as torsional dynamic wind loads on three kinds of lattice tower models are investigated using the base balance technique in a boundary layer wind tunnel. The models were specially designed, and their fundamental frequencies in the directions of the three principal axes are still in the frequency range of the spectra of wind loads on lattice towers. In order to clear contaminations to the spectra of wind loads induced by model resonance, the generalized force spectra of the first mode of the models in along-wind, across-wind and torsional directions were derived based on measured base moments of the models. The RMS generalized force coefficients are also obtained by removing the contributions of model resonance. Finally, the characteristics of the 3-D dynamic wind loads, especially those of the across-wind dynamic loads, on the three kinds of lattice towers are presented and discussed.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.367-375
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• 2020

This paper presents an integrated analysis about dynamic performance of a Floating Offshore Wind Turbine (FOWT) OC4 DeepCwind with semi-submersible platform under real sea environment. The emphasis of this paper is to investigate how the wave mean drift force and slow-drift wave excitation load (Quadratic transfer function, namely QTF) influence the platform motions, mooring line tension and tower base bending moments. Second order potential theory is being used for computing linear and nonlinear wave effects, including first order wave force, mean drift force and slow-drift excitation loads. Morison model is utilized to account the viscous effect from fluid. This approach considers floating wind turbine as an integrated coupled system. Two time-domain solvers, SIMA (SIMO/RIFLEX/AERODYN) and FAST are being chosen to analyze the global response of the integrated coupled system under small, moderate and severe sea condition. Results show that second order mean drift force and slow-drift force will drift the floater away along wave propagation direction. At the same time, slow-drift force has larger effect than mean drift force. Also tension of the mooring line at fairlead and tower base loads are increased accordingly in all sea conditions under investigation.

• Structural Engineering and Mechanics
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• 제63권4호
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• pp.509-519
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• 2017

Wind field in mountainous regions demonstrates unique distribution characteristic as compared with the wind field of the flat area, wind load and wind effect are the key considerations in structural design of television towers situated in mountainous regions. The television tower to be constructed is located at the top of Xiushan Mountain in Nanjing, China. In order to investigate the impact of terrain factors of hilltops on wind loads, firstly a wind tunnel test was performed for the mountainous area within 800m from the television tower. Then the tower basal forces such as bending moments and shear strength were obtained based on high frequency force balance (HFFB) test. Based on the experiments, the improved method for determining the load combinations was applied to extract the response distribution patterns of foundation internal force and peak acceleration of the tower top, then the equivalent static wind loads were computed under different wind angles, load conditions and equivalent goals. The impact of terrain factors, damping ratio and equivalent goals on the wind load distribution of a television tower was discussed. Finally the equivalent static wind loads of the television tower under the 5 most adverse wind angles and 5 most adverse load conditions were computed. The experimental method, computations and research findings provide important references for the anti-wind design of high-rise structure built on hilltops.

• Wind and Structures
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• 제11권1호
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• pp.1-18
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• 2008

Interference effects in five square tall buildings arranged in an L- or T-shaped pattern are investigated in the wind tunnel. Mean and fluctuating shear forces, overturning moments and torsional moment are measured on each building with a force balance mounted at its base. Results are obtained at two values of clear separation between adjacent buildings, at half and a quarter building breadth. It is found that strong interference effect exists on all member buildings, resulting in significant modifications of wind loads as compared with the isolated single building case. Sheltering effect is observed on wind loads acting along the direction of an arm of the "L" or "T" on the inner buildings. However, increase in these wind loads from the isolated single building case is found on the most upwind edge building in the arm when wind blows at a slight oblique angle to the arm. The corner formed by two arms of buildings results in some wind catchment effect leading to increased wind pressure on windward building faces. Interesting interference phenomena such as negative drag force are reported. Interference effects on wind load fluctuations, load spectra and dynamic building responses are also studied and discussed.

• Wind and Structures
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• 제12권3호
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• pp.239-257
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• 2009

This paper develops and discusses a method by which it is possible to evaluate the Equivalent Static Force (ESF) of wind in the case of long-span bridges. Attention is focused on the alongwind direction. The study herein carried out deals with the classical problems of determining the maximum effects due to the alongwind action and the corresponding ESFs. The mean value of the maximum alongwind displacement of the deck is firstly obtained both by the spectral analysis and the Gust Response Factor (GRF) technique. Successively, in order to derive the other wind-induced effects acting on the deck, the Gust Effect Factor (GEF) technique is extended to long-span bridges. By adopting the GRF technique, it is possible to define the ESF that applied on the structure produces the maximum alongwind displacement. Nevertheless the application of the ESF so obtained does not furnish the correct maximum values of other wind-induced effects acting on the deck such as bending moments or shears. Based on this observation, a new technique is proposed which allows to define an ESF able to simultaneously reproduce the maximum alongwind effects of the bridge deck. The proposed technique is based on the GEF and the POD techniques and represents a valid instrument of research for the understanding of the wind excitation mechanism.