Aerodynamic Damping Ratios Research Articles

Experimental and theoretical investigation of galloping of transversely inclined slender prisms

Galloping is characterized by large and periodical oscillations which may lead to collapse of slender structures. This study is the first attempt of a comprehensive experimental and theoretical investigation of galloping of transversely inclined prisms. A modified quasi-steady model is proposed with a constant term to estimate the galloping of a transversely inclined prism, which is later experimentally investigated by conducting a static Synchronous Multi-Pressure Sensing System (SMPSS) test and an aeroelastic test in a boundary layer wind tunnel. The galloping responses of the prisms were measured in the aeroelastic test, while the aerodynamic force coefficients were determined from the SMPSS test. These experimental results were subsequently utilized to validate the quasi-steady model. Based on the proposed model, the galloping responses of the prisms were predicted and compared with the experimental results. The experimentally measured and theoretically predicted galloping responses are discussed with respect to aerodynamic damping ratios, onset galloping wind speeds, distributed pressure coefficients, point pressure spectra and vortex shedding frequencies. Interesting findings are summarized.

Numerical analysis of aerodynamic damping for a centrifugal impeller

ABSTRACTIn order to realize the numerical analysis of aerodynamic damping for the centrifugal impellers, a numerical code integrating the flow-structure data transfer, grid deformation and flow simulation under the moving grid system is first developed. To decrease the huge consumptions of CPU time and memory space, the compactly supported radial basis function is adopted to carry out the data transfer and grid deformation, and the alternating digital tree technique is utilized to calculate the wall distances. By the test cases of an oscillating cascade and a centrifugal impeller, the correctness of the code for the flow simulations with moving boundaries and the flow fields in centrifugal impellers is validated. Then taking a centrifugal impeller as the research object, the calculations of aerodynamic damping characteristics were carried out. The results show that, the modal aerodynamic damping ratio has no relationship with the vibrating amplitude under small vibrations. For the disk-dominant vibration mode, the modal aerodynamic damping ratio decreases as the operating point shifts toward the stall point. The aerodynamic damping caused by the backward traveling wave vibration is larger than that by the forward traveling wave vibration.

Aero-elastic wind tunnel test of a high lighting pole

This paper presents a 1:25 multi-freedom aero-elastic model for a high lighting pole at the Zhoushan stadium. To validate the similarity characteristics of the model, a free vibration test was performed before the formal test. Beat phenomenon was found and eliminated by synthesis of vibration in the X and Y directions, and the damping ratio of the model was identified by the free decay method. The dynamic characteristics of the model were examined and compared with the real structure; the similarity results were favorable. From the test results, the major along-wind dynamic response was the first vibration component. The along-wind wind vibration coefficient was calculated by the China code and Eurocode. When the peak factor equaled 3.5, the coefficient calculated by the China code was close to the experimental result while Eurocode had a slight overestimation of the coefficient. The wind vibration coefficient during typhoon flow was analyzed, and a magnification factor was suggested in typhoon-prone areas. By analyzing the power spectrum of the dynamic cross-wind base shear force, it was found that a second-order vortex-excited resonance existed. The cross-wind response in the test was smaller than Eurocode estimation. The aerodynamic damping ratio was calculated by random decrement technique and the results showed that aerodynamic damping ratios were mostly positive at the design wind speed, which means that the wind-induced galloping phenomenon is predicted not to occur at design wind speeds.

Prediction of wind-induced buffeting response of overhead conductor: Comparison of linear and nonlinear analysis approaches

This study addresses the estimation of buffeting response of overhead conductor based on random vibration theory with closed-form formulations. Special attention is placed on the determination of static deformation with consideration of geometric nonlinearity, and its influence on the dynamic modal properties, aerodynamic modal damping and buffeting response. The dynamic response around the static equilibrium is separated into background and resonant components, which are calculated by using influence function and modal analysis, respectively. The aerodynamic modal damping ratios are estimated in closed-form formulations in which the influence of static swing of the conductor plane is explicitly accounted. Example studies presented in this study illustrate the accuracy and effectiveness of this linear buffeting analysis framework through comparison with nonlinear finite element model (FEM) analysis in the time domain. The importance of consideration of static deformation is revealed for the prediction of alongwind displacement and tension, especially, the resonant response component. The contributions of modal responses to various resonant responses are also examined.

나선형 형상의 초고층건물의 공력감쇠의 특성

본 연구에서는 변위 및 가속도 응답의 저감 효과에 있어서, 유리한 형상인 <TEX>$180^{\circ}$</TEX> 나선형(Helical <TEX>$180^{\circ}$</TEX>) 초고층건물을 대상으로 공력진동실험 수행하여 나선형 초고층건물의 공력감쇠율의 특성을 조사하였다. 공력감쇠율은 RD법(Random decrement technique)을 이용하여 평가하였다. 또한 RD법에서 부분 샘플의 개수와 초기 조건 값의 변화가 공력감쇠율에 어떤 영향을 미치는지 조사하였다. 실험 결과, 최소 2000개 이상의 부분 샘플을 이용하여 앙상블 평균을 적용하면 공력감쇠율의 불규칙한 변동의 폭을 줄일 수 있음을 검증했고, 기존 연구들과도 잘 부합되는 것을 알 수 있었다. 정방형 모형과 <TEX>$180^{\circ}$</TEX> 나선형 모형의 공력감쇠율의 결과를 살펴보면, 풍방향 공력감쇠율은 건물의 형상이 다름에도 불구하고 무차원 풍속에 따른 공력감쇠율은 매우 유사한 경향을 보였다. 한편, 정방형 모형에 대한 풍직각방향의 공력감쇠율은 <TEX>$180^{\circ}$</TEX> 나선형모형의 공력감쇠율의 특성과는 다른 양상을 보이는 것을 알 수 있었다. 특히 풍향 변화에 따른 <TEX>$180^{\circ}$</TEX> 나선형 모형의 Y방향에 대한 공력감쇠율은 풍향의 변화와 상관없이, 전반적으로 0에 가까운 값을 갖는 경향이 나타났고, 무차원 풍속의 증가와 함께 변동의 폭은 작지만 점진적으로 증가하는 경향을 보였다. 초기 조건 값의 변화에 따른 공력감쇠율을 평가한 결과, 초기 조건 값을 "응답의 표준편차" 또는 RD 함수에 대한 최적화 "<TEX>${\sqrt{2}}{\times}$</TEX>응답의 표준 편차"를 적용하여 평가한 공력감쇠율은 매우 유사한 결과 값과 분포를 보이는 것으로 나타났다. Characteristics of aerodynamic damping ratios of a helical <TEX>$180^{\circ}$</TEX> model which shows better aerodynamic behavior in both along-wind and across-wind responses on a super tall building was investigated by an aeroelastic model test. The aerodynamic damping ratio was evaluated from the wind-induced responses of the model by using Random Decrement (RD) technique. Further, various triggering levels in evaluation of aerodynamic damping ratios using RD technique were also examined. As a result, it was found that when at least 2000 segments were used for evaluating aerodynamic damping ratio for ensemble averaging, the aerodynamic damping ratio can be obtained more consistently with lower irregular fluctuations. This is good agreement with those of previous studies. Another notable observation was that for square and helical <TEX>$180^{\circ}$</TEX> models, the aerodynamic damping ratios in along-wind direction showed similar linear trends with reduced wind speeds regarding of building shapes. On the other hand, for the helical <TEX>$180^{\circ}$</TEX> model, the aerodynamic damping ratio in across-wind direction showed quite different trends with those of the square model. In addition, the aerodynamic damping ratios of the helical <TEX>$180^{\circ}$</TEX> model showed very similar trends with respect to the change of wind direction, and showed gradually increasing trends having small fluctuations with reduced wind speeds. Another observation was that in definition of triggering levels in RD technique on aerodynamic damping ratios, it may be possible to adopt the triggering levels of "standard deviation" or "<TEX>${\sqrt{2}}$</TEX> times of the standard deviation" of the response time history if RD functions have a large number of triggering points. Further, these triggering levels may result in similar values and distributions with reduced wind speeds and either may be acceptable.

Experimental and numerical study on the responses of a transmission tower to skew incident winds

A study on a lattice suspension tower in a four-span transmission line system subjected to skew incident wind forces is presented via experimental and numerical approaches. The purpose of this work is to investigate the response features of the tower especially to the wind not incoming along the structure's principle axes. At the geometric scaling of 1:80, the aeroelastic model is manufactured with scaled rigidity, mass, area projection and frequency. Wind tunnel tests on the model, with and without conductors, are conducted at a variety of incident angles. Then numerical simulations are applied quasi-steadily to figure out an analytical way of interpreting and supplementing experimental results. Such quasi-steady method is generally valid since the tested aerodynamic damping ratios, though scattered, roughly meet the quasi-steady formulae. Results show that for the tower without conductors the dynamic accelerations do not vary significantly with the incident angle either in the r.m.s. values or in the spectral contents, as wind forces on the tower lend dependency on both the along wind and the across wind components of fluctuating winds thus have equivalent magnitudes at different wind incidences. For the tower with conductors, the longitudinal forces on the conductor are quite different from the lateral ones according to the simulated mechanism. As the co-effect of the additional loads and extra damping provided by conductors, dynamic accelerations of the tower show distinct characteristics in different axes and at different wind incidences.

실측 데이터를 이용한 공용중인 강사장교의 버페팅 응답 분석

공용 중인 교량의 버페팅 응답을 해석적으로 평가하기 위해서는 교량 현장의 난류강도, 난류 스펙트럼, 조도계수, 거스트 계수 등 풍하중에 대한 분석이 우선되어야 하고, 해석 결과는 정적 공기력 계수, 플러터계수, 구조 감쇠비, 공기역학적 감쇠비, 고유 진동수 등 여러 변수에 의해 영향을 받는다. 본 논문에서 대상으로 한 교량은 32년째 공용 중에 있는 교량으로써 교량 주변의 지형조건은 설계 및 시공 당시에 비해 많은 변화가 발생하였으며 최근 기후 변화로 인한 풍 환경 역시 큰 변화가 있다. 이러한 이유로 대상교량에서 실측한 풍속 데이터를 분석하여 난류강도, 난류길이, 지표조도계수, 풍속 스펙트럼 등 교량 현장의 풍하중을 평가하였다. 교량 주변의 풍환경 평가 결과, 대상 교량은 해상교량임에도 불구하고 지표조도구분 II의 특성을 나타내고 있었다. 또한 실측한 구조물의 가속도, 변위 응답 데이터를 통해 대상교량의 감쇠비, 정적 공기력 계수, 고유진동수를 평가하여 계측기반 버페팅 해석 변수를 산정하였다. 계측데이터 기반의 해석 변수와 케이블강교량설계지침에 제시된 해석 변수를 적용하여 총 4가지 경우에 대한 버페팅 해석을 수행하였으며, 그 결과 10분 평균 풍속 25m/s이하에서 측정된 버페팅 응답과 계측 기반 해석 변수를 적용한 해석 응답이 가장 잘 일치함을 확인하였고, 계측 풍속과 Gumbel 확률분포를 이용하여 추정한 200년 재현기대 풍속인 45m/s에서의 버페팅 응답을 제시하였다. In order to analytically evaluate buffeting responses, the analysis of wind characteristics such as turbulence intensity, turbulence length, gust, roughness coefficient, etc must be a priority. Static aerodynamic force coefficients, flutter coefficients, structural damping ratios, aerodynamic damping ratios and natural frequencies affect the analytical responses. The bridge interested in this paper has being been used for 32 years. As the time passes, current terrain conditions around the bridge are different markedly from the conditions it was built 32 years ago. Also, wind environments were considerably varied by the climate change. For this reason, it is necessary to evaluate the turbulence intensity, length, spectrum and roughness coefficient of the bridge site from full-scale measurements using the structural health monitoring system. The evaluation results indicate that wind characteristics of bridge site is analogous to that of open terrain although the bridge is located on the coastal area. To calculate buffeting responses, the analysis variables such as damping ratios, static aerodynamic force coefficients and natural frequency were evaluated from measured data. The analysis was performed with regard to 4 cases. The evaluated variables from measured data are applied to the first and second analysis cases. And the other analysis cases were performed based on Design Guidelines for Steel Cable Supported Bridges. The calculated responses of each analysis cases are compared with the buffeting response measured at less than 25m/s wind speed. It is verified that the responses by the numerical analysis applying the estimated variables based on full-scale measurements are well agreed with the measured actual buffeting responses under wind speed 25m/s. Also, the extreme wind speed corresponding to a recurrence interval 200 years is derived from Gumbel distribution. The derived wind speed for return period of 200 years is 45m/s. Therefore the buffeting responses at wind speed 45m/s is determined by the analysis applying the estimated variables.

Effects of turbulence intensity and exterior geometry on across-wind aerodynamic damping of rectangular super-tall buildings

Across-wind aerodynamic damping ratios are identified from the wind-induced acceleration responses of 15 aeroelastic models of rectangular super-high-rise buildings in various simulated wind conditions by using the random decrement technique. The influences of amplitude-dependent structural damping ratio and natural frequency on the estimation of the aerodynamic damping ratio are discussed and the identifying method for aerodynamic damping is improved at first. Based on these works, effects of turbulence intensity Iu, aspect ratio H/B, and side ratio B/D on the across-wind aerodynamic damping ratio are investigated. The results indicate that turbulence intensity and side ratio are the most important factors that affect across-wind aerodynamic damping ratio, whereas aspect ratio indirectly affects the aerodynamic damping ratio by changing the response amplitude. Furthermore, empirical aerodynamic damping functions are proposed to estimate aerodynamic damping ratios at low and high reduced speeds for rectangular super-high-rise buildings with an aspect ratio in the range of 5 to 10, a side ratio of 1/3 to 3, and turbulence intensity varying from 1.7% to 25%.

A Study on Aerodynamic Damping and Aeroelastic Instability of Helical-shaped Super Tall Building

In this paper, aeroelastic instability and aerodynamic damping ratio of a helical model which shows better aerodynamic behavior in both along-wind and crosswind responses on a super tall building was investigated by an aeroelastic model test, and the aerodynamic damping ratio was evaluated from the wind-induced responses of the model by using Random Decrement Technique. Aerodynamic damping ratios evaluated in this study were verified through comparison with previous results obtained by quasi-steady theory. As a result, the aeroelastic instability of the helical model in crosswind direction were not occurred for any conditions with increasing the reduced wind velocity while the square model generally encounters aeroinstability due to the vortex shedding. The aerodynamic damping in along-wind direction for the helical and the square model increased monotonically both with reduced wind velocity, i.e., there is no relation with modifications of building shapes. On the other hand, in crosswind direction, the characteristics of aerodynamic damping ratio with reduced wind velocity for helical model were quit different from those of the square model.

초고층건물의 공력감쇠율

Aerodynamic damping ratios play an important role in the estimations of wind-induced responses of modern super-tall and slender buildings and structures. In the present study, along- and across-wind aerodynamic damping ratios of a square cross-sectional conventional and tapered super-tall buildings with height of 448m were investigated using the Random Decrement Technique (RDT) for the responses obtained from the aeroelastic wind tunnel tests. Wind tunnel tests were conducted under the urban flow condition. Effects of building shape, normalized velocity and wind direction on aerodynamic damping ratios were comprehensively discussed. It was found that the along-wind aeroelastic aerodynamic damping ratios show similar linear increasing trends on the normalized velocities at small wind directions regardless of building shapes. But the across-wind aerodynamic damping ratios show clear differences depending on building shapes, showing different peaks and different normalized velocities at which peaks of aerodynamic damping ratios occur and positive aerodynamic damping ratios become negative. Lastly the effect of trigging value in RDT on aerodynamic damping ratios was examined by changing it from one standard deviation to three times of standard deviation. By enlarging the trigging value, the differences in aerodynamic damping ratios increase, implying the optimal trigging values may exist between one standard deviation and <TEX>${\sqrt{2}}$</TEX> times of standard deviations in the current experimental conditions.

Analytical Formulae for Wind Turbine Tower Loading in the Parked Condition by Using Quasi-Steady Analysis

The analytical formulae are proposed to estimate the maximum value for along-wind load and across-wind load on the wind turbine towers by using the quasi-steady analysis. The critical parameters in the standard deviation such as the mode correction factors, aerodynamic damping ratios, size reduction factors and wind load ratios are investigated to identify their directional characteristics. A non-Gaussian peak factor is necessary for the along-wind load, while a Gaussian peak factor is acceptable for the across-wind load. A loads combination formula is proposed in order to consider the correlation of along-wind load and across-wind load. The proposed formulae show the favorable agreements with the full dynamic simulation.

Experimental study of across‐wind aerodynamic damping of super high‐rise buildings with aerodynamically modified square cross‐sections

SUMMARYAcross‐wind aerodynamic damping ratios are determined from the wind‐induced acceleration responses of 10 aeroelastic models of square super high‐rise buildings in an urban flow condition (exposure category C in the Chinese code) using the random decrement technique. Moreover, the influences of amplitude‐dependent structural damping ratio on the estimation of aerodynamic damping ratio are discussed. The validity of estimated damping is examined through a comparison with previous research achievements. On the basis of the estimated results, the characteristics of the across‐wind aerodynamic damping ratios of modified square high‐rise buildings are studied. The effects of aerodynamically modified cross‐sections, such as chamfered, slotted and tapered cross‐section, on the across‐wind aerodynamic damping ratio are investigated. The results indicate that modifications of cross‐sections are not always effective in suppressing the aeroelastic effects of super high‐rise buildings. Low corner‐cut ratios (chamfer ratios from 5% to 20% and slot ratios from 5% to 10%) and low taper ratio (1%) significantly decrease the magnitudes of absolute aerodynamic damping ratios. However, large modifications of cross‐sections (slot ratio of 20% and taper ratios from 3% to 5%) increase wind‐induced responses by changing the aerodynamic damping ratios. According to the database, empirical aerodynamic damping function parameters are fitted for high‐rise buildings with aerodynamically modified square cross‐sections. Copyright © 2013 John Wiley &amp; Sons, Ltd.

The acrosswind response of the downwind prism in a twin-prism system with a staggered arrangement

The flow interaction between two identical neighboring twin square prisms in a staggered arrangement in an open terrain was investigated experimentally. The downwind prism was mounted on a rigid-aeroelastic setup in an open-terrain boundary layer flow to measure its acrosswind root-mean-square responses and aerodynamic damping ratios. By varying the relative location of the upwind prism and the Scruton number associated with the downwind prism, the acrosswind aeroelastic behavior of the downwind prism was analyzed and compared to that of an isolated one. Results showed that the acrosswind root-mean-square response of the downwind prism could be either suppressed or enhanced by the wake flow produced by the neighboring upwind prism. Besides the assessment of the wake effect of the downwind prism, finally, regressed relationships were presented to describe the variation of the aerodynamic damping ratio so as to predict its acrosswind fluctuating response numerically.

Stability analysis of an aeroelastic system with friction

In this paper, harmonic balance method, exact formulation and numerical simulation method are adopted to study the effects of different friction stiffness on the stability of 1.5 degrees of freedom aeroelastic system. On this basis, the expressions of input energy and dissipated energy are deduced, and the energy method is used to reveal the mechanisms of the stable boundary and unstable boundary existing in the system and the effects of different friction stiffness on the stability of the system. Studies have shown that the stability region and the critical aerodynamic damping ratio of the system rise with the increase of the friction stiffness, while the friction stiffness has little effect on the stability boundary. In the analysis of the stability of system, the results of harmonic balance method, exact formulation and Newmark of numerical simulation method are in good agreement. Compared with exact formulation and numerical simulation method, the concept and conclusion of harmonic balance method are simple in the system stability analysis.

Experimental Study of Aerodynamic Damping of Typical Tall Buildings

Aerodynamic damping in certain conditions appears to have a negative value, which increases the dynamic response of a tall building. Six single-degree-of-freedom (SDOF) aeroelastic models of tall buildings with typical cross sections (square, square with concave or bevel corners, and rectangular) are tested in a wind tunnel with a suburban terrain flow field condition. The along-wind and across-wind aerodynamic damping ratios of the tall buildings are identified by using the eigensystem realization algorithm (ERA) method in conjunction with the random decrement technique (RDT). The effects of wind speed, corner modifications (concave or bevel corner), side ratio, and wind direction on the aerodynamic damping are studied. The results indicate that in most cases the along-wind aerodynamic damping is positive and gradually increases with the increase of reduced wind speed (<svg style="vertical-align:-3.3907pt;width:18.737499px;" id="M1" height="15.4" version="1.1" viewBox="0 0 18.737499 15.4" width="18.737499" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.112)"><path id="x1D448" d="M751 650l-6 -28q-53 -1 -69 -12.5t-24 -38.5q-23 -85 -43 -192l-13 -69q-34 -181 -130 -262q-79 -65 -185 -65t-171 57q-87 77 -54 258l42 232q12 58 0.5 73t-75.5 19l8 28h263l-6 -28q-63 -5 -78 -18t-26 -74l-41 -226q-25 -135 22 -201t139 -66q99 0 161.5 68t91.5 217&#xA;l11 57q28 149 28 193q0 28 -19 38t-79 12l6 28h247z" /></g> <g transform="matrix(.012,-0,0,-.012,13.038,15.187)"><path id="x1D45F" d="M393 379q-9 -16 -28 -29q-15 -10 -23 -2q-19 19 -36 19q-21 0 -52 -38q-57 -72 -82 -126l-40 -197q-23 -3 -75 -18l-7 7q49 196 74 335q7 43 -2 43q-7 0 -30 -14.5t-47 -37.5l-16 23q37 42 82 73t67 31q41 0 15 -113l-11 -50h4q41 71 85 117t77 46q29 0 45 -26&#xA;q13 -21 0 -43z" /></g> </svg>). The across-wind aerodynamic damping is likewise a positive value at low <svg style="vertical-align:-3.3907pt;width:18.737499px;" id="M2" height="15.4" version="1.1" viewBox="0 0 18.737499 15.4" width="18.737499" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.112)"><use xlink:href="#x1D448"/></g> <g transform="matrix(.012,-0,0,-.012,13.038,15.187)"><use xlink:href="#x1D45F"/></g> </svg> in most cases, but suddenly becomes negative when <svg style="vertical-align:-3.3907pt;width:18.737499px;" id="M3" height="15.4" version="1.1" viewBox="0 0 18.737499 15.4" width="18.737499" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.112)"><use xlink:href="#x1D448"/></g> <g transform="matrix(.012,-0,0,-.012,13.038,15.187)"><use xlink:href="#x1D45F"/></g> </svg> becomes greater than 10.5 for the square cross-section building.

Flutter prediction in turbomachinery with energy method

The study described in this article is the application of energy method for the prediction of flutter boundary and the effects of some parameters on aeroelastic stability in turbomachinery. The unsteady flow with multi-layer moving grid technique for blade oscillation was undergone for aerodynamic work with the blade passage being discretized using a background fixed H-grid and a body-fitted O-grid moving with the blade. Also, with the assumption of equivalent viscous damping, aerodynamic modal damping ratio was defined based on energy method. The numerical method, with mode shapes and nodal diameter numbers considered, was applied for a transonic compressor rotor stage for which measured flutter boundary on characteristic map was available. It was found that the calculated flutter boundary in the first bending blade mode agreed well with the measured one. Furthermore, it was concluded that the mode shapes and inter-blade phase angle were key parameters on aeroelasticity in turbomachinery and that the flutter instability was mainly induced by the co-action of shock wave and separated flow.

Experimental evaluation of aerodynamic damping of square super high-rise buildings

Aerodynamic damping often plays an important role in estimations of wind induced dynamic responses of super high-rise buildings. Across- and along-wind aerodynamic damping ratios of a square super high-rise building with a height of 300 m are identified with the Random Decrement technique (RDT) from random vibration responses of the SDOF aeroelastic model in simulated wind fields. Parametric studies on effects of reduced wind velocity, terrain type and structural damping ratio on the aerodynamic damping ratios are further performed. Finally formulas of across- and along-wind aerodynamic damping ratios of the square super high-rise building are derived with curve fitting technique and accuracy of the formulas is verified.

風向角を有する場合の正方形角柱に作用する振動依存風力とその評価

Evaluation of aerodynamic instability when wind blows aslant to a building has become increasingly important with progress in aerodynamic control of buildings. However, no evaluation method has yet been established for this case, although an evaluation method has been proposed for the case where wind blows normal to a prism. This proposed method uses a vibration-induced wind force coefficient as an index. This paper proposes an evaluation method for a vibration-induced wind force coefficient when wind blows aslant to a square building with and without a corner recess. The variation of vibration-induced wind force coefficient (Cf) with wind direction is clarified. Furthermore, variation of negative aerodynamic damping ratio with wind direction is clarified by transferring CI to it. The evaluation method is confirmed by comparing vibration tests results and negative aerodynamic damping ratios. It is thus confirmed that the proposed method can be applied to evaluate the occurrence of aerodynamic instabilities when wind blows aslant to a square type building.

Experimental evaluation of aerodynamic damping of tall buildings

Aerodynamic damping of tall buildings is evaluated by wind tunnel tests using a stick model. The model is a 1500 scale model of a building. The side ratio of the model is varied in the range 0.33–3, and the aspect ratio is varied from 4 to 6. The aerodynamic damping ratios are evaluated from the wind-induced responses of the model by using the random decrement technique.