Gust Factor Research Articles

Tropical-cyclone-wind-induced flutter failure analysis of long-span bridges

Continuously growing number and span length of long-span bridges in coastal region of China require a robust aeroelastic design to against the tropical-cyclone (TC) -induced flutter instability. Instead of using the deterministic approach, this study presents a Monte-Carlo-technique-based framework to analyze the flutter reliability of a long-span suspension bridge subjected to TC winds. A limit state function formulated as the difference between the flutter capacity and the extreme gust wind, termed as the product of a random gust factor and the TC mean wind hazard is employed. The flutter fragility curve in terms of the critical wind speed is derived using 2D and 3D flutter analysis models accounting for the structural modal and damping randomness as well as experiment-induced errors of aeroelastic flutter derivatives. The TC wind hazard curves at the height of the bridge deck described as the probability of exceedance at any given years of interest versus the extreme 10-min mean wind speed are estimated through generating a large quantity of synthetic tracks around the bridge site. The probabilistic solutions of the gust factor associated with any gust duration of interest are determined utilizing the statistics of observed TCs coupled with a theoretical model. The TC-induced flutter failure probabilities of present bridge are then predicted in different combinations of gust duration, surface roughness length and flutter analysis models, which enables the assessment of flutter risk subjected to TC winds as compared to code-suggested target reliability indices. The present reliability analysis provides some basic information to assist and enhance the flutter-resistant design of long-span bridges due to TC winds during the preliminary stage.

Assessing wind gust characteristics at wind turbine relevant height

Wind gust characteristics at wind turbine relevant height are closely tied with wind turbine design and wind power generation, however, they have not been detailed and documented. In this study, high-resolution wind data recorded by 3D sonic anemometers at a tall meteorological tower were analyzed to determine 12 descriptors of wind gusts and to identify the parent distributions that best fit these parameters. The main statistics were estimated using wind data from the 160 m height. It is found that the log-logistic distribution is most appropriate for a 10-min mean wind speed, gust magnitude, gust factor, and turbulence intensity; the gamma distribution appears to best fit peak factor, rise magnitude, lapse magnitude, lapse time, and gust length scale, while gust amplitude, rise time, and gust asymmetric factor are typically log-normally distributed. Gust factors tend to decrease with mean wind speed but increase as a function of turbulence intensity. The results also indicate that these wind gust descriptive parameters are height-dependent in which the 10-min mean wind speed, gust magnitude, gust length scale, rise time, and lapse time usually possess larger values at higher heights, whereas the remaining parameters exhibit negative correlation with height.

Full-scale monitoring of wind effects on a supertall structure during six tropical cyclones

Full-scale measurements under real wind conditions are viewed as the most reliable approach to investigating the wind effects on supertall structures. However, long-term monitoring on wind characteristics at the maximum atmospheric boundary layer height and the corresponding wind-induced responses of structures are very limited, especially under strong tropical cyclones. In this study, field monitoring of wind effects on a 600 m high supertall structure is obtained during 6 tropical cyclones by means of a sophisticated long-term structural health monitoring (SHM) system deployed on the structure. Wind characteristics (wind speed, direction, turbulence intensity, gust factor, power spectral density) of these tropical cyclones above 450 m height are presented and analyzed. The dynamic properties of the supertall structure are determined from the field measurements and compared with those stipulated in design. The damping ratios of the supertall structure are estimated by the virtual dynamic shaker (VDS) and the enhanced virtual dynamic shaker (EVDS) methods. In addition, the response amplitude-dependence of the structural natural frequencies and damping ratios is investigated. Finally, the comfort performance of the supertall structure during different tropical cyclones is assessed against four comfort criteria. The findings of this study would be beneficial to professionals and researchers engaged in wind-resistant design and practice of skyscrapers.

Wind tunnel measurement of three-dimensional turbulent flow structures around a building group: Impact of high-rise buildings on pedestrian wind environment

The wind velocity and surface pressure of the model of a group of urban blocks made of low-rise buildings with a high-rise building in the center were measured using a wind tunnel. Not only the time-averaged velocity field, but also the turbulent statistics, i.e., the turbulent kinetic energy, normal component of the Reynolds stresses, gust factor (GF), and probability density function (PDF), and power spectrum density (PSD) of instantaneous velocity components were investigated. Based on the results, the impact of high-rise buildings on the general flow structure and the surrounding pedestrian wind environment was discussed. The presence of high-rise buildings drastically changes the pedestrian wind environment around buildings in terms of time-averaged and instantaneous flow properties due to the complex interaction between the flows around the building and in and above the surrounding street canyons. High-rise buildings create a large GF region where the downwash flow and the street flow collide. A clear correlation between the GF and the time-averaged horizontal velocity magnitude was observed regardless of the height of the central building. The PDF of instantaneous velocity components around the high-rise building was characterized by a large skew not only near the building corners of the high-rise building but also on the surrounding streets. The high-rise building produces large PSDs of the velocity fluctuation components, particularly near the upwind corner at a high frequency and on the surrounding street at an intermediate frequency. Furthermore, the results of the time-averaged and instantaneous flow properties provide a useful database for computational fluid dynamics (CFD) validation and model development studies.

Meteorologically Stratified Gust Factors for Forecasting Peak Wind Gusts across the United States

ABSTRACTWind gusts are common to everyday life and affect a wide range of interests including wind energy, structural design, forestry, and fire danger. Strong gusts are a common environmental hazard that can damage buildings, bridges, aircraft, and trains, and interrupt electric power distribution, air traffic, waterways transport, and port operations. Despite representing the component of wind most likely to be associated with serious and costly hazards, reliable forecasts of peak wind gusts have remained elusive. A project at the University of Wisconsin–Milwaukee is addressing the need for improved peak gust forecasts with the development of the meteorologically stratified gust factor (MSGF) model. The MSGF model combines gust factors (the ratio of peak wind gust to average wind speed) with wind speed and direction forecasts to predict hourly peak wind gusts. The MSGF method thus represents a simple, viable option for the operational prediction of peak wind gusts. Here we describe the results of a project designed to provide the site-specific gust factors necessary for operational use of the MSGF model at a large number of locations across the United States. Gust web diagrams depicting the wind speed– and wind direction–stratified gust factors, as well as peak gust climatologies, are presented for all sites analyzed.

BOUNDARY LAYER WIND PROFILE MEASUREMENT BASED ON A SIX-ROTOR UAV ANEMOMETER

They studied the feasibility of boundary layer wind field measurement based on a six-rotor drone equipped with an anemometer, and analyzed the measured wind characteristics including average wind speed, wind direction, turbulence intensity, gust factor, the turbulence integral length and power spectrum. The results are compared with the measured results of anemometers fixed on a wind tower. The results show that the wind speed and wind direction values measured by the UAV are basically the same as the measured values on the wind tower after correction, and the error between the two is within ±3%. The accuracy of fitted wind profile by the UAV is high. The wind profile is close to the B-type geomorphic wind profile specified by the Chinese standard. The average ground roughness calculated by data fitting is 0.148. The various fluctuating wind characteristic parameters measured by the UAV are close to the measured values on the wind tower, and the error between the two is within ±5%. There is an exponential correlation between the turbulence intensity and the gust factor. The wind power spectrum measured by the UAV is basically consistent with that measured on the wind tower and is consistent with the Karman spectrum.

Extracting Time-Varying Mean Component of Non-Stationary Winds Utilizing Vondrak Filter and Genetic Algorithm: A Wind Engineering Perspective

The time-varying mean (TVM) component plays a vital role in the characterization of non-stationary winds, whereas it is difficult to extract the TVM accurately or to validate it quantitively. To deal with this problem, this paper first develops two additional conditions for the TVM extraction from the perspective of structural wind-induced vibration response, then presents an approach, based on the combination of Vondrak filter and genetic algorithm (Vondrak-G), to derive the optimal TVM from non-stationary wind speed records as well as its turbulence characteristics (i.e. gust factor, turbulence intensity, and turbulence integral length scale). Furthermore, the wind characteristics obtained by the Vondrak-G approach are compared with those by a conventional approach derived for stationary winds, demonstrating that the results by the Vondrak-G approach are evidently more accurate. This paper aims to provide an effective method for accurately extracting the TVM and then evaluating wind characteristics of the non-stationary wind.

A Field Measurement Based Wind Characteristics Analysis of a Typhoon in Near-Ground Boundary Layer

The field measurement was conducted to observe the wind field data of West Pacific typhoon “Maria” in this research. With the application of ultrasonic anemometers installed in different heights (10 m, 80 m, 100 m) of the tower, the three dimensional wind speed data of typhoon “Maria” was acquired. In addition, vane-type anemometers were installed to validate the accuracy of the wind data from ultrasonic anemometers. Wind characteristics such as the mean wind profile, turbulence intensity, integral length scale, and wind spectrum are studied in detail using the collected wind data. The relationship between the gust factor and turbulence intensity was also studied and compared with the existing literature to demonstrate the characteristics of Maria. The statistical characteristics of the turbulence intensity and gust factor are presented. The corresponding conclusion remarks are expected to provide a useful reference for designing wind-resistant buildings and structures.

Characteristics of Typhoon “Fung-Wong” Near Earth Pulsation

To study the wind field characteristics near the ground pulsation in typhoon conditions, wind field conditions in the area affected by Typhoon “Fung-Wong” were monitored using wind field instruments installed in the construction building of Wenzhou University, China. Real-time wind field data were collected during typhoons. Wind characteristic parameters such as mean wind speed, wind direction angle, turbulence intensity, gust factor, peak factor, coherence function, and autocorrelation were analyzed, and the wind field characteristics during the typhoon were summarized. The results indicated that the longitudinal and lateral turbulence intensities decreased with an increase in the mean wind speed, and there was an obvious linear relationship between them. The vertical and horizontal gust factor and peak factor decreased with an increase in mean wind speed, and the trend was more obvious in the horizontal direction. There was a significant correlation between the gust factor and the peak factor. The turbulence intensity and gust factor decreased with time, and the turbulence intensity attenuation speed increased with time. The empirical curve presented by Davenport (1961) can simulate the correlation characteristics of the fluctuating wind speed components of Typhoon Fung-Wong at some measuring points. With an increase in the time difference, the dependence of the instantaneous values at the two time points gradually decreased.

A theoretical study of the dynamic response of planar timber frames with semi-rigid moment-resisting connections subjected to wind loads

The dynamic response of semi-rigid timber frames subjected to wind loads is investigated numerically in this paper. The dynamic response of more than one million unique frames with different parameters was assessed with the frequency-domain gust factor approach, which is currently adopted by Eurocode 1, and the time-domain generalized wind load method. In the generalized wind load method, the frames were simulated for three different wind velocities with five simulations per unique combination of parameters, resulting in more than twelve million simulations in total. Qualitative and quantitative observations of the dataset were made. Empirical expressions for the accelerations, displacements, and fundamental eigenfrequency were proposed by the use of nonlinear regression applied to the obtained numerical results and a frequency reduction factor was developed. The wind-induced accelerations obtained by the two methods were compared to the corresponding serviceability criteria according to ISO10137, providing insight about the feasibility of moment-resisting frames as a lateral load-carrying system for mid-rise timber buildings. Comparison between the theoretical gust factor approach and the generalized wind load method showed that the gust factor approach was nonconservative in most cases. Finally, the effect of uniform and non-uniform mass distributions was investigated, with a theoretical reduction in top-floor accelerations of 50% and 25% respectively.

The analysis of characteristics of wind field on roof based on field measurement

An increasing number of solar energy or other devices have been installed on the roof, and the structure of which is very sensitive to wind load. The wind field on proof becomes the most critical premise for studying the wind load of structure. Due to the influence of buildings and parapet, the wind field on roof is completely different from that near the ground layer of atmospheric boundary layer. By analyzing the wind field characteristics on the roof of a multi-story building using field measurement method, this study acquires the variation rules and characteristics of wind characteristic parameters, such as the mean wind speed and yaw angle, turbulence intensity, gust factor, turbulence integral scale and fluctuating wind speed spectrum of wind field on multi-story building roof. The wind field on roof is also compared with the wind field on ground in this study so as to understand their difference. The analysis results show that the difference between wind fields on roof and ground, which should be considered when calculating the wind load of structure on roof.

An Examination of the Gust Effect Factor for Rigid High-Rise Buildings

In order to systematically investigate the gust effect factor for rigid buildings, the derivation of the gust effect factor in ASCE 7–16 is carefully reviewed and scale model pressure tests were carried out for rectangular-plan high-rise buildings with plan aspect ratios ranging from 0.11 to 9. The gust effect factor and the aerodynamic admittance function (AAF) for area-averaged pressure coefficients and base drag coefficients were obtained and discussed in detail. The results show that the AAF has direct influence on the value of the gust effect factor, depending on whether effects of non-contemporaneous gust actions or body-generated turbulence are playing a leading role. The ASCE 7–16 gust effect factor for rigid buildings underestimates the measured values for individual walls due to differences in the AAF, peak factors, and the employment of the 3 s moving average filter. However, the ASCE 7–16 gust factor for overall drag is estimated within 5% or better.

Wind climate of the Melbourne metropolitan area

This paper describes a probabilistic analysis of data recorded by the Bureau of Meteorology (BoM) for the wind climate of the Melbourne metropolitan area. It is based on 10-minute average wind data from four automatic weather stations (AWS) ‒ at Melbourne and Essendon airports, Fawkner Beacon in Port Phillip Bay, and Moorabbin Airport. Corrections to the data were made to adjust to standard terrain conditions and height. For the land stations, these were based on estimates of the surface roughness length at each site as a function of wind direction, making use of recorded gust factors. For the Fawkner Beacon, which is completely surrounded by open water, the surface roughness length is a function of mean wind speed, and the Charnock relationship was used in determining the corrections. For each station the terrain-corrected wind data were fitted with Weibull probability distributions, as an all-direction group and for sixteen direction sectors. Directional probabilities were also determined. The parameters of the all-direction Weibull distributions are very similar for all four stations, but there are differences in directional probabilities for some directions, with a geographic trend from north to south in the region being apparent. Some possible explanations based on the general topography are given.

Measurements of Overwater Gust Factor from Near Surface to Beyond Common Hub Height: A Case Study

In September 2020 Hurricane Sally affected the north central Gulf of Mexico. Making use of the anemometers data available at 4 oil rigs over the affected region, it is found that, when the atmospheric stability was near-neutral, the gust factor (G) decreases linearly with height from approximately 1.28 at 35m above the sea surface to 1.18 at 160 m. In other words, G decreases linearly at the rate around 8% per 100 m from the typical hub height to beyond common hub height. Based on the linear equation found in this study, the G extrapolated to the standard height of 10 m is approximately 1.3 which is also consistent with that measured at two buoys over the affected region. Therefore, a G of 1.3 at near surface may be useful for offshore wind energy R&D and O&M, particularly for those regions affected by tropical cyclones.

On the wind‐induced motion of unbonded fiber‐reinforced elastomeric isolators: Designing for habitability

A large number of studies have verified the satisfactory seismic performance of unbonded fiber-reinforced elastomeric isolators (UFREIs). Typically, the total height of a UFREI will be shorter than its conventional elastomeric isolator counterpart. The shorter height results in a relatively larger isolator initial horizontal stiffness. The relatively large initial stiffness and damping values of UFREIs might be potentially sufficient in many cases to meet the wind serviceability requirements. However, in real practice, this must be examined for any UFREI system. The purpose of this study is to examine the dynamic wind response of a real UFREI system that its satisfactory seismic response was previously verified through shake table tests. The stochastic wind excitations were simulated in the time domain based on the code-specified basic wind velocity, gust factor, and exposure category using the Cholesky decomposition technique. The root-mean-square (RMS) acceleration response of the UFREI system was calculated and then compared with the threshold of human comfort. The cases where the UFREI system could satisfy the wind serviceability requirements were determined. For the cases where the performance was found unsatisfactory, the wind response of the UFREI system was mitigated with the aid of a set of brittle fuses that serve as supplemental springs to increase the initial stiffness of the base isolation system. A simplified procedure is developed for the design of brittle fuses.

Reduced gust factor for extreme tropical cyclone winds over ocean

Information of gust factor (ratio between a short-duration peak gust wind speed to a long-duration mean) for extreme winds is of paramount importance for structural design and risk assessment. However, in-situ measurements were generally made for weak winds, and observations of gust factors for 10-min mean wind speeds over 50 ​m/s have been rarely reported, especially over the ocean. On August 23, 2017, the center of Super Typhoon Hato passed directly over an offshore island named Huangmaozhou in the South China Sea. An anemometer at the weather station on the island recorded a maximum 3-s gust wind speed of 84.2 ​m/s, 1-min mean wind speed of 74.0 ​m/s, and 10-min mean wind speed of 70.9 ​m/s during the typhoon. Based on the wind records from the anemometer, the variation of the gust factor with wind speed is examined in this paper. It was observed that for 1-min mean wind speeds between 10 and 70 ​m/s, the gust factor initially increased with increasing wind speed and plateaued at wind speed between 30 and 50 ​m/s before exhibiting a decreasing trend until 70 ​m/s. The reduced gust factor at very high wind speeds over ocean was observed and reported for the first time, which may have strong implications in tropical cyclone studies and engineering applications.

Observation of Typhoon Hato based on the 356-m high meteorological gradient tower at Shenzhen

Field measurements of tropical cyclone (TC) at coastal areas are of great significance for the prevention and control of TC disasters. Despite the increasing efforts on this topic in the last years, studies based on fast-response records of TC wind at multiple heights over land are still limited. To this end, a 365 ​m high meteorological observation gradient tower at Shenzhen has been constructed and put into use since 2016. It is currently the tallest mast tower in Asia and the second tallest of this kind in the world. There are 13 levels of instruments installed in a range of 10 ​m–350 ​m on the mast, to measure various weather elements at a sampling frequency utmost to 10 ​Hz. This paper presents an observational study on the wind characteristics of Typhoon Hato which made landfall with an intensity of severe typhoon at a distance of ~90 ​km from the tower on Aug. 23, 2017. The vertical profiles of mean wind speed and typical wind turbulence quantities, i.e., gust factor, turbulence intensity, integral length scale, etc., are demonstrated and compared against provisions stipulated in wind load codes. The effects of thermal stratification on these quantities are stressed.

Effects of sensor response and moving average filter duration on maximum wind gust measurements

The use of wind speed data recorded using different measuring equipment (i.e. anemometers with different response characteristics) and different signal-processing procedures can introduce errors in the characterisation of surface wind speeds. This study aims to assess the effects of a set of various moving average filter durations and turbulence intensities on the recorded maximum gust wind speeds. For this purpose, a series of wind-tunnel experiments was carried out on the widely-used Vaisala WAA151 cup anemometer. The variations of gust and peak factors, and turbulence intensities measured by the cup anemometer as a function of the averaging duration and turbulence intensity are presented. The wind-tunnel results are compared with values computed from a theoretical approach, namely random process and linear system theory, and the results were also validated against values reported in the literature where possible. The results show that the maximum gust wind speeds measured using large averaging durations (e.g. 3 s or 5 ​s) lead to up to 25%–30% negative biases compared to high frequency measurements (e.g. 4 Hz unfiltered gust measurements). This result can strongly impact subsequent meteorological, climatological and wind engineering studies, as different gust definitions have been adopted by National Weather Services and institutions around the world. Lastly, a set of correction factors (i.e. gust factor ratios) have been proposed that allows measurements at a specific gust duration to be converted to equivalent measurements at specified particular gust durations of interest.

Wind characteristics atop Shanghai Tower during typhoon Jongdari using field monitoring data

In this paper, detailed analysis of field wind data atop the Shanghai Tower is conducted to investigate the wind characteristics evolution generated by typhoon Jongdari, which can provide useful information for high altitude wind features in dense building landform to aid wind-resistant design of 600 m + super-tall buildings. The necessity of data preprocessing is discussed, and some precautions for processing wind directions are pointed out. Correlations of the mean wind speeds in different averaging times are analyzed using a non-stationary wind velocity model. The fluctuation wind characteristics at evolutional stages of the typhoon, including turbulence intensity, gust factor, integral scale of turbulence and power spectrum, are discussed and compared with several typhoons measured atop other super-tall buildings. Based on analysis, the ratio of the mean wind speeds between 10 min and 1 h averaging times remains stable. It is found that there is a slight difference between the linear and nonlinear fitting of three longitudinal parameters (i.e., the gust factor, turbulence intensity and gust duration time), but obvious error exists as to the linear fitting of the lateral parameters. Statistical results of the turbulent integral scale reflect relatively violent excitation of the turbulent wind to the structure, and the spectra of turbulent velocity are associated with various characteristics in different stages of the typhoon.

Observational study of wind characteristics, wind speed and turbulence profiles during Super Typhoon Mangkhut

On the basis of the wind records from 356-m-high Shenzhen Meteorological Gradient Tower (SZMGT) which is the tallest of its kind in Asia, this paper presents an observational study of wind characteristics during Super Typhoon Mangkhut and aims to enhance the understanding of the boundary layer wind structure of strong typhoons over land. First of all, the raw records are selected for subsequent analysis through quality control concerning flow distortion, thermal stability, stationarity, and spikes. Then wind speed profiles, as well as their associations with upstream terrain conditions, are presented and discussed. Moreover, parameters for describing atmospheric turbulence, involving gust and peak factors, turbulence intensities, turbulence integral length scales, and turbulence ratios, are investigated considering different surface roughness regimes. Furthermore, Gaussianity, power spectral density, and coherence of wind velocities are investigated. The outcome of this study is expected to facilitate the wind-resistant design of high-rise structures in typhoon-prone regions and provide references for typhoon boundary layer simulation.