Gust Factor Research Articles

Comparison of Atmospheric Turbulence Characteristics over Sea Surface and Land Surface before, during, and after Typhoons

The goal of the paper is to reveal discrepancies of turbulent variables over different surfaces (sea, island, land) based on the measurements taken on three towers during (including before and after) seven typhoon episodes from 2008 to 2018. The atmospheric stability, turbulent spectrum, friction velocity, turbulent kinetic energy, dissipative heating, and gust factor are examined. The similar turbulent characteristics over sea and on the island reinforce the previous conclusion that the turbulent measurements on the island mainly represent the sea surface. The turbulent characteristics over sea and on land are very different due to the different underlying surface roughness. The unstable (stable) condition dominates on the sea (land) surface. Turbulent spectra both over sea and on land follow the canonical Kolmogorov’s power law with the −5/3 slope. The cospectra on land are more peaked than those over sea. All of the friction velocity, turbulent kinetic energy, and dissipative heating increase with increasing 10 m wind speed, and those on land are much larger than those over sea. The distributions of gust factors widen and shift to higher on land than those over sea. The distributions of gust factors at heights of 10 m and 40 m are biased to higher values than those at heights of 160 m and 320 m on land.

Field-measurement-based local wind field characteristics on bridge deck of truss girder bridges in a deep-cutting gorge bridge site area

Affected by many factors, the local wind environment on the bridge deck is complex and changeable, and it seriously threatens traffic safety. To accurately evaluate the wind field on the bridge deck, this paper develops a system to monitor the actual local wind environment and applies it to field measurement of the wind parameters at different positions of a complex truss girder bridge. The results show that the wind parameters on the bridge deck, including wind speed, gust factor, and turbulence intensity, are different from the bridge site due to the influence of the ancillary facilities. Also, the wind profile of the local wind field on the bridge deck is more in line with the polynomial distribution, which makes the equivalent height of the wind load much higher than the vehicle gravity. It should be noted that the measured power spectrum of the bridge deck is quite different from the wind spectrum applicable to the bridge site area, so it is not appropriate to use the wind spectrum of the bridge site area to carry out the analysis of the windmill bridge, and a more suitable wind spectrum for bridge deck wind field is proposed.

CFD evaluation of mean and turbulent wind characteristics around a high-rise building affected by its surroundings

This study comprehensively investigated the accuracy of computational fluid dynamics (CFD) simulations for predicting the mean and turbulent wind characteristics around a high-rise building surrounded by low-rise street canyons. The flow field was characterized based on the complicated interaction between a high-rise building and its surrounding buildings, which has rarely been examined in previous CFD studies. We obtained the CFD results using steady Reynolds averaged Navier-Stokes equation (RANS) models and large eddy simulations (LES), which were compared with the measurement results obtained via wind tunnel experiments. Furthermore, we quantitatively investigated the impact of the presence of a high-rise building on the prediction accuracy of pedestrian wind environments, including the gust wind velocity. The results showed that the performance of both LES and RANS decreased in the presence of a high-rise building, indicating that predicting the flow around a high-rise building is more challenging than predicting the flow of a simple street canyon. Additionally, the prediction accuracies of RANS and LES for the mean wind velocity at the pedestrian level were similar in regions with high wind velocity. However, the prediction accuracy of LES in the medium- and low-wind-velocity regions was significantly better than that of RANS, which is closely related to the superior prediction accuracy of turbulent kinetic energy in LES. Although LES can predict the gust wind velocity directly with higher accuracy than that of RANS by using a gust factor, RANS can be used to predict the gust wind velocity with a certain accuracy using a peak factor.

Estimating low-occurrence wind speeds from mean velocity and turbulent kinetic energy: Development of statistical method and validation with idealized cases

A novel statistical method (namely KB method) for estimating low-occurrence strong wind speeds (LOSWSs) from mean wind velocity and turbulent kinetic energy (TKE) was developed in this study. An isolated building case and a building array case from a large-eddy simulation (LES) database were used for the statistical analysis and validation. The statistics including the coefficient of variation (CV), peak factor (PF) Kq and gust factor (GF) Gq were analyzed. It was found that the relationships of the CV to the PF and GF of the LES results are close to the theoretical relationships of the two-parameter Weibull distribution (2W). The LOSWSs sq with q = 10%, 1% and 0.1% have positive correlations with the mean wind speed ⟨s⟩ and have negative correlations with Gq. The KB method was proposed based on 2W. The shape parameter β of 2W was estimated as an empirical function of the TKE ratio k/(K+k), where K and k are the mean and turbulent kinetic energy, respectively. Then, the estimated β was used for calculating the theoretical gust factor of 2W. Finally, the LOSWS was calculated from the estimated gust factor and mean wind speed. By using the mean wind velocity and TKE from the LES database, the KB method showed high accuracy for estimating the LOSWSs with q = 10%, 1% and 0.1%. Relative errors were within 20% at most points.

Predicting Peak Wind Gusts during Specific Weather Types with the Meteorologically Stratified Gust Factor Model

Abstract Wind gusts present challenges to operational meteorologists, both to forecast accurately and also to verify. Strong wind gusts can damage structures and create costly risks for diverse industrial sectors. The meteorologically stratified gust factor (MSGF) model incorporates site-specific gust factors (the ratio of peak wind gust to mean wind speed) with wind speed and direction forecast guidance. The MSGF model has previously been shown to be a viable operational tool that exhibits skill (improvement over climatology) in forecasting peak wind gusts. This study assesses the performance characteristics of the MSGF model by evaluating peak gust predictions during several types of gust-producing weather phenomena. Peak wind gusts were prepared and verified for seven specific weather conditions over an 8-yr period at 16 sites across the United States. When coupled with two forms of model output statistics (MOS) wind guidance, the MSGF model generally shows skill in predicting peak wind gusts at forecast projections ranging from 6 to 72 h. The model performed best during high pressure and nocturnal conditions and was also skillful during conditions involving snow. The model did not perform well during the “rain with thunder” weather type. The MSGF model is a viable tool for the operational prediction of peak gusts for most gust-producing weather types. Significance Statement Wind gusts are an important and potentially costly environmental hazard. Wind gusts affect many industrial sectors, including transportation, power generation, forestry, construction, and insurance, but predicting gusts remains a challenging component of weather forecasting. Recent studies have demonstrated that the meteorologically stratified gust factor (MSGF) model shows skill in predicting peak gusts. This study shows that the MSGF model is skillful at predicting peak gusts during specific types of gust-producing weather phenomena at forecast projections up to 72 h, providing further confirmation that the MSGF model is a viable tool for the operational prediction of peak gusts.

Experimental Study of the Fluctuating Wind Characteristics of Typhoon Jangmi Measured at the Top of a Building

Based on wind field data measured during the landfall of Typhoon Jangmi in Wenzhou in 2008, this study analyzes wind field characteristics, including wind speed, wind direction, probability density, turbulence intensity, gust factor, peak factor, power spectrum, turbulence integral scale, coherence, and the autocorrelation coefficient of Typhoon Jangmi. Results showed that the wind field characteristics for the east and west measuring points were basically the same and followed an approximately similar pattern. The probability density of fluctuating wind tends to obey a Gaussian distribution. The turbulence intensity gradually decreases with increasing 10 min averaged wind speed, but the reduction rate gradually drops. The turbulence intensity is affected by the change in a time interval because turbulence intensity decreases as the time interval increases. With an increase in the 10 min average wind speed and time interval, the gust factor decreases. The peak factor decreases, though insignificantly, with increasing mean wind speed, and the distribution of peak factors is greatly scattered. The variation in the peak factor with time is in good agreement with the Durst curve. The gust factor increases as the turbulence intensity increases and is in line with the empirical curves of Ishizaki, Choi, and Cao. The power spectra of the fluctuating wind speed of Typhoon Jangmi in all directions agree well with Von Karman’s empirical spectrum. The turbulence integral scale increases slightly with increasing average wind speed, and the distribution is relatively scattered. The coherence of the fluctuating wind speed components matches the exponential function proposed by Davenport, and the autocorrelation coefficient decreases as τ increases.

Establishment of Wind Gust Estimation Equation in Bohai Sea

Wind gusts over the ocean can have a great influence on maritime transport and production operations. However, owing to the scarcity of marine observation data and the complex causes of wind gusts, the estimation and forecasting of gusts at sea are even more difficult. In this study, a gust estimation equation applicable to the Bohai Sea is established based on observation and reanalysis data, with representative observation stations on the coast and offshore in the Bohai Sea. During the process, partial correlation analysis and a significance test of correlation coefficient differences were used to further clarify the influence of average wind speed and vertical wind shear at different heights on wind gusts. The final gust estimation equation includes a mean wind speed term, a turbulence term, and a convection term, which are statistically significant contributors; in addition, there are clear physical meanings. Comparing two gust factor methods in this study, the average errors and fitting errors of the least squares gust estimation equation are the smallest. For wind gusts between 10 and 26 m/s, the fitting error in the gust estimation equation is 7.68–12.25% and 21.10–30.08% lower than those of the two gust factor methods in this study. The gust estimation equation better reflects the difference of wind gusts typical under different average wind speeds and vertical wind shear conditions, so a better prediction for wind gusts can be achieved.

Monitor wind characteristics and wind‐induced responses of a skyscraper during two typhoons

SummarySkyscrapers are wind‐sensitive structures due to their large slenderness ratio and good flexibility. Understanding the wind characteristics and wind‐induced response from the actual data provides first‐hand information for wind resistance design. This paper reports the wind properties and dynamic performance of a 632 m high‐rise building in Shanghai during the passage of typhoons Jongdari and Rumbbia. Field measurements obtained from the structural health monitoring system include acceleration and wind speed. The data analysis of turbulence intensity, turbulence integral length, and gust factor are compared and discussed. For the identification of dynamic characteristics, the stochastic subspace method and enhanced frequency domain decomposition method are employed to identify the modal parameters. Besides, the comfort assessment using peak value and root mean square of accelerations is compared with different standards. Studying the wind characteristics during the passage of typhoons and their impact on high‐rise buildings in a metropolis is expected to gain an insight into the dynamic mechanism of high‐rise buildings and collect a database for wind resistance design in typhoon‐prone regions.

Distributions of gust and peak factors at a pedestrian level in a simplified urban canopy obtained by particle image velocimetry

The complex velocity fields within an urban canopy affect the occurrence of rare weak and strong wind-speed phenomena at the pedestrian level. Although particle image velocimetry (PIV) is widely used to determine velocity components, it has not been applied to pedestrian spaces for rare wind events, owing to the surrounding buildings. Therefore, in this study, two velocity components within a simplified urban canopy layer were measured using time-resolved PIV by inserting a laser optics system into a focal block. We determined the turbulent statistics, probability densities, gust factor (GF), and peak factor (PF) at the pedestrian level within the canopy layer. The probability density functions of the velocity components at positions with a lower mean wind speed tend to be negatively skewed, whereas those at positions with a higher mean wind speed tend to become closer to the Gaussian distribution. The GF values are small in the regions where a larger velocity is observed. However, the PF shows less distribution than the GF, regardless of the measurement position. Owing to the importance of strong gusts, the PF could be a more useful index for evaluating strong winds speed within the urban canopy layer.

Wind Gusts Associated with Tornado-Scale Vortices in the Tropical Cyclone Boundary Layer: A Numerical Simulation

It has been demonstrated that the tornado-scale vortex (TSV) is one of the fine-scale structures associated with extreme updrafts in the tropical cyclone boundary layer (TCBL), but the relationship between surface wind gusts and TSVs is still unclear. In this study, the one-second model output simulated in the Weather Research and Forecast (WRF) model with the large eddy simulation (WRF-LES) is used to investigate the relationships between TSVs and surface wind gusts. Results show that surface wind gust factors in the regions where TSVs are prevalent are significantly larger than those in other regions. 88% of the maximum gust factors associated with TSVs (vertical velocity larger than 20 m s−1) are larger than 1.25 (gust factors larger than 1.25 account for only 1% of the 1-min gust factors in the TC inner core), and the mean maximum 1-min gust factor associated with a TSV is larger than 1.3, while the mean 1-min gust factor in the TC inner core is only 1.1. The surface gust factors associated with TSVs in tropical cyclone eyewall can reach about 1.8, which can cause severe surface wind hazards. This study suggests that potential risk will increase in the regions where TSVs are prevalent because of the large wind gusts and gust factors. Finer real-time observations are needed to monitor the evolution of TSVs for improving the operational TC-related surface gust warnings.

Analysis of Turbulence Parameters of Typhoon Morakot along the Southeast Coast of China

The southeast coastal region of China is frequently affected by typhoons. The observation station was chosen to be located on the roof of Wenzhou University’s architectural engineering building to collect real-time wind speed data during the landfalling of Typhoon Morakot to investigate the properties of the near-ground wind field of typhoons. The turbulence characteristics of the near-ground wind and its variation with time intervals are analyzed on the basis of real-time measured data. The results show that the turbulence intensity only changes with the mean wind speed under relatively low wind speeds. The gust factors exhibit a scattered distribution under low wind speeds and tend to cluster together when the wind speed exceeds 8 m/s. With increasing time intervals, the turbulence intensity and the gust factor gradually decrease. The relationship between turbulence intensity and gust factor is obtained by the measured data and then compared with the empirical formulas. The peak factor remains constant while the mean wind speed changes, but diminish as the time intervals rise. The turbulence integral scale of typhoons slightly increases with the increasing mean wind speed, and its value falls between 70 and 150.

Dynamic Analysis of High-Rise Structures with Outrigger Structural System Subjected To Lateral Loads

In this age of urban development and rapid modernization the need of high-rise structures is rapidly increasing as buildings have gotten taller and narrower, the structural engineering has been increasingly challenged to meet the desired stability requirements. In tall buildings, stiffness is the key to sustainability, among various types of structural systems available for tall buildings, outrigger system is one of the majorly used efficient system. The present study aims to identify the efficiency of outrigger shear walls and to find out the optimum position of outriggers in high rise structures under lateral loads. The outrigger systems are required to have additional stiffness and adequate damping, by which outrigger can be used as a structural fuse to protect the building under severe earthquake and wind conditions.This research work aims to study the dynamic analysis of high-rise structures with outrigger structural system, for this research two regular buildings of 36 & 50 storeys situated in seismic zone V having a constant area of 900sqm(30mx30m) with a typical storey height of 3m were analysed using ETABS 2018. Optimum position of outrigger is determined by considering 8 models in which positions of outriggers is varied along the building height. Response spectrum analysis is carried out to evaluate the performance of structure for earthquake loads and the Gust factor method is used for the dynamic analysis of wind loads. Parameters such as Modal Mass Participation, Base Shears, Storey Displacements, Storey Drift, Time-periods, and acceleration are compared. Upon comparison it was found that among all 36 storey models outriggers placed at extreme ends performed better than other models and among all 50 storey models’ outriggers placed at regular intervals has performed better to all other models.

Nonstationary near-ground wind characteristics and wind-induced pressures on the roof of a low-rise building during a typhoon

Wind fields in the surface layer during typhoons usually have strong nonstationary features, which cause damage to low-rise buildings, especially their roofs. It is thus required to establish accurate models of typhoon-generated near-surface wind fields and assess typhoon effects on low-rise buildings. In this paper, a framework of extracting time-varying mean component and determining time-varying fluctuating component of nonstationary signals is established, which is applied to investigate the on-site measured near-ground nonstationary wind velocities and wind-induced pressures on the roof of a typical low-rise building during a typhoon. It is observed that near-ground wind characteristic parameters (including turbulence intensities, gust factors, peak factors and turbulence integral length scales, wind spectra) and wind pressure coefficients on the roof obtained by the nonstationary analytical approach are more reasonable than those determined by the conventional stationary analytical approach. Besides, the evolutionary power spectral density is used to examine time-frequency spectra of wind velocities and wind pressures. This comparative study based on the nonstationary and stationary analysis approaches aims to further the understanding of the nonstationary surface layer wind characteristics and wind pressures on typical low-rise buildings for reduction of windstorm damages to residential buildings in typhoon-prone regions.

Assessment of gust factors and wind speed decomposition methods for thunderstorms

This paper examines wind decomposition methods for nonstationary thunderstorms based on the frequency responses. A wide range of methods have been used for this task, including weighted-average methods, Savitzky-Golay filters, and multi-resolution techniques. Two problems arise in the evaluation: (1) how to decide which methods are good, and (2) how to compare the wind properties from one decomposition to another. To determine the most suitable method, the overshoot and sharpness of their frequency responses are evaluated and compared. The half-power cutoff frequency is proposed to connect different methods, so that the wind properties, e.g., gust factor, can be compared. The choice of the cutoff frequency for thunderstorms is also examined with artificially generated nonstationary winds. Records from four thunderstorms are decomposed with the different methods and cutoff frequencies. The gust factors with different gust averaging times are calculated and compared with those for stationary winds. Underlying differences between the gust factor curves are also examined. Finally, the paper provides recommendations for the selection of decomposition method and cutoff frequency for nonstationary winds like those in thunderstorms.

Influence of Refined Wind Load Parameters and Wind-Loading Mode on Wind-Induced Responses of a Long Cross-Arm Angle-Steel Transmission Tower

This study aims to investigate refined wind load parameters on main rods and the influence of wind-loading mode on wind-induced responses of the angle-steel transmission tower. The wind load parameters discussed in this study include drag coefficients, wind load distribution factors and skewed wind load factors. To achieve the aim, wind tunnel tests were conducted to explore aerodynamic loads for integrated frame, single frame, and main rod models of cross-arm and tower body. The wind load parameters of the different models were investigated. In addition, a series of wind-induced vibration simulation was applied to examine the wind-induced responses of an ultra-high voltage (UHV) transmission tower with a long cross-arm under concentrated and distributed wind loads. The simulated results under the two types of wind loads were compared. The results show that the longitudinal drag coefficients of the main rods are smaller than the values of the integrated frame, and equivalent on average to the values of the single frame. The experimental shielding factor of the cross-arm is larger than those in different standards due to the joint drag effects of leeward, upper, and lower faces of the cross-arm in the wind tunnel test. The experimented shielding factor of the tower body is in line with those referring to the Chinese and AS/NZS standards, and slightly larger than those based on the British and JEC standards. The skewed wind load factors of the main rod models are quite different from other models for cross-arm and tower body. The wind-induced vibration simulation suggests that, the wind-loading mode has limited impact on the displacements, accelerations, and gust factors of the transmission tower, but significantly influences the maximum normal stresses (MNSs) of the rods’ cross-sections. The MNSs caused by the distributed wind loads are obviously greater than those caused by concentrated wind loads, especially for the rods at the two ends of the cross-arm.

Characterization of Wind Gusts: A Study Based on Meteorological Tower Observations

Accurate information on wind gusts is of critical importance to various practical problems. In this study, observational wind data from high-frequency response (i.e., at a sampling rate of 10 Hz), ultrasonic anemometers instrumented at four different heights (i.e., 10 m, 40 m, 160 m, 320 m) on a weather tower were collected. The observation site featured a typical suburban condition, with no significant obstacles in the immediate proximity. The data were analyzed to identify a total of twelve descriptors of wind gusts, and to find the parent distributions that estimate these parameters well via regression analysis. The results show that the gust parameters in the context of gust magnitude and amplitude with units are best fit by the Weibull model, while non-dimensional parameters in terms of gust factor and peak factor are reasonably assessed by the log-logistic distribution. The uplift time and gust nonsymmetric factor generally exhibit a lognormal distribution, while the Gamma distribution can describe the gust length scale, uplift magnitude and passage time. It is also shown that gust factors increase linearly along with turbulence intensity. Nevertheless, empirical linear formulas given in previous studies tend to over-predict. For the vertical structure of gust descriptors, it is found that the average wind speed, gust amplitude and gust length scale in 10 min monotonically increase with height, whereas the function relationship of gust amplitude, peak factor, gust factor, turbulence intensity, rise amplitude and falling amplitude tends to decrease with height.

Modeling Nonstationary Non-Gaussian Hurricane Wind Velocity and Gust Factor

This study estimated the wind gust factor and turbulence intensity for hurricane winds that are modeled as a nonstationary non-Gaussian process. The estimation considered the time-varying mean wind velocity, and the time–frequency decomposition using S-transform characterized the time-varying amplitude and frequency content of the fluctuating wind. Winds simulated by applying a newly developed algorithm were used to augment the sample size. Results indicate that the standardized power spectral density function of hurricane winds can be represented in terms of the reduced frequency but with time-varying mean wind velocity. The standardized fluctuating wind is only weakly non-Gaussian; the average skewness and kurtosis coefficients are not very sensitive to whether the 10-or 60-min time-varying mean wind speed is considered. The assessed relation between the gust factor and turbulence intensity indicates that such a relationship is influenced by whether the instantaneous aspect of the nonstationary process is considered. There is large uncertainty in the developed relationship. By removing samples associated with a low mean wind velocity, the largest value of the estimated gust factor decreases. The consideration of the non-Gaussian aspect of the fluctuating wind to estimate the gust factor could be important as turbulence intensity increases.

APPLICATION OF PSEUDO-STATIC METHOD TO DETERMINE WIND LOADING ON HIGH-RISE BUILDING IN VIETNAM

The paper presents method to determine wind load on a high-rise building by direct dynamic method (according to current Vietnam standard TCVN 2737:1995). At the same time, based on the design procedures of C. Dyrbye and S.O. Hansen, the authors proposed the formula to determine the gust factor for high-rise buildings with wind parameters according to TCVN 2737:1995 (wind profile, length scale, turbulence intensity, spectral density, power-spectral density function). Numerical example according to proposed formula to determine the gust factor and wind load.

Investigations on Wind Characteristics for Typhoon and Monsoon Wind Speeds Based on Both Stationary and Non-Stationary Models

Stationary models are usually applied for wind characteristics analysis. However, nonstationarity has been found in the field measurements of typhoons in recent studies; therefore, using traditional models with stationary assumptions to conduct wind characteristics is inadequate. In this research, data acquisition of typhoon wind speeds and monsoon are conducted based on the wind field measurements. Wind speeds of typhoon “Maria” passing through Pintan, Fujian Province, China and the monsoon from 2017.10–2018.10 were obtained to investigate wind characteristics. The run test method is utilized to show that non-stationarity exists in both typhoon and monsoon wind speed, and the percent of non-stationary increases with the increase in time interval. Additionally, results show that stronger non-stationarity exists in typhoon wind speed compared with monsoons. Based on a self-adaptive procedure to extract time varying mean wind speed, a non-stationary model is established to compare with the non-stationary model, which has been applied in the traditional wind characteristic analysis. The fluctuating wind characteristics such as turbulence intensity, gust factor, turbulence integral scale, and wind speed spectrum are analyzed to compare the two models. Results show that the difference of such characteristics between the two models increases with the time interval, indicating the necessity of consideration of non-stationary models, especially for design specifications with larger time intervals. Influences of time intervals are investigated, and relevant recommendations are provided for wind resistance specifications. Our conclusions may provide reference for wind resistance design in engineering applications.

Full-Scale Measurements of Wind Characteristics on a High-Rise Building during Typhoon Sarika

A full-scale measurement of wind characteristics atop a high-rise building (with a height of 115 m) was conducted during the passage of Typhoon Sarika on 18 October 2016. Wind field characteristics, wind speed, and wind direction atop the building were recorded synchronously, and turbulence intensity, turbulence integral scale, gust factor, and power spectrum were investigated. Meanwhile, the time and frequency domain characteristics of the wind field were analyzed. The stationarity test results of Typhoon Sarika at different time steps are researched in a runs test. And the time-frequency analysis of non-stationary samples of fluctuating wind speed are conducted by wavelet transform, the measured data are valuable for the wind-resistant design of high-rise buildings in typhoon-prone regions.