Observational study of wind characteristics, wind speed and turbulence profiles during Super Typhoon Mangkhut
Introduction
With the rapid development of construction materials and technologies, the past few decades have witnessed the erection of numerous high-rise buildings with heights over 200 m. As such tall structures are inherently vulnerable to wind actions, accurate estimates of wind loading are of paramount importance for their safety and serviceability. Considering that the wind loading on a structure is related to the wind velocity in a quadratic manner, a small error in the determination of wind velocity may be enlarged and threaten the structural integrity. Davenport wind loading chain (Davenport, 1961), which is adopted by many design codes and standards (e.g., ASCE 7-16, AIJ-RLB-2015, GB 50009-2012), formulates wind loadings and dynamic responses of structures based on the statistical characteristics of mean winds and atmospheric turbulence parameters which are quantitively expressed by wind speeds and directions, gust and peak factors, turbulence intensities and integral length scales, power spectra and coherences, etc. A thorough understanding of strong wind characteristics in the atmospheric boundary layer is therefore a prerequisite for the evaluation of design wind loadings of high-rise structures.
The design wind speed and turbulence profiles however vary between different codes and standards, partially because of various nature of extreme winds in different parts of the world (Simiu and Yeo, 2019). Extratropical gales that occur in the middle latitudes have been studied for around a half century and generally well understood (Holmes, 2015). In tropical regions, however, the extreme winds and wind actions on structures are mostly associated with tropical cyclones (or typhoons/hurricanes), which are vortex structures characterized by gusty winds, extensive sizes, and convective circulation and less well understood (Li et al., 2019).
Field observation is regarded as the most reliable way to investigate the wind characteristics, wind speed and turbulence profiles of tropical cyclones. Therefore, a few observational studies have been reported in recent years, the vast majority of which are based on (1) anemometers installed at/on meteorological stations, buildings, bridges, or cables (e,g., Cao et al. (2009), Shu et al. (2015), Li et al. (2016), Li et al. (2019), Zhao et al. (2019), and Wang et al. (2020)); (2) anemometers installed on towers (e.g., Hui et al. (2009a, 2009b) based on a 50-m-high tower; Li et al. (2015b) based on towers with heights ranging from 10 to 100 m; Song et al. (2016) based on towers with heights ranging from 70 to 112 m; Wang et al. (2017) based on a 40-m-high tower; Lin et al. (2018) based on a 50-m-high tower; Li et al. (2018) based on a 100-m-high tower; Fang et al. (2019) based on towers with heights ranging from 50 to 120 m); or (3) remote sensing instruments such as Doppler wind lidars and sodars (e.g., Tse et al. (2013) and Tsai et al. (2019)). It is noteworthy that anemometers at/on meteorological stations, bridges or cables are mostly limited within near-surface levels, while those on buildings usually suffer from flow distortion caused by the buildings. For remote sensing techniques, whether lidars and sodars can effectively measure wind speed and turbulence in adverse weather conditions during tropical cyclones is still controversial (Zhang et al., 2018; Liao et al., 2020). On the contrary, meteorological towers equipped with anemometers are favorable as they can offer promising multi-level wind records with high fidelity.
Nevertheless, due to high construction cost, meteorological towers with height above 120 m are rather rare, and almost all the previous tower-based studies of the wind structure of tropical cyclones utilized records from towers lower than 120 m. As a result, observations of the wind characteristics of tropical cyclones at comparable heights with high-rise buildings (over 200 m) have been rarely reported, and the wind speed and turbulence profiles of tropical cyclones for structural design of tall buildings and boundary layer simulation of tropical cyclones are still not firmly established. To address this issue, more high-quality, multi-level wind observations during tropical cyclones are urgently required. In this paper, on the basis of observational records from 356-m-high Shenzhen Meteorological Gradient Tower (SZMGT), which is the tallest of its kind in Asia, a comprehensive statistical study of wind characteristics during Super Typhoon Mangkhut is conducted. Vertical profiles of wind speeds, gust factors, turbulence intensities, and turbulence integral length scales as well as their associations with upwind terrain conditions are presented and discussed. Gaussianity, power spectral density, and coherence of wind velocities are also investigated. The outcome of this study is expected to contribute to the understanding of the wind structures of strong tropical cyclones, facilitate the wind-resistant design of high-rise buildings in tropical cyclones-prone regions, and provide references for boundary layer modelling of tropical cyclones in wind tunnel tests or numerical simulation by Computational Fluid Dynamics (CFD). In particular, the high-resolution, multi-level wind records obtained from 356-m-high SZMGT may benefit the wind demand characterization which is one of the essential steps for Performance-Based Wind Design (PBWD; ASCE, 2019). PBWD has the potential to overcome the drawbacks (generally too conservative design) of using current codes and standards for high-rise building design in tropical cyclone prone regions. The remainder of this paper is organized as follows. Section 2 introduces Super Typhoon Mangkhut, the observational site, and the observational records utilized in this paper. Section 3 describes the data quality control procedures. Sections 4 Mean wind characteristics and profiles, 5 Turbulence characteristics and profiles discuss the mean wind and turbulence characteristics of the typhoon, respectively. Section 6 summarizes the main findings and gives concluding remarks.
Section snippets
Typhoon Mangkhut
Typhoon Mangkhut (JMA: 1822, JTWC: WP262018) was the 22nd tropical cyclone developed over the western North Pacific in the year of 2018. Mangkhut formed as a tropical depression at 12°N, 170°E on September 7, 2018 and gradually intensified afterward. It developed into a super typhoon on 11 September and moved westward quickly. On the morning of 15 September, Mangkhut made its first landfall over Luzon, Philippines with a 1-min sustained wind speed (the highest mean wind speed over a 1-min span)
Data quality control
Before the quality control process, the raw three orthogonal wind components (ux, uy, uz) measured by CSAT3 were firstly separated into 10-min (or 1-h) segments, then transformed into the micrometeorological coordinates, where u (longitudinal wind speed) is aligned with the horizontal 10-min (or 1-h) vector mean wind speed, v (lateral wind speed) is parallel with the horizontal plane and perpendicular to u, and w (vertical wind speed) is oriented normal to the surface (Foken, 2008). The terrain
Evolution of mean wind speed and direction
The evolution of 10-min mean wind speed and direction measured by WMT703 is interpreted with contour plots in Fig. 7. The white-colored patches in the figure were caused by the lost measurements, and the shaded area represents the period when the wind measurements suffered from flow distortion caused by the tower structure (01:00–11:30/16). As shown in Fig. 7(a), the wind speed generally increased with height within 350 m above ground level, and low-level jets were not observed. The strongest
Turbulence characteristics
Parameters for describing turbulence characteristics of winds generally involve turbulence intensities, turbulence integral length scales, gust factors, and peak factors. Turbulence intensity (I) represents the ratio of wind speed fluctuation to the mean. Turbulence intensity affects the gust effect factor (G for rigid buildings or Gf for flexible buildings) in ASCE 7, which directly influences the calculation of design wind pressures. Compared with rigid buildings, errors in codified and
Conclusions
This paper presented an observational study of wind characteristics, wind and turbulence profiles during Super Typhoon Mangkhut based on the records from the 356-m-high Shenzhen Meteorological Gradient Tower. The analyzed results were compared with previous studies, existing models and structural design codes. The outcome of this study is expected to contribute to the understanding of typhoon wind structures, facilitate the wind-resistant design of high-rise buildings in typhoon-prone regions,
CRediT authorship contribution statement
J.Y. He: Conceptualization, Writing - original draft, Methodology. Y.C. He: Methodology, Investigation. Q.S. Li: Conceptualization, Writing - review & editing, Supervision, Funding acquisition. P.W. Chan: Investigation, Resources, Data curation. L. Zhang: Investigation, Resources. H.L. Yang: Investigation, Resources. L. Li: Investigation, Resources.
Declaration of competing interest
The authors declare that they have not known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The work described in this paper was fully supported by grants from the National Natural Science Foundation of China (Project No: 51978593) and from the Research Grants Council of Hong Kong (Project No: CityU 11207519).
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2023, Journal of Building EngineeringCitation Excerpt :It made landfall around 12:00 on 16th September when the storm exerted its greatest impact on the studied site. The maximum 10-min mean wind speed at the top of Zhuhai Center (324 m) was estimated as 46 m/s, in accordance with the field measurements from meteorological stations located around the studied site [25,26]. Meanwhile, easterly winds dominated during this period around the studied site, which corresponded to an open exposure (Fig. 1).