Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Civil and Environmental Engineering
Supervisor
Zhou, Wenxing
2nd Supervisor
Hong, Hanping
Co-Supervisor
3rd Supervisor
Shang, Qiulin
Co-Supervisor
Abstract
Thunderstorm wind speed varies rapidly, resulting in the time-varying mean wind speed and direction for the alongwind, and fluctuating alongwind, crosswind and vertical wind. The amplitude and frequency contents of fluctuating wind speeds are also time-varying, at least for the fluctuating alongwind and crosswind. This thesis proposed approaches for analyzing, modelling, and simulating thunderstorm winds with respect to their time- and directional-variation of the alongwind speed and direction, as well as the multidirectional fluctuating winds. The analysis and decomposition of thunderstorm winds were carried out using continuous harmonic wavelet transform and Fourier transform. The analysis results indicated that the power spectral density (PSD) functions of the fluctuating winds depend on the time-varying mean wind speed, and the fluctuating components can be treated approximately as Gaussian. Based on the time-frequency spectral analysis, the PSD functions and lagged coherence functions for the fluctuating winds in the alongwind and crosswind directions in the horizontal plane are developed; new empirical models for the time-varying mean wind speed in the alongwind direction and its corresponding direction are also established. This model was then extended to tri-directional thunderstorm winds, which involves determining the time-varying mean wind speed and direction by considering both azimuth and elevation angles and analyzing the spectra of high-frequency wind components in three orthogonal directions. The simulation of bi- or tri-directional thunderstorm winds based on the proposed models are illustrated and validated by numerical examples.
In addition to the development of stochastic models for thunderstorm winds, this thesis also develops record-based simulation methods for simulating multivariate thunderstorm winds; the methods make use of the instantaneous features of limited available data. The developed procedure is based on the framework of the iterative power and amplitude correction algorithm but with modifications and considers different time-frequency decomposition techniques. The modifications are aimed at increasing the variability of the sampled record components by randomizing the power spectral density functions of processes through a digital filter in the frequency domain, and improving the convergence by using a relaxation factor for the synchronized phase shift.
In addition to the analysis, modelling and simulation of the multi-component thunderstorm wind record, statistical analysis is carried out to investigate the effects of the time-varying mean wind speed and direction, and the nonstationary fluctuating components of thunderstorm winds on the extreme peak wind pressure and wind pressure coefficient for a low building by applying the equivalent-steady-gust model and the quasi-steady-vector model. The effect of the random orientation of wind direction on the estimated extreme wind pressure coefficient is also investigated. The gust front wind loading factors considering thunderstorm winds and atmospheric boundary layer synoptic winds are assessed based on probabilistic analysis.
Summary for Lay Audience
Thunderstorm winds have the potential to cause damage to buildings and infrastructure systems. The statistical characterization of the thunderstorm winds is important for its simulation to augment the limited actual recorded thunderstorm wind time histories. The variation in time of the thunderstorm winds differs from that of the synoptic winds; the thunderstorm wind speed projected in two horizontal orthogonal direction and a vertical direction are all important for structural engineering applications.
This thesis is focused on the analysis, modelling and simulation of the multi-component thunderstorm winds. The analysis decomposes the recorded time histories in time and frequency. The statistics of the decomposed thunderstorm winds are used as the basis to develop new models to represent the random nature of the thunderstorm wind; such a model was previously unavailable in the literature. The simulation of the thunderstorm winds is then carried out based on the developed models. Additionally, a novel seed record-based simulation technique is proposed to generate multi-component thunderstorm winds. The technique is a modified version of the iterative power and amplitude correction algorithm; it uses several time-frequency transform pairs. The adequacy of the developed model and the efficiency of the proposed simulation technique are shown through numerical examples. Finally, the evaluation of the extreme peak wind pressure and pressure coefficients on a low-rise building subjected to thunderstorm winds is carried out. The analysis revealed a few interesting statistical features of the extreme wind pressure coefficient. The results also allowed the development of new relations between the wind loading effects induced by thunderstorm winds and by the synoptic winds. The implication of the results for structural design subjected to thunderstorm wind load is highlighted.
Recommended Citation
Liu, Yongxu, "Analyzing, modelling and simulating nonstationary non-Gaussian thunderstorm winds and their use for assessing the statistics of extreme wind pressure" (2024). Electronic Thesis and Dissertation Repository. 9965.
https://ir.lib.uwo.ca/etd/9965
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