Journal of Wind Engineering and Industrial Aerodynamics最新文献

The characteristics of the multivariate wind loads field on the roof are crucial to the wind-resistant design of low-rise buildings, which contain the correlation characteristics in space and probability characteristics in the time domain. This paper proposes a framework for constructing a Joint Probability Density Function (Joint PDF) model for a multivariate wind loads field. It provides a detailed correlation analysis for the first time. This paper employs wind pressure data collected from the roof of a low-rise building during Typhoon Muifa. It was found that the correlation becomes more robust with increasing roof pitch and the wind pressures are strongly correlated with a correlation coefficient exceeding 0.50 when the roof pitch is above 15°. The mixture distribution model is applied to the probability density function fitting procedure of wind pressure time series under typhoon climate, and the fitting effect is significantly better than other classical probability density functions. The optimal copula function is determined according to the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) for estimating the Joint PDF. The results reveal that Gumbel-copula and Student-copula have the highest proportion in optimal copula functions, accounting for over 90% of the total copula functions. Then, a bivariate Joint PDF for wind pressures are established with the optimal copula function. Additionally, the comparison between measured bivariate Joint PDF and that constructed using copula functions verifies the accuracy of the proposed framework for constructing Joint PDFs. The Joint PDF of wind pressures can enhance the understanding of the stochastic characteristics of local wind load fields on roofs, and the correlation characteristics in space provide crucial references for improving the accuracy of wind load random field simulation and saving the cost of wind resistance design.

The wind loading provisions in the National Building Code of Canada (NBCC) have not been updated for decades despite developments in wind tunnel methods since the original source data. This study aims to review the Nbcc 2020 provisions compared to wind tunnel experiments, field measurements, and the ASCE 7–22 provisions for single and multi-span gable roof buildings. Field measurements and wind tunnel tests are used to collect data for an isolated building and later for a multi-span gable. The pressure coefficients from the field measurements were mostly higher than the wind tunnel, which is consistent with previous studies. The results provided evidence that NBCC provisions for single-gabled roofs (with slope $7^{\circ }<\alpha \le {27}^{\circ }$) and multi-span gabled roofs (with slope ${10}^{\circ }<\alpha \le {30}^{\circ }$) are currently underestimated. New provisions are suggested for the corner (c), edge (s), and field (r) zones of the single-span gabled roof and for gable-end-edge (s’) zone of the multi-span. It is suggested to merge Zone s into Zone c to form a new perimeter Zone p for the single gabled roof and to merge Zone s’ into Zone c for the multi-span gabled roof. The proposed changes correct the current provision underestimation and add simplicity for easier construction.

The present model on two-cell tornadoes generalizes the one-cell model of Baker and Sterling (2017) by introducing a sharpness parameter. However, we model only the outer cell. The idea was derived from Vatistas et al. (1991) model which showed that larger values of the sharpness parameter increase the sharpness of azimuthal velocity near the periphery of maximum azimuthal velocity. This generalization brings about the cherished change, which helps better fit to tornado motion. Natural tornadoes can fit different values of the sharpness parameter, indicating the limitations of Baker and Sterling’s model. The fluid is considered Newtonian, incompressible, and non-viscous while the motion is steady. Major changes concerning the sharpness parameter are observed in the axial velocity component which behaves differently for one-cell and two-cell tornadoes in two cases, i.e., parameter less than one and parameter greater than or equal to one. A remarkable observation is that the strongest updraft shifts towards the periphery of the maximum radial velocity. Moreover, the radial profile of pressure difference at the reference height behaves quite differently for two-cell tornadoes. Furthermore, sharpness parameter affects the distance traveled by flying debris and the time taken by falling debris to reach the ground.

The multi-cross-section steel tube lightning rod (MSTLR) in the substation are susceptible to along-wind buffeting and vortex-induced vibration due to their inherent flexibility, low damping properties and multi-circular-section. This paper conducted a wind tunnel experiment on a 1:5 aeroelastic model of MSTLR under three wind fields with different turbulence intensity (uniform, 4.0%, and 7.0%). The amplitude, PSD, time-frequency curves, frequency components, and trajectory of wind-induced vibration are analyzed by measuring the acceleration responses at different heights and bottom reaction responses in the along-wind and cross-wind directions. A comparison was made between the relevant wind load parameters and those specified in the Eurocode. The results indicate that the distribution of the key participating modes exhibits different patterns with the variance of wind speed and turbulence intensity. Multi-order vibrations and structural coupling in orthogonal directions are observed with total response higher than the Eurocode. With the increase of turbulence intensity from 4.0% to 7.0%, the contribution of turbulence to along-wind acceleration response reaches saturation and has the opposite effects. When the speeds are 21.55 m/s and 27.33 m/s, respectively, the vortex-shedding frequencies of section 2 and section 3 coincide with the second-order natural frequency, and the vortex-induced resonance occurs. Those two vortex-induced resonances lead to a sudden increase in the standard deviation of the cross-wind response.

Recent advancements in data-driven aeroelasticity have been driven by the wealth of data available in the wind engineering practice, especially in modeling aerodynamic forces. Despite progress, challenges persist in addressing free-stream turbulence and incorporating physics knowledge into data-driven aerodynamic force models. This paper presents a hybrid Gaussian Process (GPs) methodology for non-linear modeling of aerodynamic forces induced by gusts and motion on bluff bodies. Building on a recently developed GP model of the motion-induced forces, we formulate a hybrid GP aerodynamic force model that incorporates both gust- and motion-induced angles of attack as exogenous inputs, alongside a semi-analytical quasi-steady (QS) model as a physics-based prior knowledge. In this manner, the GP model incorporates the absent physics of the QS model, and the non-dimensional hybrid formulation enhances its appeal from an aerodynamic perspective. We devise a training procedure that leverages simultaneous input signals of gust angles, based on random free-stream turbulence, and motion angles, based on random broadband signals. We verify the methodology through analytical linear aerodynamics of a flat plate and non-linear aerodynamics of a bridge deck using Computational Fluid Dynamics (CFD). The standout feature of the presented methodology is its applicability for aeroelastic buffeting analyses, showcasing robustness when handling broadband excitation. Importantly, the non-linear hybrid model preserves its capability to capture higher-order harmonics in the motion-induced forces and remains applicable for flutter analysis, while incorporating both motion and gust angles as input. Applications of the methodology are anticipated in the aeroelastic analysis and monitoring of slender line-like structures.

This study presents an innovative approach employing an iterative Unscented Kalman Filter (IUKF) for the identification of amplitude-dependent nonlinear aerodynamic damping using wind tunnel free vibration data. The wind-structure interaction system is represented as a single-degree-of-freedom system, with the amplitude-dependent aerodynamic damping modeled as a polynomial function of structural displacement and velocity. The augmented state variables, encompassing structural vibration frequency and polynomial coefficients for aerodynamic damping, are concurrently estimated from free vibration data using the UKF technique. To enhance the robustness of the identification results against variations in initial conditions, the UKF is applied iteratively by assigning the estimated polynomial coefficients as new initial values for the state variables. Validation of the IUKF-based method is performed through a numerical example featuring a typical bridge deck sectional model, as well as experimental data from two spring-suspended sectional models experiencing vertical vortex-induced vibration (VIV) and torsional post-flutter limit cycle oscillation. The feasibility of identifying amplitude-dependent aerodynamic damping for amplitude range not covered by the displacement signal is examined.

Successful application of large-eddy simulation for wind load evaluation of ground-mounted solar panels (GMSPs) requires rigorous benchmark validation. A validation campaign exploring several LES parameters and wind tunnel model details is underway. This study is carried out on a $25°$ tilt isolated GMSP with wind tunnel data as a target. The main LES parameters investigated are mesh size, solver time-step, time-discretization scheme, and the fetch distance from the inlet. A detailed geometric parametric study is conducted to explore the impact of the pressure tubing bundles and support structures of wind tunnel models on aerodynamics. It was found that the combined effects of mesh size, solver time-step, time-discretization scheme, and sampling frequency control the maximum reduced frequency modeled by LES. The pressure tubing bundles significantly altered the lower surface pressure pattern and magnitude, increasing local mean pressure by up to $50\%$ compared to a suspended flat plate. Comparison between the final validated case and the target wind tunnel shows an agreement within $5\%$ for wind field parameters at the reference height and within $\pm 15\%$ for mean and peak surface pressure coefficients. This study's findings will enhance the next phase of benchmark validation on an array of GMSPs in various geometric configurations.

Strong winds are one of the major causes of structural damage inflicted by thunderstorms. Specialized agencies and research groups regularly provide post-disaster damage assessment reports after a severe thunderstorm has passed over an area. If the observed structural damage was caused by severe winds, an assessment of the characteristic wind gust is provided based on the wind engineering analysis of the damage. Given that high-frequency anemometer measurements of wind speed are practically never available at or close to the observed damage, this study investigates the following question: What would an anemometer measure during the storm if it was installed at the location of the observed damage? This paper presents two models for thunderstorm wind time series reconstruction based on the observed damage. One model is a simple analytical equation that provides a closed-form solution to relate the estimated wind gust that caused damage to the mean wind speed and instantaneous peak during the storm. Another model is uses constrained stochastic simulations that are based on power spectral density of turbulent winds to reproduce a thunderstorm wind record that is in statistical sense indistinguishable from a measured wind. The constrain in the stochastic model is the value of the reported dameging wind gust. The models are validated against measured thunderstorm wind records and used to reconstruct thunderstorm wind time series from the damage data.

This study examines aerodynamic performance enhancement of Vertical Axis Wind Turbine (VAWT) blades with Gurney flap (GF) modified by slits. A quasi-3D computational fluid dynamics solution based on Reynolds-averaged Navier-Stokes model is employed to evaluate the effectiveness of slit GF blades, in particular the lift-to-drag ratio. The computational domain includes three pairs of GFs and slits combination along the blade span-wise direction to allow quasi-3D flow development while applying translational periodic boundary condition on the two end-wall boundaries. The inlet velocity is 9 m/s for a VAWT configuration with Tip Speed Ratios (TSRs) of 1.44, 2.64, and 3.3, respectively and each of these TSRs represents low, medium, and high regimes of TSRs. Simulation results have shown a significant 8% drag reduction for blades with slit GFs at medium range of TSRs, albeit with a 2% decrease in lift compared to blades with clean GFs. This improves the lift-to-drag ratio and enhances moment production. The power generation also shows increases of 1.5%, 6.5%, and 11.3% at low, medium, and high TSR regimes, respectively, for the analysed slit GF blades. The drag reduction is primarily attributed to the generation of small-scale vortices by the slit, dissipating large coherent flow structures more rapidly in the near wake-field.

In the current research, the turbulent flow field and wake characteristics around a realistic heavy duty truck model and at a practical Reynolds number Re = 2.6 × 10⁶ (calculated using the free-stream velocity and the square root of the truck's frontal area) has been investigated using large eddy simulation based on an experimental wind-tunnel study conducted by National Research Council of Canada. The primary focus of this study is examining the budget terms and energy transfer from large-scale structures to the smaller scales. Major flow features and complex three-dimensional flow topology were investigated using qualitative and quantitative tools. Due to boundary layer separation, the downstream wake region was characterized by a quadrupole mean vortical structure. Evolution of budget-balance terms of turbulent kinetic energy (TKE) transport downstream of the truck model and the TKE distribution were thoroughly investigated revealing the influence of corner flow separation, side shear layer evolutions and rooftop boundary layer separation. The level of the budget terms was observed to be strongly influenced by the downstream propagation of the large-scale vortical structures. Furthermore, a frequency analysis was conducted on different components of integral aerodynamic force on the truck model and on several velocity and pressure probe data downstream of the truck model. The important Strouhal numbers indicating the correlation between flow separation, vortex shedding, and aerodynamic forces were identified.