Aerodynamic coefficients and pressure distribution on two circular cylinders with free end immersed in experimentally produced downburst-like outflows:

Thunderstorms winds are localized and transient phenomena characterized by three-dimensional non-stationary velocity fields. While numerous studies investigated the wind loading on cantilevered structures under thunderstorm downburst winds, there is a lack of fundamental research on the behavior of simple circular cylinders subjected to downburst-like outflows. This paper investigates the pressure distribution and aerodynamic coefficients of two cylinders with different diameters immersed in three different types of wind: (1) isolated downburst (DB); (2) downburst embedded in an atmospheric boundary layer (ABL) wind (DBABL); and (3) steady ABL wind. The focus of this study is to provide a comparative analysis between aerodynamic coefficients (drag and lift) and surface pressures that result from these three different wind systems. The ABL winds caused a higher drag on the thinner cylinder than the two DB-like outflows. The lift coefficients during the primary vortex passage in the DB-like outflows were negative at the base of the cylinders and approached zero or to slightly positive values close to the cylinders' top. The location of the cylinders in DB-like outflows is the dominant factor for their aerodynamics

Multiscale Wind Modelling for Sustainability and Resilience

The research presented herein is a mix of meteorological and wind engineering disciplines. In many cases, there is a gap between these two fields and this thesis is an attempt to bridge that gap through multiscale wind modelling approaches. Data and methods used in this study cover a multitude of spatial and temporal scales. Applications are in the fields of sustainability and resilience. This relationship between multiscale wind modelling and sustainability and resilience is investigated examining several case studies of three different developments: urban, rural and coastal. An urban wind modelling methodology is proposed and applied for a specific development in downtown Toronto, Canada. Micro-scale wind energy maps are created using computational fluid dynamics, analytical models, and the Canadian Wind Energy Atlas. It is demonstrated that urban wind energy projects are currently not feasible/sustainable due to decoupling between urban wind turbine power curves and wind speed histograms. Wind climatology for Toronto is calculated using the reanalysis data for the period 1948-2015. A trend analysis reveals statistically significant positive trends of the most frequent wind directions. Low-frequency wind spectra shows three distinguished peaks. The lowest frequency peak has the period of 11 year and it is linked to solar activity. The first methodology for microscale modelling of urban winds in changing climate is developed. Maximum wind speeds are more affected by climate change than the means. A wind sustainability study is performed for a unique development in South Central Kansas, United States. The analyses are conducted on the wind data obtained from the closest weather station and for the period 1984-2015. The WAsP package is used to calculate the wind atlas and wind resources at the site. Five locations suitable for installation of wind turbines are determined. A downburst that struck Livorno, Italy, on October 1, 2012 is analyzed from the wind resilience perspective. The analyses are conducted by gathering all available and relevant meteorological data. This research allowed for better understanding of downbursts, created a reference broad-band of information for the future calibration of analytical, physical and numerical models, and highlighted the potential of merging wind engineering and meteorology

Effect of surface roughness on large-scale downburst-like outflows

Downbursts are negatively buoyant descending winds coming from thunderstorm clouds that spread on the horizontal upon impinging the ground. Surface roughness is known to govern the characteristics of synoptic-scale atmospheric boundary layer (ABL) winds. This study assesses whether the same holds for downburst outflows and to which degree. The downburst winds are experimentally reproduced as a large-scale impinging jet at the WindEEE Dome, at Western University (Canada). Three different surfaces were tested and the equivalent full-scale roughness length is quantified through a best-match approach between experimentally produced ABL winds and ESDU profiles. The highest roughness produces an outflow vertical profile with maximum velocity reduced in magnitude and occurring at higher elevation with respect to the smaller-roughness cases

Investigation of the weather conditions during the collapse of the Morandi Bridge in Genoa on 14 August 2018

On 14 August 2018, Morandi Bridge in Genoa, Italy, collapsed sending vehicles and tons of rubble to the ground about 40\u2009m below and killing 43 people. Preliminary investigations indicated poor design, questionable building practices and insufficient maintenance or a combination of these factors as a possible cause of collapse. However, at the time of collapse, a thunderstorm associated with strong winds, lightning and rain was developed over the city. While it is still not clear whether or not it played a role in this disaster, the present paper documents the weather conditions during the collapse and analyzes in detail a downburst that occurred at the time of the collapse a few kilometers from the bridge. The thunderstorm is analyzed using direct and remote measurements in an attempt to describe the evolution of the cumulonimbus cloud as it approached the coast from the sea. The detected downburst is investigated using a lidar scanner and the anemometric network in the Port of Genoa. The paper shows that the unique lidar measurements enabled a partial reconstruction of the gust front shape and displacement velocity. The Weather Research and Forecasting (WRF) simulations, carried out with three different forcing conditions, forecasted the cumuliform convection at larger scales but did not accurately replicate the downburst signature at the surface that was measured by radar, lidar, and anemometers. This result demonstrates that the localized wind conditions during the collapse time could not be operationally forecasted

Investigation of the Weather Conditions During the Collapse of the Morandi Bridge in Genoa on 14 August 2018 Using Field Observations and WRF Model

On 14 August 2018, Morandi Bridge in Genoa, Italy, collapsed to the ground that was 40 m below. This tragedy killed 43 people. Preliminary investigations indicated poor design, questionable building practices, and insufficient maintenance\u2014or a combination of these factors\u2014as a possible cause of the collapse. However, around the collapse time, a thunderstorm associated with strong winds, lightning, and rain also developed over the city. While it is unclear if this thunderstorm played a role in the collapse, the present study examines the weather conditions before and during the bridge collapse. The study particularly focuses on the analysis of a downburst that was observed around the collapse time and a few kilometers away from the bridge. Direct and remote sensing measurements are used to describe the evolution of the thunderstorm during its approached from the sea to the city. The Doppler lidar measurements allowed the reconstruction of the gust front shape and the evaluation of its displacement velocity of 6.6 m s 121 towards the lidar. The Weather Research and Forecasting simulations highlighted that it is still challenging to forecast localized thunderstorms with operational setups. The study has shown that assimilation of radar reflectivity improves the timing and reconstruction of the gust front observed by local measurements

Experimental Investigation of the Near-Surface Flow Dynamics in Downburst-like Impinging Jets Immersed in ABL-like Winds

Downburst winds are strong downdrafts of cold air that embed into the atmospheric boundary layer (ABL) and produce intense horizontal outflow upon impingement on the ground. They are highly transient and three-dimensional extreme wind phenomena with a limited spatiotemporal structure that often makes the anemometric measurements in nature inadequate for reconstructing their complex flow fields. In the framework of the project THUNDERR, an experimental campaign on downburst outflows has been carried out at the WindEEE Dome at Western University, Canada. The present study analyzes the three-dimensional interaction between downburst (DB) outflows produced as large-scale impinging jets and ABL winds. Most experimental, numerical and analytical models in the literature neglect this flow interplay or treat it in an oversimplistic manner through a vector superposition. We found that the generated near-surface outflow is asymmetric, and a high-intensity wind zone develops at the interface between DB and ABL winds. The time variability of the leading edge of the outflow was investigated by synchronizing all wind measurements across the testing chamber. The three-dimensional flow structure was studied using a refined grid of Cobra probes that sampled the flow at high frequencies. The passage of the primary vortex produced a significant decrease in the height of maximum radial wind speed, predominantly in the ABL-streamwise direction. The turbulence intensity was the highest in the region where DB propagates into oppositely directed ABL winds

An appraisal of tornado-induced load provisions in ASCE/SEI 7-22 and 7-16 for residential low-rise buildings.

In this study, the loads induced by tornado-like vortices on scaled models of eight low-rise residential buildings with real-world shapes in a typical North American community are quantified and compared to the provisions provided by ASCE/SEI 7-16 and 7-22. Physical simulations of the interaction between translating tornado-like vortices representative of EF1-, EF2-and EF3-rated tornadoes and the scaled models were performed in the WindEEE Dome at the University of Western Ontario. Three internal pressure scenarios were numerically simulated. The tornado velocity gust factor was identified as a critical parameter when translating loads from model to full-scale. The load comparison results show that the provisions are safer as the rating of the design tornado increases. The uplift forces on the whole roof in the internal pressure scenarios with one dominant opening are between 44% and 63% higher than the distributed leakage scenario, highlighting the importance of keeping the integrity of the envelope. The ratios of pressures obtained from physical simulation to the ones calculated using the standard are higher on the walls than on the roof. Pressure ratios on the eaves are higher than on the other parts of the roof