Engineering Commons^™

Analyses For Assessing The Centreline Translation, Asymmetrical Wind-Field, And Velocity Fluctuations Of Tornado Vortices, Niall C. Bannigan

Electronic Thesis and Dissertation Repository

Tornadoes present an ever-increasing threat to communities worldwide, especially those with geographic conditions that place them in the path of several tornadoes annually. These conditions are likely to be exacerbated by ongoing trends in the climate. As such, it is necessary to move towards experimental and numerical tornado-like vortex studies that allow for more advanced simulation methods. Novel techniques for tracking and analysing tornado vortices simulated at high spatial and temporal resolution are presented herein. Significant wandering of the tornado's position and large peaks in the velocity field can be captured, demonstrating tangential gusting at more than 1.5 times the …

Effects Of Wind Turbine Rotor Positioning On Tornado Induced Loads, Juan P. Lopez Ortiz

Electronic Thesis and Dissertation Repository

This study investigates the loads induced by a large-scale tornado simulation on a horizontal axis wind turbine (HAWT) to assess the influence of three-dimensional flows with respect to the HAWT position. The loads were analyzed under two rotor operational conditions, idling and parked, at five radial distances. Subsequently, experimental validation of the numerical code HIW-TUR was conducted by evaluating the induced moments for various yaw and pitch angles. The experimental results demonstrated that the bending moment was the most important in terms of magnitude and variation with respect to the HAWT position. Furthermore, The HIW-TUR code accurately identified the magnitude …

Characterizing The Concurrent Occurrence Of Tornadoes And Flash Floods Across Canada, Yeu Deck Ngui

Electronic Thesis and Dissertation Repository

Compound weather extreme events, such as tornadoes and flash floods, can significantly impact societies and infrastructure systems. Disaster response agencies provide instructions to the exposed communities to retreat to safety specific to the natural hazard. However, the instructions can become confusing if natural hazards demand conflicting responses. This study characterizes the compound tornado and flash flood (TORFF) events to assess and predict the simultaneous occurrence probability of such hazards across Canada in the long term. We quantify dependencies between the tornadoes and flash floods using ground-based and reanalysis datasets. Tornado data are available based on the recorded Fujita rating for …

Behaviour Of Transmission Line Conductors Under Tornadoes, Dingyu Yao

Electronic Thesis and Dissertation Repository

Transmission line (TL) structure failures caused by tornadoes have been observed in multiple countries around the globe. The objective of this study is to develop an accurate load case that can simulate the critical tornado forces transmitted from the TL conductors to the towers. In order to achieve the goal, three different tornado wind fields, which were previously developed using computational fluid dynamic simulations, are considered. The tornado wind field provides the most critical forces on the TL conductors is determined and considered to obtain the critical load cases. Using the critical wind field, parametric studies are conducted to identify …

Behaviour Of Transmission Lines Subjected To Tornadoes Through Aeroelastic Testing And Numerical Modeling, Nima Ezami

Electronic Thesis and Dissertation Repository

Tornadoes, as a form of high intensity wind (HIW) events, represent major threats to transmission line systems in many regions around the globe. Transmission line systems are among the most vulnerable structures to tornadoes due to their expansion over hundreds of kilometers and, therefore, increased exposure to such localized wind events. A comprehensive research project has been developed over the past two decades at Western University to study this problem. The research conducted in this thesis provides a significant development to the advancement of knowledge in this area through achieving three main objectives. The first objective is to assess and …

Behavior Of Wind Turbine Towers And Blades Under Tornado Wind Fields, Mohamed Abugazia

Electronic Thesis and Dissertation Repository

The installation rate of wind turbines around the world is increasing significantly. Therefore, wind turbine farms are constructed in plentiful wind resources areas that put a considerable number of wind turbine towers under severe wind conditions. As a result, failures due to unexpected wind loads on either the blades or the tower are increasing. In addition, wind turbines are designed to resist synoptic wind loads as per the current guidelines, which do not consider high-intensity wind (HIW) events such as tornadoes. The built-in-house numerical code “HIW-WT” has been developed in this study to model wind turbines under three-dimensional wind fields …

Considerations For The Tornado-Resilient Structural Design Of Low-Rise Buildings, Cody J. Van Der Kooi

Electronic Thesis and Dissertation Repository

Building codes and standards have begun to incorporate tornado-specific loads to help protect community infrastructure against these potentially devastating storms, with a specific focus on low-rise buildings. The current tornado design loads are derived from atmospheric boundary layer (ABL) winds, even though it is relatively unclear to what extent tornado and ABL wind loads are equivalent for a given intensity. This research focuses on the tornado-resilient design of the main wind force resisting system (MWFRS) and component and cladding (C&C) elements of a low-rise gable roof building. Tornado loads derived from the results of experiments completed in a vortex simulator …

Tornado Occurrence Modelling And Equivalent Tornado Design Wind Profile For Canada, Qian Huang

Electronic Thesis and Dissertation Repository

The tornadoes can be devastating to structures and infrastructure systems. They can cause fatalities and economic losses. In this thesis, the tornado hazard for Canada is systematically assessed. The use of three spatial point processes (i.e., Poisson, zero-inflated Poisson, and negative binomial models) are first investigated in a hierarchical structure to predict the tornado occurrence rate by considering the annual cloud-to-ground lightning flash density and annual thunderstorm days as covariates. An existing historical tornado catalogue with reported tornado events up to 2009 is considered and the population bias effect in estimating the tornado occurrence rate is included. Both the Bayesian …

Behaviour Of Pre-Stressed Concrete Transmission Poles Under High Intensity Wind, Ahmed M. Ibrahim

Electronic Thesis and Dissertation Repository

Among different types of electrical transmission line structures, pre-stressed concrete transmission poles have the advantages of low installation and maintenance costs, appropriate delivery time, and high corrosion resistivity. Typically, these poles are designed to resist synoptic wind loading. Current design codes do not consider the effect of high intensity wind (HIW) events in the form of downbursts and tornadoes on pre-stressed concrete poles despite the fact that those weather events are the main cause of failure of transmission line structures. The first comprehensive study conducted to assess the behaviour of pre-stressed concrete transmission poles under HIW is presented in this …

Numerical Modeling Of Tornado-Like Vortex And Its Interaction With Bluff- Bodies, Zoheb Nasir

Electronic Thesis and Dissertation Repository

The study the flow structure of tornado-like vortices and their impact over engineering structures is important due to the extent of tornado induced fatalities and damages observed each year in North America and around the world. In the present study, a numerical modeling approach inspired by the WindEEE Dome and the modified version of Ward’s Tornado Simulator has been developed. Using a full-scale numerical simulator, tornadoes of different intensities have been simulated for different swirl ratio values to study flow structures in comparison with previous studies. The effect of topographic features on the tornado-like vortex has been investigated for the …

Numerical And Experimental Studies Of Transmission Lines Subjected To Tornadoes, Ahmed Hamada

Electronic Thesis and Dissertation Repository

The majority of worldwide weather-related transmission line failures have been attributed to High Intensity Wind (HIW) events in the form of tornadoes and downbursts. The research conducted in the current thesis presents a significant development in the understanding of the structural behaviour of transmission line systems under tornado loading. A comprehensive in-house numerical model that combines the data of computational fluid dynamic (CFD) simulations of tornado wind fields with three dimensional nonlinear structural analysis modelling is developed. A three dimensional four-nodded cable element is first formulated to simulate the nonlinear large deformation behaviour of the conductors. The support provided to …

Full-Scale Tests Of A Wood-Frame Structure Under Extreme Wind Loads, Derek A. Stedman

Electronic Thesis and Dissertation Repository

Tornadoes can produce some of the strongest winds on earth; these highly localized storms can cause massive damage. Assessments of tornado wind speeds are done using post-event observations of damage via the Enhanced Fujita Scale.

A very commonly observed failure occurs at the roof-to-wall connection where the roof breaks up or flies away, typically leaving the walls in place. However, once the roof is gone the walls are more vulnerable to the wind. If a wall subsequently fails, it increases the risk of injury or death for occupants. Significant research has been done for failures of roof-to-wall connections and roof …

Numerical Simulation Of Tornado-Like Vortices, Diwakar Natarajan

Electronic Thesis and Dissertation Repository

The thesis investigates by numerical simulation the flow characteristics of tornado like vortices produced by three types of vortex generators, namely, Ward-type Tornado Vortex Chamber (TVC), WinDEEE Dome and Atmospheric Vortex Engine (AVE).

Laboratory scale (Ward-type TVC) tornado-like vortices were simulated for swirl ratios 0.1 to 2.0 using the CFD code Fluent 6.3. The simulations with Reynolds stress model compare well with past experimental results. Multiple vortices were observed for high swirl ratios in LES simulation. These simulations have generated a comprehensive benchmark data for future modelers and experimenters.

The effects of translation and surface roughness on laboratory scale tornado-like …