International Wind Engineering seminar 1: Tornadoes – research and design

Tornadoes – research and design: Thursday October 8th 14.00 UK time

Main speaker

Identifying and classifying tornadoes in sparsely-populated regions: observations and research needs. Prof Greg Kopp, ImpactWX Chair in Severe Storms Engineering University of Western Ontario (30 minutes)

Discussion (10 mins)

Short contributions (5 minutes each) from

Full-Scale Inquiry into Tornado Wind and Loading Characteristics,  Dr Franklin T. Lombardo, University of Illinois

Compact debris flow in tornadic flow fields. Prof. Mark Sterling, Beale Professor of Civil Engineering, University of Birmingham

WHAM Research: What Flow Structure of Tornado Should We Design Against? Grace Yan, Associate Professor, Missouri University of Science and Technology

Consideration of tornado modeling based on the experimental and numerical results, Shuyang Cao, Professor, Tongji University, China; Jinxin Cao, Associate Professor, Tongji University, China

The lodging of cereal crops by tornadoes, Chris Baker, Emeritus Professor of Environmental Fluid Mechanics, University of Birmingham

Translation Speed Effects on the Static Pressure Distribution of a Tornado Vortex, Fred Haan, Jr., Professor, Calvin University, Grand Rapids, Michigan, USA

Discussion (20 mins)

Registration

The registration link for the seminar is here.

Abstracts

Identifying and classifying tornadoes in sparsely-populated regions: observations and research needs Prof Greg Kopp, ImpactWX Chair in Severe Storms Engineering University of Western Ontario. The Northern Tornadoes Project (NTP) is a new effort to identify and classify every tornado in Canada. While Canada has the second most tornadoes of any country in the world, recent studies correlating known tornado occurrences with lightning strike and population data lead to estimates that only 1/4 to 1/3 of the tornadoes are identified on average. Over 2+ years of study, NTP has increased the tornado counts across the country by 78%. However, the project has identified many continued issues with both identifying and classifying tornado occurrence in sparsely populated regions, particularly related to a lack of damage indicators. The presentation will discuss these issues and raise the research needs for obtaining accurate tornado climatologies in such regions.

Full-Scale Inquiry into Tornado Wind and Loading Characteristics  Dr Franklin T. Lombardo, University of Illinois Tornadoes cause a significant amount losses in the United States and worldwide. Recent events in the U.S., such as the Joplin, MO and Moore, OK have caused engineers to rethink philosophies on designing structures to withstand tornadoes. Currently, tornadoes are not included in design although provisions will likely be included in the next version of the U.S. wind load standard (ASCE 7-22). As tornado events are rare and transient in nature, full-scale measurements especially near the ground have been limited. Therefore, the first edition of tornado specific design will have a significant number of assumptions on properties relevant to wind loading (e.g., wind profiles, turbulence, aerodynamics). The limited full-scale wind speed data that have been collected show tornadoes possess different physical properties (e.g., rapid wind speed and direction changes, different vertical profiles, non-zero vertical wind speed) than ABL flow. Full-scale wind loading data, however, is practically non-existent.  This presentation will discuss ongoing research at the University of Illinois aimed at significantly increasing the quantity and quality of full-scale measurements of tornadoes that are relevant to wind engineering through a comprehensive scientific inquiry. Research to be discussed includes: 1) estimating wind speeds and wind field characteristics through patterns of damage observed in trees, corn and soybeans; 2) capturing wind characteristics (including turbulence) using novel and low-cost, rapidly deployable sensors; 3) exploration of tornado-like aerodynamics with a small bluff body in dustdevils and 4) various other complementary projects such as linking observations with LES and citizen science efforts. Progress on tornado loading design through the ASCE 7-22 tornado task committee over the last 2.5 years and leading the development a design profile (Kz) for tornadoes will be briefly highlighted.  

Compact debris flow in tornadic flow fields. Prof Mark Sterling, Beale Professor of Civil Engineering, University of Birmingham. The wind loading arising from tornadoes can be of significance in many parts of the world.  Such loading has received considerable interest in the past and forms the basis of a large number of current research projects.  A common feature of most tornadoes is a cloud of debris which is generated and transported as a result of the flow-field associated with the tornado.  However, the flight of windborne debris within such flow fields has received relatively little attention despite the implications that such phenomena can have on structural loading.  This presentation will combine physical and numerical simulations in order to examine the trajectory of compact debris in a tornado-like flow field. 

WHAM Research: What Flow Structure of Tornado Should We Design Against? Grace Yan, Associate Professor, Missouri University of Science and Technology. Tornadoes have induced substantial structural damage, injuries and deaths in the USA. They occur in Mainland America, mainly “Tornado Alley” and Southeast of the USA, and contribute $10B annually to the nation’s loss portfolio. The devastation from recent tornadoes (e.g., Joplin, MO, in 2011; Tuscaloosa, AL, in 2011 and Moore, OK, in 2013) left no doubt as to the vulnerability of the central and southeastern USA to tornadoes, and prompted an urgent need in developing and enforcing a tornado-resistant design for normal buildings. This requires in-depth understanding of tornadic wind effects. To find tornadic wind effects, what type of tornadoes should we look at? Tornadoes have different flow structures, single-celled single-vortex, double-celled single-vortex and multiple vortices; Even for a single tornado incident, the flow structure varies with time and location. Based on which type of tornado should the wind effects be used to modify the coefficients in the pressure calculation equation in ASCE7-16? In other words, which type of tornado induces more unfavorable wind loading?

Consideration of tornado modeling based on the experimental and numerical results, Shuyang Cao, Professor, Tongji University, China; Jinxin Cao, Associate Professor, Tongji University, China. Physical and numerical simulations of tornado-induced effects on low-rise buildings, bridges and other structures have been carried out in our lab. This short presentation will discuss following issues related to appropriate modeling of tornado effects: 1) The relationship of flow-based swirl ratio and geometry-based swirl ratio; 2) Should the vortex wander be considered as a representative of the instantaneous vortex structure? 3) Is it possible to find scale ratios from various ones that play dominant roles in determining the wind effects on structures from benchmark test results?

The lodging of cereal crops by tornadoes, Chris Baker, Emeritus Professor of Environmental Fluid Mechanics, University of Birmingham. Tornado tracks have often been observed in fields of crops and efforts have been made in the past to infer tornado strength from the width of these tracks. This presentation will briefly present work by the author in this area, and will describe a generalized model of crop lodging that has been used in the past for a variety of crops, together with a new tornado model that captures the apparent near ground velocity field. Lodging patterns similar to those seen in the field can be predicted and the model offers the possibility that it can be used in a more quantitative way if robust crop agronomic data is available.

Translation Speed Effects on the Static Pressure Distribution of a Tornado Vortex, Fred Haan, Jr., Professor, Calvin University, Grand Rapids, Michigan, USA. Tornado vortices generate regions of reduced static pressure near their cores. In tornado simulator tests or in design estimates, it is typically assumed that this static pressure acts a bit like a reference pressure that can be subtracted from the windfield-induced pressure on a building to analyze the “aerodynamic” pressure apart from the “static” pressure. The static pressure to be subtracted is often measured or modeled with a stationary vortex. This framework may be too simplistic. If one considers the unsteady effect of the translation speed of a vortex, it is clear that a translation speed dependent pressure is generated in addition to the static pressure drop associated with a stationary vortex. Potential flow simulations with a single vortex show that this speed dependent pressure can add 20% to the static pressure of a stationary vortex when the translation speed is 10% of the maximum tangential velocity. It can add 40% to the static pressure when the translation speed is 20% of maximum tangential velocity.

Other seminars

Details of other seminars in the series will be posted here when they become available.