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.

Speaker biographies

Prof Greg Kopp

Prof Greg Kopp is a Professor of Civil & Environmental Engineering at the University of Western Ontario, where he has been since 1997. He currently holds the ImpactWX Chair in Severe Storms Engineering, where he leads the Northern Tornadoes Project, which is related to the topic of his talk today. He also joined the University of Birmingham in 2019 as Professor of Wind Engineering. Greg has been active in service to the community and is currently Chair of the ASCE 49 Standards Committee on Wind Tunnel Testing for Buildings and Other Structures, amongst other roles.

Dr Frank Lombardo received his Ph.D. from Texas Tech University in 2009 studying thunderstorm wind characteristics and subsequent loading on a low-rise building. Dr. Lombardo was a postdoctoral research associate at NIST where he played a significant role in the investigation of the Joplin, Missouri tornado in 2011 and the creation of updated wind maps for ASCE 7-16. Lombardo has been at the University of Illinois at Urbana-Champaign (UIUC) since 2015. In his time at UIUC, he has been awarded competitive research projects through NOAA, NSF and NIST studying wide-ranging aspects of wind science and engineering and was the recipient of the 2019 International Association of Wind Engineering Junior Award. He also serves as vice-chair of the tornado task committee, which has proposed tornado loading provisions for ASCE 7-22.

Prof Mark Sterling is Beale Professor of Civil Engineering and Deputy Pro Vice-Chancellor (Staffing) at the UoB with over 20 years research experience in wind engineering. His research focuses on transient winds, particularly the effects of extreme winds on infrastructure, vehicles and biological systems. A member of the BSI wind loading committee responsible for updating EN1991-1-4 and a member of an ASCE committee re-writing the wind tunnel standards code of practice, both of which ensures his research effectively translates into practice.

Dr Grace Yan is Associate Professor of Missouri University of Science and Technology, Director of the Wind Hazard Mitigation (WHAM) Laboratory. She is passionate about the mitigation of hazards induced by extreme winds, such as tornadoes and hurricanes, and the achievement of community resilience. Her research includes the simulation of different wind fields numerically and experimentally, dynamic responses on civil structures induced by extreme winds, and reproduction of damage scenarios induced by extreme winds using numerical simulations. She published 47 journal papers and 57 conference papers. She is the recipient of 25 research grants with a total fund of $9.94 M.

Dr. Shuyang Cao is a professor at the Civil Engineering college of Tongji University and a professor at the State Key Laboratory for Disaster Reduction in Civil Engineering, China. Before he joined Tongji University, he was an associate professor at the wind engineering center of Tokyo Polytechnic University and an assistant professor of Tokyo Institute of Technology, Japan. Dr. Shuyang Cao works in both structural and environmental wind engineering fields. His research interest includes the development of numerical and physical modeling techniques for wind engineering problems, structure aerodynamics and wind-resistant design of structures.

Prof Chris Baker read Engineering at St Catharine’s College in Cambridge, graduating with a BA in 1975, and an MA and a PhD in 1978. Following a Research Fellowship at St Catharine’s College and the Department of Engineering, in the early 1980s he began work in the Aerodynamics Unit of British Rail Research in Derby, before moving to an academic position in the Department of Civil Engineering at the University of Nottingham. He remained there till 1998 as a lecturer, reader and professor with research interests in vehicle aerodynamics, wind engineering, environmental fluid mechanics and agricultural aerodynamics. In 1998 he moved to the University of Birmingham as Professor of Environmental Fluid Mechanics in the School of Civil Engineering. From 2003 to 2008 he was Head of Civil Engineering and was the Director of the Birmingham Centre for Railway Research and Education from 2005 to 2014. He retired at the end of 2017 and took up an Emeritus position. He continues to be involved in research in train aerodynamics, wind engineering and transport issues. In July 2020 he was awarded the Davenport Medal, the senior award of the International Association of Wind Engineering.

Prof Fred Haan is a Professor of Engineering at Calvin University in the United States. He has conducted research in wind engineering for more than 20 years primarily in experimental aerodynamics and extreme wind simulation techniques. Fred received his PhD from the University of Notre Dame in 2000, and has worked on wind-induced vibration of long-span bridges, vortex-induced vibrations, atmospheric boundary layer simulation and laboratory tornado simulations. While on the faculty at Iowa State University, he worked with Partha Sarkar to develop and build the world’s first large tornado simulator intended to test tornado-induced loading on buildings and structures.

Presentations

Due to my inability to push the Record button at the proper time, the first few minutes of each of the videos below is missing. Also Prof. Cao was unable to load his Powerpoint slides. They can thus be found here.

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