Seminars

seminar room safl

Every other week during the academic year, SAFL hosts prominent figures in environmental science and fluid mechanics. They come from all over the US and the world to share their insight and inspire us to tackle important questions in the field. These seminars are free and open to the public. Join us to learn about the latest research advancements and network with contacts in the field.


SAFL seminars are held on Tuesdays from 3:00 to 4:15 p.m. unless otherwise noted. Join us in the SAFL Auditorium or via Zoom.

 
Spring 2024 Seminar Series
Tuesday, Jan 23-Katey Anthony
Tuesday, Feb 6th-No Seminar 
Tuesday, Feb 20th-Neal Iverson
Tuesday, March 12- Jennifer Stucker 
 
Tuesday, March 26th-Mike Shelley
Tuesday, April 9th-Sergio Fagherazzi
Tuesday, April 23rd-Ruben Juanes
Tuesday, May 7th-Walter Musial

Recordings
We will record seminars and post them here when given permission by the speaker. To see if a recording is available, scroll down this page to "Past Seminars."

Seminar Notifications
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Upcoming Seminars

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Past Seminars

Breaking Internal Waves and Turbulence on Shelf Slopes

Jeffrey Koseff, Perry L. McCarty Director and Senior Fellow - Stanford Woods Institute for the Environment; William Alden Campbell and Martha Campbell Professor of Civil and Environmental Engineering, Stanford University

Internal waves, the subsurface equivalent to the more widely-known surface waves, are ubiquitous in the world’s oceans. These waves are known to be responsible for a large part of the vertical mass and momentum redistribution in the world’s stratified oceans and lakes. Internal waves are primarily generated by the winds and the tides, and are known to propagate thousands of kilometers from their generation site before they break, usually on the continental shelf or at ocean ridges. Internal waves affect numerous ocean processes including the transfer of nutrients, sediment, and larvae between deep waters and the continental shelf environment, and can cause dramatic changes in temperature, salinity, and chlorophyll levels in coral reefs. Moreover, mixing generated by internal waves is thought to play an essential role in the transport of deep, cool nutrient-rich waters into the shallower waters of critical coastal ecosystems such as Monterey Bay and Georges Bank.

In this talk I will discuss a series of laboratory and field experiments we performed in order to understand what happens when internal waves break on shelf slopes such as found in mid-ocean (seamounts) and on the continental shelf. I will look at the energetics of the breaking events as well as the characteristics of the bolus structures which often form as a result of the breaking. Because fluid mechanics is at its essence a visual science emphasis, in this talk, will be placed on visualization and imagery.

A Slippery Slope: Towards Better Understanding and Prediction of At-Risk Hillsides in Minnesota

Carrie Jennings, Research and Policy Director, Freshwater Society

Minnesota’s wettest recorded month in June 2014 led to widespread gravitational failure of sediment and rock in the metropolitan area of Minneapolis-St. Paul. The failure beneath the oxygen supply for Fairview Riverside hospital was costly enough to allow the entire state to qualify for a federal disaster declaration.  Two years prior, a similarly rainy period resulted in loss of life as well as extensive property damage.  Our goal is to develop a better predictive model of when and where failures occur in order to inform hazard response plans, best management practices and to develop model ordinance language. 

We inventoried historical failures in a broad region that included the metropolitan area by searching online sources and print newspaper archives. We interviewed Minnesota Department of Transportation personnel with extensive knowledge of problematic areas in heavily engineered landscapes near roadways. Failures were mapped onto a 1m-hillshade DEM created with LiDAR data at a density ranging from 1.5 to 8 data points per square meter.  Failure scars discovered on the DEM and not through the historical archives were noted and municipalities contacted for more information on timing.  The antecedent  precipitation for two to four weeks prior to the failure  and soil moisture conditions at the time failure were extracted from climate archives for the periods identified.  

Nearly all of the slides occurred between May and October with peaks in June and August, both periods of higher incidence of convective storms in Minnesota. The earliest record of failure was in 1879.  Wet periods in the late 1890s, early 1900s, 1980s and 1990s are reflected in an increase in reporting of slides.  The increase in slides reported since 2010 may reflect the wetter climate as well as the ease of searching  online records.  The failures were primarily located along the Mississippi and Minnesota River corridors.

Climate Variability and Extreme Events: Droughts and Typhoons

Stefan Liess, Postdoctoral Researcher in the Department of Earth Sciences at the University of Minnesota

Link to Video

https://umn.webex.com/umn/ldr.php?RCID=7f08e51907ff4e1aeb95f26369176827

During winter, Minnesota is the fastest warming state of the contiguous U.S. since the 1970s. This is related to the influence from strongly warming Arctic conditions, also known as Arctic amplification. We show with regional and global model simulations that this amplification can be enhanced by increased vegetation growth around the Arctic circle. In addition to temperature changes, increased moisture availability is an important factor related to vegetation growth. Invasive species such as the brown marmorated stink bug might be able to thrive in future climates. We project regional climate change over Minnesota by using globally available projections and down-scale these with a regional model to make these projections useful for local policy makers. These projections need to account for variability in the ocean circulation such as the El Nino mSouthern Oscillation (ENSO), which can be related to observed droughts over Minnesota for the last century.

Reliable observations for more than a century are necessary to detect multidecadal climate variability. The Atlantic Multidecadal Oscillation (AMO) has a period of 60-80 years and is thought of as a main driver for the Sahel drought from the 1970s to the 1990s. We show that the extent of this oscillation can reach East Africa and even the Indian summer monsoon. We identify a teleconnection between the Tasman sea and the Southern ocean that describes the multidecadal drought cycle over Australia and that is statistically correlated to the AMO, but no physical explanation for the latter connection has been found so far. We show in a regional simulation how atmospheric moisture content over Australia, East Africa, and India are connected via the monsoon circulation. This circulation converges with tropical easterlies over the west Pacific warm pool, where our simulation shows a series of three strong tropical cyclones, which have observed counterparts as typhoons Frankie, Gloria, and Herb during the 1996 typhoon season.

Bubbly Shock Propagation and the Transition to Partial Cavity Shedding

Lorenz G. Straub Award Ceremony and Distinguished Seminar

Distinguished Straub Lecturer: Dr. Steven Ceccio, ABS Professor of Marine and Offshore Design and Performance and the Department Chair of Naval Architecture and Marine Engineering at the University of Michigan

Link to Video

https://umn.webex.com/umn/ldr.php?RCID=f7c21b9d1388ac9fd2ea69ee76f4a481

Join us at the St. Anthony Falls Laboratory for the presentation of the 2014 Lorenz G. Straub Award at a ceremony and distinguished lecture on Tuesday, October 11. The program will begin at 3:30 p.m. with the presentation of the award and presentations by both our awardee and our distinguished lecturer. Learn more below! 

Lorenz G. Straub Award Recipient: Hang Wang, Postdoctoral Research Fellow, University of Queensland for his 2014 dissertation titled "Turbulence and Air Entrainment in Hydraulic Jumps" completed at the University of Queensland, Australia.

Abstract: 

The thesis provides a comprehensive description of the turbulent two-phase flow in hydraulic jumps based upon physical modeling. Investigated flow properties ranged from free-surface dynamics, air entrainment and transport, to characteristic turbulent scales and bubble-turbulence interactions. The spatial distributions of two-phase flow properties and turbulent scales, as well as the effects of Froude and Reynolds numbers, revealed strong coupling between physical processes of air entrainment and turbulence development. Selecting the length of hydraulic jump roller as the characteristic length scale, the two-phase flow structures can be predicted based upon a semi-analytical model, with negligible viscous scale effects in terms of air entrainment flux. The turbulence properties and flow dynamics time scales, however, are subject to scale effects and can be only accurately measured at prototype conditions. The cutting-edge knowledge of hydraulic jump and such complex turbulent multiphase flows should provide solid justification for future theoretical and numerical studies that have a long way ahead.

Distinguished Straub Lecture
Bubbly Shock Propagation and the Transition to Partial Cavity Shedding

Steven Ceccio, ABS Professor of Marine and Offshore Design and Performance and the Department Chair of Naval Architecture and Marine Engineering at the University of Michigan

Abstract: 
Using time resolved X-ray densitometry, time resolved 2-D void fraction flow fields for a variety of cavitating flows are examined. Results from the cavitating flows formed at the apex of a wedge, the flow over a hydrofoil, and the flow in the wake of a cylinder are presented.  In these cavities are obtained to identify the mechanisms of transition from closed partial cavities to open cavities exhibiting periodic shedding of large gas pockets. From the void fraction field measurements, two distinct types of cavity shedding mechanisms are identified: shedding associated with a re-entrant jet in the cavity closure region that produces intermittent shedding of smaller scale cavities, and large scale, periodic cloud shedding caused by the formation of a condensation shock within the high void-fraction flow in the separated region of partial cavitation. A discussion of the observed occurrence and properties of the shock wave, and its role in causing periodic shedding is presented based on the one-dimensional model of shock propagation in bubbly mixtures and the relationship between the transition to strong shedding as a function of the Mach number of the bubbly flow in the cavity.

About the Straub Award:

Lorenz G. Straub, Professor of Civil Engineering, is considered the mastermind for making the idea of a hydraulic laboratory at the University of Minnesota and the St. Anthony Falls into a reality. Serving as the primary architect, Straub oversaw the construction of the laboratory using Works Progress Administration (WPA) funding from 1936 -1938. He served as SAFL's director until his death in 1963. The Lorenz G. Straub Award was established in his memory. The award, made annually, is for the author of an especially meritorious dissertation in the area of hydraulic engineering or a closely related area. In reflection of Straub's world-wide professional activities, recipients can be from any school throughout the world, which has an appropriate graduate degree program. The award consists of a medal and an honorarium.

How the Ice Sheets of North America rerouted rivers, carved valleys, and changed global climate

Andrew Wickert, Assistant Professor of Earth Sciences and St. Anthony Falls Laboratory, University of Minnesota

Over the last glacial cycle, ice sheets and the resultant glacial isostatic adjustment (GIA) rearranged river systems. As these riverine threads that tied the ice sheets to the sea were stretched, severed, and restructured, they also shrank and swelled with the pulse of meltwater inputs and time-varying drainage basin areas. I will present reconstructed drainage basins and river discharge paleohydrographs across North America from the Last Glacial Maximum to present, and use these to evaluate leading models of the massive North American ice-sheet complex against terrestrial and marine geologic data. The particularly dynamic Mississippi River basin inspires a case study of its geomorphic history, where new data show that a buried 50-60-meter high waterfall heads a reach where the Mississippi has deeply incised bedrock that was once uplifted in the glacial forebulge. This event that was likely precipitated by an early ice advance that dammed the the paleo-Upper-Mississippi in Wisconsin and caused it to overtop its drainage divide and join the modern Mississippi in Iowa. Returning to the more recent geologic past, I will present a new compilation of isotopic records from the Gulf of Mexico that can help to revise the Great Lakes glacial chronology. I will close by presenting new model results of how freshwater discharge to the ocean during Meltwater Pulse 1A, the most rapid period of deglacial sea-level rise, dramatically affected the Atlantic Meridional Overturning Circulation and past climate. To obtain these results, one must link the ice sheets, terrestrial hydrology, and the oceans. By probing this link, we can link multiple data sources to critically evaluate and improve our knowledge of the late Quaternary, connect geomorphic change with climate and ice-sheet drivers, and more rigorously couple ocean circulation and climate feedbacks to deglaciation.

Wake meandering of a model wind turbine operating in two different operating regimes

Daniel Foti, PhD Candidate, Mechanical Engineering, University of Minnesota

The flows behind a model wind turbine under two different turbine operating regimes (Region 2 for turbine operating at optimal condition with the maximum power coefficient and 1.4 degrees of pitch angle, and Region 3 for turbine operating at sub-optimal condition with a lower power coefficient and 7 degrees of pitch angle) are investigated using large-eddy simulation (LES). Simulations with and without a nacelle model are carried out for each operating condition to study the influence of the nacelle on the formation of the hub vortex. The simulations with the nacelle model reveal an unstable helical hub vortex expanding outwards towards the outer wake; while the simulations without a nacelle model show a stable and columnar hub vortex. Because of the different interactions of the inner region of the wake with the outer region of the wake, a region with higher turbulence intensity is observed in the tip shear layer for the simulation with a nacelle model. The hub vortex for the turbine operating in Region 3 remains in a tight helical spiral and intercepts the outer wake a few diameters further downstream than the turbine operating in Region 2. Wake meandering, a low frequency large-scale motion of the wake, commences in the region of high turbulence intensity for all the simulations with and without a nacelle model indicating that neither a nacelle model nor unstable hub vortex is a necessary requirement for the existence of wake meandering. However, the unstable hub vortex promotes a high amplitude energetic meandering which cannot be predicted without a nacelle model. The turbine operating regime affects the shape and expansion of the hub vortex altering the location of the onset of the wake meandering and wake meander oscillating intensity.

 

NOTE: Due to the content of the presentation (unpublished material), the speaker was not comfortable posting the recording of this presentation.

Methodology of Computational Fluid-Structure Interaction with Applications for Complex Nonlinear Problems.

Anvar Gilmanov, Research Associate, St. Anthony Falls Laboratory, University of Minnesota

Computational fluid dynamics methods have advanced in recent years to be able to carry out fluid structure interaction (FSI) simulations of nonlinear problems with large deformations and displacements of flexible structures in a fluid flow. The Immersed Boundary Method (CURVIB) and Rotation-Free Shell Finite Element (FE) solvers are coupled together on a flexible solid–fluid interface, providing an efficient methodology for solving wide class of FSI problems. Various computational methodologies are discussed in order to emphasize the advantages of CURVIB-FE-FSI.  The coupled CURVIB-FE-FSI method is validated by applying it to simulate two FSI problems involving thin flexible structures: vortex-induced vibrations of a cantilever mounted in the wake of a square cylinder at different mass ratios and at low Reynolds number; and the more challenging high Reynolds number problem involving the oscillation of an elastic inverted flag. Simulations of fluid-structure interaction of flexible heart valve with pulsatile blood flow were performed on two types of aortic valve: healthy, trileaflet aortic valve (TAV) and bicuspid aortic valve (BAV), which is a congenital heart disease. The computed results reveal major differences between the TAV and BAV flow patterns, which are discussed in this presentation.

Aerosols and Deep Convective Clouds: Have We "Resolved" the Problem?

Zachary Lebo, Professor, Department of Atmospheric Science, University of Wyoming

The potential effects of changes in aerosol loading on deep convective cloud systems have received considerable attention in the recent literature, focusing on the response in precipitation, storm strength, lightning frequency, etc. In this talk, a review of the responses will be presented, focusing on two potential microphysical pathways by which an aerosol perturbation may modify the cloud and dynamical characteristics (i.e., the conventional “invigoration” mechanism and the modification of cold pool strength and/or structure). A detailed comparison between the simulated effects due to changes in aerosol loading and changes in environmental characteristics will be discussed; the effects due to changes in aerosol loading will be shown to be masked by even small changes in environmental characteristics. This conclusion suggests that observing such effects will be extremely difficult. Furthermore, the sensitivity of the model results to grid spacing will be explored and analyzed using a novel approach; this is an important consideration because many of the effects of changes in the aerosol loading are likely reliant on the entrainment/detrainment characteristics of deep convective cloud systems. Lastly, recent numerical solutions will be presented to confirm the cloud-resolving model simulations and pinpoint the processes in which deep convective cloud characteristics are likely to be most susceptible to changes in aerosol loading. These numerical solutions combined with the 3D cloud-resolving simulations will demonstrate that the “invigoration” mechanism is insignificant for strong deep convective cloud systems.

Intraseasonal Dynamics of Equatorial Atmosphere and Oceans

Nels Nelson Award Ceremony and Distinguished Lecture:

Distinguished Lecturer: Harindra FernandoProfessor, Dept of Civil & Environmental Engineering & Earth Sciences, Department of Aerospace and Mechanical Engineering, University of Notre Dame

Climate modeling intercomparison studies demonstrate a clear divergence of future climate predictions for equatorial regions, calling for better understanding of atmospheric and oceanic processes of tropics.  Current efforts of ‘seamless’ modeling from weather to climate scales require a deeper understanding of dominant processes at various scales, from meso to climate scales (e.g., synoptic, seasonal, decadal) as well as transitional phenomena in between. To this end, intraseasonal disturbances of tropical atmosphere and oceans that occupy time scales form about 10 to 60 days have gained recent attention because of its perceived relation to Boreal summer monsoons and rainfall.  Of particular importance are the migration of the Intertropical Convergence Zone, equatorial planetary waves that propagate in all directions within atmosphere and oceans, interaction of these waves with landmass (e.g. maritime continent) and ocean boundaries, and air-sea interactions associated with such disturbances. During 2012-2015, a field experimental program was conducted in the northern Indian Ocean under the sponsorship of the Office of Naval Research to study intraseasonal oscillations in tropics. These were dubbed ASIRI (Air Sea Interactions in the Northern Indian Ocean) and ASIRI-RAWI (Remote Sensing of Atmospheric Waves and Instabilities). An array of observing platforms were used, covering multiple countries and several ocean basins. Observations and associated modeling conducted during these programs will be described in this presentation, paying particular attention to intriguing phenomena that were observed and explained using analyses of fluid dynamics. 

What is the value of Minnesota's natural capital?

Bonnie Keeler, Lead Scientist, Natural Capital Project, Institute on the Environment, University of Minnesota

Accounting for the full costs of environmental change requires approaches that integrate ecological and socio-economic research.  Keeler will present new work on the social and economic impacts of changes in land management and land use, with a focus on the value of clean water. Keeler will also highlight ongoing work at the Natural Capital Project designed to inform conservation and restoration decisions in Minnesota and around the world.