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."

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Upcoming Seminars

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Past Seminars

Edward Silberman Award Ceremony & Distinguished Lecture by Neal Iverson

Presentation of the 2023 Edward Silberman Fellowship Award

Speaker: Neal Iverson, Distinguished Professor in the Department of Geological and Atmospheric Sciences at Iowa State University

Title: A universal slip law for glaciers?

Alberta

AbstractIce discharge to the oceans from ice sheets and associated sea-level rise result largely from rapid slip of marine-terminating ice streams over their beds. Slip occurs over either rough bedrock (“hard” bed) or deformable till (“soft” bed). For each bed type, glacier flow models require a constitutive law that describes the relationship between shear stress and slip velocity. Experimental studies of ice slip over a soft bed and results of a three-dimensional numerical model of glacier slip applied to measured hard-bed topography point to a slip law that has a common form for the two bed types. This finding has the potential to simplify and improve estimations of glacier discharges to the oceans. Regardless of bed type, the sensitivity of slip velocity to increasing stress on glacier beds—caused for example by the melting of buttressing ice shelves in the warming oceans—is larger than currently assumed in most ice sheet models.

AboutNeal Iverson is a Distinguished Professor in the Department of Geological and Atmospheric Sciences at Iowa State University. He received his Ph.D. from the University of Minnesota in 1989. His research focuses on glacier flow,  glacial erosion and sedimentation, and genesis of glacial landforms. He is a recipient of the Geological Society of America’s Kirk Bryan Award and Arthur L. Day Medal.  

Award Recipient: Jiaqi Li, PhD Candidate in Mechanical Engineering at the Saint Anthony Falls Laboratory

jiaqi li research

Abstract: Fluid flows, especially turbulent flows, are ubiquitous in the environment and critical for our daily life across various sectors, including healthcare and manufacturing. Our research focuses on a set of techniques to explore the dynamics of fluids and their interactions with particulates. At a larger scale, we conducted field experiments to measure the settling snow particles, using both planar and three-dimensional imaging techniques, alongside a snow particle analyzer. Our findings reveal preferential sweeping as a key mechanism in snow-turbulence interactions and demonstrate how snow morphology influences their fall behavior in low-turbulence environments, with implications for meteorological and climate predictions. On the smaller scales, we investigated the internal flow within evaporating sessile colloidal droplets. Through experimental observations and theoretical modeling, we elucidate the mechanisms governing particle deposition patterns after droplet evaporation, shedding lights on applications such as printing-based manufacturing and blood disease diagnostics. In addition, we have developed a holography-based technique for direct vorticity measurement. It has been applied to the study of elliptical vortex rings, revealing the vorticity fluctuations caused by their unsteady behaviors. This method has potential for directly measure the spatial and temporal vorticity variation of thin vortex tubes in turbulence, providing new insights into scale interactions and energy dissipation of these turbulent eddies.

About the recipient: Jiaqi Li is a PhD candidate in Mechanical Engineering at the St. Anthony Falls Laboratory of the University of Minnesota. He is currently working with Prof. Jiarong Hong on experimental fluid mechanics. His research focuses on understanding the interactions between turbulent flow and falling snow particles with various shapes for improving weather forecasting and climate modeling. He also worked extensively with digital inline holography, including developing a method for direct vorticity measurement and a snow particle analyzer for measuring snow size, shape, and density, as well as investigating internal flow and deposition patterns of sessile colloidal droplets. Before starting his PhD journey, Jiaqi received his bachelor’s degree from the University of Science and Technology of China in Energy and Power Engineering.

Permafrost thaw and methane release in the Arctic

Katey Walter Anthony is an Aquatic Ecologist and Professor at the University of Alaska Fairbanks

AbstractPermafrost thaw beneath Arctic lakes and other thermokarst (thaw) features leads to large emissions of methane, a potent greenhouse gas to the atmosphere. In turn, methane contributes to global climate warming, which leads to more permafrost thaw in a positive feedback cycle. This talk will uncover natural sources of methane in the Arctic, which come from both the organic matter decay activity of microoganisms in lake bottoms and from geologic sources deep within the Earth. This talk will also present mechanisms of carbon sequestration by the same permafrost thaw features, a natural process that mitigates greenhouse gas losses, and over the long term can lead to net climate cooling. Using field work and novel remote sensing methods, I will consider the important balance between positive and negative feedbacks in fate of permafrost thaw and climate change in the past (since the last deglaciation), present, and future (until year 2100).

katey walter anthony

AboutKatey Walter Anthony is an Aquatic Ecologist and Professor at the University of Alaska Fairbanks. Her research focuses on methane emissions from Arctic lakes, the degradation of permafrost, and its feedbacks to global climate processes through the carbon cycle. She has over 25 years’ experience conducting field work in Alaska and Russia, is a science team member of the National Aeronautics and Space Administration Arctic-Boreal Vulnerability Experiment, and a member of the Permafrost Carbon Network. She received the National Wildlife Federation Award in 2009, National Geographic Society Early Explorer’s Award in 2009, Mount Holyoke College Mary Lyon Award in 2010, WINGS WorldQuest Award in 2011, and the University of Alaska Usibelli Distinguished Research Award in 2019. Anthony received a B.A. in geology from Mount Holyoke College, an M.S. in restoration ecology from the University of California, Davis, and a Ph.D. in aquatic biology from the University of Alaska Fairbanks. She previously served on the National Academies of Sciences, Engineering, and Medicine’s Polar Research Board.


 

Dynamics of large irregular particles in turbulent flow

Margaret Byron, Assistant Professor of Mechanical Engineering at Penn State

AbstractEnvironmental flows are rarely single-phase: they often carry particles like dust, sediment, flocs, or even living organisms. The details of how these particles are transported can have significant impacts on engineering problems; we must therefore understand the physics behind their interactions with the surrounding flow. However, the particles we are interested in are frequently nonspherical, nontrivially large compared to the flow scales, and or otherwise irregular (e.g. made of multiple materials, or having a nonuniform mass distribution). Such particles are sometimes treated as point masses, or as semi-passive flow tracers—but this simplified view doesn’t capture the full variation of the particles’ behavior, especially in turbulence. In this talk, we will present results from recent laboratory experiments and explore how varying particle shape, size, and mass distribution affect their dynamics in environmental turbulence, and discuss implications for a wide range of engineering problems including sediment transport, microplastic pollution, and the global carbon cycle.

photo of Margaret Byron

AboutMargaret L. Byron is an Assistant Professor of Mechanical Engineering at Penn State University, where she directs the Environmental and Biological Fluid Mechanics (EBFM) Laboratory. She received her B.S.E. from Princeton University in Mechanical and Aerospace Engineering (2010), and her M.S. and Ph.D. from the University of California Berkeley (2012/2015). From 2015 – 2017 she was an NSF Postdoctoral Fellow in Biology at the University of California Irvine. She is a recipient of the American Chemical Society Doctoral New Investigator Award (2019), the Arnold and Mabel Beckman Foundation Young Investigator Award (2021), and the NSF CAREER Award (2022). Dr. Byron’s group studies the interactions between organisms and particles in environmental flows, with a particular focus on intermediate scales where inertial and viscous fluid forces are both important. She is interested in how animals control their position and orientation in turbulence, how swimming strategies scale with size and speed, and what this implies for their overall behavior and distribution in aquatic environments. She is also exploring the effects of particles’ size, shape, and mass properties on their kinematics in environmental flows; these problems have implications for sediment and pollutant transport.


 

Roger E.A. Arndt Fellowship Award Ceremony & Distinguished Lecture by Alfredo Soldati

Presentation of the 2023 Roger E.A. Arndt Fellowship

Distinguished Speaker: Alfredo Soldati, Professor of Fluid Mechanics at the Technische Universität Wien – TU Wien (Austria)

Title: Dynamics of complex particles in turbulence

Photo of Alfredo Soldati

Abstract: Turbulent flows with suspended anisotropic particles of non-spherical shape are a common occurrence in many industrial (e.g. paper making, pharmaceutical processing, soot emission) and natural processes (e.g. pollen species, icy clouds, and plankton and marine snow). The dynamics of small anisotropic particles is determined by velocity gradients and in turn by the smallest turbulence scales, and although we have a fundamental understanding on the dynamics of such turbulence scales, since no closed form of the drag on non-spherical particles is available, predictive understanding of the dynamics of anisotropic particles remains elusive. This insufficient knowledge is at the basis of our lack of predictive tools to describe anthropogenic oceanic pollution of plastic microfibers, which are elongated, anisotropic and of the order of the smallest scales of turbulence. In this talk, we will briefly review the models used to describe the dynamics of small ellipsoidal particles in turbulence, and then we will add a further complexity consisting on allowing the elongated particles to be slightly curved: this slight curvature will be instrumental in determining the complete rotational dynamics of the particles in turbulence. Experiments performed in the TU Wien Turbulent Water Channel will be presented elaborating on the full dynamics of small non- axisymmetric –quasi-straight to slightly curved – fibers. We will highlight the role of fibers curvature on spinning and tumbling rates and we will propose conceptual models and scalings laws.

Figure 1: Measurement of a non-axisymmetric fibre travelling close to the wall of a turbulent channel flow, represented here by the grey surface. Front view is shown. Fibre is coloured according to the instantaneous tumbling rate ΩtΩt normalised by the mean value computed over the entire track |ΩtΩt| (From M. Alipour, M. De Paoli, and A. Soldati (2022) “Influence of Reynolds number on the dynamics of long non-axisymmetric fibers in channel flow turbulence”, J. Fluid Mech. 934, A18-27.)

Figure 1: Measurement of a non-axisymmetric fibre traveling close to the wall of a turbulent channel flow, represented here by the grey surface. Front view is shown. Fibre is colored according to the instantaneous tumbling rate ΩtΩt normalized by the mean value computed over the entire track |ΩtΩt| (From M. Alipour, M. De Paoli, and A. Soldati (2022) “Influence of Reynolds number on the dynamics of long non-axisymmetric fibers in channel flow turbulence”, J. Fluid Mech. 934, A18-27.)

AboutAlfredo Soldati is a Professor of Fluid Mechanics at the Technische Universität Wien – TU Wien (Austria). The focus of the research of his group is on multiphase flows, and specifically on the fundamentals of turbulent dispersed flows of particles, bubbles, and droplets.

After his PhD in chemical Engineering at the University of Pisa (Italy), and a visiting appointment at UCSB (CA), Dr. Soldati became assistant, associate and full professor at the University of Udine. He has been guest Professor at EPFL (Switzerland), at INP Toulouse (France) and at Scuola Superiore Sant’Anna Pisa (Italy). He is fellow of the American Physical Society (APS) and of the European Mechanics Society (EUROMECH), the recipient of the 2007 Knapp award and of the 2015 Lewis F. Moody Award from the American Society of Mechanical Engineers (ASME), the recipient of the International Prize and Gold Medal Panetti–Ferrari, from Accademia delle Scienze di Torino, Italia, and is awarded the 2020 ASME Freeman Scholarship and Lecture. Dr. Soldati is currently part time professor at University of Udine, and he is the Rector of the International Center for Mechanical Sciences, CISM. Dr. Soldati is Co-Editor in Chief of International Journal of Multiphase Flow.
 

Award Recipient: Amy Tinklenberg, Aerospace Engineering and Mechanics at the University of Minnesota.

Photo of Amy Tinklenberg

Abstract: Predicting the fall speed of frozen hydrometeors in the atmosphere is complicated by their unique geometries as well as by the air turbulence. Snowflakes and ice crystals often exhibit rimed branches resembling perforated shapes, which make them permeable to the air flow. This alters their wake dynamics in ways that have not been characterized in turbulence. As analogue to plate crystals, here we consider thin disks of 3 mm in diameter and compare geometries with and without perforations. These are dropped at controlled volume fractions into a large chamber generating a large region of approximately zero-mean-flow homogeneous air turbulence. Two turbulence levels are considered and contrasted with quiescent air conditions. The disks are imaged at 4300 Hz and their linear and rotational motion is reconstructed. Comparison of the solid and perforated disk behaviors in quiescent air shows that the perforated disks fall at a slower velocity than the solid disks. The perforated disks also fall more stably compared to the solid, which may either fall flat or tumble. In turbulence, both disk types experience a reduction in their average settling velocity, as compared to quiescent air, but the perforated disks are more mildly influenced by this effect.

About the recipientAmy is a Ph.D. Candidate in Aerospace Engineering and Mechanics at the University of Minnesota. She works with advisor Filippo Coletti (ETH Zürich) and co-advisor Michele Guala (UMN). She experimentally investigates the settling dynamics of solid and perforated disks in both quiescent and turbulent air, aimed at better understanding and predicting frozen hydrometeor settling in the atmosphere. Originally from Minnesota, she received her Bachelor's in Mechanical Engineering from the University of St. Thomas (2019), followed by her Master’s in Aerospace Engineering and Mechanics from the University of Minnesota (2022). 


 

 

The role of meltwater in reshaping the structures of icy porous media

Xiaojing (Ruby) Fu, Assistant Professor of Mechanical and Civil Engineering at California Institute of Technology. 

Abstract: Icy porous materials such as snow or firn are ubiquitous in both Earth and planetary settings. Their microstructures (e.g., porosity) play an important role in dictating the reflectivity, fluid storage capacity, thermal conductivity, and mechanical properties of the larger-scale systems. Thus, understanding the complex physics that control the microstructure evolution of icy porous media is an important component in creating robust predictions of Earth’s cryosphere in response to climate warming, and in devising engineering strategies for the exploration of icy moons in our solar system. While it is well known that gravity-driven compaction leads to densification of the pore structure over depth, less is known about the role of meltwater in reshaping the structures of icy porous media across scales.


In this talk, I will describe our recent efforts in understanding how the movement of liquid water through porous ice reshapes its porosity structure via flow instability and phase transitions of water.  I will first discuss the pore-scale problem and present a phase-field model that simultaneously captures the phase transitions of water amongst its liquid, solid and vapor phases. With this model, we show that the presence of quiescent meltwater films can accelerate the microstructural coarsening of porous snow during the process of metamorphism.  Next, I will describe a Darcy-scale model that demonstrates how melt refreezing coupled with unstable infiltration reshapes the porosity structure of snow and leads to the formation of ice pipes and ice lenses commonly observed in the field. I will conclude by discussing the implications of these new physical insights for large-scale meltwater transport and hydrological processes in snow and glacial systems.

 

Xiaojing (Ruby) Fu Headshot


About: Xiaojing (Ruby) Fu is an Assistant Professor of Mechanical and Civil Engineering at California Institute of Technology. She received her BS in Applied Mathematics from Clarkson University, a MS in Computational Engineering, and a PhD in Civil & Environmental Engineering from MIT. She is awarded the Miller Postdoctoral Fellowship at UC Berkeley in 2018, hosted by the Earth & Planetary Science department. She joined Caltech in 2021 and leads the Mechanics of Porous Media Flow group. Her group studies the physics of multiphase fluid mechanics through porous media and how it shapes our natural and engineered environments, using theory, modeling, and laboratory experiments. 
 

Symmetries and asymmetries in how falling snowflakes interact with irregular turbulent atmospheric flows

Tim Garrett, professor in Atmospheric Sciences at the University of Utah and Chief Scientific Advisor at Particle Flux Analytics Inc. 

Abstract: A long-standing problem in fluid dynamics is how nonspherical inertial particles settle in a turbulent fluid. From a theoretical standpoint, the problem appears nearly intractable, at least without introducing substantial idealizations. We have approached the problem observationally by focusing on snowflakes using a combination of Lagrangian motion tracking and the first direct automated microphysical measurements of snowflake mass and density using a hotplate-based disdrometer. Examining an exceptionally broad range of turbulence and microphysical conditions, we observe that snowflakes can have settling speeds much lower or higher than the terminal fall speed in still air, and that the magnitude of the enhancement can be parameterized as a power-law function of snowflake shape and the turbulent intensity. While the distribution of the turbulence-induced settling enhancement is highly asymmetric, remarkable simplicity and symmetry is seen for turbulence-induced accelerations. Fat tails encompass ~1% of measurements forcing snowflake accelerations as high as 14 times gravity, and root-mean-square accelerations are many times higher than anticipated for fluid tracers in homogeneous isotropic turbulence. Notably a single, symmetric, rms-normalized frequency distribution describes snowflake accelerations independent of turbulent Reynolds number. Perplexingly, the same distribution even applies to Eulerian variability in snowflake terminal velocities, a quantity that is ostensibly independent of turbulence. The picture presented is that, despite the apparent complexity of the problem, the accelerations of natural, non spherical particles settling in irregular turbulence are governed by some underlying simplicity, and that there may be a hidden link between instantaneous snowflake movements measured near the ground and the microphysical processes that determine their terminal fall speed variability higher up in clouds.
          

Photo of snowflakes

About: Tim Garrett received his B.Sc in Physics from the University of Waterloo. He went on to complete his M.S. and his Ph.D. in Atmospheric Sciences from the University of Washington. He works on clouds and precipitation as they relate to climate. 

Earth Surface Processes and Biogeochemistry: Responses to Gobal W"o"rming

Kyungsoo Yoo Professor in the Department of Soil, Water, and Climate at the University of Minnesota and the lead of the Soil Geomorphology and Biogeochemstry Group

Abstract: Earthworms are fascinating animals. Where they are abundant, they are one of the biggest consumers of plant biomass. Simultaneously, they are ecosystem engineers that shape the structure of soils. In the formerly glaciated and peri-glacial regions of the world, including Minnesota, the ice and cold wiped out native earthworms before the Holocene. With climate warming, forests and prairies reoccupied the newly emerging lands following the retreating glaciers. Earthworms, however, being slow creatures, could not keep up. The vast ecosystems in High Latitudes have evolved without earthworms. Only recently, the status quo has been fundamentally and rapidly altered globally. Expanding imperialism, farming, gardening, logging, housing developments, recreational hiking and fishing, and other human activities helped spread exotic earthworms worldwide.

Here, I show the global-scale expansion of European earthworms and their drastic impacts on soils in Minnesota, Fennoscandia, and Alaska. I will also show how a new wave of jumping worms of Asian origin may replace European earthworms while creating entirely new soils. My primary goal is to excite engineers and earth scientists about the yet unexplored research opportunities in exploring how Earth's surface processes respond to Global W"o"rming.                  

Professor Yoo in Tall Grass Doing Field Research

About: Professor Yoo received his B.S. in Physics at Yonsei University in Seoul, South Korea. He went on to receive a Master's in Atomic Physics at the same university. He received his Ph.D. in Ecosystem Sciences at the University of California - Berkeley and received his Postdoctoral Fellowship at the same university studying Soil Geomorphology. He is currently a Professor in the Department. of Soil, Water, and Climate at the University of Minnesota. 

Locomotion of flagellated bacteria: From the swimming of single bacteria to the collective motion of bacterial swarm - Xiang Cheng, University of Minnesota

Xiang ChengAssociate Professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota

AbstractA flagellated bacterium exhibits fascinating swimming behaviors both as an individual cell and as a member of collectively moving swarm. I discuss two recent experimental works in my group on the swimming behaviors of Escherichia coli, a prominent example of flagellated bacteria. First, we study the motility of flagellated bacteria in colloidal suspensions of varying sizes and volume fractions. We find that bacteria in dilute colloidal suspensions display the quantitatively same motile behaviors as those in dilute polymer solutions, where a size-dependent motility enhancement up to 80% is observed accompanied by a strong suppression of bacterial wobbling. By virtue of the well-controlled size and the hard-sphere nature of colloids, this striking similarity not only resolves the long-standing controversy over bacterial motility enhancement in complex fluids, but also challenges all the existing theories using polymer dynamics in addressing the swimming of flagellated bacteria in dilute polymer solutions. We further develop a simple hydrodynamic model incorporating the colloidal nature of complex fluids, which quantitatively explains bacterial wobbling dynamics and mobility enhancement in both colloidal and polymeric fluids. Second, we study the collective motion of dense bacterial suspensions as a model of active fluids. Using a light-powered E. coli strain, we map the detailed phase diagram of bacterial flows and image the transition kinetics of bacterial suspensions towards collective motions. In particular, we examine the configuration and dynamics of individual bacteria in collective motions. Together, our study sheds light onto the puzzling motile behaviors of bacteria in complex fluids and provides insights into the collective swimming of bacterial suspensions relevant to a wide range of microbiological and biomedical processes.                  

Xiang Cheng

AboutXiang Cheng received his B.S. in physics from Peking University in China in 2002. He then moved to U.S. and obtained his Ph.D. in physics from the University of Chicago in 2009. He worked as a postdoctoral associate in the Department of Physics at Cornell University from 2009 to 2013. He is currently an associate professor at the Department of Chemical Engineering and Materials Science at the University of Minnesota. Dr. Cheng has received several academic awards, including Arthur B. Metzner Early Career Award from Society of Rheology, NSF Career Award, Packard Fellowship, DARPA Young Faculty Award, 3M non-tenured faculty award and McKnight Land-Grant Professorship. His research group studies biophysics and soft materials physics in experiments, with a special focus on the emergent flow behaviors in biological and soft matter systems. Particularly, his research interests include bacterial locomotion, hydrodynamics of active fluids, rheology of colloidal suspensions and dynamics of liquid-drop impact processes.

Nels Nelson Memorial Fellowship with Distinguished Lecture by Prof. Peter Sullivan

Join us on Tuesday, May 2nd at 3pm for a celebration of the 2023 Nels Nelson Memorial Fellowship recipient Noah Gallagher, with a distinguished lecture by Prof. Peter Sullivan.

Peter Sullivan, Senior Scientist in the Mesoscale and Microscale Laboratory at the National Center for Atmospheric Research and affiliate faculty in the Civil Engineering Department at Colorado State University

Distinguished lecture: Marine boundary layers coupled to ocean surface heterogeneity: Secondary circulations in LES process studies

Abstract: Numerical simulations of the atmospheric boundary layer often adopt a horizontally homogeneous lower boundary - a simplifying assumption that is seldom if ever found in nature.  Field observations are collected above spatially varying land and ocean surfaces, and then surface heterogeneity is a source of uncertainty when comparing simulations and observations.  The ocean surface in particular features high spatial variability in sea surface temperature (SST), currents, and surface waves over a broad range of horizontal scales. The present work uses large-eddy simulation (LES) to examine the impact of heterogeneous SST on the marine atmospheric boundary layer. The imposed heterogeneity is a single-sided warm or cold front with temperature jumps varying over a horizontal distance between $[0.1 - 6]$\,km characteristic of an upper ocean mesoscale or submesoscale regime. A specially designed numerical Fourier-fringe technique is implemented in the LES to overcome the usual assumptions of horizontally homogeneous periodic flow.  The winds oriented across (or perpendicular) to the fronts develop secondary circulations with rotation varying with the sign of the front. Warm fronts feature overshoots in the temperature field, non-linear temperature and momentum fluxes, a local maximum in the vertical velocity variance and an extended spatial evolution of the boundary layer with increasing distance from the SST front.

Eddy image

 

Large eddy simulation (LES) is also used to elucidate eddy impacts on the atmospheric boundary layer (ABL) forced by winds, convection, and an eddy with varying radius; the maximum azimuthal eddy speed is 1\,m\,s$^{-1}$.  Simulations span the unstable regime $-1/L = [0, \infty]$ where $L$ is the Monin-Obukhov (M-O) stability parameter. Eddy currents induce a surface stress anomaly that induces Ekman pumping in a dipole horizontal pattern.  The dipole is understood as a consequence of surface winds aligned or opposing surface currents.  In free convection a vigorous updraft is found above the eddy center and persists over the ABL depth. With winds and convection, current stress coupling also generates a dipole in surface temperature flux even with constant sea surface temperature.  Wind, pressure, and temperature anomalies are most sensitive to an eddy under light winds. Flow over an isolated eddy develops a coherent ABL "wake" and secondary circulations downwind.  Kinetic energy exchanges by wind-work indicate an eddy-killing effect on the oceanic eddy current, but only a spatial rearrangement of the atmospheric wind-work.

About: Peter Sullivan is a Senior Scientist in the Mesoscale and Microscale Laboratory at the National Center for Atmospheric Research and an affiliate faculty in the Civil Engineering Department at Colorado State University. Peter received his Bachelor's and Ph.D Degrees in Civil Engineering from Colorado State University and a Master's Degree in Mechanical Engineering from University of British Columbia. Prior to coming to NCAR, Peter worked for six years as a Senior Specialist Engineer in Aerodynamics Research at the Boeing Company where he worked on shock/boundary-layer interaction, drag reducing riblets, and the design of the 777 transonic airplane.

Peter's research interests at NCAR are: simulations and measurements of geophysical turbulence, subgrid-scale modeling, air-sea interaction, effects of surface gravity waves on marine boundary layers, submesoscale turbulence in the upper ocean, impacts of stratification, turbulent flow over hills, and numerical methods. He uses large-eddy and direct numerical simulations to investigate turbulent processes in both the atmospheric boundary layer and the ocean mixed layer. These turbulence simulation codes run on large parallel supercomputers. Peter has participated in and planned field campaigns, Horizontal Array Turbulence Study, Ocean Horizontal Array Turbulence Study, and Canopy Horizontal Array Turbulence Study focused on the measurement of subgrid scale variables in the atmospheric surface layer.


2023 Nels Nelson Memorial Fellowship recipient Noah Gallagher, advised by Prof. John Gulliver

Presentation titleAssessing Stormwater Adaptations for Extreme Rainfall Events

AbstractExtreme rainfall events in recent decades are more frequent and intense. The increase in precipitation has large ramifications for urban landscape design, stormwater runoff management, and flood control. This presentation will share the final results and recommendations of a research project: Climate Change Adaptation of Urban Stormwater Infrastructure, funded by the Local Road Research Board (LRRB) of MN, which evaluated several different stormwater management strategies and their effectiveness in the face of climate driven extreme rainfall events. The strategies include upsizing storm sewer pipes, adding wet ponds, retrofitting existing stormwater ponds to be “smart” ponds, adding rain gardens, and others. In order to evaluate the efficacy of a strategy, the project team used the U.S. EPA’s SWMM software to model adaptations to three Minnesota watersheds for a variety of rainfall depths and return periods. The cost of adaptations was also considered, leveraging data from the Water Research Foundation’s “Community-enabled Lifecycle Analysis of Stormwater Infrastructure Costs” (CLASIC). With these research results, stormwater managers can compare and contrast different adaptation strategies to aid their decision making when updating and adapting their stormwater management systems.

Noah Gallagher

About: Noah Gallagher is a Ph.D. student in the Department of Civil, Environmental and Geo-Engineering working with the Stormwater Research Group led by Dr. John Gulliver at St. Anthony Falls Laboratory. His research focuses on modeling extreme precipitation events, particular future events that have been enlarged by climate change. This work aims to better link watershed models to observable landscape characteristics and use results of those models to recommend the most cost effective methods for adapting to these large return interval events. Prior to starting graduate work, Noah received his Bachelors of Environmental Engineering from the University of Minnesota, where he worked with SAFL's Stormwater Group and CEGE's Novak Lab on laboratory and field measurements for a variety of projects.

Revealing the Hydrodynamics of Fish Schooling: Flow-Mediated Cohesion, Performance Benefits, and Scaling Laws - Keith Moored, Lehigh University

Keith MooredAssociate Professor in the Department of Mechanical Engineering and Mechanics at Lehigh University

AbstractFish schools are fascinating examples of self-organization in nature. They serve many purposes from enhanced foraging, and protection against predators to improved socialization and migration.  Beyond the implications for biology, engineers can take inspiration from the hydrodynamic benefits of schooling to apply to the design of schools of next-generation bio-robotic vehicles.  This new class of schooling unmanned underwater vehicles would enable unprecedented efficiency, maneuverability, agility and stealth; as well as unlock novel missions that require distributed tasks or swarming.  However, our understanding of the hydrodynamic interactions in schools is primitive.  Importantly, the links from the organization, synchronization, and kinematics of individuals to the performance and stability of a school has yet to established. 

In this talk I will present recent work examining the influence of school organization and synchronization on the locomotion performance and stability of simple interacting pitching hydrofoils.  Experiments and potential flow simulations will detail the flow interactions that occur between a pair of pitching hydrofoils – a minimal school – with an out-of-phase synchronization. It is discovered that the flow interactions provide cohesion between the foils and, specifically, that there is a two-dimensionally stable equilibrium arrangement that arises.  This stable side-by-side arrangement is verified numerically and, for the first time, experimentally for freely-swimming foils undergoing dynamic recoil motions.  Significant thrust and efficiency benefits are also determined for various organizations of the minimal school.  Focusing in on the side-by-side organization, the origin of the forces that balance to produce an equilibrium arrangement are discovered. New physics-based scaling laws are developed for the hydrofoils’ equilibrium arrangement, thrust generation, and power consumption, which are found to be in good agreement with inviscid simulations and viscous experiments.  Going beyond a minimal school, we examine stable arrangements for larger schools of foils by searching for repeating patterns of known stable arrangements.  Advances toward examining stable arrangements in real fish schools, and bio-robots alike will be discussed.

Keith Moored

AboutDr. Keith Moored is an Associate Professor in the Department of Mechanical Engineering and Mechanics at Lehigh University.  He received a B.S. in Aerospace Engineering and a B.A. in Physics at the University of Virginia in 2004, and his Ph.D. in Mechanical and Aerospace Engineering also from the University of Virginia in 2010. From 2010-2013, he was a Postdoctoral Research Associate and Lecturer in Mechanical and Aerospace Engineering at Princeton University.  Dr. Moored’s research interests are in bio-inspired propulsion, unsteady aerodynamics and fluid-structure interaction.  He is currently leading an ONR MURI topic on the hydrodynamics of schooling and has previously been a PI on another MURI topic on non-traditional propulsion.  He has received an NSF CAREER award for examining the fluid dynamic interactions among schooling swimmers.