SAFL building

Every 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., either online, in the SAFL Auditorium or as hybrid events. 

Fall 2023 Seminar Series

September 19th - Kyungsoo Yoo
October 3rd - Tim Garret
October 17th - Ruby Fu
November 7th - Daniel Griffin
November 15th - Alfredo Soldati
November 28th - Don Anderson
December 12th - Margaret Byron

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

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. 

3D Transport Parameterization of Solutes and Bacteria in Geologic Porous Media Using Positron Emission Tomography Data, Deep Learning, and Numerical Methods - Christopher Zahasky, UW-Madison

Christopher Zahasky, Assistant Professor in the Department of Geoscience at the University of Wisconsin-Madison

Abstract: Quantification and prediction of aqueous and bacterial contaminants in groundwater requires a fundamental understanding of multiscale permeability, and mechanisms of bacteria transport and attachment in geological materials. In this seminar, I’ll first discuss the use of positron emission tomography (PET) for the measurement of in situ transport processes in geologic systems, including both tracers and colloidal bacteria. Using these datasets, combined with numerical models, we construct a convolutional neural network (CNN) for rapid 3D sub-core permeability inversion of geologic cores samples. I’ll then discuss a second study using these experimental methods to quantify sub-core transport and attachment of E.coli bacteria. Our results illustrate that bacteria attachment is not uniform but can be described by statistical distributions of attachment coefficients that are dependent on system conditions. These experimental methods, combined with deep learning and numerical workflows, provides a robust approach to better understand bacterial transport mechanisms, improve model parameterization, and accurately predict how local geologic conditions can influence the fate and transport bacteria and other contaminants in groundwater.

Chris Zahasky

About: Dr. Christopher Zahasky is an assistant professor at the University of Wisconsin-Madison in the Department of Geoscience. Prior to coming to the University of Wisconsin-Madison, he was a postdoctoral scholar at Imperial College London and Stanford University. He completed his PhD and MSc degrees in Energy Resources Engineering at Stanford University. He completed his Bachelor of Science degree in Geology at the University of Minnesota. His research interests are focused on understanding the fundamental physics and mechanisms of fluid, colloid, and solute transport in geologic systems across length and time scales using experimental observations validated and generalized with analytical and numerical models.

Alvin Anderson Award Ceremony with Distinguished Lecture by Dr. Kenneth Belitz

Join us on Tuesday, April 11th at 3pm for a celebration of the 2023 Alvin Anderson Award recipient Shanti Penprase, with a distinguished lecture by Dr. Kenneth Belitz.

Kenneth Belitz, Research Hydrologist in the Water Resources Mission Area of the United States Geological Survey (USGS)

Distinguished lecture: Old problems, new approach: Applications of Ensemble-Tree Machine Learning to Hydrogeology

Abstract: Ensemble tree modeling is a machine learning method well suited for representing complex non-linear phenomena. As such, ensemble tree modeling can be applied to a wide range of questions in hydrogeology, including questions related to hydrogeologic mapping.  Some questions are problems of regression in which one seeks an estimate of a continuous variable.  For example, what is the depth to the water table across a region of interest? Other questions are problems of classification.  For example, across a region of interest and over a range of depths, is groundwater oxic or reduced?

The U.S. Geological Survey National Water Quality Assessment project (NAWQA) has used ensemble tree methods to address questions related to groundwater quality at regional and national scales. Some of our models evaluate the three-dimensional distribution of factors that can affect groundwater quality, such as pH, redox, and groundwater age. In turn, the modeled factors were used in subsequent models to map the three-dimensional distribution of contaminant concentrations. In our experience, ensemble tree models are a powerful tool for answering difficult questions. They can be used as a complement to process-based modeling and to make predictions at scales that preclude the use of process-based approaches.

Ken Belitz

About: Dr. Kenneth Belitz is a Research Hydrologist in the Water Resources Mission Area of the United States Geological Survey (USGS). He received his B.A. in Geology from Binghamton University, and Ph.D. in hydrogeology from Stanford University in 1985.  His dissertation examined the evolution of large-scale groundwater flow in the Denver Basin under the direction of Dr. John Bredehoeft. Throughout his career, Ken has simultaneously pursued two fronts: improving the fundamental hydrogeologic framework of the conterminous U.S., and employing numerical models – and, most recently, machine learning – in novel ways to better understand regional-scale groundwater quality and to project our current understanding into unsampled space.

Upon completing his Ph.D., Ken joined the USGS California Water Science Center, where he constructed a model of the western San Joaquin Valley; this model and its underlying framework became the gold standard and basis for subsequent models of this critically important aquifer system. From 1990-1997 Ken taught at Dartmouth University and Queens College of New York, before returning to the USGS in 1998 to lead an interdisciplinary team studying the water quality of the intensely urbanized Santa Ana River Basin as part of the USGS National Water Quality Assessment (NAWQA) Program. In this capacity, Ken began to develop a systematic approach to large-scale groundwater-quality assessment founded on a deep understanding of groundwater flow. From 2003-2012, Ken up-scaled this approach to obtain representative, unbiased water-quality data for the groundwater resources of the entire state of California. This work yielded new insights into the processes behind the spatial distribution of critical contaminants including perchlorate, pharmaceuticals, and hexavalent chrome. Ken then led the design and implementation of the groundwater component for the USGS NAWQA Program’s third decade. The design characterizes water quality in the most productive principal aquifers, cumulatively representing 85 percent of the Nation’s GW-derived drinking-water supplies. Ken’s work has given us an unbiased and surprising perspective on the relative risks of geogenic and anthropogenic contaminants, while evaluating constituents not previously sampled for at the national scale. Ken is a GSA Fellow and has received numerous USGS awards for his publications and service.

2023 Alvin Anderson Award recipient Shanti Penprase, advised by Prof. Andy Wickert

Presentation titleImpacts of glacially-driven base level change on river channel long profile across timescales: Whitewater River, southeastern Minnesota

AbstractChanges in water and sediment supply from the Laurentide Ice Sheet resulted in alternating episodes of aggradation and incision for the upper Mississippi River and its tributaries. In this presentation, I present work on the impacts of changing Mississippi River bed elevation on the Whitewater River, a tributary of the Mississippi whose catchment remained unglaciated during the Last Glacial Maximum. By connecting the formation of terraces in tributaries with the evolution of the mainstem Mississippi, we build on our understanding of the regional geomorphic response to base-level fluctuation. We use a combination of topographic analysis and geochronologic methods to reconstruct changes in the channel long profile of the Whitewater River during this time. This work better constrains the timing and extent of fluvial-network response to changes in the Laurentide Ice Sheet, particularly within river systems that were not directly connected to the ice front. Further, this field-based data set on river response to base-level change and terrace genesis captures real-world complexity in a natural system and can catalyze greater understanding of river long-profile response to abrupt base-level fall.

Shanti Penprase

AboutShanti Penprase is a PhD candidate in the Department of Earth & Environmental Sciences working with Professor Andy Wickert. Her research combines field methods, geochronology, and computational approaches to explore how river systems in Minnesota evolved from the most recent glacial–post-glacial transition to the start of Euro-American agriculture. Prior to UMN, she earned her BA in Geology from Carleton College and worked in water quality and community outreach in the Twin Cities for several years. In addition to research, Shanti is passionate about teaching, mentorship, and working collaboratively to build community knowledge and engagement.

Making Canoes Making Kin Making Waves: The Native Canoe Program with Ȟaȟáwakpa (Dakota) / Misi-Ziibi (Anishinaabe) / The Mississippi River - Vicente Diaz, University of Minnesota

Vicente Diaz, Department Chair and Distinguished University Teaching Professor in the Department of American Indian Studies at the University of Minnesota

AbstractThis talk presents an overview of The Native Canoe Program's engaged research, learning/teaching, and community building through Indigenous watercraft and the "craftwork" of Indigenous Ecological Knowledge about water/land/sky.  Central to the program's activities, which include building and use of Native canoes from Oceania and Turtle Island, and virtual, augmented, and mixed reality simulations in partnership with the University of Minnesota's I/V Immersive Lab, is the imperative to rebuild relations of kinship and reciprocal care with the Mississippi River and other bodies of water and their own kinship and reciprocal relations with land, sky, humans, and other-than-human life forms.

Vince Diaz

AboutVicente M. Diaz (Pohnpeian Carolinian and Filipino from Guam in the Micronesian region of the Pacific) is Distinguished University Teaching Professor, Chair of the Department of American Indian Studies, and Founder and Director of The Native Canoe Program at the University of Minnesota-Twin Cities.  Diaz works at the intersection of American Indian and Pacific Islander canoe culture revitalization, work that involves hands-on canoe building, traditional voyaging practice and ecological knowledge, Indigenous critical theory and digital media production in virtual, augmented, and mixed reality platforms. 

Beyond the Lab Seminars

At SAFL, we value learning from experts in environmental science and fluid mechanics during SAFL Seminars, as well as examining issues, ideas, and areas of study from a multitude of perspectives beyond these disciplines during Beyond the Lab Seminars. Through Beyond the Lab Seminars, we learn from experts in other fields and the community, enriching our understanding of environmental science and fluid mechanics while situating research and other concepts in a holistic context. 

Past Beyond the Lab Seminars include

Do you have an idea for a Beyond the Lab Seminar? Email Clare at

Charles C.S. Song Fellowship Award Ceremony with Distinguished Lecture by Prof. Michael Lamb

Join us on Tuesday, March 28th at 3pm for a celebration of the 2023 Charles C.S. Song Fellowship recipient Shih-Hsun Huang, with a distinguished lecture by Prof. Michael Lamb.

Michael Lamb, Professor in the Division of Geological and Planetary Sciences at the California Institute of Technology

Distinguished lecture: Mud flocculation and the global sediment cycle

AbstractRiver sediment loads are dominated by mud, which builds lowland landscapes and buries large amounts of organic carbon. While mechanistic theories exist for transport of suspended sand, mud in rivers is often thought to constitute washload—sediment with settling rates so slow that it does not interact with the land surface. The washload hypothesis, however, is seemingly at odds with the muddy terrain that abounds globally. Here I summarize recent work by our group to show that mud in many rivers is flocculated with settling velocities much larger than expected for individual particles, which allows it to interact with and deposit on the land. Our results help to explain why muddy landscapes exist today, why they were less abundant earlier in Earth history, and why anthropogenic disruption of the global sediment cycle is causing major unintended land loss.

Mike Lamb

AboutMichael Lamb is a professor in the Division of Geological and Planetary Sciences at Caltech. Lamb’s research combines theory, field observations and flume experiments to understand landscape form and dynamics through the mechanics of erosion, sediment transport and deposition. Current projects include riverbank erosion in permafrost, coastal land building at river deltas, and ancient rivers on Mars. He received his PhD from U.C. Berkeley in Earth and Planetary Science, M.S. in Oceanography from the University of Washington, and B.S. in Geology and Geophysics from the University of Minnesota. He got his start at SAFL as a “junior scientist” from 2000-2001, conducting experiments on turbidity currents in the Garcia Flume, with the help of Gary Parker, Jeff Marr, Chris Paola, Tom Hickson, Chris Ellis and others. His grandfather worked somewhat successfully with Lorenz G. Straub.

2023 Charles C.S. Song Fellowship recipient Shih-Hsun Huang, advised by Prof. Judy Yang

Presentation titleExperimental investigations of hyporheic flow in channels with vegetation and large woody debris

AbstractIn-channel aquatic vegetation and large woody debris exert drag on the surface flow and create the heterogeneity of a hydraulic head along the stream bed, which drives a bi-direction flow through the sediment-water interface, or hyporheic flow. Hyporheic flow increases the retention time of solutes, organic matter, and fine particles, which controls the biogeochemical cycles of the benthic habitats and determines the retention and degradation of contaminants in the stream. While aquatic vegetation and large woody debris have been recognized to induce hyporheic flow in recent field and numerical studies, visualization and systematic quantification of hyporheic flow induced by aquatic vegetation and large woody debris remain lacking due to the opaqueness of sediment, vegetation, and woods. I will describe how we developed a refractive index match-based method to quantify the impact of vegetation and large woody debris on hyporheic flow in a laboratory flume.

Shih-Hsun Huang

AboutShih-Hsun Huang is a PhD candidate in civil engineering at the St. Anthony Falls Laboratory, studying under Professor Judy Yang. His research is focused on the mass transport across the sediment‐water interface in an aquatic environment. He currently studies the impact of in-channel vegetation and large wood debris on the hyporheic flow. Shih-Hsun received his master's degree in civil engineering from National Taiwan University in 2018. He also completed his bachelor's degree in both civil engineering and life science from National Taiwan University in 2016.


“Stay Ashore” … Offshore Wind O&M Automation - Guiju Song, GE Research

Guiju Song, Platform Leader, Offshore Wind, at GE Research located in Niskayuna, NY

AbstractOffshore wind energy is critical to realize the world’s greenhouse gas reduction goal. In the US, the Biden administration has set up the goal of deploying 30GW of offshore wind capacity by 2030. Reducing the levelized cost of energy (LCOE) is key to the large-scale deployment. Offshore operation & maintenance (O&M) cost could potentially contribute to 35% of the LCOE. Therefore, GE launched the “Stay Ashore” O&M strategy aiming to apply digital innovations and automation to significantly lower the offshore O&M cost.  The “Stay Ashore” vision contains four element steps – connect, analyze, manage, and optimize. This seminar focuses on deep diving GE’s research projects funded by the National Offshore Wind Research and Development Consortium (NOWRDC) as the examples for the two steps of “analyze” and “manage”.

The first project is titled as “Enabling condition based- maintenance for offshore wind”. Applying digital innovations such as AI and digital twin to enable condition-based maintenance (CBM) has been proved to be effective in many industries. However, the offshore wind farms in operation today in the US water only have 42 MW of capacity commissioned in the recent few years. There is not a lot of operational history and data to track. Therefore, one of the key challenges in implementing AI and digital twin for offshore wind is lacking historical operational data required for AI/ML model development and validation. Our team was funded by NOWRDC to investigate and develop technical solutions to realize full CBM in offshore wind. To address the data sparsity challenges, we first explored the feasibility of utilizing physics-based models (digital twins) to augment the limited available operational data. Second, an AI/ML modeling method was carefully selected and developed to accurately estimate blade health state over time. Third, the limited data collected from the real-world turbines was utilized to calibrate the AI model.

The second project is titled as “Autonomous Vessel-Based Multi-Sensing System for Inspection and Monitoring”.  The current available inspection and monitoring strategies for offshore wind are either cost prohibitive or limited by varying offshore operational conditions such as weather and sea states. Our project aims to develop a multi-sensing system to conduct robust inspection at varying sea conditions. Such system can enable adaptation of proven technologies from onshore to offshore wind, advance offshore O&M strategy, reduce LCOE, and accelerate the U.S.’s ability to economically deploy offshore wind technology.

At last, I will summarize the key ingredients in our success of completing the first project and elaborate how this innovation can be leveraged and expanded to other applications. I will then reiterate our perspectives on the “Stay Ashore” vision for the offshore wind O&M. 

Guiju Song

AboutDr. Guiju Song is currently the Platform Leader, Offshore Wind, at GE Research located in Niskayuna, NY. In this role, Dr. Song leads the strategic growth and multi-generation technology planning process for Offshore Wind at GE Research. She manages a multi-million R&D project portfolio and supports transitioning the technologies developed by GE Research to new products of GE’s Offshore business. Dr. Song is also a Principal Investigator (PI) and a T2M (technology to market) manager for GE’s government funded Offshore Wind projects.  Prior to her current role, Dr. Song led a team to develop artificial intelligence (AI) and digital technologies to solve challenging industrial problems in the renewable energy and aerospace industries. During her 18+ years of professional experience, Dr. Song has been instrumental in leading multi-disciplinary teams, bridging AI/ML with physics to enable better industrial asset reliability and performance management. As a result of her innovative work in this cross-disciplinary area, Dr. Song has filed 31 US patents. Before joining GE, Dr. Song conducted postdoctoral research in Oregon Health & Science University on Bio-medical engineering. and received her Ph.D. in Optical Engineering from the Chinese Academia of Sciences in 2001.

Heinz G. Stefan Fellowship Award Ceremony with Distinguished Lecture by Prof. Grae Worster

Join us on Tuesday, March 14th at 3pm for a celebration of the 2023 Heinz G. Stefan Fellowship recipient Xiating Chen, with a distinguished lecture by Prof. Grae Worster.

Grae Worster, Professor of Fluid Dynamics in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge

Distinguished lecture: The dynamics of super-absorbent hydrogels


Abstract: Super-absorbent polymers placed in water can form hydrogels with polymer fractions of less than 1% by volume, with the water molecules being adsorbed by the hydrophilic polymer to form an elastic material.  They are used in disposable diapers, for soil remediation, for controlled drug delivery and as actuators in microfluidic devices.  The water is not fixed in place but can flow through the porous polymer scaffold to drive swelling and shrinkage.  We have developed a new continuum-mechanical approach to modelling super-absorbent hydrogels, which allows for strongly nonlinear swelling while remaining linear in deviatoric strains, in effect treating hydrogels as instantaneously incompressible, linear elastic materials but with material properties that can vary strongly with polymer concentration.  I will describe this model and illustrate its features by solving simple examples of swelling spheres, transpiration through cylinders, and by analysing a morphological instability that can arise during swelling.

Grae Worster

About: Grae Worster completed his PhD at the University of Cambridge, UK in 1983.  His early career included being an Instructor in Applied Mathematics at MIT and an Assistant Professor in Applied Mathematics and Chemical Engineering at Northwestern University.  He is currently Professor of Fluid Dynamics in the Department of Applied Mathematics and Theoretical Physics, University of Cambridge UK, and until recently was Editor of the Journal of Fluid Mechanics.  His research has included mathematical and experimental studies of buoyancy-driven flows and phase change, particularly in situations where these two phenomena interact, applying fundamental understanding to environmental problems including the mechanisms affecting brine drainage from sea ice, the flow and stability of marine ice sheets, and dynamics of frost heave.  His focus has been on formulating mathematical descriptions of multi-component systems, including alloys, colloidal suspensions and, latterly, hydrogels.  Since its foundation in 2003, Grae has been a regular lecturer at the African Institute of Mathematical Sciences (AIMS), and he wrote the first book in their library series on "Understanding Fluid Flow."

2023 Heinz G. Stefan Fellowship recipient Xiating Chen, advised by Prof. Xue Feng 

Presentation titleInteraction between green infrastructure and urban hydrology at multiple scales

Abstract: Green infrastructure and other urban greenery are widely implemented to reduce stormwater runoff and mitigate urban heat island effects, but their hydrological functions and related dominant processes differ across scales (e.g., the local, green infrastructure scale, the catchment scale, the regional watershed scale). In this presentation, I will focus on the tree-level soil-plant-atmosphere continuum with preliminary experimental results from ash trees in the City of St. Paul. Using sap flux measurements (evapotranspiration), soil moisture and canopy temperature in urban trees, we reveal some important ecophysiological features that control the urban heat-vegetation-and-water dynamics. I hope to incorporate these physical observations into the watershed-scale understanding of green infrastructure performance, further providing empirical guidelines for integrating municipal forestry and water resources management.

Xiating Chen

About: Xiating Chen is a PhD candidate in water resources engineering at the St. Anthony Falls Laboratory studying under Professor Xue Feng. Her research is focused on eco-hydrological functions of urban trees and other green infrastructure at both local and watershed-scale, through combined field observations and modeling approaches. Xiating received her Bachelor of Science in Engineering degree from Duke University.