Every two weeks 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 or in the SAFL Auditorium. 

Fall 2021 Seminar Series

September 14th - Li Li, Penn State University

September 21st - Ellen Wohl, Colorado State University

October 5th - Michael Howland, Massachusetts Institute of Technology

October 19th - Teri Oehmke, University of New Hampshire

November 2nd - Doug Jerolmack, University of Pennsylvania

November 16th - Luca Brandt, KTH Royal Institute of Technology

November 30th - Eric D'Asaro, University of Washington

December 7th - Boya Xiong, University of Minnesota

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

The Oceanography of Hurricanes with Dr. D'Asaro & Lorenz G. Straub Award Ceremony

Join us on Tuesday, November 30th at 3 pm for a seminar with Dr. Eric D'Asaro and a celebration of the 2019 Lorenz G. Straub Award recipient, Michelle DiBenedetto.

Eric D'AsaroProfessor of Oceanography in the School of Oceanography and Senior Principal Oceanographer at the Applied Physics Laboratory at the University of Washington

Abstract: Hurricanes, or more generally Tropical Cyclones, have large impacts on subtropical coastal regions, particularly in North America and southern and eastern Asia.  With climate change, we expect significant changes in these impacts. These storms operate as heat engines, drawing their energy from the transport and condensation of warm seawater against the colder upper troposphere.  Their intensity and evolution is thus affected by the temperature of the underlying ocean and thus ocean dynamics.  This talk will describe these interactions, the tools and strategies used to measure them and present outstanding problems and challenges as well as reviewing the expected changes in the future. 

Eric D'Asaro

About the speakerEric D’Asaro, Professor of Oceanography in the School of Oceanography and Senior Principal Oceanographer at the Applied Physics Laboratory, both at the University of Washington, is an oceanographer working in the upper and coastal ocean. He obtained BS and MS degrees from Harvard University in 1976 and a Ph.D. from the MIT/WHOI Joint program in oceanography in 1980.  Although primarily a physical oceanographer, he also collaborates with biological and chemical oceanographers and meteorologists on a broad range of interdisciplinary problems.  He developed the Lagrangian float, a new class of instruments to measure turbulence and mixing and their interdisciplinary impacts.  He has led numerous US and international field programs and has approximately 150 peer-reviewed publications.  He is an associate editor of the Journal of Physical Oceanography, a Fellow of the American Geophysical Union and the American Meteorological Society, the 2011 recipient of the Sverdrup Gold Medal and a member of the National Academy of Sciences.

2019 Lorenz G. Straub Recipient Michelle DiBenedetto, Assistant Professor in the Mechanical Engineering Department at the University of Washington

Michelle's work: Plastic pollution in the ocean breaks down and persists as small particles, or microplastics. Accurately assessing microplastics sources and sinks requires a thorough understanding of the transport and dispersal of microplastics in the ocean. Here I consider microplastics transport in surface gravity waves, as waves control many transport processes at the ocean surface and along the coasts where microplastic pollution is abundant. Of particular interest is how the characteristics of microplastic particles, such as their size and shape, affect their transport. Particle shape couples to transport through particle orientation. Using a finite-amplitude correction, I show how spheroidal particles tend to a preferred orientation under waves. This orientational behavior is a consequence of how the particle samples the wave flow and is found to be the angular analog of Stokes drift. The mean preferred orientation is found to be solely a function of the particle’s shape. The implications of this theoretical result were explored with both numerical and laboratory experiments, and the effects of the waves and the particle characteristics are shown to be non-trivial for predicting transport of the particles.


About: Michelle DiBenedetto is an Assistant Professor at University of Washington Seattle in the Mechanical Engineering Department. She received her B.S. from Cornell University in 2014 in Environmental Engineering, and her Ph.D. from Stanford University in 2019 in Civil & Environmental Engineering, where she studied the behavior and transport of non-spherical particles in surface gravity waves. For her dissertation work, she was awarded the 2019 Andreas Acrivos Dissertation Award in Fluid Dynamics from the American Physical Society. Prior to joining UW, she was a Weston Howland Jr. Postdoctoral Scholar at Woods Hole Oceanographic Institution in the Biology and Physical Oceanography Departments. Currently, she is an Early Career Board Member of the journal Physical Review Fluids. Her lab uses laboratory experiments, theory, and numerical simulations to study problems at the intersection of environmental fluid mechanics and particle-laden flows.

History of the Fellowship: The Lorenz G. Straub Award is awarded annually for the most meritorious thesis in hydraulic engineering, ecohydraulics, or a related field. Applicants are internationally entered and nominations may be made by any recognized civil and environmental engineering program in the world. The establishment of the Lorenz G. Straub Award was announced at the dedication of the Lorenz G. Straub Memorial Library within St. Anthony Falls Laboratory by Edward Silberman. When the Straub Award was established, it was recognized that it was unique in its nature. In the years of its existence, it has come to be widely recognized professionally and has accrued much honor to its recipients.

Past Seminars

Simulations of channel flow of finite-size particles with Dr. Brandt & Roger E.A. Arndt Award Ceremony

Join us on Tuesday, November 16th at 3 pm for a seminar with Dr. Luca Brandt and a celebration of this year's Roger E.A. Arndt Fellowship recipient, Jiyong Lee.

Luca Brandt, Professor in the Department of Engineering Mechanics (KTH, Sweden) and in the Department of Energy and Process Engineering (NTNU, Norway)

AbstractThe flow of particle suspensions is one of the fluid mechanics problems not yet resolved, and with a wide range of applications in industry and natural phenomena. In recent work, we have proposed the use of interface resolved numerical simulations, in parallel to experiments, to shed light on how the presence of rigid solid particles affects laminar and turbulent flows in channels and pipes. In particular, considering the simplest case of neutrally-buoyant spherical particles, simulations have enabled us to identify 3 distinct regimes in the parameter space defined by the particle volume fraction and Reynolds number: i) a laminar-like regime, dominated by viscous stresses in the liquid phase, ii) particle-laden turbulence at higher Reynolds number and moderate solid volume fraction, iii) particulate flow at higher volume fractions. In this regime particles tend to migrate towards the channel centre and turbulent fluctuations are quenched. Interestingly, the increase of drag due to the presence of the solid phase is approximately balanced by the turbulence attenuation induced by the high concentrations at the channel centerline, so that the turbulent drag is of the order of the single-phase values, as shown by experiments extending to Reynolds numbers larger than those typically achieved in simulations. More recent work investigated how the different flow regimes alter heat transfer in the suspensions.  This is enhanced by the presence of the particles in the laminar regime, monotonically with the increase of the solid volume fraction. In the turbulent regime, however, the presence of the particles increases the heat transfer only at low volume fractions; further increasing the number of particles, this drops to values below the single-phase turbulent flow, which is explained by the particle migration towards the channel center, where the particles move as a compact aggregate with weak relative velocities.

Luca Brandt

About the speakerLuca Brandt is professor in Fluid Mechanics at the Royal Institute of Technology (KTH), Stockholm, Sweden since 2012 and at the Department of Energy and Process Engineering, NTNU, Trondheim, Norway since 2021.  He received a Masters in Mechanical Engineering from University of Rome, La Sapienza in 1997, and PhD in Fluid Mechanics at KTH in 2003. Before joining KTH as assistant professor he spent several months at Ecole Polytechnique, Palaiseau, France and at the University of Bologna, Italy. Luca’s research interests are in the general area of multiphase turbulence, particle laden flows, heat and mass transfer, low-Reynolds-number flows and complex fluids, hydrodynamic instabilities and flow control, with focus on the development of theoretical models and high-fidelity numerical simulations. He has more than 180 peer-reviewed journal papers including 1 Annual Review Fluid Mechanics in 2022. He was the recipient of an ERC consolidator grant to study particle suspensions in 2013 and of the "outstanding young researcher" award from the Swedish Research Council in 2014.  He had been awarded the G. Gustafsson prize in 2005 and the position as outstanding researcher in Mechanics by the Swedish Research Council in 2008. Luca has served the community organizing several workshops and summer schools and is associated editor of the European Journal of Mechanics/B and of MECCANICA.

2021-2022 Roger E.A. Arndt Fellowship Recipient Jiyong Lee, Ph.D. candidate in Civil, Environmental and Geo- Engineering, advised by Michele Guala

Jiyong Lee

About the recipient: Jiyong is a 3rd year Ph.D. student in the department of Civil, Environment, and Geo-Engineering, working with Professor Michele Guala. His research focuses on improving sustainability in broad categories: renewable energy technology, river restoration, and monitoring sediment budget in a river. He seeks to achieve his research goals by understanding flow dynamics, sediment transport, landscape evolution, and their complicated interactions in riverine systems. In his PhD thesis, he studies scale-dependent riverbed dynamics and its relation to bedload transport.   

History of the FellowshipAfter completing his PhD in Civil Engineering at MIT in 1967 and working as faculty at Penn State University for several years thereafter, Professor Roger E.A. Arndt first came to the University of Minnesota in 1977 as a professor in the Department of Civil and Mineral Engineering (now the Department of Civil, Environment, and Geo- Engineering) and the Department of Aerospace Engineering (now the Department of Aerospace Engineering and Mechanics). In the over 40 years that Professor Arndt has served the University of Minnesota, he has established himself as a giant in the field of fluid mechanics and applied research. Professor Arndt also continued building SAFL’s legacy of excellence in basic and applied research in the 16 years that he served as SAFL’s director. The Fellowship is to assist and encourage students in the field of fluid dynamics and to allow further research in this area at SAFL. 

Landscapes of Glass with Douglas J. Jerolmack & Silberman Fellowship Award Ceremony

Join us on Tuesday, November 2nd for a seminar with Dr. Douglas Jerolmack and a celebration of this year's Edward Silberman Fellowship recipient, Brandon Sloan.

Douglas J. Jerolmack, Professor, Department of Earth and Environmental Science, University of Pennsylvania 


Abstract: If cooled sufficiently quickly, the disorder of a liquid can be "quenched" or locked in place; the resulting amorphous solid is glass. Although it appears to be solid on human timescales, glass continues to creep due to thermal vibrations at the molecular scale. Consider now a pile of sand; it too is a disordered system, but the grains are too massive for such thermal effects to be relevant. Yet, soils in nature relentlessly creep, on hillslopes below the angle of repose. The unchallenged dogma is that this creep is driven by churning of soil by (bio)physical disturbances, and diffusion models based on this premise underpin virtually all landscape evolution models (LEMs). River-bed sediments also creep, at flows below the threshold of motion, though this has received far less attention. In this talk I focus on recent work from my group and others that examines the origins of granular creep in hillslope and river systems, and the consequences of these findings for landscape dynamics. Our observations, arising from first-of-their-kind experiments and simulations, reveal surprises for both geologists and physicists. First, gravity-driven granular creep occurs with minimal disturbance, with rates and styles comparable to field observations. Second, this creep shares deep similarities with the behavior of glass, suggesting that mechanical disturbance in granular systems plays a role akin to thermal fluctuations in molecular systems. Third, fluid-driven creep in bed-load systems has similar behavior to gravity-driven hillslope creep. In both cases this creep acts to "harden" the bed, by compaction and the creation of structures that resist motion. Thus, sediment beds maintain a memory of their history of forcing, that dictates the threshold for landsliding (hillslopes) or entrainment (rivers). I wish that I could conclude with some new model or models that would incorporate these insights and improve LEMs. But we're just not there yet. We're still in the process of deconstructing old models with challenging observations of what grains do. My hopes, then, are the following: introduce new concepts and frameworks from glass physics that I find helpful for understanding landscapes; engage broader interest (from you!) in HOW landscapes accomplish their deformation; explain qualitative phenomenology of natural landscapes; and get insights from you on "translating" these findings to systems you may care about (or, at least care about more than a pile of sand).

About the speaker: Douglas Jerolmack holds a BS in Environmental Engineering from Drexel University and a PhD in geophysics from MIT. He was a postdoc at SAFL in 2006-2007, where he had the most fun in his academic life. Dr. Jerolmack is currently faculty in Earth and Environmental Science, and Mechanical Engineering and Applied Mechanics, at the University of Pennsylvania. He works on problems at the interface of geophysics and soft-matter physics, and that are solid, fluid and granular. His lab mostly does experiments, but also a little field work and occasionally some theory. 

2021-2022 Edward Silberman Fellowship Recipient Brandon Sloan, Ph.D. candidate in Civil, Environmental and Geo- Engineering, advised by Xue Feng

Brandon's work: Plants respond to and alter the climate by absorbing (eating) energy and CO2 while transpiring (drinking) water from the soil. However, many current climate models over-simplify a plant’s diet—especially when they are dehydrated—by ignoring the physics of how plants eat and drink. Brandon’s research explores how said physics (i.e., plant hydraulic theory) improves predictions of plant drinking habits necessary for accurate climate projection while advancing our understanding of ecosystem resilience under future water stress.

Brandon Sloan

About: Brandon Sloan is a Ph.D. candidate in Civil, Environmental and Geo- Engineering advised by Xue Feng. Born in Chippewa Falls, WI, Brandon has toured the Midwest in his academic/professional career, receiving a B.S. degree in Environmental Engineering from the University of Wisconsin – Platteville, and an M.Sc. in Water Resources from IIHR-Hydroscience and Engineering at the University of Iowa. After a three-year hiatus, working as a Water Resources Engineer in the Twin Cities, Brandon returned to academia, beginning his Ph.D. at SAFL in Fall 2016.

History of the Fellowship: The family of Professor Edward Silberman established this fellowship fund in honor of their father, to endow a lasting legacy in his name to provide fellowships to students at the University of Minnesota’s St. Anthony Falls Laboratory. Silberman earned his B.S. and M.S. from the Department of CivilEngineering in the mid-1930s. He started his career at SAFL in 1946 and took over the directorship of SAFL in 1963 after the death of founding director Lorenz Straub. Over the next decade, Silberman worked tirelessly to build the foundation of excellence from which SAFL’s successes of today are founded. The Silberman family made this gift to honor the lasting contributions of their father to SAFL and in celebration of his 90th birthday.

Shape and size effects of inertial particles in turbulent flow - Theresa B. Oehmke, University of New Hampshire

Theresa B. Oehmke, Postdoctoral Scholar, Department of Mechanical Engineering, University of New Hampshire

Abstract: Understanding how particles interact in turbulent flow is an important and open question with many industrial and natural applications. Using laboratory experiments, I investigate how particles within the inertial subrange of turbulence respond to their environment in terms of their kinematics (translation, orientation, tumbling, spinning) and dissolution rates. By first understanding how size influences motion, we can then determine how that motion should in turn impact dissolution. In this talk I will present methods and results for the 3D reconstruction of flat particle orientation that allows for examination of spinning vs tumbling rates. Then I will discuss how understanding of spinning and tumbling contributes to our knowledge of determining the impacts of shape and size on dissolution of in-house, custom made sugar particles.

Theresa Oehmke

About the speaker: Dr. Theresa B. Oehmke is a Postdoctoral Scholar in Mechanical Engineering at the University of New Hampshire. Dr. Oehmke earned a PhD in Environmental Engineering from UC Berkeley in 2021 and a Bachelor’s of Science in Environmental Engineering Science from Massachusetts Institute of Technology in 2015. Theresa does research related to Environmental Fluid Mechanics. Specifically, she is interested in the transport of particles and pollutants in turbulent flows. Prior research has included work with fibers, cuboids, and flat particles within the inertial subrange to study how size and shape influence particle motion and dissolution. Her research is funded by the National Science Foundation and she is also a recipient of the Make Our Planet Great Again (MOPGA) Fellowship and a two-time recipient of the STEM Chateaubriand Fellowship.

Wind farm optimization through collective control: The role of shear and stability in the atmospheric boundary layer - Michael F. Howland, MIT

Michael F. Howland, Assistant Professor, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology

AbstractHistorically, control protocols have optimized the performance of individual wind turbines resulting in aerodynamic wakes which typically reduce total wind farm power production 10-20%. Wake steering, the intentional yaw misalignment of turbines in a wind farm to deflect energy deficit wake regions, has demonstrated potential as a wind farm control approach to increase collective power production. The potential for wake steering depends, in part, on the power reduction of yaw misaligned turbines. In the atmospheric boundary layer (ABL), the sheared wind speed and direction may change significantly over the rotor area, resulting in a relative inflow wind speed and angle of attack to the blade airfoil which depends on the radial and azimuthal positions. In order to predict the power production for an arbitrary yaw misaligned turbine based on the incident ABL velocity profiles, we develop a blade element model which accounts for wind speed and direction changes over the rotor area, and the model is validated using experimental data from a utility-scale wind farm. Leveraging aerodynamic wind farm models, we designed a physics- and data-driven wake steering control method to increase the power production of wind farms. The method was tested in a multi-turbine array at a utility-scale wind farm, where it statistically significantly increased the power production over standard operation. The analytic gradient-based power optimization methodology we developed can optimize the yaw misalignment angles for large wind farms on the order of seconds, enabling online real-time control. To improve wake steering control in transient ABL conditions, we developed a closed-loop wake steering control strategy, which is tested in large eddy simulations of the terrestrial diurnal cycle, altogether, the results indicate that closed-loop wake steering control can significantly increase wind farm power production over greedy operation provided that site-specific wind farm data is assimilated into the aerodynamic model.

Michael Howland

About the speaker: Michael F. Howland is an Assistant Professor of Civil and Environmental Engineering at MIT. He was a Postdoctoral Scholar at Caltech in the Department of Aerospace Engineering. He received his B.S. from Johns Hopkins University and his M.S. from Stanford University. He received his Ph.D. from Stanford University in the Department of Mechanical Engineering. His work is focused at the intersection of fluid mechanics, weather and climate modeling, uncertainty quantification, and optimization and control with an emphasis on renewable energy systems. He uses synergistic approaches including simulations, laboratory and field experiments, and modeling to understand the operation of renewable energy systems, with the goal of improving the efficiency, predictability, and reliability of low-carbon energy generation. He was the recipient of the Robert George Gerstmyer Award, the Creel Family Teaching Award, and the James F. Bell Award from Johns Hopkins University. At Stanford, he received the Tau Beta Pi scholarship, NSF Graduate Research Fellowship, a Stanford Graduate Fellowship, and was awarded as a Precourt Energy Institute Distinguished Student Lecturer.

Messy Rivers are Healthy Rivers: The Role of Spatial Heterogeneity in Sustaining River Ecosystems - Ellen Wohl, Colorado State University

Ellen Wohl, University Distinguished Professor, Department of Geosciences, Colorado State University

Abstract: Perceptions of river health are strongly influenced by expectations regarding a natural river. Many observers expect clear water, a slightly sinuous river with pools and riffles, and some riparian trees. River health, however, is much more complicated and multifaceted. The physical appearance of a river, for example, depends strongly on geomorphic context and river history. I use mountainous headwater rivers in Colorado to examine the influence of physical complexity on river health. Complexity can be described with respect to the stream bed, banks, cross-sectional form, and planform of the river and floodplain. The configuration of each of these components of a riverine system has implications for habitat abundance and diversity, sensitivity and resilience of the river to natural and human-induced disturbances, retention of water, sediment and nutrients, and connectivity within the riverine system and between the river and adjacent uplands. Many types of resource use simplify rivers to the point that the river undergoes a metamorphosis, or a thorough, sustained change in channel form and function. Loss of beaver dams and channel-spanning logjams in mountainous headwater rivers in Colorado, for example, has resulted in metamorphosis of physically complex, anastomosing channels that were highly connected to adjacent floodplains. These rivers have assumed an alternate stable state as single-thread channels with limited retention and resilience. Effective, sustainable river restoration involves (i) characterizing the magnitude of different forms of physical complexity naturally present in a particular river segment, (ii) understanding the effects of physical complexity on river ecosystem function, and (iii) assessing the degree to which this level of physical complexity can be restored or mimicked. An important part of this process may be educating stakeholders regarding the importance of physical complexity – messiness – in healthy rivers.

About the Speaker: Ellen Wohl received a B.S. in geology from Arizona State University and a Ph.D. in geosciences from the University of Arizona. She has been on the faculty at Colorado State University since 1989 and is now a University Distinguished Professor. Her research focuses on interactions between physical process and form and biota in river corridors.

The shallow and deep hypothesis: linking flow paths, biogeochemical reactions, and stream chemistry in the Critical Zone - Li Li, Penn State University

Li Li, Professor, Department of Civil and Environmental Engineering, Penn State University

Abstract: Hydrological flow and biogeochemical processes in the Critical Zone (CZ) are intimately coupled, yet their respective sciences have often progressed without as much integration. This lack of integration hinders mechanistic understanding and forecasting of earth surface and water response to human- and climate-induced perturbations. This talk will highlight insights gleaned from integrated hydro-biogeochemical measurements and modeling in the CZ. In particular, recent water chemistry data (carbon, nitrogen, and geogenic solutes) and hydro-biogeochemistry modeling has propelled the idea that shallow and deep flow paths connect waters of distinct chemistries at different subsurface depths to streams under variable flow conditions; and that the extent of shallow versus deep chemistry differences shape concentration-discharge relationship in streams. This idea underscores the importance of subsurface structure and vertical hydrological connectivity relative to the extensively studied horizontal connectivity and topography. Broadly, this hypothesis can potentially serve as a conceptual framework that links CZ subsurface structure to its hydrological and biogeochemical functioning under diverse climate, geology, and land cover conditions.

About the Speaker: Dr. Li Li is a professor in Environmental Engineering at Penn State University. Li received a bachelor and master’s degree in environmental chemistry from Nanjing University in China and a doctoral degree in environmental engineering and water resources from Princeton University. She worked at the Lawrence Berkeley National Laboratory as a postdoc and as a research scientist before joining faculty at Penn State University. Her group asks questions on how external drivers and internal structure regulate water flow paths and biogeochemical processes at the watershed scale under diverse climate, geology, and land use conditions. She is active in the Critical Zone community, and collaborates broadly with biogeochemists, hydrologists, ecologists, and geologists. She has been promoting woman scientists’ work via the Women Advancing River Research (WARR) seminar series.

SAFL Spring Awards Ceremony

SAFL is excited to host a virtual special awards ceremony on May 4th, 2021 that will celebrate students in the St. Anthony Falls Laboratory (SAFL) community. We are tremendously grateful to have such talented, dedicated students at SAFL, and it is a privilege to celebrate them with awards that honor not only them and their accomplishments, but the legacies of the people who have helped SAFL become what it is today.

We will be presenting the 2020 - 2021 Alvin G. Andersen Award, the Heinz G. Stefan Fellowship, and the Nels Nelson Memorial Fellowship. Family members will be present to speak about the award namesakes, the recipients will be introduced by their respective advisors, and the recipients will give remarks on their research.  We expect the event to last approximately an hour. 

2020 - 2021 Award Recipients:

Alvin G. Anderson Award - Kerry Callaghan, former PhD student from the Department of Earth and Environmental Sciences (advisor Andrew Wickert)
Heinz G. Stefan Fellowship - Lun Gao, PhD student from the Department of Civil, Environmental, and Geo- Engineering (advisor Ardeshir Ebtehaj)
Nels Nelson Memorial Fellowship - Yuanqing Liu, PhD student from the Department of Mechanical Engineering (advisor Lian Shen)

You can learn more about this year’s recipients in this linked program

Simulation and modeling of non-canonical turbulent flows - Junlin Yuan, Michigan State University

Junlin Yuan, Assistant Professor, Department of Mechanical Engineering, Michigan State University

Abstract: The bulk of wall turbulence research has focused, perhaps disproportionately, on canonical flows along smooth flat plates with uniform freestream conditions. However, in engineering and environmental applications, such as flow around hydraulic turbine blades, navy platforms and in rivers, we see a wide range of dynamically complicated flow fields, affected by surface roughness, curvature, freestream pressure gradients, and unsteadiness. The consequence is that existing descriptions and models of turbulence have limited utility to design practice. My long term goal is to build essential physics into models, to enable a consistent description for turbulence across a wide range of flow complexities. The first part of the talk will be focused on understanding and modeling for rough-walled, equilibrium turbulence or non-equilibrium ones subjected to longitudinal pressure gradients. Using data from direct and large-eddy simulations (DNS and LES), I will show that roughness significantly modifies turbulence under strong spatial or temporal accelerations. I will also show an example of machine-learned modeling of hydrodynamic drag from roughness with arbitrary topography.

The second part of the talk is on using DNS to better understand river hyporheic exchange, a phenomenon of turbulent flow bounded by rough, permeable walls. In our understanding of riverine systems, a gap of knowledge exists in how pore-scale heterogeneities affect multiscale hydrologic and biogeochemical processes. I will show that dynamics at the scale of sediment grains and small roughness formed by uppermost-layer grains—typically ignored in existing predictive approaches—can be important for exchanges across a flat bed. Specifically, pore-resolved DNS of flows bounded by beds modeled as closely packed spheres were carried out. Results showed that bed roughness induces deep, multiscale subsurface flow paths that yield residence time distribution with a power-law tail. The main driver appears to be the interfacial pressure variation generated by roughness, a mechanism fundamentally similar to the effect of bedforms. Future work will investigate (i) pore-scale dynamics in transient or spatially varying river flows, (ii) reactive solute transport affected by pore-scale dynamics, and (iii) potential link with reduced-order transport models used for water management practice.

About the Speaker: Dr. Junlin Yuan is an assistant professor in Department of Mechanical Engineering at Michigan State University. She obtained both MS and PhD degrees (2015) from Queen's University, Canada. Her PhD research focused on simulation (DNS and LES) and modeling of turbulent flows in the context of rough hydraulic turbine blades. At MSU, she continued to use large-scale simulations to identify the dynamics of wall-bounded turbulence with various complexities, and to develop physics-based, data-driven models. Topics include turbulence responses to acceleration/deceleration, wall roughness, wall permeability, curvature, and rotation. Applications cover engineering, environmental and bio-locomotive topics. Her research group is currently funded by ONR, NSF and the industry.

Straub Award Ceremony and Distinguished Lecture, featuring Dr. Tracy Mandel and Dr. Veronica Morales

Prior to our keynote presentation, we are excited to welcome and celebrate the most recent winner of the Lorenz G. Straub Award. Dr. Tracy Mandel completed her 2018 dissertation under Jeffrey Koseff at Stanford University. She will provide a brief remarks about her graduate thesis, titled Free-surface Dynamics in the Presence of Submerged Canopies. Dr. Mandel currently serves at University of New Hampshire as an Assistant Professor in Ocean Engineering and Mechanical Engineering. Her research group uses experimental and field approaches to study turbulent environmental flows, with a focus on coastal hydrodynamics. 

Keynote Presentation: Transport Phenomena Under Spatial Heterogeneity: Bridging the Pore and Darcy Scales

Veronica Morales, Assistant Professor Civil & Environmental Engineering, University of California Davis

Abstract: Solving the flow and mass transport through environmental porous media is central to many technological applications spanning groundwater remediation, oil recovery, and geotechnical engineering. Under spatial heterogeneity, the phenomena of flow and transport significantly differ from those in uniform media. The variability of natural pore-spaces gives rise to complex flow patterns and non-Gaussian velocity fluctuations that complicate predictions. Classic models for the field-scale omit this variability and use average system parameters to solve governing equations for flow and transport. Such types of models might acceptably capture the average time of arrival of a substance (e.g., a groundwater contaminant), but consistently fail to predict the often-observed early arrival and prolonged tailing in concentration signals. Capturing the variance and skewness of such concentration signals requires more information than is contained in average system descriptors. To this end, this talk will discuss work carried out to represent large-scale transport processes as the collective phenomena resulting from interactions between the pore-scale heterogeneity and the local-scale flow. The first part of the talk will discuss the rules of particle motion ascertained at the pore-scale that are efficiently upscaled with stochastic models to describe large-scale transport problems. We demonstrate how our model accurately captures the changeover from intense to weak spreading, which is poorly understood but crucial for problems in groundwater contamination. The second part of the talk focuses on flow distribution and recasts flow path resistance into a graph-theory problem. Through this work we learn where and why preferential pathways form and offer a simple metric to estimate the time of first arrival based on structural information of the porous medium alone.

About the Speaker: As a hydrogeologist, Veronica Morales’s research focuses on the physics of flow and reactive transport in porous media with a keen interest in understanding how particles move and interact in confined spaces. In 2017, Morales joined the faculty at the University of California, Davis where she was awarded the NSF-CAREER and the AGU Early Career Award. Previously, she was a postdoctoral associate at the Environmental Fluid Mechanics lab at ETH Zürich and the Soil Physics group at the SIMBIOS Centre. She holds a PhD in Biological & Environmental Engineering from Cornell University (2011), and dual Bachelor degrees in Environmental Science and Spanish Literature from the University of California, Santa Barbara (2004).

Transform Engineering for a Climate Changed Future – What Role for Reflexive Practice? Linda Shi, Cornell University

Linda Shi, Assistant Professor, Architecture Art Planning, Cornell University and Hanne van den Berg, Urban Adaptation Expert, European Environment Agency

Abstract: These are exciting times for civil and environmental engineers, who have an immense role to play in societal transformation under climate change. Cities, funders, public agencies, and policymakers are increasingly advocating infrastructure projects that mitigate flood risks, especially in the aftermath of disasters. Whether projects are green or grey, we are seeing a resurgence of infrastructure proposals that are large in scale and ambition after decades of more decentralized stormwater management. These projects, nevertheless, respond only to the physical vulnerabilities of place by shifting water from one site to another. Decades of social science research demonstrate that vulnerability to environmental hazards are socially constructed by laws, policies, and politics that together shape a household or communities’ ability to overcome the impacts of a disaster event. From this perspective, major infrastructure works are not only a technical, apolitical, value-neutral proposition, but a physical intervention that reflects and entrenches politics of inequality. In the United States, many have disproportionately benefitted wealthier, whiter, and otherwise more privileged groups, while socially vulnerable groups whose communities were disinvested and neglected for decades have had to relocate to make way for infrastructure - often leaving for other environmentally precarious sites. 

This double-header talk presents concepts of social and spatial justice, and how water management projects have contributed to inequitable social vulnerability to hydrological risks. We then share a case study of how flood management in Houston reflects the tensions in how traditional engineering practices have contributed to inequitable local flood risks, and how engineers there have grappled with questions of equity, justice, and fairness. We argue that engineers have an opportunity and a need to reflect on the epistemological roots of the profession, mainstream modes of analysis, and cultural attitudes towards change and more diverse ways of knowing.