Seminars

seminar room safl

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


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

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

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

Seminar Notifications
To sign-up for our SAFL Seminar email list, click here.


Upcoming Seminars

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Past Seminars

Mesoscale to microscale atmospheric simulations over complex terrain

Tina Katopodes-Chow
Associate Professor
Civil & Environmental Engineering
University of California, Berkeley

Abstract:
This presentation will describe challenges that arise when simulations of the atmospheric boundary layer are performed at higher and higher grid resolution. Improved parameterizations for turbulence allow representation of intermittent turbulence that occurs under moderate to strong stable stratification. Implications for boundary layer predictions important for wind energy applications are discussed. New techniques for representing complex topography such as steep mountains and buildings are also described, allowing mesoscale simulations to move from regional to urban scales.

Simulation and control of jets in crossflow

Krishnan Mahesh
Aerospace Engineering & Mechanics
University of Minnesota

Abstract:
Jets in crossflow are central to a variety of applications; e.g. dilution jets in gas--turbine combustors, film--cooling, and fuel injection. This talk will discuss our work on the simulation and control of passive scalar mixing by turbulent jets in crossflow. We have developed an analytical scaling for jet trajectory that accounts for jet velocity profile and crossflow boundary layer thickness. Also direct numerical simulation has been performed under conditions corresponding to recent experiments. The simulation results will be used to propose physical mechanisms for entrainment and mixing. A simple model that explains jet deformation as a result of acceleration imposed by the crossflow will be discussed. The tak will then discuss the control of jets in crossflow using pulsing. The main idea pursued here is that pulsing generates vortex rings and the effect of pulsing can therefore be explained by studying the behavior of vortex rings in crossflow. A regime map is proposed that collapses optimal conditions from experiments.

Morphology and dynamics of a gravel-sand transition: Fraser River, British Columbia

Jeremy Venditti
Simon Fraser University
Burnaby, BC, Canada

Abstract:

The beds of alluvial river channels become finer grained moving downstream and often exhibit an abrupt transition from gravel to sand-bedded conditions. Most previous work documenting this phenomenon have focused on small upland streams where sediment supply to the channel is strongly connected to sediment delivery from hillslopes. Fewer studies have focused on the gravel-sand transition in large alluvial channels and none have documented the spatial variability through reaches where transitions occur. The downstream fining pattern observed in the Fraser River is widely cited as a classic example of an abrupt gravel-sand transition in a large alluvial channel. However, important questions regarding the exact current location of the transition, its morphology, and what controls its location remain unanswered.

Here, I present detailed observations bed material grain-size, river bed topography and fluid flow through the 15 km long reach where the transition is widely thought to occur in the Fraser River. Bed topography was measured using a multibeam echo-sounding system (Reson 8101 Seabat) at high flow (11,000 m3s-1) when all fractions of the bed material were mobile. Fluid flow and suspended sediment transport patterns were also mapped using an ADCP at 5 different flow stages during an annual snowmelt hydrograph. These observations indicate that there is a gravel front that occurs in the river at Yaalstrick Bar, the last bar along the river dominated by gravel (> 75% of the bar material > 2 mm). However, sorting patterns caused by the superior mobility of gravel over sand have lead to gravel patches on the upstream sides and surfaces of sand bars. There are also gravel patches along the thalweg through the apex of some river bends. Bedforms associated with sand-gravel mixtures appear on the river bed immediately downstream of Yaalstrick Bar in a sequence (sand ribbons, barchans, dunes) suggesting sand deposition from suspension. There is also a dramatic increase in bar amplitude downstream of Yaalstrick Bar, suggesting greater sand composition. Our fluid flow and sediment transport measurements do not indicate any significant downstream shear stress gradient at high flows, but there is more sand moving as bedload and suspended load in the sand-bedded part of the river. This can only happen if the sand supply from the gravel-bedded part of the river is intermittent. This implies that sediment dynamics in this transition are dominated by sand storage in the gravel-bedded reach at low flows and downstream release to the sand-bedded reach during large floods.

Marine Microfluidics: Chemotaxis and Gyrotaxis in the Ocean

Roman Stocker
Associate Professor,
Massachusetts Institute of Technology

Abstract:

It is now widely recognized that microbial activities represent one of the main forces shaping biogeochemistry and productivity in the ocean. At the level of individual microbes, the ocean is a sea of gradients. Chemical gradients define heterogeneous resource landscapes, while flow gradients exert forces and torques on organisms. Our understanding of these interactions - both chemical and fluid mechanical - has been hampered by the difficulty of studying microbial behavior at appropriate spatiotemporal scales. Modern microfluidic and millifluidic tools afford unprecedented access to this microscale world. I will show how these approaches can help shed light on microbial behavior in both resource gradients (chemotaxis) and flow gradients (gyrotaxis).

Fundamental problems in wind and hydrokinetic energy.

Leonardo Chamorro
Research Associate,
Saint Anthony Falls Laboratory, U of MN

Abstract:

Wind power is one of the most abundant and easily accessible sources of clean and renewable energy on the planet. In line with wind power another promising renewable energy source that is gaining acclaim is the guaranteed flow of river, tidal, and ocean currents. These can be converted to energy via marine hydrokinetic devices and has an incredible potential to fill the ever increasing demand for energy. In spite of the valuable efforts to date, fundamental problems related to the flow and structure interaction, scale dynamics, power maximization, structural reliability, environmental assessments, among others, persist. Continued research geared towards properly addressing these issues is necessary if we are to efficiently expand and capitalize on these vast sources of energy.

In the first part of this presentation, I will present some of the most recent insights obtained from wind tunnel experiments carried out at St. Anthony Falls Laboratory. This research included uses of different sizes and numbers of model wind turbines. The focus of these tests was placed on understanding the complex mechanisms of the flow/structure interaction; tip vortices stability, drag reduction, scalability of the problem.

Secondly I will present preliminary research collected on hydrokinetic turbines. The focus of this research is placed on the conceptual similarities and differences of the hydrokinetic turbines and their wind counterparts, and the turbine’s unsteady response with energetic coherent turbulent structures.

In conclusion these studies have provided valuable information pertaining to the turbulent flow/structure interaction needed to improve the design of wind and hydro turbines. Also, this information is being used to test and guide the development of improved parameterizations of wind turbines in high-resolution numerical models, such as large-eddy simulations (LES). The applications of this research are far reaching and important in increasing the viability and production of wind and hydrokinetic turbines, an increase that is necessary if they are to be implemented on a large enough scale to significantly generate a portion of the energy needed.

The Perilous Life of Planktonic Copepods: Overcoming Hydrodynamic Constraints

Brad Gemmell, Ph.D.
Visiting researcher from Woods Hole
Oceanographic Institution, Boston
Presently working with Ellen Longmire, Dept. of AEM, U of M.

Abstract:
opepods are found in virtually all marine environments. They provide a key link in marine food webs between photosynthetic algae and higher trophic levels. As a result copepods have evolved a powerful escape behavior at all stages of development, in response to hydrodynamic stimuli created by an approaching predator. Young copepods are strongly influenced by viscous forces and may be at a disadvantage when exposed to larger predators at cold temperatures. Results show that the nauplius exhibits a compensatory mechanism to maximize escape performance across its thermal range. Some species have developed unique mechanisms to avoid predation such as breaking the water surface and making aerial escapes to avoid predators while in other cases, the predator has developed unique morphology in order to reduce the amount of hydrodynamic disturbance in the water which improves capture success of copepods.

Orientation and Safety Seminar w/ Introductions to everyone at SAFL

Richard Christopher, St. Anthony Falls Laboratory Safety Officer, will present the Safety Seminar. 

Preceeding that will be introductions by and of all SAFL Faculty, Staff, and students.

Attendance at this seminar is mandatory for all who work and/or study at SAFL. If you cannot make it, you must notify both Richard Christopher and your Advisor. There will be a sign-in - sign-out sheet at the door. 

Transient response of sand bedforms to changes in flow

Raleigh L Martin
 PhD Student University of Pennsylvania, Department of Earth & Environmental Science

 

Abstract: Field and lab studies indicate that bedform geometries lag changes in flow through floods, producing hysteretic relationships between bed morphology, roughness, and water discharge.  Disequilibrium between bedform geometries and flow parameters complicates our ability to interpret stratigraphy for paleoenvironmental reconstruction.  This summer, I am conducting experiments in the SAFL Tilting Bed Flume to explore this bedform hysteresis.  In these experiments, repeat sonar scans are used to continuously track the response of sand bedform morphologies to abrupt changes in water discharge.   The timescale of bedform adjustment appears to be driven by three primary factors: 1. directionality of adjustment, 2. preexisting bedform geometry, and 3. sediment flux.  Directionality of adjustment (rising versus falling water discharge) determines whether bedforms grow quickly by irreversible merger (rising flows) or shrink slowly through secondary bedform cannibalization of relict larger bedforms (falling flows).  Preexisting bedform geometry (height and length) determines the amount of bed deformation required for adjustment to new equilibrium, and sediment flux determines the rate at which this change is effected.  These three factors all favor faster adjustment of bedforms to rising flows.  I will present preliminary results on bedform adjustment hysteresis for a variety of increasing and decreasing discharge changes.

Modeling fluvio-deltaic sedimentation and the importance of microbial

Jorge Lorenzo-Trueba
PhD Student
Saint Anthony Falls Laboratory
University of Minnesota

Abstract:

During almost four years I have been directly involved in one of the leading tasks of the National Center of Earth Dynamics (NCED): restoring a sustainable Mississippi Delta. One main subject of my thesis work has been to develop numerical and analytical modeling tools able to track the shoreline and the alluvial-bedrock transition of fluvial-deltas under base-level changes (e.g., sea-level and subsidence). Moreover, I have expanded this framework to explicitly account for biomass production and decay via plant growth, burial, and microbial processes; wetland vegetation plays an essential role in determining how coastal morphology and ecosystems respond to sea-level rise. I propose an explicit coupling between biogeochemical and physical processes, which offers a novel approach with significant potential to understand this important, but currently poorly understood, component of delta evolution.

Bio:

Jorge Lorenzo Trueba earned a Civil Engineering in 2006 from the Politechnic University started his doctoral studies at SAFL in 2007. His research aims at understanding how physical and biological processes, and the coupling between them, influence delta evolution across a wide range of time and space scales. His research methods focus on the development of mathematical and computational models supported by laboratory experiments and field observation

Restoring Ecological Health and Resilience to Damaged Rivers on a Changing Planet

Luther Aadland, Ph.D.
River Ecologist
Stream Habitat Program
Minnesota Department of Natural Resources

Abstract:

Rivers and watersheds have been dramatically altered through land-use changes, channelization, dam and levee construction, and increasingly, climate change. This has resulted in hydrologic and geomorphic changes, fragmentation of habitat and energy flow patterns, and impaired water quality leading to alarming extirpation and extinction rates of aquatic species. Most river management has been directed at altering and constraining hydrologic, geomorphic, and biological processes. In many cases, this strategy has resulted in further problems. While interest in river restoration has grown, it has not kept pace with ongoing degradation. In addition, restoration efforts have not always addressed underlying problems or have failed to restore fundamental ecological process and resilience. The long-term success of restoration will hinge on the extent to which human constraints are relaxed, ecological processes restored, and migratory pathways re-established. Case examples including channel and floodplain restoration, dam removal, and fish passage will be discussed in this context.

Bio:

Luther has worked as a river ecologist for the Minnesota Department of Natural Resources for the past 24 years. During that time, his work, research, and publications have included a wide variety of topics that integrate physical and biological processes of rivers and the design of river restoration, naturelike fish passage, dam removal, erosion control, and flood damage reduction projects. Primary goals of these projects have been to work with natural river processes, restore ecological functions, and eliminate or reduce maintenance needs and costs. Luther also teaches workshops on applied fluvial geomorphology, dam removal, fish passage, river assessment, aquatic habitat, and river restoration.