Warren Lecture Series Home

The Warren Lecture Series is made possible by a generous, renewing gift by Alice Warren Gaarden. The series brings in researchers and speakers from around the world. 

Live sessions are held in the Civil Engineering Building, room 210. Masks are required. You may alo attend via Zoom: z.umn.edu/Fall2021WarrenLectures, Meeting ID: 950 5374 1778, 
Passcode: SjBnf0. Recordings are available on the Warren Lecture Series YouTube channel.

You can search our extensive archive using the categories in the pull down menu.

Upcoming Warren Lectures

Warren Lecture with Michele Guala

Michele Guala
Civil, Environmental, and Geo- Engineering, University of Minnesota
"An Open Conversation about Sand Grain and Vortex Organization in Turbulent Flows"

ABSTRACT:  Remarkable geometrical and scaling similarities emerge when a turbulent boundary layer acts on a rough or erodible surface. Both sand grains and vortices self-organize into aggregates which exhibit general ramp-like patterns and hierarchies extending up to a significant fraction of the reference outer scale, e.g., the river depth or the boundary layer height. These aggregates represent ripples and dunes in rivers, and attached-eddy coherent structures in near surface atmospheric flows, respectively.

While their advection velocity displays systematic differences, leading to a scale-dependent migration of fluvial bedforms that we do not observe for coherent structures, the dependency on the shear velocity remains a hallmark feature of these aggregates. Not only that, the shear velocity also percolates down to the scaling of the respective elemental components, governing both the velocity of the moving grains and the maximum azimuthal velocity of the vortices in the flow. Hence, this qualitative comparative analysis between bedforms and flow-structures has some quantitative ramifications in the modeling, confirming that the shear velocity is indeed a star.

Guala concludes by highlighting a second order effect, represented by a weak dependency on the outer scale observed both in the scaling of bedform migrating velocity and in the largest coherent structures of the flow. The qualitative flow structures – bedforms comparison could then be extended: in the same way attached-eddy structures may be imagined as frozen into dunes, so very-large-scale motions may end up being frozen into alternate distortions of the mean river bed. 

 

Three-minute Thesis Competition

Graduate students from CEGE compete to present their thesis research within just 3 minutes.

Warren Lecture with Yanfeng Ouyang

Yanfeng Ouyang
Civil and Environmental Engineering
University of Illinois at Urbana-Champaign

 

Warren Lecture with Srijan Aggarwal

Srijan Aggarwal
Civil, Geological, and Environmental Engineering
University of Alaska Fairbanks

 

Warren Lecture with Ron Klemencic

Sehlin Lecture
Ron Klemencic, P.E., S.E., Hon. AIA
Chairman and CEO, Magnusson Klemencic Associates (MKA) 

 

Warren Lecture with David Dzombak

AAEES 2021 Kappe Lecture
David Dzombak

Civil and Environmental Engineering
Carnegie Mellon University

 

Past Warren Lectures

Warren Lecture with Michele Guala

Michele Guala
Civil, Environmental, and Geo- Engineering, University of Minnesota
"An Open Conversation about Sand Grain and Vortex Organization in Turbulent Flows"

ABSTRACT:  Remarkable geometrical and scaling similarities emerge when a turbulent boundary layer acts on a rough or erodible surface. Both sand grains and vortices self-organize into aggregates which exhibit general ramp-like patterns and hierarchies extending up to a significant fraction of the reference outer scale, e.g., the river depth or the boundary layer height. These aggregates represent ripples and dunes in rivers, and attached-eddy coherent structures in near surface atmospheric flows, respectively.

While their advection velocity displays systematic differences, leading to a scale-dependent migration of fluvial bedforms that we do not observe for coherent structures, the dependency on the shear velocity remains a hallmark feature of these aggregates. Not only that, the shear velocity also percolates down to the scaling of the respective elemental components, governing both the velocity of the moving grains and the maximum azimuthal velocity of the vortices in the flow. Hence, this qualitative comparative analysis between bedforms and flow-structures has some quantitative ramifications in the modeling, confirming that the shear velocity is indeed a star.

Guala concludes by highlighting a second order effect, represented by a weak dependency on the outer scale observed both in the scaling of bedform migrating velocity and in the largest coherent structures of the flow. The qualitative flow structures – bedforms comparison could then be extended: in the same way attached-eddy structures may be imagined as frozen into dunes, so very-large-scale motions may end up being frozen into alternate distortions of the mean river bed. 

 

Warren Lecture with Kimberly Hill

Kimberly Hill
Civil, Environmental, and Geo- Engineering, University of Minnesota
"'Granular Mud' in Natural and Human Infrastructure Materials"

“Granular mud,” i.e., mixtures of particles and viscous-like fluids are ubiquitous in natural and man-made systems, from muddy geophysical flows to hot mixed asphalt and concrete. As we strive toward a “greener economy,” predicting their behaviors in asphalt compaction toward efficient processing becomes increasingly important given the wide-spread use of asphalt in our roadways. At the same time, and at a much greater scale, predicting behaviors of this granular mud in the form of rocky/muddy geophysical flows (debris flows) would help with hazard mitigation, particularly critical in the face of their increasing frequency and intensity under recent higher intensity storms. While we don’t typically think of such vastly different materials in the same context, we have found that considering them in a similar multiscale framework sheds light on both problems. 

Hill first presents these issues in the context of hot mixed asphalt compaction, particularly in mixture design toward increasing compaction efficiency. Likely because of the wide range of particle sizes, we find that a simple single phase model is not effective in capturing the mechanistic influence of specific components. However, when we model the particle dynamics specifically at two different scales using our new two-scale discrete (or distinct) element method approach we capture changes of the compaction efficiency to material additives and grain size distributions. At the same time, because of the nature of the DEM approach in representing the motion of and forces on individual particles, the model provides intuition on the mechanics involved. Hill ends with a brief discussion of her research team's ongoing experimental and field research in which they have begun to apply this approach to understand behaviors of debris flows (large rocky/muddy flows in steep regions) and various channelization signatures on alluvial fans.  

Warren Lecture with Ardeshir Ebtehaj

Ardeshir Ebtahaj
Civil, Environmental, and Geo- Engineering, University of Minnesota
"Unraveling Changes of Global Water Cycle using Satellite Data"

ABSTRACT: Satellite observations of the Earth’s radiation in microwave bands play an indispensable role, not only for unraveling the impacts of climate change on the global water cycle but also for accurate prediction of droughts and extreme storms. On the one hand, satellite remote sensing of the water cycle involves inversion of radiative transfer equations that link the amount of water in land and atmosphere to radiation intensity, observed by spaceborne radiometers at the top of the atmosphere. On the other hand, improved predictability of the hydrologic cycle requires optimal integration of satellite observations with the outputs of Earth System Models (ESMs). Ebtehaj presents recent advances in physically informed inversion of land emission models and in multi-satellite statistical learning for high-resolution remote sensing of soil moisture and snowstorms from space. Furthermore, he presents a new paradigm for satellite data assimilation over a Riemannian manifold equipped with the Wasserstein metric. Unlike classic approaches over the Euclidean space, this new framework can formally penalize geophysical biases in a non-Gaussian state space. The advantages of this approach for improved geophysical forecasts are demonstrated using chaotic dynamical systems, representing atmospheric circulation.

 

Warren Lecture with John Gulliver

John S. Gulliver
Civil, Environmental and Geo- Engineering, University of Minnesota
"Gismos for Stormwater Runoff"

ABSTRACT: Technology for stormwater treatment has different challenges from water treatment and wastewater treatment. Stormwater control measures need to be applied throughout the watershed, such that infrequent maintenance is needed. Second, the water to be treated tends to flow more infrequently than water or wastewater, resulting in a different paradigm for stormwater control measures. Gulliver discusses three technologies to assist in the choice of stormwater control measures: a falling head infiltrometer that can be used to determine the saturated hydraulic conductivity at multiple locations simultaneously; a baffle that will turn a standard sump into a stormwater control device; and an enhanced sand filter that will remove phosphate from stormwater runoff before it reaches the receiving water body.

Warren Lecture with Nikolaos Geroliminis

Nikolaos Geroliminis
EPFL Lausanne, Switzerland
"On the Inefficiency of Ride-sourcing Services Towards Urban Congestion"

ABTRACT: The advent of shared-economy and smartphones made on-demand transportation services possible, which created additional opportunities but added more complexity to urban mobility. Companies that offer these services are called Transportation Network Companies (TNCs) due to their internet-based nature. Ride-sourcing is the most notorious service TNCs provide. Little is known about the degree to which ride-sourcing operations interfere in traffic conditions. We experimentally analyze the efficiency of TNCs using taxi trip data from a Chinese megacity and an agent-based simulation with a trip-based MFD model for determining the speed. We investigate the effect of expanding fleet sizes for TNCs, passengers’ inclination towards sharing rides, and strategies to alleviate urban congestion. 

Warren Lecture with Andrew J Whelton

Andrew J Whelton
Civil Engineering and Environmental and Ecological Engineering, Purdue University
"Preventing Future Safety and Environmental Problems: Experiences of Polymers in Water Infrastructure Systems"

ABSTRACT: As buried water infrastructure in the U.S. continues to deteriorate, many communities are racing to replace and replace these assets. Many of these communities are choosing to repair pipes in place, or replace with polymer materials. This is also the case for building systems and new construction, where polymer material use can be 90% less costly than legacy materials and methods. Whelton describes his experience with polymer prevalence in water infrastructure systems and product failures, and recommends education to lessen the chance of future failures and health impacts.

Modeling Soil-Machine Interaction: Evolving Research on Evolutionary Plasticity Problems

James Hambleton
Civil and Environmental Engineering, Northwestern University
"Modeling Soil-Machine Interaction: Evolving Research on Evolutionary Plasticity Problems"

ABSTRACT: Problems in soil-machine interaction (SMI) are ubiquitous on Earth, and they are beginning to play important roles elsewhere as we explore and perhaps eventually colonize the moon and other planets. Irrespective of the application, SMI problems are “evolutionary plasticity problems” defined characteristically by the presence of large, plastic deformation as machine components come into contact with soils. Hambleton discusses the formulation and validation of efficient analytical and semi-analytical techniques for predicting forces and deformations in SMI problems.

Impacts of Automation in Future Public Transport Systems

Constantinos Antoniou
Civil, Geo and Environmental Engineering, Technical University of Munich

ABSTRACT: Antoniou looks at some recent and ongoing research on expected impacts of automation in transforming public transport systems. He describes an integrated framework for a scenario-based impact assessment. Topics include an analysis of multiple waves of survey data collected from users of an automated bus deployment in Stockholm, as well as the development of an analytical model that provides insights into how automation may affect the design and operation of future public transport systems, applied to networks in Germany and Chile.

View Antoniou's presentation

Bottom-Up and Top-Down Approaches to the PFAS Problem: From Molecular Models to Policy Frameworks

Carla A. Ng
Civil and Environmental Engineering, University of Pittsburgh

Per- and polyfluorinated alkyl substances (PFAS) are a diverse group of chemicals used in a dizzying array of applications. Public concern is growing over ubiquitous human exposure to PFAS, and the recognition that some PFAS are bioaccumulative and can be toxic even at extremely low concentrations. This concern has prompted policy action at state, federal, and international levels. Yet the development of sound policy and decisions around PFAS is complicated by lack of data on most members of the broad class of chemicals and by the practical difficulties around a substance-by-substance approach to evaluating these chemicals, particularly given their unique properties and behavior in environmental and biological systems. Ng highlights several initiatives from her research group and collaborative work to tackle the PFAS problem at two levels. At the molecular level, she is developing integrative modeling strategies to predict the behavior and potential hazard of diverse PFAS using computational approaches that help to overcome limitations of traditional testing and increase throughput. At the policy framework level, she is collaborating with a team of international academic and regulatory scientists and policy analysts to develop scientifically sound strategies to eliminate hazardous PFAS from products and processes.

View Ng's presentation

Level Excursion Analysis of Probabilistic Quasibrittle Fracture

Jia-Liang Le
Civil, Environmental, and Geo- Engineering, University of Minnesota

ABSTRACT: It is widely acknowledged that no structure can be designed to be risk free, and therefore, reliability analysis plays a central role in the design of engineering structures. The recent focus has been placed on structures made of brittle heterogenous (a.k.a. quasibrittle) materials, such as ceramics, composites, concrete, and many more at the microscale. Le and his team recently developed a level excursion model for analyzing the probabilistic failure of quasibrittle structures, in which the structural failure probability is calculated as a first passage probability. The main feature of the model is that it captures both the spatial randomness of local material resistance and the random stress field induced by microstructures. The model represents a continuum generalization of the classical weakest-link model, which recovers the Weibull distribution as an asymptotic distribution function. In this talk, Le discusses two applications of this model.

View Le's presentation