Warren Distinguished Lecture Series

Banners that illustrate CEGE's mission and vision hang in the Charles Fairhurst Rotunda

The Warren Distinguished Lecture Series is made possible by a generous, renewing gift by Alice Warren Gaarden in 1961. Since 1989, we have been bringing in accomplished researchers and speakers from around the world to share their work with students, faculty, and friends of CEGE. Please join us for these lectures!

Upcoming Events

Mar 15  Roman Y Makhnenko, Civil & Environmental Engineering, University of Illinois Urbana-Champaign
Mar 22  Joseph Vantassel, Civil and Environmental Engineering, Virginia Tech
Mar 29  Elowyn Yager, Civil & Environmental Engineering, University of Idaho
Apr   5  Kyle Doudrick, Civil & Environmental Engineering & Earth Sciences, University of Notre Dame
Apr 12  Tim Strathmann, Civil & Environmental Engineering, Colorado School of Mines
Apr 19  Henry Liu, Civil and Environmental Engineering, and Mechanical Engineering, University of Michigan 
Apr 26  Dimitrios Lignos, Resilient Steel Structures Laboratory, École Polytechnique Fédérale de Lausanne (EPFL),  Lausanne (Switzerland)

There are no upcoming events matching your criteria.

Past Warren Lectures

The Full Cost of Headway Variability in Waiting, Crowdedness and Reliability: Two Strategies for Control

Juan Carlos Muñoz
Transport Engineering and Logistics, Pontificia Universidad Católica de Chile

ABSTRACT: The main focus of public transport operations in recent decades has been increasing speed. Increasing speed allows for faster trips and a higher frequency, reducing wait times and crowdedness inside the vehicles. A second key dimension in level of service has been ignored: reliability. Muñoz reviews impacts of an unreliable public transport service and shows how regularizing headway could improve level of service beyond the gains of simply increasing the operational speed. Regular headways positively affect comfort, reliability, travel and wait times, operational costs, and some urban impacts of bus services. Reliability is fundamental for making public transport an attractive travel alternative, and therefore must become a core goal for urban sustainability. Public transport agencies and operators should focus on reliability. Muñoz introduces methodologies to implement two different control strategies: bus holding and boarding limits through a rolling horizon optimization approach, and bus injection through a stochastic model.

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Addressing Network Challenges for Wireless Control of Civil Infrastructure

Lauren Linderman
Civil, Environmental, and Geo- Engineering, University of Minnesota

ABSTRACT: Structural control offers an approach to protect structures from natural hazards by adding devices that can introduce damping or alter the stiffness of the structure. Effective implementation of sensor and actuators networks (SANs) for civil applications has significant challenges, such as modeling and loading uncertainty, large-scale systems, and reliability. Additionally, as the field moves towards wireless SANs, deployment challenges must be considered, such as communication latency and unreliable communication, which make common centralized control strategies less feasible for wireless networks. Linderman addresses the challenges of communication delays and error through decentralized control, sensor selection, and controller implementation. Linderman’s proposed feedback and sensor selection approach does not require knowing the feedback structure or desired number of sensors a priori, which allows the optimal configuration to be considered in the design.

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Building Bridges’ through the Lens of Diversity and Inclusion

Edgar Arraiga
Chemistry and CSE Diversity & Inclusivity Alliance, University of Minnesota

ABSTRACT: Diversity and Inclusion (D&I) are two of the Core Values that the American Society for Engineering Education uses to advance innovation, excellence, and access at all levels of education for the engineering profession. These are also the attributes of top organizations who recognize diversity as one of their pillars. On the other hand, the field is concerned with disparities that challenge the ability of engineering programs to meet the future professional demands of the field. At the University of Minnesota, the College of Science and Engineering (CSE) has been making efforts to identify opportunities to advance CSE’s mission through the D&I lens. Arraiga summarizes recent D&I studies relevant to the engineering profession, discusses D&I needs and challenges, and portrays opportunities within CSE. He exhorts everyone in CEGE to use the D&I lens to define and advance CEGE’s mission.

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Meshfree Methods: Progress Made After 20 Years and Future Directions

Jiun-Shyan (JS) Chen
Structural Engineering & Center for Extreme Events Research, University of California, San Diego

ABSTRACT: In the past two decades, meshfree methods have emerged into a new class of computational methods with considerable success. In addition, a significant amount of progress has been made in addressing the major shortcomings that were present in these methods at the early stages of their development. For instance, essential boundary conditions are almost trivial to enforce by employing the techniques now available, and the need for high order quadrature has been circumvented with the development of advanced techniques, essentially eliminating the previously existing bottleneck of computational expense in meshfree methods. Given the proper treatment, nodal integration can be made accurate and free of spatial instability, making it possible to eliminate the need for a mesh entirely. Meshfree collocation methods have also undergone significant development, which also offer a truly meshfree solution. This presentation will give an overview of major progresses made in the field, the application to many challenging engineering mechanics problems, and the future directions of this research area.

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Macroscopic Modeling of Ride-Sourcing Systems: Regulation and Fundamental Diagram

Yafeng Yin
Civil and Environmental Engineering, and Industrial and Operations Engineering, University of Michigan, Ann Arbor

ABSTRACT: Ride-sourcing companies such as Uber, Lyft, and Didi Chuxing are transforming the way people travel in cities. The companies provide ride-hailing applications that intelligently match riders to drivers; drivers are private car owners who drive their own vehicles to provide ride-for-hire services for profit. Since their advent in 2009, ride-sourcing companies have enjoyed huge success, but also created many controversies. Yin presents research findings from a series of studies conducted by the Lab for Innovative Mobility Systems (LIMOS). Yin discusses two specific issues: a macroscopic modeling framework for analyzing the ride-sourcing market and deriving insight for its regulatory policies, and then, by viewing ride-sourcing as an input/output system, Yin shows that the output rate of the ride-system system (the number of riders arriving at their destinations per unit of time) can decline with accumulation (the number of riders in the system) and how control can prevent that decline.

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Critical Mechanical Structures: Topological Metamaterials and Robust Mechanisms in Messy Matter

Xiaoming Mao
Physics, University of Michigan

ABSTRACT: Critical mechanical structures are structures at the verge of mechanical instability. These structures are characterized by their floppy modes, which are deformations costing little energy. On the one hand, numerous interesting phenomena in soft matter are governed by the physics of critical mechanical structures, because they capture the critical state between solid and liquid. On the other hand, the design of mechanical metamaterials (i.e., engineered materials that gain their unusual mechanical properties, such as negative Poisson's ratio, from their structures) often rely on floppy modes to realize novel properties, and the floppy modes in this situation are called "mechanisms." Mao focuses on floppy modes in critical mechanical structures that are governed by topological invariants, and are thus called "topological edge modes." Mao proposes a new design principle, for mechanical metamaterials that are transformable between states with dramatically different properties, by manipulating topological states. Because of the topological protection, these floppy modes are highly robust against disorder. Mao also discusses recent work exploring topological floppy modes in aperiodic, messy, systems, such as fiber networks and quasicrystalline tilings, which manifest the power of "topological protection," and may lead to broad applications in biology, physics, and engineering.

Note: Recording not available

Fluid Deformation of the Solid Earth: Bending and Breaking Rock and Ice

Jerome Neufeld
Earth Sciences, Applied Mathematics and Theoretical Physics, University of Cambridge

ABSTRACT: The hydraulic fracturing of reservoirs, the propagation of magma through Earth’s crust forming dykes and sills, and the drainage of supraglacial lakes to the base of the Greenland ice sheet are examples of fluid-driven surface deformation. An understanding of these processes relies crucially on the coupling of fluids and elastic or poroelastic deformation of solids. Neufeld explores the interaction between laminar and turbulent flows on the deformation of elastic and poroelastic materials, highlighting their role in determining the transient and long-term lubrication of the Greenland ice sheet, and the fracturing of rock during the emplacement of magma in sills and laccoliths. Drawing on reduced mathematical models, laboratory experiments and field data, Neufeld shows the crucial role that physical processes at the fracture front play in the emplacement of fluids in these different settings.

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Active Mechanics of Self Locomotion

Lev Truskinovsky
Centre national de la recherche scientifique (CNRS), ESPCI Paris Tech

ABSTRACT: The ability of cells to self-propel is essential for most biological processes. While the molecular and biochemical mechanisms of such motility are basically known, the underlying mechanical theory of active continuum media is still under development. In this talk we show how to build a mathematical model which describes crawling of keratocytes, flattened cells with fibroblastic functions, that self-propel by advancing the front and retracting the rear. The two main components of such motility mechanism, protrusion, and contraction, depend on continuous supply of energy, which makes the underlying mechanics active. To bring mathematical transparency to the interplay between contraction and protrusion we use a minimal description based on the Keller–Segel type dynamical system with mechanical feedback.

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Chloramine Photochemistry for Potable Water Reuse

Haizhou Liu
Chemical and Environmental Engineering, University of California - Riverside

ABSTRACT: Ultraviolet-driven advanced oxidation processes (UV/AOP) are becoming increasingly important for potable water reuse to remove trace chemical contaminants from wastewater effluent. This seminar will discuss the unique aqueous photochemistry of the overlooked but important chloramines for water reuse applications. Membrane treatment processes including microfiltration (MF) and reverse osmosis (RO) are employed prior to any UV/AOP in water reuse facilities. Chloramines are deliberately generated in the feed water to minimize membrane biological fouling. Because of their small molecular size and neutral charge, chloramines easily diffuse through RO membranes, and subsequently will undergo photolysis in the UV/AOP. We investigated the efficiencies of chloramines in degrading 1,4-dioxane under low-pressure UV lamp photolysis. The photolysis of chloramines produced amine and halide radicals, which further transformed to a series of reactive radical species that assist the contaminant degradation. The presence of dissolved oxygen further decreased the reactivity. This study shows that the presence of chloramines in UV/AOP as carry-over chemical residuals from membrane treatment processes can also be harnessed as an oxidant beneficial to water reuse. We are also currently conducting pilot-scale photochemical experiments utilizing chloramine photolysis with our industrial partners. Considering the perspective of potable water reuse, an efficient utilization of chloramine photochemistry can lead to a more sustainable water management.

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Spiraled Boreholes: An Expression of 3D Directional Instability of Drilling Systems

Emmanuel Detournay
Civil, Environmental, and Geo- Engineering, University of Minnesota

ABSTRACT: Occurrence of borehole spiraling is predicted by analyzing the delay-differential equations governing the propagation of a borehole. These evolution equations for the borehole inclination and azimuth are obtained from considerations involving: (i) a bit/rock interaction law that relates the force and moment acting on the bit to its penetration into the rock; (ii) kinematic relationships that describe the local borehole geometry in relation to the bit penetration; and (iii) a beam model for the bottom-hole assembly (BHA) that can be used to express the force and moment at the bit from the external loads applied on the BHA and the geometrical constraints arising from the stabilizers conforming to the borehole geometry.

The analytical nature of the propagation equations makes it possible to conduct a systematic stability analysis in terms of a key dimensionless group that controls the directional stability of the drilling system. This group depends on the downhole weight on bit (WOB), on properties of the BHA, on the bluntness of the bit, and on parameters characterizing its response. The directional stability of a particular drilling system can be assessed by comparing the magnitude of this group with the bifurcation value that depends only on the BHA configuration and the bit walk. Stability curves for an ideal BHA with two stabilizers are shown to depend on the bit walk, which tends to enhance conditions for spiraling. An application to a field case is discussed. Simulations conducted by integrating the equations of borehole propagation also are presented. They illustrate that, for unstable systems, the model predicts spiraled boreholes with a pitch comparable to what is observed in the field. Furthermore, they show that a limit cycle, characterized by bounded magnitude of the oscillations, is attained if a nonlinearity is introduced in the bit response.

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