CEE Graduate Seminar Announcement - November 6! Dr. Jeffrey S. Guasto

Jeffrey S. Guasto, PhD Professor, Department of Mechanical Engineering Tufts University Friday, November 6, 2026 10:00 am 319 Benedum Hall "Lagrangian lessons on stretching and stress in polymeric flows" Abstract: Viscoelastic flows are pervasive in environmental, biological, and industrial processes, where elastic stresses trigger unstable, time-dependent flows and anomalous transport. While quantifying the distribution of polymeric stress is essential for predicting instabilities and mixing, direct measurements are challenging and simulations are computationally expensive. In contrast to the traditional Eulerian approach, we discuss the virtues of a Lagrangian perspective, which is physically intuitive and provides new insights into polymer mechanics. Using microfluidic ex-periments and simulations, we demonstrate that the topology of the polymeric stress field mir-rors the Lagrangian stretching field, which depends solely on flow kinematics. Manifolds of this stretching—and thus stress—field act as transport barriers, which we show regulate dispersion in viscoelastic porous media flows. Integrating the Lagrangian framework with constitutive models (e.g., FENE-P) enables direct evaluation of polymeric stress from experimental or simulated veloc-ity fields. Finally, the Lagrangian dynamics of single polymers (DNA) are used to reconstruct the spatially resolved conformation for comparison with model predictions. Ultimately, the interplay between polymer individualism and complex deformation history reveals important discrepancies, particularly in extensional regions. Biographical Sketch: Dr. Jeffrey S. Guasto is a Professor in the Department of Mechanical Engineering at Tufts University, where he also holds a secondary appointment in Physics and Astronomy. He received his B.S. degrees in Mechanical Engineering and Physics from Lehigh University and earned his M.S. and Ph.D. in Mechanical Engineering from Brown University. He subsequently held postdoctoral