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DTSTART;TZID=Europe/Rome:20260622T110000
DTEND;TZID=Europe/Rome:20260622T123000
DTSTAMP:20260609T095043Z
CREATED:20260609T095043Z
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UID:33410-1782126000-1782131400@www.dica.polimi.it
SUMMARY:Shallow mixing interfaces between streams of unequal densities and their relevance for understanding mixing downstream of river confluences
DESCRIPTION:On Monday\, June 22\, a seminar titled “Shallow mixing interfaces between streams of unequal densities and their relevance for understanding mixing downstream of river confluences” will be held in Grandori Room (Building 4) at 11:00 CET. \nThe seminar will be given by George Constantinescu\, Professor in the Civil and Environmental Engineering Department at the University of Iowa. \nAbstract \nAs opposed to the case of shallow mixing layers forming between parallel streams of unequal velocities and equal densities\, the spatial development of the mixing interface between two parallel streams of unequal velocities and sufficiently large density contrast is controlled by the formation of a spatially developing\, lock-exchange-like flow in transverse planes. Eddy-resolving numerical simulations conducted in a wide and very long channel are used to investigate the mean flow structure and the effects of the lock-exchange-like flow and the associated coherent structures (e.g.\, streamwise-oriented vortical cells along the interface separating the regions containing heavier and lighter fluids) on mixing and the capacity of the flow to entrain sediment from the channel bed. These results are contrasted with the limiting case of shallow mixing layers with no density contrast where the dynamics of the quasi-two-dimensional Kelvin–Helmholtz vortices controls the structure and streamwise development of the mixing layer. These results are then used to explain how mixing is affected by density contrast at natural river confluences.  Using field measurements of the mean temperature at a small river confluence\, we show that accounting for stratification effects is critical for eddy-resolving simulations to accurately capture the mean temperature distribution downstream of the confluence apex. We then show that a temperature contrast of only couple of degree Celsius can have a large effect on the position and structure of the mixing interface at one of the largest river confluences in the world. For both confluent flows over a flat bed and over natural bathymetry\, density contrast between the incoming flow enhances mixing. Most of this mixing takes place beneath the free surface and is driven by coherent structures induced by stratification effects. \nBio-sketch \nDr. Constantinescu is a Professor in the Civil and Environmental Engineering Department at the University of Iowa. Dr. Constantinescu got his Ph.D. at the University of Iowa in 1998. Following this\, he occupied various research positions at Arizona State University and at the Center for Turbulence Research and the Center for Integrated Turbulence Simulations at Stanford University where he worked on the development of novel numerical algorithms for viscous flows\, Detached Eddy Simulation and computational aero-acoustics. He then joined the University of Iowa as an Assistant Professor in 2004. His research program is based on the use of eddy-resolving simulations to understand the physics of several important classes of environmental and geo-physical flows. Dr. Constantinescu’s current research focuses on turbulence and transport in rivers and lakes\, stratified flows\, shallow flows\, eco-hydraulics\, numerical modeling of floods and dam break waves of non-Newtonian fluids and flow in porous media. \n 
URL:https://www.dica.polimi.it/it/evento/shallow-mixing-interfaces-between-streams-of-unequal-densities-and-their-relevance-for-understanding-mixing-downstream-of-river-confluences/
LOCATION:aula Grandori (ed.4)
CATEGORIES:Seminari e conferenze
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DTSTART;TZID=Europe/Rome:20260622T160000
DTEND;TZID=Europe/Rome:20260622T170000
DTSTAMP:20260615T095620Z
CREATED:20260615T095341Z
LAST-MODIFIED:20260615T095620Z
UID:33441-1782144000-1782147600@www.dica.polimi.it
SUMMARY:Seismic Wave Propagation in Complex Geological Domains: From Site Effects in Earthquakes to Diffuse Fields in Passive Seismology
DESCRIPTION:Within the PhD course on Elastic Wave Propagation with applications to Earthquake Engineering at Politecnico di Milano\, Prof. Francisco José Sánchez-Sesma\, Instituto de Ingeniería\, UNAM México\, will deliver a lecture on Seismic Wave Propagation in Complex Geological Domains: From Site Effects in Earthquakes to Diffuse Fields in Passive Seismology. \n  \n\nThe lecture will be delivered on June 22\, 2026\, at 16:00 (Italian time) in the Webex personal room: politecnicomilano.webex.com/meet/roberto.paolucci\nThis will be a repetition of the Joyner Memorial Lecture\, awarded jointly by the Earthquake Engineering Research Institute (EERI) and the Seismological Society of America (SSA)\, which recognizes outstanding individuals working at the intersection of earthquake science and engineering\, whether it involves contributions from earthquake science to earthquake engineering\, or from earthquake engineering to earthquake science. For 20 years\, these distinguished speakers have contributed to building codes\, seismic design guidelines\, probabilistic seismic hazard analysis\, and the characterization of site effects. Francisco José Sánchez-Sesma of the Universidad Nacional Autónoma de México (UNAM) delivered the 2026 Joyner Lecture at the SSA Annual Meeting in Pasadena\, CA\, and will do so again at the 13NCEE in Portland\, OR.\n\nAbstract\nThis lecture emerges from decades of research on seismic waves in complex geological media to assess ground motion\, from strong shaking to weak ambient vibrations such as microtremors and seismic noise. It is dedicated to William B. Joyner\, who bridged the gap between seismologists and engineers to achieve an earthquake-resilient society. Personally\, the 1985 Michoacán earthquake (Mw 8.1)\, which caused catastrophic damage in Mexico City\, was a key motivation. The Random Vibration Theory\, reformulated by Boore and Joyner\, helped us to craft the Mexico City building code\, which incorporated the Fourier spectrum as a design concept. Seismic hazard is a big puzzle; we take little pieces and try to solve each one. The Indirect Boundary Element Method (IBEM) enabled the study of the seismic response of topographic features and alluvial valleys to educate the intuition. The need for a geomorphological description is evident. Diffuse fields allowed us to establish the exact retrieval of Green’s functions from noise cross-correlations. This leads to a theory for the H/V spectral ratio to model ambient seismic noise measurements and infer subsurface layered structures. However\, including lateral irregularity is a major challenge. Preliminary results suggest it is possible to spot\, from H/V results\, zones that may trap energy in earthquakes.
URL:https://www.dica.polimi.it/it/evento/seismic-wave-propagation-in-complex-geological-domains-from-site-effects-in-earthquakes-to-diffuse-fields-in-passive-seismology/
LOCATION:collegamento Webex
CATEGORIES:Webinar e Workshop
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