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.
The seminar will be given by George Constantinescu, Professor in the Civil and Environmental Engineering Department at the University of Iowa.
Abstract
As 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.
Bio-sketch
Dr. 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.
The Department of Civil and Environmental Engineering (DICA) of Politecnico di Milano is pleased to announce a new collaboration with the Moganshan Geospatial Information Laboratory (MGIL), bringing the two institutions together to work in some of the most strategic fields for the future of our planet.
The agreement establishes cooperation in areas of common interest, including Geospatial Information Science, Earth Observation technologies, GeoAI, and the emerging fields that are redefining the way we observe and manage our territory. This is a partnership that goes beyond research: together, DICA and MGIL will develop concrete projects aimed at advancing the United Nations Sustainable Development Goals (SDGs).
The laboratory is based in Deqing, in Zhejiang Province, a hub that has established itself as an international reference point for geospatial information. Deqing is also home to the United Nations Global Geospatial Knowledge and Innovation Centre (UN-GGKIC), a United Nations office established by the Department of Economic and Social Affairs and operating under the guidance of the UN Statistics Division, within the framework of the Committee of Experts on Global Geospatial Information Management (UN-GGIM).
The Centre works towards the implementation of the United Nations Integrated Geospatial Information Framework (UN-IGIF), with the goal of strengthening the capacities of Member States — particularly developing countries — in geospatial information management, while promoting innovation, knowledge sharing, and cooperation. It is within this advanced ecosystem that the collaboration between DICA and MGIL takes shape, confirming the Department's international vocation and its commitment to the global challenges of sustainability.
On Monday, June 8, a seminar titled “Micro-scale evolution of pore water characteristics in unsaturated sand under triaxial compression” will be held in Fassò Room (Building 4A) at 11:00 CET.
The seminar will be given by Ryunosuke Kido, Associate Professor at Graduate School of Advanced Science and Engineering, Hiroshima University.
Abstract
Unsaturated soil consists of granular particles and pore fluids (liquid and gas), and understanding its behavior requires clarifying the relationship between microscale phenomena and macroscale responses to better understand and predict the failure of earth structures and slopes. My research focuses on microscale phenomena in unsaturated soils that cannot be captured using conventional techniques. The objective is to visualize these invisible processes during laboratory testing through X-ray micro-computed tomography (CT) and advanced image analysis. In this seminar, I will introduce the microscale evolution of pore water characteristics in unsaturated sand during triaxial compression, with a particular focus on water retention states, the spatial distribution of liquid bridges, and the curvature of air–water interfaces. These observations provide new insights into the mechanisms governing the deviatoric stress responses observed in triaxial compression tests.
Bio-sketch
Dr. Ryunosuke Kido is an Associate Professor in the Graduate School of Advanced Science and Engineering, Civil and Environmental Engineering Program at Hiroshima University, Japan. He received his Doctor of Engineering from Kyoto University in 2019. During his doctoral studies, he was awarded a Research Fellowship for Young Scientists by the Japan Society for the Promotion of Science (JSPS). Following the completion of his doctorate, he served as an Assistant Professor at Kyoto University before joining Hiroshima University as an Associate Professor in 2024. In 2023, he spent 10 months as a visiting scholar at Université Grenoble Alpes in France. Dr. Kido has received multiple awards, including Paper Awards for Young Researchers from both the Japan Society of Civil Engineers (JSCE) and the Japanese Geotechnical Society (JGS). He is an active member of the Japanese domestic committee of ISSMGE Technical Committee TC105 (Geo-Mechanics from Micro to Macro). His research focuses on the micromechanics of geomaterials using a microfocus X-ray CT, image analyses and discrete element method. Main research topics include unsaturated soils, soil-structure interaction, internal erosion/clogging, and so on.