Academic Centre
28. septembrī ar lekciju "Inverse Problems in Global Flow Diagnostics" uzstāsies prof. Tianshu Liu no Rietumu Mičiganas Universitātes ASV.
Abstract
We live in the world of fluids particularly in water and air. Therefore, our understanding of the physics of fluid flows are vitally important to sustainable civilizations. Global flow diagnostics is of fundamentally importance in various fields including aerospace and mechanical engineering, chemical engineering, biomedical sciences, atmosphere sciences, oceanology, etc.
This presentation discusses unified image-based measurement methods to determine the important physical quantities of complex flows in engineering and natural systems from flow visualizations, including velocity, pressure, temperature/heat-transfer, and skin friction. Flow visualization images represent observable quantities of flows in terms of the image intensity, including scattering particle images in particle image velocimetry (PIV), fluorescent images in planar laser-induced fluorescence (PLIF) visualizations, Schlieren and shadowgraph images of density-varying flows, transmittance images (X-ray and neutron radiography images), pressure- and temperature-sensitive-paint (PSP and TSP) images, surface luminescent oil-film images, and multi-spectral images of clouds and oceans taken by satellites and spacecraft.
From a general perspective, the determination of a physical quantity from observable quantities is an inverse problem since observed information is often not sufficient in global flow measurements. To formulate the inverse problems, the mathematical models for various flow visualizations are required to relate the observable quantities to the physical quantities to be determined. For example, to determine a vector field in flows (velocity or skin friction), the models can be written in a typical form of the transport equation in the image plane (the optical flow equation). To solve these ill-posed inverse problems, a variational method is applied, and as a result the Euler-Lagrange equation is obtained to extract a field of a physical quantity from the observable quantities. Therefore, the inverse problems in global flow diagnostics can be considered in a unified framework of the variational formulations, which is the main theme of this presentation.
Short Biography
Tianshu Liu is the John O. Hallquist Endowed Professor and the Presidential Innovation Professor at Western Michigan University. He received a Ph.D. in aeronautics and astronautics from Purdue University (West Lafayette, IN) in 1996. He was a research scientist at NASA Langley Research Center (Hampton, VA) in 1999-2004. His research areas are experimental and applied aerodynamics and fluid mechanics. In particular, he has contributed to image-based measurement techniques for the physical quantities in fluid mechanics and aerodynamics, such as velocity, pressure, temperature/heat-flux, skin friction, aeroelastic deformation, and distributed and integrated forces. His topics also include videogrammetry and vision for aerospace applications, flow control, flapping flight, flight vehicle design, turbulence and transition, and flight tests.
Savukārt, 29. septembrī ar lekciju “Diverse Science at Imaging Beamlines at the PSI SINQ Neutron Spallation Source" uzstāsies Dr. Knud Thomsen no Paula Šerrera institūta Šveicē.
Abstract
A good portion of the instruments on the neutron spallation source SINQ at PSI is devoted to imaging. After a short introduction of basic principles and specific problems it becomes clear that there is a long way from simple „shadow casting“ to quantitative scientific measurements. Selected technical topics and representative applications will be presented ranging from recent advances in the investigation of cultural heritage objects to a focus on urgent current materials‘ issues. Additive manufacturing poses questions to which advanced imaging can offer very useful hints, especially when combined with scattering measurements. The next steps for further advancing the technique then are grating-based methods where the contrast in an image is derived from small angle scattering in a specimen. Developments relating to both, hardware and software, at PSI often are driven by very specific problems; then there is a chance that they are interesting to industry and research alike. As an example, a unique set-up, in which highly radioactive probes can be investigated, will be presented in some detail. A short overview of upgrades of the imaging facilities at PSI in the near future and an invitation to continue the very useful cooperation between PSI and the University of Latvia in Riga will conclude the presentation.
Short Biography
Knud Thomsen is affiliated as external member with the Applied Materials Group, officially retired from the Paul Scherrer Institute since the beginning of the year. He received his PhD in general physics from the Technical University in Vienna, Austria with a work on laser fluorescence. After a period with the TU Vienna and the IAEA, he joined PSI as head of the space technology group in the Laboratory for Astrophysics. He continued at PSI with the management of the MEGAPIE project (first 1 MW Liquid-Metal spallation target) and later the Swiss in-kind contributions to ESS (European Spallation Source) at Lund, Sweden. Up to his retirement, K. Thomsen was the scientific secretary of the PSI Research Commission. His technical expertise includes lasers, thermal and structural design, spallation targets, Liquid-Metal related topics, and neutron imaging.
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