報告題目：Computer Vision and Global Skin Friction Diagnostics.
Tianshu Liu is a professor and the director of Applied Aerodynamics Laboratory at Western Michigan University (Kalamazoo, Michigan, USA). He received a Ph.D. in aeronautics and astronautics from Purdue University (West Lafayette, Indiana, USA) in 1996. He was a research scientist at NASA Langley Research Center (Hampton, Virginia, USA) in 1999-2004. His research areas cover experimental and applied aerodynamics, and theoretical aerodynamics models. In particular, he has contributed to image-based aerodynamic measurement techniques for various physical quantities such as surface pressure, temperature/heat-transfer, skin friction, velocity fields, aeroelastic deformation and distributed and integrated forces. Other topics include videogrammetry and vision for aerospace applications, flow control, flapping flight, flight vehicle design, transition and turbulence, flight tests, and bias error theory.
Computer vision provides necessary physical information from images for understanding of observed objects. From a perspective of flow measurements, computer vision serves as a general framework for quantitative flow diagnostics. A key is to establish the relationship between a physical quantity to be determined and a measurable quantity from images. Then, extraction of the physical quantity from images is considered as an inverse problem. This presentation will discuss the application of computer vision in global skin friction measurements.
From a unified perspective, this presentation describes global skin friction diagnostics based on surface flow visualizations. The foundations of the developed image-based methods are relations between skin friction and other measurable surface quantities (e.g. oil-film thickness, temperature, scalar density and pressure), which are derived from the relevant governing equations in fluid mechanics. Interestingly, these relations can be cast into a generic form of the optical flow equation in the image plane, and therefore skin friction fields can be extracted from surface visualization images as an optical flow problem by using the variational method. Examples in global skin friction diagnostics are given, including experimental setups, image processing, and topological analysis of extracted skin friction fields.