Joint Seminar,
Fluids, Thermal and Chemical Processes and
The Center for Fluid Mechanics
Fellow, Sidney Sussex College, Jerome Clark Hunsaker Visiting Professor at MIT | |
Abstract: Acoustically-coupled combustion instability can occur whenever combustion takes place within an acoustic resonator. Over the years, many combustors have been found to be susceptible to self-excited oscillations, but currently the occurrence of instability in lean premixed combustion systems is proving to be a major technological challenge. By burning lean, premixed and prevapourised, it is possible to reduce chemical emissions significantly. Unfortunately, these are just the conditions that make a flame particularly sensitive to inlet flow disturbances. Coupling between the rate of heat release and the flow can lead to self-excited oscillations, and the resulting pressure oscillations and/or enhanced heat transfer can cause structural damage.
This seminar will give an overview of current work at the University of Cambridge, England on the modeling of combustion oscillations. The rôles of wave analysis, low-order models for unsteady combustion, Computational Fluid Dynamics and experiment will be illustrated by examples of oscillations in aeroengine combustors and in generic premixed ducted flames.
IF YOU WOULD LIKE TO MEET WITH PROFESSOR DOWLING PLEASE CONTACT MADELINE BREWSTER TO MAKE AN APPOINTMENT (863-1414)
Brown Applied Mathematics Pattern Theory and Vision Seminar
Abstract: We treat the problem of edge detection as one of statistical inference. Local edge cues, implemented by filters, provide information about the likely positions of edges which can be used as input to higher-level models. Different edge cues can be evaluated by the statistical effectiveness of their corresponding filters evaluated on two datasets of pre-segmented images. We use information theoretic measures to determine the effectiveness of a variety of different edge detectors working at multiple scales on black and white and colour images. Our results give quantative meassures for the advantages of multi-level processing, for the use of chromaticity in addition to greyscale, and for the relative effectiveness of different detectors. Regional cues are also discussed. Finally, we briefly describe how this work enables us to compute order parameters for curve detection and descrive "Manhattan world" where the structure of edge statistics in urban scenes can be used to determine the viewer's orientation.
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