ICCS07/Liz Bradley
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[edit] LIZ BRADLEY - Nonlinear computers
Department of Computer Science
Department of Electrical and Computer Engineering
University of Colorado
Fluid flows are complicated and fascinating. They are also common in natural and engineered systems, so understanding, predicting, and controlling them is critically important. I will discuss an experimental study in which we co-opted the convective instability of a simple fluid flow to amplify small disturbances into desired downstream effects—the phenomenon known in the popular literature as the "butterly effect." More specifically, we used an array of MEMS microactuators to deliver small velocity perturbations at the boundary of a two-dimensional (planar) jet of air. This allowed us to selectively excite various natural instabilities of this jet and manipulate the geometry of its coherent flow structures.
Planar jets are somewhat unusual, both in the fluids literature and in engineering practice. We chose this geometry to make the system amenable to simultaneous experimental, analytic, and numerical analysis—an essential feature if one plans to use feedback to establish any kind of closed-loop control. Even in a simplified system like the planar jet, however, numerical solvers cannot track unmodelled effects like noise, and the complexity of fluid dynamics makes this a real issue if one wants to predict the flow, let alone to control it.
One way to address this problem is to use observations of the system being modelled—e.g., velocity field data from a fluid flow—to periodically correct the simulation. Changing the state variables of a running solver, however, can set off all sorts of unfriendly dynamics, so this data assimilation process is not trivial. Moreover, gathering and processing data can be costly, both computationally and financially, so one should apply corrections only when and where they are needed—e.g., where the flow gradients are high.
Biography:
Elizabeth Bradley did her undergraduate and graduate work at MIT, interrupted by a one-year leave of absence to row in the 1988 Olympic Games, and has been with the Department of Computer Science at the University of Colorado at Boulder since January of 1993. Her research interests include nonlinear dynamics, artificial intelligence, and control theory. She is the recipient of a NSF National Young Investigator award, a Packard Fellowship, a Radcliffe Fellowship, and the 1999 student-voted University of Colorado College of Engineering teaching award.
