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THESIS DEFENSE: Control of Underactuated Fluid-Body Systems with Real-Time Particle Image Velocimetry

Speaker: John Roberts , MIT
Date: May 18 2012
Time: 3:00PM to 4:30PM
Location: 32-D463 (Star)
Host: Russ Tedrake, MIT

Controlling the interaction of a robot with a fluid, particularly when the desired behavior is intimately related to the dynamics of the fluid, is a difficult and important problem. High-performance aircraft cannot ignore nonlinear stall effects, and robots hoping to fly and swim with performance matching that seen in birds and fish cannot treat fluid flows as quasi-steady. If we wish to match the level of performance seen in nature several major hurdles must be overcome, with one of the most difficult being the poor observability of the fluid state. Fluid dynamicists have long contended with this observability problem, and have used computationally intensive Particle Image Velocimetry (PIV) to gain an understanding of the fluid behavior after the fact. However, improvement in available computational power is now making it possible to perform PIV in real-time. With the fluid state observable PIV becomes not just an analysis tool, but a valuable sensor that can be integrated into a control loop.

In this thesis I present methods for controlling fluid-body systems in which the fluid plays a vital dynamical role, for performing real-time PIV, and for interpreting the output of PIV in a manner useful to control. The utility of these methods is demonstrated on a mechanically simple but dynamically rich experimental platform: the hydrodynamic cart-pole. This system is analogous to the well-known cart-pole system seen in the controls literature, but through its relationship with the surrounding fluid it captures many of the fundamental challenges of more general fluid-body control tasks, including: nonlinearity, underactuation, an important and unknown fluid state and a dearth of accurate and tractable models. Control results on dynamically representative experiments, including high-speed maneuvering and rejecting fluid disturbances, suggest that the new techniques will push the boundaries of what we can expect a robot in a fluid to do.

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