SCHOOL OF MECHANICAL ENGINEERING SEMINAR Monday, June 11, 2012 at 15:00 Wolfson Building of Mechanical Engineering, Room 206

Department of Mechanical Engineering, Technion - Israel Institute of Technology

The focus of this lecture is on the influence of nonlinear dissipation mechanisms on chaotic fluid-structure interaction. The identification of damping mechanisms is straightforward for linear processes governed by exponential decay or response to external harmonic excitation. However, nonlinear and chaotic processes governed by self-excited modulation or external excitation, require an intimate knowledge of nonlinear damping, without which theoretical solution topology and stability thresholds can be inaccurate, and response may spuriously grow without bound. Examples of chaotic fluid-structure-interaction where there exists discrepancies between measurements and theoretical estimates based on models with linear damping, include tethered rigid-bodies and elastic panels that undergo self-excited modulation in uniform flow or due to external or boundary excitation. In order to accurately model the effects of nonlinear damping, we employ a reduced-order nonlinear model-based estimation methodology where controlled measurements are decomposed into slowly-varying amplitude and phase, which in-turn enable construction of nonlinear frequency and damping backbone curves. The latter enable estimation of nonlinear damping mechanisms in models that can be reduced to their equivalent normal forms by multiple-scale asymptotics. Validation of the nonlinear model-based damping mechanism is obtained by comparison to independently obtained data exhibiting chaotic interaction. We will discuss nonlinear damping mechanisms estimated from a chaotic spherical pendulum, and from scattered pressure waves generated by an acoustically excited panel. Results shed light on the significance of nonlinear damping mechanisms that govern the bifurcation structure of systems exhibiting complex and chaotic-like dynamics.

The influence of nonlinear dissipation mechanisms on chaotic fluid-structure interaction

Prof. Oded Gottlieb