R Krechetnikov and J E Marsden 2009 J. Phys. A: Math. Theor. 42 412004 doi:10.1088/1751-8113/42/41/412004
R Krechetnikov1 and J E Marsden2
Show affiliationsFinite-amplitude instabilities are ubiquitous, but their theory and precise definitions require clarification. In this work, we discuss the interrelation of various notions connected with finite-amplitude instabilities and offer a precise context for these phenomena. Then we establish a connection between non-normality of linear operators, energy conservation by nonlinear operators and the existence of finite-amplitude instabilities in finite- and infinite-dimensional dynamical systems, both in the conservative and dissipative cases. Such a connection may at first appear counter-intuitive since it relates intrinsically linear and nonlinear phenomena, but it follows naturally from the properties of linear and nonlinear operators when they appear together in a dynamical system. In particular, the main theorem of this communication proves that non-normality is a necessary condition for a finite-amplitude instability. It is demonstrated that this phenomenon is relevant to a wide class of physical systems with energy-conserving nonlinearities.
47.10.ad Navier-Stokes equations
76D05 Navier-Stokes equations (See also 35Q30)
Issue 41 (16 October 2009)
Received 26 May 2009, in final form 10 September 2009
Published 29 September 2009
R Krechetnikov and J E Marsden 2009 J. Phys. A: Math. Theor. 42 412004
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