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Quasi-Classical Approximation in Vortex Filament Dynamics. Integrable Systems, Gradient Catastrophe, and Flutter


G. Ortenzi, Dipartimento di Matematica Pura ed Applicazioni, Università di Milano Bicocca, 20125 Milano, Italy; e-mail:


Quasi-classical approximation in the intrinsic description of the vortex filament dynamics is discussed. Within this approximation, the governing equations are given by elliptic system of quasi-linear partial differential equations of the first order. Dispersionless Da Rios system and dispersionless Hirota equation are among them. They describe motion of vortex filament with slow-varying curvature and torsion without or with axial flow. Gradient catastrophe for governing equations is studied. It is shown that geometrically this catastrophe manifests as a fast oscillation of a filament curve around the rectifying plane which resembles the flutter of airfoils. Analytically, it is the elliptic umbilic singularity in the terminology of the catastrophe theory. It is demonstrated that its double scaling regularization is governed by the Painlevé I equation.