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On power series solutions for the Euler equation, and theBehr–Nečas–Wu initial datum

Published online by Cambridge University Press:  04 March 2013

Carlo Morosi
Affiliation:
Dipartimento di Matematica, Politecnico di Milano, P.za L. da Vinci 32, 20133 Milano, Italy. carlo.morosi@polimi.it
Mario Pernici
Affiliation:
Istituto Nazionale di Fisica Nucleare, Sezione di Milano, Via Celoria 16, 20133 Milano, Italy; mario.pernici@mi.infn.it
Livio Pizzocchero
Affiliation:
Dipartimento di Matematica, Università di Milano, Via C. Saldini 50, 20133 Milano, ItalyIstituto Nazionale di Fisica Nucleare, Sezione di Milano, Italy; livio.pizzocchero@unimi.it

Abstract

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We consider the Euler equation for an incompressible fluid on a three dimensional torus,and the construction of its solution as a power series in time. We point out some generalfacts on this subject, from convergence issues for the power series to the role ofsymmetries of the initial datum. We then turn the attention to a paper by Behr, Nečas andWu, ESAIM: M2AN 35 (2001) 229–238; here, the authors chose avery simple Fourier polynomial as an initial datum for the Euler equation and analyzed thepower series in time for the solution, determining the first 35 terms by computer algebra.Their calculations suggested for the series a finite convergence radiusτ3 in the H3 Sobolev space, with0.32 < τ3 < 0.35; they regarded this as an indicationthat the solution of the Euler equation blows up. We have repeated the calculations of E.Behr, J. Nečas and H. Wu, ESAIM: M2AN 35 (2001) 229–238,using again computer algebra; the order has been increased from 35 to 52, using thesymmetries of the initial datum to speed up computations. As forτ3, our results agree with the original computations of E.Behr, J. Nečas and H. Wu, ESAIM: M2AN 35 (2001) 229–238(yielding in fact to conjecture that 0.32 < τ3 < 0.33).Moreover, our analysis supports the following conclusions: (a) The finiteness ofτ3 is not at all an indication of a possible blow-up. (b)There is a strong indication that the solution of the Euler equation does not blow up at atime close to τ3. In fact, the solution is likely to exist, atleast, up to a time θ3 > 0.47. (c) There is a weakindication, based on Padé analysis, that the solution might blow up at a later time.

Information

Type
Research Article
Copyright
© EDP Sciences, SMAI, 2013