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Spatial structure of shock formation

Published online by Cambridge University Press:  05 May 2017

J. Eggers*
Affiliation:
School of Mathematics, University of Bristol, University Walk, Bristol BS8 1TW, UK
T. Grava
Affiliation:
School of Mathematics, University of Bristol, University Walk, Bristol BS8 1TW, UK SISSA, via Bonomea 265, 34136 Trieste, Italy
M. A. Herrada
Affiliation:
School of Mathematics, University of Bristol, University Walk, Bristol BS8 1TW, UK E.S.I., Universidad de Sevilla, Camino de los Descubrimientos s/n 41092, Spain
G. Pitton
Affiliation:
SISSA, via Bonomea 265, 34136 Trieste, Italy
*
Email address for correspondence: jens.eggers@bris.ac.uk

Abstract

The formation of a singularity in a compressible gas, as described by the Euler equation, is characterized by the steepening and eventual overturning of a wave. Using self-similar variables in two space dimensions and a power series expansion based on powers of $|t_{0}-t|^{1/2}$ , $t_{0}$ being the singularity time, we show that the spatial structure of this process, which starts at a point, is equivalent to the formation of a caustic, i.e. to a cusp catastrophe. The lines along which the profile has infinite slope correspond to the caustic lines, from which we construct the position of the shock. By solving the similarity equation, we obtain a complete local description of wave steepening and of the spreading of the shock from a point. The shock spreads in the transversal direction as $|t_{0}-t|^{1/2}$ and in the direction of propagation as $|t_{0}-t|^{3/2}$ , as also found in a one-dimensional model problem.

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Type
Papers
Copyright
© 2017 Cambridge University Press 

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