title: Nonlinear focusing of acoustic shock waves at a caustic cusp.
abstract: The present study investigates the focusing of acoustical weak shock waves incoming on a cusped caustic. The theoretical model is based on the Khokhlov-Zabolotskaya equation and its specific boundary conditions. Based on the so-called Guiraud's similitude law for a step shock, a new explanation about the wavefront unfolding due to nonlinear self-refraction is proposed. This effect is shown to be associated not only to nonlinearities, as expected by previous authors, but also to the nonlocal geometry of the wavefront. Numerical simulations confirm the sensitivity of the process to wavefront geometry. Theoretical modeling and numerical simulations are substantiated by an original experiment. This one is carried out in two steps. First, the canonical Pearcey function is synthesized in linear regime by the inverse filter technique. In the second step, the same wavefront is emitted but with a high amplitude to generate shock waves during the propagation. The experimental results are compared with remarkable agreement to the numerical ones. Finally, applications to sonic boom are briefly discussed.
authors.affiliation: Laboratoire de Modélisation en Mécanique, Université Pierre et Marie Curie and CNRS (UMR 7607), 75252 Paris Cedex 05, France. marchi@lmm.jussieu.fr
authors.forename: Régis
authors.initials: R
authors.lastname: Marchiano
authors.forename: François
authors.initials: F
authors.lastname: Coulouvrat
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Thomas