Metastability of solitary roll wave solutions of the St. Venant equations with viscosity

We study by a combination of numerical and analytical Evans function techniques the stability of solitary wave solutions of the St. Venant equations for viscous shallowwater flow down an incline, and related models. Our main result is to exhibit examples of metastable solitary waves for the St. Venant equations, with stable point spectrum indicating coherence of the wave profile but unstable essential spectrum indicating oscillatory convective instabilities shed in its wake. We propose a mechanism based on “dynamic spectrum” of the wave profile, by which a wave train of solitary pulses can stabilize each other by de-amplification of convective instabilities as they pass through successive waves. We present numerical time evolution studies supporting these conclusions, which bear also on the possibility of stable periodic solutions close to the homoclinic. For the closely related viscous Jin-Xin model, by contrast, for which the essential spectrum is stable, we show using the stability index of Gardner–Zumbrun that solitary wave pulses are always exponentially unstable, possessing point spectra with positive real part. ∗Indiana University, Bloomington, IN 47405; [email protected]: Research of B.B. was partially supported under NSF grants no. DMS-0300487 and DMS-0801745. †Indiana University, Bloomington, IN 47405; [email protected]: Research of M.J. was partially supported by an NSF Postdoctoral Fellowship under NSF grant DMS-0902192. ‡Université de Lyon, Université Lyon 1, Institut Camille Jordan, UMR CNRS 5208, 43 bd du 11 novembre 1918, F 69622 Villeurbanne Cedex, France; [email protected]: Stay of M.R. in Bloomington was supported by Frency ANR project no. ANR-09-JCJC-0103-01. §Indiana University, Bloomington, IN 47405; [email protected]: Research of K.Z. was partially supported under NSF grants no. DMS-0300487 and DMS-0801745.