Wavevector resonance in a nonlinear multi-wavespeed chaotic billiard
  Nonlinear coupling between eigenmodes of a system leads to spectral energy redistribution. For multi-wavespeed chaotic billiards the average coupling strength can exhibit sharp discontinuities as a function of frequency related to wavevector coincidences between constituent waves of different wavespeeds. The phenomenon is investigated numerically for an ensemble of 2D square two-wavespeed billiards with rough boundaries and quadratic nonlinearity representative of elastodynamic waves. Results of direct numerical simulations are compared with theoretical predictions. 
Alexei Akolzin and Richard L. Weaver