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On the appearance of internal wave attractors due to an initial or parametrically excited disturbance

Published online by Cambridge University Press:  02 January 2013

Janis Bajars ,
Jason Frank  and
Leo R. M. Maas
Janis Bajars
Affiliation:
Centrum Wiskunde & Informatica, PO Box 94079, 1090 GB Amsterdam, The Netherlands
Jason Frank*
Affiliation:
Centrum Wiskunde & Informatica, PO Box 94079, 1090 GB Amsterdam, The Netherlands
Leo R. M. Maas
Affiliation:
Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Texel, The Netherlands
*
†Email address for correspondence: jason@cwi.nll
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Abstract

In this paper we solve two initial value problems for two-dimensional internal gravity waves. The waves are contained in a uniformly stratified, square-shaped domain whose sidewalls are tilted with respect to the direction of gravity. We consider several disturbances of the initial stream function field and solve both for its free evolution and for its evolution under parametric excitation. We do this by developing a structure-preserving numerical method for internal gravity waves in a two-dimensional stratified fluid domain. We recall the linearized, inviscid Euler–Boussinesq model, identify its Hamiltonian structure, and derive a staggered finite difference scheme that preserves this structure. For the discretized model, the initial condition can be projected onto normal modes whose dynamics is described by independent harmonic oscillators. This fact is used to explain the persistence of various classes of wave attractors in a freely evolving (i.e. unforced) flow. Under parametric forcing, the discrete dynamics can likewise be decoupled into Mathieu equations. The most unstable resonant modes dominate the solution, forming wave attractors.

JFM classification

Geophysical and Geological Flows: Geophysical and Geological Flows Geophysical and Geological Flows: Internal waves
Type
Papers
Information
Journal of Fluid Mechanics , Volume 714 , 10 January 2013 , pp. 283 - 311
Copyright
©2013 Cambridge University Press

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