Unstable surface waves in running water

Vera Mikyoung Hur; Zhiwu Lin

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arXiv · 0708.0541

Unstable surface waves in running water

Vera Mikyoung Hur·Zhiwu Lin

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Abstract

We consider the stability of periodic gravity free-surface water waves traveling downstream at a constant speed over a shear flow of finite depth. In case the free surface is flat, a sharp criterion of linear instability is established for a general class of shear flows with inflection points and the maximal unstable wave number is found. Comparison to the rigid-wall setting testifies that free surface has a destabilizing effect. For a class of unstable shear flows, the bifurcation of nontrivial periodic traveling waves of small-amplitude is demonstrated at any wave number. We show the linear instability of small nontrivial waves bifurcated at an unstable wave number of the background shear flow. The proof uses a new formulation of the linearized water-wave problem and a perturbation argument. An example of the background shear flow of unstable small-amplitude periodic traveling waves is constructed for an arbitrary vorticity strength and for an arbitrary depth, illustrating that vorticity has a subtle influence on the stability of water waves.

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Vera Mikyoung Hur, Zhiwu Lin. 2007-11-28. Unstable surface waves in running water. https://arxiv.org/abs/0708.0541

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