Quarterly of Applied Mathematics

Quarterly of Applied Mathematics

Online ISSN 1552-4485; Print ISSN 0033-569X

   
 
 

 

Harmonic stability of standing water waves


Author: Jon Wilkening
Journal: Quart. Appl. Math. 78 (2020), 219-260
MSC (2010): Primary 37G15, 37K45, 65M70, 76B07, 76B15
DOI: https://doi.org/10.1090/qam/1552
Published electronically: September 16, 2019
MathSciNet review: 4077462
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Abstract: A numerical method is developed to study the stability of standing water waves and other time-periodic solutions of the free-surface Euler equations using Floquet theory. A Fourier truncation of the monodromy operator is computed by solving the linearized Euler equations about the standing wave with initial conditions ranging over all Fourier modes up to a given wave number. The eigenvalues of the truncated monodromy operator are computed and ordered by the mean wave number of the corresponding eigenfunctions, which we introduce as a method of retaining only accurately computed Floquet multipliers. The mean wave number matches up with analytical results for the zero-amplitude standing wave and is helpful in identifying which Floquet multipliers collide and leave the unit circle to form unstable eigenmodes or rejoin the unit circle to regain stability. For standing waves in deep water, most waves with crest acceleration below $A_c=0.889$ are found to be linearly stable to harmonic perturbations; however, we find several bubbles of instability at lower values of $A_c$ that have not been reported previously in the literature. We also study the stability of several new or recently discovered time-periodic gravity-capillary or gravity waves in deep or shallow water, finding several examples of large-amplitude waves that are stable to harmonic perturbations and others that are not. A new method of matching the Floquet multipliers of two nearby standing waves by solving a linear assignment problem is also proposed to track individual eigenvalues via homotopy from the zero-amplitude state to large-amplitude standing waves.


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Additional Information

Jon Wilkening
Affiliation: Department of Mathematics, University of California, Berkeley, California 94720-3840
MR Author ID: 725944
Email: wilken@math.berkeley.edu

Keywords: Standing water waves, gravity-capillary waves, linear stability, Floquet analysis, monodromy operator, Fourier basis
Received by editor(s): March 13, 2019
Received by editor(s) in revised form: June 25, 2019
Published electronically: September 16, 2019
Additional Notes: This work was supported in part by the National Science Foundation under award number DMS-1716560 and by the Department of Energy, Office of Science, Applied Scientific Computing Research, under award number DE-AC02-05CH11231.
Dedicated: Dedicated to Walter Strauss in honor of his 80th birthday
Article copyright: © Copyright 2019 Brown University