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A plethora of three-dimensional periodic travelling gravity-capillary water waves with multipulse transverse profiles. (English) Zbl 1136.76328

Summary: This article presents a rigorous existence theory for three-dimensional gravity-capillary water waves which are uniformly translating and periodic in one spatial direction \(x\) and have the profile of a uni- or multipulse solitary wave in the other \(z\). The waves are detected using a combination of Hamiltonian spatial dynamics and homoclinic Lyapunov-Schmidt theory. The hydrodynamic problem is formulated as an infinite-dimensional Hamiltonian system in which \(z\) is the timelike variable, and a family of points \(P_{k,k+1}\), \(k = 1,2,\dots\) in its two-dimensional parameter space is identified at which a Hamiltonian \(0^20^2\) resonance takes place (the zero eigenspace and generalised eigenspace are respectively two and four dimensional). The point \(P_{k,k+1}\) is precisely that at which a pair of two-dimensional periodic linear travelling waves with frequency ratio \(k:k+1\) simultaneously exist (“Wilton ripples”). A reduction principle is applied to demonstrate that the problem is locally equivalent to a four-dimensional Hamiltonian system near \(P_{k,k+1}\). It is shown that a Hamiltonian real semisimple \(1:1\) resonance, where two geometrically double real eigenvalues exist, arises along a critical curve \(R_{k,k+1}\) emanating from \(P_{k,k+1}\). Unipulse transverse homoclinic solutions to the reduced Hamiltonian system at points of \(R_{k,k+1}\) near \(P_{k,k+1}\) are found by a scaling and perturbation argument, and the homoclinic Lyapunov-Schmidt method is applied to construct an infinite family of multipulse homoclinic solutions which resemble multiple copies of the unipulse solutions.

MSC:

76B15 Water waves, gravity waves; dispersion and scattering, nonlinear interaction
35Q35 PDEs in connection with fluid mechanics
35Q51 Soliton equations
37K05 Hamiltonian structures, symmetries, variational principles, conservation laws (MSC2010)
37N10 Dynamical systems in fluid mechanics, oceanography and meteorology