TY - JOUR

T1 - Chaos in small-amplitude surface gravity waves over slowly varying bathymetry

AU - Brown, Michael G.

AU - Tappert, Frederick D.

AU - Sundaram, Sekhar E.

PY - 1991/6

Y1 - 1991/6

N2 - We consider the motion of small-amplitude surface gravity waves over variable bathymetry. Although the governing equations of motion are linear, for general bathymetric variations they are non-separable and cannot be solved exactly. For slowly varying bathymetry, however, approximate solutions based on geometric (ray) techniques may be used. The ray equations are a set of coupled nonlinear ordinary differential equations with Hamiltonian form. It is argued that for general bathymetric variations, solutions to these equations - ray trajectories - should exhibit chaotic motion, i.e. extreme sensitivity to initial and environmental conditions. These ideas are illustrated using a simple model of bottom bathymetry, h(x, y) =h0(l + ecos (2πx/L) cos (2πy/L)). The expectation of chaotic ray trajectories is confirmed via the construction of Poincare sections and the calculation of Lyapunov exponents. The complexity of chaotic geometric wavefields is illustrated by considering the temporal evolution of (mostly) chaotic wavecrests. Some practical implications of chaotic ray trajectories are discussed.

AB - We consider the motion of small-amplitude surface gravity waves over variable bathymetry. Although the governing equations of motion are linear, for general bathymetric variations they are non-separable and cannot be solved exactly. For slowly varying bathymetry, however, approximate solutions based on geometric (ray) techniques may be used. The ray equations are a set of coupled nonlinear ordinary differential equations with Hamiltonian form. It is argued that for general bathymetric variations, solutions to these equations - ray trajectories - should exhibit chaotic motion, i.e. extreme sensitivity to initial and environmental conditions. These ideas are illustrated using a simple model of bottom bathymetry, h(x, y) =h0(l + ecos (2πx/L) cos (2πy/L)). The expectation of chaotic ray trajectories is confirmed via the construction of Poincare sections and the calculation of Lyapunov exponents. The complexity of chaotic geometric wavefields is illustrated by considering the temporal evolution of (mostly) chaotic wavecrests. Some practical implications of chaotic ray trajectories are discussed.

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U2 - 10.1017/S0022112091000022

DO - 10.1017/S0022112091000022

M3 - Article

AN - SCOPUS:0026168836

VL - 227

SP - 35

EP - 46

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -