A narrow-banded spectrum of gravity waves propagating in one horizontal direction at the surface of water with finite depth may be governed by a nonlinear Schrödinger equation (NLSE). If the depth is nonuniform, then the coefficients in the NLSE are variable and an additional linear term due to conservation of wave action flux is present, which may act as a dissipative term that causes the wave envelope to broaden and decrease in amplitude or which may act as a growth term that causes the wave envelope to focus and increase in amplitude. The addition of linear, viscous dissipation either enhances the dissipative process or competes with the growth effect. Here we consider such a variable-coefficient, dissipative NLSE. We find a solution that has uniform amplitude in the appropriate reference frame and examine its linear stability. We find that for waves propagating into shallower water, both bathymetry and viscous dissipation act to stabilize the modulational instability. For waves propagating into deeper water, bathymetry acts to enhance instability, but viscous dissipation eventually causes stabilization for small enough initial perturbation amplitudes.
All Science Journal Classification (ASJC) codes
- Applied Mathematics