Waves from an oscillating point source with a free surface in the presence of a shear current

Abstract

We investigate analytically the linearized water wave radiation problem for an oscillating submerged point source in an inviscid shear flow with a free surface. A constant depth is taken into account and the shear flow increases linearly with depth. The surface velocity relative to the source is taken to be zero, so that Doppler effects are absent. We solve the linearized Euler equations to calculate the resulting wave field as well as its far-field asymptotics. For values of the Froude number $F^2={\omega }^{2}D/g$ ($\omega$: oscillation frequency, $D$ submergence depth) below a resonant value $F_{\text{res}}^2$ the wave field splits cleanly into separate contributions from regular dispersive propagating waves and non-dispersive "critical waves" resulting from a critical layer-like street of flow structures directly downstream of the source. In the sub-resonant regime the regular waves behave like sheared ring waves while the critical layer wave forms a street of a constant width of order $D\sqrt{S/\omega }$ ($S$ is the shear flow vorticity) and is convected downstream at the fluid velocity at the depth of the source. When the Froude number approaches its resonant value, the the downstream critical and regular waves resonate, producing a train of waves of linearly increasing amplitude contained within a downstream wedge.

23 pages, 10 figures

References in corpus (4)

• Ship waves on uniform shear current at finite depth: wave resistance and critical velocity
• Initial surface disturbance on a shear current: the Cauchy--Poisson problem with a twist
• Oblique waves on a vertically sheared current are rotational
• Oscillating line source in a shear flow with a free surface: critical layer-like contributions

Cited by in corpus (6)

• Oblique waves on a vertically sheared current are rotational
• Transient wave resistance upon a real shear current
• Multiple resonances of a moving, oscillating surface disturbance on a shear current
• Oscillating line source in a shear flow with a free surface: critical layer-like contributions
• Water Waves from General, Time-Dependent Surface Pressure Distribution in the Presence of a Shear Current
• Oscillating sources in a shear flow with a free surface