The nonlinear wave pattern generated by a localized pressure source moving over a liquid free surface at speeds below the minimum phase speed ($c_{\min }$) of linear gravity-capillary waves is investigated experimentally and theoretically. At these speeds, freely propagating fully localized solitary waves, or “lumps,” are known theoretically to be possible. For pressure-source speeds far below $c_{\min }$, the surface response is a local depression similar to the case with no forward speed. As the speed is increased, a critical value is reached $c_c\approx 0.9c_{\min }$ where there is an abrupt transition to a wavelike state that features a steady disturbance similar to a steep lump behind the pressure forcing. As the speed approaches $c_{\min }$, a second transition is found; the new state is unsteady and is characterized by continuous shedding of lumps from the tips of a $\mathsf{V}$-shaped pattern.

• Received 8 September 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.214502