Evolution of Undular Surges in a Navigation Channel

Abstract

An undular surge is a secondary wave characterized by free-surface undulations over the body of a positive wave. The formation of undular surges is strongly linked to the departure of pressure distribution from hydrostatic due to the combined effects of wave nonlinearity and dispersion. In navigation channels, undular surges may be generated by the filling or emptying operation of lock chambers. The propagation of undular surges is associated with the periodic flow variations, and therewith they can cause impulse motion responses of navigation ships and even navigation accidents in some instances. In the present study, the free-surface and hydrodynamic properties of undular surges induced by the emptying operation of lock chambers were experimentally investigated. Detailed free-surface and velocity measurements were performed with a series of capacitance wave gauges and an acoustic Doppler velocimeter in a horizontal rectangular water wave channel. Both nonbreaking and breaking surges were recognized and analyzed. The results demonstrated that the wave face of a nonbreaking undular surge could be accurately described by solitary wave theory. However, the velocity distributions beneath the surge deviated significantly from the solitary wave solution. Based on the experimental results, a formula relating the longitudinal velocity component to free-surface elevation was established. Overall, this study provided new insights into the analogy of an undular surge and a solitary wave.