Laboratory generation and physics of propagation of solitary waves and water surface depressions

Solitary waves and water surface depressions are generated using a piston-type wavemaker. Different aspects of their propagation including profile evolution, establishment rate, stability, and celerity are examined experimentally.;Traditionally, solitary waves are generated in laboratory set-ups using a methodology developed by Goring (1979) that considers a wave of permanent form during the generation process. A New methodology for generation of solitary waves using piston-type wavemakers is proposed by considering the evolving nature of the wave during generation phase. The capability of the New methodology in generation of solitary waves is assessed by conducting a series of laboratory experiments in water depth, h, of 20 cm and for the dimensionless wave height, H/h, values (H -- wave height) ranging from 0.3 to 0.6. Waves generated using the Goring methodology served as a benchmark to evaluate the performance of the New methodology in generating solitary waves. Recorded waveforms are compared with theoretical solutions in terms of various wave characteristics (e.g., wave height, profile shape, wave celerity). These comparisons revealed that the New methodology is capable of generating more accurate and rapidly-established solitary waves with less wave attenuation with distance compared to the Goring methodology.;In the second part, water surface depressions are generated using the Goring methodology in water depths of 6, 10 and 30 cm and for the dimensionless trough amplitude, at/h, values (at -- trough amplitude) ranging from 0.05 to 0.6. Generated water surface depressions are in good agreement with the aimed theoretical profile in the vicinity of the wave paddle. In all experiments, generated negative solitary wave-like depression wave rapidly deforms into a triangular-like depression wave followed by a series of oscillatory trailing waves. As the depression wave propagates, as a result of nonlinear and dispersive effects its amplitude attenuates, slope of the leading edge of the depression wave becomes gentler while its rear edge slope becomes steeper. The amplitudes of the oscillatory trailing waves increase initially as the depression propagates; then the amplitudes of the oscillatory trailing waves start attenuating with distance due to viscous and dispersive effects. Celerity of the depression wave increases with distance as the depression amplitude attenuates with distance, but it never reaches the celerity of long waves in deep waters. Based on the experimental data of the present study and those reported by Hammack and Segur (1978), three empirical equations are proposed to predict the profile shape of a depression (i.e. trough amplitude, frequency of the leading half, and slope of the rear edge) for a given propagation distance.