Charvet, I.; (2012) Experimental modelling of long elevated and depressed waves using a new pneumatic wave generator. Doctoral thesis , UCL (University College London).

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Abstract

Tsunami are long propagating waves caused by the rapid displacement of a large body of water. Recent events have shown how devastating tsunami can be to urban infrastructure (e.g. Japan 2011). Tsunami are characterized by their very long period (typically 10-40min), large amplitudes close to the shore, and a large trough often preceding the positive wave. They are unusual, and their period falls between that of ocean waves and tidal flows. To study these processes, an experimental methodology is applied to analyse how long waves (with or without a depressed component) propagate and move inshore. This thesis starts by critically reviewing the state-of-the-art in numerical and physical modelling of long propagating waves, therefore identifies the limitations of numerical codes to date, and of previous experimental studies. It is found that while the generation and propagation of a long wave can be reasonably well modelled with numerical codes, the behaviour of the wave nearshore and onshore is much more complex and usually tackled using laboratory experiments. These are themselves often limited by the length and types of waves generated, as well as scale and/or parameters investigated. Therefore, a new experimental long wave generation system is developed together with HR Wallingford and used within a wave flume to study long wave dynamics. The novel aspect of the study is that the propagating waves studied have long wavelengths compared to those previously generated in tests (i.e. like field tsunami, they are in the shallow-water domain), and the new generation system enables leading depressed waves to be reproduced for the first time. The propagating waves are analysed using wave elevation time series and local velocity measurements. Finally, the results on propagating long wave runup, highlighting the role of potential energy, but also velocities in the shoreline region are presented and discussed. New relationships for runup are proposed. Some preliminary results about the evolution of pressures on a model building are introduced.

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