Parsadoust, Ali; (1995) Vertical sidewall boundary layers in combined waves and currents. Doctoral thesis (Ph.D), University of London, University College London.

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Abstract

This thesis describes a theoretical and experimental investigation into the effects of flume sidewalls on wave damping in combined flows. It proposes two different theoretical models, namely the "modified Hunt formula" (for laminar flows) and the "wave attenuation equation" (for turbulent flows). Both models account for the separate contribution of bed and sidewall boundaries. They allow researchers to successfully predict wave height attenuation after the addition of following or opposing currents, in wave dominated or current dominated flows, and near smooth or rough boundaries. To test the validity of the derived theories, experiments with parameters ranging from near deep to near shallow water waves and from wave dominated to current dominated flows were carried out. Measurements were also performed in channels with extremely low aspect ratios to isolate the rate of wave attenuation attributable to sidewalls alone. The present study is among the first to make detailed measurements (using Laser Doppler Anemometry) of orbital and steady velocity profiles near a vertical boundary for interacting waves and steady currents. The results confirmed the theoretical approach adopted to describe the flow behaviour near a sidewall. The comparison between the predictions of the developed theories and experimental data showed the ability of the two solutions to account for both the bed and sidewall contributions to wave height attenuation. These findings are projected to provide a guide to wave damping in a wide range of flow condition and environments both in still water and combined flows.

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