The majority of fundamental research on wave-driven sediment transport has been based on regular waves and regular oscillatory flows. Systematic research into isolating the effect of irregularity on oscillatory boundary layer hydrodynamics and sand transport are not presently available. This research reports on large-scale oscillatory flow tunnel experiments designed to isolate the effect of flow irregularity (specifically amplitude-modulated flows) on oscillatory flow boundary layer hydrodynamics and net sand transport rates. Two main series of experiments - one focussing on the hydrodynamics of amplitude-modulated flows over a fixed (immobile) bed and a second focussing on the sediment transport over mobile sand beds – were conducted. Detailed boundary layer velocity measurements are presented for regular and amplitude-modulated oscillatory flows over two fixed rough beds, coarse sand and gravel. The results show that amplitude-modulation of the flow has a variable effect on the hydrodynamic behaviour of the oscillatory boundary layer: the broad conclusion is that time-history effects are not significant near the bed but become more significant higher in the flow. Net transport rate measurements are presented for regular and amplitudemodulated flows for two mobile sand beds, medium and fine sand. The mobile bed experiments show that: for medium sand, net transport rates are similar for the amplitude-modulated and equivalent regular; for fine sand, net transport rates are very different for the amplitude-modulated and equivalent regular flows. The SANTOSS model-predicted sand transport rates shows that the model correctly predicts the net transport for the present experimental conditions, indicating that the major unsteady transport processes are captured in the model. The SANTOSS model is used to compare net transport rates for equivalent regular and amplitude-modulated flows across a wide range of flow conditions and two sand sizes. The results show good agreement in net transport rate between equivalent regular and amplitude-modulated flows, for conditions in which phase lag effects are weak and poor agreement when phase lags effects are strong.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:704526 |
| Date | January 2016 |
| Creators | Bhawanin, Mahesa |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=231262 |
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