Abstract
A new oscillatory water tunnel has been built in the Civil and Environmental Engineering Department's Hydraulic Laboratory at the National University of Singapore. It can accurately produce oscillatory flows that correspond to full-scale sea waves. Tests including pure sinusoidal waves and combined wave-current flows over smooth and rough bottoms have been performed. High quality measurements of the boundary layer flow fields are obtained using a PIV system. The PIV measured flow field is phase and spatially averaged to give a mean vertical velocity profile. It is found that the logarithmic profile can accurately approximate the near-bottom first-harmonic amplitude of sinusoidal waves and give highly accurate determinations of the hydrodynamic roughness and the theoretical bottom location. The bottom shear stress obtained from momentum integral is in general agreement with results from log-profile fitting. The current profiles of combined wave-current flows indicate a two-log-profile structure as suggested by simple combined wave-current flow theory. The difference between the two current shear velocities obtained from combined wave-current flows, as well as a small but meaningful third harmonic embedded in a pure sinusoidal wave, suggest the existence of a time-varying turbulent eddy viscosity.
Highlights
Sediment transport is of primary interest in coastal engineering
Accurate prediction of sediment transport processes in coastal regions requires a delicate understanding of the bottom boundary layer hydrodynamics associated with waves and combined wave-current flows
The oscillatory wave tunnels (OWT) has much smaller size compared to the large wave flume but can still generate oscillatory flows of the same Reynolds numbers
Summary
Sediment transport is of primary interest in coastal engineering. In coastal regions, waves and currents are generally present simultaneously. Accurate prediction of sediment transport processes in coastal regions requires a delicate understanding of the bottom boundary layer hydrodynamics associated with waves and combined wave-current flows. To generate prototype flow conditions of such high Reynolds numbers, the laboratory wave flume has to be very large. The OWT has much smaller size compared to the large wave flume but can still generate oscillatory flows of the same Reynolds numbers. The convenience in setting up experiments and deploying various measurement instruments makes the OWT an excellent experimental facility for studies of oscillatory boundary layer hydrodynamics. Experiments with high quality measurements and well-defined bottom roughness configurations are still lacking, especially for combined wave-current boundary layers. High quality experiments on the wave and wave-current boundary layer hydrodynamics using a new OWT are presented. 216C, MIT, Cambridge, MA02139, USA. 3 Professor and Dean of the Faculty of Engineering, NUS, Block EA #07-26, 9 Engineering Drive 1, Singapore
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
