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Coastal environment and sediment transport

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Investigators: Ole MADSEN (MIT), CHAN Eng Soon (NUS)
Students: YUAN Jing (MIT)


​The CEST objectives are to (i) verify crucial aspects of small-scale process models for hydrodynamics and sediment transport in the coastal environment through laboratory experiments in a unique Wave-Current-Sediment (WCS) facility; and (ii) develop the necessary linkages to properly account for and incorporate these small scale process models in larger, systems level, numerical models for circulation and sediment transport in the coastal environment. The WCS facility, an improved version of the Deltares Oscillating Water Tunnel (OWT), can simulate sinusoidal, nonlinear (Stokes and Forward-leaning) and spectral waves in the presence of currents at prototype scales (orbital velocities up to 2m/s for periods of 3 to 12s and current velocities up to 0.5m/s) with unprecedented accuracy.  The facility has its own dedicated PIV system for measuring velocity distributions with a vertical resolution of 0.4mm that will allow us to verify theoretical predictions of hydrodynamic features, e.g. bottom shear stress and velocity profiles, within the turbulent bottom boundary layer for a variety of combined wave-current flows. To obtain experimental data on sediment transport rates, a laser-based bottom profiling (BP) system has been designed. It consists of 24 laser units that create two laser lines along the bottom of the 10m-long test section of the WCS and 6 cameras that capture the images of these lines. Trial tests of the BP system, which is expected to be fully operational by late fall 2013, indicate an accuracy of its determination of bottom elevation better than 0.2mm. The entire WCS facility can be tilted to form a 1 on 20 sloping bottom allowing us to obtain experimental data on sediment transport rates for combined wave-current flows over a sloping bottom. Once verified experimentally, the small-scale process models for wave-current-sediment interaction will be integrated to remove temporal scales associated with the action of wind-waves, thereby providing (i) the contribution from small-scale processes within the wave boundary layer, e.g. wave-generated movable bed roughness (ripples), bed load and suspended load sediment transport rates; and (ii) the proper bottom boundary conditions for large-scale numerical circulation and sediment transport models, e.g. the bottom roughness experienced by a current in the presence of waves for the former and the reference concentration induced by waves at the outer edge of the wave boundary layer for the latter. These boundary conditions will be incorporated in open source numerical coastal circulation and sediment transport models, e.g. FVCOM, POM, and/or ROMS, to examine their performance and utility in idealized as well as realistic scenarios, with the latter being an application of the complete numerical model to Singapore waters.


 


Main features of the WCS (Wave-Current-Sediment facility located at NUS, Faculty of Engineering)


 


Dedicated PIV (Particle Image Velocimetry) system for the WCS


 

 

​Comparisons of predicted and measured velocity profiles and bottom shear stress for Stokes Waves