An Investigation Of The Characteristics Of Flow Field Over Sand Bed Under Cnoidal Waves

Wave plays an important role in the sediment transportation which may cause the siltation of channel and harbor, and finally change the element of nearshore wave in reverse. So the research of wave flow structure, turbulent characters and the mechanism of sediment transportation in coastal is very important.Cnoidal wave theory can discrible the nearshore wave characters preferably. Considered the infection to sand bed of the nonlinear character when wave approach nearshore. In this paper, the wave flume experiment and numerical simulation to investigate the interaction between cnoidal waves and sand bed, including sediment threshold under cnoidal waves and the flow characters near sand bed.In the wave flume experiments, the characteristics of flow under cnoidal waves with different sand beds include flat and 1:20 slop beds are measured systematically in flume with Acoustic Doppler Velocitimeter (ADV). Based on the high frequency turbulence signal collected, statistic parameters of wave flow are calculated, compared and analyzed, including fluctuating intensity, Reynolds stress, turbulent kinetic, velocity probability density, power spectrum density etc. As the emphasis of our study, the turbulent structure over sand ripples under cnoidal waves was carefully studied. Including the relationship between sand velocity and turbulent characteristic, the interaction between roughness or shape of sand bed and turbulent characteristic.The numerical model based on PLIC-VOF method gives the wave height and velocity agrees well with the result of laboratory experiment. After being improved the PLIC-VOF method can be selected to further study the interaction between Cnoidal waves and ripple seabed.We also studied the evaluation of sand transportation of ripples and sandbar. Photography at a fixed point and topographic measurement were applied to study.