Mechanics of Water Waves over a Viscoelastic Muddy Bed
Speaker:Dr. C.O. Ng
Department of Mechanical Engineering
The University of Hong Kong
Date & Time:21 Jan 2009 (Wednesday) 11:00 - 12:00


This talk is to introduce analytical models for the mass transport induced by a small-amplitude progressive wave propagating in water over a thin layer of viscoelastic mud modelled as a Voigt medium. Based on a sharp contrast in length scales near the bed, the boundary-layer approximation is applied to the Navier-Stokes equations in Lagrangian form, which are then solved for the first-order oscillatory motions in the mud and the near-bed water layers. On extending the analysis to the second order for the mass transport, it is pointed out that it is inappropriate as in previous studies to apply the complex viscoelastic parameter to a higher-order analysis, and also to suppose that a Voigt body can undergo continuous steady motion. In fact, the time-mean motion of a Voigt body is only transient, and will stop after a time scale given by the ratio of the viscosity to the shear modulus. Once the mud has attained its steady deformation, the mass transport in the overlying water column can be found as if it were a single-layer system.


Dr. CO Ng was born in Macau, but received most of his education in Hong Kong. He obtained a B.Sc. degree in Civil Engineering, and an M.Phil. degree in Mechanical Engineering, both from The University of Hong Kong. He received his Ph.D. degree from MIT in 1998 under the supervision of Prof. CC Mei on the geo-environmental mechanics of ground subsidence and soil vapor extraction. Since then, he has been teaching fluid mechanics in the Department of Mechanical Engineering at The University of Hong Kong. His research interests include environmental and geophysical flows, dispersion in biological systems, coastal engineering and water wave mechanics, slip flow in micro-channels, and so on.