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The conditions for energy flux, momentum flux and the resulting streaming velocity are analysed for standing waves formed in front of a fully reflecting wall. The exchange of energy between the outer wave motion and the near bed oscillatory boundary layer is considered, determining the horizontal energy flux inside and outside the boundary layer. The momentum balance, the mean shear stress and the resulting time averaged streaming velocities are determined. For a laminar bed boundary layer the analysis of the wave drift gives results similar to the original work of Longuet–Higgins from 1953. The work is extended to turbulent bed boundary layers by application of a numerical model. The similarities and differences between laminar and turbulent flow conditions are discussed, and quantitative results for the magnitude of the mean shear stress and drift velocity are presented. Full two-dimensional simulations of standing waves have also been made by application of a general purpose Navier–Stokes solver. The results agree well with those obtained by the boundary layer analysis. Wave reflection from a plane sloping wall is also investigated by using the same numerical model and by physical laboratory experiments. The phase shift of the reflected wave train is compared with theoretical and empirical models. 相似文献
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Rapid and precise measurement method for adsorbed
A new method has been developed for the determination of adsorbed
on sediments. The method utilizes sediments directly in a closed loop counting system and measures the daughter
. Because the recoil path length of
is small compared to the sediment particle size, adsorbed
is released to the gases circulating in the closed loop
counting system and
produced internally within the sediment particles is effectively excluded. The method has been calibrated against (1) multi-step Na+ displacement of
and (2) multi-step Zn2+ replacement of
. It has been found to accurately quantify the adsorbed component with a significant savings in laboratory time and with greater precision. Combined with dissolved
measurements of the porewater, distribution coefficients can be accurately calculated. This method has potential for direct application to water column
balances in estuaries, coastal water and salt marshes. When used to extract the reactive transport dynamics of
in the sediment, the method may have applications to trace metal transport in sediments. 相似文献
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