A Computational Model for Velocity Separation in Shallow Sea

Based on the hydrodynamical feature and the theoretical velocity profiles of tidal flow and wind-induced flow in shallow sea, a computational model is established for the first time, which can separate observed velocity into tidal velocity and wind-induced velocity by use of the least square method. With the model, not only the surface. velocities of tidal. flow and wind-induced flow are obtained, but also the bed roughness height is determined and the wind velocity above the water surface is estimated. For verification of the model, the observed velocity in the Yellow River Estuary and the laboratory test is separated, then it is applied to the Yangtze River Estuary. All the results are satisfactory. The research results show that the model is simple in method, feasible in process and reasonable in result. The model is a valid approach to analysis and computation of field data, and can be applied to separate the observed velocity in shallow sea; at the same time, reasonable boundary conditions of the surface and bottom can be obtained for two- and three-dimensional numerical simulation.

AN APPROACH TO SEPARATING THE CURRENT VELOCITY IN ESTUARINE AND COASTAL WATERS

In the near-shore waters, the actual flow is mainly induced by tide, wind and salinity, and the river water runoff should also be included as a component in the estuary waters. The interactions among these major components are very complicated. Many approaches were proposed to study isolated tide and wind-driven currents or run-off based on the measured velocity, with all its components taken as a whole. In this article, firstly, based on the actual hydrodynamic characteristics of estuarine and coastal waters, an approach is proposed to separate the measured velocity by considering the theoretical current velocity profiles and using the least squares method. The vertical structures of tidal, wind-driven currents, density current and runoff can be obtained as well as their proportions in the measured velocity. Then, this approach is applied to the analysis of velocity data obtained in the North Branch of Yangtze River estuary and of laboratory test data. The results are found to be satisfactory. Finally, this approach is used to separate the measured velocity in the South Branch of Yangtze River estuary, to determine not only the bed friction velocity and roughness height, but also the surface wind stress, and to estimate the wind velocity data above the water surface. The results show that this method is simple in principle, practical in use, and reasonable in obtained results. So it can be used to effectively analyze the field data.