Research On 2D Numerical Model Of Sediment Movement Under Waves And Currents

Sediment siltation has always been a big problem that affects the normal operation of ports and channels on muddy coast. 2D sediment numerical model is an efficient method to calculate the sediment deposition in the harbor and channel. In this dissertation some research will be carried out on this topic and is outlined as follows.1. Numerical simulations will be performed by using the COASTTOOL2D flow model to study the flow field, and then the model will be improved by means of theoretical analysis and strict derivation. In the numerical tests of flow field it is found that the former version of the COASTTOOL2D flow model involves significant error in the calculation of numerical flux under the condition of a steep bottom slope. The reason for the error is that the average water depth on each side of the grid is adopted when calculating the nonlinear numerical flux. In this research, a compensation term for the convective flux, which is caused by the bottom slope of the element side, is derived by means of integration and is added to the discretized equation. In this way, the COASTTOOL2D flow model can be extended to the areas where topography varies violently.2. In the treatment of movable boundary, we put forward a new discretization method for the governing equations according to a newly proposed concept——submergence index. By this method, the semi-submerged elements can transit smoothly and continuously from a dry one to a completely wet one instead of an abrupt shift, which makes it is possible to adjust the water quantity exactly according to the location of the movable boundary and to implement a unified approach in dealing with the elements at movable boundary and inner grids. It is also possible that numerical oscillation caused by abrupt shift between wet and dry elements can be avoided. The advantages of the method are that not only can we obtain a higher computational efficiency of variable element without reconstruction of element system, it is also strict in theory, convenient for application, accurate in calculation and with a high processing speed. The improved COASTTOOL2D flow model can be widely used in practical engineering.3. In the thesis, a new concept of line element is proposed, on the basis of which, the model is improved for the application of flow over a violently varying underwater topography, e.g. a submerged dike. Numerical tests indicate the success of the model to be applicable to the case of submerged dike and thus the application range of the model is further extended.4. In the flow and sediment model we incorporate the effect of wave effect. And by using the model, tide flow and sediment movement inside and around Tianjin Port are simulated.