published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

The beachface evolution in the swash zone under different single swash events is investigated by fully coupled simulations. Two fully coupled models (bed-load-only and combined load models) comprising the one dimensional shallow water equations and bed evolution equation are developed. The two coupled systems are solved by the specified time interval method of characteristics (STI MOC) (Kelly and Dodd, 2009, 2010), which can resolve shocks very accurately. The fully coupled bed-load-only simulations with six different sediment transport formulae for a single Peregrine and Williams (2001) (PW01) swash over an erodible plane beach all yield net erosion all over the swash zone. Consistent with Kelly and Dodd (2010), however, full coupling yields significantly less erosion for all the q=q(u) (q instantaneous sediment flux and u water velocity) formulae compared to the equivalent uncoupled results. It is also shown that including a dependence on h (water depth) in q can result in net deposition in the upper swash, and that with such a formula q the shoreline motion over a plane mobile beach is ballistic in the uprush. Bed shear stress described by the Chezy law is further included in fully coupled simulations, and much reduced maximum inundation and net offshore sediment transport are predicted both for q=q(u) and q=q(h,u). Although the net sediment flux at x=0 under one PW01 event is still offshore, deposition in the middle or upper swash may be predicted when bed shear stress is included. The fully coupled bed-load-only simulation with q=q(u) for a single Hibberd and Peregrine (1979) (HP79) swash event predicts considerable deposition in the swash zone. A backwash bore develops, associated with which a bed step forms when the shoreline catches up with the backwash bore. The subsequent shoreline movement is obtained by the Riemann solution for a wet-dry dam-break problem with a bed step. A bed step also occurs under a solitary wave simulation; its height is much larger than that under the HP79 simulation. Bed step height is found to depend largely on the water depth on the seaward side of the step, which is related to the swash event and the step position. The PW01 and HP79 swash events are also examined by the combined load model. Results show that suspended load results in deposition in the upper swash and erosion in the lower swash. However, pre-suspended sediment results in deposition in the lower swash, implying that net bed change due to suspended load in the lower swash could be depositional. The inclusion of suspended load has much smaller effect on the maximum inundation and swash hydrodynamics than bed load. The inclusion of bed load reduces the maximum inundation significantly; importantly, bed load results in the formation of a bed step and dominates the beach change near the bed step even when suspended load is dominant in the overall beach change.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

This thesis presents a Control Volume (CV) method for transient transport problems where the cell surface fluxes are reconstructed using local interpolation functions that besides interpolating the nodal values of the field variable, also satisfies the governing equation at some auxiliary points in the interpolation stencils. The interpolation function relies on a Hermitian Radial Basis Function (HRBF) mesh less collocation approach to find the solution of auxiliary local boundary/initial value problems, which are solved using the same time integration scheme adopted to update the global control volume solution. By the use of interpolation functions that approximate the governing equation, a form of analytical upwinding scheme is achieved without the need of using predefined interpolation stencils according to the magnitude and direction of the local advective velocity. In this way, the interpolation formula retains the desired information about the advective velocity field, allowing the use of centrally defined stencils even in the case of advective dominant problems. This new CV approach, which is referred to as the CV-HRBF method, is applied to a series of transport problems characterised by high Peclet number. This method is also more flexible than the classical CV formulations because the boundary conditions are explicitly imposed in the interpolation formula, without the need for artificial schemes (e.g. utilising dummy cells). The flexibility of the local meshless character of the CVHRBF is shown in the modelling of the saturated zone of the unconfined aquifer where a mesh adapting algorithm is needed to track the phreatic surface (moving boundary). Due to the use of a local RBF interpolation, the dynamic boundary condition can be applied in an arbitrary number of points on the phreatic surface, independently from the mesh element. The robustness of the Hermite interpolation is exploited to formulate a non-overlapping non-iterative multi-domain scheme where physical matching conditions are satisfied locally, i.e. imposing the continuity of the function and flux at the sub-domain interface.