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Title: Finite element modelling of river bed dynamics
Author: Pamudji Rahardjo, A.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1991
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Numerical modelling of Bed Dynamics in 1-D and 2-D poblems using the Two-Step Taylor Galerkin Finite Element scheme has been proposed. It has been shown that the scheme is capable of handling the coupled system that exists between unsteady hydrodynamics and a mobile bed. Fully coupled codes have been developed with an option to semi-couple the system while maintaining numerical accuracy for both the hydrodynamics and the bed level change. The semi-coupled extension enables the modelling of the hydrodynamics and the bed level change with different time steps. Coupling is maintained at common time terminals and, or, with separate computational meshes, where coupling is achieved by means of interpolation between the meshes. The Two-Step Taylor Galerkin scheme has been verified extensively for hydraulic problems related to bed dynamics, especially the interaction of progressive waves and the development of steady state flow in channels. Treatment of the boundary condition allowing waves to leave the computational domain both for the fluid and the bed have been proposed and work well. For the hydrodynamic equations, it is also demonstrated that the boundary treatment is capable of absorbing outgoing waves while incoming waves are simultaneously prescribed. These treatments are based on an examination of the characteristics of the bed dynamic system. The results of the analysis can be used to approximate the Reimann invariant vector of the bed dynamic system and this is especially useful when the fully coupled method is applied. A Von Neumann linear stability analysis of the 1-D Taylor-Galerkin scheme for a system including a source term is presented. The anlaysis is based on the graphical interpretation of an Argand Diagram representation for the amplification factor. It is found that the presence of a strong source term may reduce the time step limit.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available