Numerical modelling of wave runup on breakwaters
The design of rubble mound breakwaters is typically based on empirical formulae and physical modelling. One limitation of this approach is that different aspects of wave interaction with a breakwater, such as the elevation of the runup tip and armour stability, are treated separately. Therefore the development of a numerical model of wave runup on a rubble mound breakwater was the primary objective of the research described in this thesis.
Because of the range of slope conditions encountered with rubble mound breakwaters and revetments, two types of armour layer are considered. The first is impermeable and so only the flow within the external region is modelled. The flow is assumed to be governed by the unsteady one-dimensional shallow water wave equations and only regular waves are considered. It is shown how the use of the finite element method with a mesh of isoparametric elements that deforms and is fitted to the runup tip has a number of advantages over the traditional use of the finite difference method with a fixed grid.
Reasonably good results were obtained for the numerical modelling of wave runup on a riprap armoured l:3 impermeable slope indicating that the numerical model may, in conjunction with a physical model, be of practical use in the design of revetments. Wave runup on smooth and Dolos armoured 1:1.5 impermeable slopes was modelled poorly. Therefore the model is more appropriate for wave runup on a revetment than a rubble mound breakwater.
The second type of armour layer is permeable and so the flow within the external region and armour layer is modelled simultaneously by coupling numerical models for the respective regions. It is concluded that this approach is unlikely to give acceptable results for the runup of regular waves on a steep, permeable armour layer unless it also accounts for the non-hydrostatic distribution of pressure within the external region.
An experiment is described in which continuous time histories of wave runup and dynamic pressure due to regular waves on smooth and Dolos armoured 1:1.5 slopes were measured. The results are used to discuss the assumption of hydrostatic pressure.
A method of assessing armour stability requirements which takes into consideration the effects of armour unit interaction is proposed. It is recommended that this is examined further.