Abstract
Hydrodynamic wave loading at coastal structures is a complex phenomenon to quantify. The chaotic nature of the fluid flow field as waves break against such structures has presented many challenges to Scientists and Engineers for the design of coastal defences. The provision of installations such as breakwaters to resist wave loading and protect coastal areas has evolved predominantly through empirical and experimental observations. This is due to the challenging understanding and quantification of wave impact energy transfer processes with air entrainment at these structures. This paper presents a numerical investigation on wave loading at porous formations including the effects of air entrapment. Porous morphologies generated from cubic packed spheres with varying characteristics representing a breakwater structure are incorporated into the numerical model at the impact interface and the effect on the pressure field is investigated as the wave breaks. We focus on analysing the impulse impact pressure as a surging flow front impacts a porous wall. Thereafter we investigate the multi-modal oscillatory wave impact pressure signals which result from a transient plunging breaker wave impinging upon a modelled porous coastal protective structure. The high frequency oscillatory pressure effects resulting from air entrapment are clearly observed in the simulations. A frequency domain analysis of the impact pressure responses is undertaken. We show that the structural morphology of the porous assembly influences the pressure response signal recorded during the impact event. The findings provide good confidence on the robustness of our numerical model particularly for investigating the air bubbles formation and their mechanics at impact with porous walls.
Highlights
Severe damage can be inflicted on coastal defence structures as a result of high intensity wave forces
The influence of the porous structure on the pressure signal resulting from a surging flow front impact has first been analysed
We clearly show that a porous geometry consisting of larger elemental components reduces the magnitude of the impact pressure impulse but results in a longer pressure rise time
Summary
Severe damage can be inflicted on coastal defence structures as a result of high intensity wave forces. First we briefly introduce the theory for modelling free surface fluid flow; and the numerical methods to simulate wave impact at porous structures. Volume of fluid method The interaction of the individual fluid phase constituents in the model is important as the pressure transfer across the free surface boundary which defines an entrained air bubble is central to this study.
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