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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Special sessions : Sph modelling of coherent structures and intermittent events in the surf zone of weak plungers
Sph modelling of coherent structures and intermittent events in the surf zone of weak plungers
The prime goal of the present study is the detailed numerical simulation of surf zone hydrodynamics, due to weakly
plunging breakers on a relatively mild impermeable slope. Smoothed Particle Hydrodynamics method is used in
combination with a Smagorinsky-type model for the sub-particle scales of the flow, similarly to a Large Eddy Simulations¡¯
approach; hence the academic ¡®open-source¡¯ code SPHysics is implemented. We undertake thorough pre-processing
analysis of experimental eddy sizes in regular wave breaking and thus choose a spatial resolution approaching the
demarcation point between integral turbulence length scales and Taylor micro-scales. Moreover, a combination of
heuristic techniques for the discrimination of turbulent fluctuations from the ordered wave motion is proposed as a postprocessing
manipulation of SPH Lagrange-type data. The model is validated against experimental data, concerning
several wave features. Spectral analysis of the fluctuating components for the velocity field is used to investigate its
isotropic substance. Results in the surf zone concern wave-induced mean flows, dynamic characteristics of weak plungers
and consequent bores, coherent structures on vertical cross-sections, and intermittent events at fixed gauges. The
recurring patterns of vorticity are studied both in Eulerian and Lagrangian perspective, and reveal plausible reproduction of
classic coherent vortical structures, which define the topology and properties of the wave breaking mechanism. The latter
is supported by the derivation of coherent structures of turbulent kinetic energy (TKE) and Reynolds stresses, too.
Additionally, the cross-shore variation of intermittent fluctuations due to wave breaking is investigated by empirical
identification of coherent and intense events. The statistics of intermittency agree with experimental data; e.g. coherent
intermittent events occur only for a small portion (<20%) of the TKE time-series, but contribute significantly to its
magnitude by containing a significant amount (>50%) of all motions. Correlations between shear stresses and TKE are
detected, allowing us to define possible cross-shore sediment transport patterns related to them.
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Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Special sessions
Date Published : 13/08/2015
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