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As waves interact with the slopes of coral reefs and other steep bathymetry profiles, plunging breaking usually occurs where the free surface overturns and violent water motion is triggered. Resolving these surf zone processes pose significant challenges for conventional mesh-based hydrodynamic models, due to the rapidly-deforming nature of the free surface and associated flows. Yet the accurate prediction of these surf zone hydrodynamics is critical for predicting a wide range of nearshore processes driven by wave breaking (e.g., wave dissipation and energy transfers; mean water levels and currents; and wave runup). In this study we assess the ability of the mesh-free, Lagrangian particle-based numerical modelling approach Smoothed Particle Hydrodynamics (SPH) based on DualSPHysics, to simulate the fine-scale hydrodynamic processes driven by irregular wave transformation over a fringing reef profile, by comparing results against detailed experimental observations from a physical modelling study. To greatly improve the computational efficiency, the SPH model was coupled to the mesh-based multi-layer nonhydrostatic wave-flow model SWASH. With this coupled approach, SWASH was used to efficiently simulate the evolution of non-breaking waves from the wavemaker up to the fore reef slope, with the SPH model then used to simulate the detailed hydrodynamic processes over the reef from just offshore of the breakpoint to the shoreline. The SPH model was able to accurately reproduce the complex free surface deformations during plunging breaking, the spectral evolution of waves across the reef flat (including nonlinear wave shape), the mean water levels and currents, and wave runup at the shoreline. Using the long duration simulations (>400 wave periods), the model was able to reproduce the full range of wave motions over the reef (from sea-swell to infragravity frequencies), including the increasing dominance of low frequency waves towards the shoreline and the large cross-ree, Peer Reviewed, Postprint (author's final draft)

As waves approach the steep slopes of reefs, plunging breaking usually occurs where the free surface overturns and violent water motion is triggered. Resolving such surf zone processes poses significant challenges for conventional mesh-based hydrodynamic models due to the rapidly-deforming nature of the free surface; yet accurate prediction of these hydrodynamics is critical to a wide range of nearshore processes driven by waves (e.g. wave dissipation and energy transfers; mean water levels and currents; and wave runup). In this study we assess the ability of the mesh-free, Lagrangian particle-based numerical approach, Smoothed Particle Hydrodynamics (SPH) using DualSPHysics, to simulate the fine-scale hydrodynamic processes generated by irregular wave transformation over a fringing reef by comparing results against detailed experimental observations. To improve computational efficiency, the DualSPHysics model was coupled to the multi-layer non-hydrostatic wave-flow model SWASH to simulate waves within the deep region offshore of the reef up to the fore reef slope prior to breaking. The model was able to accurately reproduce the full range of hydrodynamic processes observed during the experiment across the reef, resolving the complex free surface deformation during plunging breaking, the spectral evolution of waves across the reef flat (including nonlinear wave shape), the mean water levels and currents, and wave runup at the shoreline. Using the long duration simulations (>400 wave periods), the model was able to reproduce the full range of wave motions over the reef (sea-swell, infragravity, and very low frequencies), including the increasing dominance of low frequency waves towards the shoreline and the large cross-reef standing wave motions excited by the reef geometry., Postprint (published version)

Long waves are generated and transform when short-wave groups propagate into shallow water, but the generation and transformation processes are not fully understood. In this study we develop an analytical solution to the linearized shallow-water equations at the wave-group scale, which decomposes the long waves into a forced solution (a bound long wave) and free solutions (free long waves). The solution relies on the hypothesis that free long waves are continuously generated as short-wave groups propagate over a varying depth. We show that the superposition of free long waves and a bound long wave results in a shift of the phase between the short-wave group and the total long wave, as the depth decreases prior to short-wave breaking. While it is known that short-wave breaking leads to free long generation, through breakpoint forcing and bound wave release mechanisms, we highlight the importance of an additional free long wave generation mechanism due to depth variations, in the absence of breaking. This mechanism is important because as free long waves of different origins combine, the total free long wave amplitude is dependent on their phase relationship. Our free and forced solutions are verified against a linear numerical model, and we show how our solution is consistent with prior theory that does not explicitly decouple free and forced motions. We also validate the results with data from a nonlinear phase-resolving numerical wave model and experimental measurements, demonstrating that our analytical model can explain trends observed in more complete representations of the hydrodynamics.

In this study we assess the capabilities of the mesh-free, Lagrangian particle method (Smooth Particle Hydrodynamics, SPH) method to simulate the detailed hydrodynamic processes generated by both spilling and plunging breaking waves within the surf zone, and present how the approach can be used to predict a broad spectrum of hydrodynamic processes relevant to coastal applications where wave breaking is important. The weakly-compressible SPH code DualSPHysics was applied to simulate wave breaking over two bathymetric profiles (a plane beach and fringing reef) and compared to experimental flume measurements of waves, currents, and mean water levels. We demonstrate how the model can accurately reproduce a broad range of relevant hydrodynamic processes, ranging from the nonlinear evolution of wave shapes across the surfzone, wave setup distributions, mean current profiles and wave runup. We compare the surfzone predictions with results from other classes of wave models, and illustrate some of the advantages of the SPH approach (particularly in resolving the hydrodynamics above the wave trough). Overall, the results reveal how the mesh-free SPH approach can accurately reproduce the detailed wave breaking processes with comparable skill to state-of-the-art mesh-based Computational Fluid Dynamic models, and how it can be used as a valuable tool to develop new physical insight into surf zone processes., Postprint (published version)

In this study we assess the capabilities of the mesh-free, Lagrangian particle method (Smooth Particle Hydrodynamics, SPH) method to simulate the detailed hydrodynamic processes generated by both spilling and plunging breaking waves within the surf zone, and present how the approach can be used to predict a broad spectrum of hydrodynamic processes relevant to coastal applications where wave breaking is important. The weakly-compressible SPH code DualSPHysics was applied to simulate wave breaking over two bathymetric profiles (a plane beach and fringing reef) and compared to experimental flume measurements of waves, currents, and mean water levels. We demonstrate how the model can accurately reproduce a broad range of relevant hydrodynamic processes, ranging from the nonlinear evolution of wave shapes across the surfzone, wave setup distributions, mean current profiles and wave runup. We compare the surfzone predictions with results from other classes of wave models, and illustrate some of the advantages of the SPH approach (particularly in resolving the hydrodynamics above the wave trough). Overall, the results reveal how the mesh-free SPH approach can accurately reproduce the detailed wave breaking processes with comparable skill to state-of-the-art mesh-based Computational Fluid Dynamic models, and how it can be used as a valuable tool to develop new physical insight into surf zone processes., Accepted Author Manuscript, Hydraulic Structures and Flood Risk

In this study we investigated the capabilities of the mesh-free, Lagrangian particle method (Smoothed Particle Hydrodynamics, SPH) to simulate the detailed hydrodynamic processes generated by both spilling and plunging breaking waves within the surf zone. The weakly-compressible SPH code DualSPHysics was applied to simulate wave breaking over two distinct bathymetric profiles (a plane beach and fringing reef) and compared to experimental flume measurements of waves, flows, and mean water levels. Despite the simulations spanning very different wave breaking conditions (including an extreme case with violently plunging waves on an effectively dry reef slope), the model was able to reproduce a wide range of relevant surf zone hydrodynamic processes using a fixed set of numerical parameters. This included accurate predictions of the nonlinear evolution of wave shapes (e.g., asymmetry and skewness properties), rates of wave dissipation within the surf zone, and wave setup distributions. By using this mesh-free approach, the model was able to resolve the critical crest region within the breaking waves, which provided robust predictions of the wave-induced mass fluxes within the surf zone responsible for the undertow. Within this breaking crest region, the model results capture how the potential energy of the organized wave motion is initially converted to kinetic energy and then dissipated, which reproduces the distribution of wave forces responsible for wave setup generation across the surf zone. Overall, the results reveal how the mesh-free SPH approach can accurately reproduce the detailed wave breaking processes with comparable skill to state-of-the-art mesh-based Computational Fluid Dynamics (CFD) models, and thus can be applied to provide valuable new physical insight into surf zone dynamics., Peer Reviewed, Postprint (author's final draft)