Mangrove forests effectively function as extensive wood fences that protect coastal communities from storms1,2 by attenuating waves and currents, and by preventing erosion3. Regardless of their economic and societal value, \(30\%\) of the mangrove forests have disappeared around the world over the last 50 years4. Mangrove deforestation can increase the exposure of the remaining forest to wave action, causing coastline retreat, and hindering the natural recovery of the forest5. Bamboo and brushwood structures have consequently been built to counteract erosion at degraded mangrove sites in South East Asia and South America3,5,6,7,8,9. Some of the configurations constructed in a pilot project in Indonesia, consisting of groups of cylindrical bamboo poles driven into the soil, are presented in Fig. 1. The width of the structures varies between 0.7 and 1.5 m in the flow direction, and their volumetric porosity ranges between \(n \approx\) 0.5 and 0.9, where n is defined as the ratio of the fluid volume to the total volume. Since waves lose energy as they pass through the structures, the calmer hydrodynamic conditions behind the poles enhance sediment deposition, and favour mangrove expansion5. Although the structures are designed for wave attenuation, they can also affect local currents, which in turns influences sediment transport and mangrove habitat creation. However, this aspect has received less attention in existing designs10. Predicting the impact of the bamboo structures on spatial flow patterns requires quantifying the resistance forces exerted by the structures in currents. The aim of this study is thus to develop a design tool t o calculate this resistance, which could be implemented in large-scale flow models to optimize the performance of future designs.
Smoothed-particle hydrodynamics (SPH) is a computational method used for simulating the mechanics of continuum media, such as solid mechanics and fluid flows. It was developed by Gingold and Monaghan[2] and Lucy[3] in 1977, initially for astrophysical problems. It has been used in many fields of research, including astrophysics, ballistics, volcanology, and oceanography. It is a meshfree Lagrangian method (where the co-ordinates move with the fluid), and the resolution of the method can easily be adjusted with respect to variables such as density.
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Smoothed-particle hydrodynamics is being increasingly used to model fluid motion as well. This is due to several benefits over traditional grid-based techniques. First, SPH guarantees conservation of mass without extra computation since the particles themselves represent mass. Second, SPH computes pressure from weighted contributions of neighboring particles rather than by solving linear systems of equations. Finally, unlike grid-based techniques, which must track fluid boundaries, SPH creates a free surface for two-phase interacting fluids directly since the particles represent the denser fluid (usually water) and empty space represents the lighter fluid (usually air). For these reasons, it is possible to simulate fluid motion using SPH in real time. However, both grid-based and SPH techniques still require the generation of renderable free surface geometry using a polygonization technique such as metaballs and marching cubes, point splatting, or 'carpet' visualization. For gas dynamics it is more appropriate to use the kernel function itself to produce a rendering of gas column density (e.g., as done in the SPLASH visualisation package). 2ff7e9595c
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