1,721,083 research outputs found
Hydrodynamics and morphodynamics of a tidal inlet: preliminary two-dimensional depth-averaged modelling
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Variable resolution for SPH in three dimensions:Towards optimal splitting and coalescing for dynamic adaptivity
Full text linkAs smoothed particle hydrodynamics (SPH) becomes increasingly popular for complex flow analysis the need to improve efficiency particularly for 3-D problems is becoming greater. Automatic adaptivity with variable particle size is therefore desirable. In this paper, a novel 3-D splitting and coalescing algorithm is developed which minimizes density error while conserving both mass and momentum using a variational principle. Accuracy is increased in refined areas unaffected by coarser particle distributions elsewhere. For particle splitting, the key criteria are the number of split (daughter) particles, their distribution, spacing and kernel size. Four different splitting arrangements are investigated including a cubic stencil with 8 particles, a cubic stencil with an additional 6 located at the face centres, an icosahedron-shaped arrangement with 14 particles, and a dodecahedron-shaped arrangement with 20 particles where particles are located at the vertices. The error analysis also examines whether retaining a particle at the centre of the arrangement is necessary revealing that regardless of the stencil adopted, to minimize the density error a daughter particle should be placed at the same position of the original particle. The optimum configuration is found to be the icosahedron-shaped arrangement while commonly used smoothing kernels such as the cubic and quintic splines and Wendland produce similar density errors, so that the optimal refinement stencil is effectively independent of the kernel choice. A new 3-D coalescing scheme completes the algorithm such that the particle resolution can be either increased or reduced locally. The SPH splitting and coalescing scheme, is tested with Poiseuille flow showing negligible loss of convergence accuracy in the refined area and the lid driven cavity for a wide range of Reynolds number showing good agreement with reference solutions again with local accuracy defined by particle distribution.</p
Simulation of floating debris in SPH shallow water flow model with tsunami application
No full textMany post-tsunami field investigations affirm that the large floating debris transported by the flow contributes significantly to the destruction of on-land buildings. However, few simulation tools have been developed to predict the debris behaviour under violent flow conditions involving complex debris–fluid, debris–debris, debris–bed surface and debris–wall (solid structure) interactions. This paper introduces a fully coupled model of three-dimensional (3-D) debris motion in shallow-water flow. The model uses Smoothed Particle Hydrodynamics (SPH) to solve the shallow-water equations (SWEs) and represents debris motion using the modified Morison equation. The Discrete Element Method (DEM) model is used for the collision mechanism. The flow model is formulated based on the Euler–Lagrange equations that provide the vertical component of velocity and can therefore be coupled with the 3-D debris motion. A new solid boundary condition for shallow flows is introduced. The open boundary condition is used for wave generation by imposing inflow and outflow in predetermined zones. The SPH solves the wet–dry interface automatically. The model is implemented in an open-source software DualSPHysics. SWE-SPH flow model is initially validated against experimental data, followed by the debris model compared with an analytical solution and physical experiments, which gives close agreement. This model is expected to be a robust tool for predicting the hazards caused by extreme floodings, such as tsunamis
Smoothed Particle Hydrodynamics: Approximate zero-consistent 2-D boundary conditions and still shallow-water tests
No full textsmoothed particle hydrodynamics; boundary conditions; shallow water equations; source terms; virtual boundary particles; still waterIn this paper, an approximate modified virtual boundary particle method (MVBP) for solid boundary conditions in a two-dimensional (2-D) smoothed particle hydrodynamics (SPH) model is presented; this is a development of the original VBP method recently proposed by Ferrari et al. (Comput. Fluids 2009; 38(6): 1203-1217). The aim is to maintain the zeroth moment of the kernel function as closely as possible to unity, a property referred to as zero-consistency, for particles close to solid boundaries. The performance of the new method in approximating zero-consistency in the presence of complicated boundaries is demonstrated where we show that the MVBP method improves the accuracy of the zeroth moment by almost an order of magnitude. Shallow-water flows are an important two-dimensional (2-D) application and provide the simple test case of still water. The shallow-water equations (SWEs) are thus considered in SPH form and the zero-consistency approximation is tested for still water in domains with different boundaries: a circle and two squares, one with an additional internal angle of 300 ring operator and one with four internal angles of 345 ring operator. We demonstrate that for an internal angle of 300 ring operator, the MVBP method demonstrates numerical convergence to still-water conditions whereas both mirror particles and the VBP method cannot. The method is also demonstrated for the dynamic case of a circular dam break interacting with an outer circular wall where conventional mirror particles fail to prevent particles passing through the solid wall. The SPH SWEs are further generalized through a new method for discretizing the bed source term allowing arbitrarily complicated bathymetries. The resulting formulation is tested by considering many different bed shapes in still water: submerged and surface-piercing humps, a submerged step, a submerged and surface-piercing parabolic bed. ?? 2011 John Wiley & Sons, Ltd
Complex dam break simulation using the 2-D depth-averaged SPH flow model: A validation for tsunami application
Full text linkDam break flow has a similar characteristic to the tsunami surge after the breaking wave. Therefore, it is often used in laboratory-scale experiments to study tsunamis and can be used as a benchmark for validating a numerical model. This paper presents a simulation of a complex dam break flow to validate the two-dimensional (2-D) depth-averaged Smoothed Particle Hydrodynamics (SPH) flow model which involves a non-submersible obstacle in the domain. The method can also be referred to as shallow-water equations SPH (SWE-SPH). With SPH, the wetting and drying interfaces are automatically solved without any additional trick or handling. Therefore, a dry bed dam break is specifically tested here. The numerical results are validated using experimental data from the literature. The model shows the ability to reproduce the flow fields, shocks, vortices and flow region transitions with reasonable accuracy compared to the experimental data, despite the vertical averaging process in the formulation. This model can be a robust tool for predicting the hazards caused by extreme floodings, such as dam breaks, flash floods and tsunamis in development planning
Accurate particle splitting for smoothed particle hydrodynamics in shallow water with shock capturing
No full textThe solution for the shallow water equations using smoothed particle hydrodynamics is attractive, being a mesh-free, automatically adaptive method without special treatment for wet-dry interfaces. However, the relatively new method is limited by the variable kernel size or smoothing length being inversely proportional to water depth causing poor resolution at small depths. Boundary conditions at solid walls have also not been well resolved. To solve the resolution problem in small depths, a particle splitting procedure was developed (conveniently into seven particles), which conserves mass and momentum by varying the smoothing length, velocity and acceleration of each refined particle. This improves predictions in the shallowest depths where the error associated with splitting is reduced by one order of magnitude in comparison to other published works. To provide good shock capturing behaviour, particle interactions are treated as a Riemann problem with Monotone Upstream-centred Scheme for Conservation Laws (MUSCL) reconstruction providing stability. For solid boundaries, the recent modified virtual boundary particle method was developed further to enable the zeroth moment to be accurately conserved where the smoothing length of particles is changing rapidly during particle splitting. The resulting method is applied to the one-dimensional and the two-dimensional axisymmetric wet-bed dam break problems showing close agreement with analytical solutions, demonstrating the need for particle splitting. To demonstrate wetting and drying in a more complex case, the scheme is applied to oscillating water in a two-dimensional parabolic basin and produces good agreement with the analytical solution. The method is finally applied to the European Concerted Action on DAm break Modelling dam-break test case representative of realistic conditions and good predictions are made of experimental measurements with a 40% reduction in the computational time when particle splitting is employed. The overall method has thus become quite sophisticated but its generality and versatility will be attractive for various shallow water problems. © 2011 John Wiley & Sons, Ltd
Large eddy simulations of bubbly flows and breaking waves with smoothed particle hydrodynamics
Full text linkFor turbulent bubbly flows, multi-phase simulations resolving both the liquid and bubbles are prohibitively expensive in the context of different natural phenomena. One example is breaking waves, where bubbles strongly influence wave impact loads, acoustic emissions and atmospheric-ocean transfer, but detailed simulations in all but the simplest settings are infeasible. An alternative approach is to resolve only large scales, and model small-scale bubbles adopting sub-resolution closures. Here, we introduce a large eddy simulation smoothed particle hydrodynamics (SPH) scheme for simulations of bubbly flows. The continuous liquid phase is resolved with a semi-implicit isothermally compressible SPH framework. This is coupled with a discrete Lagrangian bubble model. Bubbles and liquid interact via exchanges of volume and momentum, through turbulent closures, bubble breakup and entrainment, and free-surface interaction models. By representing bubbles as individual particles, they can be tracked over their lifetimes, allowing closure models for sub-resolution fluctuations, bubble deformation, breakup and free-surface interaction in integral form, accounting for the finite time scales over which these events occur. We investigate two flows: bubble plumes and breaking waves, and find close quantitative agreement with published experimental and numerical data. In particular, for plunging breaking waves, our framework accurately predicts the Hinze scale, bubble size distribution, and growth rate of the entrained bubble population. This is the first coupling of an SPH framework with a discrete bubble model, with potential for cost-effective simulations of wave-structure interactions and more accurate predictions of wave impact loads. © The Author(s), 2023. Published by Cambridge University Press
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