1,721,028 research outputs found
Multiscale Smoothed Particle Hydrodynamics based on a domain-decomposition strategy
No full textA multi-resolution algorithm for weakly-compressible Smoothed Particle Hydrodynamics is hereby proposed. The approach chosen is based on a domain decomposition to subdivide the computational domain into regions with different resolutions. Each sub-problem is closed by appropriate Dirichlet boundary conditions that are enforced via buffer regions, populated by particles whose physical quantities are obtained by means of an interpolation over adjacent sub-domains. The algorithm has been implemented into the DualSPHysics open-source code and it has been tested and validated through a series of different study cases. The capability of the numerical scheme to simulate multiscale fluid flow has been demonstrated by solving the flow past a cylinder for a Reynolds number of 9,500 and a ratio between the largest and smallest particle size equal to 28. Furthermore, the proposed SPH multi-resolution algorithm can also be used for flow around moving objects, such as an oscillating cylinder in cross-flow, and free-surface flow, such as the simulation of a triangular wedge impacting on the free surface of a quiescent liquid
Divergence cleaning for weakly compressible smoothed particle hydrodynamics
No full textThis paper presents a divergence cleaning formulation for the velocity in the weakly compressible smoothed particle hydrodynamics (SPH) scheme. The proposed hyperbolic/parabolic divergence cleaning, ensures that the velocity divergence, div(u), is minimised throughout the simulation. The divergence equation is coupled with the momentum conservation equation through a scalar field ψ. A parabolic term is added to the time-evolving divergence equation, resulting in a hyperbolic/parabolic form, dissipating acoustic waves with a speed of sound proportional to the local Mach number in order to maximise dissipation of the velocity divergence, preventing unwanted diffusion of the pressure field. The div(u)-SPH algorithm is implemented in the open-source weakly compressible SPH solver DualSPHysics. The new formulation is validated against a range of challenging 2-D test cases including the Taylor-Green vortices, patch impact test, jet impinging on a surface, and wave impact in a sloshing tank. The results show that the new formulation reduces the divergence in the velocity field by at least one order of magnitude which prevents spurious numerical noise and the formation of unphysical voids. The temporal evolution of the impact pressures shows that the div(u)-SPH formulation virtually eliminates unwanted acoustic pressure oscillations. Investigation of particle resolution confirms that the new div(u)-SPH formulation does not reduce the spatial convergence rate
Internal boundary conditions for a GPU-accelerated 2D shallow water model: Implementation and applications
No full textFlood propagation in rivers is strongly influenced by the presence of bridges and other hydraulic structures. Among the available approaches for including these elements in numerical models, the adoption of Internal Boundary Conditions (IBC), given its ability to capture backwater, is suitable for field-scale analyses for flood hazard assessment. In this paper, the implementation of internal boundary conditions in the two-dimensional shallow water code named “PARFLOOD” is presented. The application to experimental and real test cases shows that the proposed IBC model can handle both low and high flow conditions for bridges, while being flexible for other types of structures (e.g. flow-through dams). Moreover, the model is computationally efficient (physical/computational time ratio around 20–30 for domains with ~106 cells), thanks to the code parallelization on GPU
Direct numerical simulation of three-dimensional isotropic turbulence with smoothed particle hydrodynamics
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Enhancing the resilience to flooding induced by levee breaches in lowland areas: A methodology based on numerical modelling
Full text linkWith the aim of improving resilience to flooding and increasing preparedness to face levee-breach-induced inundations, this paper presents a methodology for creating a wide database of numerically simulated flooding scenarios due to embankment failures, applicable to any lowland area protected by river levees. The analysis of the detailed spatial and temporal flood data obtained from these hypothetical scenarios is expected to contribute both to the development of civil protection planning and to immediate actions during a possible future flood event (comparable to one of the available simulations in the database) for which real-time modelling may not be feasible. The most relevant criteria concerning the choice of mathematical model, grid resolution, hydrological conditions, breach parameters and locations are discussed in detail. The proposed methodology, named RESILIENCE, is applied to a 1100 km 2 pilot area in northern Italy. The creation of a wide database for the study area is made possible thanks to the adoption of a GPU-accelerated shallow-water numerical model which guarantees remarkable computational efficiency (ratios of physical to computational time up to 80) even for high-resolution meshes (2.5-5 m) and very large domains (>1000 km2)
An alternative SPH formulation: ADER-WENO-SPH
Full text linkWe present a new class of fully-discrete one-step SPH schemes based on a mesh-free ADER (Arbitrary DERivatives in space and time) reconstruction on moving particles in multiple space dimensions. In particular, the new SPH scheme computes mesh-free and local high order accurate polynomials in space and time to evaluate numerical fluxes at the midpoint between two interaction particles with a proper Riemann solver within the general SPH framework of Vila (1999) for nonlinear systems of hyperbolic conservation laws. The new scheme has been carefully tested against reference solutions for both the compressible Euler and the magneto-hydrodynamics (MHD) equations. The capability of the proposed scheme to accurately capture shocks and rarefaction waves for 1D and 2D problems with minimal amount of diffusion has been demonstrated. Via numerical evidence it has been shown that the new fully-discrete one-step ADER-WENO-SPH method is computationally more efficient than WENO-SPH schemes based on classical Runge–Kutta time-stepping. This is mainly due to the fact that with ADER timestepping the expensive stencil and neighbor search needs to be done only once per time step, while with Runge–Kutta time integrators the neighbor and stencil search is needed in each Runge–Kutta stage again
Assessment of pre-simulated scenarios as a non-structural measure for flood management in case of levee-breach inundations
Full text linkLevee breach inundations can entail large flood losses due to the high concentration of exposed assets in levee-protected floodplains and, sometimes, to the inadequacy or absence of early warning systems for this type of events. Since real-time modelling is computationally expensive and presents several uncertainties, which might prevent obtaining a reasonably accurate forecast of the flood propagation, an alternative methodology for the prompt prediction of flooded area, maximum depths, and arrival times during a real event was proposed. The strategy is based on the use of a database of pre-simulated scenarios of levee-breach inundations, obtained adopting a high-resolution two-dimensional shallow water model. The paper aims at the a posteriori assessment of the usefulness of this strategy. To this end, the December 2020 event on the Panaro River (Italy) is thoroughly analyzed. In the study area, the strategy had already been implemented before the event, and pre-simulated scenarios were consulted during the emergency. Post-event observations are also available for the ex-post model validation. The database was obtained considering two inflow synthetic hydrographs and a discrete number of breach locations, and unavoidable differences between real events and hypothetical scenarios were to be expected. However, for this case study, the closest levee-breach scenario in the database (in terms of breach position and inflow) provided reliable predictions of flood extent and maximum depths for the actual inundation. The pre-simulated database also helped identifying some critical spots, where effective emergency operations (sandbagging) helped protecting an urban district during the event. As accurate real-time forecasts of levee-breach inundations are yet to come, a database of pre-simulated scenarios is proven as an effective “surrogate” method for civil protection purposes
Comparison of two modelling strategies for 2D large-scale flood simulations
Full text linkIn this paper, two emerging strategies for the reduction of the computational time of 2D large-scale flood simulations are compared, with the aim of evaluating their strengths and limitations and of suggesting guidelines for their effective application. The analysis is based on two state-of-the-art raster flood models with different governing equations and parallelization strategies: PARFLOOD, a GPU-accelerated code that solves the fully dynamic shallow water equations, and LISFLOOD-FP, which combines a parallel implementation for CPU with simplified equations (local-inertial approximation). The results of two case studies (a river flood propagation, and a lowland inundation) suggest that, at coarse grid resolutions, the parallelized simplified model LISFLOOD-FP can represent a good alternative to fully dynamic models in terms of accuracy and runtime, while the GPU-parallel code PARFLOOD is more efficient in case of high-resolution simulations with millions of cells, despite the greater complexity of the numerical scheme
Towards a high order convergent ale-sph scheme with efficient weno spatial reconstruction
No full textThis paper studies the convergence properties of an arbitrary Lagrangian–Eulerian (ALE) Riemann-based SPH algorithm in conjunction with a Weighted Essentially Non-Oscillatory (WENO) high-order spatial reconstruction, in the framework of the DualSPHysics open-source code. A convergence analysis is carried out for Lagrangian and Eulerian simulations and the numerical results demonstrate that, in absence of particle disorder, the overall convergence of the scheme is close to the one guaranteed by the WENO spatial reconstruction. Moreover, an alternative method for the WENO spatial reconstruction is introduced which guarantees a speed-up of 3.5, in comparison with the classical Moving Least-Squares (MLS) approach
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