850 research outputs found
Local Uniform Stencil (LUST) boundary condition for arbitrary 3-D boundaries in parallel smoothed particle hydrodynamics (SPH) models
No full textThis paper presents the development of a new boundary treatment for free-surface hydrodynamics using the smoothed particle hydrodynamics (SPH) method accelerated with a graphics processing unit (GPU). The new solid boundary formulation uses a local uniform stencil (LUST) of fictitious particles that surround and move with each fluid particle and are only activated when they are located inside a boundary. This addresses the issues currently affecting boundary conditions in SPH, namely the accuracy, robustness and applicability while being amenable to easy parallelization such as on a GPU. In 3-D, the methodology uses triangles to represent the geometry with a ray tracing procedure to identify when the LUST particles are activated. A new correction is proposed to the popular density diffusion term treatment to correct for pressure errors at the boundary. The methodology is applicable to complex arbitrary geometries without the need of special treatments for corners and curvature is presented. The paper presents the results from 2-D and 3-D Poiseuille flows showing convergence rates typical for weakly compressible SPH. Still water in a complex 3-D geometry with a pyramid demonstrates the robustness of the technique with excellent agreement for the pressure distributions. The method is finally applied to the SPHERIC benchmark of a dry-bed dam-break impacting an obstacle showing satisfactory agreement and convergence for a violent flow
On the approximate zeroth and first-order consistency in the presence of 2-D irregular boundaries in SPH obtained by the virtual boundary particle methods
No full textIn this paper, a new method to impose 2-D solid wall boundary conditions in smoothed particle hydrodynamics is presented. The wall is discretised by means of a set of virtual particles and is simulated by a local point symmetry approach. The extension of a previously published modified virtual boundary particle (MVBP) method guarantees that arbitrarily complex domains can be readily discretised guaranteeing approximate zeroth and first-order consistency. To achieve this, three important new modifications are introduced: (i) the complete support is ensured not only for particles within one smoothing length distance, h, from the boundary but also for particles located at a distance greater than h but still within the support of the kernel; (ii) for a non-uniform fluid particle distribution, the fictitious particles are generated with a uniform stencil (unlike the previous algorithms) that can maintain a uniform shear stress on a particle-moving parallel to the wall in a steady flow; and (iii) the particle properties (density, mass and velocity) are defined using a local point of symmetry to satisfy the hydrostatic conditions and the Cauchy boundary condition for pressure. The extended MVBP model is demonstrated for cases including hydrostatic conditions for still water in a tank with a wedge and for curved boundaries, where significant improved behaviour is obtained in comparison with the conventional boundary techniques. Finally, the capability of the numerical scheme to simulate a dam break simulation is also shown. ? 2015 John Wiley & Sons, Ltd
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
Local Uniform STencil (LUST) Boundary Conditions for 3-D Irregular Boundaries in DualSPHysics
No full textOpening Up an Intelligent Tutoring System Development Environment for Extensible Student Modeling
Full text linkITS authoring tools make creating intelligent tutoring systems more cost effective, but few authoring tools make it easy to flexibly incorporate an open-ended range of student modeling methods and learning analytics tools. To support a cumulative science of student modeling and enhance the impact of real-world tutoring systems, it is critical to extend ITS authoring tools so they easily accommodate novel student modeling methods. We report on extensions to the CTAT/Tutorshop architecture to support a plug-in approach to extensible student modeling, which gives an author full control over the content of the student model. The extensions enhance the range of adaptive tutoring behaviors that can be authored and support building external, student- or teacher-facing real-time analytics tools. The contributions of this work are: (1) an open architecture to support the plugging in, sharing, re-mixing, and use of advanced student modeling techniques, ITSs, and dashboards; and (2) case studies illustrating diverse ways authors have used the architecture
Coupling SPH with a 1-D Boussinesq-type wave model
Full text linkInternational audienceThe high computational cost of SPH remains problematic in dealing with wave propagation, especially when the domains considered are large. In order to overcome this difficulty, we propose to couple 2-D SPH with a 1-D Finite Difference Boussinesq-type model. The latter deals with wave propagations for most of the spatial domain, whereas SPH computations focus on the shoreline or close to off-shore structures, where a complex description of the free-surface is required. The re-use of existing codes is achieved using a generic implementation based on Component Technology. The communication between software is ensured by the middleware Component Template Library (CTL). In order to deal with open domains, open-boundaries have to be implemented for SPH, with water height and velocity varying in space and time. These velocity and water height values are then driven by the Boussinesq-type model. As an illustration of the one way coupling, we present herein two simple examples of water waves, the first one with a flat bottom, the other one representing a schematic coastal protection
Coupling SPH with a 1-D Boussinesq-type wave model
No full textInternational audienceThe high computational cost of SPH remains problematic in dealing with wave propagation, especially when the domains considered are large. In order to overcome this difficulty, we propose to couple 2-D SPH with a 1-D Finite Difference Boussinesq-type model. The latter deals with wave propagations for most of the spatial domain, whereas SPH computations focus on the shoreline or close to off-shore structures, where a complex description of the free-surface is required. The re-use of existing codes is achieved using a generic implementation based on Component Technology. The communication between software is ensured by the middleware Component Template Library (CTL). In order to deal with open domains, open-boundaries have to be implemented for SPH, with water height and velocity varying in space and time. These velocity and water height values are then driven by the Boussinesq-type model. As an illustration of the one way coupling, we present herein two simple examples of water waves, the first one with a flat bottom, the other one representing a schematic coastal protection
Smoothed particle hydrodynamics (SPH) for free-surface flows:Past, present and future
No full textThis paper assesses some recent trends in the novel numerical meshless method smoothed particle hydrodynamics, with particular focus on its potential use in modelling free-surface flows. Due to its Lagrangian nature, smoothed particle hydrodynamics (SPH) appears to be effective in solving diverse fluid-dynamic problems with highly nonlinear deformation such as wave breaking and impact, multi-phase mixing processes, jet impact, sloshing, flooding and tsunami inundation, and fluid-structure interactions. The paper considers the key areas of rapid progress and development, including the numerical formulations, SPH operators, remedies to problems within the classical formulations, novel methodologies to improve the stability and robustness of the method, boundary conditions, multi-fluid approaches, particle adaptivity, and hardware acceleration. The key ongoing challenges in SPH that must be addressed by academic research and industrial users are identified and discussed. Finally, a roadmap is proposed for the future developments.</p
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