renato vacondio | Università degli Studi di Parma (Italy) (original) (raw)

Papers by renato vacondio

Computational Particle Mechanics, 2020

This paper presents a brief review of grand challenges of Smoothed Particle Hydrodynamics (SPH) m... more This paper presents a brief review of grand challenges of Smoothed Particle Hydrodynamics (SPH) method. As a meshless method, SPH can simulate a large range of applications from astrophysics to free-surface flows, to complex mixing problems in industry and has had notable successes. As a young computational method, the SPH method still requires development to address important elements which prevent more widespread use. This effort has been led by members of the SPH rEsearch and engineeRing International Community (SPHERIC) who have identified SPH Grand Challenges. The SPHERIC SPH Grand Challenges (GCs) have been grouped into 5 categories: (GC1) convergence, consistency and stability, (GC2) boundary conditions, (GC3) adaptivity, (GC4) coupling to other models, and (GC5) applicability to industry. The SPH Grand Challenges have been formulated to focus the attention and activities of researchers, developers, and users around the world. The status of each SPH Grand Challenge is present...

In this paper, a new method to impose 2-D solid wall boundary conditions in smoothed particle hyd... more In 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. Copyright © 2015 John Wiley & Sons, Ltd.

Flood events caused by the collapse of dams or river levees can have damaging consequences on bui... more Flood events caused by the collapse of dams or river levees can have damaging consequences on buildings and infrastructure located in prone areas. Accordingly, a careful prediction of the hydrodynamic load acting on structures is important for flood hazard assessment and potential damage evaluation. However, this represents a challenging task and requires the use of suitable mathematical models. This paper investigates the capability of three different models, i.e. a 2D depth-averaged model, a 3D Eulerian two-phase model, and a 3D Smoothed Particle Hydrodynamics (SPH) model, to estimate the impact load exerted by a dam-break wave on an obstacle. To this purpose, idealized dam-break experiments were carried out by generating a flip-through impact against a rigid squat structure, and measurements of the impact force were obtained directly by using a load cell. The dynamics of the impact event was analyzed and related to the measured load time history. A repeatability analysis was performed due to the great variability typically shown by impact phenomena, and a confidence range was estimated. The comparison between numerical results and experimental data shows the capability of 3D models to reproduce the key features of the flip-through impact. The 2D modelling based on the shallow water approach is not entirely suitable to accurately reproduce the load hydrograph and predict the load peak values; this difficulty increases with the strength of the wave impact. Nevertheless, the error in the peak load estimation is in the order of 10% only, thus the 2D approach may be considered appropriate for practical applications. Moreover, when the shallow water approximation is expected to work well, 2D results are comparable with the experimental data, as well as with the numerical predictions of far more sophisticated and computationally demanding 3D solvers. All the numerical models overestimate the falling limb of the load hydrograph after the impact. The SPH model ensures good evaluation of the long-time load impulse. The 2D shallow water solver and the 3D Eulerian model are less accurate in predicting the load impulse but provide similar results. A sensitivity analysis with respect to the model parameters allows to assess model uncertainty. Finally, the experimental data collected have been made available online as supplementary material for validation purpose

Computer Physics Communications, Oct 18, 2014

DualSPHysics is a hardware accelerated Smoothed Particle Hydrodynamics code developed to solve fr... more DualSPHysics is a hardware accelerated Smoothed Particle Hydrodynamics code developed to solve free-surface flow problems. DualSPHysics is an open-source code developed and released under the terms of GNU General Public License (GPLv3). Along with the source code, a complete documentation that makes easy the compilation and execution of the source files is also distributed. The code has been shown to be efficient and reliable. The parallel power computing of Graphics Computing Units (GPUs) is used to accelerate DualSPHysics by up to two orders of magnitude compared to the performance of the serial version.

Environmental Modelling & Software, Mar 6, 2014

In this paper a parallelization of a Shallow Water numerical scheme suitable for Graphics Process... more In this paper a parallelization of a Shallow Water numerical scheme suitable for Graphics Processor Unit (GPU) architectures under the NVIDIA™'s Compute Unified Device Architecture (CUDA) framework is presented. In order to provide robust and accurate simulations of real flood events, the system features a state-of-the-art Finite Volume explicit discretization technique which is well balanced, second order accurate and based on positive depth reconstruction. The model is based on a Cartesian grid and boundary conditions are implemented by means of the implicit local ghost cell approach, which enables the discretization of a broad spectrum of boundary conditions including inflow/outflow conditions. A novel and efficient Block Deactivation Optimization procedure has also been adopted, in order to increase the efficiency of the numerical scheme in the presence of wetting-drying fronts. This led to speedups of two orders of magnitude with respect to a single-core CPU. The code has been validated against several severe benchmark test cases, and its capability of producing accurate fast simulations (with high ratios between physical and computing times) for different real world cases has been shown.

A 3D numerical modeling of the wave generated by the Vajont slide, one of the most destructive ev... more A 3D numerical modeling of the wave generated by the Vajont slide, one of the most destructive ever occurred, is presented in this paper. A meshless Lagrangian Smoothed Particle Hydrodynamics (SPH) technique was adopted to simulate the highly fragmented violent flow generated by the falling slide in the artificial reservoir. The speed-up achievable via General Purpose Graphic Processing Units (GP-GPU) allowed to adopt the adequate resolution to describe the phenomenon. The comparison with the data available in literature showed that the results of the numerical simulation reproduce satisfactorily the maximum run-up, also the water surface elevation in the residual lake after the event

In this paper an adaptive algorithm for Smoothed Particle Hydrodynamics (SPH) for the Shallow Wat... more In this paper an adaptive algorithm for Smoothed Particle Hydrodynamics (SPH) for the Shallow Water Equations (SWEs) is presented. The area of a particle is inversely proportional to depth giving poor resolution in small depths without particle refinement. This is a particular limitation for flooding problems of interest here. Higher resolution is created by splitting the particles, while particle coalescing (or merging) improves efficiency by reducing the number of the particles when acceptable. The new particle coalescing procedure merges two particles together if their area becomes less than a predefined threshold value. Both particle splitting and coalescing procedures conserve mass and momentum and the smoothing length of new particles is calculated by minimizing the density error of the SPH summation. The new dynamic particle refinement procedure is assessed by testing the numerical scheme against analytical, experimental and benchmark test cases. The analytical cases show that with particle splitting and coalescing typical convergence rates remain faster than linear. For the practical test case, in comparison to using particle splitting alone, the particle coalescing procedure leads to a significant reduction of computational time, by a factor of 15. This makes the computational time of the same order as mesh-based methods with the advantage of not having to specify a mesh over a flood domain of unknown extent a priori.

In this paper a novel variable resolution method using particle splitting and coalescing for the ... more In this paper a novel variable resolution method using particle splitting and coalescing for the SPH numerical solution of the Navier-Stokes equations is presented. The key idea of the scheme is to modify dynamically the particle sizes by means of splitting and coalescing (merging) individual particles to provide good resolution only where it is needed. The SPH scheme adopted is derived using the variational principle guaranteeing that both mass and momentum are conserved for particles with different smoothing lengths. A particle shifting procedure is used to prevent unacceptable anisotropic distributions of the particles and is further generalized for treating domains with variable mass particles. The algorithm has been tested against analytical solutions for Poiseuille and Taylor-Green flows showing that the shifting algorithm is effective in increasing the accuracy, and that error introduced by the splitting and coalescing is negligible. The capability of the numerical scheme for increasing efficiency is shown for more general problems: the simulations of a moving square in a box and flow past a cylinder have shown that the particle refinement procedure is able to increase the efficiency while maintaining the same level of accuracy as a uniform distribution with the most refined resolution.

In this paper, a smoothed particle hydrodynamics (SPH) numerical model for the shallow water equa... more In this paper, a smoothed particle hydrodynamics (SPH) numerical model for the shallow water equations (SWEs) with bed slope source term balancing is presented. The solution of the SWEs using SPH is attractive being a conservative, mesh-free, automatically adaptive method without special treatment for wet-dry interfaces. Recently, the capability of the SPH–SWEs numerical scheme with shock capturing and general boundary conditions has been used for predicting practical flooding problems. The balance between the bed slope source term and fluxes in shallow water models is desirable for reliable simulations of flooding over bathymetries where discontinuities are present and has received some attention in the framework of Finite Volume Eulerian models. The imbalance because of the source term resulting from the calculation of the the water depth is eradicated by means of a corrected mass, which is able to remove the error introduced by a bottom discontinuity. Two different discretizations of the momentum equation are presented herein: the first one is based on the variational formulation of the SWEs in order to obtain a fully conservative formulation, whereas the second one is obtained using a non-conservative form of the free-surface elevation gradient. In both formulations, a variable smoothing length is considered. Results are presented demonstrating the corrections preserve still water in the vicinity of either 1D or 2D bed discontinuities and provide close agreement with 1D analytical solutions for rapidly varying flows over step changes in the bed. The method is finally applied to 2D dam break flow over a square obstacle where the balanced formulation improves the agreement with experimental measurements of the free surface

A SPH (Smoothed Particle Hydrodynamics) numerical model for the Shallow Water Equations (SWEs) is... more A SPH (Smoothed Particle Hydrodynamics) numerical model for the Shallow Water Equations (SWEs) is presented for simulating flood inundation due to rapidly‐varying flow such as dam breaks, tsunamis, levee breaches, etc. Important theoretical and numerical developments have recently been made and the model has been extended here by incorporating these and implementing open boundary conditions, resulting in a general, accurate computational tool suitable for practical application. The method is attractive for flood simulation over large domains where the extent of inundation is unknown because computation is only carried out in wet areas and is dynamically adaptive. The open boundary algorithm is quite general, based on a simplified version of the characteristics method, handling both supercritical and subcritical inflow and outflow. This is tested against reference solutions for flows over a hump involving shocks. The model is then applied, to two quite different flood inundations resulting from the Okushiri tsunami in Japan and from a hypothetical dyke breach at Thamesmead in the UK. The SPH‐SWE model compares well with established commercial and state‐of‐the‐art finite volume codes.

The solution for the shallow water equations using smoothed particle hydrodynamics is attractive,... more The 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. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, an approximate modified virtual boundary particle method (MVBP) for solid boundary... more In 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∘ and one with four internal angles of 345∘. We demonstrate that for an internal angle of 300∘, 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. Copyright © 2011 John Wiley & Sons, Ltd.

Proceedings of the 8th INTERNATIONAL SPHERIC WORKSHOP Trondheim, Norway June 4-6, 2013, 2013

Proceedings of Riverflow 2014 conference, Lausanne (Switzerland), September 2014, CRC Press, Sep 2, 2014

Proceedings of the XXXIII Convegno Nazionale di Idraulica e Costruzioni Idrauliche, Sep 2012

Buildings located near dams or river levees can be subject to flooding in case of collapse of the... more Buildings located near dams or river levees can be subject to flooding in case of collapse of these structures due to extreme events. The careful prediction of flood actions on structures is important for flood risk assessment and at the same time is a challenging task. For this purpose mathematical models are indispensable tools. This paper investigates the capabilities of 2D and 3D models of predicting impact forces over structures. Numerical results are compared with experimental data derived from a reference laboratory test widely considered in the literature in which a dam-break wave impacts over an obstacle. Despite the expected superiority of high resolution 3D models in describing the investigated phenomenon, the 2D depth-averaged model provides in the considered test case satisfactory results in behalf of safety with acceptable setting-up and computational effort, thus appearing to be the sole really usable, from a computational point of view, in large scale real field applications

Proceedings of the second European conference on FLOOD risk management

On the 9th November 2007, a storm surge in the North Sea caused severe flooding along isolated pa... more On the 9th November 2007, a storm surge in the North Sea caused severe flooding along isolated parts of the Norfolk coast in the UK, in particular along the coastline of Walcott. The coastline at Walcott is orientated approximately northwest-southeast and is prone to attack from the North Sea. When wind is combined with a North Sea surge, the water level of the sea can increase by up to 2m above the normal sea level. Such conditions have caused disastrous flooding in the town, as in 1953, and more recently in November 2007. Here we will compare the output from three different state-of-the-art coastal inundation models, namely TELEMAC-2D, LISFLOOD-FP and SWE-SPHysics, forced with time dependent wave overtopping discharges. It is shown that the inundation extent and the highest water mark are sensitive to the inflow representation and the choice of model.

Computational Particle Mechanics, 2020

This paper presents a brief review of grand challenges of Smoothed Particle Hydrodynamics (SPH) m... more This paper presents a brief review of grand challenges of Smoothed Particle Hydrodynamics (SPH) method. As a meshless method, SPH can simulate a large range of applications from astrophysics to free-surface flows, to complex mixing problems in industry and has had notable successes. As a young computational method, the SPH method still requires development to address important elements which prevent more widespread use. This effort has been led by members of the SPH rEsearch and engineeRing International Community (SPHERIC) who have identified SPH Grand Challenges. The SPHERIC SPH Grand Challenges (GCs) have been grouped into 5 categories: (GC1) convergence, consistency and stability, (GC2) boundary conditions, (GC3) adaptivity, (GC4) coupling to other models, and (GC5) applicability to industry. The SPH Grand Challenges have been formulated to focus the attention and activities of researchers, developers, and users around the world. The status of each SPH Grand Challenge is present...

In this paper, a new method to impose 2-D solid wall boundary conditions in smoothed particle hyd... more In 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. Copyright © 2015 John Wiley & Sons, Ltd.

Flood events caused by the collapse of dams or river levees can have damaging consequences on bui... more Flood events caused by the collapse of dams or river levees can have damaging consequences on buildings and infrastructure located in prone areas. Accordingly, a careful prediction of the hydrodynamic load acting on structures is important for flood hazard assessment and potential damage evaluation. However, this represents a challenging task and requires the use of suitable mathematical models. This paper investigates the capability of three different models, i.e. a 2D depth-averaged model, a 3D Eulerian two-phase model, and a 3D Smoothed Particle Hydrodynamics (SPH) model, to estimate the impact load exerted by a dam-break wave on an obstacle. To this purpose, idealized dam-break experiments were carried out by generating a flip-through impact against a rigid squat structure, and measurements of the impact force were obtained directly by using a load cell. The dynamics of the impact event was analyzed and related to the measured load time history. A repeatability analysis was performed due to the great variability typically shown by impact phenomena, and a confidence range was estimated. The comparison between numerical results and experimental data shows the capability of 3D models to reproduce the key features of the flip-through impact. The 2D modelling based on the shallow water approach is not entirely suitable to accurately reproduce the load hydrograph and predict the load peak values; this difficulty increases with the strength of the wave impact. Nevertheless, the error in the peak load estimation is in the order of 10% only, thus the 2D approach may be considered appropriate for practical applications. Moreover, when the shallow water approximation is expected to work well, 2D results are comparable with the experimental data, as well as with the numerical predictions of far more sophisticated and computationally demanding 3D solvers. All the numerical models overestimate the falling limb of the load hydrograph after the impact. The SPH model ensures good evaluation of the long-time load impulse. The 2D shallow water solver and the 3D Eulerian model are less accurate in predicting the load impulse but provide similar results. A sensitivity analysis with respect to the model parameters allows to assess model uncertainty. Finally, the experimental data collected have been made available online as supplementary material for validation purpose

Computer Physics Communications, Oct 18, 2014

DualSPHysics is a hardware accelerated Smoothed Particle Hydrodynamics code developed to solve fr... more DualSPHysics is a hardware accelerated Smoothed Particle Hydrodynamics code developed to solve free-surface flow problems. DualSPHysics is an open-source code developed and released under the terms of GNU General Public License (GPLv3). Along with the source code, a complete documentation that makes easy the compilation and execution of the source files is also distributed. The code has been shown to be efficient and reliable. The parallel power computing of Graphics Computing Units (GPUs) is used to accelerate DualSPHysics by up to two orders of magnitude compared to the performance of the serial version.

Environmental Modelling & Software, Mar 6, 2014

In this paper a parallelization of a Shallow Water numerical scheme suitable for Graphics Process... more In this paper a parallelization of a Shallow Water numerical scheme suitable for Graphics Processor Unit (GPU) architectures under the NVIDIA™'s Compute Unified Device Architecture (CUDA) framework is presented. In order to provide robust and accurate simulations of real flood events, the system features a state-of-the-art Finite Volume explicit discretization technique which is well balanced, second order accurate and based on positive depth reconstruction. The model is based on a Cartesian grid and boundary conditions are implemented by means of the implicit local ghost cell approach, which enables the discretization of a broad spectrum of boundary conditions including inflow/outflow conditions. A novel and efficient Block Deactivation Optimization procedure has also been adopted, in order to increase the efficiency of the numerical scheme in the presence of wetting-drying fronts. This led to speedups of two orders of magnitude with respect to a single-core CPU. The code has been validated against several severe benchmark test cases, and its capability of producing accurate fast simulations (with high ratios between physical and computing times) for different real world cases has been shown.

A 3D numerical modeling of the wave generated by the Vajont slide, one of the most destructive ev... more A 3D numerical modeling of the wave generated by the Vajont slide, one of the most destructive ever occurred, is presented in this paper. A meshless Lagrangian Smoothed Particle Hydrodynamics (SPH) technique was adopted to simulate the highly fragmented violent flow generated by the falling slide in the artificial reservoir. The speed-up achievable via General Purpose Graphic Processing Units (GP-GPU) allowed to adopt the adequate resolution to describe the phenomenon. The comparison with the data available in literature showed that the results of the numerical simulation reproduce satisfactorily the maximum run-up, also the water surface elevation in the residual lake after the event

In this paper an adaptive algorithm for Smoothed Particle Hydrodynamics (SPH) for the Shallow Wat... more In this paper an adaptive algorithm for Smoothed Particle Hydrodynamics (SPH) for the Shallow Water Equations (SWEs) is presented. The area of a particle is inversely proportional to depth giving poor resolution in small depths without particle refinement. This is a particular limitation for flooding problems of interest here. Higher resolution is created by splitting the particles, while particle coalescing (or merging) improves efficiency by reducing the number of the particles when acceptable. The new particle coalescing procedure merges two particles together if their area becomes less than a predefined threshold value. Both particle splitting and coalescing procedures conserve mass and momentum and the smoothing length of new particles is calculated by minimizing the density error of the SPH summation. The new dynamic particle refinement procedure is assessed by testing the numerical scheme against analytical, experimental and benchmark test cases. The analytical cases show that with particle splitting and coalescing typical convergence rates remain faster than linear. For the practical test case, in comparison to using particle splitting alone, the particle coalescing procedure leads to a significant reduction of computational time, by a factor of 15. This makes the computational time of the same order as mesh-based methods with the advantage of not having to specify a mesh over a flood domain of unknown extent a priori.

In this paper a novel variable resolution method using particle splitting and coalescing for the ... more In this paper a novel variable resolution method using particle splitting and coalescing for the SPH numerical solution of the Navier-Stokes equations is presented. The key idea of the scheme is to modify dynamically the particle sizes by means of splitting and coalescing (merging) individual particles to provide good resolution only where it is needed. The SPH scheme adopted is derived using the variational principle guaranteeing that both mass and momentum are conserved for particles with different smoothing lengths. A particle shifting procedure is used to prevent unacceptable anisotropic distributions of the particles and is further generalized for treating domains with variable mass particles. The algorithm has been tested against analytical solutions for Poiseuille and Taylor-Green flows showing that the shifting algorithm is effective in increasing the accuracy, and that error introduced by the splitting and coalescing is negligible. The capability of the numerical scheme for increasing efficiency is shown for more general problems: the simulations of a moving square in a box and flow past a cylinder have shown that the particle refinement procedure is able to increase the efficiency while maintaining the same level of accuracy as a uniform distribution with the most refined resolution.

In this paper, a smoothed particle hydrodynamics (SPH) numerical model for the shallow water equa... more In this paper, a smoothed particle hydrodynamics (SPH) numerical model for the shallow water equations (SWEs) with bed slope source term balancing is presented. The solution of the SWEs using SPH is attractive being a conservative, mesh-free, automatically adaptive method without special treatment for wet-dry interfaces. Recently, the capability of the SPH–SWEs numerical scheme with shock capturing and general boundary conditions has been used for predicting practical flooding problems. The balance between the bed slope source term and fluxes in shallow water models is desirable for reliable simulations of flooding over bathymetries where discontinuities are present and has received some attention in the framework of Finite Volume Eulerian models. The imbalance because of the source term resulting from the calculation of the the water depth is eradicated by means of a corrected mass, which is able to remove the error introduced by a bottom discontinuity. Two different discretizations of the momentum equation are presented herein: the first one is based on the variational formulation of the SWEs in order to obtain a fully conservative formulation, whereas the second one is obtained using a non-conservative form of the free-surface elevation gradient. In both formulations, a variable smoothing length is considered. Results are presented demonstrating the corrections preserve still water in the vicinity of either 1D or 2D bed discontinuities and provide close agreement with 1D analytical solutions for rapidly varying flows over step changes in the bed. The method is finally applied to 2D dam break flow over a square obstacle where the balanced formulation improves the agreement with experimental measurements of the free surface

A SPH (Smoothed Particle Hydrodynamics) numerical model for the Shallow Water Equations (SWEs) is... more A SPH (Smoothed Particle Hydrodynamics) numerical model for the Shallow Water Equations (SWEs) is presented for simulating flood inundation due to rapidly‐varying flow such as dam breaks, tsunamis, levee breaches, etc. Important theoretical and numerical developments have recently been made and the model has been extended here by incorporating these and implementing open boundary conditions, resulting in a general, accurate computational tool suitable for practical application. The method is attractive for flood simulation over large domains where the extent of inundation is unknown because computation is only carried out in wet areas and is dynamically adaptive. The open boundary algorithm is quite general, based on a simplified version of the characteristics method, handling both supercritical and subcritical inflow and outflow. This is tested against reference solutions for flows over a hump involving shocks. The model is then applied, to two quite different flood inundations resulting from the Okushiri tsunami in Japan and from a hypothetical dyke breach at Thamesmead in the UK. The SPH‐SWE model compares well with established commercial and state‐of‐the‐art finite volume codes.

The solution for the shallow water equations using smoothed particle hydrodynamics is attractive,... more The 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. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, an approximate modified virtual boundary particle method (MVBP) for solid boundary... more In 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∘ and one with four internal angles of 345∘. We demonstrate that for an internal angle of 300∘, 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. Copyright © 2011 John Wiley & Sons, Ltd.

Proceedings of the 8th INTERNATIONAL SPHERIC WORKSHOP Trondheim, Norway June 4-6, 2013, 2013

Proceedings of Riverflow 2014 conference, Lausanne (Switzerland), September 2014, CRC Press, Sep 2, 2014

Proceedings of the XXXIII Convegno Nazionale di Idraulica e Costruzioni Idrauliche, Sep 2012

Buildings located near dams or river levees can be subject to flooding in case of collapse of the... more Buildings located near dams or river levees can be subject to flooding in case of collapse of these structures due to extreme events. The careful prediction of flood actions on structures is important for flood risk assessment and at the same time is a challenging task. For this purpose mathematical models are indispensable tools. This paper investigates the capabilities of 2D and 3D models of predicting impact forces over structures. Numerical results are compared with experimental data derived from a reference laboratory test widely considered in the literature in which a dam-break wave impacts over an obstacle. Despite the expected superiority of high resolution 3D models in describing the investigated phenomenon, the 2D depth-averaged model provides in the considered test case satisfactory results in behalf of safety with acceptable setting-up and computational effort, thus appearing to be the sole really usable, from a computational point of view, in large scale real field applications

Proceedings of the second European conference on FLOOD risk management

On the 9th November 2007, a storm surge in the North Sea caused severe flooding along isolated pa... more On the 9th November 2007, a storm surge in the North Sea caused severe flooding along isolated parts of the Norfolk coast in the UK, in particular along the coastline of Walcott. The coastline at Walcott is orientated approximately northwest-southeast and is prone to attack from the North Sea. When wind is combined with a North Sea surge, the water level of the sea can increase by up to 2m above the normal sea level. Such conditions have caused disastrous flooding in the town, as in 1953, and more recently in November 2007. Here we will compare the output from three different state-of-the-art coastal inundation models, namely TELEMAC-2D, LISFLOOD-FP and SWE-SPHysics, forced with time dependent wave overtopping discharges. It is shown that the inundation extent and the highest water mark are sensitive to the inflow representation and the choice of model.