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Salvetti, Maria Vittoria
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Salvetti, Maria Vittoria
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Salvetti, M. V.
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5 results
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- PublicationRestrictedA parallel multiphase flow code for the 3D simulation of explosive volcanic eruptions(2007-08)
; ; ; ; ; ;Esposti Ongaro, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Cavazzoni, C.; CINECA, Interuniversity Computing Centre, Casalecchio di Reno (BO), Italy ;Erbacci, G.; CINECA, Interuniversity Computing Centre, Casalecchio di Reno (BO), Italy ;Neri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Salvetti, M. V.; Dip.to di Ingegneria Aerospaziale, Università degli Studi di Pisa, Pisa, Italy - Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Pisa, Italy; ; ; ; A new parallel code for the simulation of the transient, 3D dispersal of volcanic particles in the atmosphere is presented. The model equations, describing the multiphase flow dynamics of gas and solid pyroclasts ejected from the volcanic vent during explosive eruptions, are solved by a finite-volume discretization scheme and a pressure-based iterative non-linear solver suited to compressible multiphase flows. The solution of the multiphase equation set is computationally so demanding that the simulation of the transient 3D dynamics of eruptive columns would not be cost-effective on a single workstation. The new code has been parallelized by adopting an ad hoc domain partitioning scheme that enforces the load balancing in the presence of a large number of topographic blocking-cells. An optimized communication layer has been built over the Message-Passing Interface. It is shown that the present code has a remarkable efficiency on several high-performance platforms and makes it possible, for the first time, to simulate fully 3D eruptive scenarios on realistic volcano topography.175 30 - PublicationOpen AccessLarge-eddy simulation of pyroclastic density currents(2009)
; ; ; ; ;Esposti Ongaro, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Barsotti, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Neri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Salvetti, M. V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; ; ; We investigate the dynamics of turbulent pyroclastic density currents (PDCs) by adopting a 3D, Eulerian-Eulerian multiphase flow model, in which solid particles are treated as a continuum and the grain-size distribution is simplified by assuming two particulate phases. The turbulent sub-grid stress of the gas phase is modelled within the framework of Large-Eddy Simulation (LES) by means of a eddy-viscosity model together with a wall closure. Despite the significant numerical diffusion associated to the upwind method adopted for the Finite-Volume discretization, numerical simulations demonstrate the need of adopting a Sub-Grid Scale (SGS) model, while revealing the complex interplay between the grid and the SGS filter sizes. We also analyse the relationship between the averaged flow dynamic pressure and the action exerted by the PDC on a cubic obstacle, to evaluate the impact of a PDC on a building. Numerical results suggest that the average flow dynamic pressure can be used as a proxy for the force per unit surface acting on the building envelope (Fig. 5), even for such steeply stratified flows. However, it is not possible to express such roportionality as a constant coefficient such as the drag coefficient in a steady-state current. The present results indeed indicate that the large epistemic and aleatory uncertainty on initial and boundary conditions has an impact on the numerical redictions which is comparable to that of grid resolution.199 549 - PublicationOpen AccessLarge-eddy simulation of pyroclastic density currents(2010)
; ; ; ; ;Esposti Ongaro, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Barsotti, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Neri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Salvetti, M. V.; Aerospace Engineering Department, University of Pisa, Pisa, Italy; ; ; ; ; ; ; ; ;Salvetti, M. V.; Aerospace Engineering Department, University of Pisa, Pisa, Italy ;Geurts, B.; Multiscale Modeling and Simulation, Faculty EEMCS, University of Twente, Enschede, The Netherlands; Anisotropic Turbulence, Faculty Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands ;Meyers, J.; Katholieke Universiteit Leuven, Div. Appl. Mechanics & Energy Conversion, Leuven, Belgium ;Sagaut, P.; Université Pierre et Marie Curie 6, Institut Jean le Rond d'Alembert, Paris Cedex, France; ; ; We investigate the dynamics of turbulent pyroclastic density currents (PDCs) by adopting a 3D, Eulerian-Eulerian multiphase flow model, in which solid particles are treated as a continuum and the grain-size distribution is simplified by assuming two particulate phases. The turbulent sub-grid stress of the gas phase is modelled within the framework of Large-Eddy Simulation (LES) by means of a eddy-viscosity model together with a wall closure. Despite the significant numerical diffusion associated to the upwind method adopted for the Finite-Volume discretization, numerical simulations demonstrate the need of adopting a Sub-Grid Scale (SGS) model, while revealing the complex interplay between the grid and the SGS filter sizes. We also analyse the relationship between the averaged flow dynamic pressure and the action exerted by the PDC on a cubic obstacle, to evaluate the impact of a PDC on a building. Numerical results suggest that the average flow dynamic pressure can be used as a proxy for the force per unit surface acting on the building envelope (Fig. 5), even for such steeply stratified flows. However, it is not possible to express such proportionality as a constant coefficient such as the drag coefficient in a steady-state current. The present results indeed indicate that the large epistemic and aleatory uncertainty on initial and boundary conditions has an impact on the numerical predictions which is comparable to that of grid resolution.147 158 - PublicationOpen AccessPropagation of Source Grain-size Distribution Uncertainty by Using a Lagrangian Volcanic Particle Dispersal Model(2014)
; ; ; ; ; ; ; ; ; ; ;Lagrangian particle dispersal models are commonly used for tracking ash particles emitted from volcanic plumes and transported under the action of atmospheric wind fields. In this work, we adopted a Lagrangian particle model to carry out an uncertainty quantification analysis of volcanic ash dispersal in the atmosphere focused on the uncertainties affecting particle source conditions. To this aim the Eulerian fully compressible mesoscale non-hydrostatic model WRF was used to generate the driving wind field. The Lagrangian particle model LPAC (de’Michieli Vitturi et al., JGR 2010) was then used to simulate the transport of mass particles under the action of atmospheric conditions. The particle motion equations were derived by expressing the Lagrangian particle acceleration as the sum of the forces acting along its trajectory, with drag forces calculated as a function of particle diameter, density, shape and Reynolds number. The simulations were representative of weak plume events of Mt. Etna and aimed to quantify the effect on the dispersal process of the uncertainty in the mean and variance of a Gaussian density function describing the grain-size distribution of the mixture and in the particle sphericity. In order to analyze the sensitivity of particle dispersal to these uncertain parameters with a reasonable number of simulations, and therefore with affordable computational costs, response surfaces in the parameter space were built by using the generalized polynomial chaos technique. The uncertainty analysis allowed to quantify the most probable values, as well as their pdf, of the number of particles as well as of the mean and variance of the grain size distribution at various distances from the source, both in air and on the ground. In particular, results highlighted the strong reduction of the uncertainty ranges of the mean and variance of the grain-size distribution with increasing distance from source and the significant control of particle sphericity on the dispersal process.42 12 - PublicationRestrictedAn immersed boundary method for compressible multiphase flows: application to the dynamics of pyroclastic density currents(2007-09)
; ; ; ; ; ;De' Michieli Vitturi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Esposti Ongaro, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Neri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Salvetti, M. V.; Dipartimento di Ingegneria Aerospaziale, Università di Pisa, Pisa, Italy / Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Pisa, Italy ;Beux, F.; Scuola Normale Superiore di Pisa, Pisa, Italy; ; ; ; An immersed boundary technique suitable for the solution of multiphase compressible equations of gas–particle flows of volcanic origin over complex 2D and 3D topographies has been developed and applied. This procedure combines and extends different existing methods designed for incompressible flows. Furthermore, the extension to compressible multiphase flows is achieved through a flux correction term in the mass continuity equations of the immersed cells that accounts for density variations in the partial volumes. The technique is computationally accurate and inexpensive, if compared to the use and implementation of the finite-volume technique on unstructured meshes. The first applications that we consider are the simulations of pyroclastic density currents generated by the collapse of a volcanic column in 2D axisymmetric geometry and by a dome explosion in 3D. Results show that the immersed boundary technique can significantly improve the description of the no-slip flow condition on an irregular topography even with relatively coarse meshes. Although the net effect of the present technique on the results is difficult to quantify in general terms, its adoption is recommended any time that cartesian grids are used to describe the large-scale dynamics of pyroclastic density currents over volcano topographies.142 19