37 research outputs found
ASHEE: a compressible, equilibrium-Eulerian model for volcanic ash plumes
A new fluid-dynamic model is developed to numerically simulate the
non-equilibrium dynamics of polydisperse gas-particle mixtures forming volcanic
plumes. Starting from the three-dimensional N-phase Eulerian transport
equations for a mixture of gases and solid particles, we adopt an asymptotic
expansion strategy to derive a compressible version of the first-order
non-equilibrium model, valid for low concentration regimes and small particles
Stokes . When the model reduces to the dusty-gas one. The
new model is significantly faster than the Eulerian model while retaining the
capability to describe gas-particle non-equilibrium. Direct numerical
simulation accurately reproduce the dynamics of isotropic turbulence in
subsonic regime. For gas-particle mixtures, it describes the main features of
density fluctuations and the preferential concentration of particles by
turbulence, verifying the model reliability and suitability for the simulation
of high-Reynolds number and high-temperature regimes. On the other hand,
Large-Eddy Numerical Simulations of forced plumes are able to reproduce their
observed averaged and instantaneous properties. The self-similar radial profile
and the development of large-scale structures are reproduced, including the
rate of entrainment of atmospheric air. Application to the Large-Eddy
Simulation of the injection of the eruptive mixture in a stratified atmosphere
describes some of important features of turbulent volcanic plumes, including
air entrainment, buoyancy reversal, and maximum plume height. Coarse particles
partially decouple from the gas within eddies, modifying the turbulent
structure, and preferentially concentrate at the eddy periphery, eventually
being lost from the plume margins due to the gravity. By these mechanisms,
gas-particle non-equilibrium is able to influence the large-scale behavior of
volcanic plumes.Comment: 29 pages, 22 figure
Ash plume properties retrieved from infrared images: a forward and inverse modeling approach
We present a coupled fluid-dynamic and electromagnetic model for volcanic ash
plumes. In a forward approach, the model is able to simulate the plume dynamics
from prescribed input flow conditions and generate the corresponding synthetic
thermal infrared (TIR) image, allowing a comparison with field-based
observations. An inversion procedure is then developed to retrieve ash plume
properties from TIR images.
The adopted fluid-dynamic model is based on a one-dimensional, stationary
description of a self-similar (top-hat) turbulent plume, for which an
asymptotic analytical solution is obtained. The electromagnetic
emission/absorption model is based on the Schwarzschild's equation and on Mie's
theory for disperse particles, assuming that particles are coarser than the
radiation wavelength and neglecting scattering. [...]
Application of the inversion procedure to an ash plume at Santiaguito volcano
(Guatemala) has allowed us to retrieve the main plume input parameters, namely
the initial radius , velocity , temperature , gas mass ratio
, entrainment coefficient and their related uncertainty. Moreover,
coupling with the electromagnetic model, we have been able to obtain a reliable
estimate of the equivalent Sauter diameter of the total particle size
distribution.
The presented method is general and, in principle, can be applied to the
spatial distribution of particle concentration and temperature obtained by any
fluid-dynamic model, either integral or multidimensional, stationary or
time-dependent, single or multiphase. The method discussed here is fast and
robust, thus indicating potential for applications to real-time estimation of
ash mass flux and particle size distribution, which is crucial for model-based
forecasts of the volcanic ash dispersal process.Comment: 41 pages, 13 figures, submitted pape
DNS of compressible multiphase flows through the Eulerian approach
In this paper we present three multiphase flow models suitable for the study
of the dynamics of compressible dispersed multiphase flows. We adopt the
Eulerian approach because we focus our attention to dispersed (concentration
smaller than 0.001) and small particles (the Stokes number has to be smaller
than 0.2). We apply these models to the compressible ()
homogeneous and isotropic decaying turbulence inside a periodic
three-dimensional box ( cells) using a numerical solver based on the
OpenFOAM C++ libraries. In order to validate our simulations in the
single-phase case we compare the energy spectrum obtained with our code with
the one computed by an eighth order scheme getting a very good result (the
relative error is very small ). Moving to the bi-phase case,
initially we insert inside the box an homogeneous distribution of particles
leaving unchanged the initial velocity field. Because of the centrifugal force,
turbulence induce particle preferential concentration and we study the
evolution of the solid-phase density. Moreover, we do an {\em a-priori} test on
the new sub-grid term of the multiphase equations comparing them with the
standard sub-grid scale term of the Navier-Stokes equations.Comment: 10 pages, 5 figures, preprint. Direct and Large Eddy Simulations 9,
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IMEX_SfloW2D 1.0: a depth-averaged numerical flow model for pyroclastic avalanches
Abstract. Pyroclastic avalanches are a type of granular flow generated at active
volcanoes by different mechanisms, including the collapse of steep
pyroclastic deposits (e.g., scoria and ash cones), fountaining during
moderately explosive eruptions, and crumbling and gravitational collapse of
lava domes. They represent end-members of gravity-driven pyroclastic flows
characterized by relatively small volumes (less than about 1 Mm3) and
relatively thin (1–10 m) layers at high particle concentration
(10–50 vol %), manifesting strong topographic control. The simulation of
their dynamics and mapping of their hazards pose several different problems
to researchers and practitioners, mostly due to the complex and still poorly
understood rheology of the polydisperse granular mixture and to the
interaction with the complex natural three-dimensional topography, which
often causes rapid rheological changes. In this paper, we present
IMEX_SfloW2D, a depth-averaged flow model describing the granular mixture as
a single-phase granular fluid. The model is formulated in absolute Cartesian
coordinates (whereby the fluid flow equations are integrated along the
direction of gravity) and can be solved over a topography described by a
digital elevation model. The numerical discretization and solution algorithms
are formulated to allow for a robust description of wet–dry conditions (thus
allowing us to accurately track the front propagation) and an implicit
solution to
the nonlinear friction terms. Owing to these features, the model is able to
reproduce steady solutions, such as the triggering and stopping phases of the
flow, without the need for empirical conditions. Benchmark cases are discussed
to verify the numerical code implementation and to demonstrate the main
features of the new model. A preliminary application to the simulation of the
11 February pyroclastic avalanche at the Etna volcano (Italy) is finally
presented. In the present formulation, a simple semi-empirical friction model
(Voellmy–Salm rheology) is implemented. However, the modular structure of the
code facilitates the implementation of more specific and calibrated
rheological models for pyroclastic avalanches
IMEX_SfloW2D v2: a depth-averaged numerical flow model for volcanic gas–particle flows over complex topographies and water
We present developments to the physical model and the open-source numerical code IMEX_SfloW2D (de' Michieli Vitturi et al., 2019). These developments consist of a generalization of the depth-averaged (shallow-water) fluid equations to describe a polydisperse fluid–solid mixture, including terms for sedimentation and entrainment, transport equations for solid particles of different sizes, transport equations for different components of the carrier phase, and an equation for temperature/energy. Of relevance for the simulation of volcanic mass flows, vaporization and entrainment of water are implemented in the new model. The model can be easily adapted to simulate a wide range of volcanic mass flows (pyroclastic avalanches, lahars, pyroclastic surges), and here we present its application to transient dilute pyroclastic density currents (PDCs). The numerical algorithm and the code have been improved to allow for simulation of sub- to supercritical regimes and to simplify the setting of initial and boundary conditions. The code is open-source. The results of synthetic numerical benchmarks demonstrate the robustness of the numerical code in simulating transcritical flows interacting with the topography. Moreover, they highlight the importance of simulating transient in comparison to steady-state flows and flows in 2D versus 1D. Finally, we demonstrate the model capabilities to simulate a complex natural case involving the propagation of PDCs over the sea surface and across topographic obstacles, through application to Krakatau volcano, showing the relevance, at a large scale, of non-linear fluid dynamic features, such as hydraulic jumps and von Kármán vortices, to flow conditions such as velocity and runout
The effects of vent location, event scale and time forecasts on pyroclastic density current hazard maps at Campi Flegrei caldera (Italy)
This study presents a new method for producing long-term hazard maps for pyroclastic
density currents (PDC) originating at Campi Flegrei caldera. Such method is based on
a doubly stochastic approach and is able to combine the uncertainty assessments on
the spatial location of the volcanic vent, the size of the flow and the expected time of
such an event. The results are obtained by using a Monte Carlo approach and adopting
a simplified invasion model based on the box model integral approximation. Temporal
assessments are modeled through a Cox-type process including self-excitement effects,
based on the eruptive record of the last 15 kyr.Mean and percentilemaps of PDC invasion
probability are produced, exploring their sensitivity to some sources of uncertainty and to
the effects of the dependence between PDC scales and the caldera sector where they
originated. Conditional maps representative of PDC originating inside limited zones of the
caldera, or of PDC with a limited range of scales are also produced. Finally, the effect of
assuming different time windows for the hazard estimates is explored, also including the
potential occurrence of a sequence of multiple events. Assuming that the last eruption
of Monte Nuovo (A.D. 1538) marked the beginning of a new epoch of activity similar to
the previous ones, results of the statistical analysis indicate a mean probability of PDC
invasion above 5% in the next 50 years on almost the entire caldera (with a probability
peak of 25% in the central part of the caldera). In contrast, probability values reduce
by a factor of about 3 if the entire eruptive record is considered over the last 15 kyr, i.e.,
including both eruptive epochs and quiescent periods
11th EGU Galileo Conference: Solid Earth and Geohazards in the Exascale Era Consensual Document
The 11th Galileo Conference in Barcelona (May 23-26, 2023) addressed Exascale computing challenges in geosciences. With 78 participants from 15 countries, it focused on European-based research but welcomed contributions from worldwide institutions. The conference had four sessions covering HPC applications, data workflows, computational geosciences, and EuroHPC infrastructures. It featured keynote presentations, poster sessions, and breakout sessions, including Master Classes for 22 Early Career Scientists supported by EGU. This document represents the consensus among participants, capturing outcomes from breakout sessions and acknowledging diverse opinions and approaches.The 11th Galileo Conference of the European Geosciences Union (EGU) focused on "Solid Earth and Geohazards in the Exascale Era." This abstract presents the main outcomes and conclusions from the conference breakout sessions, which aimed to provide recommendations for the future of solid earth research. The discussions highlighted the challenges and opportunities associated with high-performance computing (HPC) in solid earth sciences. The key findings include the need for collaboration between computer scientists and solid earth domain-specific scientists, the importance of portability software layers for different hardware architectures, the adoption of programming models for easier development and deployment of applications, the necessity of HPC training at all career stages, the improvement of accessibility and authentication mechanisms for European machines, and the readiness of urgent computing services for natural catastrophes. The conference also emphasized the significance of sustainable funding, software engineering best practices, and the development of modular and interoperable codes and workflows. Overall, the conference provided insights into the current status of computational solid earth research and offered recommendations for future advancements in the field.European Geosciences Union (EGU), the EuroHPC Center of Excellence for Exascale in Solid Earth (ChEESE) under Grant Agreement No 101093038 (https://cheese2.eu), and the European Union's Next Generation/PRTR Program through grant PCI2022-134973-2.Peer reviewe