1,720,978 research outputs found
Pyroclastic density currents: state of the art and perspectives
No full textPyroclastic density currents (PDCs) are mixtures of twocomponents, namely solid particles and fluid (gas) phase.
Theymacroscopically behave as dense,multiphase gravity currents (flowing pyroclastic mixtures of particles and
gas) immersed in a less dense, almost isotropic fluid (the atmosphere). As for other natural phenomena, their
study needs a multidisciplinary approach consisting of direct observations, analysis of the associated deposits,
replication through laboratory experiments, and numerical simulations. This review deals with the description
of the current state of the art of PDC physics, and combines analysis of data from various methodologies. All of
the above-mentioned approaches have provided significant contributions to advancing the state of the art;
in particular, laboratory experiments and numerical simulations deserve a special mention here for their tumultuous
growth in recent years.
A paragraph of the review is dedicated to the puzzling behaviour of large-scale ignimbrites,which are (fortunately)
too rare to be directly observed; they cannot be easily reproduced through laboratory experiments, or investigated
by means of numerical simulations.
The final part is dedicated to a summary of the whole discussion, and to a comment on some perspectives for
future developments of PDC studies
Computational fluid dynamic simulations of granular flows: Insights on the flow-wall interaction dynamics
Full text linkDry volcanic granular flows are gravity-driven currents composed of solid particles where particle-particle interactions dominate the motion. The interaction with topography is a relevant factor controlling the propagation of such flows. In this paper we investigate the dynamics of channelised volcanic granular flows by comparing large-scale experiments with multiphase computational fluid dynamic simulations using the Two-Fluid Model approach, with an emphasis on the dynamics regulating the flow-wall interactions. We use the software MFIX to carry out sensitivity analysis of the boundary conditions for the solid phase implemented in the numerical code. The sensitivity analysis shows how the choice of the boundary condition and of the relevant parameters controlling the boundary conditions highly affect the dynamics of the whole flow. Finally, a preliminary benchmark of the MFIX boundary conditions with one large-scale experiment is presented, showing good agreement between the simulated and experimental flow front velocities
The 17 July 1999 Block-And-Ash Flow (BAF) at Colima Volcano: new insights on volcanic granular flows from textural analysis
No full textInvestigating the effect of polydispersity on the dynamics of multiphase flows using computational fluid dynamics tools
Full text linkGranular flows consist of discrete macroscopic particles. If they are non-cohesive, their status is determined by the interaction of particle-particle frictional forces, external boundaries and gravity. In particular, the understanding of the transport mechanisms of granular materials is of paramount importance for the characterization of volcanic granular flows and for hazard assessments associated with these flows. In order to investigate dynamics of these kinds of flows, we replicated large-scale experiments with multiphase computational fluid dynamic (CFD) simulations using the Two-Fluid Model approach, with an emphasis on the polydispersity effect on the flow behaviour. The CFD simulations were run using the software MFIX. The present work consists of: 1) investigations on the drag force relationships implemented in MFIX; 2) applications of MFIX to replicate largescale experiments on volcanic dry granular flows sliding on an inclined channel; 3) comparisons between experimental and simulated data with particular emphasis on the velocity of the granular flow front. Simulations on polydisperse granular flows demonstrated the simulated flows capability to replicate segregation dynamics active in real granular flows, and the polydispersity effects on velocities and shapes of granular flows. The nonuniformity of solid phases highly affects the dynamic of the whole flow and results in a better agreement between simulated and experimental flow velocities than the simplest monodisperse particles systems. In particular, the greater the number of the solid phases, the lower the velocity of granular flows and the mean square error, which decreases by ca. 50%
Neural network classification of granular flows from audio signals: preliminary results
No full textGranulometric analysis is a key element in the study of geological granular flows. This category of flows includes some of the most dangerous phenomena known in geology. Knowing the size of the clasts flowing in a geological granular flow is extremely important to predict its behavior and hazard. This work combines the potential of neural networks (NN) with the task of classifying from monodisperse granular flows to determine the type of material and the granular size, directly from audio recordings. For this purpose, three NN models are proposed: one to classify the material (in this case, either dacite or bearing balls) and the other two to predict the granular size of each material. In addition, a data augmentation method based on surrogate audio signals is proposed to increase the amount of data. The results of these NN models are promising, as almost 99% of the 35,100 size predictions are located within 1 phi from the true size and more than 92% of the 21,600 material classifications are correct. Although in nature geological granular flows are polydisperse and our studies refer only to monodisperse materials, they represent a very important starting point for future studies where audio recordings from granular flows could be used as a discriminative data, with strong implications for civil protection
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Predicting the block-and-ash flow inundation areas at Volcán de Colima (Colima, Mexico) based on the present day (February 2010) status
No full textVent area and depositional mechanisms of the Neapolitan Yellow Tuff (Campi Flegrei, Italy): new insights from directional fabric through Image Analysis
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