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Experimental study on the effects of fixed boundaries in channelized free surface dry granular flows
No full textINDAGINE SPERIMENTALE SULLA DINAMICA DI CORRENTI GRANULARI A SUPERFICIE LIBERA IN REGIME DI MOTO PERMANENTE
No full textExperimental investigations on free surface steady dry granular flows
No full textGeophysical flows, like rock avalanches, snow
avalanches and debris flows, involve the rapid motion of
granular media. The dynamics of these flows is still an
open problem due to the complexity of the flow
resistance mechanisms involved. In case of dry granular
flows two main resistance mechanisms have been
individuated: friction and collisions. In order to better
understand the constitutive behaviour, it is necessary to
provide local measurements of the main flow variables:
velocity and volume fraction.
To do so, we set up an experimental apparatus in which
a dry granular material was let flow in a flume with
transparent sidewalls and recorded by two high-speed
cameras to get both side-wall and free surface views.
Velocity profiles were, then, derived by PIV analysis
and a novel optical method was developed to estimate
the near-wall volume fractio
Experimental Investigation on the Effects of the Fixed Boundaries in Channelized Dry Granular Flows
No full textThe dynamics of granular mixtures, involved in several geophysical phenomena like rock avalanches and debris flows, is far from being completely understood. Several features of their motion, such as non-local and boundary effects, still represent open problems. An extensive experimental study on free-surface channelized granular flows is here presented, where the effects of the fixed boundaries are systematically investigated. The entire experimental data set is obtained by using a homogenous acetal-polymeric granular material and three different basal surfaces, allowing different kinematic boundary conditions. Velocity profiles at both the sidewall and the free surface are obtained by using high-speed cameras and the open-source particle image velocimetry code, PIVlab. Significantly, different sidewall velocity profiles are observed by varying the basal roughness and the flow depth. Owing to sidewall friction and non-local effects, such profiles exhibit a clear rheological stratification for high enough flow depths and they can be well described by recurring to composite functions, variously formed of linear, Bagnold and exponential scalings. Moreover, it has been discovered that transitions from one velocity profile to another are also possible on the same basal surface by merely varying the flow depth. This shape transition is due partly to the sidewall resistances, the basal boundary condition and, in particular, the occurrence/inhibition of basal grain rolling. In most of the experiments, the normal-to-bed velocity profiles and the velocity measurements at the free surface strongly suggest the occurrence of a secondary circulating flow, made possible by a chiefly collisional regime beneath the free surface
MISURE DI VELOCITÀ E CONCENTRAZIONE IN CORRENTI GRANULARI SECCHE IN CONDIZIONI DI MOTO PERMANENTE
No full textAlcuni aspetti della dinamica dei miscugli granulari, osservabili in natura nei debris flow e nelle valanghe
di roccia, non sono ancora del tutto compresi. In particolare, alcune caratteristiche del moto, come gli effetti
di tipo non locale, delle condizioni al contorno e la stratificazione reologica risultano ancora un problema
aperto (GDR MiDi, 2005; Jop 2015). Le indagini sperimentali a scala di laboratorio rappresentano dunque un
utile strumento per una migliore comprensione del comportamento dinamico di questo tipo di miscugli. In
particolar modo, indagini non invasive, quali i metodi di tipo ottico, risultano essere un valido strumento per
la misura delle principali grandezze che intervengono nella definizione della dinamica dei flussi granulari,
ovvero la velocità e la concentrazione solida. La particle image velocimetry (PIV) è stata recentemente
estesa con successo alle misure di velocità nei miscugli granulari (Eckart et al., 2003; Sarno et al., 2014).
Meno numerose sono, invece, le tecniche ottiche proposte per la misura della concentrazione. In questo
lavoro vengono presentati i risultati di una campagna sperimentale volta allo studio di flussi granulari secchi
in moto permanente in condizioni di scivolamento al fondo. Il flusso è stato ripreso tramite telecamere ad
alta velocità. Per la misura della concentrazione è stata utilizzata la tecnica proposta da Sarno et al. (2016)
Experimental investigations on granular flows
Full text link2017 - 2018Granular flows, such as debris avalanches, debris flows and rock avalanches, involve the rapid motion of granular mixtures consisting of sediments, water and air. They occur on steep slopes and in the hydrographic network and can effect anthropized areas causing damage to buildings, roads and, in the worst case, loss of human lives... [edited by Author]XXXI cicl
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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