1,721,157 research outputs found
Analytical and numerical solutions of the dynamic impact force of fluidized debris flows onto structures
No full textSimulation of mechanical effects due to the impact of fluid-like debris flows on structures
No full textDesign criteria usually applied to estimate the impact force acted
by a fluid-like debris flow against a structure generally neglect the
actions arising during the initial phase of the impact phenomenon.
Recent theoretical studies, mainly developed in the field of
coastal engineering, point out, however, the importance of this phase;
unfortunately, impact tests reported in literature do not supply results
useful to propose simple, but reliable, rules to design safeguarding
measures, since recorded impact pressures are widely scattered.
In the paper, the initial, impulsive phase of the impact of fluid
bodies against structures is numerically (FEA) analysed: simulations
are carried out by taking into account different models.
Proposed results allow to identify the most important physical and
mechanical governing factors, to understand their role in the time
evolution of the impact force as well as to estimate the corresponding
mechanical effects, such as structural damages and displacements
of boulders
Impact between fluids and solids: comparison between analytical and FEA results
No full textTheoretical and numerical analyses of the dynamic force acted on structures by fluid-like debris flows (d.f.) or fluids are presented. Current analyses of the interaction between d.f. and structures usually take into account a modified hydrodynamic pressure or a multiple of the hydrostatic pressure, to determine the impact force. A close examination of analytical and experimental results, mainly pertaining to hydraulic and coastal engineering, regarding the impact of water waves against coastal facilities, however, reveals that these simplified assumptions are not supported by rational presumptions. Numerical (FE) analyses have been therefore carried out and their results compared to the available theoretical and numerical results in the literature. The importance of the impulsive phase of the impact phenomenon, especially if a planar d.f. front face is parallel to the impacted structure, is put into evidence. Proposed FEA results highlight the role of fluid's speed, density and compressibility in the general problem of the impact of fluids against structures. (C) 2008 Elsevier Ltd. All rights reserved
Parameters of the Earth’s Free Core Nutation from Diurnal Strain Tides
No full textEarth deformation at the diurnal tidal frequencies includes the resonant tidal-forcing response caused by the Free Core Nutation (FCN), a retrograde mode related to the slight misalignment of the rotation axes of the outer core and mantle. We analyse data from four underground high-sensitivity laser extensometers, whose signal-to-noise ratio in the diurnal tidal band is particularly high, and provide an alternative independent estimate of the FCN complex frequency with respect to more usual techniques (nutation and gravity). Firstly, we differentiate displacements due to diurnal solid tides to obtain extension along any azimuthal direction in terms of three complex parameters (A, S, C) which depend on latitude and frequency. Then, we demonstrate that we can invert the FCN complex frequency and the sensitivity of Im(A) and Re(S) to the resonance from our data. Lastly we obtain the probability distributions of those four parameters. Our results are in full agreement with those from nutation and gravity, as well as with reference IERS (International Earth Rotation and Reference Systems Service) values. Sensitivities of Im(A) and Re(S) to the resonance are estimated here for the first time and are in agreement with values computed using reference Love and Shida numbers from IERS
Analisi dell’impatto di colate detritiche ad alta velocità contro strutture
Full text linkL’obiettivo della presente tesi è l’identificazione delle azioni esplicate dalle masse in movimento all’impatto contro strutture. A causa dell’estrema variabilità delle concentrazioni di solidi nella massa in movimento, che ne determina il comportamento, sono stati considerati modelli di comportamento semplificati: impatto di sospensioni fluide; impatto di blocchi isolati; impatto di correnti granulari asciutte.
Nel presente rapporto sono innanzitutto sinteticamente descritte soluzioni teoriche, tratte dalla letteratura tecnica, del problema dell’interazione tra fluidi e solidi; sono quindi esposti i risultati di un’attenta disamina di dati sperimentali ottenuti da ricercatori di diversi discipline (ingegneria geotecnica, idraulica, costiera) sul tema. Sono infine presentati i risultati di analisi numeriche condotte con un codice di calcolo agli elementi finiti, con lo scopo di definire le azioni che le colate con comportamento tipo fluido esplicano all’impatto contro solidi. La medesima organizzazione della trattazione è ripetuta per lo studio dell’impatto di blocchi e correnti granulari.
Il lavoro si chiude con l’esposizione di alcuni casi applicativi studiati per via numerica, volti ad identificare gli effetti meccanici dell’impatto di colate, sia con comportamento fluido, sia blocchi, e con la proposta di criteri di progettazione delle strutture di mitigazione.The report deals with the characterization of the dynamic forces acted on structures by a fast moving debris flow.
Due to the heterogeneity of the involved materials, the work has been organized into three sections: impact of fluid-like debris flows; impact of blocks, impact of dry granular matter
Inversion of synthetic geodetic data for the 1997 Colfiorito events: clues on the effects of layering, assessment of model parameter PDFs, and model selection criteria
No full textThe 1997 September-October Umbria-Marche sequence has been extensively studied in the past by analyzing
coseismic displacement data (GPS, leveling, SAR). Here we focus on synthetic data representative of the main
event of the 1997 Umbria-Marche sequence and investigate the effects of a crustal layering proper to the Colfiorito
area on surface displacements and inferred source features when inverting coseismic geodetic data without
taking into account layering. We compare bootstrapping and NA-Bayes as tools for parameter uncertainty assessment
and show how the Akaike Information Criterion can be used to select the model which is most likely
to be correct. Since SAR images offer the most complete coverage of the study area, we use synthetic line-ofsight
displacement data.JCR Journalope
Clues of Ongoing Deep Magma Inflation at Campi Flegrei Caldera (Italy) from Empirical Orthogonal Function Analysis of SAR Data
Full text linkUnderstanding the characteristics of a volcanic system is always important and becomes crucial when the volcano is in pluri-decadal unrest and located in a densely populated area, such as Campi Flegrei caldera, Italy. Ground deformation is a powerful source of information for studying the activity of magmatic sources and hydrothermal systems, even when difficult to detect otherwise. Here, we use ground displacement from ERS-ENVISAT and Sentinel-1A SAR images to investigate the 1993–2000 subsidence and part (2015–2022) of the present unrest. For each of the two time periods, we combine the line-of-sight displacements to obtain vertical and eastward displacements, and apply the empirical orthogonal function analysis to these latter time series—treated as a single data set—to decompose space-time fields into separated modes, consisting of uncorrelated spatial patterns and associated temporal evolutions. We only retain the first mode, since it captures the main deformation during both investigated periods, is the sole mode related to long-lasting (years) processes, and is less affected by noise than original data. Our analyses: (i) Confirm that most of the deformation is related to the activity of a 3–4 km deep sill-like source, which is inflated by magma and/or magmatic fluids during periods of unrest and deflates during periods of subsidence; (ii) Evidence ongoing deformation linked to local fluid migration in the Solfatara area; (iii) Identify persistent deformation features where peculiar fluid migration processes occurred during the 1982–1984 unrest; (iv) Most importantly, provide direct evidence of deep magma inflation at least since 2015, thus giving a strong warning of increasing risk at Campi Flegrei. Results demonstrate the capability of our approach to disclose hardly detectable processes and suggest a tool to monitor the activity of the deep magmatic source. Our approach can be useful also in other volcanic systems
DInSAR Data Reveal an Intriguing Contemporaneous Onset of Deep Deflation below Vesuvio and the Ongoing Campi Flegrei Uplift
No full textCampi Flegrei and Vesuvio volcanoes are only about 25 km apart, located on opposite sides of the densely inhabited area of Naples (Italy). Since neighbouring volcanoes may influence each other’s activity, it is of great interest to identify signs of any mutual interaction between Campi Flegrei and Vesuvio, or at least note coincidences in their recent deformation dynamics. After a large uplift, Campi Flegrei was generally subsiding from 1985 to 2001, while it has been uplifting—probably driven by deep magma inflation—at an accelerating rate since then. Here, we analysed the ground displacement in the whole Vesuvian area and its surroundings around the early 2000s using 1993–2010 ERS/ENVISAT ascending- and descending-orbit line-of-sight displacements obtained through the Small BAseline Subset Differential Synthetic Aperture Radar Interferometry technique. Although ground deformation is slow—a few millimetres per year—Empirical Orthogonal Function analysis shows a sudden trend change around 2001. Pre-2001 velocity maps confirm previously published results: subsidence mainly occurred inside the caldera rim—probably because of the sliding and compaction of young incoherent materials—and in a few spots around 10 km from the summital crater; eastward displacement occurred in a lobe east of Vesuvio, and westward displacement occurred in a lobe west of Vesuvio, as in the case of the spreading of the volcanic edifice and/or extensional tectonics. We attribute the subsidence spots to the previous high local number of new buildings per year. Post-2002 velocity maps provide evidence of a very different scenario: general subsidence in the whole Vesuvian area, westward displacement in a lobe east of Vesuvio, and eastward displacement in a lobe west of Vesuvio. This last arrangement of the ground displacement field is made even clearer by subtracting the post-2002 velocity from the pre-2001 value. The results of our analyses are consistent with the deflation of a deep pressurised source. Additionally, Vesuvio’s deep seismicity decreased at the beginning of 2002. The coincidence between the transition from deflation to inflation at Campi Flegrei and the onset of deflation below Vesuvio may suggest the possible transfer of magma and/or magmatic fluids between the two plumbing systems
Prime valutazioni su alcuni impianti di arboricoltura realizzati in Puglia nell'ambito della campagna 1994/96 del Reg. CEE 2080/92
No full textAn Approximate Approach to Nonisothermal Emplacement of Kilometer-Sized Kilometer-Deep Sills at Calderas
No full textCaldera unrest is often caused by kilometer-sized kilometer-deep sills. Still unanswered questions include the following: How do sills spread? Why can magma propagate for kilometers without solidifying? Why do ground deformation data rarely, if ever, detect sill propagation? We show that kilometer-sized kilometer-deep magmatic sills spread like hydraulic fractures in an infinite medium. How magma propagates depends on overburden pressure, magma viscosity, injection rate, and difference between magma and rock temperatures. A small lag, filled with vapors from the fluid and/or the rock, exists between the propagating magma and fracture fronts. If the sill spreads along an interface, the lag slightly affects isothermal sill spreading but takes a key role in the case of nonisothermal propagation: A sill would stop after few tens of meters without it, unless magma intrudes rocks that are as hot as the solidification temperature or has unrealistic overpressures, because spreading velocity decreases soon to the critical value at which the tip becomes blocked with solidified magma. The lag defers magma solidification as heat exchange between the magma and the rock is effective only behind the thermal-insulating lag, where magma has some finite thickness and sill opening grows with distance from the tip faster than thickness of solidified magma. Thus, the critical velocity decreases, allowing greater maximum sill sizes. We also show that the ground deformation pattern does not change appreciably over time if the final sill radius is smaller than 2 to 3 km, explaining why deformation is usually attributed to the inflation of a stationary source
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