A fully Eulerian solver for the simulation of multiphase flows with solid bodies: application to surface gravity waves

In this paper a fully Eulerian solver for the study of multiphase flows for simulating the propagation of surface gravity waves over submerged bodies is presented. We solve the incompressible Navier-Stokes equations coupled with the volume of fluid technique for the modeling of the liquid phases with the interface, an immersed body method for the solid bodies and an iterative strong-coupling procedure for the fluid-structure interaction. The flow incompressibility is enforced via the solution of a Poisson equation which, owing to the density jump across the interfaces of the liquid phases, has to resort to the splitting procedure of Dodd & Ferrante [12]. The solver is validated through comparisons against classical test cases for fluid-structure interaction like migration of particles in pressure-driven channel, multiphase flows, water exit of a cylinder and a good agreement is found for all tests. Furthermore, we show the application of the solver to the case of a surface gravity wave propagating over a submerged reversed pendulum and verify that the solver can reproduce the energy exchange between the wave and the pendulum. Finally the three-dimensional spilling breaking of a wave induced by a submerged sphere is considered

Beyond Shallow Water: appraisal of a numerical approach to hydraulic jumps based upon the Boundary Layer Theory

International audienceWe study the flow of a thin layer of fluid over a flat surface. Commonly, the 1-D Shallow-water or Saint-Venant set of equations are used to compute the solution of such flows. These simplified equations may be obtained through the integration of the Navier-Stokes equations over the depth of the fluid, but their solution requires the introduction of constitutive relations based on strict hypothesis on the flow régime. Here, we present an approach based on a kind of boundary layer system with hydrostatic pressure. This relaxes the need for closure relations which are instead obtained as solutions of the computation. It is then demonstrated that the corresponding closures are very dependent on the type of flow considered, for example laminar viscous slumps or hydraulic jumps. This has important practical consequences as far as the applicability of standard closures is concerned

Numerical Simulations of Vorticity Banding of Emulsions in Shear Flows

Multiphase shear flows often show banded structures that affect the global behavior of complex fluids e.g. in microdevices. Here we investigate numerically the banding of emulsions, i.e. the formation of regions of high and low volume fraction, alternated in the vorticity direction and aligned with the flow (shear bands). These bands are associated with a decrease of the effective viscosity of the system. To understand the mechanism of banding experimentally observed we have performed interface resolved simulations of the two-fluid system. The experiments were perfomed starting with a random distribution of droplets which, under the applied shear, evolves in time resulting in a phase separation. To numerically reproduce this process, the banded structures are initialized in a narrow channel confined by two walls moving in opposite direction. We find that the initial banded distribution is stable when droplets are free to merge and unstable when coalescence is prevented. In this case, additionally, the effective viscosity of the system increases, resembling the rheological behavior of suspensions of deformable particles. Droplets coalescence, on the other hand, allows emulsions to reduce the total surface of the system and hence the energy dissipation associated to the deformation, which in turn reduces the effective viscosity

A case study for spacegate point-to-point transportation: Evaluation of a reference end-to-end mission operations and assessment of the associated safety aspects

The ALTEC-conducted Spacegate feasibility study addresses the opportunities offered by the sub-orbital flight with special emphasis to future generation transportation. Pursuing the same systemic methodology of the initial Spacegate definition activities, this paper focuses on some specific aspects of suborbital operations and outlines a top level end-to-end operating cycle for a reference suborbital mission spanning from pre-flight, to flight, re-entry and post landing operations and associated Ground Segment. Special focus is given to identification of suitable locations in Italy for suborbital operations, and to liftoff and re-entry phases; the results of specific simulations are also reported, showing some lift off options and the feasibility of the spiral shaped descent maneuver that improves the pilot controllability of the vehicle during the re-entry phase. Further, this paper outlines within the selected reference mission, the main safety aspects considered as driving factors in planning and implementing future generation transportation; areas such as launch/landing range and relevant risk management/mitigation policies, as well as selection of safety driving criteria in the definition of trajectories and space transition corridors, and capabilities to monitor the vehicle ascent and re-entry will be assessed. Safety regulations will also be evaluated to protect launch range, drive spaceport site selection and consequently the ability of the spaceport to accommodate large numbers of passengers and participants, as well as a number of simultaneous operations such as training, vehicle integration tasks, and passenger preparation for flight. For human flight in general, and in particular for commercial point to point activities at this early stage, it is vital to minimize risk since a fatal accident at the very beginning of flights will put the entire business in jeopardy. The regulatory challenges with regards to safety will also be outlined in this paper, related to executing Spacegate activities in Europe and collaborations with the involved Agencies in the USA and Europe (FAA, ENAC, ENAV, SESAR, EASA) will be explored; in particular, some initiatives have already been started, that include active ALTEC participation to the IAASS Space Safety Technical Committee (SSTC) that was created to contribute to the advancement of the Safety in the area of the "Commercial Suborbital Flight"

Corpi ribelli: bullizzate e bulle nella transizione identitaria adolescenziale

Leggere il bullismo attraverso una prospettiva di genere è un’esigenza maturata grazie al riconoscimento di un gap presente in letteratura che legge i fenomeni sociali come universali neutro-maschili. A partire dalla riflessione femminista e intersezionale sull’educazione di genere e sulla base dei dati raccolti attraverso cinque focus group condotti in tre scuole veronesi con studentesse maggiorenni, l’articolo approfondisce l’articolazione del bullismo femminile a scuola. Interpretare la dinamica del bullismo alla luce della sessuazione e delle costruzioni sociali relative all’identità di genere apre a nuovi significati sull’aggressività tra ragazze altrimenti omologati a quelli tra ragazzi. In questo saggio, ci soffermeremo sui principali pattern comportamentali emersi dall’indagine e che riguardano la corporeità nella sua dimensione materiale ed estetica. In adolescenza i corpi si ribellano, diventando arene e campi di battaglia per l’affermazione identitaria delle ragazze.The need for a gender-specific reading of bullying is apparent from an examination and assessment of the literature, and the consequent recognition of the gap created in the literature by the practice of reading social phenomena as universal and gender neutral. Taking feminist and intersectional considerations of gender education as its starting point and based on the data collected through five focus groups conducted with female adult students in three schools in Verona, the article explores the articulation of female bullying at school. Interpreting the dynamics of bullying in the light of sex and social constructs related to gender identity offers new understandings of aggression between girls, which is otherwise treated as the same as that between boys. In this paper, we consider the principal behavioral patterns that emerge in the study relating to corporality in its material and aesthetic dimensions. During adolescence, bodies rebel, becoming arenas and battlefields for the affirmation of girls’ identity

MULTI-SCALE ASSESSMENT OF GROUNDWATER VULNERABILITY TO POLLUTION: STUDY CASES FROM CAMPANIA REGION (SOUTHERN ITALY)

In the Campania region (southern Italy), assessment of groundwater vulnerability is an important factor to be tackled for a proper management of risk to aquifer pollution, which is fostered by both high dependence of aqueduct systems on groundwater resources and the widespread agricultural and urbanized land uses of the territory. The different physiographic, geological and hydrogeological conditions of the region, coupled with high anthropic pressure, make such assessment complex to be dealt with, but at the same time mandatory to be accomplished. The proposed study has been developed into the framework of the “Campania Trasparente” project, which has been funded by the regional government to assess environmental factors controlling the quality of agricultural and livestock food productions. Specifically, it belongs to the research topic regarding the assessment of groundwater quality, with a special focus on the assessment of groundwater vulnerability. In this research a multi-scale approach for the assessment of groundwater vulnerability is carried out in order to propose suitable methods depending on extension of territory to be studied and related types and spatial density of available data. Scales considered were a) regional, including the whole Campania region; b) intermediate, identified with that of a single representative aquifer; c) site-specific, or local, related to a portion of aquifer for which a high spatial density of data is available.The applied methods were chosen among the many known in literature and adapted to the specific study cases. At the regional scale, the parametric SINTACS method (CIVITA & DE MAIO, 2000) has been applied to the whole region and adapted to types and spatial density of available data. At the intermediate scale, or aquifer scale, the Mt. Terminio karst aquifer was chosen as representative for the application of different parametric methods, also specifically designed for karst aquifers. At the site-specific scale, a representative sector of a shallow alluvial aquifer, located in the adjoining Casalnuovo di Napoli-Volla municipalities, in the Campania plain, at the eastern border of the city of Naples, has been studied by numerical modeling for the estimation of travel time of nitrate pollutant through the vadose zone. The obtained results can be conceived as useful for supporting a proper territorial planning aimed at the management of risk to pollution of groundwater resources

Coexistence of Ballistic and Fourier Regimes in the β Fermi-Pasta-Ulam-Tsingou Lattice

Commonly, thermal transport properties of one-dimensional systems are found to be anomalous. Here, we perform a numerical and theoretical study of the β-Fermi-Pasta-Ulam-Tsingou chain, considered a prototypical model for one-dimensional anharmonic crystals, in contact with thermostats at different temperatures. We give evidence that, in steady state conditions, the local wave energy spectrum can be naturally split into modes that are essentially ballistic (noninteracting or scarcely interacting) and kinetic modes (interacting enough to relax to local thermodynamic equilibrium). We show numerically that the well-known divergence of the energy conductivity is related to how the transition region between these two sets of modes shifts in k space with the system size L, due to properties of the collision integral of the system. Moreover, we show that the kinetic modes are responsible for a macroscopic behavior compatible with Fourier's law. Our work sheds light on the long-standing problem of the applicability of standard thermodynamics in one-dimensional nonlinear chains, testbed for understanding the thermal properties of nanotubes and nanowires

Genetic variation for the duration of pre-anthesis development in durum wheat and its interaction with vernalization treatment and photoperiod

A recombinant inbred durum wheat population was grown under three contrasting regimes: long days following vernalization (LDV), long days without vernalization (LD), and short days following vernalization (SDV). The length of several pre-anthesis stages and the number of leaves and the phyllochron were measured. Different groups of genes were involved in determining the phenology in the three treatments, as demonstrated by a quantitative trait locus (QTL) analysis. The length of the period required to reach the terminal spikelet stage was correlated with the time to anthesis only in the case of LDV- and LD-grown plants where the timing of anthesis depended on the final leaf number. However, for SDV-grown plants, anthesis date was more dependent on the length of the period between the terminal spikelet stage and anthesis and was independent of leaf number. The involvement of the phyllochron in determining the duration of pre-anthesis development was also treatment-dependent. QTL mapping of the various flowering time associated traits uncovered some novel loci (such as those associated with the phyllochron), in addition to confirming the presence of several well-established loci

Generalization and Robustness Implications in Object-Centric Learning

The idea behind object-centric representation learning is that natural scenes can better be modeled as compositions of objects and their relations as opposed to distributed representations. This inductive bias can be injected into neural networks to potentially improve systematic generalization and learning efficiency of downstream tasks in scenes with multiple objects. In this paper, we train state-of-the-art unsupervised models on five common multi-object datasets and evaluate segmentation accuracy and downstream object property prediction. In addition, we study systematic generalization and robustness by investigating the settings where either single objects are out-of-distribution -- e.g., having unseen colors, textures, and shapes -- or global properties of the scene are altered -- e.g., by occlusions, cropping, or increasing the number of objects. From our experimental study, we find object-centric representations to be generally useful for downstream tasks and robust to shifts in the data distribution, especially if shifts affect single objects