Direct numerical simulation of the oscillatory flow around a sphere resting on a rough bottom

The oscillatory flow around a spherical object lying on a rough bottom is investigated by means of direct numerical simulations of continuity and Navier-Stokes equations. The rough bottom is simulated by a layer/multiple layers of spherical particles, the size of which is much smaller that the size of the object. The period and amplitude of the velocity oscillations of the free stream are chosen to mimic the flow at the bottom of sea waves and the size of the small spherical particles falls in the range of coarse sand/very fine gravel. Even though the computational costs allow only the simulation of moderate values of the Reynolds number characterizing the bottom boundary layer, the results show that the coherent vortex structures, shed by the spherical object, can break-up and generate turbulence, if the Reynolds number of the object is sufficiently large. The knowledge of the velocity field allows the dynamics of the large scale coherent vortices shed by the object to be determined and turbulence characteristics to be evaluated. Moreover, the forces and torques acting on both the large spherical object and the small particles, simulating sediment grains, can be determined and analysed, thus laying the groundwork for the investigation of sediment dynamics and scour developments.Comment: 35 pages, 21 figure

Direct numerical simulation of open-channel flow over a fully-rough wall at moderate relative submergence

Direct numerical simulation of open-channel flow over a bed of spheres arranged in a regular pattern has been carried out at bulk Reynolds number and roughness Reynolds number (based on sphere diameter) of approximately 6900 and 120, respectively, for which the flow regime is fully-rough. The open-channel height was approximately 5.5 times the diameter of the spheres. Extending the results obtained by Chan-Braun et al. (J. Fluid Mech., vol. 684, 2011, 441) for an open-channel flow in the transitionally-rough regime, the present purpose is to show how the flow structure changes as the fully-rough regime is attained and, for the first time, to enable a direct comparison with experimental observations. The results indicate that, in the vicinity of the roughness elements, the average flow field is affected both by Reynolds number effects and by the geometrical features of the roughness, while at larger wall-distances this is not the case, and roughness concepts can be applied. The flow-roughness interaction occurs mostly in the region above the virtual origin of the velocity profile, and the effect of form-induced velocity fluctuations is maximum at the level of sphere crests. The spanwise length scale of turbulent velocity fluctuations in the vicinity of the sphere crests shows the same dependence on the distance from the wall as that observed over a smooth wall, and both vary with Reynolds number in a similar fashion. Moreover, the hydrodynamic force and torque experienced by the roughness elements are investigated. Finally, the possibility either to adopt an analogy between the hydrodynamic forces associated with the interaction of turbulent structures with a flat smooth wall or with the surface of the spheres is also discussed, distinguishing the skin-friction from the form-drag contributions both in the transitionally-rough and in the fully-rough regimes.Comment: 46 pages, 26 figure

Mingling and mixing features in basaltic Andesites of the Eastern Cordillera (Central Andes, 24°s): a petrographic and microanalytical study

The basaltic andesites of the Diego de Almagro volcanic complex (Central Andes, 24°S, 66°W) were erupted during Late Miocene at 300 km from the active arc, in the Eastern Cordillera, at the easternmost end of an important strike-slip structure, the Calama-Olocapato-El Toro. These volcanic rocks preserved traces of their pristine history in the form of xenocrysts and in the diverse populations of phenocrysts coexisting due to magma mixing. In Central Andes, crustal contamination commonly conditions the composition of magmas ascending through the thick continental crust, masking the characteristics of the mantle sources. Thus, we carried out detailed petrography and mineral chemistry studies on selected Diego de Almagro basaltic andesites, with the aim to identify the populations of crystals in equilibrium with mafic melts. The results suggested that mixing of basaltic and andesitic magmas occurred during the ascent and storage in the crust. The fraction of basaltic magma prevailed in the mixing process compared to the andesitic one. Crystal zoning and disequilibrium features indicate that magma mixing produced intimate hybridisation. The preservation of primitive crystal assemblages is probably due to the geological situation in which the Diego de Almagro complex emplaced, that favoured the formation of monogenetic volcanic centres rather than of a central volcanic edifice, thus limiting the residence of mafic magmas in the crust and their interaction with crustal partial melts.Le andesiti basaltiche appartenenti al complesso vulcanico Diego de Almagro (Ande Centrali, 24°S, 66°W) sono state emesse nel Miocene Superiore a ben 300 km verso E dall’arco attivo, nella Cordigliera Orientale, all’estremo orientale di una delle più importanti strutture trascorrenti trasversali andine, la Calama-Olocapato-El Toro. Le lave e le piroclastiti di questo complesso vulcanico conservano tracce della loro storia evolutiva sotto forma di xenocristalli e di popolazioni di cristalli in disequilibrio che coesistono grazie a processi di mixing di magmi a diversa composizione. Nelle Ande Centrali, la contaminazione crostale condiziona fortemente la composizione dei magmi che risalgono attraverso la spessa crosta continentale, mascherando le caratteristiche della sorgente mantellica. Per questo motivo, abbiamo ritenuto interessante effettuare uno studio di dettaglio della petrografia e della chimica dei minerali delle andesiti basaltiche di Diego de Almagro, allo scopo di identificare le popolazioni di cristalli in equilibrio con i magmi più primitivi. I risultati raccolti finora hanno mostrato che le andesiti basaltiche sono il prodotto di un processo di mescolamento di magma basaltico ed andesitico verificatosi durante la risalita del magma nella crosta, in condizioni pre-eruttive. Nel processo di mixing che ha prodotto le andesiti basaltiche la frazione di magma basaltico era prevalente in volume rispetto a quella di magma andesitico, e le proprietà fisicochimiche dei due magmi permisero la realizzazione di una avanzata ibridizzazione. L’associazione mineralogica primitiva si è potuta preservare grazie alla particolare situazione geologica del complesso Diego de Almagro, che favoriva la formazione di centri monogenetici piuttosto che lo sviluppo di vulcani centrali, limitando così lo stazionamento dei magmi basici nei serbatoi crostali e di conseguenza l’interazione con la crosta.Fil: Gioncada, Anna. Università degli Studi di Pisa; ItaliaFil: Hauster, Natalia. Universidad Nacional de Salta. Facultad de Ciencias Naturales; ArgentinaFil: Matteini, Massimo. Universidade do Brasília; BrasilFil: Mazzuoli, Roberto. Università degli Studi di Pisa; ItaliaFil: Omarini, Ricardo Hector. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentin

INTERNATIONALIST DIALOGICAL MONISM

The unprecedented issue I bring today for my readers’ reflection aims to propose a new monistic solution to the proble m of the relations between International Law (of Human Rights) and domestic Law. What I explain below will be incorporated in the 5th edition of my Course of Public International Law, published by the Revista dos Tribunais, and expected to arrive to the readers later this year of 2010

Tribunal Penal Internacional e o direito brasileiro

Divulgação dos SUMÁRIOS das obras recentemente incorporadas ao acervo da Biblioteca Ministro Oscar Saraiva do STJ. Em respeito à lei de Direitos Autorais, não disponibilizamos a obra na íntegra. STJ00081093 341.4 M478t 2.ed. STJ00088047 3.ed

Direct Numerical Simulations of the Pulsating Flow over a Plane Wall

The results of direct numerical simulations of the flow generated in a plane duct by a pressure gradient which is the sum of two terms are described. The first term of the pressure gradient is constant in space but it oscillates in time whereas the second term is constant both in space and in time. Therefore, a pulsating flow is generated, similar to that generated at the bottom of a monochromatic propagating surface wave when nonlinear effects are taken into account. The simulations are carried out for values of the parameters similar to those considered in previous investigations. It is shown that even a small constant pressure gradient influences the flow regime in the bottom boundary layer. In particular, turbulence strength is damped when the steady velocity component has the direction opposite to the oscillating velocity component whereas turbulence strength increases when the steady and oscillating components point in the same direction. Even though the flow is not exactly equal to that generated at the bottom of sea waves, where second order effects in the wave steepness induce a steady streaming in the direction of wave propagation, our results provide information on the interaction of the steady streaming with the oscillatory flow and are also relevant for investigating the dynamics of sediment close to the sea bottom. Indeed, since the turbulent eddies tend to pick-up the sediment from the bottom, it can be inferred that the triggering of turbulence enhances sediment transport towards the shore

Direct numerical simulations of ripples in an oscillatory flow

Sea ripples are small-scale bedforms which originate from the interaction of an oscillatory flow with an erodible sand bed. The phenomenon of sea ripple formation is investigated by means of direct numerical simulation in which the sediment bed is represented by a large number of fully-resolved spherical grains (i.e, the flow around each individual particle is accounted for). Two sets of parameter values (differing in the amplitude and frequency of fluid oscillations, among other quantities) are adopted which are motivated by laboratory experiments on the formation of laminar rolling-grain ripples. The knowledge on the origin of ripples is presently enriched by insights and by providing fluid- and sediment-related quantities that are difficult to obtain in the laboratory (e.g. particle forces, statistics of particle motion, bed shear stress). In particular, detailed analysis of flow and sediment bed evolution has confirmed that ripple wavelength is determined by the action of steady recirculating cells which tend to accumulate sediment grains into ripple crests. The ripple amplitude is observed to grow exponentially consistent with established linear stability analysis theories. Particles at the bed surface exhibit two kinds of motion depending on their position with respect to the recirculating cells: particles at ripple crests are significantly faster and show larger excursions than those lying on ripple troughs. In analogy with segregation phenomenon of polydisperse sediments the non-uniform distribution of the velocity field promotes the formation of ripples. The wider the gap between the excursion of fast and slow particles, the the larger the resulting growth rate of ripples. Finally, it is revealed that, in the absence of turbulence, the sediment flow rate is driven by both the bed shear stress and the wave-induced pressure gradient, the dominance of each depending on the phase of the oscillation period. In phases of maximum bed shear stress, the sediment flow rate correlates more with the Shields number while the pressure gradient tends to drive sediment bed motion during phases of minimum bed shear stress

A questão do reconhecimento de títulos de mestrado e doutorado provenientes dos países do MERCOSUL

O artigo examina o problema do reconhecimento de títulos de Mestrado e Doutorado provenientes dos países do MERCOSUL, cada vez mais crescente no Brasil a partir da proliferação de cursos stricto sensu nos demais países do bloco. O estudo conclui que o acordo firmado pelo Brasil no âmbito do MERCOSUL não exclui a exigência de revalidação nacional dos títulos de Mestrado e Doutorado, nos termos da Lei de Diretrizes e Bases da Educação

Direct Numerical Simulation of Oscillatory Flow Over a Wavy, Rough, and Permeable Bottom

The results of a direct numerical simulation of oscillatory flow over a wavy bottom composed of different layers of spherical particles are described. The amplitude of wavy bottom is much smaller in scale than typical bed forms such as sand ripples. The spherical particles are packed in such a way to reproduce a bottom profile observed during an experiment conducted in a laboratory flow tunnel with well-sorted coarse sand. The amplitude and period of the external forcing flow as well as the size of the particles are set equal to the experimental values and the computed velocity field is compared with the measured velocity profiles. The direct numerical simulation allows for the evaluation of quantities, which are difficult to measure in a laboratory experiment (e.g., vorticity, seepage flow velocity, and hydrodynamic force acting on sediment particles). In particular, attention is focused on the coherent vortex structures generated by the vorticity shed by both the spherical particles and the bottom waviness. Results show that the wavy bottom triggers transition to turbulence. Moreover, the forces acting on the spherical particles are computed to investigate the mechanisms through which they are possibly mobilized by the oscillatory flow. It was found that forces capable of mobilizing surface particles are strongly correlated with the particle position above the mean bed elevation and the passage of coherent vortices above them

Miocene sedimentation, volcanism and deformation in the Eastern Cordillera (24°30′ S, NW Argentina): Tracking the evolution of the foreland basin of the Central Andes

Understanding the relationships between sedimentation, tectonics and magmatism is crucial todefining the evolution of orogens and convergent plate boundaries. Here, we consider the lithostratigraphy, clastic provenance, syndepositional deformation and volcanism of the Almagro-El Toro basin of  W Argentina (24¡ã30¡ä S, 65¡ã50¡ä W), which experienced eruptive and depositional episodes between 14.3 and 6.4  a. Our aims were to elucidate the spatial and temporal record of the onset and style of the shortening and exhumation of the Eastern Cordillera in the frame of the Miocene evolution of the Central Andes foreland basin. The volcano-sedimentary sequence of the Almagro-El Toro basin consists of lower red floodplain sandstones and siltstones, medial non-volcanogenic conglomerates with localised volcanic centres and upper volcanogenic coarse conglomerates and breccia. Coarse, gravity flow-dominated (debris-flow and sheet-flow) alluvial fan systems developed proximal to the source area in the upper and medial sequence. Growing frontal and intrabasinal structures suggest that the Almagro-El Toro portion of the foreland basin accumulated on top of the eastward-propagating active thrust front of the Eastern Cordillera. Synorogenic deposits indicate that the shortening of the foreland deposits was occurring by 11.1 Ma, but conglomerates derived from the erosion of western sources suggest that the uplift and erosion of this portion of the Eastern Cordillera has occurred since ca.12.5 Ma. An unroofing reconstruction suggests that 6.5 km of rocks were exhumed. A tectono-sedimentary model of an episodically evolving thick-skinned foreland basin is proposed. In this frame, the NW-trending, transtensive Calama¨COlacapato¨CEl Toro (COT) structures interacted with the orogen, influencing the deposition and deformation of synorogenic conglomerates, the location of volcanic centres and the differential tilt and exhumation of the foreland.¡ã30¡ä S, 65¡ã50¡ä W), which experienced eruptive and depositional episodes between 14.3 and 6.4  a. Our aims were to elucidate the spatial and temporal record of the onset and style of the shortening and exhumation of the Eastern Cordillera in the frame of the Miocene evolution of the Central Andes foreland basin. The volcano-sedimentary sequence of the Almagro-El Toro basin consists of lower red floodplain sandstones and siltstones, medial non-volcanogenic conglomerates with localised volcanic centres and upper volcanogenic coarse conglomerates and breccia. Coarse, gravity flow-dominated (debris-flow and sheet-flow) alluvial fan systems developed proximal to the source area in the upper and medial sequence. Growing frontal and intrabasinal structures suggest that the Almagro-El Toro portion of the foreland basin accumulated on top of the eastward-propagating active thrust front of the Eastern Cordillera. Synorogenic deposits indicate that the shortening of the foreland deposits was occurring by 11.1 Ma, but conglomerates derived from the erosion of western sources suggest that the uplift and erosion of this portion of the Eastern Cordillera has occurred since ca.12.5 Ma. An unroofing reconstruction suggests that 6.5 km of rocks were exhumed. A tectono-sedimentary model of an episodically evolving thick-skinned foreland basin is proposed. In this frame, the NW-trending, transtensive Calama¨COlacapato¨CEl Toro (COT) structures interacted with the orogen, influencing the deposition and deformation of synorogenic conglomerates, the location of volcanic centres and the differential tilt and exhumation of the foreland.Fil: Vezzoli, Luigina. Università Degli Studi Dell'insubria; ItaliaFil: Acocella, Valerio. Università Roma Tre III; ItaliaFil: Omarini, Ricardo Hector. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mazzuoli, Roberto. Università degli Studi di Pisa; Itali