78,040 research outputs found
The incrementally zoned Miocene Ayagaures ignimbrite (Gran Canaria, Canary Islands)
No full textThe 20–25 m thick trachyphonolitic Ayagaures ignimbrite cooling unit [(AY); 11.8 Ma] exposed over 250 km2 (onshore volume ca. 4.5 km3 DRE) is the uppermost and most voluminous cooling unit of the Middle Fataga Formation (MFF), part of the Fataga Group (ca. 13.3–ca. 9 Ma) on Gran Canaria (GC), Canary Islands (28°00′ N, 15°35′ W). Up to 19 flow units (named b–t) subdividing the AY have been identified throughout most of the area from proximally to the caldera wall to distally as far as 14 km away. Individual flow units were distinguished from each other and logged using mainly chemical criteria. Single and/or packages of flow units (A, B and C) are tentatively interpreted to correspond to compositionally distinct magma bodies erupted from the same magma reservoir. These source-controlled flow units are interpreted to reflect successive eruptive pulses during incremental subsidence of Tejeda caldera.
We subdivided AY cooling unit into four welding facies. Tentative correlation with a major syn-ignimbrite turbidite drilled during ODP Leg 157 suggests a total DRE volume of > 50 km3.
The cooling unit as a whole becomes less evolved upwards as shown by major elements, trace elements and REE of bulk rock and phenocrysts. All phenocryst phases, dominantly sanidine–anorthoclase (up to 20 vol.%), with minor biotite, augite, titanite, haüyne and apatite, are unzoned and show an incremental compositional zoning in the stratigraphy. The shallow level parent magma reservoir is interpreted to have undergone strong mixing prior to starting its final compositional zoning in a thermodynamically equilibrated reservoir. Compositional zoning resulted in three main bodies. This compositional and physical layering may have been triggered by rapid growth of alkali feldspar and biotite throughout the erupted part of the magma chamber. Abundant titanite and haüyne phenocrysts in basal flow units and in a locally preserved, highly evolved fallout tephra are interpreted to reflect initial evacuation of a small volume, highly fractionated cupola.
AY represents the most evolved part of a large, partially evacuated magma reservoir. Progressive downward tapping of the reservoir is interpreted to have been controlled by incremental caldera collapse. Absence of less evolved magmas suggests that the magma chamber was only partially evacuated. Incremental compositional zoning of the cooling unit, but unzoned phenocrysts and evacuation reversals show that mixing did not occur following initiation of alkali feldspar growth
Longobardica historia que a pleris[que] Aurea legenda sanctor~u appellatur siue Passionale sanctor~u
No full textNuestra emisora cultura Frecuencia U está de aniversario
No full textNuestra emisora cultural Frecuencia U celebra sus 5 años de emisión, un gran orgullo para nuestra Universida
A Dynamic Subfilter-scale Stress Model for Large Eddy Simulations Based on Physical Flow Scales
No full textWe propose a new definition of the length scale in an eddy-viscosity model for large-eddy simulations (LES). This formulation extends and generalizes a previous proposal [Piomelli, Rouhi and Geurts, Proc. ETMM10, 2014], in which the LES length scale was expressed in terms of the integral length-scale of turbulence determined by the flow characteristics and explicitly decoupled from the simulation grid; this approach was named Integral Length-Scale Approximation (ILSA). As in the original ILSA, the model coefficient was determined by the user, and required to maintain a desired contribution of the unresolved, subfilter scales (SFS) to the global transport. We propose a local formulation (local ILSA) in which the model coefficient is local in space, allowing a precise control over SFS activity as a function of location. This new formulation preserves the properties of the global model; application to channel flow and backward-facing step verifies its features and accuracy
Large-eddy simulation of a separated flow with a sub-filter scale model based on the integral length-scale
No full textA new sub-filter scale model for large-eddy simulations, which uses a length-scale proportional to the integral scale of the turbulence instead of the grid resolution to parametrize the modelled stresses, will be assessed in the prediction of the flow of a boundary-layer over a rough surface, which includes separation and reattachment
Near Wall PIV-Measurements on the Windward Slope of a Hill
No full textThe turbulent flow over periodic hills was measured near to the wall, using planar Particle-Image-Velocimetry (PIV) at high spatial resolution. Our focus is on the near wall turbulence structure on the windward slope of the hill. For large-eddy simulation (LES) we suspect that, if this was not predicted accurately, it affects the prediction of the velocity profiles over the hill crest which in turn will affect the recirculation length downstream of the hill. Regarding the time averaged velocities, we were able to resolve the linear viscous region of the boundary layer. The velocity distribution and also the Reynolds stress does not comply with the law of the wall as it is valid for a turbulent boundary layer at equilibrium
Energy dissipation and flux laws for unsteady turbulence
No full textDirect Numerical Simulations of spatially periodic unsteady turbulence show that the high Reynolds number scalings of the instantaneous energy dissipation rate and interscale energy flux at intermediate wavenumbers are qualitatively different from the well-known cornerstone scalings of equilibrium turbulence where and are time-dependent rms velocity and integral length-scales. Instead, they both scale as where and are length and velocity scales characterizing initial/overall unsteady turbulence conditions
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Real-space Manifestations of Bottlenecks in Turbulence Spectra
No full textAn energy-spectrum bottleneck, a bump in the turbulence spectrum between the inertial and dissipation ranges, is shown to occur in the non-turbulent, one-dimensional, hyperviscous Burgers equation and found to be the Fourier-space signature of oscillations in the real-space velocity, which are explained by boundary-layer-expansion techniques. Pseudospectral simulations are used to show that such oscillations occur in velocity correlation functions in one- and three-dimensional hyperviscous hydrodynamical equations that display genuine turbulence
Braid Entropy of Faraday Waves driven 2D Turbulence
No full textWe report new experimental results that use tools from braid theory to characterize two-dimensional turbulent flows driven by Faraday waves. The average topological length of the material fluid lines is found to grow exponentially with time. It allows us to compute the braid’s topological entropy SBraid. We show that SBraid increases as the square root of the turbulence kinetic energy E ~ u^2, where u^2 is the horizontal velocity variance . At long times, the PDFs of Lbraid are positively skewed and present strong exponential tails
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