1,721,046 research outputs found
Analogous of Hartman Effect for Relativistic Particles Through “Transparent” Barrier
No full textTunneling phase time through a rectangular transparent barrier for a relativistic particl
Tempo di transito nell'effetto tunnel in acustica
No full textTesi di Dottorato depositata presso le Bibloteche Nazionali di Roma e Firenz
Properties of the hybrid RANS/LES filter
No full textOne of the most important and challenging topics in the Large Eddy Simulation of turbulent flows is the connection of the LES technique to the well known and largely used RANS approach where the Navier-Stokes equations are Reynolds averaged. The hybridation of LES and RANS is not only important for its possible practical use, (a rational use of the computational means in different zones), but also from a theoretical point of view, and one possible procedure consists of blending RANS and LES models in the transition zone. In this paper a new filtering technique based on blending filters which transitions smoothly between LES and RANS is proposed and the associated universal model for the subgrid scale stresses is derived
Binding energy and equilibrium of compact objects
No full textThe theoretical analysis of the existence of a limit mass for compact astronomic objects
requires the solution of the Einstein’s equations of general relativity together with
an appropriate equation of state. Analytical solutions exist in some special cases like
the spherically symmetric static object without energy sources that is here considered.
Solutions, i.e. the spacetime metrics, can have a singular mathematical form (the so
called Schwarzschild metric due to Hilbert) or a nonsingular form (original work of
Schwarzschild). The former predicts a limit mass and, consequently, the existence of
black holes above this limit. Here it is shown that, the original Schwarzschild metric
permits compact objects, without mass limit, having reasonable values for central
density and pressure. The lack of a limit mass is also demonstrated analytically just
imposing reasonable conditions on the energy-matter density, of positivity and decreasing
with radius. Finally the ratio between proper mass and total mass tends to 2 for
high values of mass so that the binding energy reaches the limit m (total mass seen by a
distant observer). As it is known the negative binding energy reduces the gravitational
mass of the object; the limit of m for the binding energy provides a mechanism for stable
equilibrium of any amount of mass to contrast the gravitational collapse
The elementary energy transfer between the two-point velocity mean and difference
No full textIn this paper, the elementary energy transfer between the two-point average of a velocity field and the two-point difference has been examined. The equations related to the two-point quantities are derived from the Navier-Stokes equations applied to incompressible flows. Some interesting aspects of this simple transfer of energy are discussed both from the point of view of the filtered equations associated with the two-point velocity average and from the point of view of the properties of the structure functions associated with the two-point velocity difference. A new inertial relation valid for homogeneous flows is finally presented. (C) 2007 American Institute of Physic
The filtering formulation of the mixed subgrid model
No full textn this paper a new mixed model consistent with the filtering formulation has been derived as the subgrid model associated with the product GF of a similarity filter G with a functional filter F. The case where F is the Smagorinsky eddy viscosity filter is discussed in detail, and, in particular, it is shown that some ambiguities concerning the additive coefficient of the usual mixed subgrid model are automatically removed
A new deconvolution method for large eddy simulation
No full textIn this paper we present and we briefly discuss a new way to derive approximate deconvolution subgrid models for the large eddy simulation of turbulent flow
A direct relation between the filtered subgrid stress and the second order structure function
No full textIn this Brief Communication we rewrite the filtered subgrid stress in terms of velocity increments and we directly relate its mean value to the second order structure functio
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