Mostrando recursos 181 - 200 de 106,591

  1. A preconditioning technique for Chebyshev collocated advection diffusion operators

    Pinelli, Alfredo; Benocci, C.; Deville, M.
    An original method for preconditioning Chebyshev collocated advection-diffusion operators is proposed. The preconditioner, based on an upwind finite difference approximation, is tested on one and two dimensional problems with both Neumann and Dirichlet boundary conditions.

  2. A Chebyshev collocation algorithm for the solution of advection—diffusion equations

    Pinelli, Alfredo; Benocci, C.; Deville, M.
    An original method to precondition Chebyshev collocated advection-diffusion operators is proposed. The preconditioner, based on an upwind finite difference approximation, is tested on one- and two-dimensional problems. The preconditioner behaves efficiently for advection-dominated cases and produces rates of convergence independent of the number of nodes. Finally, an 'ad hoc' designed multi-domain strategy is introduced.

  3. Control of the separated flow around an airfoil using a wavy leading edge inspired by humpback whale flippers

    Favier, J.; Pinelli, Alfredo; Piomelli, U.
    The influence of spanwise geometrical undulations of the leading edge of an infinite wing is investigated numerically at low Reynolds number, in the context of passive separation control and focusing on the physical mechanisms involved. Inspired by the tubercles of the humpback whale flippers, the wavy leading edge is modeled using a spanwise sinusoidal function whose amplitude and wavelength constitute the parameters of control. A direct numerical simulation is performed on a NACA0020 wing profile in a deep stall configuration (α=20°), with and without the presence of the leading edge waviness. The complex solid boundaries obtained by varying the sinusoidal...

  4. Infrared Space Observatory and Ground-Based Infrared Observation of the Classical Nova V723 Cassiopeiae

    Evans , A.; Gehrz, R.D.; Geballe, T.R.; Woodward, C.E.; Salama, A.; Antolin Sánchez, Roberto; Starrfield, S.G.; Krautter, S.G.; Barlow, M.; Lyke, J.E.; Hayward, T.L.; Eyres, S.P.S.; Greenhouse, M.A.; Hjellming, R.M.; Wagner, R.M.; Pequignot, D.
    We present observations of the classical nova V723 Cassiopeiae (Nova Cas 1995), obtained both with the Infrared Space Observatory (ISO) and from the ground. The infrared spectrum was dominated in the first year by H and He recombination lines, and at later times by coronal lines. The H recombination lines imply a reddening of E(B-V) = 0.78, an electron temperature of 7000 K, and an electron density of 2 × 108 cm-3 on day 250. We argue that the high-ionization species in the infrared are most likely the result of collisional ionization rather than photoionization and are therefore truly "coronal";...

  5. Digital terrain models determination by LIDAR technology : Po basin experimentation.

    Antolin Sánchez, Roberto; Brovelli, M. A.; Vismara, Francesco; Filippi, Federica
    The recent LIDAR (Light Detection and Ranging) technology allows the construction of digital surface models, characterized by high resolution and precision. This technology is based on the scansion of the territory by laser telemeters, transported on board of dedicated airplanes, whose position and attitude are determined by means of GPS differential measurements and INS (Inertial Navigation System) measurements. However, it is often necessary to produce more refined digital models, whose construction requires the identification of the existing objects on the territory (vegetation, buildings, infrastructures). The present activity enters this context, since its aim is the construction of different kinds of...

  6. LiDAR data filtering with GRASS GIS for the Determination of Digital Terrain Models.

    Antolin Sánchez, Roberto; Brovelli, M. A.

  7. Large eddy simulation of a fully turbulent plane channel flow

    Pinelli, Alfredo; Benocci, C.
    The development of a code for the large eddy simulation of wall bounded turbulent shear layers is described. The numerical approach selected is a finite difference discretization of the filtered Navier-Stokes equations, where the unresolved part of the turbulence is introduced through the Smagorinsky model of subgrid viscosity. A systematic study of the influence of mesh resolution, wall boundary condition and formulation of the advection term was performed for the case of a fully turbulent plane channel flow.

  8. Higgs effective potential in the littlest Higgs model at the one-loop level

    Dobado González, Antonio; Tabares Cheluci, Lourdes; Peñaranda , Siannah
    In this work we compute the contributions to the Higgs effective potential coming from the fermion and gauge boson sectors at the one-loop level in the context of the SU(5)/SO(5) littlest Higgs (LH) model using a cutoff Lambda and including all finite parts. We consider both, the (SU(2) x U(1))(1) x (SU(2) x U(1))(2) and the (SU(2) x U(1))(1) x (SU(2) x U(1)) gauge group versions of the LH model. We also show that the Goldstone bosons present in the model do not contribute to the effective potential at the one-loop level. Finally, by neglecting the contribution of higher dimensional...

  9. On electroweak symmetry breaking in the littlest Higgs model

    Dobado González, Antonio; Tabares Cheluci, Lourdes; Peñaranda , Siannah
    In SU(5)/SO(5) little Higgs models radiative corrections give rise to SU(2)(L)xU(1)(Y) symmetry breaking. In this work we start a program for a detailed determination of the relevant terms of the effective Higgs potential by computing the contribution of the t, b and T quarks at the one-loop level, as a starting point for a higher-loop computation. In spite of the fact that some two-loop level contributions are well known to be important, we use our preliminary one-loop result to illustrate that, by demanding the effective potential to reproduce exactly the standard model Higgs potential, and in particular the relation m(H)(2)=2...

  10. LINHE Project: Development of new protocols for the integration of digital cameras and LiDAR, NIR and Hyperspectral sensors.

    Antolín Sánchez, Roberto; Calzado-Martínez, C.; Gómez, A.; Manzanera, J.A.; Meroño, J.E.; Pedrazzani, D.; Pérez,, H.H.; Roldán-Zamarrón, A.; Santos, I.; Valbuena, R.
    The LINHE project aims to develop applications for forest management based on the combined use of LiDAR data, images from spaceborne (multi and hyperspectral) and airborne sensors (panchromatic, colour, near infrared), and NIR field data from a portable sensor. The integration of the different types of data should be performed in a rapid, intuitive, cost-effective and dynamic way. In order to achieve this objective, new algorithms were developed and existing ones were tested, for the correlation of data collected in the field and those gathered by the different sensors. Specific software (LINHE prototype viewer) was developed to support data gathering and...

  11. Chebyshev pseudospectral solution of advection-diffusion equations with mapped finite difference preconditioning

    Pinelli, Alfredo; Benocci, C.; Deville, M.
    A new Chebyshev pseudo-spectral algorithm with finite difference preconditioning is proposed for the solution of advection-diffusion equations, A mapping technique is introduced which allows good convergence for any Peclet number both for one-dimensional and two-dimensional problems. Numerical results show that first-order Lagrange polynomials are the optimal mapping procedure for the one-dimensional problem and second-order Lagrange polynomials, for the two-dimensional one.

  12. Performance of various fluid-solid coupling methods for DNS of particulate flow

    Uhlmann, Markus; Pinelli, Alfredo

  13. Turbulent channel flow concentration profile and wall deposition of a large Schmidt number passive scalar

    García Ybarra, P. L.; Pinelli, Alfredo
    The transport of a passive scalar within a turbulent plane channel flow has been theoretically analyzed by assuming that the Schmidt number Sc, associated to the molecular diffusivity of the passive scalar, is a large parameter. Throughout most of the channel cross-section the mean passive scalar density is constant, but adjacent to the walls a thin boundary layer develops embedded in the viscous sublayer, with a relative thickness of order Sc(-1/3). In this narrow region a passive scalar profile arises due to the non-vanishing flux normal to the wall. This profile is parameter independent (universal) and leads to a constant...

  14. The role of the forcing term in the large eddy simulation of equilibrium channel flow

    Benocci, C.; Pinelli, Alfredo

  15. The role of coherent structure interactions in the regeneration of wall turbulence

    Jiménez, Javier; Pinelli, Alfredo
    The near-wall region is characterized by the presence of organized structures [1], but the way in which they interact to maintain the local dynamics and to extract energy from the mean flow is still controversial. The two dominant structures are the streamwise velocity streaks and the quasi-streamwise vortices. The former consist of long (x + ~ 1000) wavy arrays of alternating streamwise jets with an average spanwise wavelength of z + ~ 100. The latter are vortical structures almost aligned with the mean flow but slightly tilted away from the wall. While it is generally accepted that the vortices induce...

  16. Immersed-boundary methods for general finite-difference and finite-volume Navier-Stokes solvers

    Pinelli, Alfredo; Naqavi, I.Z.; Piomelli, U.; Favier, J.
    We present an immersed-boundary algorithm for incompressible flows with complex boundaries, suitable for Cartesian or curvilinear grid system. The key stages of any immersed-boundary technique are the interpolation of a velocity field given on a mesh onto a general boundary (a line in 2D, a surface in 3D), and the spreading of a force field from the immersed boundary to the neighboring mesh points, to enforce the desired boundary conditions on the immersed-boundary points. We propose a technique that uses the Reproducing Kernel Particle Method [W.K. Liu, S. Jun, Y.F. Zhang, Reproducing kernel particle methods, Int. J. Numer. Methods Fluids...

  17. Chebyshev collocation method and multidomain decomposition for the incompressible Navier‐Stokes equations

    Pinelli, Alfredo; Vacca, A.
    The two-dimensional incompressible Navier-Stokes equations in primitive variables have been solved by a pseudospectral Chebyshev method using a semi-implicit fractional step scheme. The latter has been adapted to the particular features of spectral collocation methods to develop the monodomain algorithm. In particular, pressure and velocity collocated on the same nodes are sought in a polynomial space of the same order; the cascade of scalar elliptic problems arising after the spatial collocation is solved using finite difference preconditioning. With the present procedure spurious pressure modes do not pollute the pressure field. As a natural development of the present work a multidomain...

  18. A spectral multidomain method for the numerical simulation of turbulent flows

    Pinelli, Alfredo; Vacca, A.; Quarteroni, A.
    The primitive variable formulation of the unsteady incompressible Navier-Stokes equations in three space dimensions is discretized with a combined Fourier-Legendre spectral method. A semi-implicit pressure correction scheme is applied to decouple the velocity from the pressure. The arising elliptic scaler problems are first diagonalized in the periodic Fourier direction and then solved by a multidomain Legendre collocation method in the two remaining space coordinates. In particular, both an iterative and a direct version of the so-called projection decomposition method (PDM) are introduced to separate the equations for the internal nodes from the ones governing the interface unknowns. The PDM method,...

  19. Reynolds number dependence of mean flow structure in square duct turbulence

    Pinelli, Alfredo; Uhlmann, Markus; Sekimoto, Atshushi; Kawahara, Genta
    We have performed direct numerical simulations of turbulent flows in a square duct considering a range of Reynolds numbers spanning from a marginal state up to fully developed turbulent states at low Reynolds numbers. The main motivation stems from the relatively poor knowledge about the basic physical mechanisms that are responsible for one of the most outstanding features of this class of turbulent flows: Prandtl's secondary motion of the second kind. In particular, the focus is upon the role of flow structures in its generation and characterization when increasing the Reynolds number. We present a two-fold scenario. On the one...

  20. Linear instability of a corrugated vortex sheet - a model for streak instability

    Kawahara, Genta; Jiménez, Javier; Uhlmann, Markus; Pinelli, Alfredo
    The linear inviscid instability of an infinitely thin vortex sheet, periodically corrugated with finite amplitude along the spanwise direction, is investigated analytically. Two types of corrugations are studied, one of which includes the presence of an impermeable wall. Exact eigensolutions are found in the limits of very long and of very short wavelengths. The intermediate-wavenumber range is explored by means of a second-order asymptotic series and by limited numerical integration. The sheets are unstable to both sinuous and varicose disturbances. The former are generally found to be more unstable, although the difference only appears for finite wavelengths. The effect of...

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