Search results for "numerical methods"

Controlled time integration for the numerical simulation of meteor radar reflections

2016

We model meteoroids entering the Earth[U+05F3]s atmosphere as objects surrounded by non-magnetized plasma, and consider efficient numerical simulation of radar reflections from meteors in the time domain. Instead of the widely used finite difference time domain method (FDTD), we use more generalized finite differences by applying the discrete exterior calculus (DEC) and non-uniform leapfrog-style time discretization. The computational domain is presented by convex polyhedral elements. The convergence of the time integration is accelerated by the exact controllability method. The numerical experiments show that our code is efficiently parallelized. The DEC approach is compared to the volume …

Sublimation of icy aggregates in the coma of comet 67P/Churyumov–Gerasimenko detected with the OSIRIS cameras on board Rosetta

2016

Beginning in 2014 March, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov¿Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analysed the dust monitoring observations shortly after the southern vernal equinox on 2015 May 30 and 31 with the WAC at the heliocentric distance Rh = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness a…

Search for Extraterrestrial Point Sources of Neutrinos with AMANDA-II

2003

We present the results of a search for point sources of high energy neutrinos in the northern hemisphere using AMANDA-II data collected in the year 2000. Included are flux limits on several AGN blazars, microquasars, magnetars and other candidate neutrino sources. A search for excesses above a random background of cosmic-ray-induced atmospheric neutrinos and misreconstructed downgoing cosmic-ray muons reveals no statistically significant neutrino point sources. We show that AMANDA-II has achieved the sensitivity required to probe known TeV gamma-ray sources such as the blazar Markarian 501 in its 1997 flaring state at a level where neutrino and gamma-ray fluxes are equal.

An improved numerical solver of the 2D diffusive shallow waters equations over unstructured triangular meshes

2009

Simulazione numerica tridimensionale del campi de moto indotti dal vento

2006

Nell’articolo viene proposto un modello numerico tridimensionale al volume finiti, che viene utilizzato per la simulazione di campi di moto indotti dal mento in corpi idrici con batimetria complessa. I risultati numerici sono confrontati con misure sperimentali. Al fine di verificare gli effetti sul calcolo del campi idrodinamici di alcume ipotesi simplificative, relative alla distribuzione verticale della pressione e degli sforzi di Reynolds, sono stati quindi condotti alcuni test numerici, dai quali si è evidenziato che l’ipotesi di distribuzione idrostatica delle pressioni, cui si fa ricorso nelle approssinazioni di tipo “quasi-3D”, può essere utilizzata per il carcolo del profili vertic…

Minimally implicit Runge-Kutta methods for Resistive Relativistic MHD

2016

The Relativistic Resistive Magnetohydrodynamic (RRMHD) equations are a hyperbolic system of partial differential equations used to describe the dynamics of relativistic magnetized fluids with a finite conductivity. Close to the ideal magnetohydrodynamic regime, the source term proportional to the conductivity becomes potentially stiff and cannot be handled with standard explicit time integration methods. We propose a new class of methods to deal with the stiffness fo the system, which we name Minimally Implicit Runge-Kutta methods. These methods avoid the development of numerical instabilities without increasing the computational costs in comparison with explicit methods, need no iterative …

Asymptotic stability of solutions to Volterra-renewal integral equations with space maps

2012

Abstract In this paper we consider linear Volterra-renewal integral equations (VIEs) whose solutions depend on a space variable, via a map transformation. We investigate the asymptotic properties of the solutions, and study the asymptotic stability of a numerical method based on direct quadrature in time and interpolation in space. We show its properties through test examples.

Unconventional phases of attractive Fermi gases in synthetic Hall ribbons

2017

An innovative way to produce quantum Hall ribbons in a cold atomic system is to use M hyperfine states of atoms in a one-dimensional optical lattice to mimic an additional "synthetic dimension." A notable aspect here is that the SU(M) symmetric interaction between atoms manifests as "infinite ranged" along the synthetic dimension. We study the many-body physics of fermions with SU(M) symmetric attractive interactions in this system using a combination of analytical field theoretic and numerical density-matrix renormalization-group methods. We uncover the rich ground-state phase diagram of the system, including unconventional phases such as squished baryon fluids, shedding light on many-body…

Numerical methods in the design process of a sailing yacht

2014

An improved immersed boundary method for curvilinear grids

2009

Abstract In the present paper we propose an extension of the direct-forcing immersed boundary technique, recently developed and employed by Verzicco and co-authors [Fadlun EA, Verzicco R, Orlandi P, Mohd-Yusof J. Combined immersed-boundary finite-difference methods for three-dimensional complex flow simulations. J Comput Phys 2000;161:35–60; Verzicco R, Fatica M, Iaccarino G, Moin P, Khalighi B. Large eddy simulation of a road vehicle with drag-reduction devices. AIAA J 2002;40(12):2447–55; Cristallo A, Verzicco R. Combined immersed boundary/large-eddy-simulations of incompressible three-dimensional complex flows. Flow Turbul Combust 2006;77(1–4):3–26.] and successively improved by Balaras …