Search results for "hydrodynamics"
showing 10 items of 390 documents
Radiation Magnetohydrodynamic Models and Spectral Signatures of Plasma Flows Accreting onto Classical T Tauri Stars
2019
CTTSs are young stars accreting mass from their circumstellar disks. The material falls into the star at free fall velocity and hits the stellar surface producing shocks, that heat the plasma at few million degrees. In the last twenty years the X-ray and UV observations of these systems have raised several questions. In particular, the observed X-ray luminosity is systematically below the value predicted by theoretical models, and the UV lines show complex profiles which cannot be easily interpreted with current accretion models based only on magnetohydrodynamical effects. To tackle these problems we modeled the structure and the dynamics of the plasma in the impact region using 3D magnetoh…
Grid-based Methods in Relativistic Hydrodynamics and Magnetohydrodynamics
2015
An overview of grid-based numerical methods used in relativistic hydrodynamics (RHD) and magnetohydrodynamics (RMHD) is presented. Special emphasis is put on a comprehensive review of the application of high-resolution shock-capturing methods. Results of a set of demanding test bench simulations obtained with different numerical methods are compared in an attempt to assess the present capabilities and limits of the various numerical strategies. Applications to three astrophysical phenomena are briefly discussed to motivate the need for and to demonstrate the success of RHD and RMHD simulations in their understanding. The review further provides FORTRAN programs to compute the exact solution…
Building a numerical relativistic non-ideal magnetohydrodynamics code for astrophysical applications
2013
AbstractIncluding resistive effects in relativistic magnetized plasmas is a challenging task, that a number of authors have recently tackled employing different methods. From the numerical point of view, the difficulty in including non-ideal terms arises from the fact that, in the limit of very high plasma conductivity (i.e., close to the ideal MHD limit), the system of governing equations becomes stiff, and the standard explicit integrating methods produce instabilities that destroy the numerical solution. To deal with such a difficulty, we have extended the relativistic MHD code MR-GENESIS, to include a number of Implicit Explicit Runge-Kutta (IMEX-RK) numerical methods. To validate the i…
Numerical Simulations and Diagnostics in Astrophysics: A few Magnetohydrodynamics Examples
2007
We discuss some issues related to numerical simulations in Astrophysics and, in particular, to their use both as a theoretical tool and as a diagnostic tool, to gain insight into the physical phenomena at work. We make our point presenting some examples of Magneto-hydro-dynamic (MHD) simulations of astrophysical plasmas and illustrating their use. In particular we show the need for appropriate tools to interpret, visualize and present results in an adequate form, and the importance of spectral synthesis for a direct comparison with observations.
On the convexity of relativistic ideal magnetohydrodynamics
2015
We analyze the influence of the magnetic field in the convexity properties of the relativistic magnetohydrodynamics system of equations. To this purpose we use the approach of Lax, based on the analysis of the linearly degenerate/genuinely non-linear nature of the characteristic fields. Degenerate and non-degenerate states are discussed separately and the non-relativistic, unmagnetized limits are properly recovered. The characteristic fields corresponding to the material and Alfv\'en waves are linearly degenerate and, then, not affected by the convexity issue. The analysis of the characteristic fields associated with the magnetosonic waves reveals, however, a dependence of the convexity con…
MHD evolution of a fragment of a CME core in the outer solar corona
2007
Detailed hydrodynamic modeling explained several features of a fragment of the core of a Coronal Mass Ejection observed with SoHO/UVCS at 1.7 Ro on 12 December 1997, but some questions remained unsolved. We investigate the role of the magnetic fields in the thermal insulation and the expansion of an ejected fragment (cloud) traveling upwards in the outer corona. We perform MHD simulations including the effects of thermal conduction and radiative losses of a dense spherical or cylindrical cloud launched upwards in the outer corona, with various assumptions on the strength and topology of the ambient magnetic field; we also consider the case of a cylindrical cloud with an internal magnetic fi…
Magnetized relativistic jets and helical magnetic fields: II. Radiation
2021
This is the second of a series of two papers that deepen our understanding of the transversal structure and the properties of recollimation shocks of axisymmetric, relativistic, superfast magnetosonic, overpressured jets. They extend previous work that characterized these properties in connection with the dominant type of energy (internal, kinetic, or magnetic) in the jet to models with helical magnetic fields with larger magnetic pitch angles and force-free magnetic fields. In the first paper of this series, the magnetohydrodynamical models were computed following an approach that allows studying the structure of steady, axisymmetric, relativistic (magnetized) flows using one-dimensional t…
Coupled fluid-flow and magnetic-field simulation of the Riga dynamo experiment
2006
Magnetic fields of planets, stars, and galaxies result from self-excitation in moving electroconducting fluids, also known as the dynamo effect. This phenomenon was recently experimentally confirmed in the Riga dynamo experiment [ A. Gailitis et al., Phys. Rev. Lett. 84, 4365 (2000) ; A. Gailitis et al., Physics of Plasmas 11, 2838 (2004) ], consisting of a helical motion of sodium in a long pipe followed by a straight backflow in a surrounding annular passage, which provided adequate conditions for magnetic-field self-excitation. In this paper, a first attempt to simulate computationally the Riga experiment is reported. The velocity and turbulence fields are modeled by a finite-volume Navi…
Effects of non-uniform interstellar magnetic field on synchrotron X-ray and inverse-Compton γ-ray morphology of supernova remnants
2011
Context. Observations of SuperNova Remnants (SNRs) in X-ray and γ-ray bands promise to contribute important information to our understanding of the kinematics of charged particles and magnetic fields in the vicinity of strong non-relativistic shocks and, therefore, the nature of Galactic cosmic rays. The accurate analysis of SNR images collected in different energy bands requires theoretical modeling of synchrotron and inverse Compton emission from SNRs. Aims. We develop a numerical code (remlight) to synthesize, from MHD simulations, the synchrotron radio, X-ray, and inverse Compton γ-ray emission originating in SNRs expanding in a non-uniform interstellar medium (ISM) and/or non-uniform i…
Upwind Relativistic MHD Code for Astrophysical Applications
2003
We describe the status of devolpment of a 2.5D numerical code to solve the equations of ideal relativistic magnetohydrodynamics. The numerical code, based on high-resolution shock-capturing techniques, solves the equations written in conservation form and computes the numerical fluxes using a linearized Riemann solver. A special procedure is used to force the conservation of magnetic flux along the evolution.