Search results for "Magnetohydrodynamic"

MHD free convection in a liquid-metal filled cubic enclosure. I. Differential heating

2002

One-dimensional Mixed MHD Convection

2006

The parallel, fully developed flow of an electrically conducting fluid between plane parallel walls under the simultaneous influence of a driving pressure head, buoyancy, and magnetohydrodynamic (MHD) forces is studied. The fluid is assumed to be internally heated and the flow is modeled as one-dimensional and incompressible, while the Boussinesq approximation is adopted for the buoyancy terms. Analytical solutions are obtained for temperature, velocity and electrical potential under different electrical boundary conditions, forced to natural convection intensity ratios and values of the magnetic induction. Generalized working charts are presented which synthetically describe the system''s …

Three-dimensional linear stability analysis of the flow in a liquid spherical droplet driven by an alternating magnetic field

2003

The paper presents a numerical stability analysis of the flow driven by an alternating (AC) magnetic field in an electromagnetically levitated liquid metal droplet. The basic axisymmetric flow is found to become unstable at Reynolds numbers in the order of 100. The critical Reynolds number Rec and the corresponding most unstable azimuthal wave number m are found for several configurations of the magnetic field depending on the skin-depth d. For a uniform external AC magnetic field the azimuthal wave number of the most unstable mode is m=3. An additional steady (DC) magnetic field imposed along the axis of symmetry increases the stability of the flow.

Dynamic mode decomposition of magnetohydrodynamic bubble chain flow in a rectangular vessel

2021

We demonstrate the first application of dynamic mode decomposition (DMD) to bubble flow with resolved dynamic liquid/gas boundaries. Specifically, we have applied DMD to the output of numerical simulations for a system where chains of bubbles ascend through a rectangular liquid metal vessel. Flow patterns have been investigated in the vessel and bubble reference frames. We show how gas flow rate and applied magnetic affect bubble wake flow and larger-scale flow structures within the liquid metal vessel by examining the velocity field mode statistics over trajectory time and total flow time as well as the computed mode velocity fields. The results of this proof-of-concept study indicate that…

Anomalous wave structure in magnetized materials described by non-convex equations of state

2014

Agraïments: Institute for Pure and Applied Mathematics (UCLA) 2012 program on "Computational Methods in High Energy Density Plasmas. We analyze the anomalous wave structure appearing in flow dynamics under the influence of magnetic field in materials described by non-ideal equations of state. We consider the system of magnetohydrodynamics equations closed by a general equation of state (EOS) and propose a complete spectral decomposition of the fluxes that allows us to derive an expression of the nonlinearity factor as the mathematical tool to determine the nature of the wave phenomena. We prove that the possible formation of non-classical wave structure is determined by both the thermodynam…

Magnetorotational core collapse of possible GRB progenitors – II. Formation of protomagnetars and collapsars

2020

We assess the variance of the post-collapse evolution remnants of compact, massive, low-metallicity stars, under small changes in the degrees of rotation and magnetic field of selected pre-supernova cores. These stellar models are commonly considered progenitors of long gamma-ray bursts. The fate of the proto-neutron star (PNS) formed after collapse, whose mass may continuously grow due to accretion, critically depends on the poloidal magnetic field strength at bounce. Should the poloidal magnetic field be sufficiently weak, the PNS collapses to a black hole (BH) within a few seconds. Models on this evolutionary track contain promising collapsar engines. Poloidal magnetic fields smooth over…

Termination of the magnetorotational instability via parasitic instabilities in core-collapse supernovae

2016

The magnetorotational instability (MRI) can be a powerful mechanism amplifying the magnetic field in core-collapse supernovae. Whether initially weak magnetic fields can be amplified by this instability to dynamically relevant strengths is still a matter of debate. One of the main uncertainties concerns the process that terminates the growth of the instability. Parasitic instabilities of both Kelvin-Helmholtz and tearing-mode type have been suggested to play a crucial role in this process, disrupting MRI channel flows and quenching magnetic field amplification. We perform two-dimensional and three-dimensional sheering-disc simulations of a differentially rotating protoneutron star layer in …

Non-linear evolutions of magnetized thick discs around black holes: dependence on the initial data

2020

We build equilibrium solutions of magnetised thick discs around a highly spinning Kerr black hole and evolve these initial data up to a final time of about 100 orbital periods. The numerical simulations reported in this paper solve the general relativistic magnetohydrodynamics equations using the BHAC code and are performed in axisymmetry. Our study assumes non-self-gravitating, polytropic, constant angular momentum discs endowed with a purely toroidal magnetic field. In order to build the initial data we consider three approaches, two of which incorporate the magnetic field in a self-consistent way and a third approach in which the magnetic field is included as a perturbation on to an othe…

QPO emission from moving hot spots on the surface of neutron stars: a model

2009

We present recent results of 3D magnetohydrodynamic simulations of neutron stars with small misalignment angles, as regards the features in lightcurves produced by regular movements of the hot spots during accretion onto the star. In particular, we show that the variation of position of the hot spot created by the infalling matter, as observed in 3D simulations, can produce high frequency Quasi Periodic Oscillations with frequencies associated with the inner zone of the disk. Previously reported simulations showed that the usual assumption of a fixed hot spot near the polar region is valid only for misalignment angles relatively large. Otherwise, two phenomena challenge the assumption: one …

Magnetorotational Instability in Core-Collapse Supernovae

2017

We discuss the relevance of the magnetorotational instability (MRI) in core-collapse supernovae (CCSNe). Our recent numerical studies show that in CCSNe, the MRI is terminated by parasitic instabilities of the Kelvin-Helmholtz type. To determine whether the MRI can amplify initially weak magnetic fields to dynamically relevant strengths in CCSNe, we performed three-dimensional simulations of a region close to the surface of a differentially rotating proto-neutron star in non-ideal magnetohydrodynamics with two different numerical codes. We find that under the conditions prevailing in proto-neutron stars, the MRI can amplify the magnetic field by (only) one order of magnitude. This severely …