Dissertation/Thesis Abstract

CHORUS-MHD Code for Solar and Planetary Magnetohydrodynamics
by Zhang, Xiaoliang, Ph.D., The George Washington University, 2019, 149; 22618894
Abstract (Summary)

The eruptive solar activities, e.g., solar flares and coronal mass ejections (CMEs), can have a potentially detrimental effect on human space activities or electrical-grid related facilities on Earth. One of the well-known disasters on Earth caused by solar activities happened on March 13, 1989. At 2:44 am EST of that day a severe geomagnetic storm, due to a CME eruption from the Sun, struck Earth. This storm caused the collapse of the Hydro-Quebec power network due to geomagnetically induced currents and led to a nine-hour power outage that affected over 6 million people. While it is prohibitive for human beings to interfere in solar activities that pose dangers to our society it is feasible for us to mitigate the damages and get well prepared before disasters happen. To this end, the comprehensive understanding and accurate prediction of the dynamics of solar activities becomes essential.

As of today, two pioneering approaches, helioseismology, and numerical simulations, have been mainly used to study solar activities. Helioseismology is the discipline of studying the solar structure and dynamics via observing waves and oscillations traveling towards the solar surface. On the other hand, numerical simulations utilize accurate physical models and numerical schemes to simulate solar activities on massively parallel computers. Numerical simulations have the advantage of unraveling all essential physics, including magnetic fields, and providing important insights into the physical processes of the interior of the Sun. Regardless of the fact that numerical simulations have been seen as a complement tool of helioseismology and already contributed to many meaningful findings in astrophysics, numerical simulations are still facing challenging problems. One primary challenge is posed by the inherent nature of multi-scale, density-and temperature-stratified flow structures in astrophysics. The other one is due to the geometrical difficulties in representing the whole sphere or spherical shell with structured meshes.

The goal of this dissertation research is to make contributions to tackling aforementioned problems faced by numerical simulations for solar and planetary magnetohydrodynamics (MHD) via developing a high-order, unstructured-grid, robust, and massively parallel computational framework, CHORUS-MHD. Throughout the development of code CHORUS-MHD particular objectives have been set and progress has been made: (1) in order to capture multi-scale physics precisely and efficiently, an adaptive mesh refinement(AMR) method with local time stepping scheme is developed based on the high-order flux reconstruction (FR) method; (2) a modified version of artificial resistivity technique is proposed for the FR method to suppress and alleviate spurious oscillations near discontinuities; (3) an innovative partitioned divergence cleaning approach for divergence of magnetic field error is proposed, which has sub-iterative cleaning ability so that divergence B error can be reduced repeatedly; (4) a characteristic-based boundary condition (CBC) for MHD simulations on computational domains with reduced sizes is proposed. The implementation of CBC on FR method is described in detail for the first time. furthermore, the CBC is successfully applied to simulate magnetic reconnections; (5) 3D, parallel CHORUSMHD is developed. The speedup test shows CHORUS-MHD has great performance on massively parallel computers. A new solar-like dynamo benchmark is proposed and simulated by CHORUS-MHD demonstrating CHORUS-MHD's ability to handle complex turbulent MHD flows in the solar convection zone.

Indexing (document details)
Advisor: Liang, Chunlei
Commitee: Plesniak, Michael, Barba, Lorena A., Lee, James D., Gupta, Murli M.
School: The George Washington University
Department: Mechanical & Aerospace Engineering
School Location: United States -- District of Columbia
Source: DAI-B 81/2(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Fluid mechanics
Keywords: High order method, MHD, Navier-Stokes
Publication Number: 22618894
ISBN: 9781085695831
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