Engineering topics

Steinolfson, Richard S.

Publications and source records attributed to Steinolfson, Richard S..

4 records

NASA NTRS1993

Coronal heating by the resonant absorption of Alfven waves - Importance of the global mode and scaling laws

Numerical simulations of the MHD equations for a fully compressible, low-beta, resistive plasma are used to study the resonance absorption process for the heating of coronal active region loops. Comparisons with more approximate analytic models show that the major predictions of the analytic theories are, to a large extent, confirmed by the numerical computations. The simulations demonstrate that the dissipation occurs primarily in a thin resonance layer. Some of the analytically predicted features verified by the simulations are (a) the position of the resonance layer within the initial inhomogeneity; (b) the importance of the global mode for a large range of loop densities; (c) the dependence of the resonance layer thickness and the steady-state heating rate on the dissipation coefficient; and (d) the time required for the resonance layer to form. In contrast with some previous analytic and simulation results, the time for the loop to reach a steady state is found to be the phase-mixing time rather than a dissipation time. This disagreement is shown to result from neglect of the existence of the global mode in some of the earlier analyses. The resonant absorption process is also shown to behave similar to a classical driven harmonic oscillator.

Steinolfson, Richard S.↗

NASA NTRS1993

Magnetic effects in Venus/solar wind interaction

The overall objective of this research program is to better understand the interaction of a magnetized solar wind with the Venus atmosphere through the use of numerical solutions of the time-dependent, 2-D and 3-D magnetohydrodynamic (MHD) equations. Due to the more modest CPU requirements for the 2-D simulations, they were used for studies in which useful information not dependent on the third dimension could be obtained. The 2-D simulations served several purposes in addition to providing useful physical insight. They were used to determine the numerical parameters required in the 3-D studies, such as the grid spacing required to resolve particular features, and the damping that must be included to remove high-frequency oscillations. Among the specific studies performed with support from this grant that are discussed in this report are the following: comparison with other available models for purposes of testing the code and obtaining a baseline with which to evaluate the effects of additional physical processes, effects of a finite planet conductivity, bow shock standoff distance, and formation of the magnetic barrier and slippage of the magnetic field around the planet. A brief description of the methodology is presented before discussing the results.

Steinolfson, Richard S.↗

NASA NTRS1992

Coronal shock waves

The formation of magnetohydrodynamic (MHD) shocks near the leading edge of Coronal Mass Ejections (CME's) is considered using results from both shock theory and numerical simulations. By using just the shock theory results and a simplified model corona, the following is shown: a slow shock front should be concave upward (away from the solar surface); a configuration containing intermediate shocks should also be concave upward near the center of the CME and concave downward at some distance from the CME centerline; and a fast shock configuration should be concave downward. These results are verified with numerical simulations of the MHD equations for the propagation of shocks through a quiescent coronal streamer. By examining the characteristic wave speeds in the ambient streamer, it is estimated that the various shock configurations should form for CME speeds within the following speed increments: slow shocks, 200 to 300 km/sec; intermediate shocks, 300 to 900 km/sec; and fast shocks, greater than 900 km/sec.

Steinolfson, Richard S.↗

NASA NTRS1986

Dynamic evolution of coronal magnetic fields

The response of coronal magnetic fields to photospheric motion is investigated using a time-dependent, two-dimensional MHD simulation. Starting with an initially uniform field, a circular section of the loop base is slowly rotated to represent the photospheric motion. The field lines at the base move with this flow in a manner consistent with the generated electric fields. The subsequent evolution of the field and flow can be characterized as passing through several distinct configurations. In the earliest phase the kinetic energy is negligible, and the current and field are parallel throughout most of the cylinder. This is followed by a period in which the field rotation increases, the axial field at and near the axis increases, and the acial field decreases in two cylindrical regions away from the axis. When the field in an appreciable portion of the cylinder has undergone one complete rotation, a rapid change in field configuration occurs with a large portion of the field making several rotations at large radii and a corresponding large reduction in the axial field.

Steinolfson, Richard S.↗