scholarly journals Numerical Boundary Conditions for Solar Magnetic Hydrodynamic Flows Using the Method of Characteristics

1996 ◽  
Vol 154 ◽  
pp. 149-153
Author(s):  
S. T. Wu ◽  
A. H. Wang ◽  
W. P. Guo
Keyword(s):  
Boundary Conditions ◽  
Method Of Characteristics ◽  
Numerical Solutions ◽  
The Self ◽  
Time Dependent ◽  
Solar Plasma ◽  
The Method Of Characteristics ◽  
Mhd Simulations ◽  
Self Consistent ◽  
Dynamic Structures

AbstractWe discuss the self-consistent time-dependent numerical boundary conditions on the basis of theory of characteristics for magnetohydrodynamics (MHD) simulations of solar plasma flows. The importance of using self-consistent boundary conditions is demonstrated by using an example of modeling coronal dynamic structures. This example demonstrates that the self-consistent boundary conditions assure the correctness of the numerical solutions. Otherwise, erroneous numerical solutions will appear.

scholarly journals Dust Driven Winds from Pulsating Stars

1993 ◽  
Vol 137 ◽  
pp. 572-574 ◽  
Author(s):  
E.A. Dorfi ◽  
M.U. Feuchtinger ◽  
S. Höfner
Keyword(s):  
The Self ◽  
Time Dependent ◽  
Full Description ◽  
Stellar Winds ◽  
Dust Formation ◽  
Radiation Hydrodynamics ◽  
Simple Description ◽  
Pulsating Stars ◽  
Self Consistent ◽  
Different Parts

The cool extended atmospheres of late type giants are sites where dust formation takes place. Radiation pressure on the dust grains is an important force for driving the slow but massive winds observed in such objects. Existing calculations of dust driven stellar winds (e.g. Bowen 1988, Fleischer et al. 1991) suffer from the fact that they include approximations at various levels for different parts of the problem like the hydrodynamics or the dust formation. Furthermore they do not include time-dependent radiative transfer.In order to overcome these insufficiencies we plan to calculate self-consistent models of dust driven winds with a full description of both the radiation hydrodynamics and the time-dependent dust formation. As a first step, however, we concentrate our investigations on the self-consistent description of the radiation hydrodynamics adopting only a simple description of the dust opacities.

Self-consistent estimates for the viscoelastic creep compliances of composite materials

1978 ◽  
Vol 359 (1697) ◽  
pp. 251-273 ◽  
Keyword(s):  
Composite Materials ◽  
Numerical Solutions ◽  
The Self ◽  
Inclusion Problem ◽  
Inclusion Problems ◽  
Viscoelastic Creep ◽  
Self Consistent ◽  
Title Problem ◽  
Consistent Method ◽  
Selection Of

In this paper the viscoelastic creep compliances of various composites are estimated by the self-consistent method. The phases may be arbitrarily anisotropic and in any concentrations but we demand that one of the phases be a matrix and the remaining phases consist of ellipsoidal inclusions. The theory is succinctly formulated with the help of Stieltjes convolutions. In order to solve the title problem, we first solve the misfitting viscoelastic inclusion problem. Numerical solutions are given for a selection of inclusion problems and for two common composite materials, namely an isotropic dispersion of spheres, and a uni-directional fibre reinforced material.

Patterns of Airflow in Circular Tubes Caused by a Corona Jet With Concentric and Eccentric Wire Electrodes

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
Majid Molki
Keyword(s):  
Corona Discharge ◽  
Secondary Flow ◽  
Cross Section ◽  
Cross Sections ◽  
Method Of Characteristics ◽  
Numerical Solutions ◽  
Flow Patterns ◽  
Circular Tubes ◽  
The Method Of Characteristics ◽  
The Cross

A computational investigation is conducted to study the patterns of airflow induced by corona discharge in the cross section of a circular tube. The secondary flow induced by corona wind in various flow passages has been the subject of numerous investigations. The flow patterns are often identified by multiple recirculation bubbles. Such flow patterns have also been anticipated for circular cross sections where the corona discharge is activated by an electrode situated at the center of the cross section. In this investigation, it is shown that, contrary to public perception, a symmetric corona discharge does not generate a secondary flow in circular cross sections. This investigation then proceeds to demonstrate that the flow responsible for thermal enhancements in circular tubes often reported in the published literature is induced only when there is a slight asymmetry in the position of the electrode. The present computations are performed in two parts. In part one, the electric field equations are solved using the method of characteristics. In part two, the flow equations are solved using a finite-volume method. It is shown that the method of characteristics effectively eliminates the dispersion errors observed in other numerical solutions. The present computations show that the flow in the eccentric configuration is characterized by a corona jet that is oriented along the eccentricity direction and two recirculation zones situated on either sides of the jet. In addition to the computational approach, a number of analytical solutions are presented and compared with the computational results.

scholarly journals A new technique for observationally derived boundary conditions for space weather

2018 ◽  
Vol 8 ◽  
pp. A26 ◽  
Author(s):  
Paolo Pagano ◽  
Duncan Hendry Mackay ◽  
Anthony Robinson Yeates
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Boundary Conditions ◽  
Space Weather ◽  
Weather Forecasting ◽  
Interplanetary Space ◽  
Time Dependent ◽  
Magnetic Flux Ropes ◽  
Mhd Simulations ◽  
Flux Ropes

Context. In recent years, space weather research has focused on developing modelling techniques to predict the arrival time and properties of coronal mass ejections (CMEs) at the Earth. The aim of this paper is to propose a new modelling technique suitable for the next generation of Space Weather predictive tools that is both efficient and accurate. The aim of the new approach is to provide interplanetary space weather forecasting models with accurate time dependent boundary conditions of erupting magnetic flux ropes in the upper solar corona. Methods. To produce boundary conditions, we couple two different modelling techniques, MHD simulations and a quasi-static non-potential evolution model. Both are applied on a spatial domain that covers the entire solar surface, although they extend over a different radial distance. The non-potential model uses a time series of observed synoptic magnetograms to drive the non-potential quasi-static evolution of the coronal magnetic field. This allows us to follow the formation and loss of equilibrium of magnetic flux ropes. Following this a MHD simulation captures the dynamic evolution of the erupting flux rope, when it is ejected into interplanetary space. Results.The present paper focuses on the MHD simulations that follow the ejection of magnetic flux ropes to 4 R⊙. We first propose a technique for specifying the pre-eruptive plasma properties in the corona. Next, time dependent MHD simulations describe the ejection of two magnetic flux ropes, that produce time dependent boundary conditions for the magnetic field and plasma at 4 R⊙ that in future may be applied to interplanetary space weather prediction models. Conclusions. In the present paper, we show that the dual use of quasi-static non-potential magnetic field simulations and full time dependent MHD simulations can produce realistic inhomogeneous boundary conditions for space weather forecasting tools. Before a fully operational model can be produced there are a number of technical and scientific challenges that still need to be addressed. Nevertheless, we illustrate that coupling quasi-static and MHD simulations in this way can significantly reduce the computational time required to produce realistic space weather boundary conditions.

Numerical Modelling of Phase Change in Freezing and Thawing Unsaturated Soil

1993 ◽  
Vol 24 (2-3) ◽  
pp. 95-110 ◽  
Author(s):  
H. Engelmark ◽  
U. Svensson
Keyword(s):  
Boundary Conditions ◽  
Phase Change ◽  
Change Process ◽  
Numerical Solutions ◽  
Time Dependent ◽  
Total Water Content ◽  
Total Water ◽  
Freezing And Thawing ◽  
Water Ice ◽  
Temperature Boundary

This paper presents a new method for handling the phase change process in numerical simultations of freezing and thawing soils. Moisture and heat transfer in soils subjected to both freezing and thawing are discussed. Simulated freezing results of temperature and total water content (water + ice) are compared with experimental data reported by Jame (1977). Simulated and experimental results were similar. The effects of different time-dependent temperature boundary conditions were evaluated and discussed. The method was used both with abrupt and smooth temperature boundary conditions and both resulted in stable numerical solutions. Finally, results from a simulation of a freezing and thawing cycle are presented and discussed qualitatively.

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