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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Comparison of MHD simulation for the February 1986 events with interplanetary observations by the spacecraft Sakigake

During the period 3-10 February 1986 a series of major solar flares occurred on the Sun and several intense geomagnetic storms took place on the Earth. To examine the causality between the solar activity and the geomagnetic activity in this period, a magnetohydrodynamic (MHD) numerical simulation was performed using a 2 1/2 -D numerical code. In that period of February 1986, the Japanese spacecraft Sakigake was at 0.84 AU, 57 deg west of the Earth. Besides the in-situ measurements of the interplanetary plasma, Sakigake also provided Doppler scintillation observations. Comparisons between the results of the MHD simulation and the measurements made by the spacecraft Sakigake are presented.

Smith, Z.↗
NASA NTRS1987

The acceleration of winds by MHD waves in open magnetic structures

It has become increasingly clear in recent years that the available models describing the acceleration of high speed streams in solar coronal holes are inadequate. Thermal models do not result in winds with the proper thermal speed and density. In addition models which assume acceleration by Alfven waves, though promising, are not self-consistent when applied low in coronal holes where the acceleration of the wind takes place. An Alfven wave in the corona with a period of a few hundred seconds will have a wavelength of the order of 10 cm. This is of the order of the diameter of a coronal hole in the low corona, and therefore it is expected that the MHD waves are guided in some sense by the coronal hole in which they propagate. This basic idea led to the development of a leaky waveguide theory to describe MHD wave propagation in coronal holes. Recent efforts were concentrated in two areas: the development of numerical codes to properly describe the hydrodynamics of the flow, and more realistic models of the coronal hole properties such as density gradients and spherical divergence of the flux tube. Some of the important aspects of the theory are discussed, including the effect of density inhomogeneities and smooth transverse density gradients. In addition it is hoped that some early results from the numerical models will be presented. The acceleration of cool winds is a problem of interest in cool supergiants also. Some work was done on the development of wind models for these stars as well.

Davila, Joseph M.↗
NASA NTRS1988

Laser production and heating of plasma for MHD application

Experiments have been made on the production and heating of plasmas by the absorption of laser radiation. These experiments were performed to ascertain the feasibility of using laser-produced or laser-heated plasmas as the input for a magnetohydrodynamic (MHD) generator. Such a system would have a broad application as a laser-to-electricity energy converter for space power transmission. Experiments with a 100-J-pulsed CO2 laser were conducted to investigate the breakdown of argon gas by a high-intensity laser beam, the parameters (electron density and temperature) of the plasma produced, and the formation and propagation of laser-supported detonation (LSD) waves. Experiments were also carried out using a 1-J-pulsed CO2 laser to heat the plasma produced in a shock tube. The shock-tube hydrogen plasma reached electron densities of approximately 10 to the 17th/cu cm and electron temperatures of approximately 1 eV. Absorption of the CO2 laser beam by the plasma was measured, and up to approximately 100 percent absorption was observed. Measurements with a small MHD generator showed that the energy extraction efficiency could be very large with values up to 56 percent being measured.

Jalufka, N. W.↗
NASA NTRS1987

Cometary MHD and chemistry

An MHD and chemical comet-coma model was developed, applying the computer program of Huebner (1985) for the detailed chemical evolution of a spherically expanding coma and the program of Schmidt and Wegman (1982) and Wegman (1987) for the MHD flow of plasma and magnetic field in a comet to the Giotto-mission data on the ion abundances measured by the HIS ion mass spectrometer. The physics and chemistry of the coma are modeled in great detail, including photoprocesses, gas-phase chemical kinetics, energy balance with a separate electron temperature, multifluid hydrodynamics with a transition to free molecular flow, fast-streaming atomic and molecular hydrogen, counter and cross streaming of the ionized species relative to the neutral species in the coma-solar wind interaction region with momentum exchange by elastic collisions, mass-loading through ion pick-up, and Lorentz forces of the advected magnetic field. The results, both inside and outside of the contact surface, are discussed and compared with the relevant HIS ion mass spectra.

Wegmann, R.↗
NASA NTRS1988

Magnetohydrodynamic (MHD) modelling of solar active phenomena via numerical methods

Numerical ideal MHD models for the study of solar active phenomena are summarized. Particular attention is given to the following physical phenomena: (1) local heating of a coronal loop in an isothermal and stratified atmosphere, and (2) the coronal dynamic responses due to magnetic field movement. The results suggest that local heating of a magnetic loop will lead to the enhancement of the density of the neighboring loops through MHD wave compression. It is noted that field lines can be pinched off and may form a self-contained magnetized plasma blob that may move outward into interplanetary space.

Wu, S. T.↗
NASA NTRS1988

An MHD simulation of plasma flow past Io - Alfven and slow mode perturbations

The flow of plasma past Io is studied using a time dependent, three-dimensional magnetohydrodynamic (MHD) simulation. In addition to observing the 'Alfven wing', a standing Alfven wave perturbation expected from analytic theory, it is found that the other MHD modes contribute important perturbations. Standing slow mode perturbations also are present in the flow.

Linker, Jon A.↗
NASA NTRS1988

The heating of coronal loops by MHD waves

A detailed derivation of the MHD wave equation appropriate for solar coronal conditions is presented. Some general concepts are discussed regarding the propagation of MHD waves in regions where gradients in the Alfven speed exist. A solution of the ideal equation is discussed, and the ideal solution near the surface of the resonance layer is obtained. The dissipative solution is found and the matching between the ideal and dissipative solutions is demonstrated. The heating rate is calculated and the expression for the heating rate is used to estimate the wave amplitude which is necessary in the corona to explain the observed active region heating rate on the sun.

Davila, Joseph M.↗
NASA NTRS1988

Expected IPS variations due to a disturbance described by a 3-D MHD model

The variations of interplanetary scintillation due to a disturbance described by a three-dimensional, time-dependent, MHD model of the interplanetary medium are calculated. The resulting simulated IPS maps are compared with observations of real disturbances and it is found that there is some qualitative agreement. It is concluded that the MHD model with a more realistic choice of input conditions would probably provide a useful description of many interplanetary disturbances.

Tappin, S. J.↗
NASA NTRS1990

Formation, structure, and stability of MHD intermediate shocks

It was recently shown by Wu (1987) that intermediate shocks are admissible and can be formed through nonlinear wave steepening from continuous waves. In this paper, the formation, structure, and stability of intermediate shocks in dissipative MHD are considered in detail. The differences between the conventional theory and the present one are pointed out and clarified. It is shown that all four types of intermediate shocks can be formed from smooth waves. It is also shown that there are free parameters in the structure of the intermediate shocks, and that these parameters are related to the shock stability. In addition, the paper shows that a rotational discontinuity can not exist with finite width, indicates how this is related to the existence of time-dependent intermediate shocks, and shows why the conventional theory is not a good approximation to dissipative MHD solutions whenever there is rotation in magnetic field.

Wu, C. C.↗
NASA NTRS1991

Resonant behaviour of MHD waves on magnetic flux tubes. I - Connection formulae at the resonant surfaces. II - Absorption of sound waves by sunspots

The present method of addressing the resonance problems that emerge in such MHD phenomena as the resonant absorption of waves at the Alfven resonance point avoids solving the fourth-order differential equation of dissipative MHD by recourse to connection formulae across the dissipation layer. In the second part of this investigation, the absorption of solar 5-min oscillations by sunspots is interpreted as the resonant absorption of sounds by a magnetic cylinder. The absorption coefficient is interpreted (1) analytically, under certain simplifying assumptions, and numerically, under more general conditions. The observed absorption coefficient magnitude is explained over suitable parameter ranges.

Sakurai, Takashi↗
NASA NTRS1991

FLIP MHD - A particle-in-cell method for magnetohydrodynamics

The fluid-implicit-particle, or 'FLIP' method presently extended to 2D and 3D MHD flow incorporates a Lagrangian field representation and yields a grid magnetic Reynolds number of up to 16 while preserving contact continuities that retain the Galilean invariance of the MHD flow equations. Analytical arguments and numerical examples demonstrate the conservation of mass, momentum, magnetic flux, and energy; 2D calculation results for the illustrative cases of contact discontinuity convection, Rayleigh-Taylor unstable flow.

Brackbill, J. U.↗
NASA NTRS1991

Ultrahigh temperature vapor core reactor-MHD system for space nuclear electric power

The conceptual design of a nuclear space power system based on the ultrahigh temperature vapor core reactor with MHD energy conversion is presented. This UF4 fueled gas core cavity reactor operates at 4000 K maximum core temperature and 40 atm. Materials experiments, conducted with UF4 up to 2200 K, demonstrate acceptable compatibility with tungsten-molybdenum-, and carbon-based materials. The supporting nuclear, heat transfer, fluid flow and MHD analysis, and fissioning plasma physics experiments are also discussed.

Maya, Isaac↗
NASA NTRS1992

A numerical code for a three-dimensional magnetospheric MHD equilibrium model

Two dimensional and three dimensional MHD equilibrium models were begun for Earth's magnetosphere. The original proposal was motivated by realizing that global, purely data based models of Earth's magnetosphere are inadequate for studying the underlying plasma physical principles according to which the magnetosphere evolves on the quasi-static convection time scale. Complex numerical grid generation schemes were established for a 3-D Poisson solver, and a robust Grad-Shafranov solver was coded for high beta MHD equilibria. Thus, the effects were calculated of both the magnetopause geometry and boundary conditions on the magnetotail current distribution.

Voigt, G.-H.↗
NASA NTRS1993

An MHD study of the interaction between the solar wind and the interstellar medium

The overall objective of this research program is to obtain a better understanding of the interaction between the solar wind and the interstellar medium through the use of numerical solutions of the time-dependent magnetohydrodynamic (MHD) equations. The simulated results will be compared with observations where possible and with the results from previous analytic and numerical studies. The primary progress during the first two years has been to develop codes for 2-D models in both spherical and cylindrical coordinates and to apply them to the solar wind-interstellar medium interaction. Computations have been carried out for both a relatively simple gas-dynamic interaction and a flow-aligned interstellar magnetic field. The results have been shown to compare favorably with models that use more approximations and to modify and extend the previous results as would be expected. Work has also been initiated on the development of a 3-D MHD code in spherical coordinates.

Steinolfson, R. S.↗
NASA NTRS1992

The MHD structure of the plasmasheet boundary. I - Tangential momentum balance and consistency with slow mode shocks

The MHD structure of the plasmasheet boundary in the near tail is investigated on the basis of data from the AMPTE/IRM spacecraft. The relationship between the change in the tangential velocity predicted by the Rankine-Hugoniot relations for a discontinuity with a normal magnetic field and the measured change in the tangential velocity for about 80 crossings is presented. The measured change is almost always much less than the predicted value. It is suggested that either there is not usually a normal component of the magnetic field across the boundary (combined with previous work on pressure balance, this implies that the boundary is a tangential discontinuity), or the boundary is not usually well-modeled as a planar, time-stationary MHD discontinuity. It is proposed that the magnetic connection to the earth inhibits the formation of slow mode shocks.

Cattell, C. A.↗
NASA NTRS1992

MHD turbulence, reconnection, and test-particle acceleration

We examine homogeneous MHD turbulence and turbulent magnetic reconnection as possible mechanisms for accelerating cosmic ray particles. Test particle calculations are performed using fields from MHD simulations, and initially Maxwellian particle distributions are shown to evolve into power-law distributions. Simple estimates for both the maximum energy attainable and the mean energies of the accelerated particles are fairly successful and are consistent with timescales for flares and cosmic rays.

Gray, Perry C.↗
NASA NTRS1993

Plasma wave signatures in the magnetotail reconnection region - MHD simulation and ray tracing

An MHD simulation was performed to obtain a self-consistent model of magnetic field and plasma density near the X point reconnection region. The MHD model was used to perform extensive ray tracing calculations in order to clarify the propagation characteristics of the plasma waves near the X point reconnection region. The dynamic wave spectra possibly observed by the Geotail spacecraft during a typical cross-tail trajectory are reconstructed. By comparing the extensive ray tracing calculations with the plasma wave data from Geotail, it is possible to perform a kind of 'remote sensing' to identify the location and structure of potential X point reconnection regions.

Omura, Yoshiharu↗
NASA NTRS1993

Analysis and design of an ultrahigh temperature hydrogen-fueled MHD generator

A coupled gas dynamics/radiative heat transfer analysis of partially ionized hydrogen, in local thermodynamic equilibrium, flowing through an ultrahigh temperature (10,000-20,000 K) magnetohydrodynamic (MHD) generator is performed. Gas dynamics are modeled by a set of quasi-one-dimensional, nonlinear differential equations which account for friction, convective and radiative heat transfer, and the interaction between the ionized gas and applied magnetic field. Radiative heat transfer is modeled using nongray, absorbing-emitting 2D and 3D P-1 approximations which permit an arbitrary variation of the spectral absorption coefficient with frequency. Gas dynamics and radiative heat transfer are coupled through the energy equation and through the temperature- and density-dependent absorption coefficient. The resulting nonlinear elliptic problem is solved by iterative methods. Design of such MHD generators as onboard, open-cycle, electric power supplies for a particular advanced airbreathing propulsion concept produced an efficient and compact 128-MWe generator characterized by an extraction ratio of 35.5 percent, a power density of 10,500 MWe/cu m, and a specific (extracted) energy of 324 MJe/kg of hydrogen. The maximum wall heat flux and total wall heat load were 453 MW/sq m and 62 MW, respectively.

Moder, Jeffrey P.↗