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NASA NTRS1985

Parabolic harmonics in magnetospheric modeling - The main dipole and the ring current

A new representation is developed for that portion of the magnetospheric magnetic field which is produced by currents on the magnetopause or outside it. For a magnetopause which is a paraboloid of rotation and which confines all field lines of magnetospheric sources, the fields due to magnetopause currents are derived for two sources, a dipole and a two-parameter model of the ring current, each arbitrarily inclined to the earth-sun line. Methods are also developed for accomodating changes in the size of the magnetospheric cavity and for using nonparaboloidal boundaries, open at the nightside. Neutral points and polar cusps are derived, and in agreement with observations it is found that a growth of the ring current shifts them equatorward. By extrapolation from these results, it is argued that the observation of such shifts during magnetic storms may help resolve the relative importance of two processes proposed for magnetic storms.

Stern, D. P.↗

NASA NTRS1985

Young thrust-fault scarps in the highlands - Evidence for an initially totally molten moon

Attention is given to thermoelastic stress calculations implying that if only the outer few hundreds of km of a moon with a cool interior were initially molten, the lunar highlands should not have young compressional tectonic features. Extrapolations from Apollo panoramic images showing young thrust faults in the highlands suggest that about 2000 thrust fault scarps exist on the highlands, generally occurring in series or complexes of four or five scarps that are on average 5 km long. The ages of the scarps range from 60 + or - 30 to 680 + or - 250 my, with a possible factor bias of +2 to -4. The scarps are the youngest endogenic features on the moon, and indicate that the moon was initially molten.

Binder, A. B.↗

NASA NTRS1985

Sources of atmospheric methane from wetlands

Through the use of a computerized Geographic Information Service (GIS), field data on methane emissions and water inundation levels have been combined with remotely sensed vegetation cover data. This permits a more precise extrapolation of point flux measurements to regional scale flux estimates. Since the GIS allows changes in environmental variables to be included in the model, the sensitivity of emissions on large scales to changes in these parameters may be studied. Here, methane flux measurements from the Everglades marsh complex are reported, giving the flux by vegetation class.

Bartlett, K. B.↗

NASA NTRS1985

Ellipsoidal geometry in asteroid thermal models - The standard radiometric model

The major consequences of ellipsoidal geometry in an othewise standard radiometric model for asteroids are explored. It is shown that for small deviations from spherical shape a spherical model of the same projected area gives a reasonable aproximation to the thermal flux from an ellipsoidal body. It is suggested that large departures from spherical shape require that some correction be made for geometry. Systematic differences in the radii of asteroids derived radiometrically at 10 and 20 microns may result partly from nonspherical geometry. It is also suggested that extrapolations of the rotational variation of thermal flux from a nonspherical body based solely on the change in cross-sectional area are in error.

Brown, R. H.↗

NASA NTRS1985

Large-cell Monte Carlo renormalization of irreversible growth processes

Monte Carlo sampling is applied to a recently formulated direct-cell renormalization method for irreversible, disorderly growth processes. Large-cell Monte Carlo renormalization is carried out for various nonequilibrium problems based on the formulation dealing with relative probabilities. Specifically, the method is demonstrated by application to the 'true' self-avoiding walk and the Eden model of growing animals for d = 2, 3, and 4 and to the invasion percolation problem for d = 2 and 3. The results are asymptotically in agreement with expectations; however, unexpected complications arise, suggesting the possibility of crossovers, and in any case, demonstrating the danger of using small cells alone, because of the very slow convergence as the cell size b is extrapolated to infinity. The difficulty of applying the present method to the diffusion-limited-aggregation model, is commented on.

Nakanishi, H.↗

NASA NTRS1985

On the determination of laminar flame speeds from stretched flames

The effects of stretch on the determination of the laminar flame speed are experimentally studied by using the positively-stretched stagnation flame and negatively-stretched bunsen flame, and by using lean and rich mixtures of methane, propane, butane, and hydrogen with air whose effective Lewis numbers are either greater or less than unity. Results demonstrate that flame speed determination can be influenced by stretch through two factors: (1) Preferential diffusion which tends to increase or decrease the flame temperature and burning rate depending on the effective Lewis number, and (2) Flow divergence which causes the flame speed to assume higher values when evaluated at the upstream boundary of the preheat zone instead of the reaction zone. Recent data on flame speed including the present ones are then examined from the unified viewpoint of flame stretch, leading to satisfactory resolution of the discrepancies between them. The present study also proposes a methodology of determining the laminar flame speeds by using the stagnation flame and linearly extrapolating the data to zero stretch rate.

Wu, C. K.↗

NASA NTRS1985

Rheologies of H2O ices Ih, II, and III at high pressures - A progress report

Ordinary hexagonal ice (ice Ih) represents the stable crystalline form of H2O on the earth's surface. It is known that ice exists elsewhere in the solar system. Thus, several of the moons of Saturn and Jupiter are composed predominately of H2O and their surface temperatures are about 75 and 100 K. The pressures in the interior of some of the larger of the moons may be as high as 3 GPa. The involved pressures and temperatures extend far beyond the conditions over which the rheological laws for ice Ih can be confidently extrapolated. It is, therefore, necessary to obtain information regarding the rheologies of H2O ices in pressure and temperature ranges which had not yet been previously considered. Since 1981, over 100 triaxial compression tests have been conducted over a wide range of temperatures (77 to 258 K) and pressures (0.1 to 350 MPa). The present paper provides a progress report of these experiments.

Kirby, S. H.↗

NASA NTRS1986

Design requirements for the NASA Langley supersonic low-disturbance wind tunnel

The high intensity, high frequency acoustic disturbances that cause large adverse boundary layer transition effects on test models in conventional supersonic wind tunnels consist of finite length wavelets radiating from eddies in the turbulent boundary layers of the wind tunnel walls. NASA Langley has undertaken 'quiet' supersonic tunnel research that demonstrates the ability to maintain laminarity at high unit Reynolds numbers on limited upstream regions of the nozzle wall boundary layers in small, Mach 3.0, 3.5, and 5.0 pilot tunnels. The high level acoustic disturbances are then eliminated, and the transition Reynolds numbers measured on cones approach those for atmospheric flight. Attention is presently given to the design requirements that can be extrapolated from these results for a large wind tunnel facility; high quality air filtering, noise attenuation, nozzle coordinate accuracy, and surface finish, are quantified with pilot tunnel data.

Beckwith, I. E.↗

NASA NTRS1986

Exact formulas for multipole moments using Slater-type molecular orbitals

A triple infinite sum of formulas expressed as an expansion in Legendre polynomials is generated by use of computer algebra to represent the potential from the midpoint of two Slater-type orbitals; the charge density that determines the potential is given as the product of the two orbitals. An example using 1s orbitals shows that only a few terms are needed to obtain four-figure accuracy. Exact formulas are obtained for multipole moments by means of a careful study of expanded formulas, allowing an 'extrapolation to infinity'. This Loewdin alpha-function approach augmented by using a C matrix to characterize Slater-type orbitals can be readily generalized to all cases.

Jones, H. W.↗

NASA NTRS1986

Addressing the hypersonic simulation problem

The hypersonic simulation problem is solved by the meshing of bench-marked experimental data with results from validated computational fluid dynamic codes. The example presented is for the reentry of the Space Shuttle Orbiter. Mach number effects were assessed by parametrically varying free-stream Mach number and angle of attack in a series of inviscid, perfect-gas computations carried out on a modified Orbiter geometry. Real-gas effects were determined by making calculations at specific points of the reentry trajectory using equilibrium air thermodynamics and comparing with corresponding perfect-gas computations. Viscous computations were also made for both the basic Orbiter body and control surfaces. A methodology is developed that permits the extrapolation of wind tunnel data to flight situations, providing a solution to the hypersonic simulation problem.

Griffith, B. J.↗

NASA NTRS1986

Latitudinal extent of the heliospheric current sheet and modulation of galactic cosmic rays

Possible correlations were investigated between the modulation of galactic cosmic rays and changes in the maximum heliographic latitude of the heliospheric current sheet during solar maximum. Solar photospheric magnetic field data from 1976-82 were extrapolated by means of potential theory to obtain the maximum latitudinal extent of the current sheet in the northern and southern hemispheres. The latitudinal differences were compared with terrestrial neutron flux data and Pioneer 10 data on cosmic rays with energies below 200 MeV at heliocentric distances of 10-30 AU. Account was taken for the time delay for the solar wind to propagate out to the spacecraft location. The current sheet maxima were nearly symmetrical about the solar equator except during sunspot maxima, when the solar poles were reversing. Significant changes in the latitudinal symmetry were highly correlated with the neutron data and cosmic fluctuations at Pioneer 10. The sensitivity of cosmic rays to the polarity reversals is in accordance with predictions of the gradient drift model.

Smith, E. J.↗

NASA NTRS1986

Mass loss from carbon stars

The present consideration of the circumstellar envelopes around carbon stars on the basis of IRAS data indicates that the grains are composed of amorphous carbon rather than graphite, with an extrapolated outflowing material opacity that is large enough for the radiation pressure on the grains to drive the matter to infinity. At least 10 percent of the carbon stars have a mass loss rate that has changed by a factor of 2 during the past 1000 years. The stars that are losing large amounts of mass are generally long period variables. All these results are consistent with a two-step process of mass loss from most of the stars with substantial mass-outflow rates.

Jura, M.↗

NASA NTRS1985

Durability predictions of adhesively bonded composite structures using accelerated characterization methods

The utilization of adhesive bonding for composite structures is briefly assessed. The need for a method to determine damage initiation and propagation for such joints is outlined. Methods currently in use to analyze both adhesive joints and fiber reinforced plastics is mentioned and it is indicated that all methods require the input of the mechanical properties of the polymeric adhesive and composite matrix material. The mechanical properties of polymers are indicated to be viscoelastic and sensitive to environmental effects. A method to analytically characterize environmentally dependent linear and nonlinear viscoelastic properties is given. It is indicated that the methodology can be used to extrapolate short term data to long term design lifetimes. That is, the method can be used for long term durability predictions. Experimental results for near adhesive resins, polymers used as composite matrices and unidirectional composite laminates is given. The data is fitted well with the analytical durability methodology. Finally, suggestions are outlined for the development of an analytical methodology for the durability predictions of adhesively bonded composite structures.

Brinson, H. F.↗

NASA NTRS1985

On the question of interstellar travel

Arguments are presented which show that motives for interstellar travel by advanced technological civilizations based on an extrapolation of earth's history may be quite invalid. In addition, it is proposed that interstellar travel is so enormously expensive and perhaps so hazardous, that advanced civilizations do not engage in such practices because of the ease of information transfer via interstellar communication.

Wolfe, J. H.↗

NASA NTRS1986

Verification of large beam-type space structures

The verification approach here proposed for large, beam-type space structures consists of a first part, which removes the gravity effect on the substructure tested and identifies its on-orbit dynamic characteristics, on the basis of ground test measurements, and a second part which develops an adequate scaling law that extrapolates the dynamic characteristics of the prototype structure by using results from the substructure. These approaches are presently demonstrated for the cases of a wrap-rib antenna's feed support structure and a candidate Space Shuttle flight experiment.

Shih, C.-F.↗

NASA NTRS1986

Buckling behavior of Rene 41 tubular panels for a hypersonic aircraft wing

The buckling characteristics of Rene 41 tubular panels for a hypersonic aircraft wing were investigated. The panels were repeatedly tested for buckling characteristics using a hypersonic wing test structure and a universal tension/compression testing machine. The nondestructive buckling tests were carried out under different combined load conditions and in different temperature environments. The force/stiffness technique was used to determine the buckling loads of the panels. In spite of some data scattering resulting from large extrapolations of the data-fitting curve (because of the termination of applied loads at relatively low percentages of the buckling loads), the overall test data correlate fairly well with theoretically predicted buckling interaction curves. Also, the structural efficiency of the tubular panels was found to be slightly higher than that of beaded panels.

Ko, W. L.↗

NASA NTRS1986

Effects of atmosphere on slewing control of a flexible structure

Air drag forces are introduced into the equations for a slewing control maneuver of a flexible structure to assess the effects of atmosphere on the controller design. Simulated modal parameters and transient responses are compared with experiments in normal atmosphere and in vacuum. Analytical techniques for control laws are examined and verified. Physical insight into the air damping is gained so that results in vacuum can be extrapolated from results in air.

Juang, J.-N.↗

NASA NTRS1986

A fundamental problem in determining functional residual capacity or residual volume

To measure a lung volume that is not directly accessible, one often follows dilution of a single-gas tracer, present initially only in the lung or in a rebreathing bag. The final volume available to the tracer is assumed to be the sum of the two initial components. Since O2 is taken up and CO2 is eliminated during the few breaths required for mixing, the total volume changes. The error in lung volume due to this volume change can exceed 10 pct. Theoretical and experimental data is presented to demonstrate the effect of CO2 and O2 exchange. A general equation, based on N2 and Ar, which allows one to circumvent the problems created by these fluxes is introduced. The pitfall of the back-extrapolation approach for a single tracer is shown.

Boutellier, U.↗