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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 1,207 records · Page 67
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NASA NTRS1982

Spectral energy distribution /119 - 685 nm/ in 16 shell stars and a tentative model for accreting Be stars

IUE low-dispersion spectra and spectral scans made with the Lick Observatory IDS scanners have been combined for 16 shell stars. Eleven objects can be represented by Kurucz (1979) model atmospheres, although some of them display strong shell-type line spectra. Five among them are known binaries. The six remaining objects display complex spectra. A model involving continuum and line radiation from a hydrogen cloud surrounding the accreting component is proposed. A generalization of this model with optically thick segments of the cloud promises to explain even more exotic objects such as beta Lyrae, W Serpentis and possibly epsilon Aurigae.

Plavec, M. J.↗
NASA NTRS1982

Thick shell tectonics on one-plate planets - Applications to Mars

Using the zero frequency equations of a self-gravitating elastic spherical shell overlying a strengthless fluid, a theory for stress distribution in thick lithospheric shells on one-plate planets is developed. For both the compensated and flexural modes, stress distributions in lithospheres are reviewed. For compensated modes, surface stresses depend only on surface topography, whereas for flexural modes it is shown that, for long wavelengths, stress trajectories are mainly dependent on the lithospheric lateral density distribution and not on elastic properties. Computational analyses are performed for Mars, and it is found that isostatically compensated models correctly predict the graben structure in the immediate Tharsis region and a flexural loading model is satisfactory in explaining the graben in the regions surrounding Tharsis. A three-stage model for the evolution of Tharsis is hypothesized: isostasy with north-south graben formation on Tharsis, followed by flexural loading and radial graben formation on the perimeter of Tharsis, followed by a last stage of loading with little or no regional deformation.

Banerdt, W. B.↗
NASA NTRS1982

Ultraviolet shell formation at V1016 Cygni

A recent 330 minute high-resolution International Ultraviolet Explorer (IUE) spectrogram of V1016 Cygni shows splitting of the 1550 A component of the C IV resonance doublet, suggesting that a nebular shell is in the process of formation. An expansion velocity of 15 km/s is indicated by the IUE data and corresponds to the low range encountered with normal planetary nebulae, but IUE data of V1016 Cyg, taken approximately one year earlier, do not show split C IV lines. The recent IUE observations are consistent with VLA contour maps at 1.3 cm made by Newell and Hjellming (1981) and by Hjellming and Bignell (1982) that morphologically show an extended shell-type object. Thus, V1016 Cyg may have undergone an event which forms a planetary nebula.

Feibelman, W. A.↗
NASA NTRS1982

Glass shell manufacturing in space

Highly-uniform, hollow glass spheres, which are used for inertial-confinement fusion targets, are formed from metal-organic gel powder feedstock in a drop-tower furnace. The modelling of this gel-to-sphere transformation has consisted of three phases: gel thermochemistry, furnance-to-gel heat transfer, and gravity-driven degradation of the concentricity of the molten shell. The heat transfer from the furnace to the free-falling gel particle was modelled with forced convection. The gel mass, dimensions, and specific heat as well as furnace temperature profile and furnace gas conductivity, were controlled variables. This model has been experimentally verified. In the third phase, a mathematical model was developed to describe the gravity-driven degradation of concentricity in molten glass shells.

Nolen, R. L.↗
NASA NTRS1983

Vibrations of blades with variable thickness and curvature by shell theory

A procedure for analyzing the vibrations of rotating turbomachinery blades has been previously developed. This procedure is based upon shallow shell theory, and utilizes the Ritz method to determine frequencies and mode shapes. However, it has been limited heretofore to blades of uniform thickness, uniform curvature, and/or twist and rectangular planform. The present work shows how the procedure may be generalized to eliminate the aforementioned restrictions. Nonrectangular planforms are dealt with by a suitable coordinate transformation. This, as well as variable thickness, curvature and twist, require using numerical integration. The procedure is demonstrated on four examples of cantilevered blades for which theoretical and experimental data have been previously published: (1) flat plate with spanwise taper, (2) flat plate with chordwise taper, (3) twisted plate with chordwise taper, and (4) cylindrical shell with chordwise taper.

Lee, J. K.↗
NASA NTRS1985

Fabricating Thin-Shell Heat-Transfer Models

Freestanding shells produced for experimental aerodynamic-heating tests. Heat transfer shells require several steps and several precise molds. First, interlocking aluminum male and female molds fabricated. Holes for thermocouples drilled through male mold at desired locations. Wires having same diameter as thermocouple wire placed through holes in male mold flush to female mold. Epoxy exposed to vacuum to remove air bubbles poured between male and female molds to form thin female mold. Once mold cured, wires removed and aluminum molds separated.

Avery, D. E.↗
NASA NTRS1984

Space station architecture, module, berthing hub, shell assembly, berthing mechanism and utility connection channel

The geometric form of a space station is presented that includes a description of a plurality of modules and berthing hubs, joined by interconnections which are sideways connectable. The modules and hubs are fastened together in a triangular configuration in three dimensions. The interconnections include a pair of opposed, axially aligned, flanged ports and a clamp latch formed from a plurality of sections hinged along their length and extending circumferentially around the flanged ports. A hermetic seal is formed between the ports. A utilities connection channel extends between the ports. The channel has a shell with utilities connectors movable between an extended position to mating connectors in the modules and a withdrawn position. Assembly sequence and common module shell structure is detailed.

Cohen, M. M.↗
NASA NTRS1983

The infrared echo of a type II supernova with a circumstellar dust shell - Applications to SN 1979c and SN 1980k

Merrill (1980) and Telesco et al. (1981) have reported observations according to which supernovae developed a thermal infrared excess about 7-9 months after visual maximum. The two supernovae involved are SN 1979c in NGC 4321 and SN 1980k in NGC 6946. The infrared behavior of these supernovae is almost identical to that observed in several novae. The present investigation is concerned with the question whether the thermal infrared radiation from SN 1979c and SN 1980k could have been emitted by dust particles which were present in a circumstellar shell prior to the supernova event. The obtained results confirm the suggestion of Bode and Evans (1980) that the thermal emission from SN 1979c may have originated from preexisting dust present in a circumstellar shell and heated up by the UV-visual output of the supernova. The thermal infrared emission from SN 1980k may have a similar origin.

Dwek, E.↗
NASA NTRS1983

Metal shell technology

Metallic shells are fabricated for a size range from several millimeters down to less than 500 microns in diameter. The technology, developed at JPL, is based on the hollow-jet instability for the large-shell formation, and in addition, on the Bernoulli's force for the microbubble generation. Various materials were processed into hollow spheres, such as AL1100, tin, lead, and a metallic glass-forming alloy, AuPbSb. They exhibited a range of contrasting solidification behaviors and surface characteristics. Some of their potential applications will be explored in this paper.

Lee, M. C.↗
NASA NTRS1983

Ultraviolet spectroscopic observations of some Be stars of later type and A-F type shell stars

High-dispersion IUE spectra of 18 later type Be and A-F type shell stars as well as eight standard nonemission line stars have been analyzed for anomalous ionization and mass loss effects. It is found that superionization in the Be stars extends to the latest spectral subtypes but does not seem to be present in the A-F type stars. The superionized lines in the Be stars appear to be correlated with v sin i. Asymmetrical or violet-displaced resonance lines suggesting mass loss are observed in all the Be stars except one, in some of the standard stars, but not in the A-F stars. Lower limits to the mass loss rates computed from Si IV lines range between 5.3 x 10 to the -12th and 3.5 x 10 to the -11th solar masses/yr, with Be shell stars showing the largest values. Mass loss is correlated with luminosity and effective temperature but not with rotation.

Carpenter, K. G.↗
NASA NTRS1984

Observation of an oscillating magnetic field shell at three locations

The complex magnetic-pulsation event near magnetic shell L = 4.5 at 1830-1930 UT on July 14, 1982, is characterized on the basis of observations obtained by the DE-1 satellite near the equator and by magnetic stations at Siple, Antarctica, and Roberval, Quebec, Canada, at opposite ends of the L = 4.2 field line. The data are presented graphically and discussed in the light of theoretical models. The main features (in sequence) observed were a brief 120-sec compressional pulsation, a 5-nT 180-sec transverse pulsation, a weak 44-sec transverse pulsation, and a rapidly developing 240-sec azimuthal pulsation. The 180-sec and 240-sec pulsations are found to be large-scale toroidal oscillations on one and two resonant shells, respectively, while the 44-sec pulsation appears to be more localized.

Cahill, L. J.↗
NASA NTRS1984

A triangular finite element for thin plates and shells

A finite element modeling technique which utilizes a triangular element called TSHEL with 45 degrees of freedom and seven point integration was tested for analysis of thin plate and shell structures. The element formulation is based on the degenerate solid shell concept and the mixed formulation with assumed independent inplane and transverse shear strains. The effectiveness of the present modeling technique which features combined use of elements with kinematic modes and those without kinematic modes to eliminate both locking and spurious kinematic modes at the global structural levels are shown.

Lee, S. W.↗
NASA NTRS1984

The variable component of the NGC 4151 IUE spectrum - Evidence for an expanding spherical emission shell

The profile of the forbidden line of C III (1909) is the same in two pseudo-trailed, low-resolution SWP spectra of the nucleus of the Seyfert galaxy NGC 4151 obtained with the IUE in November 1980 and December 1982, respectively. In the 1980 spectrum, the C III forbidden line profile is also very nearly the same as that of the resonance line C IV (1550). In the 1982 spectrum, the continuum is 5 times higher and C IV is both much broader and much brighter. In the difference spectrum, which is interpreted to be the spectrum of a time-variable component, C IV (1550) is the only strong emission feature. The profile of this line closely resembles that of a spherical shell surrounding a less dense gas uniformly expanding from a central opaque object. From values of the profile parameters and from the observed time variability of the object, it is inferred that the shell has a radius of about 10 to the 15th cm, a mass of 0.25 solar mass, an expansion velocity of 13,000 km/s, and an electron density of 10 to the 11th per cu cm. From the line profile and the continuum, it is inferred that the opaque central source has approximate radius of 10 to the 14th cm and temperature 23,000 K.

Stoner, R.↗
NASA NTRS1984

Hybrid Semiloof elements for plates and shells based upon a modified Hu-Washizu principle

Hybrid SemiLoof elements for plates and shells are developed based upon modified Hu-Washizu principle. In the new version of the assumed stress hybrid formulation the equilibrium equations are satisfied through the introduction of internal displacement parameters as Lagrange multipliers. The inversion of the resulting H-matrices is simplified particularly when the stresses are expressed in terms of natural coordinates. A 24-DOF triangular element and a 32-DOF quadrilateral element based on shallow shell theory are derived and evaluated.

Pian, T. H. H.↗
NASA NTRS1985

The sound field in a finite cylindrical shell

The sound field excited by vibrating boundaries in a finite cylindrical space, e.g., in a cylindrical shell, differs from the pressure distribution in an infinite cylindrical shell of comparable structural wavelength by the pressure diffracted by the end caps. The latter pressure component is comparable in magnitude to the pressure generated by the vibrating cylindrical boundary, but does not introduce additional resonances or antiresonances. Finally, a third pressure component associated with end cap vibrations is formulated.

Junger, M. C.↗
NASA NTRS1986

Line Spring Model and Its Applications to Part-Through Crack Problems in Plates and Shells

The line spring model is described and extended to cover the problem of interaction of multiple internal and surface cracks in plates and shells. The shape functions for various related crack geometries obtained from the plane strain solution and the results of some multiple crack problems are presented. The problems considered include coplanar surface cracks on the same or opposite sides of a plate, nonsymmetrically located coplanar internal elliptic cracks, and in a very limited way the surface and corner cracks in a plate of finite width and a surface crack in a cylindrical shell with fixed end.

Erdogan, F.↗
NASA NTRS1985

Mixed models and reduction method for dynamic analysis of anisotropic shells

A time-domain computational procedure is presented for predicting the dynamic response of laminated anisotropic shells. The two key elements of the procedure are: (1) use of mixed finite element models having independent interpolation (shape) functions for stress resultants and generalized displacements for the spatial discretization of the shell, with the stress resultants allowed to be discontinuous at interelement boundaries; and (2) use of a dynamic reduction method, with the global approximation vectors consisting of the static solution and an orthogonal set of Lanczos vectors. The dynamic reduction is accomplished by means of successive application of the finite element method and the classical Rayleigh-Ritz technique. The finite element method is first used to generate the global approximation vectors. Then the Rayleigh-Ritz technique is used to generate a reduced system of ordinary differential equations in the amplitudes of these modes. The temporal integration of the reduced differential equations is performed by using an explicit half-station central difference scheme (Leap-frog method). The effectiveness of the proposed procedure is demonstrated by means of a numerical example and its advantages over reduction methods used with the displacement formulation are discussed.

Noor, A. K.↗
NASA NTRS1986

Electrostatic instabilities of velocity-space-shell distributions in magnetized plasmas

Electron instabilities of magnetized spherical shell distributions in velocity space with a colder Maxwellian background are investigated analytically with simulations using electrostatic particle codes. The resonant and nonresonant instabilities observed in the particle simulations are in agreement with zeros of the dielectric function, as found from the resonant approximations for waves with an electric field component along the magnetic field or by computation with a root solver code in the case of perpendicular propagation. Saturation of the instabilities is by nonlinear cyclotron resonance with the cold background in the resonant case or by nonstochastic cyclotron harmonic damping by the cold background in the nonresonant case. Instabilities invariably lead to perpendicular acceleration and heating of the cold background to velocities sometimes exceeding the shell velocity.

Sentman, D. D.↗