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At least 163 records · Page 9

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NASA NTRS1989

Reflections, diffractions, and surface waves for an interior impedance wedge of arbitrary angle

The asymptotic-impedance wedge solution for plane-wave illumination at normal incidence is examined for interior wedge diffraction. An efficient method for calculating the diffraction coefficient for arbitrary wedge angle is presented. The asymptotic solution isolates the incident, singly reflected, multiply reflected, diffracted, surface-wave, and associated-surface-wave transition fields. Multiply reflected fields (of any order) from the exact solution arise as ratios of auxiliary Maliuzhinets functions; however, by using properties of these functions, the representation can be reduced to products of reflection coefficients, much more efficient for calculation. A surface-wave transition field is added to the surface wave to retain continuity of the total field at the surface wave boundaries. This formulation is equally valid for both exterior and interior wedges with uniform but different impedances on each face, for both soft and hard polarizations.

Griesser, Timothy↗

NASA NTRS1988

SOHO: An observatory to study the solar interior and the solar atmosphere

The Solar and Heliospheric Observatory (SOHO) is described. The two main objectives of SOHO are to improve understanding of solar coronal phenomena and to study solar structure and interior dynamics from its core to the photosphere. The primary goals of the coronal and solar wind studies are to understand the coronal heating mechanism and its expansion into the solar wind. These goals will be achieved both by remote sensing of the solar atmosphere with high resolution spectrometers and telescopes and by in situ measurement of the composition and energy of the resulting solar wind and the energetic particles that propagate through it. The structure and interior dynamics are to be studied by helioseismological methods and the measurement of solar irradiance variations. The SOHO spacecraft will be three-axis stabilized and located in a halo orbit around the L1 Lagrangian point (approximately 1 percent of the distance from the Earth to the Sun). It is currently scheduled for launch in July 1995.

Domingo, V.↗

NASA NTRS1989

A preliminary design of interior structure and foundation of an inflatable lunar habitat

A preliminary structural design and analysis of an inflatable habitat for installation on the moon was completed. The concept takes the shape of a sphere with a diameter of approximately 16 meters. The interior framing provides five floor levels and is enclosed by a spherical air-tight membrane holding an interior pressure of 14.7 psi (101.4kpa). The spherical habitat is to be erected on the lunar surface with the lower one third below grade and the upper two thirds covered with a layer of lunar regolith for thermal insulation and shielding against radiation and meteoroids. The total dead weight (earth weight) of the structural aluminum, which is of vital interest for the costly space transportation, is presented. This structural dead weight represents a preliminary estimate without including structural details. The design results in two versions: one supports the weight of the radiation shielding in case of deflation of the fabric enclosure and the other assumes that the radiation shielding is self supporting. To gain some indication of the amount of structural materials needed if the identical habitat were installed on Mars and Earth, three additional design versions were generated where the only difference is in gravity. These additional design versions are highly academic since the difference will be much more than in gravity alone. The lateral loading due to dust storms on Mars and wind loads on Earth are some examples. The designs under the lunar gravity are realistic. They may not be adequate for final material procurement and fabrication, however, as the connection details, among other reasons, may effect the sizes of the structural members.

Yin, Paul K.↗

NASA NTRS1991

Flexible Interior-Impression-Molding Tray

Device used inside combustion chamber of complicated shape for nondestructive evaluation of qualities of welds, including such features as offset, warping, misalignment of parts, and dropthrough. Includes flexible polypropylene tray trimmed to fit desired interior surface contour. Two neodymium boron magnets and inflatable bladder attached to tray. Tray and putty inserted in cavity to make mold of interior surface.

Anders, Jeffrey E.↗

NASA NTRS1990

Electrical conductivity of Jupiter's shallow interior and the formation of a resonant of a resonant planetary-ionospheric cavity

The present consideration of hydrogenic atmospheric reactions on Jupiter, to a depth of 4000 km, notes the primary ion constituents at these depths to be both positive and negative ions of molecular hydrogen contributing less than 20 percent to total electrical conductivity by free electrons. An electrical surface defined by the boundary beneath which the interior is electrically conducting exists at depths which vary according to EM wave frequency, from 1100 km for 1 mHz to 3000 for 1 MHz. The presence of a lower electrical boundary within the shallow interior suggests that a planetary-ionosphere resonant cavity analogous to the earth-ionosphere cavity may exist.

Sentman, D. D.↗

NASA NTRS1991

Interiors and atmospheres of the outer planets

This theoretical/observational project constrains structure of outer planet atmospheres and interiors through observational data. The primary observation tool is through observations of occultations of stars by outer solar system objects, which yield information about atmospheric temperatures and dynamics, and planetary dimensions and oblateness. The theoretical work relates the data to interior structures in a variety of ways.

Hubbard, W. B.↗

NASA NTRS1991

Interior Noise

The generation and control of flight vehicle interior noise is discussed. Emphasis is placed on the mechanisms of transmission through airborne and structure-borne paths and the control of cabin noise by path modification. Techniques for identifying the relative contributions of the various source-path combinations are also discussed along with methods for the prediction of aircraft interior noise such as those based on the general modal theory and statistical energy analysis.

Mixson, John S.↗

NASA NTRS1992

Fourth Aircraft Interior Noise Workshop

The fourth in a series of NASA/SAE Interior Noise Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft noise with emphasis on source noise prediction; cabin noise prediction; cabin noise control, including active and passive methods; and cabin interior noise procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues.

David G. Stephens↗

NASA NTRS1992

Active control of interior noise in a large scale cylinder using piezoelectric actuators

The noise reduction effectiveness of two types of control force actuator models has been analytically investigated: (1) a point actuator, and (2) an in-plane, piezoelectric actuator. The actuators were attached to the wall of a simply supported, elastic cylinder closed with rigid end caps. Control inputs to the actuators were determined such that the integrated square of the pressure over the interior of the vibrating cylinder was a minimum. Significant interior noise reductions were achieved for all actuator configurations, but especially for the structurally dominated response. Noise reduction of 9 dB to 26 dB were achieved using point force actuators, as well as localized and extended piezoelectric actuators. Control spillover was found to limit overall performance for all cases. However, the use of extended piezoelectric actuators was effective in reducing control spillover, without increasing the number of control degrees of freedom.

Lester, H. C.↗

NASA NTRS1992

Crystallization, sublimation, and gas release in the interior of a porous comet nucleus

A numerical code is developed for evolutionary calculations of the thermal structure and composition of a porous comet nucleus made of water ice, in amorphous or crystalline form, other volatiles, dust, and gases trapped in amorphous ice. Bulk evaporation, crystallization, gas release, and free (Knudsen) flow of gases through the pores are taken into account. The numerical scheme yields exact conservation laws for mass and energy. The code is used to study the effect of bulk evaporation of ice in the interior of a comet nucleus during crystallization. It is found that evaporation controls the temperature distribution; the vapor prevents cooling of the crystallized layer of ice, by recondensation and release of latent heat. Thus high temperatures are maintained below the surface of the nucleus and down to depths of tens or hundreds of meters, even at large heliocentric distances, as long as crystallization goes on. Gas trapped in the ice and released during the phase transition flows both toward the interior and toward the surface and out of the nucleus. The progress of crystallization is largely determined by the contribution of gas fluxes to heat transfer.

Prialnik, Dina↗

NASA NTRS1991

A TOPEX/Poseidon study of oceanic effects on observations of the Earth's interior

The primary objective of our research program is the application of TOPEX/POSEIDON oceanic data to the study of various geophysical observations, thereby improving our knowledge of the Earth's interior. Observations of the Earth's solid tides, rotation, time-dependent gravity, and crustal deformation provide potentially useful constraints on properties of the solid Earth and its liquid core, but all these parameters are also sensitive to oceanic effects. Depending on the type of observation, those effects are usually either removed by modeling (often using particularly simple assumptions about the dynamics of the ocean) or ignored entirely. Useful oceanic data are rarely available. In many cases, the uncertainty in the oceanic correction is the main source of error in the geophysical interpretation of the results. We describe, below several of these geophysical observations, how their interpretation in terms of the Earth's interior is affected by the oceans, and how data from the TOPEX/POSEIDON mission can be used to improve this situation.

Wahr, John↗

NASA NTRS1992

Chemical differentiation of a convecting planetary interior - Consequences for a one plate planet such as Venus

Simple models of the thermal and chemical evolution of a planetary interior are developed to explore the possible consequences of a chemically buoyant depleted mantle layer for planetary evolution. As the depleted layer thickens the melting temperature at the top of the underlying convecting mantle also increases and the degree of partial melting of the mantle added to the depleted layer decreases. As the less depleted mantle with less positive compositional buoyancy is added, the negative thermal buoyancy of the layer eventually exceeds its positive compositional buoyancy. The depleted layer then sinks into and mixes with the convecting interior. On Venus the population of impact craters is indistinguishable from a random distribution over the surface and gives a surface age of about 500 Myr. It is suggested that the above mechanism may explain this episodic global resurfacing of Venus.

Parmentier, E. M.↗

NASA NTRS1992

Evaluation of piezoceramic actuators for control of aircraft interior noise

Results of an experiment to evaluate piezoceramic actuators as the control actuator for active control of interior noise in a large-scale fuselage model are presented. Control was demonstrated for tonal excitation using a time domain least mean squares algorithm. A maximum of four actuator channels and six error signals were used. The actuators were employed for control of noise at frequencies where interior cavity modes were the dominant response and for driven acoustic responses where a structure resonance was dominant. Global reductions of 9 to 12 dB were obtained for the cases examined. The most effective configuration of skin-mounted actuators was found to be a pure in-plane forcing function as opposed to a bending excitation. The frame-mounted actuators were found to be equally effective as the skin-mounted actuators. However, both configurations resulted in local regions of unacceptably high vibration response in the structure.

Silcox, Richard J.↗

NASA NTRS1990

SOHO - An observatory to study the solar interior and the solar atmosphere

Poland, A. I.↗

NASA NTRS1991

Active control of interior noise in a large scale cylinder using piezoelectric actuators

Lester, H. C.↗

NASA NTRS1993

Gravitational tides in the outer planets. I - Implications of classical tidal theory. II - Interior calculations and estimation of the tidal dissipation factor

Classical tidal theory is applied to the atmospheres of the outer planets. The tidal geopotential due to satellites of the outer planets is discussed, and the solution of Laplace's tidal equation for Hough modes appropriate to tides on the outer planets is examined. The vertical structure of tidal modes is described, noting that only relatively high-order meridional mode numbers can propagate vertically with growing amplitude. Expected magnitudes for tides in the visible atmosphere of Jupiter are discussed. The classical theory is extended to planetary interiors taking the effects of spherically and self-gravity into account. The thermodynamic structure of Jupiter is described and the WKB theory of the vertical structure equation is presented. The regions for which inertial, gravity, and acoustic oscillations are possible are delineated. The case of a planet with a neutral interior is treated, discussing the various atmospheric boundary conditions and showing that the tidal response is small.

Ioannou, Petros J.↗

NASA NTRS1993

The problem of exact interior solutions for rotating rigid bodies in general relativity

The (3 + 1) dyadic formalism for timelike congruences is applied to derive interior solutions for stationary, axisymmetric, rigidly rotating bodies. In this approach the mathematics is formulated in terms of three-space-covariant, first-order, vector-dyadic, differential equations for a and Omega, the acceleration and angular velocity three-vectors of the rigid body; for T, the stress dyadic of the matter; and for A and B, the 'electric' and 'magnetic' Weyl curvature dyadics which describe the gravitational field. It is shown how an appropriate ansatz for the forms of these dyadics can be used to discover exact rotating interior solutions such as the perfect fluid solution first published in 1968. By incorporating anisotropic stresses, a generalization is found of that previous solution and, in addition, a very simple new solution that can only exist in toroidal configurations.

Wahlquist, H. D.↗

NASA NTRS1993

Analytical evaluation of a surface integral expressing the coupling between interior and exterior volumes in a FE-IE approach

Recently an approach which combines the finite element technique and an integral equation to determine the fields scattered by inhomogeneous bodies of complicated shape has been proposed. Basically, a mathematical surface which encloses the scatterers is introduced, thus dividing the space into an interior and an exterior volume, in which the finite element technique and an integral equation for EM scattering, respectively, are applied. The integral equation is set up for the tangential components of the fields at the surface, while the interior volume the unknowns are the total fields. Continuity of the tangential fields at the boundary, as required by Maxwell's equations, is imposed, thus coupling the two methods to obtain a consistent solution. The coupling term is expressed by a surface integral formed by the dot product of a FE basis function and an IE testing function, or viceversa. By choosing the boundary to be a surface of revolution and by making a convenient selection of IE basis (testing) functions, it is possible to evaluate the integrals analytically on surfaces such as curved triangles, curved quadrilaterals and curved pentagons. We will illustrate the salient steps involved in setting up and carrying out these integrals and discuss what class of basis (testing) functions and analytic surfaces of revolution they are applicable to. Analytic calculations offer the advantage of better accuracy than purely numerical ones, and, when combined with them, often shed light on issues of numerical convergence and limiting values. Furthermore, they may reduce computation time and storage requirements.

Zuffada, C.↗