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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

All-theoretical prediction of cabin noise due to impingement of propeller vortices on a wing structure

Reported calculations of structure-borne cabin noise for a small twin engine aircraft powered by tractor propellers rely on the following three-stage methodological breakup of the problem: (1) the unsteady-aerodynamic prediction of wing lift harmonics caused by the whipping action of the vortex system trailed from each propeller; (2) the associated wing/fuselage structural response; (3) the cabin noise field for the computed wall vibration. The first part--the estimate of airloads--skirts a full-fledged aeroelastic situation by assuming the wing to be fixed in space while cancelling the downwash field of the cutting vortices. The model is based on an approximate high-frequency lifting-surface theory justified by the blade rate and flight Mach number of application. Its results drive a finite-element representation of the wing accounting for upper and lower skin surfaces, spars, ribs, and the presence of fuel. The fuselage, modeled as a frame-stiffened cylindrical shell, is bolted to the wing.

Martinez, R.↗
NASA NTRS1990

PATRAN-STAGS translator (PATSTAGS)

A a computer program used to translate PATRAN finite element model data into Structural Analysis of General Shells (STAGS) input data is presented. The program supports translation of nodal, nodal constraints, element, force, and pressure data. The subroutine UPRESS required for the readings of live pressure data into STAGS is also presented.

Otte, Neil↗
NASA NTRS1990

Analysis of the thermal performance of heat pipe radiators

A comprehensive mathematical model and computational methodology are presented to obtain numerical solutions for the transient behavior of a heat pipe radiator in a space environment. The modeling is focused on a typical radiator panel having a long heat pipe at the center and two extended surfaces attached to opposing sides of the heat pipe shell in the condenser section. In the set of governing equations developed for the model, each region of the heat pipe - shell, liquid, and vapor - is thermally lumped to the extent possible, while the fin is lumped only in the direction normal to its surface. Convection is considered to be the only significant heat transfer mode in the vapor, and the evaporation and condensation velocity at the liquid-vapor interface is calculated from kinetic theory. A finite-difference numerical technique is used to predict the transient behavior of the entire radiator in response to changing loads.

Boo, J. H.↗
NASA NTRS1993

Design, analysis, and fabrication of a pressure box test fixture for tension damage tolerance testing of curved fuselage panels

A pressure box test fixture was designed and fabricated to evaluate the effects of internal pressure, biaxial tension loads, curvature, and damage on the fracture response of composite fuselage structure. Previous work in composite fuselage tension damage tolerance, performed during NASA contract NAS1-17740, evaluated the above effects on unstiffened panels only. This work extends the tension damage tolerance testing to curved stiffened fuselage crown structure that contains longitudinal stringers and circumferential frame elements. The pressure box fixture was designed to apply internal pressure up to 20 psi, and axial tension loads up to 5000 lb/in, either separately or simultaneously. A NASTRAN finite element model of the pressure box fixture and composite stiffened panel was used to help design the test fixture, and was compared to a finite element model of a full composite stiffened fuselage shell. This was done to ensure that the test panel was loaded in a similar way to a panel in the full fuselage shell, and that the fixture and its attachment plates did not adversely affect the panel.

Smith, P. J.↗
NASA NTRS1994

ROSAT HRI observations of Magellanic Cloud supernova remnants

Analysis of deep ROSAT high resolution imager (HRI) observations of two oxygen-rich supernova remnants (SNR's) in the Magellanic Clouds is described. For N132D, I exploit the limited spectral information provided by the HRI to investigate arcsecond scale spectral variations. I find that there is a region of harder X-ray emission near the southern limb and regions of softer emission near the center and northwestern limb. The remnant is believed to be interacting with a molecular cloud and the harder emission to the south is explained as a result of increased absorption along the line-of-sight there. I argue that the softer emission comes from X-ray emitting material with an enhanced abundance of oxygen. For the second SNR, E0102.2 72.2, the spatial structure is investigated in detail using two-dimensional image fitting techniques. Evidence is found for a ring-like and a spherically symmetric shell-like component both of which were modeled as homogeneous regions. In addition, a significant fraction of the observed flux (approximately 11 percent) must come from a resolved clumped component. A comparison with optical and radio imagery is made to provide a physical basis for the components identified in the X-ray analysis. The mass of X-ray emitting gas in the remnant is estimated and a value of approximately 75 M(solar mass) was determined. The dominant uncertainty on this quantity is the extent of unresolved clumping in the X-ray gas. Such clumping would tend to reduce the mass estimate by f(exp 1/2), where f is the mean volume filling factor of the gas.

Hughes, John P.↗
NASA NTRS1998

Compression Strength of Composite Primary Structural Components

Research conducted under NASA Grant NAG-1-537 focussed on the response and failure of advanced composite material structures for application to aircraft. Both experimental and analytical methods were utilized to study the fundamental mechanics of the response and failure of selected structural components subjected to quasi-static loads. Most of the structural components studied were thin-walled elements subject to compression, such that they exhibited buckling and postbuckling responses prior to catastrophic failure. Consequently, the analyses were geometrically nonlinear. Structural components studied were dropped-ply laminated plates, stiffener crippling, pressure pillowing of orthogonally stiffened cylindrical shells, axisymmetric response of pressure domes, and the static crush of semi-circular frames. Failure of these components motivated analytical studies on an interlaminar stress postprocessor for plate and shell finite element computer codes, and global/local modeling strategies in finite element modeling. These activities are summarized in the following section. References to literature published under the grant are listed on pages 5 to 10 by a letter followed by a number under the categories of journal publications, conference publications, presentations, and reports. These references are indicated in the text by their letter and number as a superscript.

Johnson, Eric R.↗
NASA NTRS1999

Backus Effect on a Perpendicular Errors in Harmonic Models of Real vs. Synthetic Data

Measurements of geomagnetic scalar intensity on a thin spherical shell alone are not enough to separate internal from external source fields; moreover, such scalar data are not enough for accurate modeling of the vector field from internal sources because of unmodeled fields and small data errors. Spherical harmonic models of the geomagnetic potential fitted to scalar data alone therefore suffer from well-understood Backus effect and perpendicular errors. Curiously, errors in some models of simulated 'data' are very much less than those in models of real data. We analyze select Magsat vector and scalar measurements separately to illustrate Backus effect and perpendicular errors in models of real scalar data. By using a model to synthesize 'data' at the observation points, and by adding various types of 'noise', we illustrate such errors in models of synthetic 'data'. Perpendicular errors prove quite sensitive to the maximum degree in the spherical harmonic expansion of the potential field model fitted to the scalar data. Small errors in models of synthetic 'data' are found to be an artifact of matched truncation levels. For example, consider scalar synthetic 'data' computed from a degree 14 model. A degree 14 model fitted to such synthetic 'data' yields negligible error, but amplifies 4 nT (rmss) added noise into a 60 nT error (rmss); however, a degree 12 model fitted to the noisy 'data' suffers a 492 nT error (rmms through degree 12). Geomagnetic measurements remain unaware of model truncation, so the small errors indicated by some simulations cannot be realized in practice. Errors in models fitted to scalar data alone approach 1000 nT (rmss) and several thousand nT (maximum).

Voorhies, C. V.↗
NASA NTRS2002

A Solar Model with g-Modes

Good evidence is assembled showing that the Suit's core arid surface vary on time scales from a month to a decade arid that a number of scales are similar. The most plausible source for numerous long time scales and periodicities is long-lived global oscillations. This suggests g-modes (oscillations restored mainly by buoyancy) because they particularly affect the core and base of the convective envelope, which then indirectly modulates the surface. Also, standing g-modes have rotational properties that match many observed periodicities. But the standard solar model (SSM) has a static core and excites few if any g-modes. making new interior structures worth exploring. The model outlined here assumes two well mixed shells near 0.18 and 0.68 R, (13 = solar radius) where sound speed data shows sharp deviations from the SSM. Mixing is sustained by flows driven by the oscillations. The shells form a cavity that excludes g-modes from their main damping region below 0.1 R, assisting their net excitation and increasing their oscillation periods by at least a factor of two and probably much more. In terms of the solar luminosity L, the modes transport up through the cavity a power approx. 0.004 L as a lower limit and 0.11 L as all upper limit. The modes dissipate energy in the outer shell and cool the inner shell, asymmetrically in each case, and this stimulates occasional convective events whose response time is typically 0.8 years longer near the inner shell. Such events cool the core and reduce neutrino flux while heating the envelope and increasing solar activity. This gives a physical basis for a well mixed Sun with low neutrino flux and basis for the observed anticorrelation and lag of neutrino behind surface activity.

Wolff, Charles L.↗
NASA NTRS2002

Analysis, Design and Optimization of Non-Cylindrical Fuselage for Blended-Wing-Body (BWB) Vehicle

Initial results of an investigation towards finding an efficient non-cylindrical fuselage configuration for a conceptual blended-wing-body flight vehicle were presented. A simplified 2-D beam column analysis and optimization was performed first. Then a set of detailed finite element models of deep sandwich panel and ribbed shell construction concepts were analyzed and optimized. Generally these concepts with flat surfaces were found to be structurally inefficient to withstand internal pressure and resultant compressive loads simultaneously. Alternatively, a set of multi-bubble fuselage configuration concepts were developed for balancing internal cabin pressure load efficiently, through membrane stress in inner-stiffened shell and inter-cabin walls. An outer-ribbed shell was designed to prevent buckling due to external resultant compressive loads. Initial results from finite element analysis appear to be promising. These concepts should be developed further to exploit their inherent structurally efficiency.

Mukhopadhyay, V.↗
NASA NTRS2009

Enceladus: An Active Cryovolcanic Satellite

Enceladus is one of the most remarkable satellites in the solar system, as revealed by Cassini's detection of active plumes erupting from warm fractures near its south pole. This discovery makes Enceladus the only icy satellite known to exhibit ongoing internally driven geological activity. The activity is presumably powered by tidal heating maintained by Enceladus 2:1 mean-motion resonance with Dione, but many questions remain. For instance, it appears difficult or impossible to maintain the currently observed radiated power (probably at least 6 GW) in steady state. It is also not clear how Enceladus first entered its current self-maintaining warm and dissipative state initial heating from non-tidal sources is probably required. There are also many unanswered questions about Enceladus interior. The silicate fraction inferred from its density of 1.68 g per cubic centimeter is probably differentiated into a core, though we have only indirect evidence for differentiation. Above the core there is probably a global or regional water layer, inferred from several models of tidal heating, and an ice shell thick enough to support the ~1 kilometer amplitude topography seen on Enceladus. It is possible that dissipation is largely localized beneath the south polar region. Enceladus surface geology, ranging from moderately cratered terrain to the virtually crater-free active south polar region, is highly diverse, tectonically complex, and remarkably symmetrical about the rotation axis and the direction to Saturn. South polar activity is concentrated along the four tiger stripe fractures, which radiate heat at temperatures up to at least 167 K and are the source of multiple plumes ejecting ~200 kilograms per second of H2O vapor along with significant N2 (or C2H4), CO2, CH4, NH3, and higher-mass hydrocarbons. The escaping gas maintains Saturn's neutral gas torus, and the plumes also eject a large number of micron-sized H2O ice grains that populate Saturn's E-ring. The mechanism that powers the plumes is not well understood, and whether liquid water is involved is a subject of active debate (but likely nonetheless). Enceladus provides a promising potential habitat for life in the outer solar system, and the active plumes allow the unique opportunity for direct sampling of that zone. Enceladus is thus a prime target for Cassini's continued exploration of the Saturn system, and will be a tempting target for future missions.

Spencer, J. R.↗
NASA NTRS2016

Magnetohydrodynamic Turbulence and the Geodynamo

Recent research results concerning forced, dissipative, rotating magnetohydrodynamic (MHD) turbulence will be discussed. In particular, we present new results from long-time Fourier method (periodic box) simulations in which forcing contains varying amounts of magnetic and kinetic helicity. Numerical results indicate that if MHD turbulence is forced so as to produce a state of relatively constant energy, then the largest-scale components are dominant and quasistationary, and in fact, have an effective dipole moment vector that aligns closely with the rotation axis. The relationship of this work to established results in ideal MHD turbulence, as well as to models of MHD turbulence in a spherical shell will also be presented. These results appear to be very pertinent to understanding the Geodynamo and the origin of its dominant dipole component. Our conclusion is that MHD turbulence, per se, may well contain the origin of the Earth's dipole magnetic field.

Shebalin, John V.↗
NASA NTRS1998

Thermomechanical Postbuckling of Shells

A number of issues involving the postbuckling of doubly-curved panels exposed to a non-uniform temperature field and subjected to a system of mechanical loads are considered in this paper. Effects played by transverse shear, initial geometric imperfections, membrane and thickness-wise temperature gradient, tangential edge constraints, linear/non-linear elastic foundation are incorporated and their implications on the non-linear response behavior of shells are discussed. Issues related with the delay of the occurrence of the snap-through buckling, alleviation of its intensity and even with its removal are addressed and remarks on conditions rendering a curved panel insensitive to initial geometric imperfections are included. Results on small vibration of shells about sub- and post-critical ranges are provided and structural modeling issues playing a non-negligible role towards a reliable prediction of the postbuckling behavior of shells under complex loading conditions are discussed. Results on non-linear response of flat reinforced panels subjected to thermomechanical loads are also presented. Finally, problems not covered by this article are briefly indicated.

Librescu, Liviu↗
NASA NTRSDate not supplied

Toward the fabrication of a 5 μm resolution Wolter microscope for the National Ignition Facility

Advancements in computer-controlled polishing, metrology, and replication have led to a x-ray mirror fabrication process that is capable of producing high-resolution Wolter microscopes. The mirror is a nickel-cobalt replicated full-shell mirror that was electroformed from a finely figured and polished mandrel. This mandrel was designed and fabricated for a 8 m source-to-detector distance microscope, with 10× magnification. A computer controlled polishing process corrected the low-frequency mandrel figure to < 2.0 nm RMS error. The mandrel design was optimized to reduce shell distortions that occur mainly < 20 mm from the shell ends. This design, in combination with improved replication tooling design and refined bath parameters informed by a detailed COMSOL model, have led to reductions in replication errors in the mirror shell. X-ray tests performed on a pair of mirror shells replicated from the mandrel have demonstrated < 10 μm FWHM source plane imaging resolution. Here we discuss the development process, highlight results from metrology and x-ray testing, and define a path for achieving 5 μm FWHM resolution.

Grazing Incidence, Wolter Microscope, X-ray Optics↗
NASA NTRS1972

Jupiter trapped radiation belts

Previously developed models for trapped electron radiation belts and trapped proton radiation belts in the Jovian magnetosphere are described. The spatial distribution of flux and the L shell dependence of the characteristic energy are displayed for both models. Based on these models, the fluence accumulated by a Jupiter flyby spacecraft is given in terms of the equivalent 3-MeV fluence for electrons and the equivalent 20-MeV proton fluence. Finally, some impacts of these fluences on outer planet missions are described.

Beck, A. J., Jr.↗
NASA NTRS1991

Model-based diagnostics for Space Station Freedom

An innovative approach to fault management was recently demonstrated for the NASA LeRC Space Station Freedom (SSF) power system testbed. This project capitalized on research in model-based reasoning, which uses knowledge of a system's behavior to monitor its health. The fault management system (FMS) can isolate failures online, or in a post analysis mode, and requires no knowledge of failure symptoms to perform its diagnostics. An in-house tool called MARPLE was used to develop and run the FMS. MARPLE's capabilities are similar to those available from commercial expert system shells, although MARPLE is designed to build model-based as opposed to rule-based systems. These capabilities include functions for capturing behavioral knowledge, a reasoning engine that implements a model-based technique known as constraint suspension, and a tool for quickly generating new user interfaces. The prototype produced by applying MARPLE to SSF not only demonstrated that model-based reasoning is a valuable diagnostic approach, but it also suggested several new applications of MARPLE, including an integration and testing aid, and a complement to state estimation.

Fesq, Lorraine M.↗
NASA NTRS1990

Experimental determination of convective heat transfer coefficients in the separated flow region of the Space Shuttle Solid Rocket Motor

A series of cold flow heat transfer tests was conducted with a 7.5-percent scale model of the Space Shuttle Rocket Motor (SRM) to measure the heat transfer coefficients in the separated flow region around the nose of the submerged nozzle. Modifications were made to an existing 7.5 percent scale model of the internal geometry of the aft end of the SRM, including the gimballed nozzle in order to accomplish the measurements. The model nozzle nose was fitted with a stainless steel shell with numerous thermocouples welded to the backside of the thin wall. A transient 'thin skin' experimental technique was used to measure the local heat transfer coefficients. The effects of Reynolds number, nozzle gimbal angle, and model location were correlated with a Stanton number versus Reynolds number correlation which may be used to determine the convective heating rates for the full scale Space Shuttle Solid Rocket Motor nozzle.

Whitesides, R. Harold↗
NASA NTRS1992

Composite fuselage shell structures research at NASA Langley Research Center

Fuselage structures for transport aircraft represent a significant percentage of both the weight and the cost of these aircraft primary structures. Composite materials offer the potential for reducing both the weight and the cost of transport fuselage structures, but only limited studies of the response and failure of composite fuselage structures have been conducted for transport aircraft. The behavior of these important primary structures must be understood, and the structural mechanics methodology for analyzing and designing these complex stiffened shell structures must be validated in the laboratory. The effects of local gradients and discontinuities on fuselage shell behavior and the effects of local damage on pressure containment must be thoroughly understood before composite fuselage structures can be used for commercial aircraft. This paper describes the research being conducted and planned at NASA LaRC to help understand the critical behavior or composite fuselage structures and to validate the structural mechanics methodology being developed for stiffened composite fuselage shell structure subjected to combined internal pressure and mechanical loads. Stiffened shell and curved stiffened panel designs are currently being developed and analyzed, and these designs will be fabricated and then tested at Langley to study critical fuselage shell behavior and to validate structural analysis and design methodology. The research includes studies of the effects of combined internal pressure and mechanical loads on nonlinear stiffened panel and shell behavior, the effects of cutouts and other gradient-producing discontinuities on composite shell response, and the effects of local damage on pressure containment and residual strength. Scaling laws are being developed that relate full-scale and subscale behavior of composite fuselage shells. Failure mechanisms are being identified and advanced designs will be developed based on what is learned from early results from the LaRC research activities. Results from combined load tests will be used to validate analytical models of critical nonlinear response mechanisms as well as shell scaling laws.

Starnes, James H., Jr.↗
NASA NTRS2013

Jovian Plasmas Torus Interaction with Europa. Plasma Wake Structure and Effect of Inductive Magnetic Field: 3D Hybrid Kinetic Simulation

The hybrid kinetic model supports comprehensive simulation of the interaction between different spatial and energetic elements of the Europa moon-magnetosphere system with respect to a variable upstream magnetic field and flux or density distributions of plasma and energetic ions, electrons, and neutral atoms. This capability is critical for improving the interpretation of the existing Europa flyby measurements from the Galileo Orbiter mission, and for planning flyby and orbital measurements (including the surface and atmospheric compositions) for future missions. The simulations are based on recent models of the atmosphere of Europa (Cassidy et al., 2007; Shematovich et al., 2005). In contrast to previous approaches with MHD simulations, the hybrid model allows us to fully take into account the finite gyroradius effect and electron pressure, and to correctly estimate the ion velocity distribution and the fluxes along the magnetic field (assuming an initial Maxwellian velocity distribution for upstream background ions). Photoionization, electron-impact ionization, charge exchange and collisions between the ions and neutrals are also included in our model. We consider the models with Oþ þ and Sþ þ background plasma, and various betas for background ions and electrons, and pickup electrons. The majority of O2 atmosphere is thermal with an extended non-thermal population (Cassidy et al., 2007). In this paper, we discuss two tasks: (1) the plasma wake structure dependence on the parameters of the upstream plasma and Europa's atmosphere (model I, cases (a) and (b) with a homogeneous Jovian magnetosphere field, an inductive magnetic dipole and high oceanic shell conductivity); and (2) estimation of the possible effect of an induced magnetic field arising from oceanic shell conductivity. This effect was estimated based on the difference between the observed and modeled magnetic fields (model II, case (c) with an inhomogeneous Jovian magnetosphere field, an inductive magnetic dipole and low oceanic shell conductivity).

Jovian magnetosphere↗