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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Are some chondrule rims formed by impact processes? - Observations and experiments

The ability of high-speed impacts into a parent body regolith to account for the textures and compositions observed for rims on some chondrules is presently supported by both observational and experimental data. Experimental results obtained with a light-gas gun encompass recovered-grain characteristics ranging from fragmented projectile grains mixed with melted aerogel, demonstrating that rim-like thermal and mechanical alterations of projectiles may be due to a high-velocity encounter with a low density target. Irrespective of conclusions for other types of rims, granular and opaque rim characteristics seem inconsistent with nebular condensation.

Bunch, T. E.↗
NASA NTRS1994

Characteristics of a trapped-vortex (TV) combustor

The characteristics of a Trapped-Vortex (TV) combustor are presented. A vortex is trapped in the cavity established between two disks mounted in tandem. Fuel and air are injected directly into the cavity in such a way as to increase the vortex strength. Some air from the annular flow is also entrained into the recirculation zone of the vortex. Lean blow-out limits of the combustor are determined for a wide range of annular air flow rates. These data indicate that the lean blow-out limits are considerably lower for the TV combustor than for flames stabilized using swirl or bluff-bodies. The pressure loss through the annular duct is also low, being less than 2% for the flow conditions in this study. The instantaneous shape of the recirculation zone of the trapped vortex is measured using a two-color PIV technique. Temperature profiles obtained with CARS indicate a well mixed recirculation zone and demonstrate the impact of primary air injection on the local equivalence ratio.

Hsu, K.-Y.↗
NASA NTRS1995

Reliability Analysis of Uniaxially Ground Brittle Materials

The fast fracture strength distribution of uniaxially ground, alpha silicon carbide was investigated as a function of grinding angle relative to the principal stress direction in flexure. Both as-ground and ground/annealed surfaces were investigated. The resulting flexural strength distributions were used to verify reliability models and predict the strength distribution of larger plate specimens tested in biaxial flexure. Complete fractography was done on the specimens. Failures occurred from agglomerates, machining cracks, or hybrid flaws that consisted of a machining crack located at a processing agglomerate. Annealing eliminated failures due to machining damage. Reliability analyses were performed using two and three parameter Weibull and Batdorf methodologies. The Weibull size effect was demonstrated for machining flaws. Mixed mode reliability models reasonably predicted the strength distributions of uniaxial flexure and biaxial plate specimens.

Salem, Jonathan A.↗
NASA NTRS1999

Polar Stratospheric Descent of NO(y) and CO and Arctic Denitrification During Winter 1992-1993

Observations inside the November 1994 Antarctic stratospheric vortex and inside the April 1993 remnant Arctic stratospheric vortex by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer are reported. In both instances, elevated volume mixing ratios (VMRS) of carbon monoxide (CO) were measured. A peak Antarctic CO VMR of 60 ppbv (where 1 ppbv = 10(exp -9) per unit Volume) was measured at a potential temperature of 710 K (about 27 km), about 1 km below the altitude of a pocket of elevated NO(y) (total reactive nitrogen) at a deep minimum in N2O (<5 ppbv). The Arctic observations also show a region of elevated vortex CO with a peak VMR of 90 ppbv it 630-670 K (-25 km) but no corresponding enhancement in NO(sub y) perhaps because of stronger dynamical activity in the northern hemisphere polar winter and/or interannual variability in the production of mesospheric or lower thermospheric NO. By comparing vortex and extravortex observations of NO(y) obtained at the same N2O VMR, Arctic vortex denitrification of 5 +/- 2 ppbv at 470 K (at approximately 18 km) is inferred. We show that our conclusion of substantial Arctic winter 1992-1993 denitrification is robust by comparing our extravortex observations with previous polar measurements obtained over a wide range of winter conditions. Correlations of NO(y) with N2O measured at the same potential temperature by ATMOS in the Arctic vortex and at midlatitudes on board the ER-2 aircraft several weeks later lie along the same mixing line. The result demonstrates the consistency of the two data sets and confirms that the ER-2 sampled fragments of the denitrified Arctic vortex following its breakup. An analysis of the ATMOS Arctic measurements of total hydrogen shows no evidence for significant dehydration inside the vortex.

Rinsland, C. P.↗
NASA NTRS1998

Correlations of Stratospheric Abundances of CH4 and N2O Derived from ATMOS Measurements

Atmospheric Trace MOlecule Spectroscopy (ATMOS) measurements made over a wide range of altitudes and latitudes demonstrate compact correlations between mixing ratios of CH, and N,O. Tight but distinct correlations are observed for the tropics, the springtime Arctic vortex, and the extra-tropics/extra-vortex regions, indicating dynamical isolation between these regions. Little variability is apparent in correlations between CH4 and N20 from measurements made in different years (1992, 1993, and 1994), seasons (March/April and November), and hemispheres.

Rinsland, C. P.↗
NASA NTRS2000

The Abundances of Solid N2 and Gaseous CO2 in Interstellar Dense Molecular Clouds

We present 2338-2322 per centimeter (4.277-4.307 micrometer) infrared spectra of a number of N2-containing mixed molecular ices and demonstrate that the strength of the infrared "forbidden" band due to the N=N stretch near 2328 per centimeter (4.295 micrometer) is extremely sensitive to the composition of the ice. The strength of the 2328 per centimeter N2 fundamental is significantly enhanced relative to that of pure N2 ice when NH3, H2O, or CO2 are present, but is largely unaffected by the presence of CO, CH4 or O2. We use the laboratory data in coil junction with ISO data that probes several lines-of-sight through dense molecular clouds to place limits on the abundance of interstellar solid phase N2 and the composition of the ices. Deriving upper limits is complicated by the presence of overlapping absorptions due to CO2 gas in the clouds and, in some cases, to photospheric CO in the background star. These upper limits are just beginning to be low enough to constrain interstellar grain models and the composition of possible N2-bearing interstellar ices. We outline the search criteria that will need to be met if solid interstellar N2 is to be detected in the future. We also discuss some of the implications of the presence of warm CO2 gas along the lines-of-sight to embedded protostars and demonstrate that its presence may help resolve certain puzzles associated with the previously derived gas/solid CO2 ratios and the relative abundances of polar and nonpolar ices towards these objects. Finally, we briefly comment on the possible implications of these results for the interpretation of N2 detections on outer solar system bodies.

Sandford, Scott A.↗
NASA NTRS2004

Self-Recovery Experiments in Extreme Environments Using a Field Programmable Transistor Array

Temperature and radiation tolerant electronics, as well as long life survivability are key capabilities required for future NASA missions. Current approaches to electronics for extreme environments focus on component level robustness and hardening. However, current technology can only ensure very limited lifetime in extreme environments. This paper describes novel experiments that allow adaptive in-situ circuit redesign/reconfiguration during operation in extreme temperature and radiation environments. This technology would complement material/device advancements and increase the mission capability to survive harsh environments. The approach is demonstrated on a mixed-signal programmable chip (FPTA-2), which recovers functionality for temperatures until 28 C and with total radiation dose up to 250kRad.

space vehicle electronics↗
NASA NTRS2004

High temperature experiments using programmable transistor array

Temperature and radiation tolerant electronics, as well as long life survivability are key capabilities required for future NASA missions. Current approaches to electronics for extreme environments focus on component level robustness and hardening. Compensation techniques such as bias cancellation circuitry have also been employed. However, current technology can only ensure very limited lifetime in extreme environments. This paper presents a novel approach, based on evolvable hardware technology, which allows adaptive in-situ circuit redesign/reconfiguration during operation in extreme environments. This technology would complement material/device advancements and increase the mission capability to survive harsh environments. The approach is demonstrated on a mixed-signal programmable chip, which recovers functionality until 280oC. We show in this paper the functionality recovery at high temperatures for a variety of circuits, including rectifiers, amplifiers and filters.

Duong, Vu↗
NASA NTRSDate not supplied

Statistical Engineering Toward Commercial Supersonic Flight: NASA's Quesst Mission

NASA’s Quesst Mission has dual goals of demonstrating low-noise supersonic technology in flight and surveying public reactions to low-noise supersonic overflight. For half a century, commercial aircraft have been required to fly slower than the speed of sound over land to prevent “creating an unacceptable situation” on the ground due to sonic booms. However, aircraft shaping techniques honed through decades of research have dramatically changed the way shockwaves from supersonic flight merge together as they travel to the ground. What used to sound like a boom on the ground will be transformed into a thump. NASA is now building a full-scale, piloted demonstration aircraft called the X-59 to demonstrate low-noise supersonic flight. In 2024, the X-59 aircraft will commence a national series of community overflight surveys to collect data on how people perceive “sonic thumps.” The results will be provided to national and international noise regulators as they consider creating new standards that allow commercial supersonic flight over land at acceptably low noise levels. In this presentation we provide historical context for the current prohibitions on supersonic commercial flight. Using data collected during earlier NASA tests, we demonstrate how generalized linear mixed models can be used to inform the functional dose-response curve. We also illustrate simulation experiments of the variability of sonic thump exposure across the United States. Finally, we discuss some of the challenges in designing the future community studies and generalizing them to a nationally-representative dose-response curve.

Quesst↗
NASA NTRS2001

The Origin of Hot Subluminous Horizontal-Branch Stars in (omega) Centauri and NGC 2808

Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet (UV) color magnitude diagrams of both (omega) Cen and NGC 2808. In order to explore the evolutionary status of these subluminous stars, we have evolved a set of low-mass stars continuously from the main sequence through the helium-core flash to the HB (horizontal branch) for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous EHB stars, as well as the gap within the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the 'born-again' scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This 'flash mixing' of the stellar envelope greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous jump in the HB effective temperature. We argue that the EHB gap in NGC 2808 is associated with this theoretically predicted dichotomy in the HB morphology. Using new helium- and carbon-rich stellar atmospheres, we show that these changes in the envelope abundances of the flash-mixed stars will suppress the UV flux by the amount needed to explain the hot subluminous EHB stars in (omega) Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing lie, at most, only approximately 0.1 mag below the EHB, and hence fail to explain the observations. Flash mixing may also provide a new evolutionary channel for producing the high gravity, helium-rich sdO and sdB stars.

Sweigart, Allen V.↗
NASA NTRS2016

The Relaxation Matrix for Symmetric Tops with Inversion Symmetry: Line Mixing Effects in the V1 Band of NH3 - II

Line mixing effects have been calculated in the ν1 parallel band of self-broadened NH3. The theoretical approach is an extension of a semi-classical model to symmetric-top molecules with inversion symmetry developed in the companion paper [Q. Ma and C. Boulet, J. Chem. Phys. 144, 224303 (2016)]. This model takes into account line coupling effects and hence enables the calculation of the entire relaxation matrix. A detailed analysis of the various coupling mechanisms is carried out for Q and R inversion doublets. The model has been applied to the calculation of the shape of the Q branch and of some R manifolds for which an obvious signature of line mixing effects has been experimentally demonstrated. Comparisons with measurements show that the present formalism leads to an accurate prediction of the available experimental line shapes. Discrepancies between the experimental and theoretical sets of first order mixing parameters are discussed as well as some extensions of both theory and experiment.

Boulet, C.↗
NASA NTRS2001

The Origin of Hot Subluminous Horizontal-Branch Stars in Omega Centauri and NGC 2808

Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet color-magnitude diagrams of both omega Cen (DCruz et.al. 2000) and NGC 2808 (Brown et al. 2001). In order to investigate the origin of these subluminous stars, we have constructed a detailed set of evolutionary sequences that follow the evolution of low-mass stars continuously from the zero-age main sequence through the helium-core flash to the HB for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores (Castellani & Castellani 1993). Our results indicate that the location of the subluminous EHB stars, as well as the high temperature gap along the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the main helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed (Sweigart 1997). This phenomenon is analogous to the "born-again" scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This "flash mixing" of the envelope during a late helium-core flash greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous increase in the HB effective temperature. We argue that the hot HB gap observed in NGC 2808 is associated with this theoretically predicted dichotomy in the HB properties. Using new helium- and carbon-rich stellar atmospheres, we show that the changes in the envelope abundances due to flash mixing will suppress the ultraviolet flux in the spectra of hot EHB stars. We suggest that such changes in the emergent spectral energy distribution are primarily responsible for explaining the hot subluminous EHB stars in omega Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing lie, at most, only approximately 0.1 mag below the EHB, and hence fail to explain the observations.

Sweigart, Allen V.↗
NASA NTRS2002

A New Formation Mechanism for the Hottest Horizontal-Branch Stars

Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet color-magnitude diagrams (CMDs) of both omega Cen and NGC 2808. In order to investigate the origin of these subluminous stars, we have constructed a detailed set of evolutionary sequences that follow the evolution of low-mass stars continuously from the zero-age main sequence through the helium-core flash to the HB for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous EHB stars, as well as the high temperature gap along the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the main helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the 'born-again' scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This 'flash mixing' of the envelope during a late helium-core flash greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous increase in the HB effective temperature. We argue that the hot HB gap observed in NGC 2808 is associated with this theoretically predicted dichotomy in the RB properties. Using new helium- and carbon-rich stellar atmospheres, we show that the changes in the envelope abundances due to flash mixing will suppress the ultraviolet flux in the spectra of hot EHB stars. We suggest that such changes in the emergent spectral energy distribution are primarily responsible for explaining the hot subluminous EHB stars in omega Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing lie, at most, only approximately 0.1 mag below the EHB, and hence fail to explain the observations.

Sweigart, Allen V.↗
NASA NTRS2010

Accuracy Analysis for Finite-Volume Discretization Schemes on Irregular Grids

A new computational analysis tool, downscaling test, is introduced and applied for studying the convergence rates of truncation and discretization errors of nite-volume discretization schemes on general irregular (e.g., unstructured) grids. The study shows that the design-order convergence of discretization errors can be achieved even when truncation errors exhibit a lower-order convergence or, in some cases, do not converge at all. The downscaling test is a general, efficient, accurate, and practical tool, enabling straightforward extension of verification and validation to general unstructured grid formulations. It also allows separate analysis of the interior, boundaries, and singularities that could be useful even in structured-grid settings. There are several new findings arising from the use of the downscaling test analysis. It is shown that the discretization accuracy of a common node-centered nite-volume scheme, known to be second-order accurate for inviscid equations on triangular grids, degenerates to first order for mixed grids. Alternative node-centered schemes are presented and demonstrated to provide second and third order accuracies on general mixed grids. The local accuracy deterioration at intersections of tangency and in flow/outflow boundaries is demonstrated using the DS tests tailored to examining the local behavior of the boundary conditions. The discretization-error order reduction within inviscid stagnation regions is demonstrated. The accuracy deterioration is local, affecting mainly the velocity components, but applies to any order scheme.

Diskin, Boris↗
NASA NTRS1991

Redesign of the mixed-mode bending test for delamination toughness

The mixed-mode bending (MMB) test uses a lever to simultaneously apply mode I and mode II loading to a split-beam specimen. A nonlinear, iterative analysis that accurately predicts the measured load-displacement response and the strain energy release rate, G, of an MMB test, has shown that the errors in G calculated using linear theory can be quite large. The nonlinear analysis was used as a guide in redesigning the MMB apparatus. With the redesigned apparatus, loads are applied through a roller attached to the lever and loaded just above the midplane of the test specimen. The redesigned MMB apparatus has geometric nonlinearity errors of less than 3 percent, even for materials substantially tougher than APC2 (AS4/PEEK). This apparatus was demonstrated by measuring the mixed-mode delamination fracture toughness of APC2. The data from the redesigned MMB apparatus were analyzed with a linear analysis which yielded results similar to those found with the original apparatus and the nonlinear analysis.

Reeder, J. R.↗
NASA NTRS1992

Redesign of the mixed-mode bending delamination test to reduce nonlinear effects

The mixed-mode bending (MMB) test uses a lever to apply simultaneously mode I and mode II loading to a split-beam specimen. An iterative analysis that accounts for the geometric nonlinearity of the MMB test was developed. The analysis accurately predicted the measured load-displacement response and the strain energy release rate, G, of an MMB test specimen made of AS4/PEEK. The errors in G when calculated using linear theory were found to be as large as 30 percent in some cases. Because it would be inconvenient to use a nonlinear analysis to analyze MMB data, the MMB apparatus was redesigned to minimize the nonlinearity. With the improved apparatus, loads are applied just above the midplane of the test specimen through a roller attached to the lever. This apparatus was demonstrated by measuring the mixed-mode delamination fracture toughhess of the test specimen. The nonlinearity errors associated with testing this tough composite material were less than +/- 3 percent. The data from the improved MMB apparatus analyzed with a linear analysis were similar to those found with the original apparatus and the nonlinear analysis.

Reeder, James R.↗
NASA NTRS2017

Impact of Evolving Isoprene Mechanisms on Simulated Formaldehyde: An Inter-comparison Supported by in Situ Observations from SENEX

Isoprene oxidation schemes vary greatly among gas-phase chemical mechanisms, with potentially significant ramifications for air quality modeling and interpretation of satellite observations in biogenic-rich regions. In this study, in situ observations from the 2013 SENEX mission are combined with a constrained O-D photochemical box model to evaluate isoprene chemistry among five commonly used gas-phase chemical mechanisms: CBO5, CB6r2, MCMv3.2, MCMv3.3.1, and a recent version of GEOS-Chem. Mechanisms are evaluated and inter-compared with respect to formaldehyde (HCHO), a high-yield product of isoprene oxidation. Though underestimated by all considered mechanisms, observed HCHO mixing ratios are best reproduced by MCMv3.3.1 (normalized mean bias = -15%), followed by GEOS-Chem (-17%), MCMv3.2 (-25%), CB6r2 (-32%) and CB05 (-33%). Inter-comparison of HCHO production rates reveals that major restructuring of the isoprene oxidation scheme in the Carbon Bond mechanism increases HCHO production by only approx. 5% in CB6r2 relative to CBO5, while further refinement of the complex isoprene scheme in the Master Chemical Mechanism increases HCHO production by approx. 16% in MCMv3.3.1 relative to MCMv3.2. The GEOS-Chem mechanism provides a good approximation of the explicit isoprene chemistry in MCMv3.3.1 and generally reproduces the magnitude and source distribution of HCHO production rates. We analytically derive improvements to the isoprene scheme in CB6r2 and incorporate these changes into a new mechanism called CB6r2-UMD, which is designed to preserve computational efficiency. The CB6r2-UMD mechanism mimics production of HCHO in MCMv3.3.1 and demonstrates good agreement with observed mixing ratios from SENEX (-14%). Improved simulation of HCHO also impacts modeled ozone: at approx. 0.3 ppb NO, the ozone production rate increases approx. 3% between CB6r2 and CB6r2-UMD, and rises another approx. 4% when HCHO is constrained to match observations.

isoprene↗
NASA NTRS2019

Identification of Bare-Airframe Dynamics from Closed-Loop Data Using Multisine Inputs and Frequency Responses

Amethod is presented for computing multiple-input multiple-output frequency responses of bare-airframe dynamics for systems excited using orthogonal phase-optimized multisines and including correlated data arising from control mixing or feedback control. The estimation was posed as the solution to an underdetermined system of linear equations, for which additional information was supplied using interpolation of the frequency responses. A simulation model of the NASA T-2 aircraft having two inputs and two outputs was used to investigate the method in the open-loop configuration and under closed-loop control. The method was also applied to flight test data from the X-56A aeroelastic demonstrator having five inputs and ten outputs and flying under closed-loop control with additional control allocation mixing. Results demonstrated that the proposed method accurately estimates the bare airframe frequency responses in the presence of correlated data from control mixing and feedback control. Results also agreed with estimates obtained using different methods that are less sensitive to correlated inputs.

Grauer, Jared A.↗