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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Acoustic methodology review

It is important for industry and NASA to assess the status of acoustic design technology for predicting and controlling helicopter external noise in order for a meaningful research program to be formulated which will address this problem. The prediction methodologies available to the designer and the acoustic engineer are three-fold. First is what has been described as a first principle analysis. This analysis approach attempts to remove any empiricism from the analysis process and deals with a theoretical mechanism approach to predicting the noise. The second approach attempts to combine first principle methodology (when available) with empirical data to formulate source predictors which can be combined to predict vehicle levels. The third is an empirical analysis, which attempts to generalize measured trends into a vehicle noise prediction method. This paper will briefly address each.

Schlegel, R. G.↗
NASA NTRS1973

Fore and aft elastic response characteristics of size 34x9.9, type 7, 14 ply-rated aircraft tires of bias ply, bias belted, and radial belted design

An investigation was conducted to determine the fore-and-aft elastic response characteristics of aircraft tires of bias ply, bias-belted, and radial-belted design. The investigation consisted of: (1)static and rolling tests, (2)a statistical analysis which related the measured tire elastic characteristics to variations in the vertical load, inflation pressure, braking force and/or tire vertical deflection, and (3) a semi-empirical analysis which related the tire elastic behavior to measured wheel slippage during a steady-state braking. The results of this investigation indicate that the bias-belted tire has the largest spring constant value for most loading conditions and the radial-belted tire has the smallest spring constant value.

Tanner, J. A.↗
NASA NTRS2013

Data Mining for Anomaly Detection

The Vehicle Integrated Prognostics Reasoner (VIPR) program describes methods for enhanced diagnostics as well as a prognostic extension to current state of art Aircraft Diagnostic and Maintenance System (ADMS). VIPR introduced a new anomaly detection function for discovering previously undetected and undocumented situations, where there are clear deviations from nominal behavior. Once a baseline (nominal model of operations) is established, the detection and analysis is split between on-aircraft outlier generation and off-aircraft expert analysis to characterize and classify events that may not have been anticipated by individual system providers. Offline expert analysis is supported by data curation and data mining algorithms that can be applied in the contexts of supervised learning methods and unsupervised learning. In this report, we discuss efficient methods to implement the Kolmogorov complexity measure using compression algorithms, and run a systematic empirical analysis to determine the best compression measure. Our experiments established that the combination of the DZIP compression algorithm and CiDM distance measure provides the best results for capturing relevant properties of time series data encountered in aircraft operations. This combination was used as the basis for developing an unsupervised learning algorithm to define "nominal" flight segments using historical flight segments.

Biswas, Gautam↗
NASA NTRSDate not supplied

NASA Physics of Failure (PoF) for Reliability

An item’s reliability or longevity is dependent not only on its design but also on how it is used, manufactured, tested, and the stresses it has or will experience. Stresses include operational and environmental exposures to thermal, voltage, current, age/exposure, mechanical, and radiation mechanisms. Therefore, in reliability analysis, it is important to consider the contributions of all these factors when predicting the failure rates of components. Historically, there has been a reliance on handbook data (e.g., MIL-HDBK-217), but experience has shown that these values and distributions are not representative of actual performance. Therefore, to make more credible reliability and risk assessments for its missions, NASA must transition to estimating likelihoods of failure based on an item’s reliability or longevity factors (or the physical susceptibilities and strengths impacting the design’s performance) has or will experience, whenever possible. To facilitate this transition, a Handbook on Methodology for Physics of Failure Based Reliability Assessments has been developed by NASA to assist in applying physics experiences or experimental physics for empirical analysis and conceptualized physics exposures or theoretical physics for deterministic analysis, to develop and aggregate realistic likelihoods of failure leading to more credible forecasts of item performance and longevity. In addition, since it is NASA’s intention that this document continues to evolve based on community lessons learned and the introduction of new assessment methodologies, NASA is encouraging and appreciates the contributions of current and future authors to maintain and enhance this handbook and its supporting case studies.

PoF↗
NASA NTRS2022

NASA Physics of Failure (PoF) for Reliability

An item’s reliability or longevity is dependent not only on its design but also on how it is used, manufactured, tested, and the stresses it has or will experience. Stresses include operational and environmental exposures to thermal, voltage, current, age/exposure, mechanical, and radiation mechanisms. Therefore, in reliability analysis, it is important to consider the contributions of all of these factors when predicting the failure rates of components. Historically, there has been a reliance on handbook data (e.g., MIL-HDBK-217), but experience has shown that these values and distributions are not representative of actual performance (1,2). Therefore, to make more credible reliability and risk assessments for its missions, NASA must transition to estimating likelihoods of failure based on an item’s reliability/longevity factors (or the physical susceptibilities and strengths impacting the design’s performance) has or will experience, whenever possible. To facilitate this transition a “Handbook on Methodology for Physics of Failure Based Reliability Assessments” has been developed by NASA to assist in applying physics experiences or experiment physics for empirical analysis and conceptualized physics exposures or theoretical physics for deterministic analysis, to develop and aggregate realistic likelihoods of failure leading to more credible forecasts of item performance and longevity. In addition, since it is NASA’s intention that this document continues to evolve based on community lessons learned and the introduction of new assessment methodologies, NASA is encouraging and appreciates the contributions of current and future authors to maintain and enhance this handbook and its supporting case studies.

Physics of Failure↗
NASA NTRS2012

Multi-Angle Implementation of Atmospheric Correction for MODIS (MAIAC). Part 3: Atmospheric Correction

This paper describes the atmospheric correction (AC) component of the Multi-Angle Implementation of Atmospheric Correction algorithm (MAIAC) which introduces a new way to compute parameters of the Ross-Thick Li-Sparse (RTLS) Bi-directional reflectance distribution function (BRDF), spectral surface albedo and bidirectional reflectance factors (BRF) from satellite measurements obtained by the Moderate Resolution Imaging Spectroradiometer (MODIS). MAIAC uses a time series and spatial analysis for cloud detection, aerosol retrievals and atmospheric correction. It implements a moving window of up to 16 days of MODIS data gridded to 1 km resolution in a selected projection. The RTLS parameters are computed directly by fitting the cloud-free MODIS top of atmosphere (TOA) reflectance data stored in the processing queue. The RTLS retrieval is applied when the land surface is stable or changes slowly. In case of rapid or large magnitude change (as for instance caused by disturbance), MAIAC follows the MODIS operational BRDF/albedo algorithm and uses a scaling approach where the BRDF shape is assumed stable but its magnitude is adjusted based on the latest single measurement. To assess the stability of the surface, MAIAC features a change detection algorithm which analyzes relative change of reflectance in the Red and NIR bands during the accumulation period. To adjust for the reflectance variability with the sun-observer geometry and allow comparison among different days (view geometries), the BRFs are normalized to the fixed view geometry using the RTLS model. An empirical analysis of MODIS data suggests that the RTLS inversion remains robust when the relative change of geometry-normalized reflectance stays below 15%. This first of two papers introduces the algorithm, a second, companion paper illustrates its potential by analyzing MODIS data over a tropical rainforest and assessing errors and uncertainties of MAIAC compared to conventional MODIS products.

Lyapustin, A.↗
NASA NTRS1962

DEVELOPMENT OF DESIGN STRENGTH LEVELS FOR THE ELASTIC STABILITY OF MONOCOQUE CONES UNDER AXIAL COMPRESSION

Design relationships have been derived for the determination of elastic buckling strength levels for unpressurized monocoque truncated cones under axial compression. Theoretical implications have been considered in the establishment of a semi-empirical analysis leading to the development of probability based design expressions. Data from 170 tests by various investigators were statistically evaluated for the expected mean, 90%, and 99% probability strength levels. Dispersion of data was found to be slightly less than that of monocoque cylinders. Non-linear effects of radius to thickness ratio or strength deterioration with length to radius ratio were not discernible.

AXIAL COMPRESSION↗
NASA NTRS1972

Correlation of total sound power and peak sideline OASPL from jet exhausts

An empirical analysis of jet noise is made for convergent exhaust nozzles. An engineering approach to the correlation of total sound power and miximum sideline overall sound pressure level (OASPL), at 200 ft, is presented for both subsonic and supersonic jets based on available data. Data correlation for subsonic jets shows no dependency of total sound power and maximum sideline OASPL on jet density. The analysis for supersonic jets results in a correlation parameter for jet total sound power consisting of the conventional Lighthill parameter modified by considerations of jet Mach number and jet acoustic velocity. Similar parameters also correlate the maximum sideline OASPL for supersonic jets.

Vonglahn, U. H.↗
NASA NTRS1972

Correlation of total sound power and peak sideline OASPL from jet exhausts.

An empirical analysis of jet noise is made for convergent exhaust nozzles. This study, conducted at the Lewis Research Center, presents an engineering approach to the correlation of total sound power and maximum sideline OASPL (at 200 ft) for both subsonic and supersonic jets based on available data. Data correlation for subsonic jets shows no dependency of total sound power and maximum sideline OASPL on jet density. The analysis for supersonic jets results in a correlation parameter for jet total sound power consisting of the conventional Lighthill parameter modified by considerations of jet Mach number and jet acoustic velocity. Similar parameters also correlate the maximum sideline OASPL for supersonic jets.

Von Glahn, U. H.↗
NASA NTRS1978

Liquid propellant reorientation in a low-gravity environment

An existing empirical analysis relating to the reorientation of liquids in cylindrical tanks due to propulsive settling in a low gravity environment was extended to include the effects of geyser formation in the Weber number range from 4 to 10. Estimates of the minimum velocity increment required to be imposed on the propellant tank to achieve liquid reorientation were made. The resulting Bond numbers, based on tank radius, were found to be in the range from 3 to 5, depending upon the initial liquid fill level, with higher Bond number required for high initial fill levels. The resulting Weber numbers, based on tank radius and the velocity of the liquid leading edge, were calculated to be in the range from 6.5 to 8.5 for cylindrical tanks having a fineness ratio of 2.0, with Weber numbers of somewhat greater values for longer cylindrical tanks. It, therefore, appeared to be advantageous to allow small geysers to form and then dissipate into the surface of the collected liquid in order to achieve the minimum velocity increment. The Bond numbers which defined the separation between regions in which geyser formation did and did not occur due to propulsive settling in a spherical tank configuration ranged from 2 to 9 depending upon the liquid fill level.

Sumner, I. E.↗
NASA NTRS1979

An objective method for forecasting tropical cyclone intensity and motion using Nimbus-5 ESMR measurements and non-satellite derived descriptors

An empirical analysis program, based on finding an optimal representation of the data was applied to 120 observations of 29 1973 and 1974 North Pacific tropical cyclones. Each observation consists of a field of Nimbus-5 Electrically Scanning Microwave Radiometer radiation measurements at 267 grid points covering and surrounding the tropical cyclone plus nine other non-satellite derived discriptors. Forecast algorithms to estimate storm intensity and motion at 12, 24, 48, and 72 hours after each observation were developed using an independent eigen screening analysis. These algorithms were based on best track data. Independent testing of these algorithms showed that the performance of most of these algorithms were better than persistence and the algorithms forecasting 24, 48, and 72 hour maximum wind speed were better than those made operationally by the Joint Typhoon Warning Center for 1973 and 1974 that did not use best track data.

Hunter, H. E.↗
NASA NTRS1981

An objective method for forecasting tropical cyclone intensity using Nimbus-5 electrically scanning microwave radiometer measurements

An empirical analysis program, based on finding an optimal representation of the data, is applied to 120 observations of 29 1973 and 1974 North Pacific tropical cyclones. It is found that the algorithms developed from the Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR-5) base alone outperformed the Joint Typhoon Warning Center (JTWC) operational forecast for the 48 and 72 hour maximum wind speed. It is also found that the ESMR-5 data base, when combined with the non-satellite base, produced algorithms that improved the 24 and 48 hour maximum wind-speed forecast by as much as 10% and the 72 hour maximum wind forecast by approximately 16% as compared to the forecast obtained from the algorithms developed from the non-satellite data base alone.

Hunter, H. E.↗
NASA NTRS1981

Mass loss of TEOS-coated RCC subjected to the environment at the shuttle wing leading edge

Coated, reinforced carbon-carbon (RCC) is used for the leading edges of the Space Shuttle. The mass loss characteristics of RCC specimens coated with tetra-ethyl-ortho-silicate (TEOS) were determined for conditions which simulated the entry environment expected at the stagnation area of the wing leading edge. Maximum specimen temperature was 1632 K. Specimens were exposed for up to 100 missions. Stress levels up to 8.274 MPa caused an average increase in oxidation of 6 percent over unstressed specimens. Experimentally determined mass losses were compared with those predicted by an existing empirical analysis.

Stroud, C. W.↗
NASA NTRS1991

Surface radiation budget imagery

Linear regressions which summarize the relationships between the turbulent fluxes of heat and latent heat of vaporization leaving the surface and surface albedos are given. This observation is based on a semi-empirical analysis of the data collected from sets of Landsat/TM (Thematic Mapper) imagery as the top of the atmosphere images have been converted into maps of surface radiation budget. A preliminary analysis shows that in spite of the land surface's temporal and spatial variability, the transfer of latent and sensible heat into the atmosphere would appear to be governed by the land surface albedo.

Kim, Hongsuk H.↗
NASA NTRS1993

Spectral characteristics of time-dependent orbit errors in altimeter height measurements

A mean reference surface and time-dependent orbit errors are estimated simultaneously for each exact-repeat ground track from the first two years of Geosat sea level estimates based on the Goddard Earth model (GEM)-T2 orbits. Motivated by orbit theory and empirical analysis of Geosat data, the time-dependent orbit errors are modeled as 1 cycle per revolution (cpr) sinusoids with slowly varying amplitude and phase. The method recovers the known 'bow tie effect' introduced by the existence of force model errors within the precision orbit determination (POD) procedure used to generate the GEM-T2 orbits. The bow tie pattern of 1-cpr orbit errors is characterized by small amplitudes near the middle and larger amplitudes (up to 160 cm in the 2 yr of data considered here) near the ends of each 5- to 6-day orbit arc over which the POD force model is integrated. A detailed examination of these bow tie patterns reveals the existence of daily modulations of the amplitudes of the 1-cpr sinusoid orbit errors with typical and maximum peak-to-peak ranges of about 14 cm and 30 cm, respectively. The method also identifies a daily variation in the mean orbit error with typical and maximum peak-to-peak ranges of about 6 and 30 cm, respectively, that is unrelated to the predominant 1-cpr orbit error. Application of the simultaneous solution method to the much less accurate Geosat height estimates based on the Naval Astronautics Group orbits concludes that the accuracy of POD is not important for collinear altimetric studies of time-dependent mesoscale variability (wavelengths shorter than 1000 km), as long as the time-dependent orbit errors are dominated by 1-cpr variability and a long-arc (several orbital periods) orbit error estimation scheme such as that presented here is used.

Chelton, Dudley B.↗
NASA NTRS1994

Simultaneous soft and hard X-ray spectroscopy of AM Herculis with EXOSAT: Discovery of photospheric absorption features

We present 0.1-10 keV spectroscopic observations of AM Herculis obtained with the Transmission Grating Spectrometers and Medium Energy experiments on EXOSAT, taken when the object was in its 'reversed X-ray mode.' The observation covers over six binary orbits without interruption, enabling us to analyze the phase and intensity dependence of both the hard and the soft spectrum simultaneously. We resolve the optically thick soft X-ray spectrum, and find definite evidence for time- and phase-dependent photospheric absorption structure arising in the white dwarf atmosphere. We present a simple empirical analysis of the combined soft and hard X-ray spectra, to examine whether the effect of a better determination of the column density of neutral absorbing material, afforded by our data, would solve the problem of the large relative soft X-ray overluminosity previously observed in AM Her. We find that a single absorbing column fits the entire spectrum, and that the column densities implied are indeed substantially lower than previously estimated. However, during half the binary orbit we still determine a strong lower limit to the soft-to-hard luminosity ratio of L(sub soft)/L(sub hard) is greater than or approximately equal to 10, in conflict with the simple radiative shock models for the accretion region. We argue that this indicates the need to reexamine the luminosity problem using explicit models for the emission spectrum based on a full solution of the atmospheric radiative transfer problem.

Paerels, Frits↗
NASA NTRS1995

The stellar wind of an O8.5 I(f) star in M 31

We rediscuss the UV spectrum of OB 78#231, an O8.5 I(f) star in the Andromeda galaxy M 31, which has been obtained with the Faint Object Spectrograph on the Hubble Space Telescope by Hutchings et al. (1992). The spectrum has been re-extracted with better knowledge of background, calibration, and scattered light. The empirical analysis of the stellar wind lines results in a terminal velocity and mass loss rate similar to those typically found in comparable galactic objects. Furthermore, a comparison with an FOS spectrum of an O7 supergiant in the Small Magellanic Cloud and IUE spectra of galactic objects implies a metallicity close to galactic counterparts. These results are confirmed quantitatively by spectrum synthesis calculations using a theoretical description of O-star winds.

Haser, S. M.↗