SEARCH · Engineering Papers

Results for “model types”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54

All sources NASA NTRS DOE OSTI

NASA NTRS1982

The symbiotics as binary stars

According to the original definition, symbiotic stars have combination spectra, in which the high-excitation emission lines regularly found in planetary nebulae are superposed on a low-temperature absorption spectrum. In connection with this investigation, the coexistence of a He II emission with the TiO absorption bands is also postulated. Attention is given to a summary of observed properties of symbiotics, binaries with a late-type giant component, possible models for the symbiotics, models with an accreting main-sequence star (Algol symbiotics), T Coronae borealis as a possible cataclysmic Algol-type symbiotic, binaries with rejuvenated degenerate dwarfs (novalike symbiotics), questions regarding the existence of PN symbiotics or subdwarfs unpowered by accretion, and related binary systems which are not symbiotics.

Plavec, M. J.↗

NASA NTRS1959

Boundary-Layer Transition on Hollow Cylinders in Supersonic Free Flight as Affected by Mach Number and a Screwthread Type of Surface Roughness

The effects of Mach number and surface-roughness variation on boundary-layer transition were studied using fin-stabilized hollow-tube models in free flight. The tests were conducted over the Mach number range from 2.8 to 7 at a nominally constant unit Reynolds number of 3 million per inch, and with heat transfer to the model surface. A screwthread type of distributed two-dimensional roughness was used. Nominal thread heights varied from 100 microinches to 2100 microinches. Transition Reynolds number was found to increase with increasing Mach number at a rate depending simultaneously on Mach number and roughness height. The laminar boundary layer was found to tolerate increasing amounts of roughness as Mach number increased. For a given Mach number an optimum roughness height was found which gave a maximum laminar run greater than was obtained with a smooth surface.

James, Carlton S.↗

NASA NTRS2009

Application of TRMM PR and TMI Measurements to Assess Cloud Microphysical Schemes in the MM5 Model for a Winter Storm

Seen by the human eye, precipitation particles are commonly drops of rain, flakes of snow, or lumps of hail that reach the ground. Remote sensors and numerical models usually deal with information about large collections of rain, snow, and hail (or graupel --also called soft hail ) in a volume of air. Therefore, the size and number of the precipitation particles and how particles interact, evolve, and fall within the volume of air need to be represented using physical laws and mathematical tools, which are often implemented as cloud and precipitation microphysical parameterizations in numerical models. To account for the complexity of the precipitation physical processes, scientists have developed various types of such schemes in models. The accuracy of numerical weather forecasting may vary dramatically when different types of these schemes are employed. Therefore, systematic evaluations of cloud and precipitation schemes are of great importance for improvement of weather forecasts. This study is one such endeavor; it pursues quantitative assessment of all the available cloud and precipitation microphysical schemes in a weather model (MM5) through comparison with the observations obtained by National Aeronautics and Space Administration (NASA) s and Japan Aerospace Exploration Agency (JAXA) s Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) and microwave imager (TMI). When satellite sensors (like PR or TMI) detect information from precipitation particles, they cannot directly observe the microphysical quantities (e.g., water species phase, density, size, and amount etc.). Instead, they tell how much radiation is absorbed by rain, reflected away from the sensor by snow or graupel, or reflected back to the satellite. On the other hand, the microphysical quantities in the model are usually well represented in microphysical schemes and can be converted to radiative properties that can be directly compared to the corresponding PR and TMI observations. This study employs this method to evaluate the accuracy of the simulated radiative properties by the MM5 model with different microphysical schemes. It is found that the representations of particle density, size, and mass in the different schemes in the MM5 model determine the model s performance when predicting a winter storm over the eastern Pacific Ocean. Schemes lacking moderate density particles (i.e. graupel), with snow flakes that are too large, or with excessive mass of snow or graupel lead to degraded prediction of the radiative properties as observed by the TRMM satellite. This study demonstrates the uniqueness of the combination of both an active microwave sensor (PR) and passive microwave sensor (TMI) onboard TRMM on assessing the accuracy of numerical weather forecasting. It improves our understanding of the physical and radiative properties of different types of precipitation particles and provides suggestions for better representation of cloud and precipitation processes in numerical models. It would, ultimately, contribute to answering questions like "Why did it not rain when the forecast says it would?"

Han, Mei↗

NASA NTRS1980

Outer atmospheres of cool stars. IV - A discussion of cool stellar wind models

Possible wind models for late-type stars which appear not to have hot coronae and transition regions are investigated; taking Arcturus and the prototypical star, models with T less than approximately 20,000 K are considered, and solutions with mass loss rates of 10 to the -9th solar masses per year are sought. The radiation pressure of L-alpha resonance scattering can exceed the force of gravity in the chromosphere and initiate a net outflow, but is insufficient to sustain a wind, except perhaps in the presence of an additional momentum input term such as Alfven wave pressure. It is concluded that L-alpha radiation-pressure-initiated winds can occur in stars to the right of the Linsky-Haisch dividing line in the H-R diagram between stars with and without transition regions and presumably hot coronae, and that the existence of these winds may explain energetically the absence of hot coronae in these stars.

Haisch, B. M.↗

NASA NTRS1982

Helicopter simulation validation using flight data

A joint NASA/Army effort to perform a systematic ground-based piloted simulation validation assessment is described. The best available mathematical model for the subject helicopter (UH-60A Black Hawk) was programmed for real-time operation. Flight data were obtained to validate the math model, and to develop models for the pilot control strategy while performing mission-type tasks. The validated math model is to be combined with motion and visual systems to perform ground based simulation. Comparisons of the control strategy obtained in flight with that obtained on the simulator are to be used as the basis for assessing the fidelity of the results obtained in the simulator.

Key, D. L.↗

NASA NTRS1992

HEAO 3 limits on the Ti-44 yield in Galactic supernovae

Data fron the high-resolution gamma-ray spectroscopy experiment on HEAO 3 have been searched for line emission from the decay of Ti-44 created in recent, as yet unobserved, Galactic supernova explosions, where the ages and locations are unknown. Because the 78 yr mean life of Ti-44 is comparable to the average time between Galactic supernovae, the gamma-ray line emission from its decay should appear as Galactic point sources. No evidence was found for such emission from a point source anywhere in the Galactic plane, with a 1-sigma limit of 8.3 x 10 exp -5 photons/sq cm per sec. Detailed models were developed to simulate the Galactic gamma-ray emission from the decay of Ti-44 produced in both type I and type II supernovae. These models were used with the measured gamma-ray line limits to constrain the supernova yields and recurrence periods.

Mahoney, W. A.↗

NASA NTRS1991

Interlaminar stress analysis at the skin-stiffener interface of a grid-stiffened composite panel

Results are presented of an analysis of the interlaminar stress components at the skin-wrap, skin-core, and wrap-core interfaces for an advanced-concept stiffened panel using a global/local finite element procedure. The procedure consists of a global model of two-dimensional shell elements that is used to design a grid-stiffened panel with blade-type stiffeners, a local model of three-dimensional solid elements that is used to compute interlaminar stress components, and a scheme devised to assign displacement boundary conditions for the local model that are derived from displacement and rotation data of a few nodes of the global model. The interlaminar stresses for this panel design were found to be well below typical tensile normal and shearing strengths of a graphite-epoxy material.

Wiggenraad, J. F. M.↗

NASA NTRS1993

Pulsar distances and the galactic distribution of free electrons

The present quantitative model for Galactic free electron distribution abandons the assumption of axisymmetry and explicitly incorporates spiral arms; their shapes and locations are derived from existing radio and optical observations of H II regions. The Gum Nebula's dispersion-measure contributions are also explicitly modeled. Adjustable quantities are calibrated by reference to three different types of data. The new model is estimated to furnish distance estimates to known pulsars that are accurate to about 25 percent.

Taylor, J. H.↗

NASA NTRS1993

Material characterization and modeling with shear ography

Shearography has emerged as a useful technique for nondestructible evaluation and materials characterization of aerospace materials. A suitable candidate for the technique is to determine the response of debonds on foam-metal interfaces such as the TPS system on the External Tank. The main thrust is to develop a model which allows valid interpretation of shearographic information on TPS type systems. Confirmation of the model with shearographic data will be performed.

Workman, Gary L.↗

NASA NTRS1993

Ginga observations of Seyfert galaxies

We observed twenty-eight Seyfert 2 galaxies with the Japanese X-ray satellite, Ginga, and found Seyfert 2 galaxies, in general, have the X-ray spectral characteristics of obscured Seyfert 1 nuclei. This results agrees with the predictions from the Unified Seyfert model proposed by Antonucci and Miller. However, among the observed Seyfert 2 galaxies, there are a few galaxies with no evidence of an obscuration, contrary to the general predictions of the unified model. We note that type 2 active galactic nuclei (AGN) will contribute to the Cosmic Diffuse X-ray Background, if the unified Seyfert model can be extended to the far distant AGN such as quasars.

Awaki, H.↗

NASA NTRS1991

Geomagnetic model investigations for 1980 - 1989: A model for strategic defense initiative particle beam experiments and a study in the effects of data types and observatory bias solutions

Two suites of geomagnetic field models were generated at the request of Los Alamos National Lab. concerning Strategic Defense Initiative (SDI) research. The first is a progression of five models incorporating MAGSAT data and data from a sequence of batches as a priori information. The batch sequence is: post 1979.5 observatory data, post 1980 land survey and selected aeromagnetic and marine survey data, a special White Sands (NM) area survey by Project Magnet with some additional post 1980 marine survey data, and finally DE-2 satellite data. These models are of 13th deg and order in their main field terms, and deg and order 10 in their first derivative temporal terms. The second suite consists of four models based solely upon post 1983.5 observatory and survey data. They are of deg and order 10 in main field and 8 in a first deg Taylor series. A comprehensive error analysis was applied to both series, which accounted for error sources such as the truncated core and crustal fields, and the neglected Sq and low deg crustal fields. Comparison of the power spectrum of the MGST (10/81) model with those of this series show good agreement.

Langel, Robert A.↗

NASA NTRS1984

A study of the application of differential techniques to the global positioning system for a helicopter precision approach

The results of a simulation study to define the functional characteristics of a airborne and ground reference GPS receiver for use in a Differential GPS system are doumented. The operations of a variety of receiver types (sequential-single channel, continuous multi-channel, etc.) are evaluated for a typical civil helicopter mission scenario. The math model of each receiver type incorporated representative system errors including intentional degradation. The results include the discussion of the receiver relative performance, the spatial correlative properties of individual range error sources, and the navigation algorithm used to smooth the position data.

Mccall, D. L.↗

NASA NTRS2005

Spatial Scaling of Snow Observations and Microwave Emission Modeling During CLPX and Appropriate Satellite Sensor Resolution

Accurate estimates of snow water equivalent and other properties play an important role in weather, natural hazard, and hydrological forecasting and climate modeling over a range of scales in space and time. Remote sensing-derived estimates have traditionally been of the "snapshot" type, but techniques involving models with assimilation are also being explored. In both cases, forward emission models are useful to understand the observed passive microwave signatures and developing retrieval algorithms. However, mismatches between passive microwave sensor resolutions and the scales of processes controlling subpixel heterogeneity can affect the accuracy of the estimates. Improving the spatial resolution of new passive microwave satellite sensors is a major desire in order to (literally) resolve such subpixel heterogeneity, but limited spacecraft and mission resources impose severe constraints and tradeoffs. In order to maximize science return while mitigating risk for a satellite concept, it is essential to understand the scaling behavior of snow in terms of what the sensor sees (brightness temperature) as well as in terms of the actual variability of snow. NASA's Cold Land Processes Experiment-1 (CLPX-1: Colorado, 2002 and 2003) was designed to provide data to measure these scaling behaviors for varying snow conditions in areas with forested, alpine, and meadow/pasture land cover. We will use observations from CLPX-1 ground, airborne, and satellite passive microwave sensors to examine and evaluate the scaling behavior of observed and modeled brightness temperatures and observed and retrieved snow parameters across scales from meters to 10's of kilometers. The conclusions will provide direct examples of the appropriate spatial sampling scales of new sensors for snow remote sensing. The analyses will also illustrate the effects and spatial scales of the underlying phenomena (e.g., land cover) that control subpixel heterogeneity.

Kim, Edward J.↗

NASA NTRS2012

A New Approach to Monitoring Coastal Marshes for Persistent Flooding

Many areas in coastal Louisiana are below sea level and protected from flooding by a system of natural and man-made levees. Flooding is common when the levees are overtopped by storm surge or rising rivers. Many levees in this region are further stressed by erosion and subsidence. The floodwaters can become constricted by levees and trapped, causing prolonged inundation. Vegetative communities in coastal regions, from fresh swamp forest to saline marsh, can be negatively affected by inundation and changes in salinity. As saltwater persists, it can have a toxic effect upon marsh vegetation causing die off and conversion to open water types, destroying valuable species habitats. The length of time the water persists and the average annual salinity are important variables in modeling habitat switching (cover type change). Marsh type habitat switching affects fish, shellfish, and wildlife inhabitants, and can affect the regional ecosystem and economy. There are numerous restoration and revitalization projects underway in the coastal region, and their effects on the entire ecosystem need to be understood. For these reasons, monitoring persistent saltwater intrusion and inundation is important. For this study, persistent flooding in Louisiana coastal marshes was mapped using MODIS (Moderate Resolution Imaging Spectroradiometer) time series of a Normalized Difference Water Index (NDWI). The time series data were derived for 2000 through 2009, including flooding due to Hurricane Rita in 2005 and Hurricane Ike in 2008. Using the NDWI, duration and extent of flooding can be inferred. The Time Series Product Tool (TSPT), developed at NASA SSC, is a suite of software developed in MATLAB(R) that enables improved-quality time series images to be computed using advanced temporal processing techniques. This software has been used to compute time series for monitoring temporal changes in environmental phenomena, (e.g. NDVI times series from MODIS), and was modified and used to compute the NDWI indices and also the Normalized Difference Soil Index (NDSI). Coastwide Reference Monitoring System (CRMS) water levels from various hydrologic monitoring stations and aerial photography were used to optimize thresholds for MODIS-derived time series of NDWI and to validate resulting flood maps. In most of the profiles produced for post-hurricane assessment, the increase in the NDWI index (from storm surge) is accompanied by a decrease in the vegetation index (NDVI) and then a period of declining water. The NDSI index represents non-green or dead vegetation and increases after the hurricane s destruction of the marsh vegetation. Behavior of these indices over time is indicative of which areas remain flooded, which areas recover to their former levels of vegetative vigor, and which areas are stressed or in transition. Tracking these indices over time shows the recovery rate of vegetation and the relative behavior to inundation persistence. The results from this study demonstrated that identification of persistent marsh flooding, utilizing the tools developed in this study, provided an approximate 70-80 percent accuracy rate when compared to the actual days flooded at the CRMS stations.

Kalcic, M. T.↗

NASA NTRS2021

A Robust Hybrid Deep Learning Model for Spatiotemporal Image Fusion

Dense time-series remote sensing data with detailed spatial information are highly desired for the monitoring of dynamic earth systems. Due to the sensor tradeoff, most remote sensing systems cannot provide images with both high spatial and temporal resolutions. Spatiotemporal image fusion models provide a feasible solution to generate such a type of satellite imagery, yet existing fusion methods are limited in predicting rapid and/or transient phenological changes. Additionally, a systematic approach to assessing and understanding how varying levels of temporal phenological changes affect fusion results is lacking in spatiotemporal fusion research. The objective of this study is to develop an innovative hybrid deep learning model that can effectively and robustly fuse the satellite imagery of various spatial and temporal resolutions. The proposed model integrates two types of network models: super-resolution convolutional neural network (SRCNN) and long short-term memory (LSTM). SRCNN can enhance the coarse images by restoring degraded spatial details, while LSTM can learn and extract the temporal changing patterns from the time-series images. To systematically assess the effects of varying levels of phenological changes, we identify image phenological transition dates and design three temporal phenological change scenarios representing rapid, moderate, and minimal phenological changes. The hybrid deep learning model, alongside three benchmark fusion models, is assessed in different scenarios of phenological changes. Results indicate the hybrid deep learning model yields significantly better results when rapid or moderate phenological changes are present. It holds great potential in generating high-quality time-series datasets of both high spatial and temporal resolutions, which can further benefit terrestrial system dynamic studies. The innovative approach to understanding phenological changes’ effect will help us better comprehend the strengths and weaknesses of current and future fusion models.

spatiotemporal fusion↗

NASA NTRS1994

A toolbox and record for scientific models

Computational science presents a host of challenges for the field of knowledge-based software design. Scientific computation models are difficult to construct. Models constructed by one scientist are easily misapplied by other scientists to problems for which they are not well-suited. Finally, models constructed by one scientist are difficult for others to modify or extend to handle new types of problems. Construction of scientific models actually involves much more than the mechanics of building a single computational model. In the course of developing a model, a scientist will often test a candidate model against experimental data or against a priori expectations. Test results often lead to revisions of the model and a consequent need for additional testing. During a single model development session, a scientist typically examines a whole series of alternative models, each using different simplifying assumptions or modeling techniques. A useful scientific software design tool must support these aspects of the model development process as well. In particular, it should propose and carry out tests of candidate models. It should analyze test results and identify models and parts of models that must be changed. It should determine what types of changes can potentially cure a given negative test result. It should organize candidate models, test data, and test results into a coherent record of the development process. Finally, it should exploit the development record for two purposes: (1) automatically determining the applicability of a scientific model to a given problem; (2) supporting revision of a scientific model to handle a new type of problem. Existing knowledge-based software design tools must be extended in order to provide these facilities.

Ellman, Thomas↗

NASA NTRS1982

Structural modeling of high Reynolds number wind tunnel models

A solid uninstrumented wing and a pressure instrumented wing having a tongue and groove type joint have been structurally modeled by using SPAR Structural Analysis System. The solid wing model can be analyzed by SPAR, using either solid elements or plate elements with reasonable accuracy. The instrumented wing models with tongue and groove joint can be modeled by using solid elements. A solid model representation for the wing with tongue and groove joint can be used for the cases where an error of 6 percent in deflections is acceptable.

Mehrotra, S. C.↗

NASA NTRS1990

Spectra of late type dwarf stars of known abundance for stellar population models

The project consisted of two parts. The first was to obtain new low-dispersion, long-wavelength, high S/N IUE spectra of F-G-K dwarf stars with previously determined abundances, temperatures, and gravities. To insure high quality, the spectra are either trailed, or multiple exposures are taken within the large aperture. Second, the spectra are assembled into a library which combines the new data with existing IUE Archive data to yield mean spectral energy distributions for each important type of star. My principal responsibility is the construction and maintenance of this UV spectral library. It covers the spectral range 1200-3200A and is maintained in two parts: a version including complete wavelength coverage at the full spectral resolution of the Low Resolution cameras; and a selected bandpass version, consisting of the mean flux in pre-selected 20A bands. These bands are centered on spectral features or continuum regions of special utility - e.g. the C IV lambda 1550 or Mg II lambda 2800 feature. In the middle-UV region, special emphasis is given to those features (including continuum 'breaks') which are most useful in the study of F-G-K star spectra in the integrated light of old stellar populations.

Oconnell, R. W.↗