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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Review of TRMM/GPM Rainfall Algorithm Validation

A review is presented concerning current progress on evaluation and validation of standard Tropical Rainfall Measuring Mission (TRMM) precipitation retrieval algorithms and the prospects for implementing an improved validation research program for the next generation Global Precipitation Measurement (GPM) Mission. All standard TRMM algorithms are physical in design, and are thus based on fundamental principles of microwave radiative transfer and its interaction with semi-detailed cloud microphysical constituents. They are evaluated for consistency and degree of equivalence with one another, as well as intercompared to radar-retrieved rainfall at TRMM's four main ground validation sites. Similarities and differences are interpreted in the context of the radiative and microphysical assumptions underpinning the algorithms. Results indicate that the current accuracies of the TRMM Version 6 algorithms are approximately 15% at zonal-averaged / monthly scales with precisions of approximately 25% for full resolution / instantaneous rain rate estimates (i.e., level 2 retrievals). Strengths and weaknesses of the TRMM validation approach are summarized. Because the dew of convergence of level 2 TRMM algorithms is being used as a guide for setting validation requirements for the GPM mission, it is important that the GPM algorithm validation program be improved to ensure concomitant improvement in the standard GPM retrieval algorithms. An overview of the GPM Mission's validation plan is provided including a description of a new type of physical validation model using an analytic 3-dimensional radiative transfer model.

Smith, Eric A.↗
NASA NTRS1987

Inlets, ducts and nozzles

The internal fluid mechanics research program in inlets, ducts, and nozzles is described. The program consists of a balanced effort between the development of computational tools and the conduct of experimental research. The experiments are designed to better understand the fluid flow physics, to develop new or improved flow models, and to provide benchmark quality data sets for validation of the computational methods. The inlet, duct, and nozzle research program is described according to three major classifications of flow phenomena: highly three-dimensional flow fields; shock-boundary layer interactions; and shear layer control. Specific examples of current and future elements of the research program are described for each of these phenomena. In particular, the highly three-dimensional flow field phenomena is highlighted by describing the computational and experiemental research program in transition ducts having a round-to-rectangular area variation. In the case of shock-boundary layer interactions, the specific details of research for normal shock-boundary layer interactions are described. For shear layer control research in vortex generators and the use of aerodynamic excitation for enhancement of the jet mixing process are described. Future research in inlets, ducts, and nozzles will include more emphasis on three-dimensional full Navier-Stokes methods and corresponding experiments designed to concentrate on the appropriate three-dimensional fluid flow physics.

Abbott, John M.↗
NASA NTRS2000

Refinements to SSiB with an Emphasis on Snow-Physics: Evaluation and Validation Using GSWP and Valdai Data

Refinements to the snow-physics scheme of SSiB (Simplified Simple Biosphere Model) are described and evaluated. The upgrades include a partial redesign of the conceptual architecture to better simulate the diurnal temperature of the snow surface. For a deep snowpack, there are two separate prognostic temperature snow layers - the top layer responds to diurnal fluctuations in the surface forcing, while the deep layer exhibits a slowly varying response. In addition, the use of a very deep soil temperature and a treatment of snow aging with its influence on snow density is parameterized and evaluated. The upgraded snow scheme produces better timing of snow melt in GSWP-style simulations using ISLSCP Initiative I data for 1987-1988 in the Russian Wheat Belt region. To simulate more realistic runoff in regions with high orographic variability, additional improvements are made to SSiB's soil hydrology. These improvements include an orography-based surface runoff scheme as well as interaction with a water table below SSiB's three soil layers. The addition of these parameterizations further help to simulate more realistic runoff and accompanying prognostic soil moisture fields in the GSWP-style simulations. In intercomparisons of the performance of the new snow-physics SSiB with its earlier versions using an 18-year single-site dataset from Valdai Russia, the version of SSiB described in this paper again produces the earliest onset of snow melt. Soil moisture and deep soil temperatures also compare favorably with observations.

Mocko, David M.↗
NASA NTRS1963

A NICKEL ALLOY FOR 1900 F

Composition and physical characteristics of new nickel-base alloys for high-temperature applications

HIGH TEMPERATURE ALLOY↗
NASA NTRS1976

Study of multiple hologram recording in lithium niobate

The results of a number of theoretical and experimental studies relating to multiple hologram recording in lithium niobate are reported. The analysis of holographic gratings stored in lithium niobate has been extended to cover a more realistic range of physical situations. A new successful dynamic (feedback) theory for describing recording, nondestructive reading, erasure, enhancement, and angular sensitivity has been developed. In addition, the possible architectures of mass data storage systems have been studied.

Gaylord, T. K.↗
NASA NTRS1977

Flow phenomena peculiar to calculation of compressible turbulent boundary layers

Calculation procedures for compressible turbulent boundary layers were based upon techniques, modeling constants, etc., developed originally for the low speed case. Significant differences and new or altered physics which occur in the compressible case were considered, as compared with the low speed situation. Possible pitfalls and sources of inaccuracy in the calculations were indicated.

Source record↗
NASA NTRS1977

Reducing LANDSAT data to parameters with physical significance and signature extension: A view of LANDSAT capabilities

The premise is the LANDSAT is capable of sensing only a few physical parameters. Much of the contrast provided in LANDSAT data is provided by differences in vegetation cover. Although dominant, vegetation is not the only physical parameter that can be detected with LANDSAT; a ratio of MSS Channel 5 to MSS Channel 4 (R5,4), two visible channels, separates materials by color hue. Additional information is attained by the addition of MSS channels 5 and 4 to approximate brightness, permitting separation of materials by color value. Other spectral combinations may provide correlations with these physical parameters or new ones. An iron absorption in the infrared can also be recognized in LANDSAT data when iron content is present in sufficient percentages, Although by color, limonite-rich soils are distinctive as bright yellow, they are not unique in the R5,4. A fairly strong iron absorption is present in the infrared band MSS Channel 7 for these soils, although the wideband configuration of LANDSAT is not optimal for its enhancement and the effects of vegetation often obscure it.

Salmon-Drexler, B. C.↗
NASA NTRS1977

Pre-impact conditions and cratering processes at the Flynn Creek crater, Tennessee

A description is presented of a preliminary outline for the cratering processes at Flynn Creek, Tennessee, a large, flat-floored, terrestrial impact crater with a central uplift. The initial preimpact conditions in terms of terrain, target media, and structure are defined, taking into account the possibility of impact into a shallow sea. A brief outline is provided of the generalized sequence of events from the time of entry of the impacting body into the atmosphere through the termination of late-stage cratering motions. The abbreviated sequence of cratering events is based upon a composite of recently assembled physical constraints, including new field data, experimental laboratory impact and field explosion trials, and theoretical numerical simulation studies.

Roddy, D. J.↗
NASA NTRS1979

Clock synchronisation experiment in India using symphonie satellite

A recent clock synchronization experiment between the National Physical Laboratory (NPL), New Delhi and Space Applications Center (SAC), Ahemedabad, in India via geostationary satellite symphonie 2, stationed at 49 E longitude, is reported. A two-way transmission using a microwave transponder considered to provide the greatest precision in synchronization of two remote clocks is described.

Somayajulu, Y. V.↗
NASA NTRS1981

Precise T and F intercomparison via VLF phase measurements

Continuous phase recording of the 16kHz transmission from GBR (UK) are being made and published midday phase data of GBR are received regularly from laboratories in the US, FGR, and UK. The local time scale (UTC, India), at the National Physical Laboratory in New Delhi, and those at the foreign laboratories are intercompared using the VLF phase data. A major factor which limits the accuracy of long term comparison is the seasonal variation in the VLF over delay over long paths. By taking into account the seasonal delay variations in a semiempirical way, the accuracy of time and frequency comparisons can be improved. Over a one year period, accuracy of a few parts in 10 to the 14th power in frequency and 1 to 2 micron sec in time were obtained. The relative frequency offset difference between UTC, (India) and UTC (PTB, Germany) of (7.0 + or - 0.1) x 10 to the -13 power agrees well with that obtained in a satellite experiment.

Gupta, A. S.↗
NASA NTRS1981

Correct generalized solar radiation pressure force on a circular cylinder in an arbitrary orientation

In response to the inconsistency seen in Geogevic (1973) with respect to the solution for solar radiation pressure in the case of a circular cylinder, a succinct derivation of the correct solution is presented. Numerical comparisons of the two sets of results confirm that the new formulation yields physically reasonable results for both general and special cases. A detailed graphic representation of the mathematical model used is included.

Tang, C. C. H.↗
NASA NTRS1984

SixNyCz Fibers for Safer Composites

Silicon nitride/silicon carbide fibers prepared by pyrolysis of polycarbosilazanes proposed substitute for carbon fibers. Silicon nitride/silicon carbide fibers tested pyrolyzed from polycarbosilazanes prepared from tris(N-methylamino) methylsilane. Polycarbosilazane resin drawn into fiber from melt, treated and pyrolyzed. Pyrolyzed fibers are shiny black. Tests show new fibers have physical properties comparable to graphite but with lower conductivity.

Ledbetter, F. E., III↗
NASA NTRS1984

Comet Bowell 1980b

Optical filter photometry, and optical and ultraviolet spectrophotometry data collected between November 1980 and June 1982 of Comet Bowell are presented. It was determined that Comet Bowell began producing significant amounts of OH, though not other species, before perihelion at a heliocentric distance near 4.6 AU. As the comet approached perihelion at 3.4 AU, OH production decreased and CN and C2 species were detected at normal concentrations. An outburst in April 1982 was dominated by OH. The grains in 1982 near perihelion showed increases in albedo between 3150 and 4500 A and 1.2 and 1.6 microns. The presence of two grains populations was suggested, together with the conclusion that Comet Bowell was physically a typical new comet entering the inner solar system from the Oort cloud for the first time.

Feldman, P. D.↗
NASA NTRS1984

Research in Structures and Dynamics, 1984

A symposium on advanced and trends in structures and dynamics was held to communicate new insights into physical behavior and to identify trends in the solution procedures for structures and dynamics problems. Pertinent areas of concern were (1) multiprocessors, parallel computation, and database management systems, (2) advances in finite element technology, (3) interactive computing and optimization, (4) mechanics of materials, (5) structural stability, (6) dynamic response of structures, and (7) advanced computer applications.

Robert J Hayduk↗
NASA NTRS1989

Additives Lower Pickup Of Moisture By Polyimides

Series of new polyimide-processing additives decrease free volume and pickup of moisture in new 422 copolyimide. Physical properties of several copolyimides synthesized from linear BDSDA/ODA/MPD homopolymers investigated previously, by positron-annihilation spectroscopy, with results indicating copolyimides have unique transition molecular structure characterized by higher electron densities and stronger bonds. Transition structure permits both physical and chemical entry of water molecules into it.

St. Clair, Terry L.↗
NASA NTRS1990

CFD modeling of an arc-heated jet

On the basis of state-of-the-art numerical techniques and physical models, a new CFD program is developed for the simulation of a high-enthalpy reacting ionized thermally relaxing nitrogen plasma in a cylindrical plenum chamber. A preliminary validation by comparison with experimental results was obtained. The algorithm is shown to be very efficient, and the empirical modeling gave results of practical use for the configuration studied.

Rostand, Phillipe↗
NASA NTRS1991

Parameter identification for nonlinear aerodynamic systems

Work continues on frequency analysis for transfer function identification, both with respect to the continued development of the underlying algorithms and in the identification study of two physical systems. Some new results of a theoretical nature were recently obtained that lend further insight into the frequency domain interpretation of the research. Progress in each of those areas is summarized. Although not related to the system identification problem, some new results were obtained on the feedback stabilization of linear time lag systems.

Pearson, Allan E.↗
NASA NTRS1991

Development of a CFD Code for Analysis of Fluid Dynamic Forces in Seals

The aim is to develop a 3-D computational fluid dynamics (CFD) code for the analysis of fluid flow in cylindrical seals and evaluation of the dynamic forces on the seals. This code is expected to serve as a scientific tool for detailed flow analysis as well as a check for the accuracy of the 2D industrial codes. The features necessary in the CFD code are outlined. The initial focus was to develop or modify and implement new techniques and physical models. These include collocated grid formulation, rotating coordinate frames and moving grid formulation. Other advanced numerical techniques include higher order spatial and temporal differencing and an efficient linear equation solver. These techniques were implemented in a 2D flow solver for initial testing. Several benchmark test cases were computed using the 2D code, and the results of these were compared to analytical solutions or experimental data to check the accuracy. Tests presented here include planar wedge flow, flow due to an enclosed rotor, and flow in a 2D seal with a whirling rotor. Comparisons between numerical and experimental results for an annular seal and a 7-cavity labyrinth seal are also included.

Athavale, Mahesh M.↗