Search NASA⌕ Search

SEARCH · Search NASA

Results for “fractional models”

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.

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

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The relationship of the lunar regolith less than 10-microns fraction and agglutinates. II - Chemical composition of agglutinate glass as a test of the 'fusion of the finest fraction' /F3/ model

Agglutinate glasses from nine Apollo soils have been studied using an automated electron microprobe technique in order to test the fusion of the finest fraction model proposed by Papike (1981). The nine average agglutinate glass compositions are compared with the calculated fused-soil-free compositions, the bulk compositions and the 90-20 micron fraction compositions of the soils in which they are found. It is found that the agglutinate glass data are consistent with the composition of most of the fractions finer than 10 microns, allowing for the volatile loss of K2O and Na2O; some inconsistencies that do arise may result from the degree of soil maturity and the amount of material finer than 10 microns. It is concluded that the fusion of the finest fraction model is a good first approximation of mechanisms affecting the formation of agglutinate glass.

Walker, R. J.↗
NASA NTRS2014

Fractional Order Modeling of Atmospheric Turbulence - A More Accurate Modeling Methodology for Aero Vehicles

The presentation covers a recently developed methodology to model atmospheric turbulence as disturbances for aero vehicle gust loads and for controls development like flutter and inlet shock position. The approach models atmospheric turbulence in their natural fractional order form, which provides for more accuracy compared to traditional methods like the Dryden model, especially for high speed vehicle. The presentation provides a historical background on atmospheric turbulence modeling and the approaches utilized for air vehicles. This is followed by the motivation and the methodology utilized to develop the atmospheric turbulence fractional order modeling approach. Some examples covering the application of this method are also provided, followed by concluding remarks.

Atmospheric Turbulence Modeling↗
NASA NTRS2013

A Stochastic Fractional Dynamics Model of Space-time Variability of Rain

Rainfall varies in space and time in a highly irregular manner and is described naturally in terms of a stochastic process. A characteristic feature of rainfall statistics is that they depend strongly on the space-time scales over which rain data are averaged. A spectral model of precipitation has been developed based on a stochastic differential equation of fractional order for the point rain rate, that allows a concise description of the second moment statistics of rain at any prescribed space-time averaging scale. The model is thus capable of providing a unified description of the statistics of both radar and rain gauge data. The underlying dynamical equation can be expressed in terms of space-time derivatives of fractional orders that are adjusted together with other model parameters to fit the data. The form of the resulting spectrum gives the model adequate flexibility to capture the subtle interplay between the spatial and temporal scales of variability of rain but strongly constrains the predicted statistical behavior as a function of the averaging length and times scales. We test the model with radar and gauge data collected contemporaneously at the NASA TRMM ground validation sites located near Melbourne, Florida and in Kwajalein Atoll, Marshall Islands in the tropical Pacific. We estimate the parameters by tuning them to the second moment statistics of radar data. The model predictions are then found to fit the second moment statistics of the gauge data reasonably well without any further adjustment.

TRMM↗
NASA NTRS1993

Estimation of the fractional coverage of rainfall in climate models

The fraction of the grid cell area covered by rainfall, mu, is an essential parameter in descriptions of land surface hydrology in climate models. A simple procedure is presented for estimating this fraction, based on extensive observations of storm areas and rainfall volumes. Storm area and rainfall volume are often linearly related; this relation can be used to compute the storm area from the volume of rainfall simulated by a climate model. A formula is developed for computing mu, which describes the dependence of the fractional coverage of rainfall on the season of the year, the geographical region, rainfall volume, and the spatial and temporal resolution of the model. The new formula is applied in computing mu over the Amazon region. Significant temporal variability in the fractional coverage of rainfall is demonstrated. The implications of this variability for the modeling of land surface hydrology in climate models are discussed.

Eltahir, E. A. B.↗
NASA NTRS2002

Control Oriented Modeling and Validation of Aeroservoelastic Systems

Lightweight aircraft design emphasizes the reduction of structural weight to maximize aircraft efficiency and agility at the cost of increasing the likelihood of structural dynamic instabilities. To ensure flight safety, extensive flight testing and active structural servo control strategies are required to explore and expand the boundary of the flight envelope. Aeroservoelastic (ASE) models can provide online flight monitoring of dynamic instabilities to reduce flight time testing and increase flight safety. The success of ASE models is determined by the ability to take into account varying flight conditions and the possibility to perform flight monitoring under the presence of active structural servo control strategies. In this continued study, these aspects are addressed by developing specific methodologies and algorithms for control relevant robust identification and model validation of aeroservoelastic structures. The closed-loop model robust identification and model validation are based on a fractional model approach where the model uncertainties are characterized in a closed-loop relevant way.

Crowder, Marianne↗
NASA NTRS1972

Possible thermal history of the moon.

The possible thermal history of the moon is investigated by means of theoretical models. The calculations include the effects of melting and time-dependent redistribution of radioactive heat sources. The known constraints can best be satisfied by a model which is characterized by relatively high initial temperatures close to the melting range; melting and, consequently, fractionation and redistribution of radionuclides would occur during the first 1.5 b.y. and would then be followed by an effective cooling process. Heat flow measurements on the lunar surface should permit a distinction between such a completely fractionated model and a nonfractionated model or a model with restricted fractionation in the outer few hundred kilometers.

Fricker, P. E.↗
NASA NTRS2003

Quadrature Moments Method for the Simulation of Turbulent Reactive Flows

A sub-filter model for reactive flows, namely the DQMOM model, was formulated for Large Eddy Simulation (LES) using the filtered mass density function. Transport equations required to determine the location and size of the delta-peaks were then formulated for a 2-peak decomposition of the FDF. The DQMOM scheme was implemented in an existing structured-grid LES solver. Simulations of scalar shear layer using an experimental configuration showed that the first and second moments of both reactive and inert scalars are in good agreement with a conventional Lagrangian scheme that evolves the same FDF. Comparisons with LES simulations performed using laminar chemistry assumption for the reactive scalar show that the new method provides vast improvements at minimal computational cost. Currently, the DQMOM model is being implemented for use with the progress variable/mixture fraction model of Pierce. Comparisons with experimental results and LES simulations using a single-environment for the progress-variable are planned. Future studies will aim at understanding the effect of increase in environments on predictions.

Raman, Venkatramanan↗
NASA NTRS1990

Comment on 'A non-mass-dependent isotopic fractionation effect' by F. Robert, J. Halbout and J. Baudon

The fractionation model of Robert et al. (1988) treats the gas-phase isotopic exchange reaction between kinetically excited atoms aX and diatomic MbX yielding bX and MaX and finds an abundance-dependent fractionation superimposed on the usual mass dependent fractionation. This paper shows that the treatment of Robert et al. is in error and presents a more straightforward treatment of the same system. This model shows only mass-dependent fractionation.

Sund, Mark T.↗
NASA NTRSDate not supplied

Constraints on triple oxygen isotope kinetics

Triple oxygen isotope measurements have been used as tracers for classifying meteorites, as indicators of atmospheric chemistry and as a proxy for primary productivity among other uses. These utilities rely on the mass dependency of most chemical reactions: δ17O is proportional to δ18O by roughly a factor of 0.5. However,in detail it is known that mass-dependency factorsvary. Constraints on mass dependency are well established for equilibrium isotope effects, but similar constraints for kinetic isotope effects are lacking.Here, we provide constraints for isotope effects generated by unidirectional chemical reactions (i.e. kinetic isotope effects, KIEs). A simplified Monte Carlo model is used to estimatethe range of kinetic isotope effects. It is found that the range of KIEs exceeds the range of equilibrium isotope effects such that some mass dependent kinetic isotope effects could be mistaken for being mass-independent. For the16O-17O-18O system,Δ′17Ovariations as large 0.8‰ can be generated from a single reaction step. Two case studies from published literature, on the thermal decomposition of calcite (CaCO3) and brucite (Mg(OH)2), are used to test the extreme limits of the modeled results. Isotope fractionationsgenerated fromdensity functional theory models of the surface reaction steps are shownto match the published data. The fractionation models are strictly mass dependent thus this result suggests thermal decomposition of calcite is also mass dependent. Although oxygen is the focus here, our approach applies to any system with more than two isotopes.

J. A. Hayles↗
NASA NTRS1993

First observations of CO and HCN on Neptune and Uranus at millimeter wavelengths and the implications for atmospheric chemistry

Observations are presented which show that CO is present in both the troposphere and stratosphere of Neptune, whereas is confined to the Neptune stratosphere with a mean mole fraction in the 0.003-30 mbar pressure level range of 1.0 x 10 exp -9. CO is present in both the stratosphere and in the troposphere with a uniformly mixed model fraction of 1.2 x 10 exp -6. Upper limits of 1.0 x 10 exp -10 and 3.0 x 10 exp -8 mole fractions are derived for HCN and CO respectively on Uranus. The origin of these species in the atmosphere of Neptune and their nondetection in that of Uranus are discussed in detail. It is concluded that the most plausible scenario involves upward convection of CO and N2 from Neptune's deep interior and a failure of chemical equilibrium at deep atmospheric levels, allowing excess CO and presumably N2 to reach the upper atmosphere. Nondetection in Uranus may be explained by the lack of a significant internal heat source in the planet and consequent suppression of vertical convection.

Marten, A.↗
NASA NTRS1993

Orthopyroxenes as recorders of diogenite petrogenesis: Trace element systematics

Eucrite, howardite, and diogenite members of the achondrites are considered, by many, to be genetically related. Therefore, each provide a piece of the puzzle for reconstructing magmatic processes on the eucrite parent body (EPB). The relationship between eucrites and diogenites can be viewed within the context of two distinctly different models: (1) fractional crystallization; and (2) partial melting. In fractional crystallization models, eucrites and diogenites represent a complementary continuum of planetary fractional crystallization products in which the diogenites represent crystal accumulations during the crystallization of eucritic magmas at shallow to deep levels in the EPB. Alternatively, experimental studies may be interpreted as indicating eucrites represent peritectic partial melts of a primitive, chondritic EPB mantle. Within this type of model, the diogenites are also generally considered to be cumulates; however, their petrogenetic relationship to the eucrites is less clear. Sack et al. proposed that the olivine diogenites represent residua from the partial melting events that produced eucritic liquids. Initial trace element studies of orthopyroxene (OPX) are consistent with this model. However, this trace element modeling of the olivine diogenites is nonunique. As a further test of these models, we did the following three things: (1) analyzed OPX from cumulate diogenites to compare with the olibine diogenite data; (2) improved ion microprobe analytical techniques for the analysis of elements critical to our interpretations; and (3) selected more relevant Kd's for OPX-eucritic melt.

Shearer, C. K.↗
NASA NTRS1995

Solar wind composition

Advances in instrumentation have resulted in the determination of the average abundances of He, C, N, O, Ne, Mg, Si, S, and Fe in the solar wind to approximately 10%. Comparisons with solar energetic particle (SEP) abundances and galactic cosmic ray abundances have revealed many similarities, especially when compared with solar photospheric abundances. It is now well established that fractionation in the corona results in an overabundance (with respect to the photosphere) of elements with first ionization potentials less than 10 eV. These observations have in turn led to the development of fractionation models that are reasonably successful in reproducing the first ionization (FIP) effect. Under some circumstances it has been possible to relate solar wind observations to particular source regions in the corona. The magnetic topologies of the source regions appear to have a strong influence on the fractionation of elements. Comparisons with spectroscopic data are particularly useful in classifying the different topologies. Ions produced from interstellar neutral atoms are also found in the solar wind. These ions are picked up by the solar wind after ionization by solar radiation or charge exchange and can be identified by their velocity in the solar wind. The pick-up ions provide most of the pressure in the interplanetary medium at large distances. Interstellar abundances can be derived from the observed fluxes of solar wind pick-up ions.

Ogilvie, K. W.↗
NASA NTRS1977

The petrology of the Apollo 12 ilmenite basalt suite

Mineral chemistry data and petrographic interpretations as well as fractionation modeling determined independently indicate that the bulk chemical variations in the ilmenite suite can be reconciled with differentiation within a single cooling unit. Olivine porphyritic basalts, medium-grained basalts with evolved compositions, and coarse-grained olivine cumulates are found in the suite. It is suggested that most of the chemical variation within the suite could result from fractionation of olivine equivalent to the composition of phenocrysts in vitrophyre 12008 which serves well as a parental magma for the other textural-chemical variants. The relative cooling rate sequence within all three textural-chemical subgroups was determined, and systematic correlations between the degree of olivine addition or subtraction and the relative cooling rate is indicated.

Dungan, M. A.↗
NASA NTRS1977

Genesis of the Angra dos Reis and other achondritic meteorites

Major, minor, and trace element abundances were determined in seven Angra dos Reis samples, which included whole rocks, fassaite (clinopyroxene), olivine, and whitlockite separates, via sequential instrumental neutron activation analysis. The rare earth element abundance patterns and the trace element abundance patterns of this achondritic meteorite are discussed. A two-stage crystal-liquid fractionation model with source material containing olivine, orthopyroxene, and clinopyroxine is presented for the genesis of Angra dos Reis. Multilinear regression analysis was used to estimate possible composition and properties of the parent magmas. Angra dos Reis was compared with other achondrites, cumulate eucrites and nakhlites in particular. It is thought that the unique Angra dos Reis could not be related to those achondrites by crystal-liquid fractionation of the same parent body.

Ma, M.-S.↗
NASA NTRS2003

New Model for Agglutinitic Glass Formation from LSCC Data

Since the return of the first lunar samples it has been well known that glass-welded aggregates (agglutinates) accumulate in lunar soil as the result of multiple processes, many of which are driven by micrometeorite impacts. The proportion of agglutinates increases with increasing exposure to the space environment, and for an individual soil the proportion of agglutinates also increases with decreasing particle size. Detailed chemical and petrographic analyses of a suite of mare soils and their agglutinate constituents prepared by the Lunar Soil Characterization Consortium appeared to confirm the "Fusion of the Finest Fraction" model for agglutinate formation (or F3) proposed by Papike et al. However, recent LSCC data for highland soils are not consistent with the F3 model and alternate models for agglutinate formation must be revisited. Instead, we suggest differential melting of soil species may be more consistent with the full range of soil data to date.

Pieters, C. M.↗
NASA NTRS1983

Condensation of solids in space. Isotope fractionation in the model system C-O

The reported chemical fractionation of a single isotope O-16 under simulated space conditions provides the first experimental proof for the hypothesis that the oxygen isotopic anomaly (and other similar anomalies) seen in meteorites is a product of chemical fractionation in interstellar or circumstellar space. Work proposed on this subject was discontinued because a peer review determined that such effects could not possibly exist and that continued support of this project would be a wasted effort. A bibliography is included of articles generated during research in this area.

Arrhenius, G.↗