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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 NTRS2005

Composition of Meridiani Hematite-rich Spherules: A Mass-Balance Mixing-Model Approach

One of the great surprises of the Mars Exploration Rovers (MER) mission is the discovery at Meridiani Planum that the surface hematite signature observed from orbit is attributable largely to a surface enrichment of hematite-rich spherules, thought to be concretions, that have weathered out of rocks similar to the underlying sulfate-rich rock formation [1]. A strong hematite signature has been observed by the Mini-TES [2] and by in-situ measurements of spherule-rich targets by the Mossbauer spectrometer (MB) [3] and the alpha-particle X-ray spectrometer (APXS) [4]. The Mini-TES derived spectrum of spherule-rich targets on the plains is consistent with nearly pure coarse-grained hematite, with perhaps as little as 5-10 areal % of other components [2]. The occurrence and abundance of the spherules as the bearer of the widespread hematite signature observed by MGS TES over much of Meridiani Planum is significant for global remote sensing, and their occurrence as concretions in the outcrop lithology is significant for the diagenetic history and role of water in the formation of the sedimentary rock formation [5].

jOLLIFF, b. l.↗
NASA NTRS2006

Mixed Modeling of a SAW Delay Line Using VHDL-AMS

To aid in the development of SAW sensors for aerospace applications we have created a model of a SAW Delay line using VHDL. The model implements the Impulse Response method to calculate the frequency response, impedance, and insertion loss. The model includes optimization for the number of finger pairs in the IDTs and for the aperture height. This paper presents the model and the results from the model for a SAW delay line design.

Wilson, William C.↗
NASA NTRS2009

Chemical Mixing Model and K-Th-Ti Systematics and HED Meteorites for the Dawn Mission

The Dawn mission will explore 4 Vesta, a large differentiated asteroid believed to be the parent body of the howardite, eucrite and diogenite (HED) meteorite suite. The Dawn spacecraft carries a gamma-ray and neutron detector (GRaND), which will measure the abundances of selected elements on the surface of Vesta. This study provides ways to leverage the large geochemical database on HED meteorites as a tool for interpreting chemical analyses by GRaND of mapped units on the surface of Vesta.

Usui, T.↗
NASA NTRS2015

Trending in Pc Measurements via a Bayesian Zero-Inflated Mixed Model

Two satellites predicted to come within close proximity of one another, usually a high-value satellite and a piece of space debris moving the active satellite is a means of reducing collision risk but reduces satellite lifetime, perturbs satellite mission, and introduces its own risks. So important to get a good statement of the risk of collision in order to determine whether a maneuver is truly necessary. Two aspects of this Calculation of the Probability of Collision (Pc) based on the most recent set of position velocity and uncertainty data for both satellites. Examination of the changes in the Pc value as the event develops. Events should follow a canonical development (Pc vs time to closest approach (TCA)). Helpful to be able to guess where the present data point fits in the canonical development in order to guide operational response.

Conjuction Assessment↗
DOE OSTI2020

Modeling gas–shell mixing in ICF with separated reactants

Mixing between fuel and shell materials in ICF implosions can affect implosion dynamics and even prevent ignition. We use data from a series of separated reactant experiments on the National Ignition Facility to calibrate and test the predictive power of gas–shell mix models. Two models are used to estimate fuel–shell mix: a Reynolds-averaged turbulence model and molecular diffusion. Minor uncertainties in capsule manufacture, experimental conditions, and values for mix model parameters produce significant variation in simulation results. Using input/output pairs from 1D simulations, we train Gaussian process surrogate models to predict experimental quantities of interest. The surrogates are used to construct posteriors for mix model parameters by marginalizing over uncertainties in capsule manufacture and experimental conditions. Mix models are calibrated with a subset of experimental data (neutron yields, ion temperature, and bang time) and tested using the remaining data. In general, both the diffusion and turbulence model correctly predict experimental DT and TT neutron yields. Despite having more free parameters, the turbulence model underpredicts ion temperature at high convergence ratio. Furthermore, the simpler diffusion model correctly predicts these temperatures, suggesting nonhydrodynamic gas–shell mix. The computational model consistently overpredicts DD neutron yield, indicating possible shortcomings outside of the mix model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1982

The Apollo 15 regolith - Chemical modeling and mare/highland mixing

The chemical compositions of thirty-one A-15 soils from nine sampling stations were studied. Mixing models were calculated using five components: 'representative A-15 mare basalt', anorthosite, low-K Fra Mauro basalt, green glass, and medium-K KREEP (Laul and Papike, 1980). A linear-least-squares mixing model (Boynton et al., 1975) was used with sum check and chi-square tests of the fit of components to soil composition. The soils show significant compositional variability, in some instances over relatively small distances within a sampling station. The models indicate that green-glass abundance does not vary systematically with location and that a significant KREEP component is found in all Apennine Front soils. The models also show the soils from the rim of Hadley Rille to be the most mare-enriched, and soils from Station 2 to be the most highland-enriched. The regolith from Station 8-LM is anomalously high in KREEP component relative to the other mare soils, possibly because of ray material.

Walker, R. J.↗
NASA NTRS1994

Theoretical light curve of a Type 2p supernova

The light curve and other observable diagnostics are presented for what should be a typical Type II 'plateau' supernova, the explosion of a 15 solar mass red supergiant. The calculations are carried out using a multi-frequency radiation transport code that includes opacity from all important mechanisms-bound-bound, bound-free, free-free, and electron scattering. It is found that the inclusion of opacity sources besides electron scattering increases the computed lenght of the plateau in the 15 solar mass model by approximately 30 days. Especially important is the ultraviolet cutoff caused by a thick forest of lines. Deposition and escape of gamma-rays from radioactive decay are also accurately simulated. We find that the presence of 0.06 solar mass of ejected Ni-56 extends the length of the plateau from approximately 100 days to approximately 140 dys. Because of the large hydrogen envleope and radius in this model, mixing does not appreciably alter the bolometric light curve, although it does change the gamma-ray light curve significantly. With 0.06 solar mass of ejected Ni-56, the unmixed (mixed) model peaks in escaping gamma-rays at 576 (466) days with gamma-ray luminosity of 3 x 10(exp 38) ergs/s. Except for the local group, the gamma-rays from an extragalactic 15 solar mass SNe IIp will be too faint to detect with any exsiting detectors. However, a Galactic SNe IIp would be quite bright and easily detectable.

Eastman, Ronald G.↗
NASA NTRS1996

A priori testing of subgrid-scale models for the velocity-pressure and vorticity-velocity formulations

Subgrid-scale models for Large Eddy Simulation (LES) in both the velocity-pressure and the vorticity-velocity formulations were evaluated and compared in a priori tests using spectral Direct Numerical Simulation (DNS) databases of isotropic turbulence: 128(exp 3) DNS of forced turbulence (Re(sub(lambda))=95.8) filtered, using the sharp cutoff filter, to both 32(exp 3) and 16(exp 3) synthetic LES fields; 512(exp 3) DNS of decaying turbulence (Re(sub(Lambda))=63.5) filtered to both 64(exp 3) and 32(exp 3) LES fields. Gaussian and top-hat filters were also used with the 128(exp 3) database. Different LES models were evaluated for each formulation: eddy-viscosity models, hyper eddy-viscosity models, mixed models, and scale-similarity models. Correlations between exact versus modeled subgrid-scale quantities were measured at three levels: tensor (traceless), vector (solenoidal 'force'), and scalar (dissipation) levels, and for both cases of uniform and variable coefficient(s). Different choices for the 1/T scaling appearing in the eddy-viscosity were also evaluated. It was found that the models for the vorticity-velocity formulation produce higher correlations with the filtered DNS data than their counterpart in the velocity-pressure formulation. It was also found that the hyper eddy-viscosity model performs better than the eddy viscosity model, in both formulations.

Winckelmans, G. S.↗
NASA NTRS1982

Further considerations on modeling the sea breeze with a mixed-layer model

Mixed-layer models have been used to simulate low-level flows under a variety of situations, including flow over complex terrain and in the vicinity of coastal zones. The advantage of mixed-layer models compared to multilevel models is their simplicity and minimal computational requirements. A disadvantage is that the atmosphere above the mixed layer is not modeled explicitly and approximations pertaining to this layer become necessary. This paper examines five approximations for treating this upper layer for a simple sea-breeze circulation. Approximating the flow immediately above the mixed-layer height h by the mixed-layer velocity and using this velocity to advect potential temperature above h gives a better simulation of the sea breeze than the approximation used by Anthes et al. (1980), which neglected horizontal advection at this level.

Anthes, R. A.↗
DOE OSTI2020

Development and Validation of SAM Multi-dimensional Flow Model for Thermal Mixing and Stratification Modeling

Thermal mixing and stratification in large pools or enclosures are very important phenomena that are critical to nuclear reactor safety. Because of the wide ranges of time and length scales associated with such phenomena, accurate modeling and simulation of thermal mixing and stratification remain as the key unresolved, challenging problems for reactor transient analyses. In traditional system analysis codes, simplified zero-dimensional (0-D) models are widely used for their high numerical efficiency, but they generally suffer from very limited prediction accuracies or range of applicability. Like traditional system analysis codes, the current version of the SAM code has implemented such simplified 0-D and one-dimensional mixing models. On the other hand, high-resolution Computational Fluid Dynamics (CFD) tools are often used to model complex thermal mixing and stratification phenomena. They are, however, generally numerically expensive, and they require large amounts of computational resources. It is therefore desirable to implement advanced and efficient thermal mixing and stratification modeling capabilities embedded in a system analysis code. This approach will improve the accuracy of reactor safety analyses when thermal mixing and stratification are involved, and also avoid using the large computational resources needed for high-resolution CFD analysis. Currently, with the support of the U.S. DOE Office of Nuclear Energy’s Nuclear Energy Advanced Modeling and Simulation program, an effort has been launched to develop and implement a multi-dimensional flow model in the system analysis code SAM, and demonstrate its applications to model thermal mixing and stratification phenomena in large enclosures. The main outcomes of this research and development activity are summarized in this report, which presents an attempt to include a built-in advanced multi-dimensional flow model in a system analysis code with the focus on overcoming the simulation challenges of thermal mixing and stratification phenomena. In this report, we start with the introduction of existing SAM code capabilities to simulate thermal mixing and stratification phenomena, which is followed by a short summary of the multi-dimensional model implemented in the SAM code, including both the physical model and the Finite Element Method code implementation. In this study, two options were implemented in the SAM code to model turbulent flows: a relatively simple built-in turbulence model and an interface to accept externally computed turbulent viscosities (e.g., from a high- resolution CFD simulation). Code validation studies on this newly added capability were then carried out to compare SAM simulation results with experimental data from the SUPERCAVNA facility, which was designed to study the complex flow recirculation and thermal stratification phenomena relevant to sodium fast reactor designs. In this study, one transient and two steady-state test cases were used for code validation. Different approaches have been used to model the complex turbulence flow fields in the SUPERCAVNA facility. A highly simplified zero-equation turbulence model was first used, but it was determined that it is too simple to capture the complex turbulence flow fields in these test cases. Subsequently, the code validation continued with the use of turbulent viscosity data from high-resolution STAR-CCM+ CFD simulations to improve the accuracy of the results. Using this approach, the SAM simulation results showed very good agreement with both the SUPERCAVNA experimental data and STAR-CCM+ simulation results. In this report, we demonstrate the development, implementation, and successful validation of a multi-dimensional flow model in the SAM code, which aims to improve the simulation accuracy for complex thermal mixing and stratification phenomena. Lessons have also been learned, including that in cases where the flow fields are not well predicted by the zero-equation model, the iinput of turbulent viscosities from an external source can enhance the overall predictive capabilities needed to accurately capture complex thermal-hydraulic phenomena. Therefore, future research will be needed to further improve the code’s capabilities, such as by developing a more efficient and robust approach to capture the turbulence effects in the SAM code.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2004

Chandra Observations and Models of the Mixed Morphology Supernova Remnant W44: Global Trends

We report on the Chandra observations of the archetypical mixed morphology (or thermal composite) supernova remnant, W44. As with other mixed morphology remnants, W44's projected center is bright in thermal X-rays. It has an obvious radio shell, but no discernable X-ray shell. In addition, X-ray bright knots dot W44's image. The spectral analysis of the Chandra data show that the remnant s hot, bright projected center is metal-rich and that the bright knots are regions of comparatively elevated elemental abundances. Neon is among the affected elements, suggesting that ejecta contributes to the abundance trends. Furthermore, some of the emitting iron atoms appear to be underionized with respect to the other ions, providing the first potential X-ray evidence for dust destruction in a supernova remnant. We use the Chandra data to test the following explanations for W44's X-ray bright center: 1.) entropy mixing due to bulk mixing or thermal conduction, 2.) evaporation of swept up clouds, and 3.) a metallicity gradient, possibly due to dust destruction and ejecta enrichment. In these tests, we assume that the remnant has evolved beyond the adiabatic evolutionary stage, which explains the X-ray dimness of the shell. The entropy mixed model spectrum was tested against the Chandra spectrum for the remnant's projected center and found to be a good match. The evaporating clouds model was constrained by the finding that the ionization parameters of the bright knots are similar to those of the surrounding regions. While both the entropy mixed and the evaporating clouds models are known to predict centrally bright X-ray morphologies, their predictions fall short of the observed brightness gradient. The resulting brightness gap can be largely filled in by emission from the extra metals in and near the remnant's projected center. The preponderance of evidence (including that drawn from other studies) suggests that W44's remarkable morphology can be attributed to dust destruction and ejecta enrichment within an entropy mixed, adiabatic phase supernova remnant. The Chandra data prompts a new question - by what astrophysical mechanisms are the metals distributed so inhomogeneously in the supernova remnant.

Shelton, R. L.↗
NASA NTRS1961

Combined Effect of Contraction Ratio and Chamber Pressure on the Performance of a Gaseous Hydrogen-Liquid-Oxygen Combustor for a Given Propellant Weight Flow and Oxidant-Fuel Ratio

The effect of contraction ratio and chamber pressure on the combustion performance of a gaseous-hydrogen-liquid-oxygen combustor was investigated analytically and experimentally. The experiment was conducted with a "two-dimensional" gaseous-hydrogen-liquid-oxygen engine of about 150-pound thrust. The contraction ratio was varied from 1.5 to 6 by changing the nozzle throat area. This variation resulted in a chamber pressure variation of about 25 to 120 pounds per square inch. The experimental results were corrected for heat transfer to the engine walls and momentum pressure losses. The experimental performance, as evaluated in terms of characteristic exhaust velocity, was 98 percent of theoretical at contraction ratios greater than 3 but decreased very rapidly at smaller contraction ratios. The heat-transfer rate increased with increasing contraction ratio and chamber pressure; it was about 1 Btu per square inch per second at a contraction ratio of 1.5 and increased to about 3 at a contraction ratio of 6. The combined effects of contraction-ratio and chamber-pressure changes on performance were investigated analytically with a mixing model and a vaporization model. The mixing model predicted very poor mixing at contraction ratios below 3 and almost perfect mixing at higher contraction ratios. The performance predicted by the vaporization model was very close to 100 percent for all contraction ratios. From these results, it was concluded that the performance was limited by poor mixing at low contraction ratios and chamber pressures.

Hersch, Martin↗
NASA NTRS2001

A Numerical Study of Tropical Sea-Air Interactions Using a Cloud Resolving Model Coupled with an Ocean Mixed-Layer Model

Coupling a cloud resolving model (CRM) with an ocean mixed layer (OML) model can provide a powerful tool for better understanding impacts of atmospheric precipitation on sea surface temperature (SST) and salinity. The objective of this study is twofold. First, by using the three dimensional (3-D) CRM-simulated (the Goddard Cumulus Ensemble model, GCE) diabatic source terms, radiation (longwave and shortwave), surface fluxes (sensible and latent heat, and wind stress), and precipitation as input for the OML model, the respective impact of individual component on upper ocean heat and salt budgets are investigated. Secondly, a two-way air-sea interaction between tropical atmospheric climates (involving atmospheric radiative-convective processes) and upper ocean boundary layer is also examined using a coupled two dimensional (2-D) GCE and OML model. Results presented here, however, only involve the first aspect. Complete results will be presented at the conference.

Shie, Chung-Lin↗
DOE OSTI2021

Machine learning assisted modeling of mixing timescale for LES/PDF of high-Karlovitz turbulent premixed combustion

Accurate modeling of mixing in the transported probability density function (PDF) method remains a great challenge, especially for turbulent premixed combustion under extreme conditions such as high Karlovitz number Ka. Recently, a power-law based mixing timescale model was developed for the large-eddy simulations (LES)/PDF modeling of high-Ka number turbulent premixed flames. It is found in this work that the power-law mixing timescale model is highly sensitive to the model parameters. It is thus critically needed to develop accurate calibration of these model parameters. The empirical specification of the model parameters developed in Zhang et. al. is found to be inadequate for accurate modeling of the mixing timescale. Here, machine learning is introduced as an attractive alternative in this work for the specification of the model parameters. A high-Ka number DNS jet flame is used as the training and validation of the machine learning models. The choices of the input parameters are discussed and compared for the machine learning models. The effect of differential molecular diffusion on mixing is examined by including the effect of the Lewis number in the training of the machine learning models. The performance of different machine learning algorithms is compared for the specification of the mixing model parameters. Overall, excellent performance of the machine learning models is observed for assisting the mixing modeling. The feasibility, interpretability, applicability, generality, and portability of using machine learning are discussed in general to provide a perspective on applying data-driven machine learning for turbulent combustion modeling studies.

42 ENGINEERING↗