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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 109 records · Page 6

Molecular wake shield gas analyzer

Techniques for measuring and characterizing the ultrahigh vacuum in the wake of an orbiting spacecraft are studied. A high sensitivity mass spectrometer that contains a double mass analyzer consisting of an open source miniature magnetic sector field neutral gas analyzer and an identical ion analyzer is proposed. These are configured to detect and identify gas and ion species of hydrogen, helium, nitrogen, oxygen, nitric oxide, and carbon dioxide and any other gas or ion species in the 1 to 46 amu mass range. This range covers the normal atmospheric constituents. The sensitivity of the instrument is sufficient to measure ambient gases and ion with a particle density of the order of one per cc. A chemical pump, or getter, is mounted near the entrance aperture of the neutral gas analyzer which integrates the absorption of ambient gases for a selectable period of time for subsequent release and analysis. The sensitivity is realizable for all but rare gases using this technique.

Hoffman, J. H.↗

The physical and empirical basis for a specific clear-air turbulence risk index

An improved operational CAT detection and forecasting technique is developed and detailed. This technique is the specific clear air turbulence risk (SCATR) index. This index shows some promising results. The improvements seen using hand analyzed data, as a result of the more realistic representation of the vertical shear of the horizontal wind, are also realized in the data analysis used in the PROFS/CWP application. The SCATR index should improve as database enhancements such as profiler and VAS satellite data, which increase the resolution in space and time, are brought into even more sophisticated objective analysis schemes.

Keller, J. L.↗

A comparison of TSS and TRASYS in form factor calculation

As the workstation and personal computer become more popular than a centralized mainframe to perform thermal analysis, the methods for space vehicle thermal analysis will change. Already, many thermal analysis codes are now available for workstations, which were not in existence just five years ago. As these changes occur, some organizations will adopt the new codes and analysis techniques, while others will not. This might lead to misunderstandings between thermal shops in different organizations. If thermal analysts make an effort to understand the major differences between the new and old methods, a smoother transition to a more efficient and more versatile thermal analysis environment will be realized.

Golliher, Eric↗

An Example of Risk Informed Design

NASA Engineering requested a Probabilistic Risk Assessment (PRA) to compare the difference in the risk of Loss of Crew (LOC) and Loss of Mission (LOM) between different designs of a fluid assembly. They were concerned that the configuration favored by the design team was more susceptible to leakage than a second proposed design, but realized that a quantitative analysis to compare the risks between the two designs might strengthen their argument. The analysis showed that while the second design did help improve the probability of LOC, it did not help from a probability of LOM perspective. This drove the analysis team to propose a minor design change that would drive the probability of LOM down considerably. The analysis also demonstrated that there was another major risk driver that was not immediately obvious from a typical engineering study of the design and was therefore unexpected. None of the proposed alternatives were addressing this risk. This type of trade study demonstrates the importance of performing a PRA in order to completely understand a system's design. It allows managers to use risk as another one of the commodities (e.g., mass, cost, schedule, fault tolerance) that can be traded early in the design of a new system.

Banke, Rick↗

Stochastic Thermo-Hydro Modeling and Neural Network Surrogate Development for Thermal Resource Assessment of the Galleries-to-Calories Geobattery

The Galleries-to-Calories Geobattery concept explores the use of abandoned coal mine workings for large-scale thermal energy transport and storage. The system involves injecting waste heat from a supercomputing facility into flooded mine galleries, where groundwater flow can store and transport thermal energy for potential recovery in downgradient district heating and cooling applications. To evaluate the feasibility and performance of the Geobattery under geological and operational uncertainty, we developed a suite of stochastic thermo-hydrological (TH) simulations using Monte Carlo sampling of key uncertain parameters (e.g., permeability, porosity, thermal conductivity, specific heat capacity) and operating conditions (e.g., injection rate, injection temperature). Results identified injection rate and temperature as the most influential parameters governing thermal front propagation, while the geometry of the room-and-pillar structure played a critical role in directing the extent and orientation of thermal advancement. Optimal combinations of material properties for maximizing heat recovery were also determined. To address the high computational cost of coupled-process stochastic modeling, we trained a neural network surrogate model on 24,000 physics-based realizations, achieving an R² > 0.99 and MAE < 0.1 for temperature predictions at monitoring locations. This surrogate enabled an additional 100,000 realizations for global sensitivity analysis and probabilistic thermal resource assessment. The integrated stochastic physics–surrogate modeling framework offers a computationally efficient tool for quantifying uncertainty, identifying key drivers, and informing early-stage design decisions for Geobattery systems.

15 - GEOTHERMAL ENERGY↗

Large-Eddy Simulation of an n-Dodecane Spray Flame Under Different Ambient Oxygen Conditions

An n-dodecane spray flame was simulated using a dynamic structure large eddy simulation (LES) model coupled with a detailed chemistry combustion model to understand the ignition processes and the quasi-steady state flame structures. This study focuses on the effect of different ambient oxygen concentrations, 13%, 15% and 21% at an ambient temperature of 900 K and an ambient density of 22.8 kg/m3, which are typical diesel-engine relevant conditions with different levels of exhaust gas recirculation (EGR). The liquid spray was treated with a traditional Lagrangian method. A 103-species skeletal mechanism was used for the n-dodecane chemical kinetic model. It is observed that the main ignitions occur in rich mixture and the flames are thickened around 35 to 40 mm off the spray axis due to the enhanced turbulence induced by the strong recirculation upstream, just behind the head of the flames at different oxygen concentrations. At 1 ms after the start of injection, the soot production is dominated by the broader region of high temperature in rich mixture instead of the stronger oxidation of the high peak temperature. Multiple realizations were performed for the 15% O2 condition to understand the realization to realization variation and to establish best practices for ensembleaveraging diesel spray flames. Two indexes are defined. The structure-similarity index analysis suggests at least 5 realizations are needed to obtain 99% similarity for mixture fraction if the average of 16 realizations are used as the target at 0.8 ms. However, this scenario may be different for different scalars of interest. It is found that 6 realizations would be enough to reach 99% of similarity for temperature, while 8 and 14 realizations are required to achieve 99% similarity for soot and OH mass fraction, respectively. Similar findings are noticed at 1 ms. More realizations are needed for the magnitude-similarity index for the similar level of similarity as the structure-similarity index

Pei, Yuanjiang↗

Large Eddy Simulation of an n-Dodecane Spray Flame Under Different Ambient Oxygen Conditions

An n-dodecane spray flame was simulated using a dynamic structure large eddy simulation (LES) model coupled with a detailed chemistry combustion model to understand the ignition processes and the quasi-steady state flame structure at different ambient oxygen concentrations, 13\%, 15\% and 21\% at ambient temperature of 900 K and ambient density of 22.8 kg/m3, which are typical diesel-engine relevant conditions with different levels of exhaust gas recirculation (EGR). The liquid spray was treated with a traditional Lagrangian method. A 103-species skeletal mechanism was used for n-dodecane chemical kinetic model. It is observed that the main ignitions occur in rich mixture and the flames are thickened around 35 to 40 mm off the spray axis due to the enhanced turbulence induced by the strong recirculation upstream just behind the head of the flames at different oxygen concentrations. At 1 ms after start of injection, the soot production is dominated by the broader region of high temperature in rich mixture instead of the stronger oxidation of the high peak temperature. Multiple realizations were performed for the 15\% O$_2$ condition to understand the realization to realization variation and to establish best practices for ensemble-averaging diesel spray flames. Two indexes are defined. The structure-similarity index analysis suggests at least 5 realizations are needed to obtain 99\% similarity for mixture fraction if average of 16 realizations are used as the target at 0.8 ms. However, this scenario may be different for different scalars of interest. It is found that 2 realizations would be enough to reach 99\% of similarity for temperature, while 8 and 14 realizations are required to achieve 99\% similarity for soot and OH mass fraction, respectively. Similar findings are noticed at 1 ms. More realizations are needed for the magnitude-similarity index for the similar level of similarity as the structure-similarity index.

Pei, Yuanjiang↗

XRD Analysis of Cement Paste Samples Exposed to the Simulated Environment of a Deep Repository - 12239

Portland cement materials are widely used as engineered barriers in repositories for radioactive waste. The capacity of such barriers to avoid the disposed of radionuclides to entering the biosphere in the long-term depends on the service life of those materials. Thus, the performance assessment of structural materials under a series of environmental conditions prevailing at the environs of repositories is a matter of interest. The durability of cement paste foreseen as backfill in a deep borehole for disposal of disused sealed radioactive sources is investigated in the development of the repository concept. Results are intended to be part of the body of evidence in the safety case of the proposed disposal technology. This paper presents the results of X-Ray Diffraction (XRD) Analysis of cement paste exposed to varying temperatures and simulated groundwater after samples received the radiation dose that the cement paste will accumulate until complete decay of the radioactive sources. The XRD analysis of cement paste samples realized in this work allowed observing some differences in the results of cement paste specimens that were submitted to different treatments. The cluster analysis of results was able to group tested samples according to the applied treatments. Mineralogical differences, however, are tenuous and, apart from ettringite, are hardly observed. The absence of ettringite in all the seven specimens that were kept in dry storage at high temperature had hardly occurred by natural variations in the composition of hydrated cement paste because ettringite is observed in all tested except the seven specimens. Therefore this absence is certainly the result of the treatments and could be explained by the decomposition of ettringite. Although the temperature of decomposition is about 110-120 deg. C, it may be initially decomposed to meta-ettringite, an amorphous compound, above 50 deg. C in the absence of water. Influence of irradiation on the mineralogical composition was not observed when the treatment was analyzed individually or when analyzed under the possible synergic effect with other treatments. However, the radiation dose to which specimens were exposed is only a fraction of the accumulated dose in cement paste until complete decay of some sources. Therefore, in the short term, the conditions deemed to prevail in the repository environment may not influence the properties of cement paste at detectable levels. Under the conditions presented in this work, it is not possible to predict the long term evolution of these properties. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

PYSIMFRAC: A Python library for synthetic fracture generation and analysis

In this paper, we introduce PYSIMFRAC, an open-source python library for generating 3-D synthetic fracture realizations, integrating with fluid simulators, and performing analysis. PYSIMFRAC allows the user to specify one of three fracture generation techniques (Box, Gaussian, or Spectral) and perform statistical analysis including the autocorrelation, moments, and probability density functions of the fracture surfaces and aperture. This analysis and accessibility of a python library allows the user to create realistic fracture realizations and vary properties of interest. In addition, PYSIMFRAC includes integration examples to two different pore-scale simulators and the discrete fracture network simulator, dfnWorks. The capabilities developed in this work provides opportunity for quick and smooth adoption and implementation by the wider scientific community for accurate characterization of fluid transport in geologic media. We present PYSIMFRAC along with integration examples and discuss the ability to extend PYSIMFRAC from a single complex fracture to complex fracture networks.

58 GEOSCIENCES↗

Ground Vibration Testing at NASA Armstrong, Emphasizing on Passive Aeroelastic Tailored Wing Ground Vibration Test Using Fixed Base Correction Method

How does experimental mechanics contribute to aircraft aeroelastic airworthiness? The aviation community is always improving analysis and testing techniques to realize quicker, cheaper, reliable solutions. A ground vibration test (GVT) is conducted to identify structural mode shapes, frequencies, and damping values to validate analytical models used for flutter analysis, which shows whether a structure has acceptable aeroelastic flutter margins for airworthiness. The FLL recently conducted a GVT of the Passive Aeroelastic Tailored (PAT) Wing using an experimental modal technique called Fixed Base Correction (FBC). The GVT objective was to obtain the PAT wing modal characteristics to compare test results with finite element model (FEM) results for the tow-steered wingbox.

loads testing↗

Shared Dosimetry Error in Epidemiological Dose-Response Analyses

Radiation dose reconstruction systems for large-scale epidemiological studies are sophisticated both in providing estimates of dose and in representing dosimetry uncertainty. For example, a computer program was used by the Hanford Thyroid Disease Study to provide 100 realizations of possible dose to study participants. The variation in realizations reflected the range of possible dose for each cohort member consistent with the data on dose determinates in the cohort. Another example is the Mayak Worker Dosimetry System 2013 which estimates both external and internal exposures and provides multiple realizations of "possible" dose history to workers given dose determinants. This paper takes up the problem of dealing with complex dosimetry systems that provide multiple realizations of dose in an epidemiologic analysis. In this paper we derive expected scores and the information matrix for a model used widely in radiation epidemiology, namely the linear excess relative risk (ERR) model that allows for a linear dose response (risk in relation to radiation) and distinguishes between modifiers of background rates and of the excess risk due to exposure. We show that treating the mean dose for each individual (calculated by averaging over the realizations) as if it was true dose (ignoring both shared and unshared dosimetry errors) gives asymptotically unbiased estimates (i.e. the score has expectation zero) and valid tests of the null hypothesis that the ERR slope β is zero. Although the score is unbiased the information matrix (and hence the standard errors of the estimate of β) is biased for β≠0 when ignoring errors in dose estimates, and we show how to adjust the information matrix to remove this bias, using the multiple realizations of dose. Use of these methods for several studies, including the Mayak Worker Cohort and the U.S. Atomic Veterans Study, is discussed.

epidemiological analysis↗

Imagine Moving Off the Planet

Moving off the planet will be a defining moment of this century as landing on the Moon was in the last. For that to happen for humans to go where humans cannot go-- simulation is the sole solution. NASA supports simulation for life-cycle activities: design, analysis, test, checkout, operations, review and training. We contemplate time spans of a century and more, teams dispersed to different planets and the need for systems that endure or adapt as missions, teams and technology change. Without imagination such goals are impossible. But with imagination we can go outside our present perception of reality to think about and take action on what has been, is and, especially, what might be. Consciously maturing an imagined, possibly workable, idea through framing it to optimization to design, and building the product provides us with a new approach to innovation and simulation fidelity. We address options, analyze, test and make improvements in how we think and work. Each step includes increasingly exact information about costs, schedule, who will be needed, where, when and how. NASA i integrating such thinking into its Exploration Product Realization Hierarchy for simulation and analysis, test and verification, and stimulus response goals. Technically NASA follows a timeline of studies, analysis, definition, design, development and operations with concurrent documentation. We have matched this Product Realization Hierarchy with a continuum from image to realization that incorporates commitment, current and needed research and communication to ensure superior and creative problem solving as well as advances in simulation. One result is a new approach to collaborative systems. Another is a distributed observer network prototyped using game engine technology bringing advanced 3-D simulation of a simulation to the desktop enabling people to develop shared consensus of its meaning. Much of the value of simulation comes from developing in people their ability to make good decisions and reflexes supporting impressive achievement. Synthesizing imagination systematically into our work - and thus our success - is a challenge. NASA engineers have inventive minds, and the task is determining how best to enable them to devise the simulation and other innovations that will make a story so clear and so intellectually sound that people can carry out the mission for 50-100 years. This demands skills and knowledge traditionally under-respected and under-represented in technology organizations. But we are beginning to see that the process encourages efficiency and enables us to attain more effective results. We have to elicit imaginative, intelligent and effective ways to make better use than ever of the minds we have and will have available. We have to accept the challenge to accomplish tasks among dispersed interdisciplinary teams who must overcome changing priorities and technology, time and distance in order to maximize interactivity and innovation as never before. Attention to the process of innovation is a practical means to increase the efficiency of our intelligence. We have an obligation to reexamine and improve the process by which we approach and exercise innovation as we accept the charge to move off the planet.

Elfrey, Priscilla R.↗

Performance assessment modeling of a generic SNF/HLW repository in salt with coupled thermal-hydrologic effects - 15423

This paper describes advances in performance assessment modeling of deep geologic repositories facilitated by a massively parallel, high-performance computing (HPC) environment. Our new Generic Disposal System Analysis (GDSA) Framework utilizes the massively parallel PFLOTRAN multi-physics code to simulate repository performance in the presence of coupled thermal-hydrologic-chemical processes, linked to DAKOTA, an HPC uncertainty sampling and propagation code that provides nested parallelism for multi-realization performance assessment and sensitivity analysis. This enhanced performance assessment (PA) modeling capability is demonstrated with deterministic and probabilistic simulations of a generic repository for SNF and HLW in bedded salt host rock, by comparing repository performance between a case with heat-generating waste ('thermal' case) and a case without heat generation ('isothermal' case). The simulation results provide preliminary insights into the effect of multi-physics processes and thermal-hydrologic coupling on the long-term behavior of a reference-case salt repository. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

An empirical analysis of the distribution of the duration of overshoots in a stationary gaussian stochastic process

This analysis utilizes computer simulation and statistical estimation. Realizations of stationary gaussian stochastic processes with selected autocorrelation functions are computer simulated. Analysis of the simulated data revealed that the mean and the variance of a process were functionally dependent upon the autocorrelation parameter and crossing level. Using predicted values for the mean and standard deviation, by the method of moments, the distribution parameters was estimated. Thus, given the autocorrelation parameter, crossing level, mean, and standard deviation of a process, the probability of exceeding the crossing level for a particular length of time was calculated.

Parrish, R. S.↗

Validation of the DESI DR2 Ly$α$ forest full-shape analysis

We present the validation of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) Lyman-$α$ (Ly$α$) forest full-shape analysis. This analysis combines three-dimensional Ly$α$ forest auto-correlations and cross-correlations with quasars to extract information from both the baryon acoustic oscillation (BAO) feature and the broadband clustering signal, with primary emphasis on the Alcock-Paczynski (AP) measurement. Compared to the DESI DR1 analysis, the DR2 validation uses substantially larger and more realistic mock datasets, including CoLoRe 2LPT and AbacusSummit Ly$α$ forest simulations. The modeling framework is also improved through analytic marginalization over small scales ($<10$$h^{-1}$Mpc) and the impact of ultraviolet background fluctuations. The validation program was completed prior to unblinding and defines quantitative requirements for the cosmological parameters of interest, which are evaluated using hundreds of mock realizations. We further test the analysis through independent fits to the auto- and cross-correlations, multiple catalog splits, and a broad suite of analysis and modeling variations applied to both mocks and blinded observational data. We find that the BAO and AP parameters satisfy all validation requirements and remain stable across all tests. In contrast, mock studies reveal a significant bias in the inferred growth-rate parameter $fσ_8$, leading us to exclude this measurement from the final analysis. The consistency across mocks, data splits, and robustness tests demonstrates that the DR2 Ly$α$ full-shape analysis provides a reliable and substantially improved broadband AP measurement over previous Ly$α$ forest studies.

Herbold, M. [Chicago U., KICP; Ohio State U.] (ORC↗

Large eddy simulation of a reacting spray flame with multiple realizations under compression ignition engine conditions

An n-dodecane spray flame (Spray A from Engine Combustion Network) was simulated using a detailed combustion model along with a dynamic structure LES model to evaluate its performance at engine-relevant conditions and understand the transient behavior of this turbulent flame. The liquid spray was treated with a traditional Lagrangian method and the gas-phase reaction was modeled using a detailed combustion model. A 103-species skeletal mechanism was used for the n-dodecane chemical kinetic model. Significantly different flame structures and ignition processes are observed for the LES compared to those of RANS predictions. The LES data suggests that the first ignition initiates in lean mixture and propagates to rich mixture, and the main ignition happens in rich mixture, preferable less than 0.14 in mixture fraction space. LES was observed to have multiple ignition spots in the mixing layer simultaneously while the main ignition initiates in a clearly asymmetric fashion. The temporal flame development also indicates the flame stabilization mechanism is auto-ignition controlled and modulated by flame propagation. Soot predictions by LES present much better agreement with experiments compared to RANS both qualitatively and quantitatively. Multiple realizations for LES were performed to understand the realization to realization variation and to establish best practices for ensemble-averaging diesel spray flames. The relevance index analysis suggests that an average of 2 and 5 realizations can reach 99\% of similarity to the target average of 16 realizations on the temperature and mixture fraction fields, respectively. However, more realizations are necessary for OH and soot mass fraction due to their high fluctuations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

FRET Tutorial

In this tutorial, we present the FRET tool for writing, understanding, formalizing and analyzing requirements. In practice, requirements are typically written in natural language, which is ambiguous and consequently not amenable to formal analysis. Since formal, mathematical notations are unintuitive, requirements in FRET are entered in a restricted, natural language, called FRETish with precise unambiguous meaning. This tutorial explains how requirements can be captured in FRETish and subsequently formalized in temporal logics and in the synchronous data flow language Lustre. We show, through multiple examples, how FRET assists users in understanding FRETish requirements and clarifying subtle semantic issues through English and diagrammatic explanations as well as interactive simulation. FInally, this tutorial describes how FRET can be used to perform realizability checking for identifying conflicting requirements and the connection of FRET with (1) the CoCoSim automated analysis tool for the verification of Simulink and Stateflow models, and (2) the Copilot runtime monitoring tool for the analysis of C programs.

FRET↗

A geostatistics-informed hierarchical sensitivity analysis method for complex groundwater flow and transport modeling

Sensitivity analysis is an important tool for development and improvement of mathematical models, especially for complex systems with a high dimension of spatially correlated parameters. Variance-based global sensitivity analysis has gained popularity because it can quantify the relative contribution of uncertainty from different sources. However, its computational cost increases dramatically with the complexity of the considered model and the dimension of model parameters. As such, in this study, we developed a new sensitivity analysis method that integrates the concept of variance-based method with a hierarchical uncertainty quantification framework. Different uncertain inputs are grouped and organized into a multilayer framework based on their characteristics and dependency relationships to reduce the dimensionality of the sensitivity analysis. A set of new sensitivity indices are defined for the grouped inputs using the variance decomposition method. Using this methodology, we identified the most important uncertainty source for a dynamic groundwater flow and solute transport model at the Department of Energy (DOE) Hanford site. The results indicate that boundary conditions and permeability field contribute the most uncertainty to the simulated head field and tracer plume, respectively. The relative contribution from each source varied spatially and temporally. By using a geostatistical approach to reduce the number of realizations needed for the sensitivity analysis, the computational cost of implementing the developed method was reduced to a practically manageable level. The developed sensitivity analysis method is generally applicable to a wide range of hydrologic and environmental problems that deal with high-dimensional spatially distributed input variables.

58 GEOSCIENCES↗