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Results for “observation geometry”

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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Oxidation of 3D-printed SiC in air and steam environments

Here, the high-temperature oxidation of additively manufactured and chemically vapor infiltrated (3D-printed SiC) has been compared to chemical vapor deposited (CVD) SiC. 100-h isothermal exposures were conducted at 1425° and 1300°C at 1 atm under both dry air and steam environments. A SiC reaction tube was utilized to reduce silica volatility. After steam oxidation at 1425° and 1300°C, on the 3D-printed SiC surface, which was intrinsically rougher than the CVD surface, scales were 70%–90% thicker at the convex regions compared to concave/flat regions. In the convex regions, large cracks perpendicular to the oxidizing interface were observed. After dry air oxidation, scale thicknesses were comparable between 3D-printed SiC and CVD SiC, regardless of geometry. Finite element modeling, conducted to elucidate the relationship between SiC geometry and ß- to α-cristobalite transformation stress, determined cristobalite transformation tensile stresses to be on the order of 103 MPa during cool down, assuming a 6 vol% reduction. Compared to flat SiC substrates, tensile transformation stresses were elevated at concave regions and relaxed at convex regions. Combined with specimen mass gain (accounting for the rougher surface) of 3D-printed SiC being 15%–32% higher for 3D-printed SiC after 1300°C and 1425°C steam oxidation, the work presented concludes that the increased oxidation of 3D-printed SiC is primarily caused by tensile hoop stresses driven by oxidation volume expansion. Lastly, the efficacy of the 3D-printing method is demonstrated through the production of tristructural isotropic imbedded 3D-printed SiC fuel forms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A detection of the sea level fingerprint of Greenland Ice Sheet melt

Rapid melting of ice sheets and glaciers drives a unique geometry, or fingerprint, of sea level change. However, the detection of individual fingerprints has been challenging because of sparse observations at high latitudes and the difficulty of disentangling ocean dynamic variability from the signal. Here we predict the fingerprint of Greenland Ice Sheet (GrIS) melt using recent ice mass loss estimates from radar altimetry data and model reconstructions of nearby glaciers and compare this prediction to an independent, altimetry-derived sea surface height trend corrected for ocean dynamic variability in the region adjacent to the ice sheet. A statistically significant correlation between the two fields (P < 0.001) provides an unambiguous observational detection of the near-field sea level fingerprint of recent GrIS melting in our warming world.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Machine learning-based inversion for acoustic impedance with large synthetic training data: Workflow and data characterization

Where wells are sparse or training data are difficult to label with high-quality wireline-derived impedance logs, machine learning (ML)-based inversion of acoustic impedance typically depends on small training data sets, leading to biased prediction. We have advanced a novel workflow that applies large synthetic seismic training data to reduce facies-related bias. Using a geologically realistic model as the truth model, we randomly select sparse seed wells to perform sequential Gaussian simulation (SGS) for impedance models of the same geometry and simulate facies variability. We implement random forest regression on 30 features extracted from the synthetic volume. We observe that more seed wells tend to reduce facies-induced bias by sampling more types of facies, resulting in a better prediction. We then focus on the responses of SGS models to facies changes, the number of seed wells necessary for a useful synthetic model, and how much a synthetic model can help ML-based inversion. Here, we observe that the SGS synthetic training model outperforms well-direct training in general. For modeled clastic shore-zone systems in Miocene Gulf of Mexico, two or more seed wells are necessary for a significant reduction of root-mean-square error and outliners, and improvement of facies imaging. In a field-data test, we apply a similar workflow to quantitatively predict acoustic impedance, which is then converted to a sand-volume map at a high-frequency sequence (10–100 m), revealing detailed facies and sandstone patterns. Such results are valuable in many geologic and engineering applications, such as hydrocarbon and CO 2 reservoir prospecting, reserve estimation, simulation, etc.

3D seismic↗
DOE OSTI2021

Coordination Sphere of Lanthanide Aqua Ions Resolved with Ab Initio Molecular Dynamics and X-ray Absorption Spectroscopy

To resolve the fleeting structures of lanthanide Ln 3+ aqua ions in solution, we (i) performed the first ab initio molecular dynamics (AIMD) simulations of the entire series of Ln 3+ aqua ions in explicit water solvent using pseudopotentials and basis sets recently optimized for lanthanides and (ii) measured the symmetry of the hydrating waters about Ln 3+ ions (Nd 3+ , Dy 3+ , Er 3+ , Lu 3+ ) for the first time with extended X-ray absorption fine structure (EXAFS). EXAFS spectra were measured experimentally and generated from AIMD trajectories to directly compare simulation, which concurrently considers the electronic structure and the atomic dynamics in solution, with experiment. In this study, we performed a comprehensive evaluation of EXAFS multiple-scattering analysis (up to 6.5 Å) to measure Ln–O distances and angular correlations (i.e., symmetry) and elucidate the molecular geometry of the first hydration shell. This evaluation, in combination with symmetry-dependent L 3 - and L 1 -edge spectral analysis, shows that the AIMD simulations remarkably reproduces the experimental EXAFS data. The error in the predicted Ln–O distances is less than 0.07 Å for the later lanthanides, while we observed excellent agreement with predicted distances within experimental uncertainty for the early lanthanides. Our analysis revealed a dynamic, symmetrically disordered first coordination shell, which does not conform to a single molecular geometry for most lanthanides. This work sheds critical light on the highly elusive coordination geometry of the Ln 3+ aqua ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

On various mechanisms of shear wave generation from underground chemical explosions in hard rocks

Significant shear waves observed during underground explosions can make them look similar to natural earthquakes. In the near field, they can be caused by the source geometry and emplacement conditions, heterogeneous and anisotropic properties of the rock mass, relaxation of a non-uniform in situ stress around the source after the departure of the shock wave as well as by activation of nearby faults. Here, the stress relaxation mechanism is important at depth when the difference in main principal stresses becomes significant. Another mechanism of shear motion generation is due to explosive gas flow from the source cavity into the cracks initiated by the shock wave and joints connected to the cavity. Also, the shock wave from the explosion can cause weakening of the rock either due to permanent damage or shock-induced liquefaction at saturated joints. Numerical modelling of underground chemical explosions in hard rock at various confinement stresses has been conducted to compare various mechanisms of shear wave generation and their seismic characteristics with that of a simple fault rupture process observed during an earthquake.

58 GEOSCIENCES↗
DOE OSTI2023

Correlation of Broad Absorption Band with Small Singlet‐Triplet Energy Gap in Organic Photovoltaics

Abstract Organic photovoltaics (OPV) are one of the most effective ways to harvest renewable solar energy, with the power conversion efficiency (PCE) of the devices soaring above 19 % when processed with halogenated solvents. The superior photocurrent of OPV over other emerging photovoltaics offers more opportunities to further improve the efficiency. Tailoring the absorption band of photoactive materials is an effective way to further enhance OPV photocurrent. However, the field has mostly been focusing on improving the near‐infrared region photo‐response, with the absorption shoulders in short‐wavelength region (SWR) usually being neglected. Herein, by developing a series of non‐fullerene acceptors (NFAs) with varied side‐group conjugations, we observe an enhanced SWR absorption band with increased side‐group conjugation length. The underpinning factors of how molecular structures and geometries improve SWR absorption are clearly elucidated through theoretical modelling and crystallography. Moreover, a clear relationship between the enhanced SWR absorption and reduced singlet‐triplet energy gap is established, both of which are favorable for the OPV performance and can be tailored by rational structure design of NFAs. Finally, the rationally designed NFA, BO‐TTBr, affords a decent PCE of 18.5 % when processed with a non‐halogenated green solvent.

Chemistry↗
DOE OSTI2024

Effects of size, geometry, and testing temperature on additively manufactured Ti-6Al-4V titanium alloy

This article presents a comprehensive study concerning size and geometry effect on the ambient and high-temperature mechanical behavior of additively manufactured laser powder bed fusion Ti-6Al-4V alloy. Key mechanical property metrics are presented, including strain hardening rate, yield strength, and Young’s modulus as a function of thickness and testing temperature (ambient, 250 °C, and 450 °C). Here, the effect of specimen size on manufacturing-induced microstructural feature formation is demonstrated and discussed. A detailed analysis regarding Young’s modulus, yield strength, and strain hardening rate variation at elevated temperatures is also presented. Size effect and temperature-sensitive deformation mechanisms are linked to the underlying microstructural deformation mechanisms activated at respective temperatures. Counter-intuitively, this study determined that irrespective of the geometry, strain hardening rates increased as temperature increased. An in-depth microstructural examination is presented to explain the stated observation. The texture of Interrupted tensile test samples examined for ambient, 250 °C, and 450 °C post-yield was observed to be unchanged, indicating the strain hardening behavior was not texture dependent. Schmid factor analysis, coupled with experimental findings from previous work, was implemented to generate a hypothesis. This hypothesis suggests that the drop in critical resolved shear stress for basal and pyramidal slip systems, as temperature increases, paired with the high dislocation density of laser powder bed fusion Ti-6Al-4V, leads to dislocation entanglement and results in increased strain hardening at elevated temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetic charge propagation upon a 3D artificial spin-ice

Magnetic charge propagation in spin-ice materials has yielded a paradigm-shift in science, allowing the symmetry between electricity and magnetism to be studied. Recent work is now suggesting the spin-ice surface may be important in mediating the ordering and associated phase space in such materials. Here, we detail a 3D artificial spin-ice, which captures the exact geometry of bulk systems, allowing magnetic charge dynamics to be directly visualized upon the surface. Using magnetic force microscopy, we observe vastly different magnetic charge dynamics along two principal directions. For a field applied along the surface termination, local energetics force magnetic charges to nucleate over a larger characteristic distance, reducing their magnetic Coulomb interaction and producing uncorrelated monopoles. In contrast, applying a field transverse to the surface termination yields highly correlated monopole-antimonopole pairs. Detailed simulations suggest it is the difference in effective chemical potential as well as the energy landscape experienced during dynamics that yields the striking differences in monopole transport.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Deep learning approaches for instantaneous laser absorptance prediction in additive manufacturing

Abstract The quantification of absorbed light is essential for understanding laser-material interactions and melt pool dynamics in order to minimize defects in additively manufactured metal components. The geometry of a vapor depression formed during laser melting is closely related to laser energy absorption. This relationship has been observed by the state-of-the-art in situ high-speed synchrotron X-ray visualization and integrating sphere radiometry. These two techniques create a temporally resolved dataset consisting of vapor depression images and corresponding laser absorptance. In this work, we propose two different approaches to predict instantaneous laser absorptance. The end-to-end approach uses deep convolutional neural networks to learn implicit features of X-ray images automatically and predict the laser energy absorptance. The two-stage approach uses a semantic segmentation model to engineer geometric features and predict absorptance using classical regression models. While having distinct advantages, both approaches achieved a consistently low mean absolute error of less than 3.3%.

Chemistry↗
DOE OSTI2023

Structural complexity biases vegetation greenness measures

Vegetation ‘greenness’ characterized by spectral vegetation indices (VIs) is an integrative measure of vegetation leaf abundance, biochemical properties and pigment composition. Surprisingly, satellite observations reveal that several major VIs over the US Corn Belt are higher than those over the Amazon rainforest, despite the forests having a greater leaf area. This contradicting pattern underscores the pressing need to understand the underlying drivers and their impacts to prevent misinterpretations. Here we show that macroscale shadows cast by complex forest structures result in lower greenness measures compared with those cast by structurally simple and homogeneous crops. The shadow-induced contradictory pattern of VIs is inevitable because most Earth-observing satellites do not view the Earth in the solar direction and thus view shadows due to the sun–sensor geometry. The shadow impacts have important implications for the interpretation of VIs and solar-induced chlorophyll fluorescence as measures of global vegetation changes. For instance, a land-conversion process from forests to crops over the Amazon shows notable increases in VIs despite a decrease in leaf area. In conclusion, our findings highlight the importance of considering shadow impacts to accurately interpret remotely sensed VIs and solar-induced chlorophyll fluorescence for assessing global vegetation and its changes.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Motif magnetism and quantum many-body scars

In this work, we generally expect quantum systems to thermalize and satisfy the eigenstate thermalization hypothesis (ETH), which states that finite-energy-density eigenstates are thermal. However, some systems, such as many-body localized systems and systems with quantum many-body scars, violate ETH and have high-energy athermal eigenstates. In systems with scars, most eigenstates thermalize, but a few atypical scar states do not. Scar states can give rise to a periodic revival when time-evolving particular initial product states, which can be detected experimentally. Recently, a family of spin Hamiltonians was found with magnetically ordered three-colored eigenstates that are quantum many-body scars [Lee et al., Phys. Rev. B 101, 241111(R) (2020)]. These models can be realized in any lattice that can be tiled by triangles, such as the triangular or kagome lattices, and have been shown to have close connections to the physics of quantum spin liquids in the Heisenberg kagome antiferromagnet. In this paper, we introduce a generalized family of n-colored Hamiltonians with “spiral colored” eigenstates made from n-spin motifs such as polygons or polyhedra. We show how these models can be realized in many different lattice geometries and provide numerical evidence that they can exhibit quantum many-body scars with periodic revivals that can be observed by time-evolving simple product states. The simple structure of these Hamiltonians makes them promising candidates for future experimental studies of quantum many-body scars.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Response of 304L stainless steel and 6061-T651 aluminum alloy at -40 °C

The objective of this work is to extend the thermal-mechanical, elastic-plastic calibrations for 304L stainless steel [1] and and 6061-T651 aluminum alloy [2] to the regime between room temperature and -40 °C. The basis to extend the calibration consisted of new uniaxial tension tests conducted at -40 °C using the same plate material stocks, circular cylindrical specimen geometries and testing apparatus as previously, followed by attempts to fit power-law hardening functions to replicate the response observed in the specimens and then extend the yield, hardening constant, hardening exponent and rate constant functions in the calibrations to cover the new temperature regime.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cryo-GCMS Outgassing Screening: Thermal Filler Materials

A study was conducted to investigate the outgassing characteristics of four thermal filler materials. The purpose of this screening was to identify any outgassing products that might be considered reactive, specifically compounds that could result in corrosion in the systems where these materials are used. A range of compounds was observed in the sample headspaces, though most do not stand out as being known reactive species of concern. However, several halogenated compounds and sulfurous compounds- classes compounds known to facilitate corrosion reactions under certain conditions- were observed in low concentrations. The TFLEX 760 exhibited the highest total outgassing, while the GR130 had the lowest. Therm-a-Gap75 and the Si thermal grease exhibited very similar outgassing profiles. It is difficult to predict the extent to which any given compound observed in an analysis of this type might pose a risk in an actual system; factors such as temperature, system geometry, concentration, and gas conductance all play a role in the kinetics governing chemical reactions. It is recommended that the results of these analyses are shared with pertinent materials SMEs familiar with the system(s) in question to evaluate potential risks.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Observable signatures of initial state momentum anisotropies in nuclear collisions

In this work, we show that the correlation between the elliptic momentum anisotropy v 2 and the average transverse momentum [ p T ] at fixed multiplicity in small system nuclear collisions carries information on the origin of the observed momentum anisotropy. A calculation using a hybrid IP-Glasma+ music +UrQMD model that includes contributions from final state response to the initial geometry as well as initial state momentum anisotropies of the color glass condensate predicts a characteristic sign change of the correlator ρ ^ ( v 2 2 , [ p T ] ) as a function of charged particle multiplicity in p + Au and d + Au collisions at s = 200 GeV , and p + Pb collisions at s = 5.02 TeV . This sign change is absent in calculations without initial state momentum anisotropies. The model further predicts a qualitative difference between the centrality dependence of ρ ^ ( v 2 2 , [ p T ] ) in Au + Au collisions at s = 200 GeV and Pb + Pb collisions at s = 5.02 TeV , with only the latter showing a sign change in peripheral events. Predictions for O + O collisions at different collision energy show a similar behavior. Experimental observation of these distinct qualitative features of ρ ^ ( v 2 2 , [ p T ] ) in small and large systems would constitute strong evidence for the presence and importance of initial state momentum anisotropies predicted by the color glass condensate effective theory.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Surface fluctuating hydrodynamics methods for the drift-diffusion dynamics of particles and microstructures within curved fluid interfaces

Here we introduce fluctuating hydrodynamics approaches on surfaces for capturing the drift-diffusion dynamics of particles and microstructures immersed within curved fluid interfaces of spherical shape. We take into account the interfacial hydrodynamic coupling, traction coupling with the surrounding bulk fluid, and thermal fluctuations. For fluid-structure interactions, we introduce Immersed Boundary Methods (IBM) and related Stochastic Eulerian-Lagrangian Methods (SELM) for curved surfaces. We use these approaches to investigate the statistics of surface fluctuating hydrodynamics and microstructures. For velocity autocorrelations, we find characteristic power-law scalings $τ^{-1}, τ^{-2}$, and plateaus can emerge. This depends on the physical regime associated with the geometry, surface viscosity, and bulk viscosity. This differs from the characteristic $τ^{-3/2}$ scaling for bulk three dimensional fluids. We develop theory explaining these observed power-laws associated with time-scales for dissipation within the fluid interface and coupling to the surrounding fluid. We then use our introduced methods to investigate a few example systems and roles of hydrodynamic coupling and thermal fluctuations including for the kinetics of passive particles and active microswimmers in curved fluid interfaces.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Balancing performance of active magnetic regenerators: a comprehensive experimental study of aspect ratio, particle size, and operating conditions

Abstract Effective and, at the same time, efficient active magnetic regenerator (AMR) performance requires balanced geometry and operating conditions. Here the influence of regenerator shape, magnetocaloric material size, operating frequency, and utilization on the performance of gadolinium packed-particle bed AMRs is demonstrated experimentally. Various metrics are applied to assess effectiveness and efficiency. Observed temperature spans and cooling powers across a wide range of operating conditions are used to evaluate system performance and estimate exergetic cooling power and exergetic power quotient. A new metric combining exergetic cooling power and pump power provides an estimate of the maximum achievable second law efficiency. Five regenerator geometries with equal volumes and the aspect ratio from 1.0 to 3.8, and four different ranges of Gd spherical particles between 182 and 354 µ m, are investigated. Improvements in system performance are demonstrated by a boost in specific cooling power of gadolinium from 0.85 to 1.16 W g −1 and maximum temperature span from 8.9 to 15.1 K. The optimum exergetic cooling power is observed for 1.37 utilization and 3 Hz operating frequency, exergetic power quotient exhibits a maximum at the same utilization but at 2 Hz frequency, while the highest efficiency is recorded at 1 Hz and utilization of 0.5, demonstrating that multiple performance metrics must be balanced to achieve regenerator design meeting all performance targets.

42 ENGINEERING↗
DOE OSTI2025

Confinement-induced chirality in phase-separated achiral polymer solutions

Self-organization of polymers in constrained geometries largely determines their applications in high-strength materials, photonics, and electronics. Chiral organization under confinement is well established for polymers with intrinsic molecular chirality; however, it has not been observed for achiral polymers. Here, we report the emergence of chirality in spatially confined solutions of achiral rigid-rod polymers. We show that kinetically arrested phase separation of polymer solutions confined to narrow capillaries resulted in alternating segments of isotropic and chiral nematic phases. The chiral structure of the nematic segments originated from the interplay between the constrained geometry, surface anchoring, orientational wetting, and elastic anisotropy of rigid-rod polymers. The catenoidal shape of the chiral structure recapitulated the morphology of biological chiral structures. These findings provide insight into the organization of soft matter under spatial confinement and offer a straightforward way to form chiral structures from achiral synthetic polymers.

Science & Technology - Other Topics↗
DOE OSTI2025

Experimental characterization of a triply periodic minimal surface PCM-to-air thermal energy storage device

Here, the expansion of energy production has intensified research into thermal energy storage (TES) to manage variability and improve system efficiency. Heat exchanger design is critical to achieving high power densities in TES systems. This study presents a high-surface-area phase change material (PCM)-to-air heat exchanger fabricated via resin-based stereolithography with a novel gyroid-based geometry tailored for enhanced performance. Material properties of the commercial PCM and resin were characterized using analytical techniques. A controlled air loop was used to evaluate heat transfer and pressure drop at various flow rates and inlet temperatures. Results show a strong dependence on the inlet temperature difference (ΔT) relative to the PCM melting point. During charging at the highest flow rate, increasing the inlet air temperature from ΔT = 5 °C to 20 °C above the melting point increased the average heat transfer rate by 187%. During discharging, decreasing the inlet temperature by the same ΔT below the melting point led to a 232% increase. Notably, the high-surface-area design enabled nearly symmetric charging and discharging behavior, a novel result for PCM-based TES systems which are often restricted by natural convection and other effects. The overall heat transfer coefficient was calculated and compared to values from standard design correlations. The maximum thermal effectiveness reached 95% at ΔT = 20 °C and a moderate flow rate of 34 m 3 /h. Peak coefficients of performance (COP) of 7 during charging and 6.4 during discharging were observed at ΔT = 20 °C and a low flow rate of 20 m 3 /h. These results demonstrate the viability of additively manufactured geometries for advanced TES applications.

25 ENERGY STORAGE↗