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All sources NASA NTRS DOE OSTI

NASA NTRS2023

Thermomechanical Real-Time Hybrid Simulation: Conceptual Framework and Control Requirements

Real-time hybrid simulation (RTHS) is an enabling technology that has transformed engineering experimentation and helped researchers expand modeling capabilities. However, breakthroughs are necessary to expand the range of hybrid simulation methods and, thus, enable experiments with loading conditions representing multiple hazards. This paper discusses the development of a new thermomechanical RTHS framework and a systematic approach to determining RTHS control requirements. First, the framework is established using a representative finite element model of a layered structural system subjected to thermal loading. A complete two-layer system model serves as the reference system, and it is then partitioned into a numerical layer and an experimental layer that share interface conditions. Next, a thermal actuator is introduced to impose dynamic thermal loading on the experimental subsystem, serving as a transfer system. Finally, control and performance metrics are defined to evaluate the realization of interface boundary conditions and map this to the RTHS execution. Through an illustrative example considering the influence of temperature on a lunar habitat, we demonstrate how to establish controller requirements for RTHS and demonstrate that this approach can be used to conduct RTHS on structures with thermomechanical loading.

Herta Montoya↗

DOE OSTI2016

Influence of nano-dispersive modified additive on cement activity

In the work the influence of single-walled carbon nanotubes (SWCNT) on the cement activity and the processes of structure formation of the hardened cement paste in different periods of hydration are studied. The changes in the kinetic curves of the sample strength growth modified with SWCNT in amount of 0.01 and 0.0005 % are stipulated by the results of differential scanning colorimetry, scanning electronic and ionic microscopy, X-ray-phase analysis. It was found that the nano-modified additive may increase in the axis compressive strength of the system by 1.4–6.3 fold relatively to the reference samples and may reach 179.6 MPa. It may intensify the hydration process of calcium silicates as well as influence on the matrix of hardened cement paste. The studies are conducted on the structural changes in the hardened cement paste, the time periods of increase and decrease of the compressive strength of the samples, the amount of the calcium hydroxide and tobermorite-like gel as well as the degree of hydration C{sub 3}S and β-C{sub 2}S.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

On the structural origin of the single-ion magnetic anisotropy in LuFeO 3

The electronic structure for the conduction bands of both hexagonal and orthorhombic LuFeO 3 thin films have been measured using x-ray absorption spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectral features and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridizations. While the oxidation states have not changed, the spectra are sensitive to the changes in the local environments of the Fe 3+ and Lu 3+ sites in the hexagonal and orthorhombic structures. Using the crystal-field splitting and the hybridizations that are extracted from the measured electronic structures and the structural distortion information, we derived the occupancies of the spin minority states in Fe 3+ , which are non-zero and uneven. The single ion anisotropy on Fe 3+ sites is found to originate from these uneven occupancies of the spin minority states via spin–orbit coupling in LuFeO 3 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Graphene-modified nanostructured vanadium pentoxide hybrids with extraordinary electrochemical performance for Li-ion batteries

The long-standing issues of low intrinsic electronic conductivity, slow lithium-ion diffusion and irreversible phase transitions on deep discharge prevent the high specific capacity/energy (443 mAh g -1 and 1,550 Wh kg -1 ) vanadium pentoxide from being used as the cathode material in practical battery applications. Here we develop a method to incorporate graphene sheets into vanadium pentoxide nanoribbons via the sol–gel process. The resulting graphene-modified nanostructured vanadium pentoxide hybrids contain only 2 wt. % graphene, yet exhibits extraordinary electrochemical performance: a specific capacity of 438 mAh g -1 , approaching the theoretical value (443 mAh g -1 ), a long cyclability and significantly enhanced rate capability. Such performance is the result of the combined effects of the graphene on structural stability, electronic conduction, vanadium redox reaction and lithium-ion diffusion supported by various experimental studies. Finally, this method provides a new avenue to create nanostructured metal oxide/graphene materials for advanced battery applications.

25 ENERGY STORAGE↗

DOE OSTI2015

Thermal conductivity of Bi{sub 2}Te{sub 3} tilted nanowires, a molecular dynamics study

Evidence for an excellent compromise between structural stability and low thermal conductivity has been achieved with tilted Bi{sub 2}Te{sub 3} nanowires. The latter ones were recently fabricated and there is a need in modeling and characterization. The structural stability and the thermal conductivity of Bi{sub 2}Te{sub 3} nanowires along the tilted [015]* direction and along the [010] direction have been explored. For the two configurations of nanowires, the effect of the length and the cross section on the thermal conductivity is discussed. The thermal conductivity of infinite size tilted nanowire is 0.34 W/m K, significantly reduced compared to nanowire along the [010] direction (0.59 W/m K). This reveals that in Bi{sub 2}Te{sub 3} nanowires the structural anisotropy can be as important as size effects to reduce the thermal conductivity. The main reason is the reduction of the phonon mean free path which is found to be 1.7 nm in the tilted nanowires, compared to 5.3 nm for the nanowires along the [010] direction. The fact that tilted Bi{sub 2}Te{sub 3} nanowire is mechanically stable and it has extremely low thermal conductivity suggests these nanowires as a promising material for future thermoelectric generation application.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Artificial Neural Network Models for Octane Number and Octane Sensitivity: A Quantitative Structure Property Relationship Approach to Fuel Design

Octane sensitivity (OS), defined as the research octane number (RON) minus the motor octane number (MON) of a fuel, has gained interest among researchers due to its effect on knocking conditions in internal combustion engines. Compounds with a high OS enable higher efficiencies, especially within advanced compression ignition engines. RON/MON must be experimentally tested to determine OS, requiring time, funding, and specialized equipment. Thus, predictive models trained with existing experimental data and molecular descriptors (via quantitative structure-property relationships (QSPRs)) would allow for the preemptive screening of compounds prior to performing these experiments. Here, the present work proposes two methods for predicting the OS of a given compound: using artificial neural networks (ANNs) trained with QSPR descriptors to predict RON and MON individually to compute OS (derived octane sensitivity (dOS)), and using ANNs trained with QSPR descriptors to directly predict OS. Twenty-five ANNs were trained for both RON and MON and their test sets achieved an overall 6.4% and 5.2% error, respectively. Twenty-five additional ANNs were trained for both dOS and OS; dOS calculations were found to have 15.3% error while predicting OS directly resulted in 9.9% error. A chemical analysis of the top QSPR descriptors for RON/MON and OS is conducted, highlighting desirable structural features for high-performing molecules and offering insight into the inner mathematical workings of ANNs; such chemical interpretations study the interconnections between structural features, descriptors, and fuel performance showing that connectivity, structural diversity, and atomic hybridization consistently drive fuel performance.

09 BIOMASS FUELS↗

DOE OSTI2018

Ionic Tuning of Cobaltites at the Nanoscale

Control of materials through custom design of ionic distributions is one of the most promising approaches for developing future technologies ranging from spintronic logic and memory devices to energy storage. Perovskites have shown particular promise for ionic-devices due to their high ion mobility and sensitivity to chemical stoichiometry. In this work, we demonstrate control of ion distributions in (La,Sr)CoO3. Commensurate with control of the oxygen stoichiometry, the Co valence and saturation magnetization show a smooth continuous variation. In contrast, magnetoresistance measurements show a sharp, step-wise transition in the magnetic anisotropy and resistivity over the same range of oxygen stoichiometry. These results suggest significant phase separation, with conductive magnetic regions and oxygen-deficient, insulating, non-magnetic regions, forming percolated networks. Indeed, X-ray diffraction identifies oxygen vacancy ordering, including the emergence of Brownmillerite ordering. The unusual appearance of the Brownmillerite phase under ambient temperature is further confirmed by high resolution scanning transmission electron microscopy. This work demonstrates room-temperature ionic control of magnetism, electrical conductivity and crystalline structure, in a 40 nm film, presenting new opportunities for ionic devices that leverage multiple material properties.

thin films, magnetism, xmcd, pnr, STEM, defects↗

DOE OSTI2025

Raman Laser-Induced Structural Modification in CVD-Grown Monolayer MoS 2 for Multi-Purposed Nanofabrication

Molybdenum disulfide (MoS 2 ) has been extensively explored to be utilized as an electronic material in a variety of device applications. In particular, the tunability of MoS 2 enhances its electrical properties making it an intriguing candidate for field-effect transistors (FETs), while also extending beyond electrical properties to structural phase engineering. Laser-induced modifications, particularly with Raman lasers, offer a straightforward method to modulate materials via thermal processes with precise patterning control and energy-level flexibility. However, most studies on the modification of MoS 2 have focused on multilayered structures or have been conducted under low-power laser conditions, leaving the feasibility of structural modifications in monolayer MoS 2 elusive. In this study, we fundamentally elucidated the effects of high-power Raman laser irradiation on the surface of chemical vapor deposition (CVD)-grown monolayer MoS 2 under ambient conditions and uncovered the underlying mechanisms of laser-induced modifications by applying intense photon energy with highly interactive reactions. Our results revealed both etching and deposition phenomena in two discernible regions, and it can be demonstrated by intensity regimes based on the spatial distribution of laser irradiance within the laser-irradiated spot. Furthermore, phase transition was found to be inhibited due to the promoted oxidation and the deposition of hydrogenated amorphous carbon (a-C:H), and p-type doping was observed, likely occurring in the region beneath the a-C:H deposition as substitutional doping on the 2H phase of MoS 2 . To compare the thermal effects, MoS 2 modifications were further analyzed using simplified heat transfer estimations. In conclusion, these findings deepen our understanding of how Raman laser irradiation modifies MoS 2 under ambient conditions, providing guidelines for optimizing its modification processes.

36 MATERIALS SCIENCE↗

DOE OSTI2014

A new metal-organic hybrid material with intrinsic resistance-based bistability: monitoring in situ room temperature switching behavior

Two new silver containing materials with TCNQ derivatives were prepared by electrocrystallization. Synchrotron radiation diffraction studies were conducted to determine the structures of the new phases which exhibit unprecedented high room temperature conductivity. The I–V characteristics reveal a room-temperature switching behaviour and memory effect based on intrinsic negative differential resistance (NDR). EPR spectroscopic measurements performed under an applied electric field indicate a g-tensor shift that is correlated to the amplitude of current.

Zhang, Zhongyue↗

NASA NTRS1972

Test report: Shock test of the electron/proton spectrometer structural test unit

A shock test of the electron-proton spectrometer structural test unit was conducted. The purpose of the shock test was to verify the structural integrity of the electron-spectrometer design and to obtain data on the shock response of the electronics and electronic housing. The test equipment is described and typical shock response data are provided.

Vincent, D. L.↗

NASA NTRS1986

Structural qualification of large spacecraft

Over the past twenty-five (25) years of the space program, the major challenge in the structural qualification of the primary structure has shifted from conducting a test that simulated the environment to accurately predicting the structural member loads in flight. Once the flight loads are avaliable, a number of different test methods are used to qualify the structure by subjecting it to the proper loads. The qualification challenge for future large spacecraft will be to adequately predict its dynamic characteristic in space to assure that it can be controlled to meet the mission objectives. A new test concept that may allow acquisition of modal data by ground tests for verification of mathematical models of large flexible space structures which can't be ground tested by conventional methods is discussed.

Wada, Ben K.↗

DOE OSTI2023

Ground and excited electronic structures of electride and alkalide units: The cases of Metal-Tren, -Azacryptand, and -TriPip222 complexes

A systematic electronic structure analysis was conducted for M(L) n molecular electrides and their corresponding alkalide units M(L) n @M' (M/M' = Na, K; L = Tren, Azacryptand, TriPip222; n = 1, 2). All complexes belong to the “superalkali” category due to their low ionization potentials. The saturated molecular electrides display M+(L) n - form with a greatly diffuse quasispherical electron cloud. They were identified as “superatoms” considering the contours of populating atomic-type molecular orbitals. The observed superatomic Aufbau order of M(Tren) 2 is 1S, 1P, 1D, 1F, 2S, 2P, and 1G and it is consistent with those of M(Azacryptand) and M(TriPip222) up to the analyzed 1F level. Their excitation energies decrease gradually moving from M(Tren) 2 to M(Azacryptand) and to M(TriPip222). The studied alkalide complexes carry [M(L) n ] + @M' - ionic structure and their dissociation energies vary in the sequence of K(L) n @Na > Na(L) n @Na > K(L) n @K > Na(L) n @K. Similar to molecular electrides, the anions of alkalide units occupy electrons in diffuse Rydberg-like orbitals. In this work, excited states of [M(L) n @M'] 0/+/- and their trends are also analyzed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Lithium insertion properties of Li{sub x}TiNb{sub 2}O{sub 7} investigated by neutron diffraction and first-principles modelling

TiNb{sub 2}O{sub 7}, a good candidate as anode in lithium batteries, was treated with n-butyllithium to synthesize Li{sub x}TiNb{sub 2}O{sub 7} phases similar to those formed during electrochemical reactions. The Li{sub 2.67}TiNb{sub 2}O{sub 7} and Li{sub 3.33}TiNb{sub 2}O{sub 7} compounds, monoclinic C2/m, were studied by time-of-flight powder neutron diffraction. Their crystal structures, containing 3×3 blocks of (Ti,Nb)O{sub 6} octahedra, were Rietveld refined including Li positions. The Li atoms are distributed in similar amounts over sites with (Li–O) Coordination Numbers 5 and 4, although CN=5 should be preferred for having lower energy. Quantum-mechanical calculations were also performed, determining the average charge–discharge voltages to be 1.415 and 1.571 V for Li{sub 3.33}TiNb{sub 2}O{sub 7} and Li{sub 2.67}TiNb{sub 2}O{sub 7}, respectively, in good agreement with experimental results. An analysis of the theoretical charge distribution shows that, on lithiation, the chemical reduction of Ti and Nb atoms concentrates in the more condensed peripheral octahedra of the 3×3 block. This corresponds to electrons moving into a partly spin-polarized small band which gives rise to semi-metallic conductivity. - Graphical abstract: Structure of monoclinic Li{sub 3.33}TiNb{sub 2}O{sub 7}, and corresponding electron density of states. - Highlights: • Lithium was chemically inserted into the battery anode material TiNb{sub 2}O{sub 7}. • Li atoms are distributed over four- and fivefold oxygen coordinated sites. • On lithiation Nb and Ti atoms are reduced according to a peculiar structural pattern. • Theoretically predicted charge–discharge voltages fit experiments very well.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

EPRI Demonstration of an Autonomous Site Characterization Vehicle - 20523

A substantial effort is applied in performing radiological characterization of structures and land areas during decommissioning of a nuclear facility. This includes multiple surveys of land areas and large structures to support eventual site release under the Multi Agency Survey and Site Investigation Manual (MARSSIM, Reference 1). These surveys are typically performed using manually delivered systems, which is time consuming and labor intensive. Radiological surveys intentionally follow a prescribed protocol with respect to areas covered, scan speeds, responses to elevated readings, required detector offsets, the need for repeat measurements, etc. Based on these attributes, combined with the repetitive effort of performing surveys over large areas, automation of radiological characterization techniques has a high potential to be successful and promises substantial benefit. EPRI has performed a project that resulted in the development and demonstration of an autonomous site characterization system. This EPRI project focused on building surfaces and the surfaces of large land areas as these configurations lend themselves more readily to automated survey. The project included: - Identification of the requirements for an autonomous site characterization system; - A survey of existing control systems that use automation to conduct characterization of structures and land areas. - As no fully adequate systems were identified, a complete system was developed that utilized commercially available detection and analysis systems and a self driving vehicle owned by EPRI. The system was demonstrated at the Kewaunee nuclear power plant site in the fall of 2019. The demonstration included: - Autonomous surveys of floor areas inside the Auxiliary Building at Kewaunee after manually controlled mapping of the survey areas. - For land areas, the vehicle autonomously surveyed areas using travel paths had been preprogrammed onto an internet available map of area. In this case, GPS coordinates from the preprogramming were used for navigation by the vehicles guidance system. This paper summarizes the characterization system development and system demonstration which will also be published in an EPRI report in the first half of 2020. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2018

Residence time distribution in a structured packing unit for monitoring aerosol emissions

Solvent absorption in a structured packed column has been demonstrated as a viable option for post-combustion carbon capture. Amine emissions in the form of aerosol particles pose a major challenge that severely impacts the separation efficiency of the packed column. The aerosol particles quickly achieve the motion of the gas flow. In this context, residence time distribution (RTD) of the gaseous phase will provide insights for managing aerosol particles, thereby controlling amine loss in the packed column. Computational fluid dynamics (CFD) modeling of such columns is a multiscale problem because of a wide range of disparity in length scales. Accordingly, three-dimensional CFD simulations in the representative elementary unit of a structured packing are conducted using OpenFOAM. The RTD is analyzed in terms of residence time distribution function, mean residence time, and variance. Effects of the diffusivity and flow rates on RTD are extensively studied, and the dispersion coefficient is calculated using a one-dimensional axial dispersion model. Furthermore, RTDs computed in a smaller domain are extrapolated to a larger domain using a convolution integral. The computed and corresponding CFD models derived from the convolution integral match well at different flow rates and domain sizes. A comparison of RTD among different packing designs also is presented at a fixed number of repeating units and different flow rates.

structured packings, residence time distribution↗

DOE OSTI2017

Pressure Induced Phase Transformations in Ceramics

The study of materials with unusual properties offers new insight into structure-property relations as well as promise for the design of novel composites. In this spirit, the PIs seek to (1) understand fundamental mechanical phenomena in ceramics that exhibit pressure-induced phase transitions, negative coefficient of thermal expansion (CTE), and negative compressibility, and (2) explore the effect of these phenomena on the mechanical behavior of composites designed with such ceramics. The broad and long-term goal is to learn how to utilize these unusual behaviors to obtain desired mechanical responses. While the results are expected to be widely applicable to many ceramics, most of the present focus is on silicates, as they exhibit remarkable diversity in structure and properties. Eucryptite, a lithium aluminum silicate (LiAlSiO 4 ), is specifically targeted because it exhibits a pressure-induced phase transition at a sufficiently low pressure to be accessible during conventional materials processing. Thus, composites with eucryptite may be designed to exhibit a novel type of transformation toughening. The PIs have performed a combination of activities that encompass synthesis and processing to control structures, atomistic modeling to predict and understand structures, and characterization to study mechanical behavior. Several materials behavior discoveries were made. It was discovered that small amounts of Zn (as small as 0.1 percent by mol) reverse the sign of the coefficient of thermal expansion of beta-eucryptite from negative to slightly positive. The presence of Zn also significantly mitigates microcracking that occurs during thermal cycling of eucryptite. It is hypothesized that Zn disrupts the Li ordering in beta-eucryptite, thereby altering the thermal expansion behavior. A nanoindentation technique developed to characterize incipient plasticity was applied to examine the initial stages of the pressure induced phase transformation from beta to epsilon-eucryptite and show that the transformation nucleation is related to the motion of the tetrahedral units making up the structure. It was revealed that the conduction of Li ions through the structure is also dictated by the tetrahedral unit arrangement and how their positions change with temperature. The critical pressure to obtain the high pressure phase of eucryptite was shown to depend on the grain size. The structure of the high pressure phase was determined with a combination of atomistic modeling and in situ x-ray diffraction experiments.

36 MATERIALS SCIENCE↗

NASA NTRS1982

Shape control of large space structures

A survey has been conducted to determine the types of control strategies which have been proposed for controlling the vibrations in large space structures. From this survey several representative control strategies were singled out for detailed analyses. The application of these strategies to a simplified model of a large space structure has been simulated. These simulations demonstrate the implementation of the control algorithms and provide a basis for a preliminary comparison of their suitability for large space structure control.

Hagan, M. T.↗

DOE OSTI2026

Transition from Vehicular to Structural Ionic Transport in Electrified Alkali Aqueous Solutions

A molecular understanding of the solvation and dynamics of ions under static electric fields is crucial for modelling a wide range of natural and technological processes. Yet, traditional simulation methods suffer from a trade-off that has to be made between accuracy and statistical convergence. To bridge this gap, herein we extend our recently introduced Perturbed Neural Network Potential Molecular Dynamics (PNNP MD) approach to investigate the solvation structures and ionic transport mechanisms of electrified alkali cationic solutions. We obtain ionic conductivities for Li+, Na+ and Cs+ from the field dependence of the ionic current density in good agreement with experiment. Surprisingly, the migration mechanism is found to be strikingly different for the three ions despite their similar ionic conductivities. While Li+ conducts predominantly through vehicular migration of a stable 4-fold coordinated ion at all field strengths, Cs+ conducts strictly through a structural diffusion mechanism, where 9-12 transient first shell water coordination bonds are broken and renewed. Notably, aqueous Na+ emerges as a “Goldilocks” ion: its ion-water interactions are strong enough to maintain distinct 5-6 fold coordination shells at zero field (unlike Cs+) yet labile enough to be strongly perturbed by electric fields (unlike Li+). As a consequence, we observe an electric field-induced transition from vehicular to structural ionic transport for Na+ that is accompanied by a marked increase in the ionic current density. Our results imply that the conductance mechanism of ions with moderate ion-solvent interactions can be effectively tuned by external electric fields.

Joll, Kit↗