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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
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Molecular dynamics studies of grain boundary mobility and anisotropy in BCC γ-uranium

Grain morphologies such as grain size and aspect ratio in uranium-based metallic fuels are important microstructural features that can impact various fuel performance properties such as fission-gas-induced swelling, thermal transport, high burnup structure formation, and radiation resistance. Accurate prediction of the fuel grain morphologies requires knowledge of critical grain growth parameters such as grain boundary (GB) mobility and anisotropy. In this work, molecular dynamics simulations were performed to study the GB mobility and its anisotropy in pure body-centered-cubic (BCC) γ uranium. Nine GBs with different combinations of misorientation angles (20°, 30°, 45°) and rotation axes (<100>, <110>, <111>), as well as an additional <111> 38.2° GB were studied using three interatomic potentials. Here, it is found that the GB mobility anisotropy has complex trends, depending on both rotation axis and misorientation. However, in general the <110> rotation axis has the fastest GB mobility at the same misorientation. The results of this work can be used as not only baselines for future studies of GB mobility in uranium-based alloys such as uranium-molybdenum (U-Mo) fuels, but also input for mesoscale modeling of grain growth in uranium-based alloys.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1987

Dynamic recrystallization and grain boundary migration in B2 FeAl

Transmission electron microscopy and optical microscopy were used to examine polycrystalline specimens of the B2-structured alloy FeAl strained under tension to fracture at elevated temperature. Strain-induced grain boundary migration was observed above 900 K and dynamic recrystallization was found at 1000 K and 1100 K. Little evidence of dynamic recovery was evident but some networks were formed at 1100 K.

Baker, I.↗
DOE OSTI2022

Modelling of edge plasma dynamics with active wall boundary conditions

A self-consistent 2D model is presented for transport in boundary plasma and plasma-facing material walls. Plasma dynamics in the domain is represented by a 2D collisional plasma fluid model in the edge-plasma code UEDGE, and transport of hydrogen and heat in the wall is represented by a system of reaction–diffusion equations in the 1D wall code FACE. To account for variation of parameters along the wall, in the coupled model multiple instances of the FACE code run in parallel. Here, the coupled model provides a tool for investigating a range of dynamic plasma–material interactions phenomena in 2D. For demonstration of its capability, one application of particular interest is the role of active wall in tokamak strike point sweeping proposed for mitigation of divertor heat loads. In the present study, the coupled calculations are applied to investigation of the impact of heat and hydrogen transport in the material wall on the divertor plasma and target heat load during sweeping of the target strike point for parameters of a high-power tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

A molecular dynamics survey of grain boundary energy in uranium dioxide and cerium dioxide

Uranium dioxide (UO 2 ) is the primary fuel material that is used in current nuclear reactors. As one of the most fundamental material parameters, grain boundary (GB) energy strongly influences many fuel properties, and the influences depend on the characters and properties of individual GBs. Using molecular dynamics simulations, a high throughput survey of GB energy in UO 2 was carried out for the purpose of elucidating the roles of GB geometry such as misorientation and inclination, as well as the bonding nature of UO 2 , in affecting GB energy. GB energies in CeO 2 were calculated as well for comparison with UO2toinvestigate the generality of GB energy anisotropy in fluorite phase oxides. The results show significant GB energy anisotropy in both UO 2 and CeO 2 that is associated with the cubic symmetry of the fluorite structure. More interestingly, the GB anisotropy is found to be dependent not only on the crystal structure but also the ionic bonding. As such, the GB energy anisotropy in fluorite oxides has significant differences compared with that in fcc metals. We report that the data obtained and the increased knowledge on GB anisotropy will facilitate GB engineering for nuclear fuels with improved properties

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Molecular dynamics study of grain boundaries as defect sinks under irradiation in LiAlO 2 and LiAl 5 O 8

Lithium aluminate ceramics, LiAlO 2 and LiAl 5 O 8 , show promise in nuclear environments due to their excellent radiation tolerance. Molecular dynamics simulations investigate grain boundaries (GB) and their role in defect evolution. Results reveal that GBs act as efficient defect sinks, with Li and Al atoms exhibiting distinct behaviors during displacement cascades. Tritium migration in LiAlO 2 is also studied, showing rapid diffusion and stable configurations with oxygen, corroborated by ab initio simulations from the literature. The calculated tritium diffusion coefficient of 1.33 × 10 - ¹⁴ m²/s aligns with the literature, validating the model. LiAl 5 O 8 demonstrates superior defect healing compared to LiAlO 2 , attributed to enhanced atomic transfer between grains and GBs. These findings reveal key insights into defect dynamics, providing essential insights for their application in tritium-producing burnable absorber rods (TPBARs).

36 MATERIALS SCIENCE↗
NASA NTRS1990

Dynamic substructuring by the boundary flexibility vector method of component mode synthesis

Component mode synthesis (CMS) is a method of dynamic analysis, for structures having a large number of degrees of freedom (DOF). These structures often required lengthy computer CPU time and large computer memory resources, if solved directly by the finite-element method (FEM). In CMS, the structure is divided into independent components in which the DOF are defined by a set of generalized coordinates defined by displacement shapes. The number of the generalized coordinates are much less than the original number of physical DOF, in the component. The displacement shapes are used to transform the component property matrices and any applied external loads, to a reduced system of coordinates. Reduced system property matrices are assembled, and any type of dynamic analysis is carried out in the reduced coordinate system. Any obtained results are back transformed to the original component coordinate systems. In all conventional methods of CMS, the mode shapes used for components are dynamic mode shapes, supplemented by static deflected shapes. Historically, all the dynamic mode shapes used in conventional CMS are the natural modes (eigenvectors) of components. A new method of CMS, namely the boundary flexibility vector method of CMS, is presented. The method provides for the incorporation of a set of static Ritz vectors, referred to as boundary flexibility vectors, as a replacement and/or supplement to conventional eigenvectors, as displacement shapes for components. The generation of these vectors does not require the solution of a costly eigenvalue problem, as in the case of natural modes in conventional CMS, and hence a substantial saving in CPU time can be achieved. The boundary flexibility vectors are generated from flexibility (or stiffness) properties of components. The formulation presented is for both free and fixed-interface components, and for both the free and forced vibration problems. Free and forced vibration numerical examples are presented to verify the accuracy of the method and the saving in CPU time. Compared to conventional methods of CMS, the results indicate that by using the new method, more accurate results can be obtained with a substantial saving in CPU time.

Abdallah, Ayman Ahmed↗
NASA NTRSDate not supplied

Numerical Simulation of the High-Speed Leg of the National Transonic Facility

Numerical simulations for the flow inside the high-speed leg of the National Transonic Facility was conducted. The NASA Tetrahedral Unstructured Software System (TetrUSS) with its USM3D_ME solver was used to perform the numerical simulations. USM3D_ME is developed and maintained by NASA Langley Research Center. Simulations were conducted for three configurations: empty tunnel, body of revolution installed, and NASA Common Research Model installed in the test section. Simulations were performed for a test section Mach number of 0.7 and 0.85 and a corresponding Reynolds number of 8 million per ft. A controller was developed that automated dynamic outflow boundary and streamlined the process of running multiple simulations. The use of a dynamic outflow boundary was the key parameter to drive simulation to the desired tunnel conditions. The numerical simulations captured expected flow features in NTF test section and in the tunnel plenum. The simulations depicted that separation of the flow inside the diffuser appears to be asymmetric and more extensive toward the top and bottom walls. Analysis of the flow field were conducted, and the computed drag coefficient compared to wind tunnel data.

NTF↗
NASA NTRS1988

Development of boundary layer rolls from dynamic instabilities

Using three three-dimensional spectral models of flow in a neutral atmosphere, the development of atmospheric boundary layer rolls from the inflection point and parallel instabilities is examined. Using the Ekman profile, the ability of the various models to reproduce the modes arising from the parallel and inflection point instability mechanisms was tested by comparing the results from the spectral models with the results from larger models used by other investigators. It was found that the truncated spectral models used in this investigation yielded preferred values of orientation angle and aspect ratio that agreed with those produced by the larger models, as well as with the observations data taken on September 1981 during the West-German KonTur experiment.

Stensrud, David J.↗
NASA NTRS1992

An experimental examination of the effects of incoming boundary layer modifications on the dynamics of a turbulent compression corner interaction

This experimental study examines the effects of modifications to the incoming turbulent boundary layer on the highly separated shock wave/boundary layer interaction generated by an unswept compression corner. Particular focus is placed on the motion of the unsteady separation shock wave. The flowfield was generated by a 28 deg ramp in a Mach 5 flow with a freestream Reynolds number of 50 x 10 exp 6/m. The incoming turbulent boundary layer transitioned naturally and developed under near-adiabatic wall conditions. Modification of the flow entering the interaction was effected through either a single plate boundary layer manipulator (BLM) or riblets. The BLM reduced the length of separation by 35-45 percent and reduced the streamwise extent of the separation shock motion by 36-74 percent. Examination of the flowfield downstream of the BLM showed this result to be due to the inviscid preturning of the flow by the BLM, and not by changes to the boundary layer dynamics. The riblets had no measurable effect on the compression corner interaction.

Mcclure, W. B.↗
NASA NTRS1990

The scatterometer - Data and applications

The techniques used to extract oceanographic and meteorological parameters from satellite radar scatterometer data are described and demonstrated, primarily on the basis of Seasat data. The principles of backscatter measurement and the general relationships between wind and wave fields are summarized, and the construction of geophysical data records from scatterometer swaths is explained. Particular attention is given to surface-layer dynamics and stresses; planetary-boundary-layer dynamics; averaging methods; the estimation of heat, moisture, and CO2 flux coefficients; the determination of pressure fields; storm monitoring; synoptic-scale analysis; climate analysis; and ocean dynamics. The capabilities and potential applications of the planned ERS-1, NSCAT, and SCANSCAT satellite scatterometers are briefly indicated.

Brown, R. A.↗
NASA NTRS2017

Dynamics of Coronal Hole Boundaries

Remote and in situ observations strongly imply that the slow solar wind consists of plasma from the hot, closed-field corona that is released onto open magnetic field lines. The Separatrix Web theory for the slow wind proposesthat photospheric motions at the scale of supergranules are responsible for generating dynamics at coronal-holeboundaries, which result in the closed plasma release. We use three-dimensional magnetohydrodynamicsimulations to determine the effect of photospheric flows on the open and closed magnetic flux of a model coronawith a dipole magnetic field and an isothermal solar wind. A rotational surface motion is used to approximatephotospheric supergranular driving and is applied at the boundary between the coronal hole and helmet streamer.The resulting dynamics consist primarily of prolific and efficient interchange reconnection between open andclosed flux. The magnetic flux near the coronal-hole boundary experiences multiple interchange events, with someflux interchanging over 50 times in one day. Additionally, we find that the interchange reconnection occurs allalong the coronal-hole boundary and even produces a lasting change in magnetic-field connectivity in regions thatwere not driven by the applied motions. Our results show that these dynamics should be ubiquitous in the Sun andheliosphere. We discuss the implications of our simulations for understanding the observed properties of the slowsolar wind, with particular focus on the global-scale consequences of interchange reconnection.

Higginson, A. K.↗
NASA NTRS1988

Inflow/outflow boundary conditions and global dynamics of spatial mixing layers

The numerical simulation of incompressible spatially-developing shear flows poses a special challenge to computational fluid dynamicists. The Navier-Stokes equations are elliptic and boundary equations need to be specified at the inflow and outflow boundaries in order to compute the fluid properties within the region of interest. It is, however, difficult to choose inflow and outflow conditions corresponding to a given experimental situation. Furthermore the effects that changes in the boundary conditions or in the size of the computational domain may induce on the global dynamics of the flow are presently unknown. These issues are examined in light of recent developments in hydrodynamic stability theory. The particular flow considered is the spatial mixing layer but it was expected that similar phenomena were bound to occur in other cases such as channel flow, the boundary layer, etc. A short summary of local/global and absolute/convective instability concepts is given. The results of numerical simulations are presented which strongly suggest that global resonances may be triggered in domains of finite streamwise extent although the evolution of the perturbation vorticity field is everywhere locally convective. A relationship between finite domains and pressure sources which might help in devising a scheme to eliminate these difficulties is discussed.

Buell, J. C.↗
DOE OSTI2020

Dynamic concurrent learning method to neutralize cyber attacks and faults for industrial asset monitoring nodes

Input signals may be received from monitoring nodes of the industrial asset, each input signal comprising time series data representing current operation. A neutralization engine may transform the input signals into feature vectors in feature space, each feature vector being associated with one of a plurality of overlapping batches of received input signals. A dynamic decision boundary may be generated based on the set of feature vectors, and an abnormal state of the asset may be detected based on the set of feature vectors and a predetermined static decision boundary. An estimated neutralized value for each abnormal feature value may be calculated based on the dynamic decision boundary and the static decision boundary such that a future set of feature vectors will be moved with respect to the static decision boundary. An inverse transform of each estimated neutralized value may be performed to generate neutralized signals comprising time series data that are output.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2017

Combustion Dynamic Characteristics Identification in a 9-point LDI Combustor Under Choked Outlet Boundary Conditions

Combustion dynamics data were collected at the NASA Glenn Research Center's CE-5 flame tube test facility under combustor outlet choked conditions. Two 9-point Swirl-Venturi Lean Direct Injection (SV-LDI) configurations were tested in a rectangular cuboid combustor geometry. Combustion dynamic data were measured at different engine operational conditions up to inlet air pressure and temperature of 24.13 bar and 828 K, respectively. In this study, the effects of acoustic cavity resonance, precessing vortex core (PVC), and non-uniform thermal expansion on the dynamic noise spectrum are identified by comparing the dynamic data that collected at various combustor inlet conditions along with combustor geometric calculations. The results show that the acoustic cavity resonance noises were seen in the counter-rotating pilot configuration but not in the co-rotating pilot configuration. Dynamic pressure noise band at around 0.9 kHz was only detected at the P'41 location (9.8 cm after fuel injector face) but not at the P'42 location (29 cm after the fuel injector face); the amplitude of this noise band depended on the thermal expansion ratio (T4/T3). The noise band at around 1.8 kHz was found to depend on the inlet air pressure or the air density inside the combustor. The PVC frequency was not observed in these two configurations.

lean direct injection↗
DOE OSTI2020

Mesoscale to Microscale Simulations over Complex Terrain with the Immersed Boundary Method in the Weather Research and Forecasting Model

Improvements to the Weather Research and Forecasting (WRF) Model are made to enable multiscale simulations over highly complex terrain with dynamically downscaled boundary conditions from the mesoscale to the microscale. Over steep terrain, the WRF Model develops numerical errors that are due to grid deformation of the terrain-following coordinates. An alternative coordinate system, the immersed boundary method (IBM), has been implemented into WRF, allowing for simulations over highly complex terrain; however, the new coordinate system precluded nesting within mesoscale simulations using WRF’s native terrain-following coordinates. Here, the immersed boundary method and WRF’s grid-nesting framework are modified to seamlessly work together. This improved framework for the first time allows for large-eddy simulation over complex (urban) terrain with IBM to be nested within a typical mesoscale WRF simulation. Simulations of the Joint Urban 2003 field campaign in Oklahoma City, Oklahoma, are performed using a multiscale five-domain nested configuration, spanning horizontal grid resolutions from 6 km to 2 m. These are compared with microscale-only simulations with idealized lateral boundary conditions and with observations of wind speed/direction and SF 6 concentrations from a controlled release from intensive observation period 3. The multiscale simulation, which is configured independent of local observations, shows similar model skill predicting wind speed/direction and improved skill predicting SF 6 concentrations when compared with the idealized simulations, which require use of observations to set mean flow conditions. Use of this improved multiscale framework shows promise for enabling large-eddy simulation over highly complex terrain with dynamically downscaled boundary conditions from mesoscale models.

42 ENGINEERING↗
DOE OSTI2025

Speciation and diffusive dynamics in hydrated grain boundaries of complex oxide Gd2Ti2O7

Abstract Grain boundaries in polycrystalline materials significantly affect their properties, such as ionic transport, corrosion, and chemical durability. The pyrochlore compound (Gd 2 Ti 2 O 7 ) is employed as a model for complex oxides and is known for its diverse applications, including nuclear waste immobilization. Density functional theory-based first-principles molecular dynamics simulations were performed at different temperatures on the hydrated grain boundary system. The results show extensive transformations within the grain boundaries among hydrous water species (OH − , H 2 O, and H 3 O + ). The temperature dependence of self-diffusion coefficients follows Arrhenius behavior, with an activation energy of 35.9 kJ/mol for hydrogen and 46.3 kJ/mol for oxygen. The lifetime of OH − is about three to four times longer than that of H 2 O at temperatures from 800 to 2100 K, suggesting the greater stability of OH − over H 2 O, a unique characteristic of the grain boundaries. The estimated lifetime of the hydrous species decreases as the temperature increases, with an activation energy of 9.9 kJ/mol for OH − and 13.4 kJ/mol for H 2 O. While Gd 3 + is more mobile than Ti 4+ , both the Gd 3 + and Ti 4+ cations are orders of magnitude less mobile than the water species. The results suggest that water species are much more mobile within grain boundaries than in the bulk crystal and have the potential to penetrate deep into polycrystalline materials through grain boundaries, leading to grain boundary degradation and dissolution. The different mobilities of cations in complex oxides can lead to leaching of certain cations and incongruent dissolution during the chemical weathering of Earth and industrial materials.

B. Ghosh, Dipta↗
NASA NTRS1972

The problem of the boundary conditions in thermosphere dynamics.

A simple analytic solution for the generation and propagation of tidal waves at thermospheric heights is presented. It is used to show that a unique solution of tidal wave propagation within the thermosphere depends on the boundary conditions of the model, and that radiation conditions lead to such a unique solution.

Volland, H.↗