Search NASA⌕ Search

SEARCH · Search NASA

Results for “dynamic processes”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Control of Basin Water Depth On Channel Morphology and Autogenic Timescales in Deltaic Systems

River channel geometry is often controlled by upstream boundary conditions, including fluvial discharge and sediment properties. At the coast, downstream boundary conditions (e.g., tides, waves, water depth) also strongly influence channel formation and evolution. Here, we conducted a set of experiments to determine the effects of basin water depth (i.e., a downstream boundary condition) on the evolution and geometry of fluviodeltaic channels and lobes. Internal dynamics (autogenic processes) in the fluviodeltaic system drive channel avulsion through cycles of sediment storage and release. Experimental results indicate an increase in the timescale of autogenic storage and release with increasing basin water depth. Deeper basin water requires a larger volume to be filled within the delta front, thus more time to complete one autogenic storage and release cycle for a given sediment discharge. While a relationship between delta-front volume and autogenic storage and release timescales is expected, we show that autogenically generated morphological changes in the delta topset and distributary channels also exert control on timescales of storage and release. Deltas building into deeper basins develop steeper topsets, and deeper distributary channels that cause high-magnitude topset slope fluctuations, which contribute to the long autogenic timescales. Deposits in shallow basins exhibit both shallower topset slopes and shallower channels. Channel bed slopes are similar (~0.06) across all experiments, but lateral channel migration rates varied with basin depth. Deltas building into shallow basins had rapid lateral channel migration, such that channels quickly reworked the delta topset. For deep basins, channel migration rates were much slower, so the topset was reworked less often, allowing the topset to build to steeper slopes before being reworked. These experiments indicate an intimate relationship between lateral channel migration and topset aggradation. In addition, the deeper and more stable channels in deeper basins generally developed a wider range of channel widths, some of which produced elongate lobes. Finally, we conclude that the downstream boundary has a strong control on fluviodeltaic morphology, which can result in a striking difference in the autogenic timescale.

58 GEOSCIENCES↗
DOE OSTI2015

High Fidelity Simulations of Large-Scale Wireless Networks

The worldwide proliferation of wireless connected devices continues to accelerate. There are 10s of billions of wireless links across the planet with an additional explosion of new wireless usage anticipated as the Internet of Things develops. Wireless technologies do not only provide convenience for mobile applications, but are also extremely cost-effective to deploy. Thus, this trend towards wireless connectivity will only continue and Sandia must develop the necessary simulation technology to proactively analyze the associated emerging vulnerabilities. Wireless networks are marked by mobility and proximity-based connectivity. The de facto standard for exploratory studies of wireless networks is discrete event simulations (DES). However, the simulation of large-scale wireless networks is extremely difficult due to prohibitively large turnaround time. A path forward is to expedite simulations with parallel discrete event simulation (PDES) techniques. The mobility and distance-based connectivity associated with wireless simulations, however, typically doom PDES and fail to scale (e.g., OPNET and ns-3 simulators). We propose a PDES-based tool aimed at reducing the communication overhead between processors. The proposed solution will use light-weight processes to dynamically distribute computation workload while mitigating communication overhead associated with synchronizations. This work is vital to the analytics and validation capabilities of simulation and emulation at Sandia. We have years of experience in Sandia’s simulation and emulation projects (e.g., MINIMEGA and FIREWHEEL). Sandia’s current highly-regarded capabilities in large-scale emulations have focused on wired networks, where two assumptions prevent scalable wireless studies: (a) the connections between objects are mostly static and (b) the nodes have fixed locations.

Onunkwo, Uzoma↗
DOE OSTI2016

Velocimetry Overview for visitors from the DOD

We are in the midst of a transformative period in which technological advances are making fundamental changes in the measurement techniques that form the backbone of nuclear weapon certification. Optical velocimetry has replaced electrical shorting pins in “Hydrotests,” which measure the dynamic implosion process. This advance has revolutionized nuclear weapons certification during the last 5 years. We can now measure the implosion process that drives a nuclear detonation with many orders of magnitude more resolution in both space and time than was possible just 10 years ago. It has been compared to going from Morse Code to HDTV, resulting in a dozen or more improvements in models of these weapons. These Hydrotests are carried out at LANL, LLNL and the NNSS, with the later holding the important role of allowing us to test with nuclear materials, in sub-critical configurations (i.e., no yield.) Each of these institutions has largely replaced pins with hundreds of channels of optical velocimetry. Velocimetry is non-contact and is used simultaneously with the X-ray capability of these facilities. The U1-a facility at NNSS pioneered this approach in the Gemini series in 2012, and continues to lead, both in channel count and technological advances. Close cooperation among LANL, LLNL and NSTec in these advances serves the complex by leveraging capabilities across sites and accelerating the pace of technical improvements.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2018

Complete Status Report Documenting the Development of Friction Stir Welding for Producing a Butt Joint in Thin Wall Tubing of ODS Alloys

A challenging attempt using friction stir welding to produce a butt joint between two 1.0 mm thick plates of 14YWT was nearly successful. The modified tool pin mostly penetrated the thickness of the adjoined thin plate samples resulting in a small blunt notch on the bottom surface of the butt joint. A bend occurred in the thin plate sample due to formation of stresses from clamping the thin plate sample during FSW. The peak displacement of the bend occurred along the center line of the butt joint. The weld zone showed good microstructure mixing with some flashing mostly on the retreating side that suggested excess heat input by friction between the traveling and spinning tool pin and thin plates of 14YWT. Neutron diffraction experiments were performed on the bent sample of 14YWT to measure the residual stresses in the butt joint on the HB-2B beam line at the Neutron Residual Stress Facility at HFIR. However, the neutron scattering to background noise ratio was very low during data acquisition. Measurements of lattice strains were obtained in the rolling (RD) and normal (ND) directions but not in the extrusion direction (ED) of the thin plate sample. Unfortunately, the quality of the data was not sufficient for determining the residual stresses in the butt joint. From the previous neutron scattering experiments conducted on four hot rolled plates (R1, R2, R3 and R4) of 14YWT, the residual stresses were calculated from lattice strain data and plotted in 2-D color contour maps for ED, RD and ND. The results showed variations in the magnitude and spatial position of residual stresses in the microstructure of the four plates. The magnitude in residual stresses in ED and RD increased gradually with increasing rolling deformation for R1 (50%) to R2 (76%), followed by larger increases in R3 (89%) and R4 (95%). The maximum peaks in residual stresses for R4 was ~710-730 MPa in ED and RD. The residual stresses in ND were below ~300 MPa for each of the 4 rolled plates, with a maximum residual stress in R4 (95%) of ~400 MPa. These results indicated that significant residual stresses representing ~57% of the yield stress of 14YWT (SM13) had accumulated in the 14YWT plate after hot rolling to the 1 mm thickness, which was used in the FSW experiments. The microstructure analysis of the 1.0 mm thick plate of 14YWT containing the butt joint produced by FSW revealed significant changes in the grain structure and texture between the unaffected zone (UZ) of the rolled plate and the butt joint weld. In the UZ, the grains were severely elongated after 95% deformation and mainly possessed the {101} texture component in the ED. Two predominant grain misorientation angles were observed: one consisting of small misorientations of <5º between highly elongated grains and the other consisting of large misorientations of >15º in pockets of small grains that might have formed by dynamic recrystallization processes during rolling of the plate at 1000ºC. The morphology and texture of grains in the heat affected zone (HAZ) were similar to those in UZ, except the grains had coarsened due to excess heat input during FSZ. A population of pores formed and the grains both coarsened and changed to isotropic morphology in the microstructure of the butt joint on both the advancing and retreating sides. The texture of grains in both regions were randomly orientated between the 3 poles {001}, {101} and {111}. The main difference in texture of grains between the advancing side and retreating side was with the misorientation angles of neighboring grains. Most of the grains in the advancing side had misorientation angles of >5º indicating that these grains experienced recrystallization. On the retreating side, areas containing larger grains showed high misorientation angles of >15º compared to areas appearing as bands of grains with misorientation angles of <5º and between 5º-15º. Numerous small pockets of grains with low misorientation angles of <5º were distributed in the microstructure among the grains showing high misorientation angles of >15º. It was determined that the grains associated with low misorientation angles contained sub-grain structures, which was consistent with both recrystallization and recovery mechanisms for grains located on the retreating side of the butt joint. These results demonstrate the complex microstructure that evolves in the microstructure of 14YWT resulting from the input of high temperatures and severe deformations during FSW.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Bubble-Size Evolution during Polyurethane Foam Expansion

We are developing computational models to elucidate the expansion and dynamic filling process of a polyurethane (PMDI) foam used to encapsulate electronic components or to produce lightweight structural parts. The polyurethane of interest is a chemically blown foam, where carbon dioxide is produced via the reaction of water, a blowing agent, and isocyanate. Here, we take a careful look at the evolution of the bubble sizes during blowing. This information will help the development of subgrid models to predict bubble formation, growth, coalescence and collapse, drainage, and, hence, eventually the development of engineering models to predict foam expansion into a mold. Close-up views of bubbles at a transparent wall of a narrow, temperature-controlled channel are recorded during the foaming reaction and analyzed with image processing. Because these bubbles are pressed against the wall, the bubble sizes in the last frames after the expansion has stopped are compared to scanning electron microscope (SEM) images of the interior of some of the cured samples to determine if the presence of the wall significantly changes the bubble sizes. In addition, diffusing wave spectroscopy (DWS) is used to determine the average bubble sizes across the width of a similar channel as the bubbles change with time. DWS also gives information about microstructural changes as bubbles rearrange upon bubble collapse or coalescence. In this paper we conclude qualitatively that the bubble size distribution is heavily dependent on the formulation of foam being tested, temperature, the height in the foam bar, the proximity to a wall, and the degree of over-packing.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Fuel/Basket Degradation and Waste Package Pressure Effects Modeling (Progress Report)

Progress is reported on development and testing of the Fuel/Basket Degradation Model, and the Waste Package Breach Model. The work follows on reported FY19 model development (SNL-ICG 2019). Modeling has addressed questions framed in the deliverable description: 1) how fuel/basket damage, including from seismic ground motion, could impact reactivity; 2) whether dynamic degradation processes (e.g., caused by seismic ground motion) should be targets for further model development; and 3) what are the key model parameters and how do they affect the likelihood and energy of criticality events. For basket structure made from aluminum-based metal-matrix composite material, basket collapse would coincide with loss of neutron absorbers, and would occur within a few hundred years after waste package breach. Degradation models discussed in this report have thus far focused on a generic 32-PWR (pressurized water reactor fuel) basket with aluminum-based plates

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

2021 Summer SPE Project

SPE is a project in order to develop new, more physics-based, seismic models of explosions (see Nelson et al. 2013). One key component of this effort is numerical modeling enabled by modern state-of-art code/software. Accurate modeling of the shape and amplitude of seismic waves from their generation to their propagation to remote monitoring seismic stations is important to our ability to determine the origin and strength of the source from remote recording. In this project, the modeling is performed by coupling two codes HOSS and SPECFEM3D. HOSS models the dynamic nonlinear processes happening near the explosion. SPECFEM3D computes the propagation of seismic waves as they travel through 3D complex Earth models. SPECFEM3D was modified in order to be driven by a set of time-series calculated by HOSS in lieu of a seismic source. The goal of this summer project is the investigation of several questions pertinent to the establishment of a full end-to-end modeling capability from the high-rate strain regime area to remote distances where seismic station record seismic waves generated by explosions. The investigated questions are: (1) How to perform proper filtering? Direct-solution modeling only sustains a limited range of frequency depending on the grid size. As we go from one modeling domain to the other via coupling, the mesh size is getting coarser to allow modeling at large scale but also to account for the fact that high-frequency waves do not physically travel to large distances. So filtering of the time-series generated by the near-field hydrodynamic modeling is a current practice often employed but its effects on the modeled waveforms has to be investigated. (2) Quantitative assessment of the efficiency of attenuation to remove high-frequency content of the wavefield. This assessment will allow to create meshes with a grid size appropriate to the actual physics of wave propagation for a given explosion. (3) Checking that the coupling process and the two codes respect the cylindrical symmetry that is expected in the case of a pure explosion in a half-space. (4) The effect of the state-of-stress in the near-source area on the modeled seismic waveforms. These questions will be investigated through the modeling of SPE-4P, the fourth explosion of this series because it was designed to have little interaction with the geologic surrounding and the free surface of the Earth so that it is the most explosion-like experiment, with the most symmetries to be verified.

58 GEOSCIENCES↗
DOE OSTI2021

CRADA Number NFE1706843 with SkyNano LLC (CRADA Final Report)

Cooperative Research and Development Agreement (CRADA) NFE-17-06843 between Oak Ridge National Laboratory (ORNL) and SkyNano LLC focused on studying and developing a better fundamental understanding of SkyNano’s technology to capture and convert CO 2 into solid carbon nanostructures, including carbon nanotubes (CNTs), using electrochemistry at elevated temperatures in molten salts. The project focused on developing a fundamental scientific understanding of how electrochemistry influences the dynamic catalytic processes that drive the formation of CNTs on electrodes, while developing synthesis and processing technology relevant to implementation of the technology – including chemical engineering to aid in recapturing the lithium carbonate electrolyte essential to the process, and the modeling and testing of systems with the required thermal management at practical scales.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

ML based control systems for nuclear physics experiments

The Experimental Physics Software and Computing Infrastructure (EPSCI) group at Jefferson Lab is leading the use of machine learning (ML) to enhance control systems in nuclear physics experiments. Collaborating closely with domain experts and data scientists, we have developed an ML-based control system that uses a Gaussian process to dynamically adjust the high voltage of the GlueX Central Drift Chamber. This results in stable detector performance by adapting to environmental changes, thereby reducing the offline calibration effort. Furthermore, we are developing ML-driven systems for optimizing the polarization of photon beams and polarized cryotargets. These systems will maintain the optimal microwave frequency in cryogenic targets and make real-time adjustments to diamond radiators for polarized photon sources, tasks traditionally handled by human operators. By automating these functions, we aim to optimize the polarization, reduce downtime, and minimize human error. This talk will highlight the development of reliable ML-based control systems and the policies to ensure they are both effective and trustworthy.

Jeske, Torri↗
DOE OSTI2021

Modelled land use and land cover change emissions – a spatio-temporal comparison of different approaches

Abstract. Quantifying the net carbon flux from land use and land cover changes (fLULCC) is critical for understanding the global carbon cycle and, hence, to support climate change mitigation. However, large-scale fLULCC is not directly measurable and has to be inferred from models instead, such as semi-empirical bookkeeping models and process-based dynamic global vegetation models (DGVMs). By definition, fLULCC estimates are not directly comparable between these two different model types. As an important example, DGVM-based fLULCC in the annual global carbon budgets is estimated under transient environmental forcing and includes the so-called loss of additional sink capacity (LASC). The LASC results from the impact of environmental changes on land carbon storage potential of managed land compared to potential vegetation and accumulates over time, which is not captured in bookkeeping models. The fLULCC from transient DGVM simulations, thus, strongly depends on the timing of land use and land cover changes mainly because LASC accumulation is cut off at the end of the simulated period. To estimate the LASC, the fLULCC from pre-industrial DGVM simulations, which is independent of changing environmental conditions, can be used. Additionally, DGVMs using constant present-day environmental forcing enable an approximation of bookkeeping estimates. Here, we analyse these three DGVM-derived fLULCC estimations (under transient, pre-industrial, and present-day forcing) for 12 models within 18 regions and quantify their differences as well as climate- and CO2-induced components and compare them to bookkeeping estimates. Averaged across the models, we find a global fLULCC (under transient conditions) of 2.0±0.6 PgC yr−1 for 2009–2018, of which ∼40 % are attributable to the LASC (0.8±0.3 PgC yr−1). From 1850 onward, the fLULCC accumulated to 189±56 PgC with 40±15 PgC from the LASC. Around 1960, the accumulating nature of the LASC causes global transient fLULCC estimates to exceed estimates under present-day conditions, despite generally increased carbon stocks in the latter. Regional hotspots of high cumulative and annual LASC values are found in the USA, China, Brazil, equatorial Africa, and Southeast Asia, mainly due to deforestation for cropland. Distinct negative LASC estimates in Europe (early reforestation) and from 2000 onward in the Ukraine (recultivation of post-Soviet abandoned agricultural land), indicate that fLULCC estimates in these regions are lower in transient DGVM compared to bookkeeping approaches. Our study unravels the strong dependence of fLULCC estimates on the time a certain land use and land cover change event happened to occur and on the chosen time period for the forcing of environmental conditions in the underlying simulations. We argue for an approach that provides an accounting of the fLULCC that is more robust against these choices, for example by estimating a mean DGVM ensemble fLULCC and LASC for a defined reference period and homogeneous environmental changes (CO2 only).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Atmospheric Radiation Measurement (ARM) airborne field campaign data products between 2013 and 2018

Airborne measurements are pivotal for providing detailed, spatiotemporally resolved information about atmospheric parameters and aerosol and cloud properties, thereby enhancing our understanding of dynamic atmospheric processes. For 30 years, the US Department of Energy (DOE) Office of Science supported an instrumented Gulfstream 1 (G-1) aircraft for atmospheric field campaigns. Data from the final decade of G-1 operations were archived by the Atmospheric Radiation Measurement (ARM) Data Center and made publicly available at no cost to all registered users. To ensure a consistent data format and to improve the accessibility of the ARM airborne data, an integrated dataset was recently developed covering the final 6 years of G-1 operations (2013 to 2018, https://doi.org/10.5439/1999133; Mei and Gaustad, 2024). The integrated dataset includes data collected from 236 flights (766.4 h), which covered the Arctic, the US Southern Great Plains (SGP), the US West Coast, the eastern North Atlantic (ENA), the Amazon Basin in Brazil, and the Sierras de Córdoba range in Argentina. These comprehensive data streams provide much-needed insight into spatiotemporal variability in the thermodynamic quantities and aerosol and cloud properties for addressing essential science questions in Earth system process studies. This paper describes the DOE ARM merged G-1 datasets, including information on the acquisition, data collection challenges and future potentials, and quality control processes. It further illustrates the usage of this merged dataset to evaluate the Energy Exascale Earth System Model (E3SM) with the Earth System Model Aerosol–Cloud Diagnostics (ESMAC Diags) package.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1972

A conceptual study of the rotor systems research aircraft

The analytical comparison of the two candidate Rotor Systems Research Aircraft (RSRA) configurations selected by the Government at the completion of Part 1 of the RSRA Conceptual Predesign Study is presented. The purpose of the comparison was to determine the relative suitability of both vehicles for the RSRA missions described in the Government Statement of Work, and to assess their versatility in the testing of new rotor concepts. The analytical comparison was performed primarily with regard to performance and stability and control. A weights, center-of-gravity, and inertia computation was performed for each iteration in the analysis process. The dynamics investigation was not concerned so much with a comparison of the two vehicles, but explored the dynamic problems attending operation of any RSRA operating with large rotor RPM and diameter ranges over large forward speed ranges. Several means of isolating in- and out-of-plane rotor vibrations were analyzed. An optimum isolation scheme was selected.

Source record↗
NASA NTRS1973

Mineral Resources, Geological Structure and Landform Surveys

Significant results are presented of ERTS-1 investigations of landform surveys, mineral resources, and geological structures. The report covers four areas: (1) mapping investigations; (2) dynamic surface processes and landforms; (3) structural elements; and (4) mineral deposits.

Short, M. N.↗
NASA NTRS1974

Modular digital computer system design

Automatically-Reconfigurable Modular Multiprocessor System (ARMMS) provides redundant processing with dynamic mode switching in real time. Design will provide higher computer capability than that presently available for same amount of hardware and will furnish modular system which is responsive to diverse problems effectively.

Source record↗
NASA NTRS1973

Ar-40/Ar-36 variations in Apollo 15 and 16 regolith

Values of Ar-40/Ar-36 have been determined for a large number of Apollo 15 and Apollo 16 fines, including samples from a range of depths in the Apollo 15 and 16 deep drill cores. Most of the Ar-40 in these samples is 'excess Ar-40' in that it has not been produced by in situ decay of K. Values of Ar-40/Ar-36 range from 0.74 to 4.35 and demonstrate that the regolith is not well mixed over depths of several cm or over surface distances greater than about 100 m. However, fines collected over surface distances of less than a few tens of meters tend to possess similar ratios. Values of Ar-40/Ar-36 in the Apollo 15 drill core increase with depth by nearly a factor of four (0.74 to 2.86) in the 0 to 80 cm depth range, then decrease for greater depths. Values of Ar-40/Ar-36 in the Apollo 16 drill core are nearly constant at about 1.3, except for the deepest sample analyzed (about 2.7). Concentrations of glass-bonded agglutinate particles in the fines tend to correlate with lower Ar-40/Ar-36, and may indicate that dynamic regolith processes also affect the trapped Ar-40/Ar-36.

Bogard, D. D.↗
NASA NTRS1974

Mineral resources, geological structures, and landform surveys

Since March 1973 there has been a shift in ERTS results in geology from the initial show-and-tell stage to a period in which scientific studies predominated, and now to an emphasis on effective applications having economic benefits and clearcut relevance to national needs. Many years will be spent on geological tasks resulting from ERTS alone; reconnaissance mapping in inaccessible regions, map revisions, regional or synoptic analysis of crustal fractures, assessment of dynamic surficial processes, systematic search for mineral wealth, use of sophisticated enhancement techniques, recognition of potential geologic hazards, and many more applications that still need to be defined.

Short, N. M.↗