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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Stochastic Nonlinear Response of Woven CMCs

It is well known that failure of a material is a locally driven event. In the case of ceramic matrix composites (CMCs), significant variations in the microstructure of the composite exist and their significance on both deformation and life response need to be assessed. Examples of these variations include changes in the fiber tow shape, tow shifting/nesting and voids within and between tows. In the present work, the influence of scale specific architectural features of woven ceramic composite are examined stochastically at both the macroscale (woven repeating unit cell (RUC)) and structural scale (idealized using multiple RUCs). The recently developed MultiScale Generalized Method of Cells methodology is used to determine the overall deformation response, proportional elastic limit (first matrix cracking), and failure under tensile loading conditions and associated probability distribution functions. Prior results showed that the most critical architectural parameter to account for is weave void shape and content with other parameters being less in severity. Current results show that statistically only the post-elastic limit region (secondary hardening modulus and ultimate tensile strength) is impacted by local uncertainties both at the macro and structural level.

Kuang, C. Liu↗
NASA NTRS2015

Investigation of North American Vegetation Variability under Recent Climate: A Study Using the SSiB4/TRIFFID Biophysical/Dynamic Vegetation Model

Recent studies have shown that current dynamic vegetation models have serious weaknesses in reproducing the observed vegetation dynamics and contribute to bias in climate simulations. This study intends to identify the major factors that underlie the connections between vegetation dynamics and climate variability and investigates vegetation spatial distribution and temporal variability at seasonal to decadal scales over North America (NA) to assess a 2-D biophysical model/dynamic vegetation model's (Simplified Simple Biosphere Model version 4, coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics Model (SSiB4/TRIFFID)) ability to simulate these characteristics for the past 60 years (1948 through 2008). Satellite data are employed as constraints for the study and to compare the relationships between vegetation and climate from the observational and the simulation data sets. Trends in NA vegetation over this period are examined. The optimum temperature for photosynthesis, leaf drop threshold temperatures, and competition coefficients in the Lotka-Volterra equation, which describes the population dynamics of species competing for some common resource, have been identified as having major impacts on vegetation spatial distribution and obtaining proper initial vegetation conditions in SSiB4/TRIFFID. The finding that vegetation competition coefficients significantly affect vegetation distribution suggests the importance of including biotic effects in dynamical vegetation modeling. The improved SSiB4/TRIFFID can reproduce the main features of the NA distributions of dominant vegetation types, the vegetation fraction, and leaf area index (LAI), including its seasonal, interannual, and decadal variabilities. The simulated NA LAI also shows a general increasing trend after the 1970s in responding to warming. Both simulation and satellite observations reveal that LAI increased substantially in the southeastern U.S. starting from the 1980s. The effects of the severe drought during 1987-1992 and the last decade in the southwestern U.S. on vegetation are also evident from decreases in the simulated and satellite-derived LAIs. Both simulated and satellite-derived LAIs have the strongest correlations with air temperature at northern middle to high latitudes in spring reflecting the effect of these climatic variables on photosynthesis and phenological processes. Meanwhile, in southwestern dry lands, negative correlations appear due to the heat and moisture stress there during the summer. Furthermore, there are also positive correlations between soil wetness and LAI, which increases from spring to summer. The present study shows both the current improvements and remaining weaknesses in dynamical vegetation models. It also highlights large continental-scale variations that have occurred in NA vegetation over the past six decades and their potential relations to climate. With more observational data availability, more studies with differentmodels and focusing on different regions will be possible and are necessary to achieve comprehensive understanding of the vegetation dynamics and climate interactions.

climate variability↗
NASA NTRS2016

Change in Mouse Bone Turnover in Response to Microgravity on RR-1

Mechanical unloading during spaceflight is known to adversely affect mammalian physiology. Our previous studies using the Animal Enclosure Module on short duration Shuttle missions enabled us to identify a deficit in stem cell based-tissue regeneration as being a significant concern for long-duration spaceflight. Specifically, we found that mechanical unloading in microgravity resulted in inhibition of differentiation of mesenchymal and hematopoietic stem cells in the bone marrow compartment. Also, we observed overexpression of a cell cycle arrest molecule, CDKN1ap21, in osteoprecursor cells on the bone surface, chondroprogenitors in the articular cartilage, and in myofibers attached to bone tissue. Specifically in bone tissue during both short (15-day) and long (30-day) microgravity experiments, we observed significant loss of bone tissue and structure in both the pelvis and the femur. After 15-days of microgravity on STS-131, pelvic ischium displayed a 6.23 decrease in bone fraction (p0.005) and 11.91 decrease in bone thickness (p0.002). Furthermore, during long-duration spaceflight we observed onset of an accelerated aging-like phenotype and osteoarthritic disease state indicating that stem cells within the bone tissue fail to repair and regenerate tissues in a normal manner, leading to drastic tissue alterations in response to microgravity. The Rodent Research Hardware System provides the capability to investigate these effects during long-duration experiments on the International Space Station. During the Rodent Research-1 mission 10 16-week-old female C57Bl6J mice were exposed to 37-days of microgravity. All flight animals were euthanized and frozen on orbit for future dissection. Ground (n10) and vivarium controls (n10) were housed and processed to match the flight animal timeline. During this study we collected pelvis, femur, and tibia from all animal groups to test the hypothesis that stem cell-based tissue regeneration is significantly altered after 37-days of spaceflight. To do this, we will analyze differences in bone morphometric parameters using MicroCT. The pelvis, femur, and tibia are key in supporting and distributing weight under normal conditions. Therefore, we expect to see altered remodeling in flight animals in response to microgravity with respect to ground controls. In combination with histomorphometry, these results will help elucidate the complex mechanisms underlying bone tissue maintenance and stem cell regeneration.

bone↗
NASA NTRS2016

Changes in Mouse Bone Turnover in Response to Microgravity

Mechanical unloading during spaceflight is known to adversely affect mammalian physiology. Our previous studies using the Animal Enclosure Module on short duration Shuttle missions enabled us to identify a deficit in stem cell based-tissue regeneration as being a significant concern for long-duration spaceflight. Specifically, we found that mechanical unloading in microgravity resulted in inhibition of differentiation of mesenchymal and hematopoietic stem cells in the bone marrow compartment. Also, we observed overexpression of a cell cycle arrest molecule, CDKN1a/p21, in osteoprecursor cells on the bone surface, chondroprogenitors in the articular cartilage, and in myofibers attached to bone tissue. Specifically in bone tissue during both short (15-day) and long (30-day) microgravity experiments, we observed significant loss of bone tissue and structure in both the pelvis and the femur. After 15-days of microgravity on STS-131, pelvic ischium displayed a 6.23% decrease in bone fraction (p=0.005) and 11.91% decrease in bone thickness (p=0.002). Furthermore, during long-duration spaceflight we observed onset of an accelerated aging-like phenotype and osteoarthritic disease state indicating that stem cells within the bone tissue fail to repair and regenerate tissues in a normal manner, leading to drastic tissue alterations in response to microgravity. The Rodent Research Hardware System provides the capability to investigate these effects during long-duration experiments on the International Space Station. During the Rodent Research-1 mission 10 16-week-old female C57Bl/6J mice were exposed to 37-days of microgravity. All flight animals were euthanized and frozen on orbit for future dissection. Ground (n=10) and vivarium controls (n=10) were housed and processed to match the flight animal timeline. During this study we collected pelvis, femur, and tibia from all animal groups to test the hypothesis that stem cell-based tissue regeneration is significantly altered after 37-days of spaceflight. To do this, we will analyze differences in bone morphometric parameters using MicroCT. The pelvis, femur, and tibia are key in supporting and distributing weight under normal conditions. Therefore, we expect to see altered remodeling in flight animals in response to microgravity with respect to ground controls. In combination with histomorphometry, these results will help elucidate the complex mechanisms underlying bone tissue maintenance and stem cell regeneration.

microgravity↗
NASA NTRS2018

An Investigation of Glaciated Cloud Capabilities in the NASA Glenn Icing Research Tunnel

In 2015 the FAA added Appendix D to Part 33 engine certification requirements that included Mixed Phase and Ice Crystal Icing to aircraft engine certification. Replicating the ice crystal environment that is seen in nature has proven to be a challenge, which multiple engine ground testing facilities and icing wind tunnels have achieved to varying degrees. The Icing Research Tunnel (IRT) at NASA Glenn has always been focused on super-cooled liquid water to produce FAA Part 23 and Part 25 regulations, targeting Appendix C and lately also Appendix O. However, due to a growing interest in the field of ice crystals and the high cost of operating engine icing facilities, the IRT staff have recently completed testing using the Multi-Element Sensor (also known as the multi-wire) to measure glaciated cloud conditions. Results indicate that turning off the heat to the nozzle air and water supply can create a stable, fully glaciated cloud in the test section for a small range of conditions: drop-size distribution values below 20 microns (median volumetric diameter), air temperatures as warm as -7 deg C, and airspeeds between 100 and 250 knots. These tests also revealed how varying the total temperature, airspeed, nozzle air pressure, and nozzle water pressure affect the glaciation of the IRT cloud.

ice water content↗
NASA NTRSDate not supplied

A CFD Framework for Film Boiling and Quenching in Cryogenic Chilldown

Tests of cryogenic chilldown in a vertical stainless-steel tube are simulated using computational fluid dynamics (CFD). Subcooled liquid nitrogen enters a room-temperature tube at one end, resulting in film boiling and eventual quenching of the tube walls. A CFDbased modeling framework employing the mixture multiphase model was developed to simulate this chilldown process and was applied to validate it against experimental data. Extensive sensitivity studies have been performed to create a consistent modeling framework, and a range of test conditions are simulated to assess the modeling capability. The importance of the rewetting temperature and its relation to the foam limit temperature is discussed and considered in the CFD framework. The presented results demonstrate a qualitatively consistent representation of the film boiling and quenching regime. However, the quantitative accuracy of the simulations varies with the test conditions. In addition, simulated distributions of the vapor volume fraction are presented, but the current lack of experimental volume fraction data prevents comparisons.

Computational Fluid Dynamics↗
NASA NTRSDate not supplied

A CFD Framework for Film Boiling and Quenching in Cryogenic Chilldown

Tests of cryogenic chilldown in a vertical stainless-steel tube are simulated using computational fluid dynamics (CFD). Subcooled liquid nitrogen enters a room-temperature tube at one end, resulting in film boiling and eventual quenching of the tube walls. A CFDbased modeling framework employing the mixture multiphase model was developed to simulate this chilldown process and was applied to validate it against experimental data. Extensive sensitivity studies have been performed to create a consistent modeling framework, and a range of test conditions are simulated to assess the modeling capability. The importance of the rewetting temperature and its relation to the foam limit temperature is discussed and considered in the CFD framework. The presented results demonstrate a qualitatively consistent representation of the film boiling and quenching regime. However, the quantitative accuracy of the simulations varies with the test conditions. In addition, simulated distributions of the vapor volume fraction are presented, but the current lack of experimental volume fraction data prevents comparisons.

Computational Fluid Dynamics↗
DOE OSTI2018

Development of predictive capability of cycle-to-cycle variation in dual-fuel engines using supercomputing-based computational fluid dynamics

Cycle-to-cycle variation (CCV) in internal combustion engines is expected due to variabilities in operating conditions such as in-cylinder fuel stratification, mixing behavior, manifold air pressure, injection timing etc. Generally, engine experimental studies provide averaged quantities such as cylinder pressure, emissions, indicated mean effective pressure (IMEP) from multiple cycles and their CCV of IMEP, and CCV of cylinder pressure from consecutive cycles for a given test condition. Capturing 3D spatial distributions of relevant measures such as fuel-air mixing, temperature, turbulence levels and emissions from such experiments is challenging. Computational Fluid Dynamics (CFD) is an alternative to experiments, that can be used effectively to understand the spatial and temporal distributions of parameters of interest.Quantitative understanding of CCV in dual-fuel (DF) engines will accelerate the development and deployment of engines that provide fuel flexibility, economic advantage and emission compliance. Earlier work [1] performed to develop an understanding of the physics of CCV in large-bore, medium-speed, dual-fuel engines was partially successful. That effort entailed a sparse design of experiment (DOE) of full-cylinder geometry, closed-cycle, dual-fuel CFD simulations in which variabilities within some of the identified global parameters were exercised. The Coefficient of Variation (COV) of cylinder pressure was promising compared with experimental COV. This reinforced the understanding of which global parameters are significant contributors to CCV in DF combustion.The authors have used several high-performance supercomputing facilities in the process of developing predicting capability of CCV in large-bore engines, while operating in dual-fuel, diesel and natural gas (NG), combustion mode [1, 2]. In the current study CCV influencing parameters in a diesel-natural gas dual-fuel engine was studied using a 4th order DOE consisting of 137 concurrent cases. These full-geometry, closed-cycle, CFD simulations were run on the Mira supercomputing facility at the Argonne National Laboratory (ANL). This paper describes key learnings of that study along with a validation of the DOE. Further, the CCV prediction methodology, which is applicable to simulation-based design and testing, is described.

Gubba, Sreenivasa Rao↗
DOE OSTI2019

Subharmonic power line carrier based island detection systems and methods

Systems and methods for identifying an island condition in a power distribution system and disconnecting distributed generators in the case of islanding. The systems and methods are used to enable reliable detection of island formation with high false-trip immunity, for any combination of distributed energy resources, and for distributed energy resources using grid support functions.

Ropp, Michael↗
DOE OSTI2020

Considerations for Long-Term Load Forecasting in Morocco

There are many factors that determine how demand for electricity may change over time. These factors include GDP, population size, and technology diffusion and adoption. We employ a simple extrapolation of current trends in Morocco GDP to estimate how the peak demand and annual consumption may change through the year 2030. We discuss the many factors that this approach does not take into account (such as adoption of air conditioning, electric vehicles, and distributed generation).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Apparent Monte Carlo Source Convergence Problem with BWR Fuel Depleted with Partial Control Blade Insertion

Oak Ridge National Laboratory (ORNL) and the US Nuclear Regulatory Commission (NRC) have initiated a multiyear project to investigate application of burnup credit (BUC) to boiling-water reactor (BWR) fuel in storage and transportation casks and spent fuel pools (SFPs). Ideally, a single combination of all operating parameters including moderator density and axial burnup profiles, control blade exposure, and others can be identified to allow a simple, bounding approach to BWR BUC. One aspect of this investigation involves examining the effect of control blade insertion during operation on discharged assembly reactivity. In the course of these calculations, an apparent source convergence problem was discovered for fuel that has experienced partial blade insertion for the entire lifetime of the assembly. The source convergence problem appears not to impact k{sub eff}, but it manifests in predictions of the axial fission density profile. This phenomenon is of interest in identifying areas of concern with BWR BUC since it has not been studied as thoroughly as BUC for pressurized-water (PWR) reactor fuel. There may also be interest in this configuration for further study of a realistic source Monte Carlo convergence problem as opposed to some earlier manufactured source convergence problems through careful selection of initial conditions. This summary presents the depletion conditions used to generate the problem, a description of the models, a background based on well-behaved calculations, the identification of the problem, and attempts made to resolve the problem. Only a brief description of the depletion conditions and models is possible within the limited scope of this summary. Finally, conclusions are presented. This summary identifies a source convergence problem in the process of investigating BUC for BWR spent fuel. The depletion scenario which created the depleted fuel and burnable absorber compositions included a control blade inserted in the bottom 14 nodes throughout the entire depletion. This insertion is slightly over half the length of the assembly, and it appears to create two regions of nearly equal reactivity. As expected, one region is near the top of the assembly, and the other region is near the middle of the assembly. This node includes significant {sup 239}Pu generation as a result of rodded operation, but it is also the top node of the full lattice zone. While the calculated k{sub eff} values appear to be statistically equivalent, the axial neutron production profile varies significantly among independent simulations of the same model. A range of standard approaches has been used to attempt to resolve the source convergence problem and determine the true axial neutron production profile. This profile is of interest in cask criticality safety analysis because it influences the interaction among assemblies loaded in the cask. The forthcoming SCALE 6.2 release will include source convergence testing based on Shannon entropy, which may assist in identifying these types of problems in the future. It should be noted that this source convergence problem results from the depletion conditions and the final distribution of fissile and absorber material within the discharged fuel assembly. The results, while entirely generated within the SCALE code system, are representative of any Monte Carlo program attempting to calculate k{sub eff} for such a system. The most important conclusion of this work is that the BUC criticality safety community must be aware of the potential for this type of source convergence problem. Analysts must approach such partially rodded scenarios with caution and critically examine the results. Fortunately, it is extremely unlikely that BWR assemblies would experience the bladed operation necessary to create this particular source convergence problem. These results may also have some bearing on the analysis of PWR BUC for new plant designs such as AP1000 that incorporate significant rodded operations. In a broader context, the source convergence problem identified here could have been magnified if it had occurred in a Monte Carlo depletion simulation. It may be possible to identify this type of problem in a depletion calculation by comparing the apparently converged fluxes between steps to ensure that no oscillations or other serious shifts are occurring. The depletion calculations performed in this work were performed with a two-dimensional deterministic code and are therefore not subject to this problem. These results may also raise questions about the validity of 2D depletion models with extruded geometry in the 3D k{sub eff} calculation. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Stability, intermittency and universal Thorpe length distribution in a laboratory turbulent stratified shear flow

Stratified shear flows occur in many geophysical contexts, from oceanic overflows and river estuaries to wind-driven thermocline layers. In this study, we explore a turbulent wall-bounded shear flow of lighter miscible fluid into a quiescent fluid of higher density with a range of Richardson numbers $0.05\lesssim Ri\lesssim 1$ . In order to find a stability parameter that allows close comparison with linear theory and with idealized experiments and numerics, we investigate different definitions of $Ri$ . We find that a gradient Richardson number defined on fluid interface sections where there is no overturning at or adjacent to the maximum density gradient position provides an excellent stability parameter, which captures the Miles–Howard linear stability criterion. For small $Ri$ the flow exhibits robust Kelvin–Helmholtz instability, whereas for larger $Ri$ interfacial overturning is more intermittent with less frequent Kelvin–Helmholtz events and emerging Holmboe wave instability consistent with a thicker velocity layer compared with the density layer. We compute the perturbed fraction of interface as a quantitative measure of the flow intermittency, which is approximately 1 for the smallest $Ri$ but decreases rapidly as $Ri$ increases, consistent with linear theory. For the perturbed regions, we use the Thorpe scale to characterize the overturning properties of these flows. The probability distribution of the non-zero Thorpe length yields a universal exponential form, suggesting that much of the overturning results from increasingly intermittent Kelvin–Helmholtz instability events. Finally, the distribution of turbulent kinetic energy, conditioned on the intermittency fraction, has a similar form, suggesting an explanation for the universal scaling collapse of the Thorpe length distribution.

58 GEOSCIENCES↗
NASA NTRS1951

Low-speed static longitudinal and lateral stability characteristics of two low-aspect-ratio wings cambered and twisted to provide a uniform load at a supersonic flight condition

A delta wing and a tapered sweptback wing of aspect ratios 1.56 and 2.00, respectively, both of which were cambered and twisted so as to provide a uniform load distribution for a supersonic flight condition, were tested in combination with a fuselage at Reynolds numbers between 384,000 and 1,550,000 in order to determine the low-speed lift-drag and static stability characteristics of such wings.

REYNOLDS NUMBER EFFECTS - COMPLETE WINGS↗
NASA NTRS1974

Global temperature distributions from OGO-6 6300 A airglow measurements

The OGO-6 6300 A airglow temperature measurements have been used to develop models of the global temperature distributions under solstice and equinox conditions for the altitude region from 240 to 300 km and for times ranging from dawn in this altitude region to shortly after sunset. The distributions are compared with models derived from satellite orbital decay and incoherent scatter sounding. The seasonal variation of the temperature as a function of latitude is shown to be very different from that derived from static diffusion models with constant boundary conditions.

Blamont, J. E.↗
DOE OSTI2024

Distributed Coordination of Networked Microgrids for Voltage Support in Bulk Power Grids

The increasing deployment of distributed energy resources (DERs) and microgrids (MGs) in power distribution systems has enabled the adjustment of reactive power consumption as seen at the substation, which can be used to provide voltage support for the bulk power system (BPS). Leveraging this new capability will provide greater resiliency to the power system as a whole. Here, the goal of this paper is to develop and compare three different algorithms, namely distributed optimal power flow, distributed consensus algorithm, and fully decentralized collaborative autonomy for unbalanced distribution systems for microgrid coordination. These algorithms use networked MGs to support the BPS voltage when a contingency at the bulk grid results in abnormally low voltages, which may be a precursor to voltage collapse. Our comparative analysis includes both qualitative and quantitative assessments of the three algorithms and a discussion of the trade-offs between the decentralized and distributed methods in normal and disrupted conditions. Each algorithm was evaluated on the modified IEEE 13-bus system and a real power distribution system at Chattanooga, Tennessee, that encompasses more than 4500 buses. Each algorithms excels differently and may be suited for different scenarios depending on the condition, operations, and priorities of the power and communication systems.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2021

Transport Upscaling under Flow Heterogeneity and Matrix-Diffusion in Three-Dimensional Discrete Fracture Networks

For this work, we investigate the combined effects of network scale flow variability and retention due to matrix-diffusion on the scaling behavior of transport through fractured media. Two of the principal mechanisms controlling the transport of solutes through fractured low-permeability media are broad distributions of flow velocities and retention times in the solid matrix. We study the relative impact of these two processes under different initial conditions using a set of three-dimensional discrete fracture network simulations. We use these simulations to develop and calibrate an upscaled continuous time random walk (CTRW) approach for advective transport based on an Ornstein-Uhlenbeck model for the particle velocities that accounts for the fracture-matrix coupling using a compound Poisson process. This CTRW model can be conditioned on the initial solute distribution and allows to observe late-time scaling behavior at distances beyond what is feasible to observe using high-fidelity direct numerical simulations. We determine that the initial distribution of particles leads to marked differences in the persistent long-term scale behavior in the solute travel time distributions, even those undergoing retention due to matrix diffusion through implementation and analysis of the model.

54 ENVIRONMENTAL SCIENCES↗