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At least 1,549 records · Page 86

All sources NASA NTRS DOE OSTI

DOE OSTI2021

Numerical investigation of active control of tearing mode by magnetic coils and the role of Δ'

Magnetic feedback stabilization of the tearing mode (TM) is numerically investigated, utilizing the MARS-F code (Liu et al 2000 Phys. Plasmas 7 3681) for toroidal tokamak equilibria. With control coil configurations assumed in this study, magnetic feedback partially or fully stabilizes the TM, with either vanishing or finite equilibrium pressure. The best control is achieved by the combination of internal active coils and internal poloidal sensors. The internal and external tearing indices are evaluated for the close-loop system, based on the MARS-F computed mode eigenvalue and eigenfunction, respectively. In the absence of the favorable curvature effect, these two indices are real-valued and quantitatively agree well with each other. For the equilibrium with finite pressure gradient at the mode rational surface, the favorable average curvature effect becomes important and the close-loop tearing index also becomes complex-valued, partly due to interaction of the feedback system with the dissipative wall eddy current response. Isolating the inner layer and outer region response to magnetic feedback, with either proportional or proportional-derivative actions, allows to establish that feedback stabilization of the TM occurs mainly due to modification of the behavior of the external ideal solution, further confirming the analytic result reported in He et al 2021 Phys. Plasmas 28 012504.

Physics↗

DOE OSTI2022

Driven superconducting vortex dynamics in systems with twofold anisotropy in the presence of pinning

Abstract We examine the dynamics of superconducting vortices with twofold anisotropic interaction potentials driven over random pinning, and compare the behavior under drives applied along the hard and the soft anisotropy directions. As the driving force increases, the number of topological defects reaches a maximum near the depinning threshold, and then decreases as the vortices form one-dimensional (1D) chains. This coincides with a transition from a pinned nematic to a moving smectic aligned with the soft anisotropy direction. The system is generally more ordered when the drive is applied along the soft direction of the anisotropy. For driving along the hard direction, there is a critical value of the twofold anisotropy above which the system remains aligned with the soft direction. Hysteretic behavior appears upon cycling the driving force, with 1D vortex chains persisting during the decreasing leg below the threshold for chain formation for increasing drive. More anisotropic systems have a greater amount of structural disorder in the moving state. For lower anisotropy, the system forms a moving smectic-A state, while at higher anisotropy, a moving nematic state appears instead.

36 MATERIALS SCIENCE↗

NASA NTRS1993

The FK5 Extension on the FK4 system

This paper reports on the computations necessary to place the FK5 Extension (epoch of place B1950.0) on the B1950.0/FK4 system from its published form and the availability of this version of the catalog. An application of the utility of the new version of the FK5 Extension, to the AGK3U, is given too. This confirms both the system of the AGK3U and the estimated values of its equatorial coordinate and proper motion mean errors. In addition, we have fully exploited the flexibility of the method of infinitely overlapping circles to compute a mean epoch of place/FK4 version of the FK5 Extension which we also make available. These modifications include taking into account the changes induced by the new system of general precession constants, adjusting for the e-terms of aberration, correcting for both the FK5/FK4 equinox offset and motion, and the FK5/FK4 positional and the proper motion systematic differences.

Lattanzi, M. G.↗

DOE OSTI2020

Heterostructure design to achieve high quality, high density GaAs 2D electron system with g -factor tending to zero

Hydrostatic pressure is a useful tool that can tune several key parameters in solid state materials. For example, the Landé g-factor in GaAs two-dimensional electron systems (2DESs) is expected to change from its bulk value g ≃ -0.44 to zero and even to positive values under sufficiently large hydrostatic pressure. Although this presents an intriguing platform to investigate electron-electron interaction in a system with g = 0, studies are quite limited because the GaAs 2DES density decreases significantly with increasing hydrostatic pressure. Here, we show that a simple model, based on pressure-dependent changes in the conduction band alignment, quantitatively explains this commonly observed trend. Furthermore, we demonstrate that the decrease in the 2DES density can be suppressed by more than a factor of 3 through an innovative heterostructure design.

Physics↗

DOE OSTI2020

Uncertainty about the Uncertainty [Slides]

A golden standard in science is to repeat an experiment a statistically significant number of times, recording data using the same set of detectors and the same data analysis methodology. In such case experimental error includes both the range of true values generated by repetitions of the experiment, and measurement uncertainty caused by the detector. They are independent. It is a huge and too frequently used simplification, to assume that one can measure multiple repetitions of an identical experiment, resulting in identical true experimental value. Repetitions, as similar is it is experimentally achievable result in a range of the true values rather than in a single value. When modern, very sensitive and well calibrated measurement systems are used, this range is not negligible, and sometimes dominates, in comparison to the measurement uncertainty. Range of true values depends on the physics of the experiment, while measurement uncertainty depends on the measurement method (properties of the detector not of the experiment). When data from one–of–a kind experiment are analyzed, only the measurement uncertainty is reported. It gives no information about the range, in which the true values of experiment would spread if the experiment was repeated. A frequently used approximation, that if a physical quantity is measured as a function of time, only measurement of this quantity, produces uncertainty is also in some real experiments fare to strong. Example: In reaction history time measurement uncertainty propagated to alpha dominated under certain conditions over the flux measurement uncertainty propagated to alpha. Reliability of a data point is in general independent from its measurement uncertainty. However, in practice reliable measurement methods frequently have high measurement uncertainty, while low reliability methods are applied to limit measurement uncertainty. Comparison of reliable data with high measurement uncertainty to not so reliable data measured with low uncertainty is discussed – in different scenarios different data analysis methods are applicable.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2023

AI-Based Faster-Than-Real-Time Stability Assessment of Large Power Systems with Applications on WECC System

Achieving clean energy goals will require significant advances in regard to addressing the computational needs for next-generation renewable-dominated power grids. One critical obstacle that lies in the way of transitioning today’s power grid to a renewable-dominated power grid is the lack of a faster-than-real-time stability assessment technology for operating a fast-changing power grid. This paper proposes an artificial intelligence (AI) -based method that predicts the system’s stability margin information (e.g., the frequency nadir in the frequency stability assessment and the critical clearing time (CCT) value in the transient stability assessment) directly from the system operating conditions without performing the conventional time-consuming time-domain simulations over detailed dynamic models. Since the AI method shifts the majority of the computational burden to offline training, the online evaluation is extremely fast. This paper has tested the AI-based stability assessment method using multiple dispatch cases that are converted and tuned from actual dispatch cases of the Western Electricity Coordinating Council (WECC) system model with more than 20,000 buses. The results show that the AI-based method could accurately predict the stability margin of such a large power system in less than 0.2 milliseconds using the offline-trained AI agent. Therefore, the proposed method has great potential to achieve faster-than-real-time stability assessment for practical large power systems while preserving sufficient accuracy.

24 POWER TRANSMISSION AND DISTRIBUTION↗

NASA NTRS1990

Graphite fluoride fibers and their applications in the space industry

Characterization and potential space applications of graphite fluoride fibers from commercially available graphitized carbon fibers are presented. Graphite fluoride fibers with fluorine to carbon ratios of 0.65 and 0.68 were found to have electrical resistivity values of 10(exp 4) and 10(exp 11) Ohms-cm, respectively, and thermal conductivity values of 24 and 5 W/m-K, respectively. At this fluorine content range, the fibers have tensile strength of 0.25 + or - 0.10 GPa (36 + or - 14 ksi), Young's modulus of 170 + or - 30 GPa (25 + or - 5 Msi). The coefficient of thermal expansion value of a sample with fluorine to carbon ratio of 0.61 was found to be 7 ppm/C. These properties change and approach the graphite value as the fluorine content approach 0. Electrically insulative graphite fluoride fiber is at least five times more thermally conductive than fiberglass. Therefore, it can be used as a heat sinking printed circuit board material for low temperature, long life power electronics in spacecraft. Also, partially fluorinated fiber with tailor-made physical properties to meet the requirements of certain engineering design can be produced. For example, a partially fluorinated fiber could have a predetermined CTE value in -1.5 to 7 ppm/C range and would be suitable for use in solar concentrators in solar dynamic power systems. It could also have a predetermined electrical resistivity value suitable for use as a low observable material. Experimental data indicate that slightly fluorinated graphite fibers are more durable in the atomic oxygen environment than pristine graphite. Therefore, fluorination of graphite used in the construction of spacecraft that would be exposed to the low Earth orbit atomic oxygen may protect defect sites in atomic oxygen protective coatings and therefore decrease the rate of degradation of graphite.

Hung, Ching-Chen↗

NASA NTRS1992

The LiAl/FeS2 battery power source for the future

Advanced high power density rechargeable batteries are currently under development. These batteries have the potential of greatly increasing the power and energy densities available for space applications. Depending on whether the system is optimized for high power or high energy, values up to 150 Wh/kg and 2100 W/kg (including hardware) are projected. This is due to the fact that the system uses a high conductivity molten salt electrolyte. The electrolyte also serves as a separator layer with unlimited freeze thaw capabilities. Life of 1000 cycles and ten calendar years is projected. The electrochemistry consists of a lithium aluminum alloy negative electrode, iron disulfide positive electrode, and magnesium oxide powder immobilized molten salt electrolyte. Processed powders are cold compacted into circular discs which are assembled into bipolar cell hardware with peripheral ceramic salts. The culmination of the work will be a high energy battery of 40 kWh and a high power battery of 28 kWh.

Briscoe, J. Douglass↗

NASA NTRS1980

Solar energy system performance evaluation: Seasonal report for IBM System 1B, Carlsbad, New Mexico

A hot solar heating and hot water system's operational performance from April 1979 through March 1980 is evaluated. The space heating and hot water loads were near expected values for the year. Solar energy provided 43 percent of the space heating and 53 percent of the hot water energy. The system did not meet the total system solar fraction design value of 69 percent because of a combination of higher estimated space heating load than was actually encountered and the apportioning of solar energy between the space heating and the domestic hot water loads. System losses and high building temperatures also contributed to this deviation. Total net savings were 23.072 million BTUs. Most of the energy savings came during the winter months, but hot water savings were sufficient to justify running the system during the summer months.

Source record↗

DOE OSTI2020

Solid Electrolytes for Li–S Batteries: Solid Solutions of Poly(ethylene oxide) with Li x PON- and Li x SiPON-Based Polymers

We report here efforts to synthesize free-standing, dry polymer electrolytes that exhibit superior ionic conductivities at ambient for Li–S batteries. Co-dissolution of poly(ethylene oxide) (PEO) (M n 900k) with Li x PON and Li x SiPON polymer systems at a ratio of approximately 3:2 followed by casting provides transparent, solid-solution films 25–50 μm thick, lowering PEO crystallinity, and providing measured impedance values of 0.1–2.8 × 10 –3 S/cm at ambient. These values are much higher than simple PEO/Li + salt systems. These solid-solution polymer electrolytes (PEs) are (1) thermally stable to 100 °C; (2) offer activation energies of 0.2–0.5 eV; (3) suppress dendrite formation; and (4) enable the use of lithium anodes at current densities as high as 3.5 mAh/cm 2 . Here, galvanostatic cycling of SPAN/PEs/Li cell (SPAN = sulfurized, carbonized polyacrylonitrile) shows discharge capacities of 1000 mAh/g sulfur at 0.25C and 800 mAh/g sulfur at 1C with high coulumbic efficiency over 100 cycles.

25 ENERGY STORAGE↗

NASA NTRS1984

Changes of LISM Characteristics in the Heliospheric Interface

The LISM properties can be deduced from observations of interstellar neutral gases in the inner solar system. Parameters accessible by this method are the interstellar wind vector and the densities and temperatures of hydrogen and helium, implying also the deduction of the relative abundance ratios and the degree of ionization in the LISM. Direct inference from observations, for example resonance luminescence measurements of Ly-alpha and He-58.4 nm radiation, yields values appropriate only for the inner solar system, i.e. for the regions within the heliopause dominated by the solar wind plasma. Particularly the subsonic LISM plasma interface ahead of the heliopause causes profound changes in the properties of the neutral LISM gas traversing this region. Mainly p-H charge exchange processes ive rise to the destruction of primary hydrogen and the production of secondary hydrogen atoms, the net effect being a depletion of the neutral hydrogen component of the LISM by about 50%. Details on the depletion mechanisms, the hydrogen and oxygen extinctions, and the consequences for the Ly-alpha resonance luminescence intensity interpretations are presented.

Ripken, H. W.↗

NASA NTRS1950

Method for determining the frequency-response characteristics of an element or system from the system transient output response to a known input function

A method is presented for the determination of the frequency-response characteristics of an element or system by utilizing the transient output response to a known but arbitrary input to the system. Since the application of special inputs, such as step functions or sinusoids, is often imperfect or impractical, a method for utilizing arbitrary inputs is desirable. Simple flight-test data may be reduced by this method to give the frequency response of an aircraft. Examples are given as determinations of aircraft frequency responses; however, the method can be applied to any type of dynamic system, such as automatic-control components, vibration-absorption equipment, and many types of instruments. The method requires that the arbitrary input function tend to a finite value after a finite time and that the system or element output be measured as a representative quantity having a static sensitivity. (author)

Curfman, Howard J↗

NASA NTRS1999

Thermal Conductivity and Elastic Modulus Evolution of Thermal Barrier Coatings under High Heat Flux Conditions

Laser high heat flux test approaches have been established to obtain critical properties of ceramic thermal barrier coatings (TBCs) under near-realistic temperature and thermal gradients that may he encountered in advanced engine systems. Thermal conductivity change kinetics of a thin ceramic coating were continuously monitored in real time at various test temperatures. A significant thermal conductivity increase was observed during the laser simulated engine heat flux tests. For a 0.25 mm thick ZrO2-8%Y2O3 coating system, the overall thermal conductivity increased from the initial value of 1.0 W/m-K to 1. 15 W/m-K, 1. 19 W/m-K and 1.5 W/m-K after 30 hour testing at surface temperatures of 990C, 1100C, and 1320C. respectively. Hardness and modulus gradients across a 1.5 mm thick TBC system were also determined as a function of laser testing time using the laser sintering/creep and micro-indentation techniques. The coating Knoop hardness values increased from the initial hardness value of 4 GPa to 5 GPa near the ceramic/bond coat interface, and to 7.5 GPa at the ceramic coating surface after 120 hour testing. The ceramic surface modulus increased from an initial value of about 70 GPa to a final value of 125 GPa. The increase in thermal conductivity and the evolution of significant hardness and modulus gradients in the TBC systems are attributed to sintering-induced micro-porosity gradients under the laser-imposed high thermal gradient conditions. The test techniques provide a viable means for obtaining coating data for use in design, development, stress modeling, and life prediction for various thermal barrier coating applications.

Zhu, Dongming↗

DOE OSTI2025

Hybrid Power Plants for Energy Resilience: A Case Study

As renewable energy technologies are increasingly adopted, they pose an opportunity to improve the sustainability and resilience of distributed grids, especially when their design and operation is coordinated as a hybrid power plant. When included in hybrid power plants, distributed wind turbines in particular have the potential to enhance the resilience of distributed grids in areas with good wind resource, due to their ability to provide more consistent generation and ancillary services as compared to photo-voltaic (PV) solar panels. Despite this benefit, U.S. distributed wind adoption is lower than other comparable renewable energy technologies. In this study, we seek to demonstrate how hybrid power plants that include distributed wind turbines can contribute to distribution grid resilience by meeting loads (especially critical loads) more consistently, increasing reserve capacity, and providing value to customers during outages. To demonstrate these contributions, we integrate three separate frameworks and apply them to a case study in a rural electric cooperative in Iowa. Through this case study, we simulate and compare hybrid power plant design and operation during two hazard events: a tornado that causes a 48-hour distribution outage and a winter weather event that causes a 6-hour generation outage. The inclusion of a hybrid power plant that leverages 1) increased battery duration and 2) advanced forecasting and dispatch strategies that reserve capacity leading up to a hazard event best reduce lost loads as well as diesel consumption that would otherwise be used to meet those loads during short- and long-duration hazard events. Depending on the hybrid power plant capacity and operation, we find that the outage mitigation value of a hybrid power plant (measured in value to customers to avoid an outage and avoided lost revenues for the utility) is significant in both hazard events; adding wind, solar, and battery assets to the existing system adds about $50-$100M in avoided lost load and at least $4-$8k in utility value in the tornado hazard event, and $570k-$2.2M in avoided lost load and at least $220-$650 in utility value in the winter hazard scenario. In both the tornado and winter hazard scenarios, optimizing the operation of the hybrid system for resilience can lend similar value as increasing battery duration by 5 MWh for the lower capacity systems considered.

17 WIND ENERGY↗

DOE OSTI2024

A Local Macroscopic Conservative (LoMaC) Low Rank Tensor Method for the Vlasov Dynamics

Abstract In this paper, we propose a novel Local Macroscopic Conservative (LoMaC) low rank tensor method for simulating the Vlasov-Poisson (VP) system. The LoMaC property refers to the exact local conservation of macroscopic mass, momentum and energy at the discrete level. This is a follow-up work of our previous development of a conservative low rank tensor approach for Vlasov dynamics ( arXiv:2201.10397 ). In that work, we applied a low rank tensor method with a conservative singular value decomposition to the high dimensional VP system to mitigate the curse of dimensionality, while maintaining the local conservation of mass and momentum. However, energy conservation is not guaranteed, which is a critical property to avoid unphysical plasma self-heating or cooling. The new ingredient in the LoMaC low rank tensor algorithm is that we simultaneously evolve the macroscopic conservation laws of mass, momentum and energy using a flux-difference form with kinetic flux vector splitting; then the LoMaC property is realized by projecting the low rank kinetic solution onto a subspace that shares the same macroscopic observables by a conservative orthogonal projection. The algorithm is extended to the high dimensional problems by hierarchical Tuck decomposition of solution tensors and a corresponding conservative projection algorithm. Extensive numerical tests on the VP system are showcased for the algorithm’s efficacy.

Guo, Wei↗

NASA NTRS1996

Earth benefits of interdisciplinary CELSS-related research by the NSCORT in Bioregenerative Life Support

Earth benefits of research from the NSCORT in Bioregenerative Life Support will include the following: development of active control mechanisms for light, CO2, and temperature to maximize photosynthesis of crop plants during important phases of crop development; automation of crop culture systems; creation of novel culture systems for optimum productivity; creation of value-added crops with superior nutritional, yield, and waste-process characteristics; environmental control of food and toxicant composition of crops; new process technologies and novel food products for safe, nutritious, palatable vegetarian diets; creation of menus for healthful vegetarian diets with psychological acceptability; enzymatic procedures to degrade recalcitrant crop residues occurring in municipal waste; control-system strategies to ensure sustainabilty of a CELSS that will enable management of diverse complex systems on Earth.

NASA Discipline Number 93-10↗

DOE OSTI2020

Impacts of uncertain feedstock quality on the economic feasibility of fast pyrolysis biorefineries with blended feedstocks and decentralized preprocessing sites in the Southeastern United States

Abstract This study performs techno‐economic analysis and Monte Carlo simulations (MCS) to explore the effects that variations in biomass feedstock quality have on the economic feasibility of fast pyrolysis biorefineries using decentralized preprocessing sites (i.e., depots that produce pellets). Two biomass resources in the Southeastern United States, that is, pine residues and switchgrass, were examined as feedstocks. A scenario analysis was conducted for an array of different combinations, including different pellet ash control levels, feedstock blending ratios, different biorefinery capacities, and different biorefinery on‐stream capacities, followed by a comparison with the traditional centralized system. MCS results show that, with depot preprocessing, variations in the feedstock moisture and feedstock ash content can be significantly reduced compared with a traditional centralized system. For a biorefinery operating at 100% of its designed capacity, the minimum fuel selling price (MFSP) of the decentralized system is $3.97–$4.39 per gallon gasoline equivalent (GGE) based on the mean value across all scenarios, whereas the mean MFSP for the traditional centralized system was $3.79–$4.12/GGE. To understand the potential benefits of highly flowable pellets in decreasing biorefinery downtime due to feedstock handling and plugging problems, this study also compares the MFSP of the decentralized system at 90% of its designed capacity with a traditional system at 80%. The analysis illustrates that using low ash pellets mixed with switchgrass and pine residues generates a more competitive MFSP. Specifically, for a biorefinery designed for 2,000 oven dry metric ton per day, running a blended pellet made from 75% switchgrass and 25% pine residues with 2% ash level, and operating at 90% of designed capacity could make an MFSP between $4.49 and $4.71/GGE. In contrast, a traditional centralized biorefinery operating at 80% of designed capacity marks an MFSP between $4.72 and $5.28.

09 BIOMASS FUELS↗

DOE OSTI2020

Degradation of the contrast of a short light pulse in a CPA system

We have calculated the effect of four-wave mixing of the main radiation pulse with the background radiation components on the value of the output radiation contrast in a chirped pulse amplification system of petawatt laser facilities. Formulae are presented that make it possible to quantify the contributions of two mechanisms, i.e. Kerr nonlinearity of the refractive index of the amplifying medium and gain saturation. For typical values of the nonlinear refractive index, both contributions are comparable. The possibility of mutual quenching of nonlinear contributions is noted. The influence of spectral filtering of radiation on the output pulse contrast is considered. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗