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At least 433 records · Page 24

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NASA NTRS2017

Interaction of Delaminations and Matrix Cracks in a CFRP Plate, Part II: Simulation Using an Enriched Shell Finite Element Model

Numerical simulations are presented of a recently developed test which creates multiple delaminations in a CFRP laminate specimen that grow and interact via transverse matrix cracks. A novel shell element enriched with the Floating Node Method, and a damage algorithm based on the Virtual Crack Closure Technique, were used to successfully simulate the tests. Additionally, a 3D high mesh fidelity model based on cohesive zones and continuum damage mechanics was used to simulate the tests and act as a representative of other similar state-of-the-art high mesh fidelity modeling techniques to compare to the enriched shell element. The enriched shell and high mesh fidelity models had similar levels of accuracy and generally matched the experimental data. With runtimes of 36 minutes for the shell model and 55 hours for the high mesh fidelity model, the shell model is 92 times faster than the high- fidelity simulation.

Mark W McElroy↗

DOE OSTI2023

Nitrogen fixation as NO x using air plasma coupled with heterogeneous catalysis at atmospheric pressure

Here, this study presents insights into the use of activated Al 2 O 3 catalysts to improve the energy efficiency of NO x production in atmospheric pressure air plasma. The introduction of catalysts in the direct current glow discharge system reduces the energy cost of NO x production by up to 45% at low gas flow rates. Notably, even when positioned away from the plasma zone, the catalyst enhanced NO x production, suggesting a significant role for the catalytic activation of downstream neutral species. The study also introduced a novel approach involving an air plasma jet infused with floating catalyst powder. This method significantly increased energy efficiency at higher discharge currents, with an associated energy cost of 2.9 MJ/mol for NO x production.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS2014

Ionosphere Plasma State Determination in Low Earth Orbit from International Space Station Plasma Monitor

A plasma diagnostic package is deployed on the International Space Station (ISS). The system - a Floating Potential Measurement Unit (FPMU) - is used by NASA to monitor the electrical floating potential of the vehicle to assure astronaut safety during extravehicular activity. However, data from the unit also reflects the ionosphere state and seems to represent an unutilized scientific resource in the form of an archive of scientific plasma state data. The unit comprises a Floating Potential probe and two Langmuir probes. There is also an unused but active plasma impedance probe. The data, at one second cadence, are collected, typically for a two week period surrounding extravehicular activity events. Data is also collected any time a visiting vehicle docks with ISS and also when any large solar events occur. The telemetry system is unusual because the package is mounted on a television camera stanchion and its data is impressed on a video signal that is transmitted to the ground and streamed by internet to two off center laboratory locations. The data quality has in the past been challenged by weaknesses in the integrated ground station and distribution systems. These issues, since mid‐2010, have been largely resolved and the ground stations have been upgraded. Downstream data reduction has been developed using physics based modeling of the electron and ion collecting character in the plasma. Recursive algorithms determine plasma density and temperature from the raw Langmuir probe current voltage sweeps and this is made available in real time for situational awareness. The purpose of this paper is to describe and record the algorithm for data reduction and to show that the Floating probe and Langmuir probes are capable of providing long term plasma state measurement in the ionosphere. Geophysical features such as the Appleton anomaly and high latitude modulation at the edge of the Auroral zones are regularly observed in the nearly circular, 51 deg inclined, 400 km altitude ISS orbit. Evidence of waves in the ion collection current data is seen in geographic zones known to exhibit the spread‐F phenomenon. An anomaly in the current collection characteristic of the cylindrical probe appears also too be organized by the geomagnetic field.

Kramer, Leonard↗

NASA NTRS2018

Simulating the Clamped Tapered Beam Specimen Under Quasi-Static and Fatigue Loading Using Floating Node Method

As part of the NASA Advanced Composites Project (ACP), a sub-element has been designed to provide validation data for progressive damage analysis models. The clamped tapered beam is a cross-ply laminated composite specimen designed to validate the simulation of the onset of matrix cracks and their interaction with delaminations, including delamination migration. A tapered geometry was used to localize the first damage occurrence in the tapered region, without prescribing an initial crack. The boundary and loading conditions were chosen to favor delamination growth and subsequent migration after the first damage occurrence. The typical sequence of events consists of a matrix crack located at the tapered region, leading to delamination onset, followed by delamination growth and subsequent delamination migration to a different interface via a dominant matrix crack. The Clamped Tapered Beam (CTB) was tested in both quasi-static and fatigue regimes. The results obtained are used in this study to assess and validate a methodology based on the Floating Node Method (FNM) implemented as an Extended Interface Element. In this methodology, quasi-static and fatigue damage formation and development are modeled by combining FNM to represent crack networks, with Directional Cohesive Zone Elements (DCZE) and Virtual Crack Closure Technique (VCCT), respectively. Qualitatively, the methodology is capable of predicting the sequence of events and overall failure morphology. Quantitatively, the simulation results generally bound the experimental data, based on the range of the characterization data used. In this paper, the results from quasi static and fatigue simulations are compared and correlated with experimental data.

Seshadri, B. R.↗

NASA NTRS2019

Antarctic Ice Shelf Thickness Change from Multimission Lidar Mapping

We calculate rates of ice thickness change and bottom melt for ice shelves in West Antarctica and the Antarctic Peninsula from a combination of elevation measurements from NASA–CECS Antarctic ice mapping campaigns and NASA Operation IceBridge corrected for oceanic processes from measurements and models, surface velocity measurements from synthetic aperture radar, and high-resolution outputs from regional climate models. The ice thickness change rates are calculated in a Lagrangian reference frame to reduce the effects from advection of sharp vertical features, such as cracks and crevasses, that can saturate Eulerian-derived estimates. We use our method over different ice shelves in Antarctica, which vary in terms of size, repeat coverage from airborne altimetry, and dominant processes governing their recent changes. We find that the Larsen-C Ice Shelf is close to steady state over our observation period with spatial variations in ice thickness largely due to the flux divergence of the shelf. Firn and surface processes are responsible for some short-term variability in ice thickness of the Larsen-C Ice Shelf over the time period. The Wilkins Ice Shelf is sensitive to short-timescale coastal and upper-ocean processes, and basal melt is the dominant contributor to the ice thickness change over the period. At the Pine Island Ice Shelf in the critical region near the grounding zone, we find that ice shelf thickness change rates exceed 40m/yr, with the change dominated by strong submarine melting. Regions near the grounding zones of the Dotson and Crosson ice shelves are decreasing in thickness at rates greater than 40m/yr, also due to intense basal melt. NASA–CECS Antarctic ice mapping and NASA Operation IceBridge campaigns provide validation datasets for floating ice shelves at moderately high resolution when coregistered using Lagrangian methods.

Sutterley, Tyler C.↗

DOE OSTI2022

Two-Phase Flow Mechanisms Controlling CO2 Intrusion into Shaly Caprock

Abstract Geologic carbon storage in deep saline aquifers has emerged as a promising technique to mitigate climate change. CO 2 is buoyant at the storage conditions and tends to float over the resident brine jeopardizing long-term containment goals. Therefore, the caprock sealing capacity is of great importance and requires detailed assessment. We perform supercritical CO 2 injection experiments on shaly caprock samples (intact caprock and fault zone) under representative subsurface conditions. We numerically simulate the experiments, satisfactorily reproducing the observed evolution trends. Simulation results highlight the dynamics of CO 2 flow through the specimens with implications to CO 2 leakage risk assessment in field practices. The large injection-induced overpressure drives CO 2 in free phase into the caprock specimens. However, the relative permeability increase following the drainage path is insufficient to provoke an effective advancement of the free-phase CO 2 . As a result, the bulk CO 2 front becomes almost immobile. This implies that the caprock sealing capacity is unlikely to be compromised by a rapid capillary breakthrough and the injected CO 2 does not penetrate deep into the caprock. In the long term, the intrinsically slow molecular diffusion appears to dominate the migration of CO 2 dissolved into brine. Nonetheless, the inherently tortuous nature of shaly caprock further holds back the diffusive flow, favoring safe underground storage of CO 2 over geological time scales.

58 GEOSCIENCES↗

DOE OSTI2021

A Study of Cost-Saving Potential of Load Flexibility Measures in Grid-Interactive Multifamily Buildings

With recent advances in smart technologies, more and more smart devices are penetrating the residential and commercial buildings market. The introduction of these smart devices is also helping IoT companies emerge with load aggregator roles in the sector. With more utility companies on the track of supporting OpenADR protocols, the aggregators could play a significant role in providing load flexibilities by automatically responding to demand response (DR) events and coordinating load flexibility measures between customers. This would benefit utility companies by reducing stress on the grid during critical peak demand hours as well as customers by allowing them to utilize utility rate structures advantageous to those able to reduce electric usage during high-demand hours. This study evaluates cost and energy savings from adopting multiple load flexibility measures in multifamily buildings. Combinations of different load flexibility measures, including space temperature floating, light dimming, automatic window shading, and water heater temperature floating, are considered. The simulations are performed using OpenStudio®, an open-source U.S. Department of Energy (DOE) simulation platform. For the case study, we used a midrise apartment building with weather conditions from Denver, Colorado. To compare climate zone differences, simulations were also performed for Los Angeles, California, and Chicago, Illinois. Initial results indicate that the application of automated load flexibility measures without careful consideration of dispatching strategies and DR program enrollments could significantly affect the savings. To get meaningful cost savings, aggregators need to encourage tenant awareness to curtail energy usage through occupant behavior in addition to dispatching automatic load flexibility measures. The outcomes from this study are believed to help load aggregators understand the risks and benefits of load flexibility opportunities.

building energy modeling↗

DOE OSTI2023

Year-long buoy-based observations of the air–sea transition zone off the US west coast

Abstract. Two buoys equipped with Doppler lidars owned by the US Department of Energy (DOE) were deployed off the coast of California in autumn of 2020 by Pacific Northwest National Laboratory. The buoys collected data for an entire annual cycle at two offshore locations proposed for offshore wind development by the Bureau of Ocean Energy Management. One of the buoys was deployed approximately 50 km off the coast near Morro Bay in central California in 1100 m of water. The second buoy was deployed approximately 40 km off Humboldt County in northern California in 625 m of water. The buoys provided the first-ever continuous measurements of the air–sea transition zone off the coast of California. The atmospheric and oceanographic characteristics of the area and estimates of annual energy production at both the Morro Bay and Humboldt wind energy areas show that both locations have a high wind energy yield and are prime locations for future floating offshore wind turbines. This article provides a description and comprehensive analysis of the data collected by the buoys, and a final post-processed dataset is uploaded to a data archive maintained by the DOE. Additional analysis was conducted to show the value of the data collected by the DOE buoys. All post-processed data from this study are available on the Wind Data Hub website: https://a2e.energy.gov/data# (last access: 14 September 2023). Near-surface, wave, current, and cloud datasets for Humboldt and Morro Bay are provided at https://doi.org/10.21947/1783807 (Krishnamurthy and Sheridan, 2023b) and https://doi.org/10.21947/1959715 (Krishnamurthy and Sheridan, 2023a), respectively. Lidar datasets for Humboldt and Morro Bay are provided at https://doi.org/10.21947/1783809 (Krishnamurthy and Sheridan, 2023d) and https://doi.org/10.21947/1959721 (Krishnamurthy and Sheridan, 2023c), respectively.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1985

The magma ocean concept and lunar evolution

The model of lunar evolution in which the anorthositic plagioclase-rich oldest crust of the moon is formed over a period of 300 Myr or less by crystallization as it floats on a global ocean of magma tens or hundreds of km thick is examined in a review of petrological and theoretical studies. Consideration is given to the classification of lunar rocks, the evidence for primordial deep global differentiation, constraints on the depth of the molten zone, the effects of pressure on mineral stability relationships, mainly-liquid vs mainly-magmifer ocean models, and the evidence for multiple ancient differentiation episodes. A synthesis of the model of primordial differentiation and its aftereffects is presented, and the generalization of the model to the earth and to Mars, Mercury, Venus, and the asteroids is discussed.

Warren, P. H.↗

NASA NTRS2013

Methanol Droplet Combustion in Oxygen-Inert Environments in Microgravity

The Flame Extinguishment (FLEX) experiment that is currently underway in the Combustion Integrated Rack facility onboard the International Space Station is aimed at understanding the effects of inert diluents on the flammability of condensed phase fuels. To this end, droplets of various fuels, including alkanes and alcohols, are burned in a quiescent microgravity environment with varying amounts of oxygen and inert diluents to determine the limiting oxygen index (LOI) for these fuels. In this study we report experimental observations of methanol droplets burning in oxygen-nitrogen-carbon dioxide and oxygen-nitrogen-helium gas mixtures at 0.7 and 1 atmospheric pressures. The initial droplet size varied between approximately 1.5 mm and 4 mm to capture both diffusive extinction brought about by insufficient residence time at the flame and radiative extinction caused by excessive heat loss from the flame zone. The ambient oxygen concentration varied from a high value of 30% by volume to as low as 12%, approaching the limiting oxygen index for the fuel. The inert dilution by carbon dioxide and helium varied over a range of 0% to 70% by volume. In these experiments, both freely floated and tethered droplets were ignited using symmetrically opposed hot-wire igniters and the burning histories were recorded onboard using digital cameras, downlinked later to the ground for analysis. The digital images yielded droplet and flame diameters as functions of time and subsequently droplet burning rate, flame standoff ratio, and initial and extinction droplet diameters. Simplified theoretical models correlate the measured burning rate constant and the flame standoff ratio reasonably well. An activation energy asymptotic theory accounting for time-dependent water dissolution or evaporation from the droplet is shown to predict the measured diffusive extinction conditions well. The experiments also show that the limiting oxygen index for methanol in these diluent gases is around 12% to 13% oxygen by volume.

Nayagam, Vedha↗

NASA NTRS2012

Plasma Potential and Langmuir Probe Measurements in the Near-field Plume of the NASA 300M Hall Thruster

In order to aid in the design of high-power Hall thrusters and provide experimental validation for existing modeling efforts, plasma potential and Langmuir probe measurements were performed in the near-field plume of the NASA 300M Hall thruster. A probe array consisting of a Faraday probe, Langmuir probe, and emissive probe was used to interrogate the plume from approximately 0.1 - 2.0 DT,m downstream of the thruster exit plane at four operating conditions: 300 V, 400 V, and 500 V at 20 kW as well as 300 V at 10 kW. Results show that the acceleration zone and high-temperature region were contained within 0.3 DT,m from the exit plane at all operating conditions. Isothermal lines were shown to strongly follow magnetic field lines in the nearfield, with maximum temperatures ranging from 19 - 27 eV. The electron temperature spatial distribution created large drops in measured floating potentials in front of the magnetic pole surfaces where the plasma density was small, which suggests strong sheaths at these surfaces. The data taken have provided valuable information for future design and modeling validation, and complements ongoing internal measurement efforts on the NASA 300 M.

Herman, Daniel A↗

DOE OSTI2016

GLOBULAR CLUSTERS AS CRADLES OF LIFE AND ADVANCED CIVILIZATIONS

Globular clusters are ancient stellar populations in compact dense ellipsoids. There is no star formation and there are no core-collapse supernovae, but several lines of evidence suggest that globular clusters are rich in planets. If so, and if advanced civilizations can develop there, then the distances between these civilizations and other stars would be far smaller than typical distances between stars in the Galactic disk, facilitating interstellar communication and travel. The potent combination of long-term stability and high stellar densities provides a globular cluster opportunity. Yet the very proximity that promotes interstellar travel also brings danger, as stellar interactions can destroy planetary systems. We find, however, that large portions of many globular clusters are “sweet spots,” where habitable-zone planetary orbits are stable for long times. Globular clusters in our own and other galaxies are, therefore, among the best targets for searches for extraterrestrial intelligence (SETI). We use the Drake equation to compare the likelihood of advanced civilizations in globular clusters to that in the Galactic disk. We also consider free-floating planets, since wide-orbit planets can be ejected to travel through the cluster. Civilizations spawned in globular clusters may be able to establish self-sustaining outposts, reducing the probability that a single catastrophic event will destroy the civilization. Although individual civilizations may follow different evolutionary paths, or even be destroyed, the cluster may continue to host advanced civilizations once a small number have jumped across interstellar space. Civilizations residing in globular clusters could therefore, in a sense, be immortal.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2012

Plasma Potential and Langmuir Probe Measurements in the Near-field Plume of the NASA-300M Hall Thruster

In order to aid in the design of high-power Hall thrusters and provide experimental validation for existing modeling efforts, plasma potential and Langmuir probe measurements were performed in the near-field plume of the NASA-300M Hall thruster. A probe array consisting of a Faraday probe, Langmuir probe, and emissive probe was used to interrogate the plume from approximately 0.1 - 2.0 mean thruster diameters downstream of the thruster exit plane at four operating conditions: 300 V, 400 V, and 500 V at 20 kW as well as 300 V at 10 kW. Results show that the acceleration zone and high-temperature region were contained within 0.3 mean thruster diameters from the exit plane at all operating conditions. Isothermal lines were shown to strongly follow magnetic field lines in the near-field, with maximum temperatures ranging from 19 - 27 eV. The electron temperature spatial distribution created large drops in measured floating potentials in front of the magnetic pole surfaces where the plasma density was low, which suggests strong sheaths at these surfaces. The data taken have provided valuable information for future design and modeling validation, and complements ongoing internal measurement efforts on the NASA-300M.

Herman, Daniel A.↗

NASA NTRS1981

Solar extinction radiometry

Work on the spectral line parameters of hydroxyl radical band was completed. The UV-visible data obtained during 1977 balloon flights were used for zone quantification. The region between from 3100 A to 3500 A appears to be the best region to use for determining ozone columns with the three wavelength method. Ozone volume mixing ratios determined for the 1977 data were compared with standard middle latitude ozone profiles. Numerous high and low Sun scans were obtained during ascent and from float altitude (1981 balloon flight) at 0.003 A resolution in the 3068 A to 3089 A region. The spectra are being studied for OH identification and quantification.

Goldman, A.↗

DOE OSTI2023

Modeling Assessment of Residential Air-to-Water Heat Pumps Coupled with Cooling Thermal Storage

This study explored the performance and operating cost viability of air-to-water heat pumps (AWHPs) coupled with thermal energy storage (TES) in efficient new residential construction. AWHPs are an emerging technology in this country, but offer promise in terms of high efficiency, fully contained and factory charged outdoor refrigeration system, and hydronic delivery capabilities, which facilitates zoning, ducts in conditioned space, and TES integration for summer load-shifting. Although this AWHP+TES strategy is not yet mainstream, the authors feel that in ten years as decarbonization efforts proceed and TOU rates become more common, strategies such as this will be more accessible. Validated EnergyPlus simulation models were developed based on detailed monitoring data collected over several years at Pacific Gas and Electric's CVRH laboratory test homes located in Stockton, California. One of the CVRH test homes (1,962 ft 2 two-story) had been testing various AWHP systems and configurations over the past six years. The validated model was then updated with high efficiency IECC ZERH envelope and component requirements for climate zones 1-5, including ducts in conditioned space thermal distribution. Simulations were completed for the 1,962 ft 2 home in each climate zone for a minimum efficiency ASHP, an AWHP coupled with a fan coil, and an AWHP coupled with TES sized to eliminate summer on-peak compressor operation. To maintain consistency in reporting energy use estimates, all cases were run with a similar indoor thermostat control strategy to pre-cool the house below the nominal 76 degrees Fahrenheit set point prior to the on-peak period and float slightly above the set point during the peak period. The AWHP+TES configuration was controlled to alternately condition the indoor space or to charge the TES tanks prior to the beginning of the on-peak. Three composite TOU rates were developed based on existing TOU rates across the U.S. to provide differing economic scenarios to evaluate customer bill impacts throughout the summer. Two of the TOU rates had short three-hour peak periods, while the third rate had a longer seven-hour duration peak period. AWHP modeling projections were based on the observed field performance of the Chiltrix CX34 variable speed unit. Other products on the market or entering the market in the near term would likely perform differently.

25 ENERGY STORAGE↗

DOE OSTI2023

On the melt pool dynamic of voxel-controlled metal matrix composites via hybrid additive manufacturing: Laser powder bed fusion and ink-jetting

In this study, the effect of the addition of reinforcement nanoparticles to the 316L matrix by adopting ex-situ and in-situ method (drop on demand jetting) to produce 316L/Al 2 O 3 nanocomposite was investigated. In the ex-situ method, the Al 2 O 3 nanoparticles (NPs) were lightly mixed with 316L powder and processed by laser powder bed fusion. In the in-situ method, an ethanol-based ink containing Al 13 nanoclusters (NCs) was added to 316L powder and then processed by laser. Both ex-situ and in-situ method produced nanocomposites with Al-Si-Mn-O-enriched precipitations within the 316L matrix. The addition of NPs/NCs to the 316L matrix, altered the geometrical characteristic of the single-track melt pools. At the same laser power, with increasing the amount of Al 2 O 3 NPs and Al 13 NCs the melt pool deepened due to reduced thermal conductivity and prolonged liquid presence. Further, as a result, 316L/1 wt% Al 13 NCs deposited single track showed larger grains in comparison to 316L single track. At a high laser power of 150W, the Marangoni flow and the buoyancy force caused the nanoparticles to agglomerate and float to the top surface of tracks; therefore, the wt% fraction of precipitation was drastically reduced due to the loss of Al. The 316L/Al 2 O 3 NPs and 316L/Al 13 NCs exhibited the microhardness of 285 ± 13 HV and 293 ± 7 HV, respectively, higher than the deposited 316L single track, 265 ± 15 HV. Lastly, a hybrid LPBF+ink-jet printer was adopted to selectively change the composition of different zones by adding Al 13 NCs ink to 316L and producing a voxel-controlled metal matrix composite.

316L↗

NASA NTRS2017

Simulating Matrix Crack and Delamination Interaction in a Clamped Tapered Beam

Blind predictions were conducted to validate a discrete crack methodology based on the Floating Node Method to simulate matrix-crack/delamination interaction. The main novel aspects of the approach are: (1) the implementation of the floating node method via an 'extended interface element' to represent delaminations, matrix-cracks and their interaction, (2) application of directional cohesive elements to infer overall delamination direction, and (3) use of delamination direction and stress state at the delamination front to determine migration onset. Overall, good agreement was obtained between simulations and experiments. However, the validation exercise revealed the strong dependence of the simulation of matrix-crack/delamination interaction on the strength data (in this case transverse interlaminar strength, YT) used within the cohesive zone approach applied in this work. This strength value, YT, is itself dependent on the test geometry from which the strength measurement is taken. Thus, choosing an appropriate strength value becomes an ad-hoc step. As a consequence, further work is needed to adequately characterize and assess the accuracy and adequacy of cohesive zone approaches to model small crack growth and crack onset. Additionally, often when simulating damage progression with cohesive zone elements, the strength is lowered while keeping the fracture toughness constant to enable the use of coarser meshes. Results from the present study suggest that this approach is not recommended for any problem involving crack initiation, small crack growth or multiple crack interaction.

De Carvalho, N. V.↗

DOE OSTI2025

OC7 phase I: Toward practical sea-state-dependent modeling of hydrodynamic viscous drag and damping

Here, this article presents a collaborative research campaign under the OC7 project on refining the engineering modeling approach for hydrodynamic viscous drag and damping on floating wind platforms, focusing on the adjustment of hydrodynamic drag and damping coefficients for different sea states. The participant simulation results show significant improvements over the previous OC6 project in predicting the low-frequency resonance motion under nonoperational conditions. The improvements are mainly due to enhanced modeling, including the adoption of wave stretching, and directly tuning the coefficients to measured platform motion in waves instead of free decay. For accurate predictions of mean- and slow-drift motion, the better performing models use a decreasing column splash zone drag coefficient and increasing surge damping/drag with increasing wave height. The model tuning for heave and pitch resonance shows less consistency. Generally, both quadratic drag and additional heave or pitch damping are needed for accurate predictions. Alternatively, a quadratic drag formulation with velocity filtering for the rectangular pontoons leads to improved predictions without additional damping. This model is also potentially more predictive, requiring minimal adjustment to its parameters for different conditions.

17 WIND ENERGY↗