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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Investigation into the instantaneous centre of rotation for enhanced design of floating offshore wind turbines

The dynamic behaviour of floating offshore wind turbines (FOWTs) involves complex interactions of multivariate loads from wind, waves, and currents, which result in complex motion characteristics. Although methods for analysing global motion responses are well-established, the time- and location-dependent kinematics remain underexplored. This paper investigates the instantaneous centre of rotation (ICR), a point of zero velocity at a time instance of general plane motion. Understanding and strategically positioning the ICR can reduce the dynamic motion in critical structural locations, enhancing the performance and structural robustness of FOWTs. The paper presents a method for computing the ICR using time-domain simulation results and proposes a statistical analysis approach suitable for design studies. Building on prior research, it examines the sensitivity of the ICR to external loading and design features, providing insights into how these factors influence motion response and how the motion response influences the statistics of the ICR, structural loads, and other performance metrics of interest. The study explores two FOWT configurations, a spar and a semisubmersible, identifying design variables that most effectively control the ICR statistics and identifying the ICR statistics most correlated with the responses of interest. Finally, through two case studies, we demonstrate how to apply these new insights in a practical design scenario. By adjusting the design variables most correlated with the ICR (fairlead vertical position and centre of mass for the spar and mooring line length and offset column diameter for the semisubmersible), we successfully modified the designs of the floating support structures to reduce the loads in the mooring lines, tower base, and blade roots, improving the ultimate strength and fatigue characteristics compared to the original designs.

17 WIND ENERGY↗
NASA NTRS1999

Polar/Tide Observations of Field Aligned O(+) Flows at 5000 km Altitude over the Auroral Regions in Comparison to UVI Auroral Images

Measurements of thermal O(+) ion parameters from the Thermal Ion Dynamics Experiment (TIDE) on POLAR obtained near 5000 km altitude are compared with auroral images from the Ultra Violet Imager (UVI), for southern perigee passes. Ion parameters, including parallel velocity, density, and flux are combined with simultaneous auroral images to investigate relationships between their properties and the structure and brightness of the auroral forms. Results indicate field aligned upflowing O(+) ions over bright auroral regions and downward flows over dark regions. These and other relationships will be presented for several POLAR passes when both ion measurements and auroral images are observed under favorable conditions for comparison.

Stevenson, Benjamin Adam↗
NASA NTRS2007

Effects of Artificial Gravity and Bed Rest on Spatial Orientation and Balance Control

While the vestibular system should be well-adapted to bed rest (a condition it experiences approximately 8/24 hrs each day), questions remain regarding the degree to which repeated exposures to the unusual gravito-inertial force environment of a short-radius centrifuge might affect central processing of vestibular information used in spatial orientation and balance control. Should these functions be impaired by intermittent AG, its feasibility as a counter-measure would be diminished. We, therefore, examined the effects of AG on spatial orientation and balance control in 15 male volunteers before and after 21 days of 6 HDT bed rest (BR). Eight of the subjects were treated with daily 1hr AG exposures (2.5g at the feet; 1.0g at the heart) aboard a short radius (3m) centrifuge, while the other seven served as controls (C). Spatial orientation was assessed by measures of ocular counter-rolling (OCR; rotation of the eye about the line of sight, an otolith-mediated reflex) and subjective visual vertical (SVV; perception of the spatial upright). Both OCR and SVV measurements were made with the subject upright, lying on their left sides, and lying on their right sides. OCR was measured from binocular eye orientation recordings made while the subjects fixated for 10s on a point target directly in front of the face at a distance of 1 m. SVV was assessed by asking subjects (in the dark) to adjust to upright (using a handheld controller) the orientation of a luminous bar randomly perturbed (15) to either side of the vertical meridian. Balance control performance was assessed using a computerized dynamic posturography (CDP) protocol similar to that currently required for all returning crew members. During each session, the subjects completed a combination of trials of sensory organization test (SOT) 2 (eyes closed, fixed platform) and SOT 5 (eyes closed, sway-referenced platform) with and without static and dynamic pitch plane head movements (plus or minus 20 deg., dynamic paced by an audible tone at 0.33Hz). OCR and CDP performance were unaffected by BR and BR+AG; post-BR measures were unchanged from baseline for both AG and C groups. Similarly, BR did not affect SVV in the C group. However, BR+AG disrupted one measure of spatial orientation: SVV error was significantly increased on R+0 and R+1 following BR in the AG group. These results suggest a transient untoward effect on central vestibular processing may accompany repeated exposure to intermittent AG, a potential side-effect that should be studied more closely in future studies.

Paloski, William H.↗
DOE OSTI2020

Implementing an aerosol dynamic shape factor for cerium oxide powder

The shape factor (X B ) of bulk powder CeO 2 (cerium oxide) particles is estimated to be X B = 1.34 (dimensionless). This is defined in relation to the measured aerated bulk density (0.91 g cm -3 , Hosokawa Micron, Summit NJ, 2018) of the CeO 2 powder. This information is used to determine the RRF (respirable release factor), and other parameters during drop test experiments of nuclear material storage containers at Los Alamos National Laboratory. The calculation is based on an experimental shape factor (X P = 2.66 dimensionless) for CeO 2 particles of the same (chain aggregate) morphology studied by other researchers. In that work, the shape factor was defined in terms of the maximum possible (compacted) density of CeO 2 material (7.13 g cm -3 ).

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2020

Mechanical Regulation of Photosynthesis in Cyanobacteria

Photosynthetic organisms regulate their responses to many diverse stimuli in an effort to balance light harvesting with utilizable light energy for carbon fixation and growth (source–sink regulation). This balance is critical to prevent the formation of reactive oxygen species that can lead to cell death. However, investigating the molecular mechanisms that underlie the regulation of photosynthesis in cyanobacteria using ensemble-based measurements remains a challenge due to population heterogeneity. Here, to address this problem, we used long-term quantitative time-lapse fluorescence microscopy, transmission electron microscopy, mathematical modelling and genetic manipulation to visualize and analyse the growth and subcellular dynamics of individual wild-type and mutant cyanobacterial cells over multiple generations. We reveal that mechanical confinement of actively growing Synechococcus sp. PCC 7002 cells leads to the physical disassociation of phycobilisomes and energetic decoupling from the photosynthetic reaction centres. We suggest that the mechanical regulation of photosynthesis is a critical failsafe that prevents cell expansion when light and nutrients are plentiful, but when space is limiting. These results imply that cyanobacteria must convert a fraction of the available light energy into mechanical energy to overcome frictional forces in the environment, providing insight into the regulation of photosynthesis and how microorganisms navigate their physical environment.

BASIC BIOLOGICAL SCIENCES,BIOMASS FUELS↗
DOE OSTI2023

Coherent light control of a metastable hidden state

Metastable phases present a promising route to expand the functionality of complex materials. Of particular interest are light-induced metastable phases that are inaccessible under equilibrium conditions, as they often host new, emergent properties switchable on ultrafast timescales. However, the processes governing the trajectories to such hidden phases remain largely unexplored. Here, using time- and angle-resolved photoemission spectroscopy, we investigate the ultrafast dynamics of the formation of a hidden quantum state in the layered dichalcogenide 1T-TaS 2 upon photoexcitation. Our results reveal the nonthermal character of the transition governed by a collective charge-density-wave excitation. Using a double-pulse excitation of the structural mode, we show vibrational coherent control of the phase-transition efficiency. Our demonstration of exceptional control, switching speed, and stability of the hidden state are key for device applications at the nexus of electronics and photonics.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Global, Collisional Model of High-Energy Photoelectrons

A previously-developed colissional, interhemispheric flux tube model for photoelectrons (PE) has been extended to three dimensions by including transport due to vector E x vector B and magnetic gradient-curvature drifts. Using this model, initial calculations of the high-energy (greater then 50 eV) PE distribution as a function of time, energy, pitch angle, and spatial location in the equatorial plane, are reported for conditions of low geomagnetic activity. To explore both the dynamic and steady behaviors of the model, the simulation starts with the abrupt onset of photoelectron excitation, and is followed to steady state conditions. The results illustrate several features of the interaction of photoelectrons with typical magnetospheric plasmas and fields, including collisional diffusion of photoelectrons in pitch angle with flux tube filling, diurnal intensity and pitch angle asymmetries introduced by directional sunlight, and energization of the photoelectron distribution in the evening sector. Cross-field drift is shown to have a long time scale, taking 12 to 24 hours to reach a steady state distribution. Future applications of the model are briefly outlined.

Khazanov, G. V.↗
NASA NTRS1997

Upwelling-Induced Primary Productivity in Coastal Waters of the Black Sea: Impact on Algorithms for Remote Sensing

This research program was a collaborative effort to investigate the impact of rapid changes in the water column during coastal upwelling, on biological and optical properties. These properties are important for constructing region or event-specific algorithms for remote sensing of pigment concentration and primary productivity and for comparing these algorithms with those used for the development of large scale maps from ocean color. We successfully achieved the primary objective of this research project which was to study in situ the dynamics of rapid spatial and temporal changes in properties of the water column during, coastal upwelling off the Crimean Coast in the Black Sea. The work was a collaborative effort between a group of biological and physical oceanographers from the Woods Hole Oceanographic Institution and from two oceanographic research institutions in the Crimea, Ukraine, located near the study site, the Marine Hydrophysical Institute (MHI) and the Institute of Biology of the Southern Seas (IBSS). The site was an ideal experimental model, both from a technical and economic standpoint, because of the predictable summer upwelling that occurs in the region and because of the availability of both a ship on call and laboratory and remote sensing facilities at the nearby marine institutes. We used a combination of shipboard measurements and remote sensing to investigate the physical evolution of rapid upwelling events and their impact on photoplankton and water column optical properties. The field work involved a two day cruise for mooring, deployment and a three day baseline survey cruise, followed by an eleven day primary cruise during, a summer upwelling event (anticipated by monitoring local winds and tracked by remote sensing imaging). An MHI ship was outfitted and used for these purposes.

Goldman, Joel C.↗
NASA NTRS1997

Ring Current Modeling in a Realistic Magnetic Field Configuration

A 3-dimensional kinetic model has been developed to study the dynamics of the storm time ring current in a dipole magnetic field. In this paper, the ring current model is extended to include a realistic, time-varying magnetic field model. The magnetic field is expressed as the cross product of the gradients of two Euler potentials and the bounce-averaged particle drifts are calculated in the Euler potential coordinates. A dipolarization event is modeled by collapsing a tail-like magnetosphere to a dipole-like configuration. Our model is able to simulate the sudden enhancements in the ring current ion fluxes and the corresponding ionospheric precipitation during the substorm expansion.

Fok, M.-C.↗
NASA NTRS2000

Case Study of Solar Wind and IMF Influence on Ionospheric Outflow

We examine ionospheric outflows in the high attitude magnetospheric polar cap during the POLAR satellite's apogee on 04/19/96 using the TIDE instrument. The pass has a fairly constant flux of H+ which is similar to many other passes, but there is a large amount of O+ present. The elevated levels of O+ may be due both to the geophysical conditions during the apogee pass (Kp=5) and prior to the pass. When the outflows for many high altitude polar cap passes are analyzed the O+ density correlates well with the dynamic pressure. There are several aspects of this pass which are interesting besides the abundance of O+ relative to H+. In this pass both the H+ and O+ outflow velocity correlate with both the solar wind speed and Interplanetary Magnetic Field (IMF) Bx. The geophysical conditions are such that the solar wind speed and IMF Bx are highly correlated with each other. For this case the dynamic pressure of the solar wind is fairly constant and has an average value of about 2.5 nPa which is typical for the solar wind, but the average solar wind speed is about 695 km/s which is greater than 450 km/s which is typical for the solar wind at I AU. The ion outflow measurements themselves are interrelated. The H+ density and parallel speed are anticorrelated which results in the constant flux. The 0+ density does not have as large of a anticorrelation with its parallel speed as H+ does with its parallel speed.

Elliott, H. A.↗
NASA NTRS2015

Magnetospheric Multiscale Overview and Science Objectives

Magnetospheric Multiscale (MMS), a NASA four-spacecraft constellation mission launched on March 12, 2015, will investigate magnetic reconnection in the boundary regions of the Earth's magnetosphere, particularly along its dayside boundary with the solar wind and the neutral sheet in the magnetic tail. The most important goal of MMS is to conduct a definitive experiment to determine what causes magnetic field lines to reconnect in a collisionless plasma. The significance of the MMS results will extend far beyond the Earth's magnetosphere because reconnection is known to occur in interplanetary space and in the solar corona where it is responsible for solar flares and the disconnection events known as coronal mass ejections. Active research is also being conducted on reconnection in the laboratory and specifically in magnetic-confinement fusion devices in which it is a limiting factor in achieving and maintaining electron temperatures high enough to initiate fusion. Finally, reconnection is proposed as the cause of numerous phenomena throughout the universe such as comet-tail disconnection events, magnetar flares, supernova ejections, and dynamics of neutron-star accretion disks. The MMS mission design is focused on answering specific questions about reconnection at the Earth's magnetosphere. The prime focus of the mission is on determining the kinetic processes occurring in the electron diffusion region that are responsible for reconnection and that determine how it is initiated; but the mission will also place that physics into the context of the broad spectrum of physical processes associated with reconnection. Connections to other disciplines such as solar physics, astrophysics, and laboratory plasma physics are expected to be made through theory and modeling as informed by the MMS results.

Space plasma physics↗
DOE OSTI2024

Data for Microbial-Explicit Processes and Refined Perennial Plant Traits Improve Modeled Ecosystem Carbon Dynamics

Globally, soils hold approximately half of ecosystem carbon and can serve as a source or sink depending on climate, vegetation, management, and disturbance regimes. Understanding how soil carbon dynamics are influenced by these factors is essential to evaluate proposed natural climate solutions and policy regarding net ecosystem carbon balance. Soil microbes play a key role in both carbon fluxes and stabilization. However, biogeochemical models often do not specifically address microbial-explicit processes. Here, we incorporated microbial-explicit processes into the DayCent biogeochemical model to better represent large perennial grasses and mechanisms of soil carbon formation and stabilization. We also take advantage of recent model improvements to better represent perennial grass structural complexity and life-history traits. Specifically, this study focuses on: 1) a plant sub-model that represents perennial phenology and more refined plant chemistry with downstream implications for soil organic matter (SOM) cycling though litter inputs, 2) live and dead soil microbe pools that influence routing of carbon to physically protected and unprotected pools, 3) Michaelis-Menten kinetics rather than first-order kinetics in the soil decomposition calculations, and 4) feedbacks between decomposition and live microbial pools. We evaluated the performance of the plant sub-model and two SOM cycling sub-models, Michaelis-Menten (MM) and first-order (FO), using observations of net ecosystem production, ecosystem respiration, soil respiration, microbial biomass, and soil carbon from long-term bioenergy research plots in the mid-western United States. The MM sub-model represented seasonal dynamics of soil carbon fluxes better than the FO sub-model which consistently overestimated winter soil respiration. While both SOM sub-models were similarly calibrated to total, physically protected, and physically unprotected soil carbon measurements, the models differed in future soil carbon response to disturbance and climate, most notably in the protected pools. Adding microbial-explicit mechanisms of soil processes to ecosystem models will improve model predictions of ecosystem carbon balances but more data and research are necessary to validate disturbance and climate change responses and soil pool allocation.

Field Data↗
NASA NTRS1988

The development of a facility for full-scale testing of airfoil performance in simulated rain

NASA Langley's Aircraft Landing Dynamics Facility has been adapted in order to test the performance of airfoils in a simulated rain environment, at rainfall rates of 2, 10, 30, and 40 inches/hour, and thereby derive the scaling laws associated with simulated rain in wind tunnel testing. A full-scale prototype of the rain-generation system has been constructed and tested for suitable rain intensity, uniformity, effects of crosswinds on uniformity, and drop size range. The results of a wind tunnel test aimed at ascertaining the minimum length of the simulated rain field required to yield an airfoil performance change due to the rain environment are presented.

Taylor, John T.↗
NASA NTRSDate not supplied

Ice Growth Model and Lunar Tanker for Polar Water Extraction

In-Situ Resource Utilization (ISRU) is a major component of sustainable and cost-effective missions to the Moon and beyond. Ever since it has been identified in the Permanently Shadowed Regions (PSRs) of the Moon, water has become a resource of interest for it’s wide range of uses such as life support and hydrogen and oxygen rocket propellant. It is ice-bound in the regolith, so separation typically involves heating to sublimation temperatures and capturing at very low pressure. One option is to then store it in ice form and transport it out of the PSR and into a sunlit ridge. From here, processes such as electrolysis can be performed. An understanding of frost growth dynamics under rarefied conditions is necessary for successful water production, though. An analytical model was developed using a Diffusion-Limited Aggregation (DLA) approach to evaluate bulk thermal conductivity changes of frost under varying conditions. This model will be evaluated using a one-dimensional frost growth experiment on a horizontal, flat plate under vacuum and cryogenic conditions. The tests will measure frost growth rate and bulk density, and the thermal conductivity of the ice layer as a function of thickness for different plate temperatures. The test data will then be used to validate and improve the analytical model.

Lunar water↗
NASA NTRS1973

Solution of the stochastic control problem in unbounded domains.

Bellman's dynamic programming equation for the optimal index and control law for stochastic control problems is a parabolic or elliptic partial differential equation frequently defined in an unbounded domain. Existing methods of solution require bounded domain approximations, the application of singular perturbation techniques or Monte Carlo simulation procedures. In this paper, using the fact that Poisson impulse noise tends to a Gaussian process under certain limiting conditions, a method which achieves an arbitrarily good approximate solution to the stochastic control problem is given. The method uses the two iterative techniques of successive approximation and quasi-linearization and is inherently more efficient than existing methods of solution.

Robinson, P.↗
DOE OSTI2023

Measurements of fusion reaction history in inertially confined burning plasmas

Direct evidence of inertially confined fusion ignition appears in the abrupt temperature increase and consequent rapid increase in the thermonuclear burn rate as seen in the reaction history. The Gamma Reaction History (GRH) and Gas Cherenkov Detector (GCD) diagnostics are γ-based Cherenkov detectors that provide high quality measurements of deuterium–tritium fusion γ ray production and are, thus, capable of monitoring the thermonuclear burn rate. Temporal shifts in both peak burn time and burn width have been observed during recent high-yield shots (yields greater than 1017 neutrons) and are essential diagnostic signatures of the ignition process. While the current GRH and GCD detectors are fast enough to sense the changes of reaction history due to alpha heating, they do not have enough dynamic range to capture the onset of alpha heating. The next generation of instrumentation, GRH-15m, is proposed to increase the yield-rate coverage to measure the onset of alpha-heating.

42 ENGINEERING↗
NASA NTRS1998

Survey of the Polar Wind near 1 and 8Re with POLAR

Recent theoretical/modeling developments as well as measurements by Akebono and other spacecraft have created renewed interest in the polar wind. This interest arises generally from two principal aspects: (a) Understanding the physics of such plausible influences as photo-electron-driven parallel electric fields and convection-driven centrifugal acceleration on the polar wind transport; and (b) Understanding the intermediate fate of the polar wind--in particular, its contribution to the plasma content of such magnetospheric domains as the plasma sheet and tail lobes. In this talk, we will describe the results of a new survey of the intermediate(lR(sub E)) and high(8 R(sub E)) polar wind, based on high-resolution core ion measurements with the Thermal Ion Dynamics Experiment(TIDE) on POLAR. These new measurements of H(+), He(+), and O(+) densities, parallel flow velocities, Mach numbers and fluxes, and parallel and perpendicular temperatures, will be used to explore such issues as: (1) Supersonic vs. subsonic polar wind flows; (2) Upward and downward O(+) flows, and the origin of the polar cap ions; (3) Parallel flow speeds for various polar wind ion species in the context of various acceleration/transport mechanisms; and (4) Relationships of polar wind bulk parameters to solar zenith angle and to magnetospheric day-night distance, and their implications for the origin and transport of the polar wind.

Horwitz, J. L.↗
NASA NTRS2019

Initial Results from the New Horizons Exploration of 2014 MU69, a Small Kuiper Belt Object

The Kuiper Belt is a broad, torus-shaped region in the outer Solar System beyond Neptune’s orbit. It contains primordial planetary building blocks and dwarf planets. NASA’s New Horizons spacecraft conducted a flyby of Pluto and its system of moons on 14 July 2015. New Horizons then continued farther into the Kuiper Belt, adjusting its trajectory to fly close to the small Kuiper Belt object (486958) 2014 MU69 (henceforth MU69; also informally known as Ultima Thule). Stellar occultation observations in 2017 showed that MU69 was ~25 to 35 km in diameter, and therefore smaller than the diameter of Pluto (2375 km) by a factor of ~100 and less massive than Pluto by a factor of ~106. MU69 is located about 1.6 billion kilometers farther from the Sun than Pluto was at the time of the New Horizons flyby. MU69’s orbit indicates that it is a “cold classical” Kuiper Belt object, thought to be the least dynamically evolved population in the Solar System. A major goal of flying past this target is to investigate accretion processes in the outer Solar System and how those processes led to the formation of the planets. Because no small Kuiper Belt object had previously been explored by spacecraft, we also sought to provide a close-up look at such a body’s geology and composition, and to search for satellites, rings, and evidence of present or past atmosphere. We report initial scientific results and interpretations from that flyby.

S. A. Stern↗