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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Modelling a single phase voltage controlled rectifier using Laplace transforms

The development of a 20 kHz, AC power system by NASA for large space projects has spurred a need to develop models for the equipment which will be used on these single phase systems. To date, models for the AC source (i.e., inverters) have been developed. It is the intent of this paper to develop a method to model the single phase voltage controlled rectifiers which will be attached to the AC power grid as an interface for connected loads. A modified version of EPRI's HARMFLO program is used as the shell for these models. The results obtained from the model developed in this paper are quite adequate for the analysis of problems such as voltage resonance. The unique technique presented in this paper uses the Laplace transforms to determine the harmonic content of the load current of the rectifier rather than a curve fitting technique. Laplace transforms yield the coefficient of the differential equations which model the line current to the rectifier directly.

Kraft, L. Alan↗
NASA NTRS2006

Repeat Ground Track Lunar Orbits in the Full-Potential Plus Third-Body Problem

A high degree and order Lunar gravitational field is superimposed on the Earth-Moon Restricted Three Body model to capture the dominating forces on a spacecraft in the vicinity of the Moon. For the synchronously rotating Moon, periodic orbits in this model map repeat ground tracks and represent higher order solutions to the frozen orbit problem. The near-circular, stable or near-stable solutions are found over a wide range of defining characteristics making them suitable for long-lifetime parking applications such as science orbits, crew exploration vehicle parking orbits, and global coverage constellation orbits. A full ephemeris is considered for selected orbits to evaluate the validity of the time-invariant, simplified model. Of the most promising results are the low-altitude families of near-circular, inclined orbits that maintain long-term stability despite the highly non-spherical Lunar gravity. The method is systematic and enables rapid design and analysis of long-life orbits around any tidally-locked celestial body with an arbitrarily high degree and order spherical harmonic gravity field. .

periodic↗
DOE OSTI2020

Likelihood Methods for CMB Experiments

A great deal of experimental effort is currently being devoted to the precise measurements of the cosmic microwave background (CMB) sky in temperature and polarization. Satellites, balloon-borne, and ground-based experiments scrutinize the CMB sky at multiple scales, and therefore enable to investigate not only the evolution of the early Universe, but also its late-time physics with unprecedented accuracy. The pipeline leading from time ordered data as collected by the instrument to the final product is highly structured. Moreover, it has also to provide accurate estimates of statistical and systematic uncertainties connected to the specific experiment. In this paper, we review likelihood approaches targeted to the analysis of the CMB signal at different scales, and to the estimation of key cosmological parameters. We consider methods that analyze the data in the spatial (i.e., pixel-based) or harmonic domain. We highlight the most relevant aspects of each approach and compare their performance.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Global land use for 2015–2100 at 0.05° resolution under diverse socioeconomic and climate scenarios

Abstract Global future land use (LU) is an important input for Earth system models for projecting Earth system dynamics and is critical for many modeling studies on future global change. Here we generated a new global gridded LU dataset using the Global Change Analysis Model (GCAM) and a land use spatial downscaling model, named Demeter, under the five Shared Socioeconomic Pathways (SSPs) and four Representative Concentration Pathways (RCPs) scenarios. Compared to existing similar datasets, the presented dataset has a higher spatial resolution (0.05° × 0.05°) and spreads under a more comprehensive set of SSP-RCP scenarios (in total 15 scenarios), and considers uncertainties from the forcing climates. We compared our dataset with the Land Use Harmonization version 2 (LUH2) dataset and found our results are in general spatially consistent with LUH2. The presented dataset will be useful for global Earth system modeling studies, especially for the analysis of the impacts of land use and land cover change and socioeconomics, as well as the characterizing the uncertainties associated with these impacts.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Global land use for 2015-2100 at 0.05° resolution under diverse socioeconomic and climate scenarios

Global future land use (LU) is an important input for Earth system models for projecting Earth system dynamics and is critical for many modeling studies on future global change. Here we generated a new global gridded LU dataset using the Global Change Analysis Model (GCAM) and a land use spatial downscaling model, named Demeter, under the five Shared Socioeconomic Pathways (SSPs) and four Representative Concentration Pathways (RCPs) scenarios. Compared to existing similar datasets, the presented dataset has a higher spatial resolution (0.05°×0.05°) and spreads under a more comprehensive set of SSP-RCP scenarios (in total 15 scenarios), and considers uncertainties from the forcing climates. We compared our dataset with the Land Use Harmonization version 2 (LUH2) dataset and found our results are in general spatially consistent with LUH2. The presented dataset will be useful for global Earth system modeling studies, especially for the analysis of the impacts of land use and land cover change and socioeconomics, as well as the characterizing the uncertainties associated with these impacts.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1999

Acoustic Reflection and Transmission of 2-Dimensional Rotors and Stators, Including Mode and Frequency Scattering Effects

A reduced order modeling scheme has been developed for the unsteady acoustic and vortical coupling between blade rows of a turbomachine. The essential behavior of the system is governed by modal scattering coefficients (i.e., reflection and transmission coefficients) of the rotor, stator, inlet and nozzle, which are calculated as if they were connected to non-reflecting ducts. The objective of this report is to identify fundamental behavior of these scattering coefficients for a better understanding of the role of blade row reflection and transmission in noise generation. A 2D flat plate unsteady cascade model is used for the analysis with the expectation that the general behavior presented herein will carry over to models that include more realistic flow and geometry. It is shown that stators scatter input waves into many modes at the same frequency whereas rotors scatter on frequency, or harmonic order. Important cases are shown here the rotor reflection coefficient is greater than unity; a mode at blade passing frequency (BPF) traveling from the stator with unit sound power is reflected by the rotor with more than unit power at 2xBPF and 3xBPE Analysis is presented to explain this unexpected phenomenon. Scattering curves are presented in a format chosen for design use and for physical interpretation. To aid in interpretation of the curves, formulas are derived for special condition where waveforms are parallel to perpendicular to the rotor.

Hanson, Donald B.↗
NASA NTRS1932

A New Principle of Sound Frequency Analysis

In connection with the study of aircraft and propeller noises, the National Advisory Committee for Aeronautics has developed an instrument for sound-frequency analysis which differs fundamentally from previous types, and which, owing to its simplicity of principle, construction, and operation, has proved to be of value in this investigation. The method is based on the well-known fact that the Ohmic loss in an electrical resistance is equal to the sum of the losses of the harmonic components of a complex wave, except for the case in which any two components approach or attain vectorial identity, in which case the Ohmic loss is increased by a definite amount. The principle of frequency analysis has been presented mathematically and a number of distinct advantages relative to previous methods have been pointed out. An automatic recording instrument embodying this principle is described in detail. It employs a beat-frequency oscillator as a source of variable frequency. A large number of experiments have verified the predicted superiority of the method. A number of representative records are presented.

Theodorsen, Theodore↗
DOE OSTI2021

Josephson detection of time-reversal symmetry broken superconductivity in SnTe nanowires

A Josephson junction (JJ) couples the supercurrent flowing between two weakly linked superconductors to the phase difference between them via a current-phase relation (CPR). While a sinusoidal CPR is expected for conventional junctions with insulating weak links, devices made from some exotic materials may give rise to unconventional CPRs and unusual Josephson effects. In this work, we present such a case: we investigate the proximity-induced superconductivity in SnTe nanowires by incorporating them as weak links in JJs and observe a deviation from the standard CPR. We report on indications of an unexpected breaking of time-reversal symmetry in these devices, detailing the unconventional characteristics that reveal this behavior. These include an asymmetric critical current in the DC Josephson effect, a prominent second harmonic in the AC Josephson effect, and a magnetic diffraction pattern with a minimum in critical current at zero magnetic field. The analysis examines how multiband effects and the experimentally visualized ferroelectric domain walls give rise to this behavior, giving insight into the Josephson effect in materials that possess ferroelectricity and/or multiband superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

WormBase in 2022—data, processes, and tools for analyzing Caenorhabditis elegans

WormBase (www.wormbase.org) is the central repository for the genetics and genomics of the nematode Caenorhabditis elegans. We provide the research community with data and tools to facilitate the use of C. elegans and related nematodes as model organisms for studying human health, development, and many aspects of fundamental biology. Throughout our 22-year history, we have continued to evolve to reflect progress and innovation in the science and technologies involved in the study of C. elegans. We strive to incorporate new data types and richer data sets, and to provide integrated displays and services that avail the knowledge generated by the published nematode genetics literature. Here, we provide a broad overview of the current state of WormBase in terms of data type, curation workflows, analysis, and tools, including exciting new advances for analysis of single-cell data, text mining and visualization, and the new community collaboration forum. Concurrently, we continue the integration and harmonization of infrastructure, processes, and tools with the Alliance of Genome Resources, of which WormBase is a founding member.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Role of the Porras factor in phase matching of high-order harmonic generation driven by focused few-cycle laser pulses

We investigate the role of the Porras factor (or laser focusing effect) on the macroscopic high-order harmonic generation (HHG) driven by a focused broadband few-cycle laser beam. By employing a non-adiabatic phase-matching analysis method, we reveal that phase mismatch due to the induced-dipole phase varies with the Porras factor, which is dominant in phase matching at low gas pressure. We also find that in a strongly ionized medium when gas pressure is high, the nonlinear propagation is dominated by a plasma effect such that the focusing effect is mitigated, resulting in similar poor phase matching of HHG regardless of the Porras factor. Our results are expected to assist experimentalists identifying optimal conditions for HHG using ultrashort laser pulses.

Optics↗
NASA NTRS1980

Aerodynamic analysis of a supersonic cascade vibrating in a complex mode

An analysis is presented which has been used to predict the unsteady aerodynamic behavior of a finite supersonic cascade of airfoils forced in harmonic oscillation with airfoil-to-airfoil variations in amplitude. Theoretical predictions are compared with some recent experimental results at a reduced frequency representative of actual fan or compressor flutter cases. The similarity of the experimental situation in the finite cascade to the flutter of a severely mistuned rotor is noted.

Caruthers, J. E.↗
NASA NTRS1990

Helicopter rotor dynamics and aeroelasticity - Some key ideas and insights

Four important current topics in helicopter rotor dynamics and aeroelasticity are discussed: (1) the role of geometric nonlinearities in rotary-wing aeroelasticity; (2) structural modeling, free vibration, and aeroelastic analysis of composite rotor blades; (3) modeling of coupled rotor/fuselage areomechanical problems and their active control; and (4) use of higher-harmonic control for vibration reduction in helicopter rotors in forward flight. The discussion attempts to provide an improved fundamental understanding of the current state of the art. In this way, future research can be focused on problems which remain to be solved instead of producing marginal improvements on problems which are already understood.

Friedmann, Peretz P.↗
NASA NTRS1989

A study of fundamental issues in higher harmonic control using aeroelastic simulation

This paper describes a higher harmonic control (HHC) study of a four-bladed helicopter rotor using a coupled flap-lag-torsional aeroelastic stability and response analysis which incorporates finite-state, time-domain aerodyamics. The rotor trim condition is determined using a simplified flap-lag-torsional aeroelastic analysis. Deterministic and cautious controllers based on local and global HHC models are implemented to reduce 4/rev hub loads on roughly equivalent articulate and hingeless rotors. Results obtained for the case when the objective function requires reduction of hub shears alone are compared with results obtained when hub shears and moments are reduced simultaneously. The effects of HHC on blade aeroelastic stability are also considered. Finally, the power requirements for implementing HHC on a hingeless rotor are compared with those obtained for an articulated rotor. It is concluded that hingeless rotors require considerably more power and higher control angles than comparable articulated rotors.

Robinson, Lawson H.↗
NASA NTRS2006

Fast Scattering Code (FSC) User's Manual: Version 2

The Fast Scattering Code (version 2.0) is a computer program for predicting the three-dimensional scattered acoustic field produced by the interaction of known, time-harmonic, incident sound with aerostructures in the presence of potential background flow. The FSC has been developed for use as an aeroacoustic analysis tool for assessing global effects on noise radiation and scattering caused by changes in configuration (geometry, component placement) and operating conditions (background flow, excitation frequency).

Tinetti, Ana F.↗
NASA NTRSDate not supplied

Implementation of an Unsteady PSP System in the NASA Transonic Dynamics Tunnel

An unsteady pressure-sensitive paint (uPSP) system has been developed to provide time-resolved pressure measurements in the NASA Langley Transonic Dynamics Tunnel (TDT). Obtaining these measurements necessitated the development of environmental enclosures to protect the high-speed camera and ultraviolet lights required for uPSP from the harsh environment present during tunnel operation. Since the facility main drive was non-functioning during the testing window, performance of the uPSP system was demonstrated using an impinging jet with a passive oscillator attachment to provide unsteady flow with a known frequency independent of amplitude. Measurements were obtained for tunnel pressures ranging from 565 to 2116 psf, and model angles of attack between -4 degrees and 4 degrees. Results indicate that the system is capable of measuring surface pressure differentials on the order of 0.01 psi at full scale with a camera frame rate of at least 10 kHz. Spectral analysis shows that the fundamental frequency of the oscillating jet is captured by the uPSP system, as are the second and third harmonics. Dynamic mode decomposition highlights the dominant coherent spatial structures of the surface pressure, along with the associated frequency and growth rate of each mode, allowing for a de-noised reconstruction of the uPSP measurements. The experimental campaign outlined within this report also confirmed compatibility of the uPSP system with the TDT facility data acquisition system, and verified the successful integration with existing processing capabilities within the NASA advanced supercomputing environment.

unsteady pressure-sensitive paint↗
NASA NTRSDate not supplied

Implementation of an Unsteady PSP System in the NASA Transonic Dynamics Tunnel

An unsteady pressure-sensitive paint (uPSP) system has been developed to provide time-resolved pressure measurements in the NASA Langley Transonic Dynamics Tunnel (TDT). Obtaining these measurements necessitated the development of environmental enclosures to protect the high-speed camera and ultraviolet lights required for uPSP from the harsh environment present during tunnel operation. Since the facility main drive was non-functioning during the testing window, performance of the uPSP system was demonstrated using an impinging jet with a passive oscillator attachment to provide unsteady flow with a known frequency independent of amplitude. Measurements were obtained for tunnel pressures ranging from 565 to 2116 psf, and model angles of attack between -4 degrees and 4 degrees. Results indicate that the system is capable of measuring surface pressure differentials on the order of 0.01 psi at full scale with a camera frame rate of at least 10 kHz. Spectral analysis shows that the fundamental frequency of the oscillating jet is captured by the uPSP system, as are the second and third harmonics. Dynamic mode decomposition highlights the dominant coherent spatial structures of the surface pressure, along with the associated frequency and growth rate of each mode, allowing for a de-noised reconstruction of the uPSP measurements. The experimental campaign outlined within this report also confirmed compatibility of the uPSP system with the TDT facility data acquisition system, and verified the successful integration with existing processing capabilities within the NASA advanced supercomputing environment.

unsteady pressure-sensitive paint↗
NASA NTRSDate not supplied

Implementation of an Unsteady PSP System in the NASA TDT

An unsteady pressure-sensitive paint (uPSP) system has been developed to provide time-resolved pressure measurements in the NASA Langley Transonic Dynamics Tunnel (TDT). Obtaining these measurements necessitated the development of environmental enclosures to protect the high-speed camera and ultraviolet lights required for uPSP from the harsh environment present during tunnel operation. Since the facility main drive was non-functioning during the testing window, performance of the uPSP system was demonstrated using an impinging jet with a passive oscillator attachment to provide unsteady flow with a known frequency independent of amplitude. Measurements were obtained for tunnel pressures ranging from 565 to 2116 psf, and model angles of attack between -4 degrees and 4 degrees. Results indicate that the system is capable of measuring surface pressure differentials on the order of 0.01 psi at full scale with a camera frame rate of at least 10 kHz. Spectral analysis shows that the fundamental frequency of the oscillating jet is captured by the uPSP system, as are the second and third harmonics. Dynamic mode decomposition highlights the dominant coherent spatial structures of the surface pressure, along with the associated frequency and growth rate of each mode, allowing for a de-noised reconstruction of the uPSP measurements. The experimental campaign outlined within this report also confirmed compatibility of the uPSP system with the TDT facility data acquisition system, and verified the successful integration with existing processing capabilities within the NASA advanced supercomputing environment. Note: this presentation is an MP4 video with sound, color with a run time of 10 minutes 37 seconds.

unsteady pressure-sensitive paint↗