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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Micro Ring Grating Spectrometer with Adjustable Aperture

A spectrometer includes a micro-ring grating device having coaxially-aligned ring gratings for diffracting incident light onto a target focal point, a detection device for detecting light intensity, one or more actuators, and an adjustable aperture device defining a circular aperture. The aperture circumscribes a target focal point, and directs a light to the detection device. The aperture device is selectively adjustable using the actuators to select a portion of a frequency band for transmission to the detection device. A method of detecting intensity of a selected band of incident light includes directing incident light onto coaxially-aligned ring gratings of a micro-ring grating device, and diffracting the selected band onto a target focal point using the ring gratings. The method includes using an actuator to adjust an aperture device and pass a selected portion of the frequency band to a detection device for measuring the intensity of the selected portion.

Park, Yeonjoon↗
DOE OSTI2019

Two-tier model reduction of viscoelastically damped finite element models

Transient simulations of linear viscoelastically damped structures necessitate critical computational resources to directly integrate the full-order finite element model with time-stepping algorithms. Traditional modal reduction techniques are not directly applicable to these systems since viscoelastic materials depend on time and frequency. A more appropriate reduction basis is obtained from the nonlinear, complex eigenvalue problem, whose eigenvectors capture the appropriate kinematics and enable frequency-based mode selection; unfortunately, the computational cost is prohibitive for computing these modes from large-scale engineering models. To address this shortcoming, this work proposes a novel two-tier reduction procedure to reduce the upfront cost of solving the complex, nonlinear eigenvalue problem. The first reduction step reduces the full-order model with real mode shapes linearized about various centering frequencies to capture the kinematics over a full range of viscoelastic material behavior (glassy, rubbery, and glass-transition zones). This tier-one reduction preserves time-temperature superposition and allows the equations to depend parametrically on operating temperature. The second-level reduction then solves the complex, nonlinear eigenmode solutions in the tier-one reduced space about a fixed temperature to further reduce the equations-of-motion. The method is demonstrated on a cantilevered sandwich plate to display its accuracy and efficiency in comparison to full-order model predictions.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Reorientation of the ‘free OH’ group in the top-most layer of air/water interface of sodium fluoride aqueous solution probed with sum-frequency generation vibrational spectroscopy

Many experimental and theoretical studies have established the specific anion, as well as cation effects on the hydrogen-bond structures at the air/water interface of electrolyte solutions. However, the ion effects on the top-most layer of the air/water interface, which is signified by the non-hydrogen-bonded so-called ‘free O-H’ group, has not been discussed or studied. In this report, we present the measurement of changes of the orientational angle of the ‘free O-H’ group at the air/water interface of the sodium fluoride (NaF) solutions at different concentrations using the interface selective sum-frequency generation vibrational spectroscopy (SFG-VS) in the ssp and ppp polarizations. The polarization dependent SFG-VS results show that the average tilt angle of the ‘free O-H’ changes from about 35.3 degrees ± 0.5 degrees to 43.4 degrees ± 2.1degrees as the NaF concentration increase from 0 to 0.94M (nearly saturated). Such tilt angle change is around the axis of the other O-H group of the same water molecule at the top-most layer at the air/water interface that is hydrogen-bonded to the water molecules below the top-most layer. These results provide quantitative molecular details of the ion effects of the NaF salt on the structure of the water molecules at the top-most layer of the air/water interfacial, even though both the Na+ cation and the F- anion are believed to be among the most excluded ions from the air/water interface.

air-water interface↗
NASA NTRS1998

Precision Spectroscopy, Diode Lasers, and Optical Frequency Measurement Technology

This compilation is a selected set of reprints from the Optical Frequency Measurement Group of the Time and Frequency Division of the National Institute of Standards and Technology, and consists of work published between 1987 and 1997. The two main programs represented here are (1) development of tunable diode-laser technology for scientific applications and precision measurements, and (2) research toward the goal of realizing optical-frequency measurements and synthesis. The papers are organized chronologically in five, somewhat arbitrarily chosen categories: Diode Laser Technology, Tunable Laser Systems, Laser Spectroscopy, Optical Synthesis and Extended Wavelength Coverage, and Multi-Photon Interactions and Optical Coherences.

DIODE LASERS↗
NASA NTRS2000

The Use of Additional GPS Frequencies to Independently Determine Tropospheric Water Vapor Profiles

It is well known that the currently employed L1 and L2 GPS/MET frequencies (1.2 - 1.6) Ghz) do not allow for the separation of water vapor and density (or temperature) from active microwave occultation measurements in regions of the troposphere warmer than 240 K Therefore, additional information must be used, from other types of measurements and weather analyses, to recover water vapor (and temperature) profiles. Thus in data sparse regions, these inferred profiles can be subject to larger errors than would result in data rich regions. The use of properly selected additional GPS frequencies enables a direct, independent measurement of the absorption associated with the water vapor profile, which may then be used in the standard GPS/MET retrievals to obtain a more accurate determination of atmospheric temperature throughout the water vapor layer. This study looks at the use of microwave crosslinks in the region of the 22 Ghz water vapor absorption line for this purpose. An added advantage of using 22 Ghz frequencies is that they are only negligibly affected by the ionosphere in contrast to the large effect at the GPS frequencies. The retrieval algorithm uses both amplitude and phase measurements to obtain profiles of atmospheric pressure, temperature and water water vapor pressure with a vertical resolution of 1 km or better. This technique also provides the cloud liquid water content along the ray path, which is in itself an important element in climate monitoring. Advantages of this method include the ability to make measurements in the presence of clouds and the use of techniques and technology proven through the GPS/MET experiment and several of NASA's planetary exploration missions. Simulations demonstrating this method will be presented for both clear and cloudy sky conditions.

Herman, B.M.↗
NASA NTRS2012

Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics

Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin can be caused by the aerodynamic undamping one of the lower-frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis show a reduced or even negative aerodynamic damping.Amethod of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping, and mass matrices. The results are compared with the damping and frequency computed from unsteady computational aeroelasticity and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady computational aeroelastic results.

Bartels, Robert E.↗
DOE OSTI2023

Rhodium-Catalyzed Alkenylation of Arenes with Multi-Substituted Olefins: Comparison of Selectivity and Reaction Rate as a Function of Olefin Identity

Rhodium-catalyzed arene alkenylation using Cu(II) carboxylates as the in situ oxidant and mono-substituted olefins has been previously reported (e.g., J. Am. Chem. Soc. 2019, 139, 5474; J. Am. Chem. Soc. 2018, 140, 17007; Organometallics 2019, 38, 3860; J. Am. Chem. Soc. 2020, 142, 10534). Herein, studies are extended to multi-substituted olefins with the goal of evaluating the effect of olefin substitution pattern and substituent identity on selectivity and turnover frequency. The influence of olefin substitution is probed by comparing the conversion of benzene to alkenyl arenes with ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene, isobutene, 2-methyl-2-butene, and tetramethylethylene as well as the phenyl-substituted olefins and isomers of propenylbenzene. The rate of oxidative hydrophenylation for multi-substituted olefins follows the trend monosubstituted > disubstituted > trisubstituted, and tetrasubstituted olefins are unreactive. To probe the effect of substituent size on Markovnikov/ anti-Markovnikov regioselectivity, cyclohexyl, tert-butyl, isopropyl, ethyl, and methyl substituted α-olefins are compared. Selectivity for anti-Markovnikov products generally increases as substituent steric bulk is increased. Tolerance for some functionalized olefins is demonstrated. Here, the ortho/meta/para regioselectivity with mono-substituted arenes reveals that arene and olefin identity influences selectivity. Further mechanistic studies provide evidence for Curtin–Hammet control of ortho/meta/para regioselectivity with monosubstituted arenes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Field Measurement and Analysis of Frequency and RoCoF for Low-Inertia Power Systems

The frequency measurement and rate of change of frequency (RoCoF) calculations are important for active power, frequency control, and frequency-related protection in power system operations. With the rapid decrease in inertia under modern power systems, however, multiple power variations introduced by variable renewable energy bring large RoCoF and introduce oscillations in frequency measurements. To shed light on this issue, this article proposes a frequency measurement and RoCoF analysis technology, as well as the sensitivity analysis for the real low-inertia power grid. First, a real-world event in an island power grid is analyzed as an example, and an event numerical model is estimated considering four uncertainties, including event RoCoF, oscillation magnitude, oscillation frequency, and underfrequency load-shedding threshold. Then, a sensitivity analysis is performed using the Sobol indices method and quasi-Monte Carlo simulations to identify the dominant uncertainties based on the event model. Here, the dominant uncertainties are compared to provide a guideline for the frequency estimation algorithm selection under different event cases. This algorithm is compared with an enhanced zero-crossing algorithm and gives a 3.41% better RoCoF error rate. Finally, an experiment is conducted using universal grid analyzers to validate the simulation results and the theoretical analysis.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2016

Hurricane Resilient Wind Plant Concept Study Final Report

Hurricanes occur over much of the U.S. Atlantic and Gulf coasts, from Long Island to the U.S.-Mexico border, encompassing much of the nation's primary offshore wind resource. Category 5 hurricanes have made landfall as far north as North Carolina, with Category 3 hurricanes reaching New York with some frequency. Along the US West coast, typhoons strike with similar frequency and severity. At present, offshore wind turbine design practices do not fully consider the severe operating conditions imposed by hurricanes. Although universally applied to most turbine designs, International Electrotechnical Commission (IEC) standards do not sufficiently address the duration, directionality, magnitude, or character of hurricanes. To assess advanced design features that could mitigate hurricane loading in various ways, this Hurricane-Resilient Wind Plant Concept Study considered a concept design study of a 500-megawatt (MW) wind power plant consisting of 10-MW wind turbines deployed in 25-meter (m) water depths in the Western Gulf of Mexico. This location was selected because hurricane frequency and severity provided a unique set of design challenges that would enable assessment of hurricane risk and projection of cost of energy (COE) changes, all in response to specific U.S. Department of Energy (DOE) objectives. Notably, the concept study pursued a holistic approach that incorporated multiple advanced system elements at the wind turbine and wind power plant levels to meet objectives for system performance and reduced COE. Principal turbine system elements included a 10-MW rotor with structurally efficient, low-solidity blades; a lightweight, permanent-magnet, direct-drive generator, and an innovative fixed substructure. At the wind power plant level, turbines were arrayed in a large-scale wind power plant in a manner aimed at balancing energy production against capital, installation, and operation and maintenance (O&M) costs to achieve significant overall reductions in COE.

17 WIND ENERGY↗
DOE OSTI2016

Natural selection underlies apparent stress-induced mutagenesis in a bacteriophage infection model

We present that the emergence of mutations following growth-limiting conditions underlies bacterial drug resistance, viral escape from the immune system and fundamental evolution-driven events. Intriguingly, whether mutations are induced by growth limitation conditions or are randomly generated during growth and then selected by growth limitation conditions remains an open question. Here, we show that bacteriophage T7 undergoes apparent stress-induced mutagenesis when selected for improved recognition of its host's receptor. In our unique experimental set-up, the growth limitation condition is physically and temporally separated from mutagenesis: growth limitation occurs while phage DNA is outside the host, and spontaneous mutations occur during phage DNA replication inside the host. We show that the selected beneficial mutations are not pre-existing and that the initial slow phage growth is enabled by the phage particle's low-efficiency DNA injection into the host. Thus, the phage particle allows phage populations to initially extend their host range without mutagenesis by virtue of residual recognition of the host receptor. Finally, mutations appear during non-selective intracellular replication, and the frequency of mutant phages increases by natural selection acting on free phages, which are not capable of mutagenesis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Surface modifications and optical variations of (−1 1 1) lattice oriented CuO nanofilms for solar energy applications

Graphical abstract: - Highlights: • The films are grown using a low cost SILAR method. • The pH value is found to play a significant role in the property of the resulting films. • The fabrication of band pass filters between 450 nm and 1000 nm is envisaged. • Electrical conductivity and optical band gap values were found to be 68.1 × 10{sup −3} Ω{sup −1} cm{sup −1} and 1.08 eV. • Coating may aid the small band of frequencies could pave way for enhancing the efficiency. - Abstract: This paper reports on the preparation and characterization of Successive Ionic Layer by Adsorption and Reaction (SILAR) grown CuO thin films. The films were deposited onto glass substrates at various solution pH values. The thickness of the film is increased with increase of solution pH values. X-ray diffraction analysis revealed that the prepared films exhibited the monoclinic structure with (−1 1 1) predominant orientation. The optimized pH value is 11 ± 0.1. The microstructure, morphology, optical and electrical properties are studied and reported. The transmission spectra (T) at normal incidence revealed that the films exhibit indirect transitions and may be tailored for passing selected bands of frequencies in visible near IR range. The activation energy is estimated to be about 0.29 eV.

36 MATERIALS SCIENCE↗
NASA NTRS1983

Application of an adaptive blade control algorithm to a gust alleviation system

The feasibility of an adaptive control system designed to alleviate helicopter gust induced vibration was analytically investigated for an articulated rotor system. This control system is based on discrete optimal control theory, and is composed of a set of measurements (oscillatory hub forces and moments), an identification system using a Kalman filter, a control system based on the minimization of the quadratic performance function, and a simulation system of the helicopter rotor. The gust models are step and sinusoidal vertical gusts. Control inputs are selected at the gust frequency, subharmonic frequency, and superharmonic frequency, and are superimposed on the basic collective and cyclic control inputs. The response to be reduced is selected to be that at the gust frequency because this is the dominant response compared with sub- and superharmonics. Numerical calculations show that the adaptive blade pitch control algorithm satisfactorily alleviates the hub gust response. Almost 100% reduction of the perturbation thrust response to a step gust and more than 50% reduction to a sinusoidal gust are achieved in the numerical simulations.

Saito, S.↗
NASA NTRS1984

Application of an adaptive blade control algorithm to a gust alleviation system

The feasibility of an adaptive control system designed to alleviate helicopter gust induced vibration was analytically investigated for an articulated rotor system. This control system is based on discrete optimal control theory, and is composed of a set of measurements (oscillatory hub forces and moments), an identification system using a Kalman filter, a control system based on the minimization of the quadratic performance function, and a simulation system of the helicopter rotor. The gust models are step and sinusoidal vertical gusts. Control inputs are selected at the gust frequency, subharmonic frequency, and superharmonic frequency, and are superimposed on the basic collective and cyclic control inputs. The response to be reduced is selected to be that at the gust frequency because this is the dominant response compared with sub- and superharmonics. Numerical calculations show that the adaptive blade pitch control algorithm satisfactorily alleviates the hub gust response. Almost 100 percent reduction of the perturbation thrust response to a step gust and more than 50 percent reduction to a sinusoidal gust are achieved in the numerical simulations.

Saito, S.↗
NASA NTRS1985

Method and apparatus for Delta Kappa synthetic aperture radar measurement of ocean current

A synthetic aperture radar (SAR) employed for delta k measurement of ocean current from a spacecraft without the need for a narrow beam and long observation times. The SAR signal is compressed to provide image data for different sections of the chirp band width, equivalent to frequencies and a common area for the separate image fields is selected. The image for the selected area at each frequency is deconvolved to obtain the image signals for the different frequencies and the same area. A product of pairs of signals is formed, Fourier transformed and squared. The spectrum thus obtained from different areas for the same pair of frequencies are added to provide an improved signal to noise ratio. The shift of the peak from the center of the spectrum is measured and compared to the expected shift due to the phase velocity of the Bragg scattering wave. Any difference is a measure of current velocity v sub o (delta k).

Jain, A.↗
NASA NTRS2007

Airframe Noise Results from the QTD II Flight Test Program

With continued growth in air travel, sensitivity to community noise intensifies and materializes in the form of increased monitoring, regulations, and restrictions. Accordingly, realization of quieter aircraft is imperative, albeit only achievable with reduction of both engine and airframe components of total aircraft noise. Model-scale airframe noise testing has aided in this pursuit; however, the results are somewhat limited due to lack of fidelity of model hardware, particularly in simulating full-scale landing gear. Moreover, simulation of true in-flight conditions is non-trivial if not infeasible. This paper reports on an investigation of full-scale landing gear noise measured as part of the 2005 Quiet Technology Demonstrator 2 (QTD2) flight test program. Conventional Boeing 777-300ER main landing gear were tested, along with two noise reduction concepts, namely a toboggan fairing and gear alignment with the local flow, both of which were down-selected from various other noise reduction devices evaluated in model-scale testing at Virginia Tech. The full-scale toboggan fairings were designed by Goodrich Aerostructures as add-on devices allowing for complete retraction of the main gear. The baseline-conventional gear, faired gear, and aligned gear were all evaluated with the high-lift system in the retracted position and deployed at various flap settings, all at engine idle power setting. Measurements were taken with flyover community noise microphones and a large aperture acoustic phased array, yielding far-field spectra, and localized sources (beamform maps). The results were utilized to evaluate qualitatively and quantitatively the merit of each noise reduction concept. Complete similarity between model-scale and full-scale noise reduction levels was not found and requires further investigation. Far-field spectra exhibited no noise reduction for both concepts across all angles and frequencies. Phased array beamform maps show inconclusive evidence of noise reduction at selective frequencies (1500 to 3000 Hz) but are otherwise in general agreement with the far-field spectra results (within measurement uncertainty).

Elkoby, Ronen↗
NASA NTRS1995

Microwave and infrared simulations of an intense convective system and comparison with aircraft observations

A three-dimensional cloud model, radiative transfer model-based simulation system is tested and validated against the aircraft-based radiance observations of an intense convective system in southeastern Virginia on 29 June 1986 during the Cooperative Huntsville Meteorological Experiment. NASA's ER-2, a high-altitude research aircraft with a complement of radiometers operating at 11-micrometer infrared channel and 18-, 37-, 92-, and 183-GHz microwave channels provided data for this study. The cloud model successfully simulated the cloud system with regard to aircraft- and radar-observed cloud-top heights and diameters and with regard to radar-observed reflectivity structure. For the simulation time found to correspond best with the aircraft- and radar-observed structure, brightness temperatures T(sub b) are simulated and compared with observations for all the microwave frequencies along with the 11-micrometer infrared channel. Radiance calculations at the various frequencies correspond well with the aircraft observations in the areas of deep convection. The clustering of 37-147-GHz T(sub b) observations and the isolation of the 18-GHz values over the convective cores are well simulated by the model. The radiative transfer model, in general, is able to simulate the observations reasonably well from 18 GHz through 174 GHz within all convective areas of the cloud system. When the aircraft-observed 18- and 37-GHz, and 90- and 174-GHz T(sub b) are plotted against each other, the relationships have a gradual difference in the slope due to the differences in the ice particle size in the convective and more stratiform areas of the cloud. The model is able to capture these differences observed by the aircraft. Brightness temperature-rain rate relationships compare reasonably well with the aircraft observations in terms of the slope of the relationship. The model calculations are also extended to select high-frequency channels at 220, 340, and 400 GHz to simulate the Millimeter-wave Imaging Radiometer aircraft instrument to be flown in the near future. All three of these frequencies are able to discriminate the convective and anvil portions of the system, providing useful information similar to that from the frequencies below 183 GHz but with potentially enhanced spatial resolution from a satellite platform. In thin clouds, the dominant effect of water vapor is seen at 174, 340, and 400 GHz. In thick cloudy areas, the scattering effect is dominant at 90 and 220 GHz, while the overlaying water vapor can attenuate at 174, 340, and 400 GHz. All frequencies (90-400 GHz) show strong signatures in the core.

Prasad, N.↗
DOE OSTI2014

Synthesis and Characterization of Supported Cobalt-Manganese Nanoparticles as Model Catalysts for Fischer-Tropsch Synthesis

Supported Co is an effective catalyst for the Fischer-Tropsch synthesis of various hydrocarbon products that can be converted to diesel. Recent studies have shown that the formation of methane can be suppressed and the formation of C 5+ products enhanced by promoting Co with Mn. Because the activity and product selectivity of Co-based catalysts are dependent on the size of Co nanoparticles and the extent of Co promotion by Mn, it is desirable to understand these effects by investigating the performance of Co nanoparticles with well-defined size and elemental composition. The present study was undertaken with the aim of producing well-defined nanoparticles of Co and Co-Mn and then supporting them on silica. Co and Co-Mn particles were synthesized through the polyol reduction of Co and Mn acetylacetonates. By controlling synthesis conditions, Co particles with diameters of 7-10 nm and similarly sized Co-Mn (Mn/Co=0.1) particles were prepared. XRD and elemental mapping with scanning TEM-energy-dispersive X-ray spectroscopy and scanning TEM-electron energy loss spectroscopy studies suggested that most of the Mn species was associated with the Co particles. Ex situ prepared Co and Co-Mn nanoparticles were first supported on silica and then investigated for the catalytic activity for the Fischer-Tropsch synthesis. The turnover frequencies and product distributions obtained with silica-supported Co and Co-Mn nanoparticles were similar to those obtained with catalysts prepared by using the conventional incipient wetness impregnation method. However, the rate of CO consumption per mass of Co was much lower for the catalysts produced by supporting ex situ prepared nanoparticles. This effect was attributed to the sintering of the nanoparticles during their calcination and reduction. Magnetic interactions among nanoparticles during their immobilization and thermal pretreatment were identified as the primary cause of sintering. Balancing yin and yang energy: The immobilization of well-defined cobalt-manganese nanoparticles on porous supports leads to the formation of Fischer-Tropsch catalysts with turnover frequencies and product selectivities comparable to those of conventionally prepared catalysts. The catalytic activity per cobalt mass is found to be significantly lower owing to sintering. Finally, magnetic interactions among nanoparticles during immobilization and thermal pretreatment are identified as the primary cause of this phenomenon.

cobalt↗
DOE OSTI2018

Characterization of core–shell nanostructure consisting Si–Au–SiO{sub 2} based on manipulation of optical properties

In this article, we investigated some physical characteristics of core–shell nanostructure in optical regime and perturbation has been also introduced as an effective method in shaping of optical properties. The proposed nanostructures are composed of the selected materials as: Silicon, Silicon Dioxide and Gold. At first, the extinction cross section spectra are calculated for multilayer core–shell nanostructures in optical range and the configuration effect of the constructed materials in a multilayer nanostructure are investigated for determination of Plasmon range. Then, the new structures of core–shell nanoparticles (gold–silicon) are presented, which have an amount of impurity particle in their shells as perturbation and also their extinction cross section spectra are calculated. The obtained results in this article give a proper approach about perturbation effect in broadening, sharpening and shifting of optical response which are decisive factors especially nano-network systems. Indeed, it has been proposed that the impurity particles in the shells can be a mechanism for tuning of optical characteristics of the presented nanoparticles in practical fields and also creation of local oscillations as plasmonic resonances in a considered optical range. Besides, redshift in extinction cross section can be also created by particle perturbation. At the end, the effective permittivity of the perturbed core-shells are extracted. The optional frequency range is selected between 300 and 900 (THz).

77 NANOSCIENCE AND NANOTECHNOLOGY↗