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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

An AOTV aeroheating and thermal protection study

The aerothermodynamics and thermal protection of aerobraking orbital transfer vehicles are studied with a view toward design methodology and technology requirements. A particular class of geometries is investigated: the ellipsoidally blunted raked-off elliptic cone. Discussed are the influence of various geometrical parameters on the trajectory and the heat flux as well as heating prediction methods ranging from an engineering correlation formula to computational solutions of the Navier-Stokes equations. Finite-rate catalytic thermal protection materials and gas radiation are considered. Estimates of the specific mass of possible thermal protection systems indicate that support structure is a large contributor to the aerobrake mass as compared with the thermal protection insulation itself. Sizing curves are included which enable the designer to estimate the size aerobrake required from heating considerations for different mass vehicles having aerobrakes of several specific masses.

Scott, C. D.↗
NASA NTRS1984

Remarks on a vibronic origin for the diffuse band spectrum

It has been demonstrated that the diffuse band spectrum could not originate as a series of vibronic transitions from atomic impurities in interstellar MgO grains as has recently been proposed since laboratory spectra of such materials show no evidence for such complex structure. Furthermore, recent observational evidence indicates that the extinction feature at 160 nm in the standard interstellar extinction curve upon which the identification of interstellar MgO was founded is actually the result of a calibration error in the original observational data.

Nuth, J. A.↗
NASA NTRS1985

The composition and origin of the Iapetus dark material

In order to investigate the composition of the Iapetus dark material and the reasons for its peculiar distribution, telescopic observations, laboratory simulations, and photogeological studies are conducted. New telescopic spectra of superior accuracy and wavelength coverage for leading and trailing hemispheres are obtained over the range 0.3-2.6 microns. A mixing model is used to correct the leading-hemisphere spectra for the presence of polarcaps. It is shown that the spectral curve of pure Iapetus dark material is highly reddened in the visible, but gradually flattens near 2.0 microns. Structures along the bright-dark boundary, visible in Voyager 2 images, are inconsistent with an eruptive origin for the dark material; this zone is probably the region of grazing impacts of dust spiraling from Phoebe and the dark material is probably a minor component of the ice-dominated surface concentrated in the upper regolith produced by Phoebe-dust bombardment. An Iapetus-like bombardment regime may account for the hemispheric dichotomy of regolith properties on Callisto.

Bell, J. F.↗
NASA NTRS1990

A counterrotating core in the merger remnant candidate NGC 3656 (ARP 155)

A study is presented of the internal velocity structure of NGC 3656, a galaxy with several morphological signatures of being in an advanced merger stage. Rotation curves obtained for two slit-position angles show that the inner 1 kpc rotates around an axis roughly perpendicular to the rotation axis in the main body of the galaxy. There are indications that the galaxy is not dynamically relaxed at intermediate radii. The presence of an orthorotating core in a dynamically young galaxy with a dust disk and a shell system provides strong evidence linking kinematically peculiar cores to mergers. However, relating the various merger signatures in this system is not straightforward, as the core and the dust disk rotate around axes perpendicular to each other, which may indicate an independent origin.

Balcells, Marc↗
NASA NTRS1994

Time-dependent analysis of 8 days of CN spatial profiles in comet P/Halley

CN profiles in comet P/Halley were constructed from observations taken at three observatories during an 8 day period in April 1986. These data provide a time series of CN spatial profiles spanning just over one 7.37 day period from 1986 April 7 to April 15 and sample distances from the nucleus from just over 10(exp 3) km to 10(exp 6) km. The effect of the 7.37 day periodic variation on the CN distribution in P/Halley has been examined by using the time-dependent model applied earlier to a subset of the data. Because of the large spatial scale of the data on April 7, 8, and 9 (approx. 10(exp 6) km), and the corresponding transport time in the coma, information present in the spatial profiles regarding the gas production rate actually covers nearly two full periods. These spatially extended profiles clearly show the wavy structures outside 10(exp 5) km. Such structures were predicted in a previous analysis (Combi & Fink 1993) that was based solely on the photometric light curve and on profiles which only extended to distances less than 10(exp 5) km. We are now able to reproduce the highly variable Halley correction for the variation in gas production rate.

Combi, Michael↗
NASA NTRS2020

Computationally-efficient Structural Models for Analysis of Woven Composites

The paper presents a novel approach to model woven composite using the computationally efficient one-dimensional models. The framework is built within the scheme of the Carrera Unified Formulation (CUF), a generalized hierarchical formulation that generates variable kinematic structural theories. Various components of the woven composite unit cell are modeled using a combination of straight and curved one-dimensional CUF models. By employing a component-wise approach, a modeling technique within CUF, the complex geometry of the woven composite components is modeled precisely. The ability of CUF models to accurately resolve stress and strain fields are exploited to capture complex deformation within a woven composite unit cell. Numerical results include analyses of a non-crimped textile composite, a curved tow under tension, and a dry woven textile unit cell.

Kaleel, Ibrahim↗
NASA NTRSDate not supplied

Goniometric and Polarized Imaging Spectroscopic Lab Measurements ofSpacecraft Materials

To better characterize the spectral response of common spacecraft materials, the following laboratory measurements are presented to support the Space Situational Awareness community in the analysis of remotely sensed observational data. Of interest is classifying material reflective properties using spectral bidirectional reflectance distribution function (BRDF) data and spatially resolved polarized imaging spectroscopy, allowing laboratory data to be applicable to ground-based optical telescope observations. The team acquired a typical CubeSat solar panel and a sample of multi-layer insulation commonly used on spacecraft for initial measurements. The data were collected at the Goniometer of the Rochester Institute of Technology (GRIT) laboratory with a field and laboratory goniometer housing two Analytical Spectral Device (ASD) spectrometers and a Headwall micro-Hyperspec E-Series imaging spectrometer with an adjustable linear polarizer. The goniometer provides spectral reflectance over a broad spectral range from 350-2500 nm at 1 nm spacing with 3 nm spectral resolution in the visible and near infrared and 8 nm in the shortwave infrared. The Headwall imager covers a spectral range from 400-1000 nm with 1.6 nm spectral resolution. We present the results from these initial measurements that show highly reflective regions at various locations in the angular domain for both materials. In addition, the solar cell spectra exhibited strong interference effects typically observed with thin films. Our team is pursuing a variety of typical solar cells to assess variations in product type. The spatially resolved polarization ratio maps show variability across the materials due to surface structure and varying material composition. Based on these results, we outline a plan for simulating spectral radiance light curves of the materials in various orbital configurations as they would be measured from ground- based telescopes for a clear observing sky during twilight. The paper will also present a plan for expanding ours of interest to determine if the results presented are unique to these samples and to categorize the spectral response for different material classes.

Chris H. Lee↗
DOE OSTI2017

Why wind-farm developers should care about measuring atmospheric turbulence? [Chaos in the Air: Unraveling the Complex Relationship Between Wind Power and Atmospheric turbulence]

The role of atmospheric turbulence in influencing wind-turbine power production remains an unsolved mystery despite a growing number of researchers who have attempted to make sense of this issue. Turbulence, a term for short-term deviations around the average wind speed, can cause fluctuations in turbine power production and structural loads. While research strongly suggests that ignoring atmospheric turbulence can result in significant errors in power-curve measurements and annual energy production, it appears that there may be no universal relationship between turbulence and power production. Typically when we think of a wind farm operating in a turbulent atmosphere, we picture a waked turbine, battered by vortex eddies (circular wind flow) shed from turbine blades upwind. However, turbulence is present nearly everywhere, and is constantly produced and diminished over a wide range of temporal and spatial scales. This article aims to unravel some of the complex factors that remain unsolved regarding turbulence and wind power

17 WIND ENERGY↗
DOE OSTI2015

Additive Manufacturing Materials Study for Gaseous Radiation Detection

Additive manufacturing (AM) techniques may lead to improvements in many areas of radiation detector construction; notably the rapid manufacturing time allows for a reduced time between prototype iterations. The additive nature of the technique results in a granular microstructure which may be permeable to ingress by atmospheric gases and make it unsuitable for gaseous radiation detector development. In this study we consider the application of AM to the construction of enclosures and frames for wire-based gaseous radiation tracking detectors. We have focussed on oxygen impurity ingress as a measure of the permeability of the enclosure, and the gas charging and discharging curves of several simplistic enclosure shapes are reported. A prototype wire-frame is also presented to examine structural strength and positional accuracy of an AM produced frame. We lastly discuss the implications of this study for AM based radiation detection technology as a diagnostic tool for incident response scenarios, such as the interrogation of a suspect radiation-emitting package. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Thermoluminescence and glow curves analysis of γ-exposed Eu{sup 3+} doped K{sub 3}Y(PO{sub 4}){sub 2} nanophosphors

Highlights: • First time, a detailed comparative study of the glow curves and kinetic parameters was made on K{sub 3}Y(PO{sub 4}){sub 2} nanophosphor. • Combustion method was employed to synthesize the Eu{sup 3+} doped K{sub 3}Y(PO{sub 4}){sub 2} nanophosphor. • The nanophosphor exhibited sublinear response suggesting that it is suitable for TL dosimetry. - Abstract: Eu{sup 3+} doped K{sub 3}Y(PO{sub 4}){sub 2} nanophosphor was synthesized by combustion synthesis using urea as a fuel. The crystal structure and particle morphology of the nanophosphor were investigated by using X-ray diffraction and transmission electron microscopy, respectively. A Thermoluminescence (TL) study was carried out after exposing the samples to gamma radiation. The TL glow curves exhibited a prominent peak at 407 K and a small hump at 478 K. The intensity of the peaks increased with the increase in the dose of the gamma rays (0.01–5 kGy). The K{sub 3}Y(PO{sub 4}){sub 2}: Eu{sup 3+} (2.5 mol%) nanophosphor exhibited sublinear TL response to γ-radiation over a wide range of gamma doses (0.01–5 kGy). The TLanal program was used to analyze the glow curves of the K{sub 3}Y(PO{sub 4}){sub 2} nanophosphor at different doses (0.2–5 kGy) and different heating rates (3–10 K/s). A comparative study was done for kinetic trapping parameters that were determined by the peak shape methods of Chen, Grossweiner and Lushchik. The frequency factors (s) for each glow peak were also calculated. The values of the activation energy (E) obtained by the TLanal program were in good agreement with those obtained by the peak shape methods. The effect of different amount of doses and different heating rates are discussed.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Five micron limb-darkening and the structure of the Jovian atmosphere

A combined radiative, dynamical, and chemical model of the Jovian atmosphere is presented which reproduces the observed IR limb-darkening curves for several regions on the disk of Jupiter. Two approaches are used to perform the inversion required for determination of the source function, and a power-series-expansion model is examined, along with a convective-equilibrium model, cloud and intermediate-zone models, and a thin-shell model. The statistical methods used in the analysis are outlined, and model fits to the observations are discussed. The chemistry of phase transitions in the hot spots of Jupiter's equatorial belt is briefly investigated.

Newman, W. I.↗
NASA NTRS1991

Evolution of three-dimensionality in stable and unstable curved mixing layers

Results are presented of an experimental study tracing the effects of mild streamwise curvature (delta/R is less than 5 percent) on the 3D structure of a two-stream mixing layer at high Reynolds number (about 27,000). Measurements of the mean and fluctuating velocities were obtained on fine cross-plane grids at 11 streamwise locations using a rotatable cross-wide probe. Well-organized streamwise vorticity was generated in both cases through the braid instability. Although the vortex structures decayed with streamwise distance in both cases, the rate of decay for the unstable case was lower. As a result, the unstable layer exhibited noticeable spanwise variations in the mean velocity and Reynolds stresses. Both cases achieved linear growth, but the rate of growth for the unstable case was higher. The far-field spanwise-averaged peak Reynolds stresses were significantly higher for the destabilized case compared to the stabilized case, which exhibited levels comparable to those of a straight case.

Plesniak, Michael W.↗
DOE OSTI2018

Grain Refinement by Authigenic Inoculation Inherited from the Medium-Range Order Structure of Ni-Cr-W Superalloy

The combination of liquidus casting and thermal control solidification furnace was applied to obtain a fine-grained ingot. A rapid quenching method and x-ray diffraction measurement were used to investigate the effect of authigenic inoculation on grain refinement. The structure factor S(Q) of liquid Ni-Cr-W superalloy at 1400 °C (Liquidus temperature) and bright-field image of the microstructures quenched from 1400 °C have been measured by the high-temperature x-ray diffractometer and the transmission electron microscopy (TEM), respectively. The results show that a pre-peak exists on a S(Q) curve at the liquidus temperature. The clusters of atom in rapidly quenched microstructures obtained by isothermal heat treatment at 1400 °C were studied using TEM. Meanwhile, the effect of isothermal different temperatures on rapidly quenched microstructures was studied. The results also show that there are only the globular, equiaxed grains distributed in the solidification structure. These particles are inherited from the medium-range order structure, which is beneficial for grain refinement. The normalized work-hardening rate-strain curve indicates the work-hardening rate of fine grain is higher than that of conventional grain at the same temperature and the same deformation.

36 MATERIALS SCIENCE↗
NASA NTRS2015

Aeroelastic Analysis of a Flexible Wing Wind Tunnel Model with Variable Camber Continuous Trailing Edge Flap Design

This paper presents data analysis of a flexible wing wind tunnel model with a variable camber continuous trailing edge flap (VCCTEF) design for drag minimization tested at the University of Washington Aeronautical Laboratory (UWAL). The wind tunnel test was designed to explore the relative merit of the VCCTEF concept for improved cruise efficiency through the use of low-cost aeroelastic model test techniques. The flexible wing model is a 10%-scale model of a typical transport wing and is constructed of woven fabric composites and foam core. The wing structural stiffness in bending is tailored to be half of the stiffness of a Boeing 757-era transport wing while the torsional stiffness is about the same. This stiffness reduction results in a wing tip deflection of about 10% of the wing semi-span. The VCCTEF is a multi-segment flap design having three chordwise camber segments and five spanwise flap sections for a total of 15 individual flap elements. The three chordwise camber segments can be positioned appropriately to create a desired trailing edge camber. Elastomeric material is used to cover the gaps in between the spanwise flap sections, thereby creating a continuous trailing edge. Wind tunnel data analysis conducted previously shows that the VCCTEF can achieve a drag reduction of up to 6.31% and an improvement in the lift-to-drag ratio (L=D) of up to 4.85%. A method for estimating the bending and torsional stiffnesses of the flexible wingUWAL wind tunnel model from static load test data is presented. The resulting estimation indicates that the stiffness of the flexible wing is significantly stiffer in torsion than in bending by as much as 9 to 1. The lift prediction for the flexible wing is computed by a coupled aerodynamic-structural model. The coupled model is developed by coupling a conceptual aerodynamic tool Vorlax with a finite-element model of the flexible wing via an automated geometry deformation tool. Based on the comparison of the lift curve slope, the lift prediction for the rigid wing is in good agreement with the estimated lift coefficients derived from the wind tunnel test data. Due to the movement of the VCCTEF during the wind tunnel test, uncertainty in the lift prediction due to the indicated variations of the VCCTEF deflection is studied. The results show a significant spread in the lift prediction which contradicts the consistency in the aerodynamic measurements, thus suggesting that the indicated variations as measured by the VICON system may not be reliable. The lift prediction of the flexible wing agrees very well with the measured lift curve for the baseline configuration. The computed bending deflection and wash-out twist of the flexible wing also match reasonably well with the aeroelastic deflection measurements. The results demonstrate the validity of the aerodynamic-structural tool for use to analyze aerodynamic performance of flexible wings.

Wind Tunnel↗
NASA NTRS2016

Unsteady Aerodynamic Force Sensing from Measured Strain

A simple approach for computing unsteady aerodynamic forces from simulated measured strain data is proposed in this study. First, the deflection and slope of the structure are computed from the unsteady strain using the two-step approach. Velocities and accelerations of the structure are computed using the autoregressive moving average model, on-line parameter estimator, low-pass filter, and a least-squares curve fitting method together with analytical derivatives with respect to time. Finally, aerodynamic forces over the wing are computed using modal aerodynamic influence coefficient matrices, a rational function approximation, and a time-marching algorithm. A cantilevered rectangular wing built and tested at the NASA Langley Research Center (Hampton, Virginia, USA) in 1959 is used to validate the simple approach. Unsteady aerodynamic forces as well as wing deflections, velocities, accelerations, and strains are computed using the CFL3D computational fluid dynamics (CFD) code and an MSC/NASTRAN code (MSC Software Corporation, Newport Beach, California, USA), and these CFL3D-based results are assumed as measured quantities. Based on the measured strains, wing deflections, velocities, accelerations, and aerodynamic forces are computed using the proposed approach. These computed deflections, velocities, accelerations, and unsteady aerodynamic forces are compared with the CFL3D/NASTRAN-based results. In general, computed aerodynamic forces based on the lifting surface theory in subsonic speeds are in good agreement with the target aerodynamic forces generated using CFL3D code with the Euler equation. Excellent aeroelastic responses are obtained even with unsteady strain data under the signal to noise ratio of -9.8dB. The deflections, velocities, and accelerations at each sensor location are independent of structural and aerodynamic models. Therefore, the distributed strain data together with the current proposed approaches can be used as distributed deflection, velocity, and acceleration sensors. This research demonstrates the feasibility of obtaining induced drag and lift forces through the use of distributed sensor technology with measured strain data. An active induced drag control system thus can be designed using the two computed aerodynamic forces, induced drag and lift, to improve the fuel efficiency of an aircraft. Interpolation elements between structural finite element grids and the CFD grids and centroids are successfully incorporated with the unsteady aeroelastic computation scheme. The most critical technology for the success of the proposed approach is the robust on-line parameter estimator, since the least-squares curve fitting method depends heavily on aeroelastic system frequencies and damping factors.

shape sensing↗
DOE OSTI2018

Systematics of the Third Row Transition Metal Melting: The HCP Metals Rhenium and Osmium

The melting curves of rhenium and osmium to megabar pressures are obtained from an extensive suite of ab initio quantum molecular dynamics (QMD) simulations using the Z method. In addition, for Re, we combine QMD simulations with total free energy calculations to obtain its phase diagram. Our results indicate that Re, which generally assumes a hexagonal close-packed (hcp) structure, melts from a face-centered cubic (fcc) structure in the pressure range 20–240 GPa. We conclude that the recent DAC data on Re to 50 GPa in fact encompass both the true melting curve and the low-slope hcp-fcc phase boundary above a triple point at (20 GPa, 4240 K). A linear fit to the Re diamond anvil cell (DAC) data then results in a slope that is 2.3 times smaller than that of the actual melting curve. The phase diagram of Re is topologically equivalent to that of Pt calculated by us earlier on. Regularities in the melting curves of Re, Os, and five other 3rd-row transition metals (Ta, W, Ir, Pt, Au) form the 3rd-row transition metal melting systematics. We demonstrate how this systematics can be used to estimate the currently unknown melting curve of the eighth 3rd-row transition metal Hf.

36 MATERIALS SCIENCE↗
NASA NTRS1933

Comparison of Three Methods for Calculating the Compressive Strength of Flat and Slightly Curved Sheet and Stiffener Combinations

This report gives a comparison of the accuracy of the three methods for calculating the compressive strength of flat sheet and stiffener combinations such as occur in stressed-skin or monocoque structures for aircraft. Of the three methods based upon various assumptions with regard to the interaction of sheet and stiffener, the method based upon mutual action of the stiffener and an effective width as a column gave the best agreement with the results of the tests. An investigation of the effect of small curvature resulted in the conclusion that the compressive strength of the curved panels is, for all practical purposes, equal to the strength of flat panels except for thick sheet where non-uniform curvature throughout the length may cause the strength of the curved panel to be 10 to 15 percent less than that of a corresponding flat panel.

STRESSED SKIN↗