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All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Hi-5: A Potential High-Contrast Thermal Near-Infrared Imager for the VLTI

Hi-5 is a high-contrast (or high dynamic range) infrared imager project for the VLTI. Its main goal is to characterize young extra-solar planetary systems and exozodiacal dust around southern main-sequence stars. In this paper, we present an update of the project and key technology pathways to improve the contrast achieved by the VLTI. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5 μm) and advanced fringe tracking strategies. We also address the strong exoplanet science case (young exoplanets, planet formation, and exozodiacal disks) offered by this wavelength regime as well as other possible science cases such as stellar physics (fundamental parameters and multiplicity) and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed.

exozodiacal dust↗
NASA NTRS2009

Impact of Lake Okeechobee Sea Surface Temperatures on Numerical Predictions of Summertime Convective Systems over South Florida

The NASA Short-term Prediction Research and Transition (SPoRT) Center, the Florida Institute of Technology, and the NOAA/NWS Weather Forecast Office at Miami, FL (MFL) are collaborating on a project to investigate the impact of using high-resolution, 2-km Moderate Resolution Imaging Spectroradiometer (MODIS) sea surface temperature (SST) composites within the Weather Research and Forecasting (WRF) prediction system. The NWS MFL is currently running WRF in real-time to support daily forecast operations, using the National Centers for Environmental Prediction Nonhydrostatic Mesoscale Model dynamical core within the NWS Science and Training Resource Center's Environmental Modeling System (EMS) software. Twenty-seven hour forecasts are run daily initialized at 0300, 0900, 1500, and 2100 UTC on a domain with 4-km grid spacing covering the southern half of Florida and adjacent waters of the Gulf of Mexico and Atlantic Ocean. The SSTs are initialized with the NCEP Real-Time Global (RTG) analyses at 1/12deg resolution. The project objective is to determine whether more accurate specification of the lower-boundary forcing over water using the MODIS SST composites within the 4-km WRF runs will result in improved sea fluxes and hence, more accurate e\~olutiono f coastal mesoscale circulations and the associated sensible weather elements. SPoRT conducted parallel WRF EMS runs from February to August 2007 identical to the operational runs at NWS MFL except for the use of MODIS SST composites in place of the RTG product as the initial and boundary conditions over water. During the course of this evaluation, an intriguing case was examined from 6 May 2007, in which lake breezes and convection around Lake Okeechobee evolved quite differently when using the high-resolution SPoRT MODIS SST composites versus the lower-resolution RTG SSTs. This paper will analyze the differences in the 6 May simulations, as well as examine other cases from the summer 2007 in which the WRF-simulated Lake Okeechobee breezes evolved differently due to the SST initialization. The effects on wind fields and precipitation systems will be emphasized, including validation against surface mesonet observations and Stage IV precipitation grids.

Case, Jonathan L.↗
NASA NTRS1988

Numerical simulation of helicopter multi-bladed rotor flow

A numerical method for solving the Euler equations for multiblade rotors has been developed. The computed results, including one nonlifting forward-flight and several lifting hovering cases, are compared with experimental data. For forward-flight case, the unsteady growth and decay of the shock agree well with experimental results. For hovering case, at low and moderate transonic tip speed, the results show good agreement with experimental data in the tip region. The near-wake effects can be captured without wake modeling.

Chen, C. L.↗
NASA NTRS2024

Wilson Corners, Solid Waste Management Unit 001(SWMU 01) 2023 Annual Long-Term Monitoring Report

This report presents a summary of the long-term monitoring (LTM) activities that occurred in 2023 at Wilson Corners, Solid Waste Management Unit 001, at Kennedy Space Center (KSC), Florida. Annual LTM of groundwater is being conducted at the site. Based on results from groundwater sampling activities performed during the 2019 through 2020 LTM reporting period and the 2020 and 2021 DPT groundwater sampling, it was determined that the LTM sampling plan was no longer meeting the goal of LTM because delineation was not verified and the installation of an air sparge (AS) system to treat the area of the High Concentration Plume was recommended. The AS System was installed in late 2022 and early 2023. System start-up activities were initiated in April 2023. Following system startup, several site wells required retrofitting to equip wellheads for withstanding the air pressure released from air sparge wells during system operation. Some site wells also required repair or abandonment, and replacement. Survey of location and top-of-casing of newly installed monitoring wells was combined with scheduled AS system survey activities and was completed in January 2024. The activities presented in this report include the February and April 2023 LTM monitoring well installations; March and April 2023 LTM and performance monitoring well water level gauging and sampling; November 2023 LTM well retrofits and repairs; a summary of December 2023 LTM well abandonments and installations (complete site well abandonment activities will be presented under a separate cover); and January 2024 LTM well survey. During the March and April 2023 sampling events, the low-flow sampling method was used, and samples were analyzed for a select list of volatile organic compounds. In March 2023, groundwater flow for the site was generally to the west was generally consistent with historical observations at the site. The Low Concentration Plume (LCP) continues to extend both horizontally and vertically beyond the terminal depth of the current monitoring well network. Data, inclusive of the 2023 LTM and baseline performance monitoring sampling events, indicate that the LCP encompasses an estimated 19.5 acres, compared to the 2021 LCP footprint, inclusive of the 2020 and 2021 DPT sampling events of 20.7 acres. The vertical extent of VOCs was historically delineated by monitoring wells screened greater than 48 feet below land surface (bls). The results from the three vertical extent monitoring wells screened below 48 feet bls that were sampled during the 2023 LTM indicate that groundwater vinyl chloride concentrations in these three wells are greater than the GCTL. As presented in the 2021 Long-Term Monitoring Report (NASA 2022), the KSCRT agreed to delay deeper investigations in this area to prevent the creation of additional pathways for vertical migration. Based on groundwater sampling activities performed in 2023, recommendations are to perform the next annual LTM sampling event, scheduled for April 2024 and to conduct quarterly performance monitoring of the AS System. The current selection of monitoring wells in the recommended 2024 LTM plan will provide an adequate data set for monitoring groundwater plume behavior; however, the LTM monitoring well network will be evaluated and refined based on 2024 LTM and year one performance monitoring data.

King Linnea↗
NASA NTRS2004

Aquarius Instrument Science Calibration During the Risk Reduction Phase

This final report presents the results of work performed under NASA Grant NAG512726 during the period 15 January 2003 through 30 June 2004. An analysis was performed of a possible vicarious calibration method for use by Aquarius to monitor and stabilize the absolute and relative calibration of its microwave radiometer. Stationary statistical properties of the brightness temperature (T(sub B)) measured by a low Earth orbiting radiometer operating at 1.4135 GHz are considered as a means of validating its absolute calibration. The global minimum, maximum, and average T(sub B) are considered, together with a vicarious cold reference method that detects the presence of a sharp lower bound on naturally occurring values for T(sub B). Of particular interest is the reliability with which these statistics can be extracted from a realistic distribution of T(sub B) measurements that would be observed by a typical sensor. Simulations of measurements are performed that include the effects of instrument noise and variable environmental factors such as the global water vapor and ocean surface temperature, salinity and wind distributions. Global minima can vary widely due to instrument noise and are not a reliable calibration reference. Global maxima are strongly influenced by several environmental factors as well as instrument noise and are even less stationary. Global averages are largely insensitive to instrument noise and, in most cases, to environmental conditions as well. The global average T(sub B) varies at only the 0.1 K RMS level except in cases of anomalously high winds, when it can increase considerably more. The vicarious cold reference is similarly insensitive to instrument effects and most environmental factors. It is not significantly affected by high wind conditions. The stability of the vicarious reference is, however, found to be somewhat sensitive (at the several tenths of Kelvins level) to variations in the background cold space brightness, T(sub c). The global average is much less sensitive to this parameter and so using two approaches together can be mutually beneficial.

Ruf, Christopher S.↗
NASA NTRS2004

Unsteady Validation of a Mean Flow Boundary Condition for Computational Aeroacoustics

In this work, a previously developed mean flow boundary condition will be validated for unsteady flows. The test cases will be several reference benchmark flows consisting of vortical gusts convecting in a uniform mean flow, as well as the more realistic case of a vortical gust impinging on a loaded 2D cascade. The results will verify that the mean flow boundary condition both imposes the desired mean flow as well as having little or no effect on the instantaneous unsteady solution.

Hixon, R.↗
NASA NTRS1992

Low gravity quenching of hot tubes with cryogens

An experimental proceedure for examining flow boiling in low gravity environment is presented. The proceedure involves both ground based and KC-135 flight experiments. Two experimental apparati were employed, one for studying subcooled liquid boiling and another for examining saturated liquid boiling. For the saturated flow experiments, liquid nitrogen was used while freon 113 was used for the subcooled flow experiments. The boiling phenomenon was investigated in both cases using flow visualization techniques as well as tube wall temperature measurements. The flow field in both cases was established by injecting cold liquid in a heated tube whose temperature was set above the saturation values. The tubes were both vertically and horizontally supported with the liquid injected from the lower end of the tube. The results indicate substantial differences in the flow patterns established during boiling between the ground based, (1-g), experiments and the flight experiments, (low-g). These differences in the flow patterns will be discussed and some explanations will be offered.

Antar, Basil N.↗
NASA NTRS1984

A survey of strength analysis methods for laminates with holes

The methods for predicting the strength of composite laminates with fastener holes are reviewed for the cases of unloaded as well as loaded holes. Three categories of methods are discussed: (1) the hole-boundary stress (HBS) methods which compare the peak stresses and the laminate strength; (2) the linear elastic fracture (LEFM) methods which assume cracks emanating from the hole and predict failure when the stress intensity factor for a crack equals the laminate fracture toughness; and (3) two different two-parameter (TP) methods: the average-stress (ASTP) method, which predicts failure when the average stress over a distance from the hole equals the laminate strength; and the point-stress (PSTP) Whitney-Nuismer (1974) approach, which predicts failure when the stress near the hole equals the material strength. The PSTP is relatively accurate and is by far the most widely used of all the prediction methods. However, for large ranges of variables and cases, the current strength predictions may not always be accurate.

Crews, J. H., Jr.↗
NASA NTRS2017

Summary of Propagation Cases of the Second AIAA Sonic Boom Prediction Workshop

A summary is provided for the propagation portion of the second AIAA Sonic Boom Workshop held January 8, 2017 in conjunction with the AIAA SciTech 2017 conference. Near-field pressure waveforms for two cases were supplied and ground signatures at multiple azimuthal angles as well as their corresponding loudness metrics were requested from 10 participants, representing 3 countries. Each case had some required, as well as some optional runs. The required cases included atmospheric profiles with measured data including winds, using Radiosonde balloon data at multiple geographically spread locations. The humidity profiles provided for the optional cases were taken from ANSI guidance, as the authors were unaware of an accepted standard at the time the cases were released to the participants. Participants provided ground signatures along with the requested data, including some loudness metrics using their best practices, which included lossy as well as lossless atmospheric propagation schemes. All the participants’ submissions, for each case, are compared and discussed. Noise or loudness measures are calculated and detailed comparisons and statistical analyses are performed and presented. It has been observed that the variation in the loudness measures and spread between participants’ submissions increased as the computation proceeded from under-track locations towards the lateral cut-off. Lessons learned during this workshop are discussed and recommendations are made for potential improvements and possible subsequent workshops as we collectively attempt to refine our analysis methods.

Rallabhandi, Sriram↗
NASA NTRS1991

Equilibrium wave spectrum and sea state bias in satellite altimetry

For a well-developed sea at equilibrium with a constant wind, the energy-containing range of the wavenumber spectrum for wind-generated gravity waves is approximated by a generalized power law involving the angular spread function and mu, interpreted as a fractal codimension of a small surface patch. Dependence of mu on the wave age is estimated, and the 'Phillips constant', beta, along with the low-wavenumber boundary, k0, of the inertial subrange are analyzed on the basis of the wave action and energy conservation principles. The resulting expressions are employed to evaluate various non-Gaussian statistics of a weakly nonlinear sea surface, which determine the sea state bias in satellite altimetry. The locally accelerated decay of the spectral density function in a high-wavenumber dissipation subrange is pointed out as an important factor of wave dynamics and the geometrical optics treatment of the sea state bias. The analysis is carried out in the approximation of a unidirectional wave field and confined to the case of a well-developed sea.

Glazman, Roman E.↗
NASA NTRS2008

Verification of a Constraint Force Equation Methodology for Modeling Multi-Body Stage Separation

This paper discusses the verification of the Constraint Force Equation (CFE) methodology and its implementation in the Program to Optimize Simulated Trajectories II (POST2) for multibody separation problems using three specially designed test cases. The first test case involves two rigid bodies connected by a fixed joint; the second case involves two rigid bodies connected with a universal joint; and the third test case is that of Mach 7 separation of the Hyper-X vehicle. For the first two cases, the POST2/CFE solutions compared well with those obtained using industry standard benchmark codes, namely AUTOLEV and ADAMS. For the Hyper-X case, the POST2/CFE solutions were in reasonable agreement with the flight test data. The CFE implementation in POST2 facilitates the analysis and simulation of stage separation as an integral part of POST2 for seamless end-to-end simulations of launch vehicle trajectories.

Tartabini, Paul V.↗
NASA NTRS1997

An Experimental Investigation on the Static Equilibria and Dynamics of Liquid Bridges

A liquid bridge is a volume of liquid held between two or more solid supports. In the case of small disk supports with a sharp edge, the contact line between the bridge and the support disk will be anchored along the edge of the disk. For these cases the solid presents a geometrical singularity and the contact angle is indeterminate within a given range. This dissertation presents research conducted on liquid bridges with anchored contact lines. The three major topics covered are: determining the role of support geometry on static equilibria, liquid bridge dynamical behavior, and forces exerted by a liquid bridge on a support structure. The work was primarily experimental and conducted in a "Plateau tank" that allowed for the simulation of equivalent low-gravity conditions. The main thrust of the experimental work involved the use of a high resolution optical measurement system for imaging the dynamic zone shape, measurement of the static and dynamic contact angles and non-invasive analysis of excited surface modes. The liquid bridge was manipulated by computer controlled linear actuators which allowed precise control over the physical characteristics of the bridge. Experiments have been carried out to locate a bifurcation point along the maximum volume axisymmetric stability margin. Below the critical slenderness the bifurcation from an axisymmetric to a stable nonaxisymmetric configuration is supercritical. However, above this critical slenderness, the bifurcation is subcritical. A series of experiments analyzed the effect on axisymmetric bridge stability by using support disks of different radii, The shape behavior as transition points were approached, as well as the limiting case of a vanishing support radius was investigated. Experiments were performed to determine the resonant frequencies of axisymmetric bridges subject to lateral vibrations. Anomolous results led to a series of experiments to characterize nonlinearities present in the dynamic bridge shape. Finally, an attempt was made to experimentally measure the force exerted by the bridge on the lower support disk. This was done through use of a force balance apparatus. Particular attention was paid to the behavior of the bridge as the minimum volume stability limit was approached.

Resnick, Andrew Howard↗
NASA NTRS1993

An analysis of isothermal, bithermal, and thermomechanical fatigue data of Haynes 188 and B1900+Hf by energy considerations

The low-cycle fatigue behavior of Haynes 188 and B1900+Hf under isothermal, bithermal, and thermomechanical loading conditions has been analyzed on the basis of the total hysteresis energy expended per cycle. It has been observed that in the case of isothermal fatigue the total hysteresis energy correlates well with the fatigue life. In the case of bithermal 'high rate' fatigue, for a given total hysteresis energy per cycle, the fatigue life is equal to or greater than the isothermal fatigue life at the maximum bithermal temperature. This observation could be used to establish a lower bound on life for design purposes. In one case of bithermal creep-fatigue and in thermomechanical fatigue, the life is shorter than that corresponding to the isothermal life at the maximum temperature. The energy supplied, per se, may not always give a systematic correlation with the fatigue life in the cases where time-dependent creep and environmental effects are encountered. Thus, in bithermal creep-fatigue and thermomechanical fatigue, the role of creep and environment and their dependence on the energy supplied have to be properly accounted for before the energy term can be used for life prediction.

Radhakrishnan, V. M.↗
NASA NTRS1982

Review of factors that influence fretting wear

An assessment is made of presently obtained as well as published results in order to characterize the effects of contact conditions, environmental conditions, and material properties and behavior on fretting wear. The importance of material properties is discussed on the basis of interaction with other factors during fretting. While the isolated effect of contact load, fretting amplitude, temperature and atmosphere have been well explored, especially for the case mild steel, a deficiency is noted in studies of the effects of contact geometry and relative humidity, as well as the interaction of various fretting parameters.

Bill, R. C.↗
NASA NTRS2017

Summary of Propagation Cases of the Second AIAA Sonic Boom Prediction Workshop

A summary is provided for the propagation portion of the second AIAA Sonic Boom Workshop held January 8, 2017 in conjunction with the AIAA SciTech 2017 conference. Near-field pressure waveforms for two cases were supplied and ground signatures at multiple azimuthal angles as well as their corresponding loudness metrics were requested from 10 participants, representing 3 countries. Each case had some required runs, as well as some optional runs. The required cases included atmospheric profiles with measured data including winds, using Radiosonde balloon data at multiple geographically spread locations, while the optional cases included temperature and pressure profiles from the US Standard atmosphere. The humidity profiles provided for the optional cases were taken from ANSI guidance, as the authors were unaware of an accepted standard at the time the cases were released to the participants. Participants provided ground signatures along with the requested data, including some loudness metrics using their best practices, which included lossy as well as lossless schemes. All the participants' submissions, for each case, are compared and discussed. Noise or loudness measures are calculated and detailed comparisons and statistical analyses are performed and presented. It has been observed that the variation in the loudness measures and spread between participants' submissions increased as the computation proceeded from under-track locations towards the lateral cut-off. Lessons learned during this workshop are discussed and recommendations are made for potential improvements and possible subsequent workshops as we collectively attempt to refine our analysis methods.

Rallabhandi, Sriram↗
NASA NTRS1971

Surface field analysis of splitting of orbitals of atoms and ions approaching a metal surface.

The splitting of p- and d-orbitals of an atom or an ion which is caused by the locally varying potential near the surface of a realistic metal has been studied for bcc and fcc substrates. A quasi-ionic model is reasonable at close distance, inasmuch as the electron gas does not completely screen the ionic cores. The arrangement of ion cores near the surface causes the potential to vary in three dimensions. Expressions for energy levels were derived for an unsymmetric group using the quasi-ionic model and techniques used in the treatment of crystal field of nearest neighbors. A number of cases involving ions, as well as atoms in the vicinity of a metal substrate were numerically evaluated.

Rao, P. V. S.↗
NASA NTRS1973

Application of holography to the determination of flow conditions within the rotating blade row of a compressor

The double-pulse, double-exposure holography technique was applied to visualize the flow field within a transonic compressor rotor with a tip speed of 1800 ft/sec. The principal objective was to visualize the shock waves created in the flow field which was supersonic relative to the rotating blade row. The upstream rotor blade bow shocks and, at high speed, the outermost portion of the leading edge passage shock were successfully observed in the holograms. Techniques were devised for locating these shocks in three dimensions, and the results were compared with theoretical predictions. Density changes between the two pulses due to motion of the shocks were large and, therefore, it was not possible to resolve the fringe systems in detail for the 100% speed conditions. However, gross features of the shocks were easily observed, and the upstream shocks were well displayed. In all cases the shock angles were somewhat larger than predicted by theory, and a distinct increase in angle near the outer wall was observed, which may be attributed to endwall boundary layer effects. The location and orientation of the observed leading edge passage shocks were in good agreement with static pressure contours obtained from measurements in the outer casing over the rotor tip.

Hantman, R. G.↗