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At least 451 records · Page 25

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NASA NTRS1996

Non-Contact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites

A 13 mJ NdYAG 1064 nm, 4 ns, laser pulse was employed to produce ultrasonic plate waves in 20 percent porous SiC/SiC composite tensile specimens of three different architectures. An air coupled 0.5 MHz transducer was used to detect and collect the waveforms which contained first antisymmetric plate wave pulses for determining the shear wave velocity (VS). These results were compared to VS values determined on the same specimens with 0.5 MHz ultrasonic transducers with contact coupling. Averages of four noncontact determinations on each of 18 specimens were compared to averages of four contact values. The noncontact VS's fall in the same range as the contact. The standard deviations for the noncontact VS's averaged 2.8 percent. The standard deviations for the contact measurements averaged 2.3 percent, indicating similar reproducibility. Repeated laser pulsing at the same location always lead to deterioration of the ulu-"nic signal. The signal would recover in about 24 hr in air however, indicating that no permanent damage was produced.

Kautz, Harold E.↗

NASA NTRS1996

A technique for determining cloud free vs cloud contaminated pixels in satellite imagery

Since the first earth orbiting satellite sent pictures of the earth back to them, atmospheric scientists have been focused on the possibilities of using that information as both a forecasting tool and as a meteorological research tool. With the latest generation of Geostationary Operational Environmental Satellites (GOES) now entering service, that view of the earth yields views at a frequency and resolution never before available. These satellites have imagers with a five band multi-spectral capability with high spatial resolution. In addition, the sounder has eighteen thermal infrared (IR) channels plus one low-resolution visible band. With a resolution as small as one kilometer, GOES provides scientists with a powerful eye on the atmosphere. Menzel and Purdom (1994) detail both the imager and sounder capability as well as other systems on the GOES satellites. Immediately apparent in the visible channel are the patterns of clouds swirling over both oceans and continents. These clouds range in size from huge planetary systems covering thousands of kilometers to puffy fair weather cumulus clouds on the order of half a kilometer in size. With the IR sensors temperature patterns are observed. High clouds appear very cold, while low stratus field show temperatures near that of the surface. The surface, in turn, generally appears warmer than the clouds. It would seem then a simple manner to determine cloud and surface temperature from the imagery, but such is not the case. While most of the atmospheric constituents are well mixed and homogeneous, water vapor is not. The water molecule, because of its unique structure and vibration modes, affects the transmittance of the atmosphere most notably in the infrared regions. There are regions of the IR spectrum where water vapor acts as a strong absorber, and at others it is nearly transparent. The transparent wavelengths are called windows, and one such window occurs at 11.2 microns. Adjacent to this window at 12.7 microns which is strongly absorbed by water vapor. These two wavelengths form what is known as a split window, the utility of which was used. Using the linearized form of the radiative transfer equation, they were able to use the split window to determine the amount of water vapor present in the atmosphere. Jedlovec developed the physical split-window (PSW) technique which determines the integrated water content (IWC). The PSW method using Visible Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) found on the older versions of the GOES satellites was used. Recently, Jedlovec and colleagues have been attempting to apply the PSW method using full disk IR imagery obtained by the new generation of GOES satellites. IWC is essential for improved analysis and prediction of convective storms which have been observed to develop in regions of both strong and rapidly evolving moisture gradients. It has also been used in the prediction of clouds and precipitation.

Wohlman, Richard A.↗

NASA NTRS1994

The Determination of Forces and Moments on a Gimballed SRM Nozzle Using a Cold Flow Model

The Solid Rocket Motor Air Flow Facility (SAF) at NASA Marshall Space Flight Center was used to characterize the flow in the critical aft end and nozzle of a solid propellant rocket motor (SRM) as part of the design phase of development. The SAF is a high pressure, blowdown facility which supplies a controlled flow of air to a subscale model of the internal port and nozzle of a SRM to enable measurement and evaluation of the flow field and surface pressure distributions. The ASRM Aft Section/Nozzle Model is an 8 percent scale model of the 19 second burn time aft port geometry and nozzle of the Advanced Solid Rocket Motor, the now canceled new generation space Shuttle Booster. It has the capability to simulate fixed nozzle gimbal angles of 0, 4, and 8 degrees. The model was tested at full scale motor Reynolds Numbers with extensive surface pressure instrumentation to enable detailed mapping of the surface pressure distributions over the nozzle interior surface, the exterior surface of the nozzle nose and the surface of the simulated propellant grain in the aft motor port. A mathematical analysis and associated numerical procedure were developed to integrate the measured surface pressure distributions to determine the lateral and axial forces on the moveable section of the nozzle, the effective model thrust and the effective aerodynamic thrust vector (as opposed to the geometric nozzle gimbal angle). The nozzle lateral and axial aerodynamic loads and moments about the pivot point are required for design purposes and require complex, three dimensional flow analyses. The alignment of the thrust vector with the nozzle geometric centerline is also a design requirement requiring three dimensional analyses which were supported by this experimental program. The model was tested with all three gimbal angles at three pressure levels to determine Reynolds number effects and reproducibility. This program was successful in demonstrating that a measured surface pressure distribution could be integrated to determine the lateral and axial loads, moments and thrust vector alignment for the scaled model of a large space booster nozzle. Numerical results were provided which are scaleable to the full scale rocket motor and can be used as benchmark data for 3-D CFD analyses.

Whitesides, R. Harold↗

NASA NTRS1994

The Relationship Between Area-Time Integrals Determined from Satellite Infrared Data by Means of a Fixed-Threshold Approach and Convective Rainfall Volumes

The relationship of the rainfall from convective clouds to area-time integrals determined from satellite infrared data using a fixed infrared-temperature threshold is investigated. Concurrent radar and rapid-scan satellite data obtained during field projects in the northern High Plains and the southeastern United States were used in this study. The fixed IR threshold appropriate for each region was determined by an optimization procedure that identified the brightness threshold that yields the strongest relationship between estimated rainfall from a cloud cluster and its satellite Area-Time Integral (ATI) for each dataset. For the North Dakota-Montana area the optimization procedure indicated that the area enclosed by the -22.5 C isotherm provides satellite ATI values most closely related to the estimated rainfalls. For the southeastern United States project, the optimized tem- perature threshold was 8.5'C. The difference between the thresholds determined for the two geographic areas suggests that a different 'calibration' for each distinct area may be needed to make use of this relationship. Slopes of the two log-log rainfall-ATI regressions are less than unity, indicating that a relative horizontal expansion and/or increase in persistence of a cloud cluster exceeds the associated increase in precipitation. Implications for the Geostationary Operational Environmental Satellite precipitation index are discussed. New results concerning the rain volume-radar ATI relationship for the southeastern United States are also appended to the paper.

Johnson, L. Ronald↗

NASA NTRS1997

A Predictive Attitude Determination Algorithm

In this paper, a new and efficient algorithm is developed for attitude determination from vector observations. The new algorithm, called the Predictive Attitude Determination (PAD) algorithm, is derived from a general nonlinear predictive filter approach. Traditional deterministic algorithms are shown to be suboptimal for anisotropic measurement errors. The major advantage of the PAD algorithm is that it can be easily applied to the case where anisotropic measurement errors exist. Also, an analytical expression is derived for the steady-state attitude error covariance, which is shown to be equivalent to the optimal covariance derived from maximum likelihood techniques. Simulation studies indicate that the new algorithm is able to accurately determine the attitude of a spacecraft, even for radically anisotropic measurement errors.

Markley, F. Landis↗

NASA NTRS1997

Use of Variable Angle Spectroscopic Ellipsometry in Order to Determine Contaminant Optical Properties

In order to measure contaminant levels found in the manufacture of the Redesigned Solid Rocket Motor (RSRM), optical properties of the contaminants are needed to develop standards for calibration purposes. Specific to our efforts is the determination of the complex index of refraction for a hydrocarbon mixture and a commercial methyl siloxane. Using ellipsometric measurements with multiple angles of incident and a range of wavelengths in the near infrared a determination of the index of refraction and the extinction coefficient were made for the contaminants. This paper will present the optical techniques and modeling approach used to determine these optical constants of the hydrocarbon mixture and the methyl siloxane studied.

Hughes, C.↗

NASA NTRS1998

Global Qualitative Flow-Path Modeling for Local State Determination in Simulation and Analysis

For qualitative modeling and analysis, a general qualitative abstraction of power transmission variables (flow and effort) for elements of flow paths includes information on resistance, net flow, permissible directions of flow, and qualitative potential is discussed. Each type of component model has flow-related variables and an associated internal flow map, connected into an overall flow network of the system. For storage devices, the implicit power transfer to the environment is represented by "virtual" circuits that include an environmental junction. A heterogeneous aggregation method simplifies the path structure. A method determines global flow-path changes during dynamic simulation and analysis, and identifies corresponding local flow state changes that are effects of global configuration changes. Flow-path determination is triggered by any change in a flow-related device variable in a simulation or analysis. Components (path elements) that may be affected are identified, and flow-related attributes favoring flow in the two possible directions are collected for each of them. Next, flow-related attributes are determined for each affected path element, based on possibly conflicting indications of flow direction. Spurious qualitative ambiguities are minimized by using relative magnitudes and permissible directions of flow, and by favoring flow sources over effort sources when comparing flow tendencies. The results are output to local flow states of affected components.

Malin, Jane T.↗

NASA NTRS1998

Determination of Yield and Flow Surfaces for Inconel 718 Under Axial-Torsional Loading at Temperatures Up to 649 C

An experimental program to determine flow surfaces has been established and implemented for solution annealed and aged IN718. The procedure involved subjecting tubular specimens to various ratios of axial-torsional stress at temperatures between 23 and 649 C and measuring strain with a biaxial extensometer. Each stress probe corresponds to a different direction in stress space, and unloading occurs when a 30 microstrain (1 micro eplison = 10(exp -6) mm/mm) offset is detected. This technique was used to map out yield loci in axial-torsional stress space. Flow surfaces were determined by post-processing the experimental data to determine the inelastic strain rate components. Surfaces of constant inelastic strain rate (SCISRS) and surfaces of constant inelastic power (SCIPS) were mapped out in the axial-shear stress plane. The von Mises yield criterion appeared to closely fit the initial loci for solutioned IN718 at 23 C. However, the initial loci for solutioned IN718 at 371 and 454 C, and all of the initial loci for aged IN718 were offset in the compression direction. Subsequent loci showed translation, distortion, and for the case of solutioned IN718, a slight cross effect. Aged IN718 showed significantly more hardening behavior than solutioned IN718.

Gil, Christopher M.↗

NASA NTRS1958

Analytical and Experimental Determination of the Coupled Natural Frequencies and Mode Shapes of a Dynamic Model of a Single-Rotor Helicopter

A combined analytical and experimental determination is made of the coupled natural frequencies and mode shapes in the longitudinal plane of symmetry for a dynamic model of a single-rotor helicopter. The analytical phase is worked out on the basis of a seven-degree-of-freedom system combining elastic deflections of the rotor blades, rotor shaft, pylon, and fuselage. The calculated coupled frequencies are first compared with calculated uncoupled frequencies to show the general effects of coupling and then with measured coupled frequencies to determine the extent to which the coupled frequencies can be calculated. The coupled mode shapes are also calculated and were observed visually with stroboscopic lights during the tests. A comparison of the coupled and uncoupled natural frequencies shows that significant differences exist between these frequencies for some of the modes. Good agreement is obtained between the measured and calculated values for the coupled natural frequencies and mode shapes. The results show that the coupled natural frequencies and mode shapes can be determined by the analytical procedure presented herein with sufficient accuracy if the mass and stiffness distributions of the various components of the helicopter are known.

Silveira, Milton A.↗

NASA NTRS1998

Determination of Yield in Inconel 718 for Axial-Torsional Loading at Temperatures up to 649 C

An experimental program has been implemented to determine small offset yield loci under axial-torsional loading at elevated temperatures. The nickel-base superalloy Inconel 718 (IN718) was chosen for study due to its common use in aeropropulsion applications. Initial and subsequent yield loci were determined for solutioned IN718 at 23, 371, and 454 C and for aged (precipitation hardened) IN718 at 23 and 649 C. The shape of the initial yield loci for solutioned and aged IN718 agreed well with the von Mises prediction. However, in general, the centers of initial yield loci were eccentric to the origin due to a strength-differential (S-D) effect that increased with temperature. Subsequent yield loci exhibited anisotropic hardening in the form of translation and distortion of the locus. This work shows that it is possible to determine yield surfaces for metallic materials at temperatures up to at least 649 C using multiple probes of a single specimen. The experimental data is first-of-its-kind for a superalloy at these very high temperatures and will facilitate a better understanding of multiaxial material response, eventually leading to improved design tools for engine designers.

Gil, Christopher M.↗

NASA NTRS1998

Determination of Yield in Inconel 718 for Axial-Torsional Loading at Temperatures up to 649 C

Gil, Christopher M.↗

NASA NTRS1999

Determination of the Corrosive Conditions Present within Aircraft Lap-Splice Joints

The complexity of airframe structure lends itself to damage resulting from crevice corrosion. Fuselage lap-splice joints are a particularly important structural detail in this regard because of the difficulty associated with detection and measurement of corrosion in these occluded regions. The objective of this work is to develop a laboratory corrosion test protocol to identify the chemistry to which lap joints are exposed and to develop a model of the corrosion within the joints. A protocol for collecting and identifying the chemistry of airframe crevice corrosion has been developed. Capillary electrophoresis (CE) is used to identify the ionic species contained in corrosion product samples removed from fuselage lap splice joints. CE analysis has been performed on over sixty corrosion product samples removed from both civilian and military aircraft. Over twenty different ions have been detected. Measurements of pH of wetted corroded surfaces indicated an alkaline occluded solution. After determining the species present and their relative concentrations, the resultant solution was reproduced in bulk and electrochemical tests were performed to determine the corrosion rate. Electrochemical analyses of the behavior of AA2024-T3 in these solutions gave corrosion rates of up to 250 microns per year (10 mpy). Additional tests have determined the relative importance of each of the detected ions in model solutions used for future predictive tests. The statistically significant ions have been used to create a second generation solution. Laboratory studies have also included exposure tests involving artificial lap joints exposed to various simulated bulk and crevice environments. The extent and morphology of the attack in artificial lap joints has been compared to studies of corroded samples from actual aircraft. Other effects, such as temperature and potential, as well as the impact of the environment on fatigue crack growth have also been studied.

Lewis, Karen S.↗

NASA NTRS1967

A System Analysis for Determining Alternative Technological Issues for the Future

A systems engineering methodology is provided, by which future technological ventures may be examined utilizing particular national, corporate, or individual value judgments. Three matrix analyses are presented. The first matrix is concerned with the effect of technology on population increase, war, poverty, health, resources, and prejudice. The second matrix explores an analytical technique for determining the relative importance of different areas of technology. The third matrix explores how an individual or corporate entity may determine how its capability may be used for future technological opportunities. No conclusions are presented since primary effort has been placed on the methodology of determining future technological issues.

Magistrale, V. J.↗

NASA NTRS1971

The Determination of Trace Metals in Saline Waters and Biological Tissues Using the Heated Graphite Atomizer

A selective, volatalization technique utilizing the heated graphite atomizer atomic absorption technique has been developed for the analysis of iron in sea water. A similar technique may be used to determine vanadium, copper, nickel and cobalt in saline waters when their concentrations are higher than those normally encountered'in unpolluted sea waters. A preliminary solvent extraction using ammonium pyrolidine dithiocarbamate and methyl iso-butyl ketone permits the determination of a number of elements including iron, copper, zinc, nickel, cobalt and lead in sea water. The heated graphite atomized technique has also been applied to the determination of a range of trace transition elements in marine plant and animal tissues.

Segar, D. A.↗

NASA NTRS1999

Quantitative Computer Tomography for Determining Composition of Microgravity and Ground Based Solid Solutions

Advances in x-ray Computer Tomography (CT) have been led by the medical profession, and by evaluation of industrial products, particularly castings. Porosity can readily be determined as a function of the density of a material, and CT is thus an industrially important NDE tool. Providing high purity, 100% dense standards of pure elements and compounds can be fabricated, the composition of solid solution alloys can be determined by measuring the CT number, which is a function of the absorption of the sample. Average densities across slices 1 mm thick can generally be determined to better than 1 percent. With present technology this spatial sensitivity is less than ideal, but important benefits can nevertheless be obtained by using CT, particularly single crystals, prior to making any destructive assault upon the sample. The sample can in fact be examined prior to removal from the mold within which it has been grown and, in the cases of microgravity flight samples, before removal from the cartridge assembly. This greatly assists the researcher in the characterization of the products, particularly as a guide to cutting and sampling. Examples of work with germanium-silicon alloys and mercury cadmium telluride taken with a radioactive cobalt source will be demonstrated.

Gillies, D. C.↗

NASA NTRS1998

BATSE Observations and Orbit Determination of the Be/X-Ray Transient EXO 2030+375

The Be/X-ray binary transient pulsar EXO 2030+375 (P(sub s) approx equal 42 s) has been observed with the large area detectors (LADs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO). Beginning in May 1991, twenty-two outbursts were observed over four years. Thirteen outbursts between February 1992 and August 1993 occurred consecutively at intervals of approx equal 46 days, close to the orbital period determined by Parmar et al. (1989) using EXOSAT data. The pulse profiles from the BATSE data are double-peaked and show no significant energy or luminosity dependence, unlike the EXOSAT observations of May-August 1985. An exponential model was used to fit the observed hard X-ray energy spectra from the thirteen consecutive outbursts. When EXOSAT discovered this pulsar during a giant outburst in May 1985, the X-ray luminosity peaked at L(sub x) = 1.0 x 10(esp 38) erg/ s (1-20 keV), assuming a 5 kpc distance to the source. The BATSE outbursts are found to be weaker 0.3 x 10(exp 37) less than or equal to L(sub x)(I-20 keV) less than or equal to 3.0 x 10(exp 37) erg/ s after extrapolating the observed flux (20-50 keV) to the EXOSAT energy band. Pulse phases derived from the thirteen outbursts were fit to two different models to determine a binary orbit. The new orbit is used to estimate 95% confidence limits for the mean peak spin frequency change during the out- bursts observed with BATSE. This, and the mean peak flux, are compared to the spin-up rates and fluxes determined by EXOSAT from the 1985 giant outburst, where disk accretion was thought to have occurred. It is unclear if these normal outbursts were driven by wind or disk accretion.

Strollberg, Mark T.↗

NASA NTRS1999

Corona Structure and Heating Constraints Determined from SERTS Observations

Intensities of the Extreme-ultraviolet (EUV) spectral lines were measured as a function of radius off the solar limb by two flights of the Goddard's Solar Extreme-ultraviolet Rocket Telescope and Spectrograph (SERTS) for three quiet sun regions. Density scale heights were determined for the different spectral lines. Limits on the filling factor were determined. In the one case where an upper limit was determined it was much less than unity. Coronal heating above 1.15 solar radii is required for all three regions studied. For reasonable filling factors, local heating is needed.

Falconer, D. A.↗

NASA NTRS2000

Spacecraft Attitude Determination Methods

This document is presentation in viewgraph form, which outlines the methods of determining spacecraft attitude. The presentation reviews several parameterizations relating to spacecraft attitude, such as Euler's Theorem, Rodriques parameters, and Euler-Rodriques parameters or Quaternion. Onboard attitude determination is the norm, using either single frame or filtering methods. The presentation reviews several mathematical representations of attitude. The mechanisms for determining attitude on board the Hubble Space Telescope, the Tropical Rainfall and Measuring Mission and the Solar Anomalous and Magnetospheric Particle Explorer are reviewed. Wahba's problem, Procrustes Problem, and some solutions are also summarized.

Markley, F. Landis↗