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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 883 records · Page 49

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NASA NTRS1986

Influence of Rayleigh-Doppler broadening on the selection of H2O dial system parameters

Computer simulations have enabled the performance of a H2O Differential Absorption Lidar (DIAL) system to be studied by spectrally analyzing the forward propagating and backscattered laser energy. The simulations were done for a high altitude (21 km) DIAL system operating in a nadir-viewing mode. The influence of Rayleigh Doppler broadening on DIAL measurement accuracies were evaluated and show that the Rayleigh broadening influence, which can be corrected to first order in regions free of large aerosol gradients, reduces the sensitivity of DIAL H2O measurement errors in the upper tropospheric region. The ability to correct the Rayleigh broadening and the selection of H2O DIAL parameters when all the systematic effects are combined, were discussed.

Ismail, S.↗

NASA NTRS1987

DYCAST: A finite element program for the crash analysis of structures

DYCAST is a nonlinear structural dynamic finite element computer code developed for crash simulation. The element library contains stringers, beams, membrane skin triangles, plate bending triangles and spring elements. Changing stiffnesses in the structure are accounted for by plasticity and very large deflections. Material nonlinearities are accommodated by one of three options: elastic-perfectly plastic, elastic-linear hardening plastic, or elastic-nonlinear hardening plastic of the Ramberg-Osgood type. Geometric nonlinearities are handled in an updated Lagrangian formulation by reforming the structure into its deformed shape after small time increments while accumulating deformations, strains, and forces. The nonlinearities due to combined loadings are maintained, and stiffness variation due to structural failures are computed. Numerical time integrators available are fixed-step central difference, modified Adams, Newmark-beta, and Wilson-theta. The last three have a variable time step capability, which is controlled internally by a solution convergence error measure. Other features include: multiple time-load history tables to subject the structure to time dependent loading; gravity loading; initial pitch, roll, yaw, and translation of the structural model with respect to the global system; a bandwidth optimizer as a pre-processor; and deformed plots and graphics as post-processors.

Pifko, A. B.↗

NASA NTRS1986

Cloud-top meridional momentum transports on Saturn and Jupiter

Cloud-tracked wind measurements reported by Sromovsky et al. were analyzed to determine meridional momentum transports in Saturn's northern middle latitudes. Results are expressed in terms of eastward and northward velocity components (u and v), and eddy components u and v. At most latitudes between 13 and 44 deg N (planetocentric), the transport by the mean flow ( ) is measurably southward, tending to support Saturn's large equatorial jet, and completely dominating the eddy transport. Meridional velocities are near zero at the peak of the relatively weak westward jet; along the flanks of that jet, measurements indicate divergent flow out of the jet. In this region the dominant eddy transport ( ) is northward on the north side of the jet, but not resolvable on the south side. Eddy transports at most other latitudes are not significantly different from measurement error. The conversion of eddy kinetic energy to mean kinetic energy, indicated by the correlation between and d /dy (where y is meridional distance) is clearly smaller than various values reported for Jupiter, and not significantly different from zero. Both Jovian and Saturnian results may be biased by the tendency for cloud tracking to favor high contrast features, and thus may not be entirely representative of the cloud level motions as a whole.

Stromovsky, L. A.↗

NASA NTRS1987

A comprehensive estimate of the static aerodynamic forces and moments of the 8 x 8 x 20 ft. cargo container

A comprehensive static aerodynamic simulation model of the 8 by 8 by 20 ft MILVAN cargo container is determined by combining the wind tunnel data from a 1972 NASA Ames Research Center study taken over the restricted domain (0 is less than or equal to phi is less than or equal to 90 degrees; 0 is less than or equal to alpha is less than or equal to 45 degrees) with extrapolation relations derived from the geometric symmetry of rectangular boxes. It is found that the aerodynamics of any attitude can be defined from the aerodynamics at an equivalent attitude in the restricted domain (0 is less than phi is less than 45 degrees; 0 is less than alpha is less than 90 degrees). However, a similar comprehensive equivalence with the domain spanned by the data is not available; in particular, about two-thirds of the domain with the absolute value of alpha is greater than 45 degrees is unrelated to the data. Nevertheless, as estimate can be defined for this region consistent with the measured or theoretical values along its boundaries and the theoretical equivalence of points within the region. These descrepancies are assumed to be due to measurement errors. Data from independent wind tunnel studies are reviewed; these are less comprehensive than the NASA Ames Research Center but show good to fair agreement with both the theory and the estimate given here.

Cicolani, Luigi↗

NASA NTRS1987

Static calibration of the RSRA active-isolator rotor balance system

The Rotor Systems Research Aircraft (RSRA) active-isolator system is designed to reduce rotor vibrations transmitted to the airframe and to simultaneously measure all six forces and moments generated by the rotor. These loads are measured by using a combination of load cells, strain gages, and hydropneumatic active isolators with built-in pressure gages. The first static calibration of the complete active-isolator rotor balance system was performed in l983 to verify its load-measurement capabilities. Analysis of the data included the use of multiple linear regressions to determine calibration matrices for different data sets and a hysteresis-removal algorithm to estimate in-flight measurement errors. Results showed that the active-isolator system can fulfill most performance predictions. The results also suggested several possible improvements to the system.

Acree, C. W., Jr.↗

NASA NTRS1987

Optical strain measurement system development

A laser speckle, differential strain measurement system has been built and tested for future applications in hostile environments. One-dimensional electronic correlation of speckle pattern movement allows a quasi-real time measure of strain. The system has been used successfully to measure uniaxial strain reaching into plastic deformation of a test specimen, at temperatures ranging to 450 C. A resolution of 16 microstrain is given by the photodiode array sensor pitch and the specimen to sensor separation. The strain measurement error is estimated to be +/-18 microstrain +/-3 percent of the strain reading. The upper temperature limit of the gauge is determined by air density perturbations causing decorrelation of the reference and shifted speckle patterns, and may be improved by limiting convective flow in the immediate vicinity of the test specimen.

Lant, Christian T.↗

NASA NTRS1986

Modeling Pluto-Charon mutual eclipse events. I - First-order models

The present 'first order' analytical and numerical models of light curves due to mutual events between close planetary binaries, the effects of shadowing are included. Attention is given to the case of the Pluto-Charon system. The results of the analytical and numerical approaches agree to well within the expected light curve measurement error. The model predicts that the current mutual eclipse event series will end by November 1990.

Dunbar, R. Scott↗

NASA NTRS1987

Fast-response, high-precision carbon monoxide sensor using a tunable diode laser absorption technique

A tunable diode laser instrument, denoted as DACOM (Differential Absorption CO Measurement), has been developed to meet the fast-response, high-precision CO measurement needs of the GTE (Global Tropospheric Experiment) program. Under the GTE program, DACOM participated in the three field missions of CITE 1 (Chemical Instrumentation Test and Evaluation 1), a project involving the intercomparison of trace gas measurement techniques. DACOM performance, including analyses of measurement error sources, is discussed for the ground-based mission at Wallops Island, VA (summer 1983), and two missions on the NASA CV-990 (fall 1983 and spring 1984). Examples of fast-response (about 1 s), high-precision (+ or - 1 part per billion by volume, + or - 1.5 percent of reading) airborne data are included to illustrate the capability of this instrument.

Sachse, Glen W.↗

NASA NTRS1987

The effect of the dynamic wet troposphere on radio interferometric measurements

A statistical model of water vapor fluctuations is used to describe the effect of the dynamic wet troposphere on radio interferometric measurements. It is assumed that the spatial structure of refractivity is approximated by Kolmogorov turbulence theory, and that the temporal fluctuations are caused by spatial patterns moved over a site by the wind, and these assumptions are examined for the VLBI delay and delay rate observables. The results suggest that the delay rate measurement error is usually dominated by water vapor fluctuations, and water vapor induced VLBI parameter errors and correlations are determined as a function of the delay observable errors. A method is proposed for including the water vapor fluctuations in the parameter estimation method to obtain improved parameter estimates and parameter covariances.

Treuhaft, R. N.↗

NASA NTRS1987

Fine-scale motion in the central Orion nebula

The inner region of M42 has been mapped in the O III N1 forbidden line at an unprecedented combination of velocity and spatial resolution and photometric accuracy. Three separate velocity systems along the line of sight are identified. Differential mass flow is present in two of these systems. All three systems show random fluctuations in velocity well above their measurement errors. The point-by-point velocities are used to determine the diagnostic statistical parameter, the structure function. The random motions show correlation with spatial separation, as expected for turbulence; but comparison with the predictions of classical theory for nebular turbulence shows poor agreement. If Kolmogorov (1941, 1942) theory applies, then the energy must be input at many scales.

Castaneda, Hector O.↗

NASA NTRS1987

A systematic search for long-term variability in a large sample of X-ray sources

A method which uses the correct measurement error distribution (Poisson) and which naturally takes into account detections as well as upper limits has been developed to search for flux variability in X-ray sources. The method is applied to 256 sources observed at least twice with the Einstein Observatory Imaging Proportional Counter. These sources have, in the very large majority of cases, an X-ray flux in the range 1 x 10 to the -13th to 6 x 10 to the -12th erg/sq cm/s (0.2-3.5 keV). Thirty-one sources show flux variations with amplitude ranging from about 20 percent to a factor of 6. Flux variations of small amplitude seem to be fairly common, but can be detected only in bright sources or in sources observed with very long exposures. Variations of a factor of 2 or more are seen in about 15 percent of the sources for which variations of such an amplitude are detectable.

Maccacaro, Tommaso↗

NASA NTRS1987

Studies of multi-baseline spaceborne interferometric synthetic aperture radars

A set of Seasat SAR data that were obtained in nearly repeat ground track orbits is utilized to simulate the performance of spaceborne interferometric synthetic aperture radar (ISAR) systems. A qualitative assessment of the topography measurement capability is presented. A phase measurement error model is described and compared with the data obtained at various baseline separations and signal-to-noise ratios. Finally, the implications of these results on the future spaceborne ISAR design are discussed.

Li, F.↗

NASA NTRS1988

Sine-Bar Attachment For Machine Tools

Sine-bar attachment for collets, spindles, and chucks helps machinists set up quickly for precise angular cuts that require greater precision than provided by graduations of machine tools. Machinist uses attachment to index head, carriage of milling machine or lathe relative to table or turning axis of tool. Attachment accurate to 1 minute or arc depending on length of sine bar and precision of gauge blocks in setup. Attachment installs quickly and easily on almost any type of lathe or mill. Requires no special clamps or fixtures, and eliminates many trial-and-error measurements. More stable than improvised setups and not jarred out of position readily.

Mann, Franklin D.↗

NASA NTRS1987

Non-linearity in measurement systems: Evaluation method and application to microwave radiometers

A simple method for determination and correction of nonlinaearity in measurement systems is presented. The technique is applicable to a wide range of measuring systems. The basic concept, an analysis, and a sample application are given. Nonlinearity of the Goldstone DSS 13 low noise HEMT 2.3 GHz (S-band) radiometer system results in noise temperature measurement errors. These errors are successfully correct with this method.

Stelzried, C. T.↗

NASA NTRS1988

A multivariate variational objective analysis-assimilation method. Part 1: Development of the basic model

The variational method of undetermined multipliers is used to derive a multivariate model for objective analysis. The model is intended for the assimilation of 3-D fields of rawinsonde height, temperature and wind, and mean level temperature observed by satellite into a dynamically consistent data set. Relative measurement errors are taken into account. The dynamic equations are the two nonlinear horizontal momentum equations, the hydrostatic equation, and an integrated continuity equation. The model Euler-Lagrange equations are eleven linear and/or nonlinear partial differential and/or algebraic equations. A cyclical solution sequence is described. Other model features include a nonlinear terrain-following vertical coordinate that eliminates truncation error in the pressure gradient terms of the horizontal momentum equations and easily accommodates satellite observed mean layer temperatures in the middle and upper troposphere. A projection of the pressure gradient onto equivalent pressure surfaces removes most of the adverse impacts of the lower coordinate surface on the variational adjustment.

Achtemeier, Gary L.↗

NASA NTRS1988

Synchronous response modelling and control of an annular momentum control device

Research on the synchronous response modelling and control of an advanced Annular Momentun Control Device (AMCD) used to control the attitude of a spacecraft is described. For the flexible rotor AMCD, two sources of synchronous vibrations were identified. One source, which corresponds to the mass unbalance problem of rigid rotors suspended in conventional bearings, is caused by measurement errors of the rotor center of mass position. The other sources of synchronous vibrations is misalignment between the hub and flywheel masses of the AMCD. Four different control algorithms were examined. These were lead-lag compensators that mimic conventional bearing dynamics, tracking notch filters used in the feedback loop, tracking differential-notch filters, and model-based compensators. The tracking differential-notch filters were shown to have a number of advantages over more conventional approaches for both rigid-body rotor applications and flexible rotor applications such as the AMCD. Hardware implementation schemes for the tracking differential-notch filter were investigated. A simple design was developed that can be implemented with analog multipliers and low bandwidth, digital hardware.

Hockney, Richard↗

NASA NTRS1988

Optical strain measurement system development

A laser speckle, differential strain measurement system has been built and tested for future applications in hostile environments. One-dimensional electronic correlation of speckle pattern movement allows a quasi-real time measure of strain. The system has been used successfully to measure uniaxial strain reaching into plastic deformation of a test specimen, at temperatures ranging to 450 C. A resolution of 126 microstrain is given by the photodiode array sensor pitch and the specimen to sensor separation. The strain measurement error is estimated to be +/-18 microstrain +/-3 percent of the strain reading. The upper temperature limit of the gauge is determined by air density perturbations causing decorrelation of the reference and shifted speckle patterns, and may be improved by limiting convective flow in the immediate vicinity of the test specimen.

Lant, Christian T.↗

NASA NTRS1988

Measurement of the properties of lossy materials inside a finite conducting cylinder

A computer code was developed to automatically perform swept frequency reflection and transmission measurements using a HP5510B Network Analyzer and computer. This software is used in conjunction with a modified high temperature test rig to obtain reflection measurements from a flat material sample. The software allows data processing to eliminate measurement errors and to obtain a reflection coefficient in the frequency or time domain. A description of the program is presented.

Caldecott, R.↗