SEARCH · Engineering Papers

Results for “confidence”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57

All sources NASA NTRS DOE OSTI

NASA NTRS1987

Laboratory study of the spectrum of highly ionized calcium in the 100-250 A range applied to solar flare diagnostics

Calcium was introduced into the TEXT tokamak, and its spectral emission was recorded in the 50-360 A range by an absolutely calibrated grazing incidence spectrometer. These observations of highly ionized species of calcium at known conditions of plasma electron temperature and density allow testing of line brightness ratio predictions based on theoretical values of temperature-dependent electron excitation rates. The confirmation of the expected ratios in Be I-like to O I-like calcium allows more confident use of these ratios as a density diagnostic of remote astrophysical sources such as solar flares.

Lippmann, S.↗

NASA NTRS1987

Periodicities of the flare occurrence rate in solar cycle 19

The occurrence rate of major flares during solar cycle 19 has been analyzed. A periodicity of 51 d is found, which is one-third of the period found from the flare rates of solar cycles 20 and 21 by various authors. The statistical significance of the periodicity is estimated to be at 99.85-percent confidence level. This periodicity is though to be related to the 153-d periodicity. The template of the phase diagram is well described by a constant plus a sine function. Additionally, an 18-month periodicity is found in the flare rate of the northern hemisphere.

Bai, T.↗

NASA NTRS1985

In-flight measurement of rotor hub drag using the RSRA - A feasibility demonstration

The Rotor Systems Research Aircraft (RSRA) is a compound helicopter that was test flown as a fixed-wing aircraft, with the main rotor blades removed and the rotor hub installed. An onboard rotor load-measurement system measured the resulting rotor hub drag and lift. Measured hub drag and lift are plotted for comparison to that predicted by full-scale and 1/6-scale model wind-tunnel tests. The success of the demonstration gives confidence that planned improvements to the RSRA will allow high-accuracy hub drag and lift measurements to be made in flight on a routine research basis.

Acree, C. W., Jr.↗

NASA NTRS1987

Wind-tunnel preflight test program for aeroassist flight experiment

A proposed Aeroassist Flight Experiment (AFE) will simulate return from geosynchronous orbit to low-earth orbit to provide fundamental information about the hypersonic flow conditions surrounding aeroassisted orbital transfer vehicles (AOTV's). Future AOTV design must rely heavily on computational fluid dynamic (CFD) computer codes now under development, since the entry conditions are beyond the simulation capabilities of ground-based test facilities. However, existing codes and best available ground-based test facilities must provide for design of the AFE. The AFE ground-based test program provides data for calibration of existing and developing pertinent CFD codes. Confidence in code prediction capability increases with ability to predict forces and moments, pressure and heat-transfer distributions, shock shapes, and surface streamline directions. The ground-based test program provides these data over a wide range of hypersonic test parameters. This paper describes the test program, models, facilities, and some representative results.

Wells, William L.↗

NASA NTRS1986

Comparison of two models of total electron content at three midlatitude stations

TEC values calculated with the Bent model were used instead of actual data for the Madrid Deep Space Communications Complex during most of the Voyager Uranus approach and encounter. These values were used from December 1, 1985 to January 16, 1986 for Voyager Uranus, and for March 1986 to support the Pathfinder mission; thus, the Halley flybys of Vega 1 and 2 and Giotto were included. Provided sunspot numbers are below 130, the Bent model can be used with confidence to calculate TEC values for midlatitude stations when actual TEC data or monthly averages are not available.

Royden, H. N.↗

NASA NTRS1987

A comparison of SAGE 1, SBUV, and Umkehr ozone profiles including a search for Umkehr aerosol effects

Using a spatially weighted average for the stratospheric aerosol and gas experiment 1 (SAGE 1) events derived from an autocorrelation analysis, 337 colocated SAGE 1 and Umkehr ozone profiles are found. The total column ozone in layers two through nine measured by SAGE 1 is found to be 4.6 + or - 1.3 percent higher at the 95 percent confidence level than the approximate total column ozone measured by Umkehr. Average layer ozone differences indicate that most of this discrepancy resides in the lower layers. Intercomparison of SAGE 1, Nimbus 7 solar backscattered ultraviolet (SBUV), and Umkehr ozone at stations north of 30 deg indicates that, in layer six, Umkehr values are consistently higher than both SAGE 1 and SBUV by about 10 percent. In layer eight, SBUV ozone is higher than both SAGE 1 and SBUV by about 10 percent. In the upper stratosphere, the SAGE 1-Umkehr ozone differences are small for low stratospheric aerosol optical depth cases, but vary from -3 percent in layer six to -8 percent in layer nine for high optical depth cases.

Newchurch, M. J.↗

NASA NTRS1988

Processing Welding Images For Robot Control

Image data from two distinct windows used to locate weld features. Analyzer part of vision system described in companion article, "Image Control in Automatic Welding Vision System" (MFS-26035). Horizontal video lines define windows for viewing unwelded joint and weld pool. Data from picture elements outside windows not processed. Widely-separated local features carry no significance, but closely spaced features indicate welding feature. Image processor assigns confidence level to group of local features according to spacing and pattern.

Richardson, Richard W.↗

NASA NTRS1987

The global interaction of comets with the solar wind

The recent in-situ measurements of the plasma-neutral gas environment of comet Halley by the GIOTTO and VEGA spacecraft have confirmed the global theory of the comet-solar wind interaction. The ionopause, cometopause, and bow shock distances are the primary predictions of the model, although various momentum collisional cross-sections can also be estimated. With this greater confidence in the global model, the sharp Sunward intensity decrease in the spatial H2O+ profiles observed for comet Halley between 2.14 AU pre- and post-perihelion are interpreted as the cometopause boundary. This interpretation may then be used to determine the solar wind conditions local to the comet.

Houpis, Harry L. F.↗

NASA NTRS1987

A critical assessment of wind tunnel results for the NACA 0012 airfoil

A large body of experimental results, obtained in more than 40 wind tunnels on a single, well-known two-dimensional configuration, has been critically examined and correlated. An assessment of some of the possible sources of error has been made for each facility, and data which are suspect have been identified. It was found that no single experiment provided a complete set of reliable data, although one investigation stands out as superior in many respects. However, from the aggregate of data the representative properties of the NACA 0012 airfoil can be identified with reasonable confidence over wide ranges of Mach number, Reynolds number, and angles of attack. This synthesized information can now be used to assess and validate existing and future wind tunnel results and to evaluate advanced Computational Fluid Dynamics codes.

Mccroskey, W. J.↗

NASA NTRS1987

Earthquake source mechanisms and transform fault tectonics in the Gulf of California

The source parameters of 19 large earthquakes in the Gulf of California were determined from inversions of long-period P and SH waveforms. The goal was to understand the recent slip history of this dominantly transform boundary between the Pacific and North American plates as well as the effect on earthquake characteristics of the transition from young oceanic to continental lithosphere. For the better recorded transform events, the fault strike is resolved to + or - 4 deg at 90 percent confidence. The slip vectors thus provide important constraints on the direction of relative plate motion. Most centroid depths are poorly resolved because of tradeoffs between depth and source time function. On the basis of waveform modeling, historical seismicity, and other factors, it is appropriate to divide the Gulf into three distinct zones. The difference in seismic character among the three zones is likely the result of differing levels of maturity of the processes of rifting, generation of oceanic crust, and formation of stable oceanic transform faults. The mechanism of an earthquake on the Tres Marias Escarpment is characterized by thrust faulting and likely indicates the direction of relative motion between the Rivera and North American plates. This mechanism requires revision in plate velocity models which predict strike slip motion at this location.

Goff, John A.↗

NASA NTRS1987

Some data processing requirements for precision Nap-Of-the-Earth (NOE) guidance and control of rotorcraft

Nap-Of-the-Earth (NOE) flight in a conventional helicopter is extremely taxing for two pilots under visual conditions. Developing a single pilot all-weather NOE capability will require a fully automatic NOE navigation and flight control capability for which innovative guidance and control concepts were examined. Constrained time-optimality provides a validated criterion for automatically controlled NOE maneuvers if the pilot is to have confidence in the automated maneuvering technique. A second focus was to organize the storage and real-time updating of NOE terrain profiles and obstacles in course-oriented coordinates indexed to the mission flight plan. A method is presented for using pre-flight geodetic parameter identification to establish guidance commands for planned flight profiles and alternates. A method is then suggested for interpolating this guidance command information with the aid of forward and side looking sensors within the resolution of the stored data base, enriching the data content with real-time display, guidance, and control purposes. A third focus defined a class of automatic anticipative guidance algorithms and necessary data preview requirements to follow the vertical, lateral, and longitudinal guidance commands dictated by the updated flight profiles and to address the effects of processing delays in digital guidance and control system candidates. The results of this three-fold research effort offer promising alternatives designed to gain pilot acceptance for automatic guidance and control of rotorcraft in NOE operations.

Clement, Warren F.↗

NASA NTRS1987

Evaluation of closed cubic failure criterion for graphite/epoxy laminates

An analytical method has been developed to ensure closure of the cubic form of the tensor polynomial strength criterion. The intrinsic complexity of the cubic function is such that special conditions must be met to close the failure surface in three-dimensional stress space. These requirements are derived in terms of non-intersecting conditions for asymptotes and an asymptotic plane. To demonstrate the validity of this approach, closed failure surfaces were derived for two graphite/epoxy material systems (3M SP288-T300 and IM7 8551-7). The agreement of test data with this model clearly shows that it is possible to use a higher order cubic failure theory with confidence.

Tennyson, R. C.↗

NASA NTRS1987

Embedded expert system for space shuttle main engine maintenance

The SPARTA Embedded Expert System (SEES) is an intelligent health monitoring system that directs analysis by placing confidence factors on possible engine status and then recommends a course of action to an engineer or engine controller. The technique can prevent catastropic failures or costly rocket engine down time because of false alarms. Further, the SEES has potential as an on-board flight monitor for reusable rocket engine systems. The SEES methodology synergistically integrates vibration analysis, pattern recognition and communications theory techniques with an artificial intelligence technique - the Embedded Expert System (EES).

Pooley, J.↗

NASA NTRS1987

Optimal application of Morrison's iterative noise removal for deconvolution. Appendices

Morrison's iterative method of noise removal, or Morrison's smoothing, is applied in a simulation to noise-added data sets of various noise levels to determine its optimum use. Morrison's smoothing is applied for noise removal alone, and for noise removal prior to deconvolution. For the latter, an accurate method is analyzed to provide confidence in the optimization. The method consists of convolving the data with an inverse filter calculated by taking the inverse discrete Fourier transform of the reciprocal of the transform of the response of the system. Various length filters are calculated for the narrow and wide Gaussian response functions used. Deconvolution of non-noisy data is performed, and the error in each deconvolution calculated. Plots are produced of error versus filter length; and from these plots the most accurate length filters determined. The statistical methodologies employed in the optimizations of Morrison's method are similar. A typical peak-type input is selected and convolved with the two response functions to produce the data sets to be analyzed. Both constant and ordinate-dependent Gaussian distributed noise is added to the data, where the noise levels of the data are characterized by their signal-to-noise ratios. The error measures employed in the optimizations are the L1 and L2 norms. Results of the optimizations for both Gaussians, both noise types, and both norms include figures of optimum iteration number and error improvement versus signal-to-noise ratio, and tables of results. The statistical variation of all quantities considered is also given.

Ioup, George E.↗

NASA NTRS1987

Measurements of the cosmic background radiation

Maps of the large scale structure (theta is greater than 6 deg) of the cosmic background radiation covering 90 percent of the sky are now available. The data show a very strong 50-100 sigma (statistical error) dipole component, interpreted as being due to our motion, with a direction of alpha = 11.5 + or - 0.15 hours, sigma = -5.6 + or - 2.0 deg. The inferred direction of the velocity of our galaxy relative to the cosmic background radiation is alpha = 10.6 + or - 0.3 hours, sigma = -2.3 + or - 5 deg. This is 44 deg from the center of the Virgo cluster. After removing the dipole component, the data show a galactic signature but no apparent residual structure. An autocorrelation of the residual data, after substraction of the galactic component from a combined Berkeley (3 mm) and Princeton (12 mm) data sets, show no apparent structure from 10 to 180 deg with a rms of 0.01 mK(sup 2). At 90 percent confidence level limit of .00007 is placed on a quadrupole component.

Lubin, P.↗

NASA NTRS1988

Search for bound states of the eta-meson in light nuclei

A search for nuclear-bound states of the eta meson was carried out. Targets of lithium, carbon, oxygen, and aluminum were placed in a pion(+) beam at 800 MeV/c. A predicted eta bound state in O-15* (E sub x approx. = 540 MeV) with a width of approx. 9 MeV was not observed. A bound state of a size 1/3 of the predicted cross section would have been seen in this experiment at a confidence level of 3sigma (P is greater than 0.9987).

Chrien, R. E.↗

NASA NTRS1988

Large antenna experiments aboard the space shuttle: Application of nonuniform sampling techniques

Future satellite communication and scientific spacecraft will utilize antennas with dimensions as large as 20 meters. In order to commercially use these large, low sidelobe and multiple beam antennas, a high level of confidence must be established as to their performance in the 0-g and space environment. Furthermore, it will be desirable to demonstrate the applicability of surface compensation techniques for slowly varying surface distortions which could result from thermal effects. An overview of recent advances in performing RF measurements on large antennas is presented with emphasis given to the application of a space based far-field range utilizing the Space Shuttle and the concept of a newly developed nonuniform sampling technique.

Rahmatsamii, Y.↗

NASA NTRS1986

Study of Comet Nucleus Gamma-Ray Spectrometer Penetration System

A penetrator system has been suggested as an approach for making in situ measurements of the composition and physical properties of the nucleus of a comet. This study has examined in detail the feasibility of implementing the penetrator concept. The penetrator system and mission designs have been developed and iterated in sufficient detail to provide a high level of confidence that the concept can be implemented within the constraints of the Mariner Mark 2 spacecraft.

Adams, G. L.↗