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At least 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A verification of unsteady Navier-Stokes solutions around oscillating airfoils

A finite difference solution code for the two dimensional Navier-Stokes equations was combined with a moving-grid system. The thin layer Navier-Stokes equations with a turbulence model are solved in a time-accurate manner in order to study the unsteady aerodynamics around airfoils undergoing small amplitude pitching or heaving motions in the transonic regime. The accuracy of the solutions obtained by the use of the present moving-grid technqiue is investigated. The effects of the minimum grid size and the integrating time-step size on the solutions are also checked. Some of the solutions obtained by the present method are compared with experimental results. It is demonstrated that the unsteady aerodynamics around oscillating airfoils can be predicted fairly well by the present code for cases in which the dynamic angle of attack or displacement is small.

Nakamichi, J.↗
NASA NTRS1987

Verification of mesoscale objective analyses of VAS and rawinsonde data using the March 1982 AVE/VAS special network data

Various combinations of VAS (Visible and Infrared Spin Scan Radiometer Atmospheric Sounder) data, conventional rawinsonde data, and gridded data from the National Weather Service's (NWS) global analysis, were used in successive-correction and variational objective-analysis procedures. Analyses are produced for 0000 GMT 7 March 1982, when the VAS sounding distribution was not greatly limited by the existence of cloud cover. The successive-correction (SC) procedure was used with VAS data alone, rawinsonde data alone, and both VAS and rawinsonde data. Variational techniques were applied in three ways. Each of these techniques was discussed.

Doyle, James D.↗
NASA NTRS1986

Verification results for a two-scale model of microwave backscatter from the sea surface

The backscatter model of Donelan and Pierson (1986) was adjusted to fit Ku-Band at 13.9 GHz. Data from L to Ka-band are used to test the model. In general, there is no power law. When the wind drops below certain threshold speeds there may be no detectable Bragg backscatter. Saturation may occur at high winds. Results from the Seasat-SASS are used to substantiate the predictions of the model. Suggestions for experiments for determining the overall validity of the model are made.

Pierson, W. J., Jr.↗
NASA NTRS1986

Ground facility for large space structures dynamics and control verification

NASA Marshall Space Flight Center has developed a facility in which closed loop control of Large Space Structures (LSS) can be demonstrated and verified. The main objective of the facility is to verify LSS control system techniques so that on-orbit performance can be unsured. The facility consists of an LSS test article or payload which is connected to a 3-axis angular pointing mount assembly that provides control torque commands. The angular pointing mount assembly is attached to a base excitation system which will simulate disturbances most likely to occur for Orbiter and DOD payloads. The control computer contains the calibration software, the reference systems, the alignment procedures, the telemetry software, and the control algorithms. The total system is suspended in such a fashion that the LSS test article has the characteristics common to all LSS.

Waites, Henry↗
NASA NTRS1987

The terminal area simulation system. Volume 2: Verification cases

The numerical simulation of five case studies are presented and are compared with available data in order to verify the three-dimensional version of the Terminal Area Simulation System (TASS). A spectrum of convective storm types are selected for the case studies. Included are: a High-Plains supercell hailstorm, a small and relatively short-lived High-Plains cumulonimbus, a convective storm which produced the 2 August 1985 DFW microburst, a South Florida convective complex, and a tornadic Oklahoma thunderstorm. For each of the cases the model results compared reasonably well with observed data. In the simulations of the supercell storms many of their characteristic features were modeled, such as the hook echo, BWER, mesocyclone, gust fronts, giant persistent updraft, wall cloud, flanking-line towers, anvil and radar reflectivity overhang, and rightward veering in the storm propagation. In the simulation of the tornadic storm a horseshoe-shaped updraft configuration and cyclic changes in storm intensity and structure were noted. The simulation of the DFW microburst agreed remarkably well with sparse observed data. The simulated outflow rapidly expanded in a nearly symmetrical pattern and was associated with a ringvortex. A South Florida convective complex was simulated and contained updrafts and downdrafts in the form of discrete bubbles. The numerical simulations, in all cases, always remained stable and bounded with no anomalous trends.

Proctor, F. H.↗
NASA NTRS1986

Design and verification by nonlinear simulation of a Mach/CAS control law for the NASA TCV B737 aircraft

A Mach/CAS control system using an elevator was designed and developed for use on the NASA TCV B737 aircraft to support research in profile descent procedures and approach energy management. The system was designed using linear analysis techniques primarily. The results were confirmed and the system validated at additional flight conditions using a nonlinear 737 aircraft simulation. All design requirements were satisfied.

Bruce, Kevin R.↗
NASA NTRS1987

Impact verification of space suit design for space station

The ballistic limits of single sheet and double sheet structures made of 6061 T6 Aluminum of 1.8 mm and larger nominal thickness were investigated for projectiles of 1.5 mm diameter fired in the Vertical Gun Range Test Facility and NASA Ames Research Center. The hole diameters and sheet deformation behavior were studied for various ratios of sheet spacing to projectile diameter. The results indicate that for projectiles of less than 1.5 mm diameter the ballistic limit exceeds the nominal 10 km/sec orbital debris encounter velocity, if a single-sheet suit of 1.8 mm thickness is behind a single bumper sheet of 1 mm thickness spaced 12.5 mm apart.

Fish, Richard H.↗
NASA NTRS1986

Verification of performance results for a low-speed 15 percent elliptical circulation control airfoil

Low-speed wind tunnel tests performed by the Naval Ship Research and Development Center (NSRDC) on a circulation control airfoil model was repeated by the Joint Institute for Aerodynamics and Acoustics in an attempt to reproduce the performance results. The model used was a 15% ellipse with interchangeable trailing edges. Surface pressure measurements were taken to obtain lift and pitching moment coefficients as functions of jet blowing momentum, and the momentum deficit in the wake was measured and used to calculate the drag coefficient. The effects of spanwise slot height variation and of leading edge blowing on performance were also investigated. The performance results showed that of the three slot heights tested, a slot height/chord ratio of 0.0022 produced the most lift coefficient for a given blowing rate. Lift obtained in the current test ranged from 2 to 35% lower than the NSRDC test. However, the two data sets compared reasonably well considering wind tunnel and wall blowing scheme differences. The spanwise lift distribution showed less change in lift due to a variation in slot height than expected. The leading edge blowing results demonstrated that although lift initially decreased, a positive lift increment was possible at higher leading edge blowing rates.

Rodman, L. C.↗
NASA NTRS1987

Verification of flexible structures by ground test

The validation of math models of large space structures (LSS) by ground tests is attempted. Concepts for two types of LSS are presented: continuous type and linked subsystems. It was concluded that ground test which simulate space conditions are not entirely reliable, that there should be an integration of testing and analyses, which then should be validated with laboratory and flight experiments.

Wada, Ben K.↗
NASA NTRS1987

Quantification of observed flare parameters in relation to a shear-index and verification of MHD models for flare prediction

The goal for the SAMEX magnetograph's optical system is to accurately measure the polarization state of sunlight in a narrow spectral bandwidth over the field of view of an active region to make an accurate determination of the magnetic field in that region. The instrumental polarization is characterized. The optics and coatings were designed to minimize this spurious polarization introduced by foreoptics. The method developed to calculate the instrumental polarization of the SAMEX optics is described.

Wu, S. T.↗
NASA NTRS1984

Advanced manufacturing development of a composite empennage component for L-1011 aircraft. Phase 3: Production readiness verification testing

Twenty-two specimens of each of two key structural elements of the Advance Composite Vertical Fin (ACVF) were fabricated and tested. One element represented the front spar at the fuselage attachment area and the other element represented the cover at the fuselage joint area. Ten specimens of each element were selected for static testing. The coefficient of variation resulting from the tests was 3.28 percent for the ten cover specimens and 6.11 percent for the ten spar specimens, which compare well with metallic structures. The remaining twelve cover and twelve spar specimens were durability tested in environmental chambers which permitted the temperature and humidity environment to be cycled as well as the applied loads. Results of the durability tests indicated that such components will survive the service environment.

Jackson, A.↗
NASA NTRS1987

Design verification of SIFT

A SIFT reliable aircraft control computer system, designed to meet the ultrahigh reliability required for safety critical flight control applications by use of processor replications and voting, was constructed for SRI, and delivered to NASA Langley for evaluation in the AIRLAB. To increase confidence in the reliability projections for SIFT, produced by a Markov reliability model, SRI constructed a formal specification, defining the meaning of reliability in the context of flight control. A further series of specifications defined, in increasing detail, the design of SIFT down to pre- and post-conditions on Pascal code procedures. Mechanically checked mathematical proofs were constructed to demonstrate that the more detailed design specifications for SIFT do indeed imply the formal reliability requirement. An additional specification defined some of the assumptions made about SIFT by the Markov model, and further proofs were constructed to show that these assumptions, as expressed by that specification, did indeed follow from the more detailed design specifications for SIFT. This report provides an outline of the methodology used for this hierarchical specification and proof, and describes the various specifications and proofs performed.

Moser, Louise↗
NASA NTRS1986

Ultrasonic verification of microstructural changes due to heat treatment

Ultrasonic attenuation was measured for polycrystalline samples of nickel and copper with various grain-size distributions produced by heat treatment. Attenuation as a function of frequency was determined for a sample having a known mean grain diameter. Once this function was determined, it could be scaled to determine the mean grain size of other samples of the same material with different mean grain diameters. These results were obtained by using broadband pulse-echo ultrasound in the 25 to 100 MHz frequency range. The results suggest an ultrasonic, nondestructive approach for verifying heat treatment of metals.

Generazio, E. R.↗
NASA NTRS1986

Verification of a SEU model for advanced 1-micron CMOS structures using heavy ions

Modeling and test results are reported for 1 micron CMOS circuits. Analytical predictions are correlated with experimental data, and sensitivities to process and design variations are discussed. Unique features involved in predicting the SEU performance of these devices are described. The results show that the critical charge for upset exhibits a strong dependence on pulse width for very fast devices, and upset predictions must factor in the pulse shape. Acceptable SEU error rates can be achieved for a 1 micron bulk CMOS process. A thin retrograde well provides complete SEU immunity for N channel hits at normal incidence angle. Source interconnect resistance can be important parameter in determining upset rates, and Cf-252 testing can be a valuable tool for cost-effective SEU testing.

Cable, J. S.↗
NASA NTRS1987

3-D axial blade row flow field inviscid finite volume prediction and verification

A modification of the unsteady finite volume three-dimensional Euler scheme of Denton (1982) is developed to provide more accurate steady state solutions at enhanced convergence rates, and it is assessed for application to detailed axial blade row flow predictions by correlating predictions with data for a wide range of flow fields. Radial and pitchwise smoothing are minimized by the elimination of under-relaxing while time marching, by the addition of an internal transient averaging scheme, and by the use of the maximum stable local time step for each grid element. Results show that the flow field is accurately predicted in regions of primarily axial pressure gradients, though the predictions do not correlate well with the data in regions of strong nonaxial pressure gradients. Though the scheme is second order accurate in the axial direction, it is first order accurate in the other dimensions, smearing the flow field details.

Zacharias, Robert M.↗
NASA NTRS1986

Verification of small-scale water vapor features in VAS imagery using high resolution MAMS imagery

The Multispectral Atmospheric Mapping Sensor (MAMS), a modification of NASA's Airborne Thematic Mapper, is described, and radiances from the MAMS and the VISSR Atmospheric Sounder (VAS) are compared which were collected simultaneously on May 18, 1985. Thermal emission from the earth atmosphere system in eight visible and three infrared spectral bands (12.3, 11.2 and 6.5 microns) are measured by the MAMS at up to 50 m horizontal resolution, and the infrared bands are similar to three of the VAS infrared bands. Similar radiometric performance was found for the two systems, though the MAMS showed somewhat less attenuation from water vapor than VAS because its spectral bands are shifted to shorter wavelengths away from the absorption band center.

Menzel, Paul W.↗
NASA NTRS1986

Load cell verification of the uprated high pressure oxygen turbopump for the Space Shuttle Main Engine

The high pressure turbomachinery of the Space Shuttle Main Engine has the highest power-to-weight ratio of any operational machine known. Subsynchronous rotor whirl of the high pressure oxygen turbopump occurred in development testing at full-power level (109 percent thrust). The means by which the turbopump was successfully uprated is presented herein. The subsynchronous motion was determined to be driven by impeller destabilizing forces in combination with low net damping and bearing degradation. The degradation resulted from ball wear due primarily to an excessive loading condition of operating too near the lightly damped rotor second critical speed while under a large static load and, secondarily, from reverse bearing loading or loss of internal clearance and coolant during simulated flight conditions. The rotor response was reduced by stiffening the shaft and supports, optimizing the stiffness and damping of annular seals, and increasing the bearing deadband. The uprated oxygen turbopump configuration was verified by converting the pump and bearing support into a load cell for the purpose of systematically quantifying the load reduction benefits relative to baseline turbopumps. The damped second critical speed margin and the load sharing have been substantially improved which has resulted in reduced bearing loads for improved service life of the machine at full-power level.

Beatty, R. F.↗
NASA NTRS1986

Ground facility for Large Space Structures dynamics and control verification

NASA Marshall Space Flight Center has developed a facility in which closed loop control of Large Space Structures (LSS) can be demonstrated and verified. The main objective of the facility is to verify LSS control system techniques so that on-orbit performance can be ensured. The facility consists of an LSS test article or payload which is connected to a 3-axis angular pointing mount assembly that provides control torque commands. The angular pointing mount assembly is attached to a base excitation system which will simulate disturbances most likely to occur for Orbiter and DOD payloads. The control computer contains the calibration software, the reference systems, the alignment procedures, the telemetry software, and the control algorithms. The total system is suspended in such a fashion that the LSS test article has the characteristics common to all LSS.

Waites, Henry↗

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