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At least 343 records · Page 19

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NASA NTRS1986

IUE observations of V Sagittae

Observations of the nova-like variable V Sge are discussed, and the ground-based light curve is analyzed, compensating for the component interaction effect. Low-dispersion IUE spectra indicate that interstellar reddening is smaller than suggested from visible-band observations. The UV and visible continuum are modeled by a He-rich model and by a simple accretion disk, and the UV spectrum emission lines are used to determine ionization temperatures and a lower N(e) limit. The present data are consistent with the picture of the companion to the He star being embedded in an accretion disk, with the disk being large (of dimension comparable to that of the embedding Roche lobe as a result of vigorous mass transfer) at the time of the ground-based data, and with the disk having been diminished to a radius of the order of 200 times of the neutron star, at the time of the IUE spectra.

Koch, R. H.↗

NASA NTRS1987

Integrated Analysis Capability Program

Integrated Analysis Capability (IAC) software system provides highly effective, interactive analysis tool for integrated design of large structures. Developed to serve as interface for programs from fields of structures, thermodynamics, controls, and system dynamics with executive system and data base to yield highly-efficient multidisciplinary system. Written in FORTRAN 77.

Frisch, Harold P.↗

NASA NTRS1986

The effect of Cr, Co, Al, Mo and Ta on a series of cast Ni-base superalloys on the stability of an aluminide coating during cyclic oxidation in Mach 0.3 burner rig

The influence of varying the content of Co, Cr, Mo, Ta, and Al in a series of cast Ni-based gamma/gamma'superalloys on the behavior of aluminide coatings was studied in burner rig cyclic oxidation tests at 1100 C. The alloys had nominally fixed levels of Ti, W, Cb, Zr, C, and B. The alloy compositions were based on a full 2(sup 5)-fractional statistical design supplemented by 10 star point alloys and a center point alloy. This full central composite design of 43 alloys plus two additional alloys with extreme Al levels allowed a complete second degree estimating equation to be derived from the 5-compositional variables. The weight change/time data for the coated samples fitted well to the paralinear oxidation model and enabled a modified oxidation attack parameter, K'(sub a) to be derived to rank the alloys and log K' (sub a ) to be used as the dependent variable in the estimating equation to determine the oxidation resistance of the coating as a function of the underlying alloy content. The most protective aluminide coatings are associated with the highest possible base ally contents of CR and Al and at a 4 percent Ta level. The Mo and Co effects interact but at fixed levels of 0, 5, or 10% Co. A 4% Mo level is optimum.

Zaplatynsky, I.↗

NASA NTRS1986

Development of a ROT22 - DATAMAP interface

This report (Contract NAS2-10331- Mod 10), outlines the development and validation of an interface between the three-dimensional transonic analysis program ROT22 and the Data from Aeromechanics Test and Analytics-Management and Analysis Package (DATAMAP). After development of the interface, the validation is carried out as follows. First, the DATAMAP program is used to analyze a portion of the Tip Aerodynamics and Acoustics Test (TAAT) data. Specifically, records 2872 and 2873 are analyzed at an azimuth of 90 deg, and record 2806 is analyzed at 60 deg. Trim conditions for these flight conditions are then calculated using the Bell performance prediction program ARAM45. Equivalent shaft, pitch, and twist angles are calculated from ARAM45 results and used as input to the ROT22 program. The interface uses the ROT22 results and creates DATAMAP information files from which the surface pressure contours and sectional pressure coefficients are plotted. Twist angles input to ROT22 program are then iteratively modified in the tip region until the computed pressure coefficients closely match the measurements. In all cases studied, the location of the shock is well predicted. However, the negative pressure coefficients were underpredicted. This could be accounted for by blade vortex interaction effects.

Shenoy, K. R.↗

NASA NTRS1987

Fatigue damage interaction behavior of PWA 1480

The fatigue damage interaction behavior of PWA 1480 single crystal alloy has been experimentally established for the two-level loading case in which a block of low-cycle fatigue loading is followed by high-cycle fatigue loading to failure. A relative life ratio N1/N2 (where N1 and N2 are the low- and high-cycle fatigue baseline lives, respectively) of approximately 0.002 was explored to assess the interaction behavior. The experimental results thus far show evidence of a loading order interaction effect to a similar degree of detriment as has been observed in polycrystalline materials. Current generation single crystal alloys in general, and PWA 1480 in particular, contain pores; indeed, it was observed in all cases that specimen failure initiated from pores connected with or immediately below the surface. Detailed fractographic and metallographic studies are currently being made to assess the nature of the porosity in terms of its effect on fatigue life.

Mcgaw, Michael A.↗

NASA NTRS1987

Transonic flow visualization using holographic interferometry

An account is made of some of the applications of holographic interferometry to the visualization of transonic flows. In the case of the compressor shock visualization, the method is used regularly and has moved from being a research department invention to a design test tool. With the implementation of automatic processing and simple digitization systems, holographic vibrational analysis has also moved into routine nondestructive testing. The code verification interferograms were instructive, but the main turbomachinery interest is now in 3 dimensional flows. A major data interpretation effort will be required to compute tomographically the 3 dimensional flow around the leading or the trailing edges of a rotating blade row. The bolt on approach shows the potential application to current unsteady flows of interest. In particular that of the rotor passing and vortex interaction effects is experienced by the new generation of unducted fans. The turbocharger tests presents a new area for the application of holography.

Bryanston-Cross, Peter J.↗

NASA NTRS1987

Stigmatically focusing partial pressure analyzer with dual chamber ion source

The partial pressure analyzer developed has a high absolute sensitivity and high resolution. Interaction effects, as they occur in conventional partial pressure analyzers between the heating filament for the emission of electrons and the residual gas, are suppressed by removing the heating filament from the measurement area. The electron beam is generated in an auxiliary vacuum compartment, and passes subsequently through an aperture into the ionization compartment. The probability is small, therefore, that the presence of substances produced at the heating filament by chemical reactions and thermal decompositions will have disturbing effects. The high sensitivity and resolution of the instrument are obtained with the aid of an electron path configuration of unconventional characteristics.

Rasskopf, Klaus F.↗

NASA NTRS1986

On the atomic roughness of solid-vapor interfaces - Significance of many-body interactions

Published experimental data on the atomic roughness of solid-vapor interfaces (SVIs) are compiled in a table and compared with the predictions of theoretical models based on the Bragg-Williams approximation (e.g., Jackson, 1958). Significant discrepancies are observed, and a new model employing site-dependent bond strengths based on many-body-interaction effects is developed and demonstrated. Predictions for Cu, Pb, and Zn are presented in extensive tables and graphs and characterized in detail: good agreement with experimental observations of anisotropic melting is obtained.

Chen, Jenn-Shing↗

NASA NTRS1987

Oscillator strengths for S I, S II, and S III

A series of calculations for atomic data of various sulfur and oxygen ions is examined. Recent observations of the Io plasma torus obtained with the Voyager UV Spectrometer, the IUE satellite short wavelength spectrograph, and the rocket-borne faint object telescope are discussed. The calculation of oscillator strengths for S II, the P I sequence, S I, and S III in terms of configuration interaction effects is described. The derivation of orbital wave functions is considered. The use of the close coupling method to estimate collision strengths is studied. The accuracy of these calculations depends on: (1) the number of states used in the close coupling expansion; (2) resonance contributions to the thermally averaged collision strength; and (3) the quality of the target state wave functions. Tables of the derived oscillator strengths are presented.

Ho, Y. K.↗

NASA NTRS1987

Scientific customer needs - NASA user

Some requirements for scientific users of the Space Station are considered. The use of testbeds to evaluate design concepts for information systems, and for interfacing between designers and builders of systems is examined. The need for an information system that provides an effective interaction between ground-based users and their space-based equipment is discussed.

Black, David C.↗

NASA NTRS1987

Exploratory studies of actuated forebody strakes for yaw control at high angles of attack

Wind-tunnel studies have been conducted to evaluate the potential of actuated forebody strakes to provide increased levels of yaw control on fighter aircraft at extremely high angles of attack where conventional aerodynamic controls are ineffective. The studies involved low-speed wind-tunnel tests of actuated forebody strake concepts applied to a generic fighter model and included circumferential pressure and flow visualization surveys on an isolated forebody. Results showed that the actuated forebody strake concept can provide high levels of yaw control over wide ranges of angle-of-attack and sideslip. However, when lifting surfaces were placed in close proximity to the forebody/strake combination, significant interaction effects occurred which reduced the yaw control effectiveness of the strakes and induced coupled rolling and pitching moments.

Murri, Daniel G.↗

NASA NTRS1987

Thermocapillary migration of a gas bubble in an arbitrary direction with respect to a plane surface

The thermocapillary migration of a gas bubble in an unbounded fluid in the presence of a neighboring rigid plane surface is considered in the limit of negligible Reynolds and Marangoni numbers. Results are given for a scalar interaction parameter defined as the ratio of the speed of the bubble in the presence of the plane surface to the speed in its absence. It is suggested that the weaker interaction effects noted for the case of thermocapillary migration relative to the case of motion due to a body force such as that caused by a gravitational field is attributable to the more rapid decay, away from the bubble, of the disturbance velocity and temperature gradient fields. The surface is found to exert the greatest influence in the case of motion normal to it, and the weakest influence in the case of parallel motion.

Meyyappan, M.↗

NASA NTRS1988

Sound transmission through the walls of light aircraft: An investigation of structure-borne noise in a Handley Page 137 Jetstream 3 aircraft

This study indicates that the structureborne noise due to wing/vortex interation for the Handley Page-137 Jetstream may be significant at frequencies above 500 Hz. It was found that by preventing such interaction, noise reductions between 1 to 3 dB were attainable. However, this study did not show any significant contribution due to this phenomena at the first blade passage tone. It is suspected that the wing/vortex interaction effect varies from plane to plane.

Bernhard, R. J.↗

NASA NTRS1988

Surface and interfacial properties of carbon fibers

Differences in the adhesion of three carbon fibers (Hercules AS1 and AS4, and Hysol-Grafil XAS) to polycarbonate (PC) have been shown to correlate with the absorptivity of PC on the three fiber types. The absorptivity (energy of absorption) was determined using retention time liquid chromatography and the adhesion was measured using the single embedded filament tensile test. A correlation was also found between adhesion strength and the O/N surface element ratio using XPS analysis. The chemical details for these correlations have not yet been determined. A study of filament fracture statistics has been initiated using single and multiple embedded filament tensile tests. Filament fracture has been measured as a function of strain and for different interfiber distances. Preliminary results indicate that fiber fracture is a discontinuous function of increasing strain and may in fact occur at discrete strain intervals. Fiber-fiber interaction effects on fiber fracture have been found for interfiber distances of up to two to three fiber diameters.

Bascom, W. D.↗

NASA NTRS1987

Free surfaces and multilayer interfaces in the GaAs/AlAs system

Semiempirical potential energy functions have been utilized for a variety of calculations in the Ga-Al-As system. Surface energies have been calculated for several orientations of GaAs. Ledge energies for the GaAs (0 0 -1) (As-terminated) surface show long-range interaction effects with the ledge energy increasing with spacing. GaAs (001)/AlAs (001) superlattices have been simulated for a range of interlayer spacings with the excess interfacial energy per interlayer increasing from 5 erg/sq cm at an interlayer spacing of 1 molecular layer (5.8 A) to 50 erg/sq cm at an interlayer spacing of 18 molecular layers (103.8 A).

Choi, D. K.↗

NASA NTRS1989

The 3-D Euler and Navier-Stokes calculations for aircraft components

An explicit multistage Runge-Kutta type of time-stepping scheme is used for solving transonic flow past a transport type wing/fuselage configuration. Solutions for both Euler and Navier-Stokes equations are obtained for quantitative assessment of boundary layer interaction effects. The viscous solutions are obtained on both a medium resolution grid of approximately 270,000 points and a find grid of 460,000 points to assess the effects of grid density on the solution. Computed pressure distributions are compared with the experimental data.

Vatsa, Veer N.↗

NASA NTRS1989

Aerobrake heating rate sensitivity study for the Aeroassist Flight Experiment (AFE)

The sensitivities associated with the prediction of the Aeroassist Flight Experiment (AFE) vehicle's aerothermodynamic environment are presently evaluated in order to assess the heating-rate uncertainties of the AFE's aerobrake component, as a function of time in various trajectories, and as a function of distance around the aerobrake. Relative importance is evaluated by means of the Boundary Layer Integral Matrix Procedure for such areas of uncertainty as the trajectory parameters, the catalycity of the thermal-protection tiles, the nose radius variation/surface pressure distribution, and viscous interaction effects.

Rochelle, W. C.↗

NASA NTRS1989

An investigation of counterrotating tip vortex interaction

A tip vortex interaction model originally developed for compressors has been extended and adapted for use with counterrotating open rotors. Comparison of available acoustic data with predictions (made with and without the tip vortex model included) illustrate the importance of this interaction effect. This report documents the analytical modeling, a limited experimental verification, and certain key parametric studies pertaining to the tip vortex as a noise source mechanism for the unsteady loading noise of counterrotating properllers.

Majjigi, R. K.↗