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At least 1,747 records · Page 97

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NASA NTRS1985

Multiple-input experimental modal analysis

The development of experimental modal analysis techniques is reviewed. System and excitation assumptions are discussed. The methods examined include the forced normal mode excitation method, the frequency response function method, the damped complex exponential response method, the Ibrahim time domain approach, the polyreference approach, and mathematical input-output model methods. The current trend toward multiple input utilization in the estimation of system parameters is noted.

Allemang, R. J.↗

NASA NTRS1985

An elastic strip with multiple cracks and applications to tapered specimens

In this paper an infinite elastic strip containing arbitrarily oriented cracks and subjected to uniform tension and a pair of concentrated forces is formulated in terms of a system of singular integral equations. Even though the technique is sufficiently general to solve new multiple crack problem, with the objective of applying the results to tapered specimens, only a certain symmetric crack geometry and loading conditions are considered. The stress intensity factors are calculated for edge cracks in the strip under uniform tension and for a 'compact' and a 'slender' tapered specimen (the latter simulating the double cantilever beam) under concentrated forces or crack surface wedge forces.

Liu, X.-H.↗

NASA NTRS1986

Rarefied aerodynamics and upper atmosphere density from multiple orbiter flight measurements

Flight data from six flights of the experimental High Resolution Accelerometer Package (HIRAP), a micro-g accelerometer system, have been analyzed to produce rarefied flow aerodynamic coefficients of the Orbiter and freestream density in the altitude range from 60 km to 160 km. The direct measurements of the lift to drag ratio (L/D) are used to obtain individual normalized body-axis force coefficients in a least-squares regression scheme. An aerodynamics model based on an exponential function of Knudsen number is used for the individual coefficients. The calculated L/D from the flight determined coefficients agree with the multiple flight data measurements to within about 5 percent. Simultaneously, an upper altitude density variation is also obtained from the data. Density altitude profiles exhibit a wave feature on all flights. The wave has an amplitude of about + or - 25 percent relative to the 1962 Standard atmosphere model.

Buck, G. M.↗

NASA NTRS1985

Photometry of rough planetary surfaces - The role of multiple scattering

Topographic features affect the scattering properties of planetary surfaces by casting shadows and altering the local incidence and emission angles. Measurements of this phenomenon were obtained on the Cornell goniometer for both high and low albedo surfaces. For the low albedo surface, the decrease in reflected radiation due to topography increases sharply with increasing phase angle, whereas for the high albedo sample the effects are approximately constant between phase angles of 30 and 70 deg. The observations are in good agreement with a theoretical model in the case of the dark surface. However, for the high albedo surface the model overestimates the effects by a factor of 2, since it does not include the partial illumination of shadows by multiple scattering. For both high and low albedo surfaces, the effects of topography do not become significant until a phase angle of 30-40 deg.

Buratti, B. J.↗

NASA NTRS1986

15 meter multiple mirror telescope design study

Taking as a starting point the existing Multiple Mirror Telescope (MMT), a concept for a larger and more advanced instrument has been developed. It makes use of four 7.5-m diameter paraboloidal glass primaries of the honeycomb sandwich type being developed by the University of Arizona. These are mounted quite close together in a square configuration, with their axes coaligned. Separate optical configurations are provided, for optical and infrared applications. To minimze telescope emissivity in the thermal infrared at the combined focus, all the beam combining and streering optics that follow the tertiary mirrors are enclosed in a large central dewar and cooled with liquid nitrogen. The diffraction-limited resolution at the combined focus of 0.11 arcsec at 10 micrometers wavelength is equivalent to that of a 20.5 meter filled aperture. Diffraction-limited resolution should be routinely achievable at 10 and 20 micrometers, if active correction of large-scale wavefront errors is implemented.

Angel, J. R. P.↗

NASA NTRS1986

Effect of multiple strain-anneal cycles on the 1000 C creep behaviour of gamma/gamma prime-alpha

Various multiple strain-anneal cycles (1000 C) were imposed on specimens of the directionally solidified eutectic (DSE) alloy gamma/gamma prime-alpha to identify thermomechanical processing methods (TMP) which would improve the creep behavior. Specimens of the Ni-32.3Mo-6.3Al wt pct alloy were grown with a modified Bridgeman technique. Some of the cylindrical specimens were alternately heat-treated at 900 C, then strained, or heat-treated only, while other specimens were annealed at 900 C after swaging and then worked at ambient temperature. The specimens were all examined microstructurally using transmission electron microscopy, some before and after being exposed to constant-load compression tests at 1000 C. The creep strain increased for all TMP specimens for strain rates of at least 2 millionths per sec. Strain rates of about 2 ten millionths per sec were only improved with strain annealing with 13 percent work at ambient temperature. A slight improvement, compared to as-grown materials, was observed in the 1000 C creep behavior of materials annealed at 900 C. Strain-annealing was found to introduce three-dimensional dislocation networks into the gamma-prime matrix.

Whittenberger, J. D.↗

NASA NTRS1985

A multiple scattering theory for EM wave propagation in a dense random medium

For a dense medium of randomly distributed scatterers an integral formulation for the total coherent field has been developed. This formulation accounts for the multiple scattering of electromagnetic waves including both the twoand three-particle terms. It is shown that under the Markovian assumption the total coherent field and the effective field have the same effective wave number. As an illustration of this theory, the effective wave number and the extinction coefficient are derived in terms of the polarizability tensor and the pair distribution function for randomly distributed small spherical scatterers. It is found that the contribution of the three-particle term increases with the particle size, the volume fraction, the frequency and the permittivity of the particle. This increase is more significant with frequency and particle size than with other parameters.

Karam, M. A.↗

NASA NTRS1985

To speak or not to speak - A multiple resource perspective

The desirability of employing speech response in a dynamic dual task situation was discussed from a multiple resource perspective. A secondary task technique was employed to examine the time-sharing performance of five dual tasks with various degrees of resource overlap according to the structure-specific resource model of Wickens (1980). The primary task was a visual/manual tracking task which required spatial processing. The secondary task was either another tracking task or a spatial transformation task with one of four input (visual or auditory) and output (manual or speech) configurations. The results show that the dual task performance was best when the primary tracking task was paired with the visual/speech transformation task. This finding was explained by an interaction of the stimulus-central processing-response compatibility of the transformation task and the degree of resource competition between the time-shared tasks. Implications on the utility of speech response were discussed.

Tsang, P. S.↗

NASA NTRS1986

Multiple boundary condition test (MBCT) approach to update mathematical models of large flexible structures

A major challenge to the structural dynamicist is to validate mathematical models of large space structures which cannot be ground tested because of its size and/or flexibility. The paper presents a Multiple Boundary Condition Test (MBCT) approach which allows a systematic validation of the mathematical model by performing a number of ground tests on a large structure with variable boundary conditions. A numerical simulation is presented which illustrates the validity of the MBCT including some of the potential limitations.

Wada, B. K.↗

NASA NTRS1986

Multiple Boundary Condition Tests (MBCT) for verification of large space structures

The Multiple Boundary Condition Tests (MBCT) approach is evaluated and recent modifications are described. For the application of MBCT, 12 different boundary conditions are selected and the results of applying MBCT in conjunction with a nonlinear formulation are indicated schematically. It is concluded that the nonlinear formulation enhances the ability to implement the MBCT test approach on large space structures which cannot be ground tested without the artificial boundary conditions incorporated in MBCT. In addition, it leads to significant improvements in the convergence to the correct solution.

Wada, B. K.↗

NASA NTRS1986

Multiple instrument coverage analysis

In the Space Station era comprehensive investigations of the physical processes of the earth will rely on observations from several types of space-based instruments. Preliminary studies indicate that, due to projected limitations on spacecraft and launch-vehicle capability, these complementary instrument sets may have to be distributed among several spacecraft. The task of analyzing the coincident coverage areas between instruments operating from multiple spacecraft will be complex. Such factors as the instruments' observing capabilities, orbital parameters, and viewing constraints will have to be considered. To aid in this analysis a computer model is being developed. This model has the capability, among others, to compute the coincident coverage areas between two independently orbiting instruments. This paper describes the model, its capabilities, and several sample applications.

Horvat, G. M.↗

NASA NTRS1986

Multiple star formation and the dynamical evolution of B335

The detection of a second high-velocity bipolar flow in the dark cloud B335 located in the diffuse envelope to the east of the core is reported. This flow has the same orientation as the first one. The visual extinction in the region between the redshifted and blueshifted lobes is less than or about 1 mag and is not coincident with a condensation. The flow is not associated with any known infrared source in the IRAS catalog. The new flow is about three times older than the first, and its energetics are somewhat smaller. The flows are aligned not only with each other but also with the long axis of the structure of B335 as outlined by CO maps, suggesting that magnetic fields have a role in guiding the flow. From the presence of multiple flows and the structure of the envelope, it is concluded that B335 is at the end of its starbearing life, rather than a young cloud beginning star formation, as previously supposed.

Langer, W. D.↗

NASA NTRS1987

Position Control for Non-linear, Multiple-Link Robots

Several approaches to complicated control problem examined. Report surveys methods for controlling motion of robot manipulators. Applies to coupled, highly nonlinear multiple-link robots. Presents adaptive control technique based on discrete linear model of robot arm, obtained by linearizing nonlinear dynamical equations about nominal trajectory. Parameters of model calculated with adaptive parameter-identification algorithm. Based on system model, optimal control input computed using position and velocity feedback.

Seraji, H.↗

NASA NTRS1987

Interface for a Multiple-User Computer System

Diverse hardware and software connected with minimal inconvenience to users. Central controller for large multiple-user computer network makes various computer services compatible regardless of diversity of hardware and software. Users readily gain access to host computer and other terminals and services. Need be familiar only with language and procedures of their own terminals, even when communicating with normally incompatible services or users.

Headley, Paul A.↗

NASA NTRS1987

Tester for Multiple-Conductor Cables

Portable testing circuit enables technician to determine quickly wiring errors in multiple-conductor electrical cable or terminal connectors. Active unit tester made of inexpensive integrated circuits and other readily available components. Timer and one-shot generate pulses counted by shift registers. Shift-register output terminals wired to connector pins so voltage applied to each pin in sequence.

Wirth, Manfred N.↗

NASA NTRS1984

Development of a turbomachinery design optimization procedure using a multiple-parameter nonlinear perturbation method

An investigation was carried out to complete the preliminary development of a combined perturbation/optimization procedure and associated computational code for designing optimized blade-to-blade profiles of turbomachinery blades. The overall purpose of the procedures developed is to provide demonstration of a rapid nonlinear perturbation method for minimizing the computational requirements associated with parametric design studies of turbomachinery flows. The method combines the multiple parameter nonlinear perturbation method, successfully developed in previous phases of this study, with the NASA TSONIC blade-to-blade turbomachinery flow solver, and the COPES-CONMIN optimization procedure into a user's code for designing optimized blade-to-blade surface profiles of turbomachinery blades. Results of several design applications and a documented version of the code together with a user's manual are provided.

Stahara, S. S.↗

NASA NTRS1986

Wavelength dependence of aerosol backscatter coefficients obtained by multiple wavelength Lidar measurements

Aerosols are often classified into several general types according to their origins and composition, such as maritime, continental, and stratospheric aerosols, and these aerosol types generally have different characteristics in chemical and physical properties. The present study aims at demonstrating the potential for distinguishing these aerosol types by the wavelength dependence of their backscatter coefficients obtained from quantitative analyses of multiple wavelength lidar signals. Data from the NASA Airborne Differential Abosrption lidar (DIAL) S ystems, which can measure aerosol backscatter profiles at wavelenghts of 300, 600, and 1064 nm and ozone profiles of backscatter coefficients for these three wavelength were derived from the observations of aerosols of different types. Observations were performed over the Atlantic Ocean, the Southwestern United States, and French Guyana.

Sasano, Y.↗

NASA NTRS1986

Multiple scattering measurements in laboratory and foggy atmosphere

Multiple scattering affects propagation of light beams in turbid media. Backscattering or forward scattering based measurements of atmospheric parameters are influenced by this effect. Although largely studied theoretically, the effect needs measurements in control of situations due to the large variety of situations of practical importance. The results of laboratory measurements pertaining to the transmission of a collimated light beam (Helium-Neon souce, 10 mW) through suspensions of latex spheres in water are presented and a comparison was made with the predictions of calculation in a foggy atmosphere will also be presented.

Bruscaglioni, P.↗