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At least 271 records · Page 15

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NASA NTRS1977

On the existence of finite amplitude, transverse Alfven waves in the interplanetary magnetic field

Interplanetary magnetic field data from the Mariner 10 spacecraft were examined for evidence of small and finite amplitude transverse Alfven waves, general finite amplitude Alfven waves, and magnetosonic waves. No evidence for transverse Alfven waves was found. Instead, the field fluctuations were found to be dominated by the general finite amplitude Alfven wave. Such wave modes correspond to non-plane-wave solutions of the nonlinear magnetohydrodynamic equations.

Sari, J. W.↗

NASA NTRS1977

Electrical structure in a region of the Transverse Ranges, southern California

Magnetotelluric sounding at a site in the Transverse Ranges province in southern California indicates a low-resistivity region in the lower crust and possibly also the upper mantle. A two-dimensional model fit to the data indicates that the resistivity of this region is between 1 and 10 ohm-meters. The depth to the top surface of this zone is between 15 and 20 km. The lateral extent of this feature, which strikes N65 deg W, appears to be confined to the Transverse Ranges province. The petrological characteristics of this region cannot be deduced unambiguously from the magnetotelluric sounding alone.

Reddy, I. K.↗

NASA NTRS1978

Interaction of a turbulent-jet noise source with transverse modes in a rectangular duct

A turbulent jet was used to excite transverse acoustic modes in a rectangular duct. The pressure spectrum showed asymmetric singularities (pressure spikes) at the resonant frequencies of the duct modes. This validates previously published theoretical results. These pressure spikes occurred over a range of jet velocities, orientations, and inlet turbulence levels. At the frequency of the spike, the measured transverse pressure shape matched the resonant mode shape.

Succi, G. P.↗

NASA NTRS1978

Transverse flat plate heat pipe experiment

This paper describes a Shuttle-launched flight experiment to evaluate the performance of a transverse flat plate heat pipe that serves as an integral temperature control/mounting panel for electronic equipment. A transverse heat pipe is a gas-controlled variable conductance heat pipe that can handle relatively large thermal loads. An experiment designed to flight test the concept over a 6-9 month period is self-sufficient with respect to electrical power, timing sequences, and data storage.

Edelstein, F.↗

NASA NTRS1979

Elastic moduli of transversely isotropic graphite fibers and their composites

The paper demonstrates that it is possible to calculate the complete set of elastic mechanical properties for graphite-epoxy fiber-reinforced materials at any fiber-volume fraction by modifying equations previously developed to include transversely isotropic graphite-fiber properties. Experimental verification of the modified equations is demonstrated by using these equations to curve fit elastic-property data obtained ultrasonically over a range of fiber-volume fractions. Material systems under consideration are T300/5208, AS-3501 and Modomor II/LY558 graphite epoxy. Using the modified equations it is possible to extrapolate for fiber properties. From Modomor II/LY558 ultrasonic data, it is shown that five out of seven extrapolated graphite-fiber properties are consistent with the assumption that graphite fibers are transversely isotropic. Elastic properties for T300/5208 and AS-3501 are ultrasonically evaluated by propagating stress waves through six individual specimens cut at various angles from a block of unidirectional material. Particular attention is devoted to specimen dimensions. To demonstrate the need for accurately calculating or experimentally measuring all lamina elastic properties, a brief discussion is included on the effect that variations in lamina elastic properties have on calculating interlaminar stresses.

Kriz, R. D.↗

NASA NTRS1979

Wave propagation in transversely impacted composite laminates

An experimental study was conducted to determine the wave-propagation characteristics, transient strains and residual properties of unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicon-rubber projectiles at velocities up to 250 m/sec. Results include the following: (1) the predominant wave is the flexural wave propagating at different velocities in different directions; (2) peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers; (3) strain rates up to 640/sec were measured; and (4) unidirectional laminates under impact showed appreciable modulus and strength degradation in the direction transverse to fibers.

Daniel, I. M.↗

NASA NTRS1979

Scattering and distortion of the unsteady motion on transversely sheared mean flows

It is shown that the pressure and velocity fluctuations of the unsteady motion on a transversely sheared mean flow can be expressed entirely in terms of the derivatives of two potential functions. One of these is a convected quantity that can be specified as a boundary condition and is related to a transverse component of the upstream velocity field. The other can be determined by solving an inhomogeneous wave equation whose source term is also a convected quantity that can be specified as a boundary condition in any given problem. The general theory is used to study the interaction of an unsteady flow with a semi-infinite plate embedded in a shear layer. The acoustic field produced by this interaction is calculated in the limits of low and high frequency. The results are compared with experimental one-third octave sound pressure level radiation patterns. The agreement is found to be excellent, especially in the low frequency range, where the mean-flow and convective effects are shown to have a strong influence on the directivity of the sound.

Goldstein, M. E.↗

NASA NTRS1979

Remote measurement of the transverse wind velocity component using a laser Doppler velocimeter

The wind speed transverse to the line-of-sight of a laser Doppler radar has been measured using the intensity fluctuations of the returned signal. These measurements were made at a range of 100 m with a CO2 CW laser Doppler velocimeter, which was simultaneously performing its design function of determining the radial velocity component. The transverse component measurements are compared with those obtained using a u, v, w Gill propeller anemometer.

Kennedy, L. Z.↗

NASA NTRS1980

Longitudinal and transverse magnetic field program procedure and detailed specification for Sigma 5

A computer program and procedure for plotting the contour of the data transferred from the Marshall Space Flight Center solar magnetography is presented. The plotted data then can be easily compared with solar data from other sources, such as the Solar Maximum Mission. From the data file for circular polarization the longitudinal program plots the contours for filtered longitudinal plot and intensity plot by choosing the positive and negative contour levels, intensity levels, and also X,Y plotting ranges which need to be used. In a similar manner the transverse program generates the transverse contour plot, azimuth plot, and intensity plot from the linear polarization data files.

Wang, C. K.↗

NASA NTRS1980

A numerical study of candidate transverse fuel injector configurations in the Langley scramjet engine

A computer program has been developed that numerically solves the two-dimensional Navier-Stokes and species equations near one or more transverse hydrogen fuel injectors in a scramjet engine. The program currently computes the turbulent mixing and reaction of hydrogen fuel and air, and allows the study of separated regions of the flow immediately preceding and following the injectors. The complex shock-expansion structure produced by the injectors in this region of the engine can also be represented. Results are presented that describe the flow field near two opposing transverse fuel injectors and two opposing staged (multiple) injectors, and comparisons between the two configurations are made to assess their mixing and flameholding qualities.

Drummond, J. P.↗

NASA NTRS1980

Drag characteristics of V-groove and transverse curvature riblets

The paper examines the drag characteristics of longitudinally ribbed surfaces where the rib dimensions are the order of the initial turbulent wall burst region near the wall. Direct drag measurements are presented for symmetric and unsymmetric V-groove, and (larger wavelength) transverse curvature riblets. The direct drag data indicate net drag reductions as large as 7% for certain V-groove riblets with heights in terms of law of the wall coordinates h+ less than 30. For one of the riblet models, the drag reduction is confirmed by reductions in the momentum thickness, turbulent velocity fluctuations, and Reynolds stress profiles. Although the direct drag data for the transverse curvature riblets showed drag increases, certain models did show that the drag increase diminished with increasing velocity. This trend is opposite to the normal one found for rough surfaces and should be investigated further.

Walsh, M. J.↗

NASA NTRS1981

Transversely accelerated ions in auroral arcs

Ionospheric ions apparently accelerated transversely to the geomagnetic field in the topside ionosphere are regularly detected by the soft particle spectrometers on the ISIS satellites. Such gyro-accelerated ions are observed in association with precipitating auroral electrons. A detailed study of their relationship with such electrons and with field-aligned currents, together with simultaneous measurements of the local plasma composition and density, reveals the specific conditions present in the topside ionosphere during the generation of such transversely accelerated ions (TAI). A proposed mechanism for generation of TAI involving acceleration by electrostatic ion cyclotron waves is consistent with the present observations.

Klumpar, D. M.↗

NASA NTRS1982

Analysis of a turbine rotor containing a transverse crack at Oak Creek Unit 17

Transient increases in one, two and three per revolution vibration characteristics of a low pressure steam turbine were observed during steam temperature reduction operations. Vibration and fracture mechanics analyses suggested the presence of a transverse shaft crack which was eventually identified by ultrasonic inspection and confirmed by destructive sectioning. Signature analyses of vibration data recorded over a two-year period prior to crack identification are correlated with fatigue crack growth, which occurred intermittently during transient temperature decreases. The apparent increased response of the rotor to vibration is due to asymmetric stiffness changes introduced by the growing transverse crack. The vibration response is predicted to increase with increasing crack depths in excess of 10% of the shaft diameter. Fracture mechanics analyses predict that fatigue crack growth occurred during periods of steam temperature decrease, when high surface tensile stresses are present. These same transient thermal stresses are shown to have retarded and prevented subsequent fatigue crack growth during steady operation.

Rogers, G. W.↗

NASA NTRS1983

The in situ transverse lamina strength of composite laminates

The objective of the work reported in this presentation is to determine the in situ transverse strength of a lamina within a composite laminate. From a fracture mechanics standpoint, in situ strength may be viewed as constrained cracking that has been shown to be a function of both lamina thickness and the stiffness of adjacent plies that serve to constrain the cracking process. From an engineering point of view, however, constrained cracking can be perceived as an apparent increase in lamina strength. With the growing need to design more highly loaded composite structures, the concept of in situ strength may prove to be a viable means of increasing the design allowables of current and future composite material systems. A simplified one dimensional analytical model is presented that is used to predict the strain at onset of transverse cracking. While it is accurate only for the most constrained cases, the model is important in that the predicted failure strain is seen to be a function of a lamina's thickness d and of the extensional stiffness bE theta of the adjacent laminae that constrain crack propagation in the 90 deg laminae.

Flaggs, D. L.↗

NASA NTRS1984

Pipelined digital SAR azimuth correlator using hybrid FFT-transversal filter

A synthetic aperture radar system (SAR) having a range correlator is provided with a hybrid azimuth correlator which utilizes a block-pipe-lined fast Fourier transform (FFT). The correlator has a predetermined FFT transform size with delay elements for delaying SAR range correlated data so as to embed in the Fourier transform operation a corner-turning function as the range correlated SAR data is converted from the time domain to a frequency domain. The azimuth correlator is comprised of a transversal filter to receive the SAR data in the frequency domain, a generator for range migration compensation and azimuth reference functions, and an azimuth reference multiplier for correlation of the SAR data. Following the transversal filter is a block-pipelined inverse FFT used to restore azimuth correlated data in the frequency domain to the time domain for imaging.

Wu, C.↗

NASA NTRS1983

Interpretation of vector magnetograph data including magneto-optic effects. I - Azimuth angle of the transverse field

In this paper, the presence of Faraday rotation in measurements of the orientation of a sunspot's transverse magnetic field is investigated. Using observations obtained with the Marshall Space Flight Center's (MSFC) vector magnetograph, the derived vector magnetic field of a simple, symmetric sunspot is used to calculate the degree of Faraday rotation in the azimuth of the transverse field as a function of wavelength from analytical expressions for the Stokes parameters. These results are then compared with the observed rotation of the field's azimuth which is derived from observations at different wavelengths within the Fe I 5250 A spectral line. From these comparisons, it is found: the observed rotation of the azimuth is simulated to a reasonable degree by the theoretical formulations if the line-formation parameter is varied over the sunspot; these variations are substantiated by the line-intensity data; for the MSFC system, Faraday rotation can be neglected for field strengths less than 1800 G and field inclinations greater than 45 deg; to minimize the effects of Faraday rotation in sunspot umbrae, MSFC magnetograph measurements must be made in the far wings of the Zeeman-sensitive spectral line.

West, E. A.↗

NASA NTRS1984

Postbuckling of long orthotropic plates loaded in combined transverse compression and longitudinal compression or shear

The postbuckling behavior of simply supported, rectangular, isotropic and orthotropic composite plates under combined loading is determined analytically. Results are presented for a long plate loaded beyond its buckling load in either a combination of longitudinal and transverse compression or a combination of transverse compression and inplane shear. Results show that orthotropic plates may behave differently than isotropic plates for these loading conditions. Results also show that the postbuckling behavior of plates in shear with constrained edge displacements is markedly different than their behavior with stress free edges.

Stein, M.↗

NASA NTRS1983

Transverse acceleration of ions on auroral field lines

This paper examines transverse ion heating on auroral field lines associated with current-driven electrostatic ion cyclotron waves theoretically and by numerical simulations. The auroral plasma is assumed to consist of drifting electrons and stationary hydrogen and oxygen ions. Depending on the ratio of the electron drift speed to the thermal speed and the ratio of hydrogen to oxygen concentrations, preferential heating of either hydrogen or oxygen ions can take place. It is found that unless the oxygen ions are a minority species, oxygen transverse heating generally exceeds that of hydrogen ions. Theory and numerical simulations are in good agreement.

Ashour-Abdalla, M.↗