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At least 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

'Coriolis resonance' within a rotating duct

An investigation of the unsteady disturbances of a fixed frequency within a radial duct rotating at a set speed is presented. The flow is assumed to be compressible, inviscid, and of a fluid which is a perfect gas. Equations are developed for the steady and the unsteady parts of the flow in cylindrical coordinates. The unsteady disturbances are expressed by Fourier decomposition in angular position, distance into the duct, and in time. It is found that a resonance is possible when the frequency of flow disturbances is twice the shaft-rotation frequency, considering only the radial and tangential disturbances and not the radial and circumferential disturbances. The particular point at which the resonance occurs indicates the occurrence is due to the Coriolis force, which is only present in the radial and tangential directions. It is noted that the Coriolis force can only be present in open-ended ducts, such as those found in centrifugal compressors.

Kurosaka, M.↗
NASA NTRS1982

Identification of 1980S27 and 1980S26 resonances in Saturn's A ring

The Voyager 2 ultraviolet spectrometer observation of a stellar occultation by Saturn's rings contains evidence for features associated with at least 31 resonances due to the F ring shepherd satellites 1980S27 and 1980S26. A limited analysis of density wave patterns associated with eight of these resonances yields surface mass densities for the A ring consistent with previous estimates.

Holberg, J. B.↗
NASA NTRS1983

AK-cut crystal resonators

Calculations have predicted the existence of crystallographically doubly rotated quartz orientations with turnover temperatures which are considerably less sensitive to angular misorientation then comparable AT- or BT-cuts. These crystals are arbitrarily designated as the AK-cut. Experimental data is given for seven orientations, phi-angle variations between 30-46 deg and theta-angle variations between 21-28 deg measured on 3.3-3.4 MHz fundamental mode resonators vibrating in the thickness shear c-mode. The experimental turnover temperatures of these resonators are between 80 C and 150 C, in general agreement with calculated values. The normalized frequency change as a function of temperature has been fitted with a cubic equation.

Kahan, A.↗
NASA NTRS1982

Density measurement in compressible flows using off-resonant laser-induced fluoresence

Measurement of molecular number density in compressible flows using laser-induced fluorescence is complicated by collisional quenching of the exicited state. It is shown that by exciting the fluorescence off-resonance the signal becomes proportional to number density and independent of collisional effects. Quantitative measurement of density in an underexpanded jet of nitrogen is demonstrated using off-resonant fluoresence from iodine seed molecules irradiated with the 514.5 nm line of the argon-ion laser.

Mcdaniel, J. C.↗
NASA NTRS1982

Ferromagnetic resonance intensity - A rapid method for determining lunar glass bead origin

Ferromagnetic resonance intensity, I(s), relies on the absence or presence of single-domain Fe formed during impact melting by autoreduction of Fe(2+) in the melt to distinguish volcanic from impact glass spherules in the lunar soil. SEM inspection of individual glass bead surfaces gave reliable evidence of the mode of glass genesis. Ferromagnetic resonance intensity was tested against the Apollo 15 and 17 volcanics. I(s) values of less than one were found in 94% of the volcanic glasses, implying the absence of single-domain Fe, while 75% of the impact glasses had elevated I(s) values. These samples lack single-domain Fe, and may represent impact melts of bedrock with little or no regolith contribution. Both the primary discrimination of volcanic and impact glasses, and the secondary one of bedrock-derived impact melts from impact melts partially or entirely derived from regolith, have been demonstrated for the I(s) technique.

Stone, C. D.↗
NASA NTRS1983

Experimental investigation of the scattering effects of a sphere in a cylindrical resonant chamber

Resonance frequency, acoustic pressure, and quality factor measurements for transverse and longitudinal modes of a cylindrical chamber are presented as a function of the position of a sphere along the chamber axis. The tests were performed over a wide range of sample-to-chamber ratios, and formulations were devised of the resonance frequency shift as a function of the components of the volume ratios. Departures from linearity were explored for intermediate ratios. The results are considered significant for acoustic levitation operations in space, where the acoustic radiation may alter the acoustic properties of the chamber.

Barmatz, M.↗
NASA NTRS1983

Further observations on resonance cones in non-Maxwellian plasmas

Results on the angular distribution of the electrostatic potential of a pulsating point charge in a warm magnetized plasma permeated by an electron beam are presented. The theoretical formulation for a finite magnetic field is given, and the solution of the resonance cone dispersion relation is presented. Numerical results on the angular distribution of the potential are shown, and the propagation of waves outside the resonance cones is described. It is demonstrated that with the inclusions of a finite magnetic field, the field patterns of a point charge are qualitatively similar to those obtained for a uniaxial plasma. The Cerenkov radiation occurs at angles much smaller than the cold-cone angle, even with the finite magnetic field. When the beam velocity is well above the thermal velocity of the background electrons, a characteristic wave propagation occurs between the cold-cone angles.

Thiemann, H.↗
NASA NTRS1983

Electron acceleration by Landau resonance with whistler mode wave packets

Recent observations of electrostatic waves associated with whistler mode chorus emissions provide evidence that electrons are being trapped by Landau resonance interactions with the chorus. In this paper, the trapping, acceleration and escape of electrons in Landau resonance with a whistler mode wave packet are discussed. It is shown that acceleration can occur by both inhomogeneous and dispersive effects. The maximum energy gained is controlled by the points where trapping and escape occur. Large energy changes are possible if the frequency of the wave packet or the magnetic field strength increase between the trapping and escape points. Various trapping and escape mechanisms are discussed.

Gurnett, D. A.↗
NASA NTRS1983

Laser Resonator

An optical resonator cavity configuration has a unitary mirror with oppositely directed convex and concave reflective surfaces disposed into one fold and concertedly reversing both ends of a beam propagating from a laser rod disposed between two total internal reflection prisms. The optical components are rigidly positioned with perpendicularly crossed virtual rooflines by a compact optical bed. The rooflines of the internal reflection prisms, are arranged perpendicularly to the axis of the laser beam and to the optical axes of the optical resonator components.

Harper, L. L.↗
NASA NTRS1984

The Laplacian resonance and tidal dissipation

The Laplacian resonance amongst Io, Europa, and Ganymede was examined, taking into account tidal dissipation in Jupiter, Io and Europa. In equilibrium, it is not possible to neglect dissipation in Europa nor the torques of Jupiter on Europa and Ganymede. A formal calculation was made on the assumption that the tidal torques and the torques in orbit-orbit resonance reached an equilibrium such that the rates of decrease of the mean motions of the satellites are in the ratios 4:2:1. Q(j)/k(j)=167 Q(1)/k(1), Q(2)/k(2) = 0.44 Q(1)/K(1), where Q denotes the quality at the body's frequency of rotation, k its second degree Love number and the subscripts J, 1 and 2 denote Jupiter, Io, and Europa. The Q(J) found is at Jupiter's frequency of rotation. The rate of tidal dissipation in Europa comes to 1/5 that of Io. Such a low value of Q(2)/K(2) is plausible if dissipation in both Io and Europa is due to tidal friction in fluid against underlying and overlying solid layers.

Cook, A. F.↗
NASA NTRS1984

Manifestation of the Fermi resonance in surface polariton spectra

The method of disturbed full internal reflection (DFIR) is used to detect and interpret the resonance splitting of the surface polariton. The effect in the spectra of oscillatory SP which are reflected by the DFIR method in Otto geometry was experimentally recorded. It is concluded that the resonance splitting of the dispersion branch of SP may serve as an effective method for detecting weak oscillations and for measuring their parameters.

Puchkovskaya, G. A.↗
NASA NTRS1983

Effects of specimen resonances on acoustic-ultrasonic testing

Frequency response is studied at two different transducer locations in the 10-280 kHz range, for the case of the response of a solid 6061-T6 aluminum alloy block to the fracture of an 0.5 mm-diameter pencil lead, as well as to the impact of 0.159 and 0.318 cm-diameter stainless steel spheres. Prominent peaks in the pencil lead fracture and sphere impact spectra from the two transducer locations are found to exactly correspond to the alloy block's resonant frequencies, indicating that these have dominated the spectral content of the output signal. The spectral content is further influenced by the transducer location, relative to the resonant frequency nodal lines. The implications of these results for acoustic-ultrasonic parameters and measurements are discussed.

Williams, J. H., Jr.↗
NASA NTRS1983

A large-signal dynamic simulation for the series resonant converter

A simple nonlinear discrete-time dynamic model for the series resonant dc-dc converter is derived using approximations appropriate to most power converters. This model is useful for the dynamic simulation of a series resonant converter using only a desktop calculator. The model is compared with a laboratory converter for a large transient event.

King, R. J.↗
NASA NTRS1984

Resonances of coronal loops

It is pointed out that any theoretical demonstration that the solar corona can be heated by waves requires a demonstration that the required energies can actually be carried from the convection zone to the corona by waves. In addition, it must be shown that the waves can dissipate their energy into heat in the corona. The present investigation is concerned specifically with the heating of closed magnetic structures in the corona, taking into account coronal loops or active region loops. Attention is given to the MHD Alfven wave. It is shown analytically that coronal active region loops can behave much like interference filters. The coronal part of the loop acts like a resonant cavity for Alfven waves. When the resonances are excited, large energy fluxes can be carried into the loop by Alfven waves which are generated in the solar convection zone. It is estimated that the energy fluxes can power the observed loops.

Hollweg, J. V.↗
NASA NTRS1984

Frequency shifts of an electric-dipole resonance near a conducting surface

The resonance frequency of an electric dipole placed near a conducting surface is shifted by the dipole-surface interaction. The observation and measurement of these shifts at optical frequencies is reported for an experimental system that consists of a metal-island film spaced a distance d from a continuous Ag film. The dependence of the shift in the frequency of the island resonance on d shows good agreement with that predicted by a classical theory of the dipole-surface interaction.

Holland, W. R.↗
NASA NTRS1984

Two-frequency microwave resonance measurements from an aircraft - A quantitative estimate of the directional ocean surface spectrum

The use of the two-frequency microwave-resonance technique for airborne measurements of ocean surface-wave spectral components is examined in a summary of experiments conducted with a coherent Ku-band radar flown on a P-3 aircraft in the 1979 MARSEN and 1980 ARSLOE projects. The 1D theoretical formulation used in the analysis of the MARSEN data by Johnson et al. (1982) is extended to the 2D case; the experimental conditions are described in detail; and typical data are presented graphically, analyzed, and compared with independent measurements obtained with a surface-contour radar. The 3.5-deg pencil-beam configuration used in ARSLOE is shown to produce spectra with good directional characteristics (strong resonances at angles of incidence 13-48 deg). It is found that the proper inversion of radar data to surface-elevation spectra requires surface-reflectivity-modulation sources in addition to the long-wave orbital velocity.

Johnson, J. W.↗
NASA NTRS1984

Resonant heating - An interpretation of coronal loop data

It is shown that the resonant heating theory of Hollweg can be used to organize the coronal loop data of Golub et al. (1980). When combined with a reasonable form for the input power spectrum, the resonant heating theory is fully compatible with the loop data.

Hollweg, J. V.↗
NASA NTRS1984

Experimental on-stream elimination of resonant whirl in a large centrifugal compressor

Resonant whirl condition during operation of a multi-stage centrifugal compressor at higher than anticipated speeds and loads was reported. The condition was diagnosed by a large scale computerized Machinery Condition Monitoring System (MACMOS). This computerized system verified that the predominant subsynchronous whirl frequency locked in on the first resonant frequency of the compressor rotor and did not vary with compressor speed. Compressor stability calculations showed the rotor system had excessive hearing stiffness and inadequate effective damping. An optimum bearing design which was developed to minimize the unbalance response and to maximize the stability threshold is presented.

Bhat, G. I.↗