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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Improvement of a large-amplitude sinusoidal pressure generator for dynamic calibration of pressure transducers

Results of research on the improvement of a sinusoidal pressure generator are presented. The generator is an inlet-area-modulated, gas-flow-through device (siren type) which was developed to dynamically calibrate pressure transducers and pressure probes. Tests were performed over a frequency range of 100 Hz to 20 kHz at average chamber pressures (bias pressure) between 30 and 50 psia (21 and 35 N/sq cm abs) and between 150 and 300 psia (104 and 207 N/sq cm abs). Significant improvements in oscillation pressure waveform were obtained but with reduction in available generator oscillation pressure amplitude range. Oscillation pressure amplitude, waveform, and waveform spectral content are given as functions of frequency for the two bias pressure conditions. The generator and instrumentation for frequency, amplitude, and spectrum measurements are described.

Robinson, R. E.↗
NASA NTRS1971

Amplitude and polarization asymmetries in a ring laser

Asymmetric amplitude effects between the oppositely directed traveling waves in a He-Ne ring laser are analyzed both theoretically and experimentally. These effects make it possible to detect angular orientations of an inner-cavity bar with respect to the plane of the ring cavity. The amplitude asymmetries occur when a birefringent bar is placed in the three-mirror ring cavity, and an axial magnetic field is applied to the active medium. A simplified theoretical analysis is performed by using a first order perturbation theory to derive an expression for the polarization of the active medium, and a set of self-consistent equations are derived to predict threshold conditions. Polarization asymmetries between the oppositely directed waves are also predicted. Amplitude asymmetries similar in nature to those predicted at threshold occur when the laser is operating in 12-15 free-running modes, and polarization asymmetry occurs simultaneously.

Campbell, L. L.↗
NASA NTRS1972

Finite-amplitude pressure waves in the radial mode of a cylinder

A numerical study of finite-strength, isentropic pressure waves transverse to the axis of a circular cylinder was made for the radial resonant mode. The waves occur in a gas otherwise at rest, filling the cylinder. A method of characteristics was used for the numerical solution. For small but finite amplitudes, calculations indicate the existence of waves of permanent potential form. For larger amplitudes, a shock is indicated to occur. The critical value of the initial amplitude parameter in the power series is found to be 0.06 to 0.08, under various types of initial conditions.

Kubo, I.↗
NASA NTRS1973

A general conclusion regarding the large amplitude flexural vibration of beams and plates.

Use is made of the two coupled partial differential equations that govern the large amplitude flexural vibration of flat plates. On the basis of an assumed vibration mode taken to be separable in the space coordinates and time, the modal equation is obtained. In the case of a one-term solution, it is shown that the modal equation is the same as the dynamic equation of a mass-spring combination where the restoring force of the nonlinear spring is a cubic and an odd function of the displacement. Since the modal equation is a nonlinear, ordinary differential equation with positive coefficients, it is shown that the nonlinearity associated with the large amplitude flexural vibration of beams and plates is of the hardening type, that is, the frequency increases with amplitude.

Pandalai, K. A. V.↗
NASA NTRS1974

A relation between ELF hiss amplitude and plasma density in the outer plasmasphere

Simultaneous observations of ELF hiss amplitude and plasma density on Ogo 5 have been investigated. Passes through the region of variable plasma density in the outer plasmasphere have yielded a quantitative relation between the hiss amplitude, the plasma density, and the plasma density corresponding to the threshold of wave detection. It is suggested that this dependence of wave amplitude on plasma density is a source effect and is related to the wave-particle interaction in the outer plasmasphere that gives rise to hiss.

Chan, K.-W.↗
NASA NTRS1974

Large-amplitude hydromagnetic waves

Several aspects of the theory of large-amplitude hydromagnetic waves and their behavior in the interplanetary medium are examined. The characteristic modes of the full (i.e., nonlinearized) MHD equations and their modification by collisionless and finite-frequency effects are considered. Special attention is paid to the transverse Alfven mode, which is undamped and characterized by strictly constant pressure, density, and B; this seems to be the predominant propagating fluctuation at 1 AU. It is shown that its propagation in the small-wavelength (WKB) approximation is essentially identical to that of the small-amplitude Alfven wave of linearized theory. It is also suggested that its presence at 1 AU may provide a natural explanation of the observed power anisotropy of the fluctuations. A second-order analysis is used to study fluctuations that are not characteristic modes. It is found that for a small range of propagation directions, and subject to third-order effects, a finite-amplitude wave can exist that is linearly polarized with delta B perpendicular to both B sub zero and k; such a wave can damp nonlinearly.

Barnes, A.↗
NASA NTRS1975

Some results of the hydrodynamic theory of finite-amplitude waves

Standing waves can be interpreted as free waves between two vertical walls; for a standing wave in an unlimited container there is no transport of liquid mass in the horizontal direction. Standing waves of finite amplitude also possess the following properties not possessed by the waves of the linear theory: (1) there are no motionless points, (2) the points of maximum amplitude (crests and troughs) are fixed, and coincide with the antinodes of the original linear wave, (3) the ordinates of the wave crests are greater in absolute magnitude than the ordinates of the troughs; the wave is similar to a trochoid curve; (4) the wave profile never becomes straight; and (5) the frequency of the oscillations depends not only on the wave length but also on the amplitude.

Sekerzh-Zenkovich, Y. I.↗
NASA NTRS1975

Glauber exchange amplitudes

The extrapolation method of Ochkur, valid for intermediate energies (about 50 eV), is applied to the exchange form of the Glauber amplitudes. In the case of elastic scattering of electrons from hydrogen atoms at 54.4 Ev the 'post' and 'prior' forms of the exchange amplitude are equivalent, whereas for the case of inelastic scattering there is a minute discrepancy between the two forms of the amplitude. The results are compared with the close-coupling calculation. The investigation is expected to be useful for optically forbidden exchange-allowed transitions due to electron impact at intermediate energies.

Madan, R. N.↗
NASA NTRS1975

Amplitude effects on the dynamic performance of a hydrostatic gas thrust bearing

The Reynolds' equation is applied to a strip gas thrust bearing to analyze amplitude disturbance effects on its dynamic performance. The Reynolds' equation is numerically approximated using finite difference techniques. The time dependent load carrying capacity is represented by a Fourier series up to and including the third harmonics. Design curves for the load capacity and the linear stiffness and damping are presented as a function of inlet location, restrictor coefficient, supply pressure, amplitude of oscillation, and squeeze number. For the range of amplitudes investigated the dimensionless load capacity, stiffness and damping does not exhibit an appreciable change in magnitude; thus, only one design curve is needed to represent each relationship. A design methodology is presented.

Stiffler, A. K.↗
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

Approximate theory of large-amplitude wave propagation

An orbit perturbation procedure is applied to the description of monochromatic, large-amplitude, electrostatic plasma wave propagation. In the lowest-order approximation, untrapped electrons are assumed to follow constant-velocity orbits and trapped electrons are assumed to execute simple harmonic motion. The deviations of these orbits from the actual orbits are regarded as perturbations. The nonlinear damping rate and frequency shift are then obtained in terms of simple functions. The results are in good agreement with previous less approximate analyses. A significant feature of the analysis is that it treats a single wave by techniques previously applied to turbulent spectra. The analysis can consequently be extended to the case of a large-amplitude wave interacting with a lower-amplitude spectrum of waves.

Kim, H.↗
NASA NTRS1978

Modulational instability of finite-amplitude, circularly polarized Alfven waves

The simple theory of the decay instability of Alfven waves is strictly applicable only to a small-amplitude parent wave in a low-beta plasma, but, if the parent wave is circularly polarized, it is possible to analyze the situation without either of these restrictions. Results show that a large-amplitude circularly polarized wave is unstable with respect to decay into three waves, one longitudinal and one transverse wave propagating parallel to the parent wave and one transverse wave propagating antiparallel. The transverse decay products appear at frequencies which are the sum and difference of the frequencies of the parent wave and the longitudinal wave. The decay products are not familiar MHD modes except in the limit of small beta and small amplitude of the parent wave, in which case the decay products are a forward-propagating sound wave and a backward-propagating circularly polarized wave. In this limit the other transverse wave disappears. The effect of finite beta is to reduce the linear growth rate of the instability from the value suggested by the simple theory. Possible applications of these results to the theory of the solar wind are briefly touched upon.

Derby, N. F., Jr.↗
NASA NTRS1980

Modelling of equatorial phase and amplitude scintillations from OGO-6 and AE irregularity data

The technique of modelling equatorial phase and amplitude scintillations from in-situ measurements of irregularity amplitude, ambient ionization density and irregularity power spectrum is outlined. The in-situ measurements do not directly provide information on irregularity layer thickness for which radar backscatter observations are utilized. The equatorial scintillation models developed from OGO-6 and AE-C in-situ measurements during the two solstices are presented. Considerable differences in the longitude variation of scintillations are predicted during the two solstices. The model estimates are in good agreement with the available ground based phase and amplitude measurements. Problems associated with the use of bottomside spread-F data for transionospheric propagation modelling at VHF/UHF are also discussed.

Basu, S.↗
NASA NTRS1981

Large amplitude stationary Rossby waves in the Southern Hemisphere

Large Amplitude stationary waves downstream of South America, and in the lee of Australia were investigated using Tiros N photographs. These waves appear to be Rossby lee waves associated with anomalous poleward flow over the Andes and by continental heating over Australia. The waves have a maximum amplitude near 300 mb between 20 and 40 deg S and correlate well with observed precipitation bands in the Atlantic and Pacific Oceans. The orientation of these waves is such that they transfer zonal momentum to the roaring forties latitudes. Stationary Rossby waves, in the Northern Hemisphere, have a characteristic wavelength of the order of 120 deg longitude. In January the observed stationary wavelengths have a wavelength of less than 60 deg longitude with an amplitude in the upper tropospheric meridional wind of more than 15 m sec E-1.

Kalnay, E.↗
NASA NTRS1986

Large amplitude, low frequency plasma fluctuations at Comet Giacobini-Zinner

Very large amplitude fluctuations in electron density, temperature, and flow velocity were a prominent aspect of the solar wind interaction with Comet Giacobini-Zinner during the ICE encounter in September 1985. These fluctuations were detected at a distance of at least 900,000 km and grew in amplitude as ICE approached the comet, peaking in amplitude 60,000 km from closest approach. A typical period associated with the fluctuations was about 2 min, which corresponds to a scale length in the solar wind frame of about 50,000 km. For the most part these fluctuations appear to be a product of one or more plasma instabilities associated with the solar wind pick up of cometary ions.

Gosling, J. T.↗
NASA NTRS1986

Periodic amplitude variations in Jovian continuum radiation

An analysis of periodic variations in the amplitude of continuum radiation near 3 kHz trapped in the Jovian magnetosphere shows structure with periods near both five and ten hours. Contrary to a plausible initial idea, the continuum amplitudes are not organized by position of the observer relative to the dense plasma sheet. Instead, there seem to be preferred orientations of system III longitude with respect to the direction to the sun which account for the peaks. This implies a clock-like modulation of the continuum radiation intensity as opposed to a searchlight effect. The importance of the dipole longitude-solar wind alignment to the amplitude of the continuum radiation implies the source region of the radiation is near the magnetopause and may indirectly tie the generation of the radio waves to the clocklike modulation of energetic electron fluxes from Jupiter.

Kurth, W. S.↗
NASA NTRS1987

Influence of the Dirac-Hartree-Fock starting potential on the parity-nonconserving electric-dipole-transition amplitudes in cesium and thallium

The parity-nonconserving electric-dipole-transition amplitudes for the 6s1/2-7s1/2 transition in cesium and the 6p1/2-7p1/2 transition in thallium have been calculated by the Dirac-Hartree-Fock method. The effects of using different Dirac-Hartree-Fock atomic core potentials are examined and the transition amplitudes for both the length and velocity gauges are given. It is found that the parity-nonconserving transition amplitudes exhibit a greater dependence on the starting potential for thallium than for cesium.

Perger, W. F.↗