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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Stable and unstable near-resonant states in multilevel, severely truncated, quasi-geostrophic models

Multilevel, severely truncated, quasi-geostrophic models with damping that extend from the surface to 100 km, are used to study the stationary-wave response to orography and the concomitant feedbacks on the zonal flow. For a typical winter zonal-wind profile, it is shown that large amplitude or resonant planetary waves of intermediate zonal wavenumbers of about 4 or 5 occur with an equivalent barotropic structure. It is also shown that wave-zonal flow interaction with a mountain torque and temperature transport is stable to small perturbations on the low side of resonance and unstable on the high side of resonance. Resonant zonal wavenumbers of lower wave wavenumber also occur for the same zonal profile and have a node in the vertical with a small amplitude maximum near the surface and a larger amplitude maximum in the stratosphere. Instability depends on the presence of the orography and the basic asymmetric state as Newtonian damping and surface friction are sufficient to damp the baroclinic instability associated with a linear inviscid model.

Roads, J. O.↗
NASA NTRS1982

Motion of the Jovian commensurability resonances and the character of the celestial mechanics in the asteroid zone - Implication for kinematics and structure

The motion of the Jovian commensurability resonances during the early evolution of the solar system induced by the dissipation of the accretion disk results in fundamental differences in the celestial mechanics of objects over which a resonance passes from that observed for a stationary resonance. Objects experiencing resonance passage acquire irreversible increases of average eccentricity to large values accounting for the present-day random velocities of the asteroids. Semi-major axes are similarly irreversibly decreased by amounts capable of clearing the Kirkwood gaps. The gap widths are in agreement with observation.

Torbett, M.↗
NASA NTRS1982

Orbital resonances and planetary formation sites

A cascaded resonance structure where planetesimal growth was accelerated at 2:1 interior and 1:2 exterior resonances, with an early-formed Jupiter producing runaway growth of planetary embryos, is hypothesized in a solar system formation model. The planetary embryos produce their own resonances, and these in turn lead to additional embryos in a process that successively propagates inwardly and outwardly to generate a resonant configuration of embryos. The early presence of Jupiter would in this way have imposed a harmonic structure on the accumulating planetesimal swarm. The positions of the planetary embryos can be moved into a degree of agreement with most of the present planetary positions which is comparable to that given by the Titius-Bode law, for the case of an accretion disk whose surface density obeys a power law of index -1.2.

Torbett, M.↗
NASA NTRS1984

Resonance in flows with vortex sheets and edges

It is shown that the vortex sheet in a slot between two semi-infinite plates does not admit incompressible resonant perturbations. The semi-infinite vortex sheet entering a duct does admit incompressible resonance. These results indicate that the vortex-sheet approximation is less useful for impinging shear flows than for non-impinging flows. They also suggest an important role of downstream vortical disturbances in resonant flows. The general solution for perturbations to flow with a vortex sheet and edges is written in terms of a Cauchy integral. Requirements on the behavior of this solution at edges and at downstream infinity fix the criteria for resonance.

Durbin, P. A.↗
NASA NTRS1984

Spectrum of squeezing in resonance fluorescence

A spectral analysis of the squeezing in resonance fluorescence is accomplished via a study of a phase sensitive correlation function. In the case of resonance fluorescence from a two-level system, the initial state is a coherent state for the laser mode, a vacuum for the other states of the radiation field, and the atoms in the lower level. Maximum squeezing for resonance excitation is obtained for near resonant frequencies of the fluorescent light. Possible experimental configurations are discussed in order to detect spectral squeezing.

Collett, M. J.↗
NASA NTRS1984

Orbital resonances among Saturn's satellites

When orbital properties constituted most of our knowledge of Saturn's satellites, resonances provided important clues to physical properties and history. With the discoveries of the 1980s, including close-up direct observations of physical and geological properties, resonances are more important than ever. This chapter reviews the kinetics of the various classes of resonances represented among the classical and newly discovered satellites and describes how resonances have played a fundamental role in shaping the Saturn system as it is seen today.

Greenberg, R.↗
NASA NTRS1986

The wave magnetic field amplitude threshold for nonlinear trapping of energetic gyroresonant and Landau resonant electrons by nonducted VLF waves in the magnetosphere

A recently developed theory is used to calculate the wave magnetic field amplitude threshold, B-tau, necessary to allow the nonlinear trapping of energetic gyroresonant and Landau resonant electrons by VLF whistler mode waves in the magnetosphere propagating at an arbitrary angle, psi, with respect to the earth's magnetic field. A detailed raytracing study is carried out to establish the variation of psi with position along each magnetic shell in the range L = 2-5 and for frequencies 5-17.8 kHz. It is found that the minimum values of B-tau along each L shell generally occur at points of second-order resonance. In general, for nonducted fixed frequency signals there is only one point of second-order resonance on each L shell, and this is located within a few degrees of the magnetic equator. However, over a narrow range of L, there are as many as three points of second-order resonance and as many as three associated minima in B-tau. At least one of these points is located more than 10 deg from the magnetic equator.

Bell, T. F.↗
NASA NTRS1986

The Helmholtz resonance behavior of single and multiple rooms

The results of exploratory measurements of the noise fields inside rooms which are excited to resonance either acoustically or mechanically are presented. The data illustrate the nature and extent of the sound pressure level enhancements in single rooms and also how multiple rooms may resonate by means of either acoustic or mechanical coupling. Sound pressure level enhancements of about 5 dB were measured during resonance of rooms having flexible walls. For such conditions the sound pressure levels in the room were essentially uniform and in phase. Variability of up to 20 dB was measured in a room hallway complex having significant acoustic interactions. Resonant frequency prediction methods which work well at model scale, give only fair results for rooms.

Hubbard, H. H.↗
NASA NTRS1987

Why no orbital resonances among the satellites of Uranus?

Most of the orbital resonances among the satellites of the major planets are thought to be assembled by differential tidal expansion of their orbits. Why this has not occurred for the Uranus system can be investigated by determining the resonances which would be encountered for various values of Uranus' tidal effective Q. The comparison and the possible escape of Ariel-Umbriel from the 5:3 resonance mean that it is not unreasonable that no orbital resonances are found among these satellites.

Peale, S. J.↗
NASA NTRS1986

Resonant AC power system proof-of-concept test program

Proof-of-concept testing was performed on a 20-kHz, resonant power system breadboard from 1981 through 1985. The testing began with the evaluation of a single, 1.0-kW resonant inverter and progressed to the testing of breadboard systems with higher power levels and more capability. The final breadboard configuration tested was a 25.0-kW breadboard with six inverters providing power to three user-interface modules over a 50-meter, 20-kHz bus. The breadboard demonstrated the ability to synchronize multiple resonant inverters to power a common bus. Single-phase and three-phase 20-kHz power distribution was demonstrated. Simple conversion of 20-kHz to dc and variable-frequency ac was demonstrated as was bidirectional power flow between 20-kHz and dc. Steady state measurements of efficiency, power-factor tolerance, and conducted emissions and conducted susceptibility were made. In addition, transient responses were recorded for such conditions as start up, shut down, load changes. The results showed the 20-kHz resonant system to be a desirable technology for a spacecraft power management and distribution system with multiple users and a utility-type bus.

Wappes, Loran J.↗
NASA NTRS1987

Control of turbulence through a row of Helmholtz resonators

The manipulation of turbulent boundary layers is useful in a variety of situations including drag reduction and separation delay. In this study a passive method of altering the turbulence in a boundary layer is investigated. Ten Helmholtz resonators were imbedded in a spanwise row under a turbulent boundary layer. At certain airspeeds the resonators were strongly excited by the turbulence. In turn, the resonator motions interact to modify the turbulence and mean velocity profiles in the boundary layer. Tests were conducted to measure the response of the resonators as a function of freestream speed. Additional tests, conducted at the conditions for maximum response, documented the affect on the mean and turbulent velocity profiles.

Panton, Ronald L.↗
NASA NTRS1987

Resonance absorption of magnetohydrodynamic surface waves Physical discussion

It is shown how the phenomenon of MHD surface wave resonance absorption can be described in simple terms, both physically and mathematically, by applying the 'thin flux tube equations' to the finite-thickness transition layer which supports the surface wave. The thin flux tubes support incompressible slow-mode waves that are driven by fluctuations in the total pressure which exist due to the presence of the surface wave. It is shown that the equations for the slow-mode waves can be reduced to a simple equation, equivalent to a driven harmonic oscillator. Certain field lines within the transition layer are equivalent to a harmonic oscillator driven at resonance, and neighboring field lines are effectively driven at resonance as long as a given condition is satisfied. Thus, a layer which secularly extracts energy from the surface wave develops. The analysis indicates that nonlinear effects may destroy the resonance which is crucial to the whole effect.

Hollweg, Joseph V.↗
NASA NTRS1987

Galilean satellites - Evolutionary paths in deep resonance

While the Laplace resonance among the three inner Galilean satellites possesses stable configurations where the mean motions taken by pairs are in nearly 2:1 ratios, or 'deep resonance', the current satellite configuration is unstable near this exact commensurability. There is presently noted, however, a continuous path of stable conditions branching toward deep resonance which furnishes a track for the tidal evolution of the system and renders scenarios involving (probably episodic) evolution from deep resonance viable; this eliminates the requirement for rapid tidal dissipation of Jupiter by the alternative equilibrium hypothesis.

Greenberg, Richard↗
NASA NTRS1988

X-band resonant ring operation at 450 kW

The operation of the X-band (7.2 GHz) ring resonator was documented at a power level of 450 kW, which represents the highest power level achieved in the resonator to date. The ring resonator and the overall experimental setup are summarized. The motivation for the present ring resonator experiment is described, and specific results are presented. More general observations made while operating the ring at these power levels are described, and conclusions are drawn.

Hoppe, D.↗
NASA NTRS1987

Analysis of twin supersonic plume resonance

Recent experiments conducted at NASA Langley show that twin supersonic jets separating by a distance of approximately two nozzle diameters (center to center) exhibit resonant oscillations under a wide range of operating conditions. In this paper the mechanism responsible for the synchronized resonant oscillations is investigated. A vortex sheet jet model is used in the analysis. The model shows that kinematically two modes of twin jet resonance can occur. One mode involves flapping motion of both jets symmetric with respect to the mid-plane separating the two jets. The other mode involves antisymmetric flapping motion. The symmetric mode is consistent with experimental observations. The vortex sheet jet model is, however, unable to provide quantitative estimates of the shift in screech frequency (as compared to a single jet) due to the resonance phenomenon. The reason for this is discussed. Possible improvement of the model and directions for future work are indicated.

Tam, Christopher K. W.↗
NASA NTRS1988

Microwave and millimeter-wave resonant-tunneling devices

Resonant-tunneling devices in microelectronic component form, whose structure is the electron analog of a Fabry-Perot resonator, encompass oscillators, self-oscillating mixers, and harmonic multipliers. The negative differential resistance characteristic of these devices has been obtained at room temperature, and resonant-tunneling transistors capable of operation in the THz-frequency range appear to be feasible. Three-terminal resonant-tunneling device development is in its infancy, as is that of devices for digital applications.

Sollner, T. C. L. Gerhard↗
NASA NTRS1989

Gaussian-Beam Laser-Resonator Program

Gaussian Beam Laser Resonator Program models laser resonators by use of Gaussian-beam-propagation techniques. Used to determine radii of beams as functions of position in laser resonators. Algorithm used in program has three major components. First, ray-transfer matrix for laser resonator must be calculated. Next, initial parameters of beam calculated. Finally, propagation of beam through optical elements computed. Written in Microsoft FORTRAN (Version 4.01).

Cross, Patricia L.↗
NASA NTRS1988

Dynamic characteristics of a 20 kHz resonant power system - Fault identification and fault recovery

A detailed simulation of a dc inductor resonant driver and receiver is used to demonstrate the transient characteristics of a 20 kHz resonant power system during fault and overload conditions. The simulated system consists of a dc inductor resonant inverter (driver), a 50-meter transmission cable, and a dc inductor resonant receiver load. Of particular interest are the driver and receiver performance during fault and overload conditions and on the recovery characteristics following removal of the fault. The information gained from these studies sets the stage for further work in fault identification and autonomous power system control.

Wasynczuk, O.↗