Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Oscillating”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

A finite difference method for the solution of the transonic flow around harmonically oscillating wings

A finite difference method for the solution of the transonic flow about a harmonically oscillating wing is presented. The partial differential equation for the unsteady transonic flow was linearized by dividing the flow into separate steady and unsteady perturbation velocity potentials and by assuming small amplitudes of harmonic oscillation. The resulting linear differential equation is of mixed type, being elliptic or hyperbolic whereever the steady flow equation is elliptic or hyperbolic. Central differences were used for all derivatives except at supersonic points where backward differencing was used for the streamwise direction. Detailed formulas and procedures are described in sufficient detail for programming on high speed computers. To test the method, the problem of the oscillating flap on a NACA 64A006 airfoil was programmed. The numerical procedure was found to be stable and convergent even in regions of local supersonic flow with shocks.

Ehlers, E. F.↗
NASA NTRS1973

Field-determined oscillations in the magnetosheath as possible source of medium-period, daytime micropulsations

Studies of the magnetosheath show it to be characterized by the variable occurrence of large amplitude, sometimes quasiperiodic, field oscillations at diverse distances inward from the bow shock, including the region in proximity with the magnetopause. One established cause of such oscillations near the shock is local oblique orientation of the interplanetary field to the nominal shock surface, and there is evidence that the oscillations, or pulsations, composing the oblique structure appear also downstream in the sheath. It is suggested that medium-period micropulsations, exemplified by pc 3, might be excited in the magnetosphere when proper alignment of the interplanetary field allows shock pulsations to be convected to the magnetopause by plasma flow through the subsolar section of the magnetosheath.

Greenstadt, E. W.↗
NASA NTRS1974

Study of multilayered insulation pipe penetration. Thermal acoustic oscillation

Tests were conducted to determine the net heat leak to a source of liquid nitrogen caused by a metal penetration through the blanket of multilayer insulation. The conditions under which the tests were conducted are described. A graph of the theoretical and experimental temperature distribution is developed for comparison. The variables involved in the computer program to process the data are defined. A study was conducted to develop analytical methods for predicting the effect and magnitudes of thermoacoustic oscillations on the penetration heat leak to cryogens. The oscillations develop as a result of large thermal gradients imposed on a compressible fluid. The predominant amplitudes and frequencies of the thermal acoustic oscillations were investigated.

Lovin, J. K.↗
NASA NTRS1974

A stable, linear frequency-modulated oscillator, part 1

The development of a push-pull frequency-modulated oscillator employing field-effect transistors is described. The advantages of field-effect transistors for use in a frequency-stable oscillator are presented. Linearization of the frequency deviation was accomplished by utilizing the square-law characteristic of an FET used as a modulating amplifier. The push-pull oscillator model produced a linear frequency deviation of more than 10 MHz at a center frequency of approximately 100 MHz. Output power is within 0.6 db of a nominal +8.5 dBm over the desired frequency range, and the modulation bandwidth is dc to 10 MHz. Frequency variation with temperature after compensation with a negative-temperature-coefficient capacitor is within + or - 0.05% from 0 to 60 C.

Honnell, M. A.↗
NASA NTRS1975

On the oscillation of the laterally heterogeneous earth, 1

The perturbative effects, as cause by lateral inhomogeneities in the earth structure and by Coriolis force, contaminate the originally toroidal and spheroidal earth's oscillations, making them of mixed type. For this reason, in order to make the computation of the perturbations more uniform and homogeneous, it was suggested that the earth's free oscillations be expanded into a series in terms of generalized harmonics familiar from the theory of angular momentum in quantum mechanics. Making use of Gibbsian symbolism and of some operators from the theory of angular momentum, explicit expressions were deduced for the perturbative terms in the differential equation of the earth's free oscillations. Decomposition of the strain tensor in terms of canonical vectors was also obtained.

Musen, P.↗
NASA NTRS1975

Modulation linearization of a frequency-modulated voltage controlled oscillator, part 3

An analysis is presented for the voltage versus frequency characteristics of a varactor modulated VHF voltage controlled oscillator in which the frequency deviation is linearized by using the nonlinear characteristics of a field effect transistor as a signal amplifier. The equations developed are used to calculate the oscillator output frequency in terms of pertinent circuit parameters. It is shown that the nonlinearity exponent of the FET has a pronounced influence on frequency deviation linearity, whereas the junction exponent of the varactor controls total frequency deviation for a given input signal. A design example for a 250 MHz frequency modulated oscillator is presented.

Honnell, M. A.↗
NASA NTRS1974

Distinctive patterns on the surface of slowly rotating stars whose oscillations are nonlinearly coupled

Slowly rotating stars which are oscillating at small amplitude in a broad spectrum of g-modes should display strong surface nonuniformities if even weak nonlinear coupling exists between the modes. Oscillatory power will be concentrated into distinctive patterns which rotate rigidly in spite of differential rotation in the outer stellar layers. Each pattern rotates at a constant rate slower than the star as a whole according to a very simple law of rotation. Virtually all the rotation rates are within 9 per cent of the stellar rate. Evidence is cited that the sun may be oscillating, so other stars along the main sequence may be oscillating, also. If zones obeying the predicted rotation law can be detected in a star, then the rotation rate of the stellar interior becomes known, and differential rotation is negligible over most of the stellar mass.

Wolff, C. L.↗
NASA NTRS1975

Energy storage and subharmonic oscillations in Josephson junctions

The energy stored in the magnetic and electric field near a superconducting point contact is typically the same magnitude as the coupling energy which produces the Josephson effect in the weakly coupled superconductors. One consequence of energy storage in both the electric and magnetic field is that the junction can oscillate at a fundamental frequency. The dynamics of these subharmonic oscillations have been studied for a model in which the magnetic and electric energies are represented as being stored in an inductance and a capacitance respectively. The model was studied numerically for various biasing conditions, and the behavior compared to experimental data. A simple analytic approximation was developed that gives physical insight into the mechanism that creates the subharmonic oscillations.

Dempsey, D. G.↗
NASA NTRS1975

Skylab fluid mechanics demostration - A study of water droplet oscillations in space

In the Skylab experiment a drop of water was caused to oscillate at its natural oscillation frequency. The drop was observed until its oscillation began to decay due to its internal damping. A determination of the change in amplitude with time made it possible to verify the applicability of a theoretical model. The fundamental concept of the model is that fluid surfaces tend to an equilibrium shape produced by the balance of the forces of fluid pressure and surface tension. The theoretical model is based on the assumption that the wave amplitude is small compared with the wavelength.

Vaughan, O. H.↗
NASA NTRS1976

Experimental investigation of oscillations in flows over shallow cavities

Wind tunnel experiments were carried out with three axisymmetric models to study laminar axisymmetric flows over shallow cavities at low subsonic speeds. The first model had a hemispherical nose, the second an ogive-shape nose, and the third an elliptic nose. Constant-temperature hot-wire anemometry was used in measuring both mean and fluctuating quantities. Flow around the cavity was visualized by heating the first model. To study the effect of mass injection on cavity oscillations, air was injected circumferentially all along the base of the cavity. Major results are that the cavity depth has little effect on oscillations in shallow cavities except when the depth is of the order of the thickness of the cavity shear flow, that downstream corner is the key factor in inducing self-sustained oscillations in the cavity shear layer, and that the presence of a back face results in an integral relation between wave length of the propagating disturbances and the cavity width in each mode of cavity operation.

Sarohia, V.↗
NASA NTRS1977

Analysis of the development of dynamic stall based on oscillating airfoil experiments

The effects of dynamic stall on airfoils oscillating in pitch were investigated by experimentally determining the viscous and inviscid characteristics of the airflow on the NACA 0012 airfoil and on several leading-edge modifications. The test parameters included a wide range of frequencies, Reynolds numbers, and amplitudes-of-oscillation. Three distinct types of separation development were observed within the boundary layer, each leading to classical dynamic stall. The NACA 0012 airfoil is shown to stall by the mechanism of abrupt turbulent leading-edge separation. A detailed step-by-step analysis of the events leading to dynamic stall, and of the results of the stall process, is presented for each of these three types of stall. Techniques for flow analysis in the dynamic stall environment are discussed. A method is presented that reduces most of the oscillating airfoil normal force and pitching-moment data to a single curve, independent of frequency or Reynolds number.

Carr, L. W.↗
NASA NTRS1976

Absolute oscillator strengths for the iron group - A correction to the data of Warner for the second spectra and a comment on some of the semiempirical results of Kurucz and Peytremann

It has already been shown that the Fe II absolute oscillator strengths (f-values) measured by Warner (1967) contain a systematic error, the magnitude of which depends on the energy of the transition's upper level. The present paper demonstrates that this error affects all of Warner's oscillator strengths for the second spectra of the iron group and develops a correction formula for Warner's results. A comparison of the corrected f-values with other measured f-values for Ti II, V II, and Fe II indicates that the correction improves the usefulness of Warner's data and that the corrected f-values have no large systematic dependence on wavelength, level energy, or line strength. Solar abundances for iron-group elements computed using the original and corrected f-values are compared with recently suggested abundances, and it is found that the corrected f-values yield more consistent results. Semiempirical oscillator strengths calculated by Kurucz and Peytremann (1975) for Fe I, Ti II, and V II are also compared with measured data to evaluate the accuracy of the calculations. It is found that the absolute scales of these results are roughly correct, but some of them are subject to very large errors.

Smith, P. L.↗
NASA NTRS1977

Oscillator strengths of Cr I lines lying between 200 and 541 nm from hook-method and absorption measurements in a furnace

Measurements of 148 oscillator strengths of neutral chromium transitions were made on Cr vapor in a high-temperature furnace by the hook and absorption methods for strong and weak lines, respectively. With the aid of a 5D-z 5F0 multiplet, the product of the oscillator strengths of the lines of this multiplet with the column densities of their respective lower levels could be determined, and by using estimated oscillator strengths for these lines, all data could be put on a common relative scale. This scale was altered so that the results were matched with relative emission intensities. Results are compared with other authors' results. A correction to the hook method constant was also determined.

Huber, M. C. E.↗
NASA NTRS1977

Chromospheric oscillations observed in the 1336-A C II line with OSO-8

Satellite observations of velocity and intensity oscillations of the upper-chromospheric C II line at 1336 A were made. The dominant period of oscillation is 300 s, with little evidence of the power peak in the range 150-200 s which has been observed in other chromospheric lines. Peak-to-peak amplitudes are 2 km/s and 8% in velocity and intensity, respectively. Tentative evidence for a 900-s periodicity is presented. Relative phase measurements show that the maximum intensity for the 300-s oscillation leads the maximum blueshift by approximately 145 s. Comparison of line and background (scattered light) intensity variation shows upward wave propagation with time delays between the 1800-A continuum and the 1336-A C II variation of 27 s and 70 s for different cases.

Chipman, E. G.↗
NASA NTRS1978

A temporary threshold shift for self-motion detection following sustained, oscillating linear acceleration

Thresholds for detecting linear motion (self-motion) increased following exposure of human observers to sustained linear oscillation (fatiguing stimulus) at 0.26 Hz and approximately 0.5 G peak-to-peak for durations up to 30 min. Recovery to preexposure levels took place over a period of 10 to 15 min following the sustained oscillation termination. Differences in threshold shift magnitudes following sustained oscillation in various orientations support the interpretation that the observed threshold shifts resulted from fatigue of the utricular otolith receptors. Threshold shifts were not obtained following exposure of the human observers to sustained, unidirectional linear acceleration (2G) for durations up to 10 min with a centrifuge. The results of this study suggest a previously unobserved response property of the otolith organs, namely, that these organs can be fatigued in a manner analogous to other receptor systems.

Parker, D. E.↗
NASA NTRS1978

Some calculations of transonic potential flow for the NACA 64A006 airfoil with oscillating flap

A method for calculating the transonic flow over steady and oscillating airfoils was developed by Isogai. It solves the full potential equation with a semi-implicit, time-marching, finite difference technique. Steady flow solutions are obtained from time asymptotic solutions for a steady airfoil. Corresponding oscillatory solutions are obtained by initiating an oscillation and marching in time for several cycles until a converged periodic solution is achieved. In this paper the method is described in general terms, and results are compared with experimental data for both steady flow and for oscillations at several values of reduced frequency. Good agreement for static pressures is shown for subcritical speeds, with increasing deviation as Mach number is increased into the supercritical speed range. Fair agreement with experiment was obtained at high reduced frequencies with larger deviations at low reduced frequencies.

Bennett, R. M.↗
NASA NTRS1978

Composite oscillator systems for meeting user needs for time and frequency

Frequency standards are used in most navigation and telecommunications systems to provide a long term memory of either frequency, phase, or time epoch. From a systems point of view, the performance aspects of the frequency standard are weighed against other systems characteristics, such as overall performance, cost, size, and accessibility; a number of examples are very briefly reviewed. The theory of phase lock and frequency lock systems is outlined in sufficient detail that total oscillator system performance can be predicted from measurements on the individual components. As an example, details of the performance of a high spectral purity oscillator phase locked to a long term stable oscillator are given. Results for several systems, including the best system stability that can be obtained from present commercially available 5-MHz sources, are shown.

Stein, S. R.↗
NASA NTRS1979

Present obliquity oscillations of Mars - Fourth-order accuracy in orbital e and I

A long period analysis of solar system orbital evolution, correct to fourth order in orbital eccentricities and inclinations (Bretagnon, 1974), and an improved value of the planet's moment of inertia (Reasenberg, 1977) have been incorporated in a recalculation of the obliquity oscillations of Mars. A linearized solution predicts a maximum oscillation amplitude of 13.6 deg centered on a long-term average value of 24.4 deg. A numerical integration of the obliquity for the past 10,000,000 years is also presented. Epochs of minimal oscillation like the present occur at intervals of the order of 4 m.y.

Ward, W. R.↗