SEARCH · Engineering Papers

Results for “PERIODICITY”

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.

SourceResearch connectionFrom yearThrough year

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

At least 1,189 records · Page 66

All sources NASA NTRS DOE OSTI

NASA NTRS1983

Periodic motions (close to stationary) of an axisymmetric satellite with magnetic damping

Close to stationary periodic motions of an axisymmetric satellite in a circular orbit are considered. The satellite was equipped with a spherical magnetic damper. The investigation was conducted on the assumption that a strong magnet was installed on the damper float. Stationary rotations of the satellite around the axis of symmetry are selected as the generating solutions. The solutions are constructed in the form of power series of the smaller parameter, and they are extended numerically to the region of random values of the damping coefficient. The stability of the resulting solutions was investigated.

Ovchinnikov, M. Y.↗

NASA NTRS1983

Composites with periodic microstructure

For an elastic body containing periodically distributed inhomogeneities, a general procedure is developed for estimating the overall properties of the composite in terms of several infinite series which, for the isotropic matrix (but anisotropic inclusions), depend only on the geometry of the inhomogeneities and hence can be calculated once and for all for each geometry. These infinite series are obtained and tabulated for ellipsoidal inhomogeneities, and the results are used to estimate the overall elastic moduli of composites which contain spherical or ellipsoidal voids or elastic inclusions.

Iwakuma, T.↗

NASA NTRS1982

Data from ISEE-3 for the IMS period

The International Sun-Earth Explorer (ISEE) Project represents a joint effort between the European Space Agency and NASA. The primary objective of the project is the study of the outer magnetosphere. A review is presented concerning the data available from ISEE-3 up to the end of the International Magnetospheric Study (IMS) period (December 31, 1979), taking into account the approaches used to obtain the data. Attention is given to the ISEE-3 as an upstream monitor, ISEE-3 an an observer of the magnetosphere, aspects of ISEE-3 data availability, questions regarding the data link, and the definitive orbit position of ISEE-3 throughout the IMS.

Von Rosenvinge, T. T.↗

NASA NTRS1983

The nonlocal theory of periodic density drift instabilities

The nonlocal theory of electrostatic density drift instabilities is developed for an arbitrary, periodic variation in plasma density. Linear Vlasov theory is applied to Fourier series representations of the plasma density, and the resulting equations are solved numerically. The growth rates of the universal drift instability are compared by using local and nonlocal theories. It is demonstrated that the local theory is inadequate if the nonlocal eigenfunctions of the electrostatic modes have significant amplitude over spatial regions wider than the regions of large plasma density gradients. Nonlocal effects can enhance wave-particle diffusion of a triangular-shaped variation and reduce wave-particle dissipation of a square-shaped irregularity.

Bernhardt, P. A.↗

NASA NTRS1983

Phase coherence of solar cycle minima over two 178-year periods

The phases of solar cycle minima are compared with an 'ideal' sunspot cycle of the mean period of 11.4 years. The observed departures from the ideal model form a pattern over 16 cycles (approximately 178 years) which appears to be repeated over the next 16 cycles. Both in mathematic sign and amplitude the two 178-year cycles are coherent to a statistically significant level of 98 percent. If true, this furnishes a basis for predicting sunspot cycle minima.

Fairbridge, R. W.↗

NASA NTRS1983

Steady, periodic, and aperiodic atmospheric flows

Atmospheric weather patterns usually occur on scales of a 1000 km or 5000 km and greater, and quasisteady situations can be caused by the appearance of high pressure, blocking zones. Attention is given to the wave-wave interactions and their effects on atmospheric flows on the large scale. The discussion is performed with the beta-plane model for a spherical geometry and a large number of degrees of freedom. The barotropic potential vorticity equation is defined, and discretization of the topography of the sphere results in a spectral truncation with 25 components. The solutions are generated as a function of a forcing and a dissipative parameter. The model yields steady, periodic, and aperiodic solutions, which are shown to be analogous to zonal and blocked atmospheric flows.

Legras, B.↗

NASA NTRS1983

Rise in the frequency of cloud cover in LANDSAT data for the period 1973 to 1981

Percentages of cloud cover in LANDSAT imagery were used to calculate the cloud cover monthly average statistic for each LANDSAT scene in Brazil, during the period of 1973 to 1981. The average monthly cloud cover and the monthly minimum cloud cover were also calculated for the regions of north, northeast, central west, southeast and south, separately.

Parada, N. D. J.↗

NASA NTRS1984

A generalized behavioral model for rotating short period comets with spectral orbital elements and axial orientation

A generalized model for short period comets is developed which integrates in a fairly rigorous manner the isolation history of regions on rotating comets with specified axial orientation and the complex feedback processes involving heat, gas and dust transport, dust mantle development and coma opacity. Attention is focused on development, reconfiguration and partial or complete launching of dust mantles and the reciprocal effects of these three processes on ice surface temperature and gas and dust production. The dust mantle controls the H2O flux not only by its effect on the temperature at the ice interface but (dominantly) by its dynamic stability which strongly influences vapor diffusivity. The model includes the effects of latitude, rotation and spin axis orientation are included and applied to an initially homogeneous sphere of H2O ice and silicate using the orbital parameters of comet Encke. Numerous variations of the model, using combinations of grain size distribution, dust-to-ice ratio, latitude and spin axis orientation, are presented and discussed. Resulted for a similar nonrotating, constant Sun orientation models are also included.

Fanale, F. P.↗

NASA NTRS1984

Periodic control of the individual-blade-control helicopter rotor

Results of an investigation into methods of controller design for an individual helicopter rotor blade in the high forward-flight speed regime are described. This operating condition poses a unique control problem in that the perturbation equations of motion are linear with coefficients that vary periodically with time. The design of a control law was based on extensions to modern multivariate synthesis techniques and incorporated a novel approach to the reconstruction of the missing system state variables. The controller was tested on both an electronic analog computer simulation of the out-of-plane flapping dynamics, and on a four foot diameter single-bladed model helicopter rotor in the M.I.T. 5x7 subsonic wind tunnel at high levels of advance ratio. It is shown that modal control using the IBC concept is possible over a large range of advance ratios with only a modest amount of computational power required.

Mckillip, R. M., Jr.↗

NASA NTRS1984

Statistical structure of convective periods derived from satellite ground based data

The documentation of characteristics of Vertical Atmospheric Soundings (VAS) through the use of statistical structure and correlation functions is presented. A measure of random error is also provided. Rawinsonde data from various periods is analyzed. Structure and correlation functions are used to compare VAS retrievals obtained using a physical algorithm with those from a regression technique. Results from both procedures are evaluated against those from a mesoscale network of rawinsonde stations. The parameters documented include temperature, mixing ratio, geopotential height, thickness, and precipitable water. Calculation are performed at several layers in the lower and upper troposphere.

Meyer, P. J.↗

NASA NTRS1984

A search for the 10-micron silicate feature in periodic Comet Grigg-Skjellerup

A 10-micron spectrum of periodic Comet Grigg-Skjellerup was obtained on 22 June 1982 with the UCL array spectrometer at the United Kingdom Infrared Telescope, Mauna Kea. No emission feature is obvious in the spectrum. The observed spectrum can be fit equally well by a model of small hot absorbing grains or by a composite model with less than or equal to 30 percent (3sigma) warm, 'dirty' silicate grains. The latter model is consistent with the silicate abundance in Comet Kohoutek, which did display an emission feature at 10 microns.

Hanner, M.↗

NASA NTRS1984

The use of hot-wire anemometry in transonic periodic flow

The unsteady wake profiles of an airfoil with an oscillating flap were measured in the NASA Ames 11 x 11-foot transonic wind tunnel. Laser Doppler Velocimetry (LDV) and holography techniques were used in limited region where optical accessability is available. X-hot-film wire was used to measure the wake profiles in the complete region to obtain magnitude and direction of the flow. A thorough calibration was carried out to determine the sensitivity coefficients of the hot-wire in three different tunnels at transonic speeds. A calculation procedure is established to resolve the hot-wire signals at transonic speeds and applied in the measurements of steady and periodic wake profiles. The effect of flow incidence on the hot-wire signals is evaluated and incorporated in the analyses. Typical hot-wire results are compared with the results of LDV, holography and pitot-static tube embedded with Kulite transducers.

Bodapati, S.↗

NASA NTRS1984

The Presidents' Day cyclone of 18-19 February 1979 - Synoptic overview and analysis of the subtropical jet streak influencing the pre-cyclogenetic period

A detailed examination is undertaken of the subtropical jet (STJ) streak revealed by an analysis of the Presidents' Day cyclone of February 18-19, 1979. During its 24 h period, the STJ's flow became increasingly supergeostrophic and apparently unbalanced, while ageostrophic wind speeds increased to more than 30 m/sec in association with a significant cross-contour component, directed toward lower values of the Montgomery streamfunction, as the flow along the STJ became more divergent with time. These phenomena are linked to the increasing confluence in the entrance region of the jet streak and the decreasing wavelength of the trough-ridge system in which the jet streak was embedded. The upper level divergence and upward vertical motion near the axis of the STJ are found to be important factors in the development of the cyclone's first area of heavy snow.

Uccellini, L. W.↗

NASA NTRS1984

IUE spectrophotometry of the DA4 primary in the short-period white dwarf-red dwarf spectroscopic binary Case 1

Low-resolution ultraviolet International Ultraviolet Explorer spectra of the DA white dwarf Case 1 are presented. The spectra show the presence of the 1400 A feature, already discovered in several other DA stars, and of a shallower trough in the 1550-1700 A range. A model atmosphere analysis of the ultraviolet energy distribution of the Ly-alpha red wing yields T(e) = 13,000 + or - 500 K. Possible interpretations of the 1400 A feature are reviewed. Case 1 is the coolest white dwarf found in a short-period, detached white dwarf-red dwarf binary, and its cooling time is consistent with estimates of the efficiency of angular momentum removal mechanisms in the phases subsequent to common envelope binary evolution.

Sion, E. M.↗

NASA NTRS1984

Active control of transition by periodic suction-blowing

A numerical study is conducted to investigate a new method of transition control by periodic suction-blowing. It is shown that significant reduction in the amplitudes of two- and three-dimensional finite-amplitude disturbances can be obtained by the application of this method to transition in plane channel flow.

Biringen, S.↗

NASA NTRS1984

Microwave thermal emission from periodic surfaces

The emissivity of a periodic surface is calculated from one minus the reflectivity by using the reciprocity principle. The reflectivity consists of the sum of all scattered power as determined from the modal theory which obeys both the principle of reciprocity and the principle of energy conservation. The theoretical results are matched to experimental data obtained from brightness temperature measurements as functions of viewing angle for soil moisture in plowed fields. The threshold phenomenon with regard to the appearing and disappearing of modes in their contributions to the scattered field amplitudes is discussed in connection with the theoretical results. It is shown that this approach for calculating the emissivity greatly reduces computational efforts by requiring substantially smaller matrix sizes.

Kong, J. A.↗

NASA NTRS1984

A simple derivation of the formula to calculate synthetic long-period seismograms in a heterogeneous earth by normal mode summation

A simple modification of Gilbert's formula to account for slight lateral heterogeneity of the earth leads to a convenient formula to calculate synthetic long period seismograms. Partial derivatives are easily calculated, thus the formula is suitable for direct inversion of seismograms for lateral heterogeneity of the earth. Previously announced in STAR as N83-29893

Tanimoto, T.↗

NASA NTRS1983

Buckling of imperfect periodic lattice structures

A simplified buckling analysis is presented for a family of periodic lattice structures such as those proposed for large space structures. A transcendental 6 x 6 matrix of eigenvalues is shown to be sufficient for modeling buckling behavior because member stiffnesses are based on an exact solution of the beam-column equation. Exact stiffnesses are derived for a curved member, thus allowing modeling of imperfect lattice structures. Comparisons of predictions of the lattice model with those available from shell and beam theory underscore the inaccuracies introduced by treating the lattice structure as a continuum. Sample calculations are provided for an isogrid cylinder and a three element double-laced truss.

Anderson, M. S.↗