Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “linear scaling”

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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Direct numerical simulation and analysis of shock turbulence interaction

Two kinds of linear analysis, rapid distortion theory (RDT) and linear interaction analysis (LIA), were used to investigate the effects of a shock wave on turbulence. Direct numerical simulations of two-dimensional isotropic turbulence interaction with a normal shock were also performed. The results from RDT and LIA are in good agreement for weak shock waves, where the effects of shock front curvature and shock front unsteadiness are not significant in producing vorticity. The linear analyses predict wavenumber-dependent amplification of the upstream one-dimensional energy spectrum, leading to turbulence scale length scale decrease through the interaction. Instantaneous vorticity fields show that vortical structures are enhanced while they are compressed in the shock normal direction. Entrophy amplfication through the shock wave compares favorably with the results of linear analyses.

Lee, Sangsan↗
NASA NTRS1984

Two time scale stabilization of systems with output feedback

The problem of constant gain output feedback regulator design for linear systems with ill-conditioned dynamics is considered in the context of singular perturbation theory. A design approach is developed in which gains can be separately calculated to stabilize reduced-order slow and fast subsystem models. By employing the notion of combined control and observation spillover suppression, conditions are derived assuring that these gains will stabilize the full-order system, assuming sufficient frequency separation between the slow and fast subsystems. An LQ design procedure is described in which the spillover suppression conditions are satisfied by adjoining penalty functions to the subsystem performance indices. The theory is demonstrated in a controller design for a flexible space structure.

Moerder, D. D.↗
NASA NTRS1991

Planetary-scale waves in the Southern Hemisphere winter and early spring stratosphere - Stability analysis

A barotropic stability model linearized about a zonally symmetric flow is used to examine the stability characteristics of horizontal zonal-mean flow profiles representative of the Southern Hemisphere middle stratosphere during winter and early spring, with emphasis on periods when planetary wave growth appears confined to the stratosphere. Unstable modes of eastward-travelling waves 2 and 3 are found to have period sand spatial structures, similar to observations. Wave-2 and wave-3 momentum fluxes are similar in observations and model results and are consistent with the transfer of kinetic energy from the zonal-mean flow to the wave. When a barotropic model with a zonally symmetric basic flow is used, wave 3 is usually most unstable. Including a stationary wave 1 in the basic flow destabilizes both wave 2 and wave 3, but has little effect on their periods or spatial structures. The similarity between observed fields and model results in a number of cases when wave 2 appears to grow within the stratosphere suggests that in situ instabilities play a role in the evolution of the eastward-traveling wave-2 characteristic of the Southern Hemisphere winter and early spring stratosphere.

Manney, G. L.↗
NASA NTRS1990

Instability of a supersonic shock-free elliptic jet

A comparison of the measured and the computed spatial stability properties of an aspect ratio 2, supersonic, shock free, elliptic jet is presented. The shock free nature of the elliptic jet furnishes a perfect test of the validity of modeling the large scale coherent structures in the initial mixing region of noncircular supersonic jets with the linear hydrodynamic stability theory. Aerodynamic and acoustic data are measured to compute the mean velocity profiles and to provide a description of the spatial composition of pressure waves in the elliptic jet. The measured mean velocity profiles are employed to provide a qualitative model for the cross sectional geometry and the smooth velocity profiles utilized in the stability analysis. It is shown that the measured frequency associated with peak amplitude noise radiation agrees with that frequency predicted to dominate the large scale structure near the end of the potential core.

Baty, Roy S.↗
NASA NTRS1976

Stochastic simulation of vertically nonhomogeneous gusts

The small-scale horizontal gust structure of detailed wind profiles along the vertical in the first 20 km of the atmosphere is a vertically nonhomogeneous process. A linear stochastic model is developed for the process based on the process covariance function. This model is formulated through the use of a scaling hypothesis that transforms the nonhomogeneous gust process into a nondimensional gust process which is homogeneous in a nondimensional height coordinate. The velocity scaling parameter for the gust process is the gust standard deviation, and the length scale used to nondimensionalize the altitude is the vertical space lag associated with the first zero of the gust covariance function. State space theory is used to derive a digital filter from the model, which can be readily used to simulate gusts for space vehicle design applications.

Fichtl, G. H.↗
NASA NTRS1973

First look analyses of five cycles of ERTS-1 imagery over County of Los Angeles: Assessment of data utility for urban development and regional planning

Significant results have been obtained from the analyses of ERTS-1 imagery from five cycles over Test Site SR 124 by classical photointerpretation and by an interactive hybrid multispectral information extraction system (GEMS). The synopticity, periodicity and multispectrality of ERTS coverage, available for the first time to LA County planners, have opened up both a new dimensionality in data and offer new capability in preparation of planning inputs. Photointerpretation of ERTS images has produced over 25 overlays at 1:1,000,000 scale depicting regional relations and urban structure in terms of several hundred linear and areal features. To mention only one such result, a possible new fault lineament has been discovered on the northern slope of the Santa Monica mountains in the scene 1144-18015, composited of MSS bands 4, 5, 6,. GEMS analysis of the ERTS products has provided new or improved information in the following planning data categories: urban vegetation; land cover segregation; man-made and natural impact monitoring; urban design; and suitability. ERTS data analysis has allowed planners to establish trends that directly impact planning policies. This new source of information will not only assist current methods to be more efficient, but permits entirely new planning methodologies to be employed.

Raje, S.↗
NASA NTRS1971

The lateral/directional stability characteristics of a four-propeller tilt-wing V/STOL model in low-speed steep descent

Lateral-directional dynamic stability derivatives are presented for a O.1-scale model of the XC-142A tilt-wing transport. The tests involved various descending flight conditions achieved at constant speed and wing incidence by varying the vehicle angle of attack. The propeller blade angle and the speed were also changed in the steepest descent case. The experimental data were analyzed assuming that the dynamic motions of the vehicle may be described by linearized equations, with the lateral-directional characteristics of the full-scale aircraft also presented and discussed. Results from this experimental investigation indicated that the full-scale aircraft would have a stable lateral-directional motion in level flight, with the dynamic motion becoming less stable as the descent angle was increased.

Dicarlo, D. J.↗
NASA NTRS1973

Attitude control of a spinning flexible spacecraft

The dynamics of rotational motion of a spinning orbiting spacecraft consisting of two rigid bodies connected by a flexible joint and arbitrary number of flexible appendages (two of which are flexible massless booms having masses on their tips) is analyzed. Active attitude control is provided by momentum exchange devices (e.g. control moment gyroscopes) or a mass expulsion system. The linearized equations of motion describing the vehicle are presented, and a large scale digital simulation that has been developed at the Marshall Space Flight Center is presented. A simplified model of the geometrically complex vehicle is selected to make it analytically tractable. The simplified model consists of a single rigid core body with two attached flexible massless booms having tip masses. The states of the vehicle are defined as small perturbations about its steady-state spin. An analysis is performed to determine the domain of stability.

Seltzer, S. M.↗
NASA NTRS1979

Large lunar secondary craters - Size-range relationships

The relationship between primary crater diameter and mean maximum secondary crater diameter for lunar craters is essentially linear for primary diameters from 0.5 to 260 km. The mean range from the primary to the largest secondary craters is also nearly linearly related to primary diameter. Extrapolation of these results to lunar basin scale supports the contention that basin secondaries of large diameter are to be found across much of the moon.

Allen, C. C.↗
NASA NTRS1979

Magnetometer bias determination and attitude determination for near-earth spacecraft

A simple linear-regression algorithm is used to determine simultaneously magnetometer biases, misalignments, and scale factor corrections, as well as the dependence of the measured magnetic field on magnetic control systems. This algorithm has been applied to data from the Seasat-1 and the Atmosphere Explorer Mission-1/Heat Capacity Mapping Mission (AEM-1/HCMM) spacecraft. Results show that complete inflight calibration as described here can improve significantly the accuracy of attitude solutions obtained from magnetometer measurements. This report discusses the difficulties involved in obtaining attitude information from three-axis magnetometers, briefly derives the calibration algorithm, and presents numerical results for the Seasat-1 and AEM-1/HCMM spacecraft.

Lerner, G. M.↗
NASA NTRS1986

Finite-amplitude behavior of a single baroclinic wave with multiple vertical modes - Effects of thermal damping

A quasi-geostrophic, beta-plane model possessing high vertical resolution is used to investigate the effects of thermal damping on the finite amplitude behavior of a baroclinic wave; both the wave field and zonal-mean flow of the model are, however, truncated to a single horizontal mode, so that the wave-mean flow interaction is purely baroclinic. For sufficiently strong thermal damping steady wave flows are obtained, while for weaker damping, nonsteady vacillating behavior is found. In the steady wave flows, the mean flow is linearly neutral. An especially interesting vacillation, characterized by two widely separated time scales, occurs in the model nonsteady regime and appears to be similar in some respects to behavior found in the two-layer model with only lower layer dissipation.

Barnes, J. R.↗
NASA NTRS1987

Optical and near-infrared observations of BL Lacertae objects and active quasars

UBVRI and JHK photometric and polarimetric observations, obtained using the 1.5-m UCSD/UM telescope at Mount Lemmon, AZ during 1982-1984, are reported for a sample of 10 BL Lac objects, eight optically violent variable quasars, and the low-polarization quasar 3C 273. The data are presented in extensive tables and graphs and analyzed in detail. Most of the objects are found to have undergone large polarization variations on time scales ranging from 1 d to several months; five objects had fractional linear polarization P greater than 30 percent at least once during the period of observation, but four never had P greater than 10 percent. Of four objects which exhibited a preferred polarization position angle (theta), three had theta within 20 deg of the jet position angle determined by VLBI.

Smith, Paul S.↗
NASA NTRS1988

Linear statistical analysis of maneuver optimization techniques

It is shown how a method for maneuver design during the Jovian satellite tour phase of the Galileo mission requires a full-scale redesign of the tour at each maneuver. Software was developed to provide insight into the statistical properties of this process; it is based on the use of linear perturbations to provide trajectory propagation and a least squares representation of the optimization. The result is a Monte Carlo program, making it possible to evaluate the proposed strategy.

Maize, Earl H.↗
NASA NTRS1989

Formation of large-scale structure from cosmic strings and massive neutrinos

Numerical simulations of large-scale structure formation from cosmic strings and massive neutrinos are described. The linear power spectrum in this model resembles the cold-dark-matter power spectrum. Galaxy formation begins early, and the final distribution consists of isolated density peaks embedded in a smooth background, leading to a natural bias in the distribution of luminous matter. The distribution of clustered matter has a filamentary appearance with large voids.

Scherrer, Robert J.↗
NASA NTRS1992

Application of a linear spectral model to the study of Amazonian squall lines during GTE/ABLE 2B

A linear nonhydrostatic spectral model is run with the basic state, or large scale, vertical profiles of temperature and wind observed prior to convective development along the northern coast of South America during the GTE/ABLE 2B. The model produces unstable modes with mesoscale wavelength and propagation speed comparable to observed Amazonian squall lines. Several tests with different vertical profiles of low-level winds lead to the conclusion that a shallow and/or weak low-level jet either does not produce a scale selection or, if it does, the selected mode is stationary, indicating the absence of a propagating disturbance. A 700-mbar jet of 13 m/s, with a 600-mbar wind speed greater or equal to 10 m/s, is enough to produce unstable modes with propagating features resembling those of observed Amazonian squall lines. However, a deep layer of moderate winds (about 10 m/s) may produce similar results even in the absence of a low-level wind maximum. The implications in terms of short-term weather forecasting are discussed.

Silva Dias, Maria A. F.↗
NASA NTRS1993

Complex QSO absorbers: High-redshift clusters of galaxies?

Using the PSPC instrument on the ROSAT satellite, we have obtained deep exposures of the fields centered on the QSO's 1556+335, 1037-271, and 0854+191 in an effort to search for extended X-ray emission corresponding to complex QSO absorption-line systems (QALS's) that could be indicative of clusters of galaxies at high redshift. The QSO 1556+335 is known to have a pair of complicated C IV absorption systems at z equals 1.610 (Delta v = 988 km/s) and z equals 1.650 (Delta v = 1677 km/s) near the z equals 1.641 QSO redshift. It has been suggested that the absorption may be due to two rich clusters, one containing the QSO itself. The QSO 0854+191 (z(sub em) = 1.89) has 6 strong C IV absorption systems in 2 close groups at z equals 1.2954, 1.2973,1.3019 and z equals 1.3522, 1.3543, 1.3558. Assuming q(sub O) equals 0.5 and H(sub O) equals 50 km/s Mpc(exp -l), the redshift range of this absorption-line cluster corresponds to a radial distance of 44 Mpc. Interestingly, there is a nearby (approximately 30') QSO (0856+189) with a projected separation of 16 Mpc whose redshift (z = 1.29) is similar to that of the absorbing material toward 0854+191. In the case of 1037-271 (Z(sub em) = 2.18), common QALSs have been observed at z equals l.90, 1.96, 2.02, 2.08, and 2.14 (a radial range of 66 Mpc) in its spectrum and that of its neighbor Tol 1038-272 (Z(sub em) = 2.32) whose 18' separation corresponds to a linear distance of 9 Mpc at z approximately equals 2. The length scales implied by the absorbers toward 0854+191 and 1037-271 are interesting in that they suggest structures more akin to superclusters than clusters.

Meyer, David M.↗
NASA NTRS1995

Impulse-response functions and anthropogenic CO2

Non-linearities in the carbon cycle make the response to atmospheric CO2 perturbations dependent on emission history. We show that even when linear representations of the carbon cycle are used, the calculation of time scales characterizing the removal of excess CO2 depends on past emissions.

Tubiello, Francesco N.↗