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Results for “variability analysis”

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 451 records · Page 25

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NASA NTRS1973

Traffic study of a computer system.

A study which may guide the operations of existing computer installations, as well as the design of future networks, is described. Performance data and evaluations are considered with reference to interarrival time, users' habits, waiting time for execution, time spent in a partition, figures of merit, and states of the system. The analysis of the variables proceeds from examination of typical data with appropriate statistical tests to conclusions about the possible state of nature.

Cramer, R. L.↗

NASA NTRS1973

Controllability of discrete bilinear systems with bounded control.

Controllability of time-invariant discrete-time bilinear systems is discussed. Bilinear systems are classified into two categories: homogeneous and inhomogeneous. Sufficient conditions which ensure the global controllability of discrete-time bilinear systems are obtained by localized analysis in control variables.

Tarn, T. J.↗

NASA NTRS1973

Controllability of discrete bilinear systems with bounded control.

The subject of this paper is the controllability of time-invariant discrete-time bilinear systems. Bilinear systems are classified into two categories; homogeneous and inhomogeneous. Sufficient conditions which ensure the global controllability of discrete-time bilinear systems are obtained by localized analysis in control variables.

Tarn, T. J.↗

NASA NTRS1974

Effects of porosity on weld-joint tensile strength of aluminum alloys

Tensile properties in defect-free weldments of aluminum alloys 2014-T6 and 2219-T87 (sheet and plate) are shown to be related to the level or concentration of induced simulated porosity. The scatter diagram shows that the ultimate tensile strength of the weldments displays the most pronounced linear relationship with the level of porosity. The relationships between yield strength or elongation and porosity are either trivial or inconsequential in the lower and intermediate levels of porosity content. In highly concentrated levels of porosity, both yield strength and elongation values decrease markedly. Correlation coefficients were obtained by simple straight line regression analysis between the variables of ultimate tensile strength and pore level. The coefficients were greater, indicating a better correlation, using a pore area accumulation concept or pore volume accumulation than the accumulation of the pore diameters. These relationships provide a useful tool for assessing the existing aerospace radiographic acceptance standards with respect to permissible porosity. In addition, these relationships, in combination with known design load requirements, will serve as an engineering guideline in determining when a weld repair is necessary based on accumulative pore level as detected by radiographic techniques.

Lovoy, C. V.↗

NASA NTRS1978

Aeromechanical stability of helicopters with a bearingless main rotor. Part 1: Equations of motion

Equations of motion for a coupled rotor-body system were derived for the purpose of studying air and ground resonance characteristics of helicopters that have bearingless main rotors. For the fuselage, only four rigid body degrees of freedom are considered; longitudinal and lateral translations, pitch, and roll. The rotor is assumed to consist of three or more rigid blades. Each blade is joined to the hub by means of a flexible beam segment (flexbeam or strap). Pitch change is accomplished by twisting the flexbeam with the pitch-control system, the characteristics of which are variable. Thus, the analysis is capable of implicitly treating aeroelastic couplings generated by the flexbeam elastic deflections, the pitch-control system, and the angular offsets of the blade and flexbeam. The linearized equations are written in the nonrotating system retaining only the cyclic rotor modes; thus, they comprise a system of homogeneous ordinary differential equations with constant coefficients. All contributions to the linearized perturbation equations from inertia, gravity, quasi-steady aerodynamics, and the flexbeam equilibrium deflections are retained exactly.

Hodges, D. H.↗

NASA NTRS1978

Shear strength of fillet welds in aluminum alloy 2219

Fillet size is discussed in terms of theoretical or design dimensions versus as-welded dimensions, drawing attention to the inherent conservatism in the design load sustaining capabilities of fillet welds. Emphasis is placed on components for the solid rocket motor, external tank, and other aerospace applications. Problems associated with inspection of fillet welds are addresses and a comparison is drawn between defect counts obtained by radiographic inspection and by visual examination of the fracture plane. Fillet weld quality is related linearly to ultimate shear strength. Correlation coefficients are obtained by simple straight line regression analysis between the variables of ultimate shear strength and accumulative discontinuity summation. Shear strength allowables are found to be equivalent to 57 percent of butt weld A allowables (F sub tu.)

Lovoy, C. V.↗

NASA NTRS1981

Investigation of remote sensing techniques of measuring soil moisture

Major activities described include development and evaluation of theoretical models that describe both active and passive microwave sensing of soil moisture, the evaluation of these models for their applicability, the execution of a controlled field experiment during which passive microwave measurements were acquired to validate these models, and evaluation of previously acquired aircraft microwave measurements. The development of a root zone soil water and soil temperature profile model and the calibration and evaluation of gamma ray attenuation probes for measuring soil moisture profiles are considered. The analysis of spatial variability of soil information as related to remote sensing is discussed as well as the implementation of an instrumented field site for acquisition of soil moisture and meteorologic information for use in validating the soil water profile and soil temperature profile models.

Newton, R. W.↗

NASA NTRS1983

The measurement of solar spectral irradiances at wavelengths between 40 and 4000 A

Two 1/8-meter Ebert-Fastie spectrometers were refurbished and upgraded in order to measure the solar spectral irradiances between 1160 A and 3100 A. An evacuated 1/4-meter normal-incidence spectrometer was also fabricated for spectral irradiance measurements over the wavelength range from 1250 A to 250 A. Procedures were developed for the calibration of all three instruments utilizing standards at the National Bureau of Standards. The two 1/8-meter spectrometers were flown to measure the solar spectral irradiances near solar maximum on two different dates. Data from these flights were analyzed. The performance of the spectrometers, and the results of an analysis of the variabilities of the solar spectral irradiances over the solar cycles 20 and 21 are discussed.

Timothy, J. G.↗

NASA NTRS1984

Toward a balanced assessment of collinearity diagnostics

The present investigation is concerned with a review of the foundations upon which regression methodology is based, taking into account a study of regression diagnostics conducted by Belsey et al. (1980). It is found that one of the most difficult and controversial problems facing data analysts is related to redundant predictor variables in a regression analysis. Collinearity diagnostics are only meaningful when interpreted in terms of 'basic variables' which are 'structurally interpretable'. Conflicting perspectives are discussed, giving attention to the role of centering when diagnosing collinearity. The definition of collinearity and collinearity measures are considered along with questions regarding 'structural interpretability' as a universally accepted principle in model formulation, and the importance of the detection of collinearity with the constant term.

Gunst, R. F.↗

NASA NTRS1985

Intermediate and narrow band photometry of Epsilon Aurigae

Intermediate band blue (4530A), far red (7790A) and H-alpha intermediate and narrow band photoelectric observations of the peculiar, 27 year eclipsing binary, Epsilon Aurigae were made from December 1981 through the present (December 1984). BD +42 1170 served as the primary comparison star because of its angular proximity to the variable star. The analysis of this data along with other available photometry was undertaken to study the characteristics of the low amplitude, semi-regular light variations that appear inside and outside of eclipse. It appears that these short term light variations arise from nonradial pulsations of the luminous f supergiant in the system. Furthermore, the semi-regular light variations found for Epsilon Aurigae are similar to those found for other luminous A-F supergiants. Also, the preliminary results from the analyses of the light variations produced by the eclipse of the F-supergiant by the mysterious cooler component is discussed.

Donovan, R. A.↗

NASA NTRS1985

Extraction of information from major element chemical analyses of lunar basalts

Major element chemical analyses often form the framework within which similarities and differences of analyzed specimens are noted and used to propose or devise models. When percentages are formed the ratios of pairs of components are preserved whereas many familiar statistical and geometrical descriptors are likely to exhibit major changes. This ratio preserving aspect forms the basis for a proposed framework. An analysis of compositional variability within the data set of 42 major element analyses of lunar reference samples was selected to investigate this proposal.

Butler, J. C.↗

NASA NTRS1985

Samics on the IBM PC

An updated version of the Solar Array Manufacturing Industry Costing Standards (SAMICS) was presented. This version will run on the IBM PC-XT or compatibles, and embodies user friendly input screens and numerous help options. Use of this microcomputer version will still produce the old main frame direct cost driven analysis, although at some cost in turnaround time. A typical simulation will take about 4 hours. The program allows for unattended report printout. Also available is the IBM PC (or compatibles) version of the Improved Price Estimation Guidelines (IPEG). This program allows rapid analysis of process variables using SAMICS-generated coefficients.

Chamberlain, R.↗

NASA NTRS1986

Comparison of viscous shock layer and boundary layer reentry heating techniques for Orbiter nose cap

A comparison of two viscous shock layer methods and one boundary layer method for predicting the aerodynamic heating around the Orbiter nose cap during STS-5 entry is presented. The object of the study was to compare these methods with one another and with the measured Orbiter flight data for this trajectory. The nonequilibrium, chemically reacting viscous flow fields obtained by these methods are evaluated, and effects on heating rate of wall catalycity variation with time are presented. The effects of shock slip and combined wall/shock slip are considered at high altitudes (above 300,000 ft). Using the variable wall catalycity analysis, it is shown that heating rates can be predicted within a 5.7 percent flight data band for altitudes between 175,000 ft and 265,000 ft in this trajectory.

Ting, P. C.↗

NASA NTRS1986

Phase 3 study of selected tether applications in space. Volume 1: Executive summary

A tethered launch assist from the Shuttle for payloads with up to 10,000 kg mass for the mission model and the tethering of a 15,000 kg science platform for the space station were addressed. Also encompassed was the design and cost analysis for a variable g device that could be placed on the tether and allow ultralow g or other types of experiments to be conducted. Numerous tether applications were examined and their theoretical feasibility and technology requirements were assessed.

Source record↗

NASA NTRS1988

Correlations between optical/near-infrared and UV extinction parameters and the prediction of UV extinction from ground-based photometry

An analysis of the variability of absolute UV extinction, A lambda derived through the ratio total-to-selective extinction, R Av/E(B-V), for 31 lines of sight for which UV extinction parameters were derived, is presented. For these data, which sample a wide range of environments and which are characterized by R = 2.5 to 6.0, differences in the shapes of UV extinction curves are largely due to variations in optical/near-UV extinction through changes in R. From this, it is found that UV extinction curves can be reproduced with reasonable accuracy by simply knowing R. Detection of an A2175/E(B-V) = 10 + or - 1 mag implies that the total extinction at 2175 A can be estimated from E(B-V) alone.

Cardelli, Jason A.↗

NASA NTRS1989

Domain decomposition methods for systems of conservation laws: Spectral collocation approximations

Hyperbolic systems of conversation laws are considered which are discretized in space by spectral collocation methods and advanced in time by finite difference schemes. At any time-level a domain deposition method based on an iteration by subdomain procedure was introduced yielding at each step a sequence of independent subproblems (one for each subdomain) that can be solved simultaneously. The method is set for a general nonlinear problem in several space variables. The convergence analysis, however, is carried out only for a linear one-dimensional system with continuous solutions. A precise form of the error reduction factor at each iteration is derived. Although the method is applied here to the case of spectral collocation approximation only, the idea is fairly general and can be used in a different context as well. For instance, its application to space discretization by finite differences is straight forward.

Quarteroni, Alfio↗

NASA NTRS1989

An interpretation of the line profile variations in the IUE spectrum of the Wolf-Rayet binary Gamma(2) Velorum

An analysis of the variable profiles of the high-temperature resonance lines of Si IV in the IUE spectrum of gamma(2) Vel has made it possible to describe these profiles as a superposition of two different profiles, namely, a P Cygni profile that remains practically stationary throughout the orbital cycle and an absorption profile that moves back and forth with phase. To these two profiles is added a very sharp, strong absorption that ought to arise in the layers of the extended gaseous envelope that merge with the interstellar medium. The absorption that moves back and forth during the system's orbital revolution has been interpreted as suggesting a stream going away from the system at an angle of some 110 deg from the direction of the radius vector joining the Wolf-Rayet star with its companion. Such a stream seems to project upon a dense concentration of matter that is located somewhere in the volume between the two stars and moves away at some -700 km/s, and should result from the collision of the winds from the two components. The high-temperature resonance lines of N V and C IV very likely behave similarly to Si IV.

Brandi, Estela↗

NASA NTRS1990

Radiative properties of Cirrus clouds: FIRE IFO case October 28, 1986

A description of the radiative properties of two cirrus clouds sampled on 10/28/88 in the FIRE cirrus IFO is presented. The clouds are characterized in terms of the broadband infrared effective emittance, cloud fractional absorptance, shortwave heating rate, cloud albedo and vertical velocity. The broadband fluxes used in these calculations were obtained from measurements made by pyranometers and pyrgeometers. The shortwave irradiances were corrected to a horizontal plane and normalized to the same time by taking into account Sabreliner flight information (i.e., pitch, roll, heading and angle of attack), as well as sun-earth geometry considerations. Since only one aircraft was used, broadband fluxes at different levels in the cloud were not measured simultaneously. As a result, sampling errors may occur due to the nonsteady state of the cloud field or due to the possibility that the flight legs were not flown directly above or below each other. To minimize these errors and to simplify the analysis, the necessary variables were averaged and the averages used in the calculations. The downwelling shortwave and longwave irradiances were used as selection criteria to remove cloud free data encountered along the data sampling leg.

Hein, Paul F.↗