SEARCH · Search NASA

Results for “Model Theory”

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 379 records · Page 21

All sources NASA NTRS DOE OSTI

NASA NTRS1974

International Cosmic Ray Conference, 13th, University of Denver, Denver, Colo., August 17-30, 1973, Proceedings. Volumes 1 & 2

Topics discussed include diffuse gamma rays, gamma ray sources (in particular, the Crab Nebula and Crab Pulsar), X-ray sources, isotopic and nuclear composition, spectra of nuclei, searches for antinuclei, studies of VH and VVH nuclei, measurements of electrons and positrons, the spectra of high-energy electrons, cosmic gamma rays, cosmic ray sources, interplanetary radial gradients, the theory and observation of electron modulation, short-period cosmic ray intensity variations, atmospheric and coupling effects on neutron monitors and muon telescopes, secondary particles and photons in the atmosphere, harmonics of diurnal variations, geomagnetic effects and cutoffs, planetary and interplanetary effects, solar particle access observations, long-term cosmic ray intensity modulation by solar activity and interplanetary effects, Forbush decreases, modulation and anisotropy of low-energy particles, the theory and models of solar particle propagation, solar flare particle composition, and relativistic solar particles. Individual items are announced in this issue.

Source record↗

NASA NTRS1974

International Cosmic Ray Conference, 13th, University of Denver, Denver, Colo., August 17-30, 1973, Proceedings. Volumes 3 & 4

Volumes 3 and 4 contain papers dealing with measurements of muons and neutrinos, ultrahigh-energy interactions, extensive air showers, and details of experimental techniques and instrumentation. Attention is given to the zenith angle and underground depth dependence of cosmic ray muons, muon charge ratios and energy spectra, extraterrestrial sources of neutrinos, strong interaction data from new accelerators, searches for quarks and other new particles, hadron fluxes and propagation in the atmosphere, high-energy gamma-ray measurements, and new models and theories for high-energy strong interactions. Extensive air showers are examined in papers dealing with associated Cerenkov light, radio emission, structure, the hadron content, and primaries. The design, operation, and performance of various detectors are explained. Individual items are announced in this issue.

Source record↗

NASA NTRS1975

Experimental and analytical investigation of 0 G condensation in a mechanical refrigeration system application

Basic equations of momentum and energy are presented and discussed with respect to heat transfer and pressure drop for forced flow condensation in horizontal tubes under 1-g and 0-g conditions. Some experimental results are presented for condensing refrigerant-12 in a system of three parallel-connected quartz tubes (3-mm inside diameter, G = 1.037 to 3.456 x 105 lbm/hr-sq. ft). From high speed photographs, measurements were obtained of film thickness, phase velocities, disturbance wavelengths, and flow regimes and their transitions. Based upon these measurements various dimensionless force ratios (flow and instability parameters) were calculated. Under 0-g conditions a uniformly thick redistribution of liquid condensate about the tube walls was found to result in a lowered heat transfer coefficient as compared with 1-g conditions, based upon fundamental heat transfer theory. A model is proposed that takes into account the difference in heat transfer due to condensate distribution under 1-g and 0-g conditions.

Keshock, E. G.↗

NASA NTRS1974

Cross correlation between cosmic-ray fluctuations and interplanetary magnetic-field fluctuations

Study of the cross-correlation between cosmic-ray intensity fluctuations and the interplanetary magnetic field, using the low-frequency limit of the theory of the interplanetary scintillations of cosmic rays. Cross-spectral analysis of the flux of the Alert neutron monitor and simultaneous values of the interplanetary magnetic field components are presented which support the theory. A model of cosmic-ray fluctuations is described, with effects of gradients and interplanetary sector structure dominating for very low frequencies (less than or about equal to .000005 Hz) and magnetic-field induced interplanetary scintillations of cosmic rays dominating for higher frequencies.

Jokipii, J. R.↗

NASA NTRS1976

Navigation between the planets

Recent advances in spacecraft tracking, chronometry, ephemerides, and orbit and trajectory determinations are reviewed. Improvements in timekeeping are reviewed, as well as precision distance and range measurements; orbit determinations, trajectory-correction maneuvers, flight path optimization, and information provided by rotation of the tracking station with the earth's surface. Doppler and tropospheric wave propagation effects are dealt with. Nongravitational perturbations (solar radiation pressure, release of gases from the spacecraft, stochastic unmodeled accelerations and sequential estimation to cope with them), the effect of the target planet's gravitational field upon close approach, and navigation problems in the outer reaches of the solar system (TV data telemetered back for inertial navigation) are covered. By-products of the research include: refined data on the mass of planets, on planetary mass distributions, planet configurations, on physical properties of the atmospheres and ionospheres of planets, and opportunities for refined tests of gravitation and relativity theories and models.

Melbourne, W. G.↗

NASA NTRS1975

Current theories of man-machine systems

Theories and models conventionally employed to analyze man machine systems such as remotely manned vehicles and processes are reviewed. Basic ideas of supervisory or heirarchical manning, and needs for modeling are discussed.

Sheridan, T. B.↗

NASA NTRS1977

Nonlinear viscoelasticity and relaxation phenomena of polymer solids

In the light of a three-chain model of statistical network theories of rubberlike elastic models, it is assumed that the free energy function of incompressible viscoelastic polymer solids is a separable, symmetric function of the principle stretch ratios and the hidden thermodynamic coordinates along the same directions. This assumption leads to a characterization of those viscoelastic polymer solids which exhibit the property of factorizability between the time and strain functions.

Peng, S. T. J.↗

NASA NTRS1976

On the use of two hardening rules of plasticity in incremental and pseudo force analysis

The tangent stiffness and pseudo force forms of the equations of motion are first derived within the context of a total Lagrangian formulation. After a brief discussion of available incremental theory plasticity models, the small strain formulations and computational procedures of the mechanical sublayer model and combined kinematic-isotropic hardening as used in the general purpose structural analysis program AGGIE I are presented. Several sample problems are then presented along with recommended guidelines for use of the two plasticity models.

Hunsaker, B., Jr.↗

NASA NTRS1978

Computational Fluid Dynamics (CFD): Future role and requirements as viewed by an applied aerodynamicist

The problem of designing the wing-fuselage configuration of an advanced transonic commercial airliner and the optimization of a supercruiser fighter are sketched, pointing out the essential fluid mechanical phenomena that play an important role. Such problems suggest that for a numerical method to be useful, it must be able to treat highly three dimensional turbulent separations, flows with jet engine exhausts, and complex vehicle configurations. Weaknesses of the two principal tools of the aerodynamicist, the wind tunnel and the computer, suggest a complementing combined use of these tools, which is illustrated by the case of the transonic wing-fuselage design. The anticipated difficulties in developing an adequate turbulent transport model suggest that such an approach may have to suffice for an extended period. On a longer term, experimentation of turbulent transport in meaningful cases must be intensified to provide a data base for both modeling and theory validation purposes.

Yoshihara, H.↗

NASA NTRS1978

Perseveration effects in detection tasks with correlated decision intervals

An investigation of the behavior of the human decisionmaker is described for a task related to the problem of a pilot using a traffic situation display to avoid collisions. This sequential signal detection task is characterized by highly correlated signals with time varying strength. Experimental results are presented and the behavior of the observers is analyzed using the theory of Markov processes and classical signal detection theory. Mathematical models are developed which describe the main result of the experiment: that correlation in sequential signals induced perseveration in the observer response and a strong tendency to repeat their previous decision, even when they were wrong.

Gai, E. G.↗

NASA NTRS1979

Shock structure in transonic compressor rotors

The inadequacy of axisymmetric theory in modeling the structure of the shock system in a transonic compressor rotor is shown with a simple model. A more accurate model for the flow near the sonic radius is proposed, which is supported by some flow visualization data and three-dimensional computations.

Epstein, A. H.↗

NASA NTRS1979

Fatigue crack growth in fiber reinforced plastics

Fatigue crack growth in fiber composites occurs by such complex modes as to frustrate efforts at developing comprehensive theories and models. Under certain loading conditions and with certain types of reinforcement, simpler modes of fatigue crack growth are observed. These modes are more amenable to modeling efforts, and the fatigue crack growth rate can be predicted in some cases. Thus, a formula for prediction of ligamented mode fatigue crack growth rate is available.

Mandell, J. F.↗

NASA NTRS1979

Wind-tunnel investigation of the validity of a sonic-boom-minimization concept

The Langley unitary plan unitary plan wind tunnel was used to determine the validity of a sonic-boom-minimization theory. Five models - two reference and three low-boom constrained - were tested at design Mach numbers of 1.5 and 2.7. Results show that the pressure signatures generated by the low-boom models had significantly lower overpressure levels than those produced by the reference models and that small changes in the Mach number and/or the lift caused relatively small changes in the signature shape and overpressure level. Boundary-layer effects were found in the signature shape and overpressure level. Boundary-layer effects were found to be sizable on the low-boom models, and when viscous corrections were included in the analysis, improved agreement between the predicted and the measured signatures was noted. Since this agreement was better at Mach 1.5 than at Mach 2.7, it was concluded that the minimization method was definitely valid at Mach 1.5 and was probably valid at Mach 2.7, with further work needed to resolve the uncertainty.

Mack, R. J.↗

NASA NTRS1982

Nonlinear viscoelastic characterization of polycarbonate

Uniaxial tensile creep and recovery data from polycarbonate at six temperatures and six stress levels are analyzed for nonlinear viscoelastic constitutive modeling. A theory to account for combined effects of two or more accelerating factors is presented.

Caplan, E. S.↗

NASA NTRS1983

The need for an intermediate mass scale in GUTs

The minimal SU(5) grand unified field theory (GUT) model fails to resolve the strong charge parity (CP) problem, suffers from the cosmological monopole problem, sheds no light on the nature of the 'dark' mass in the universe, and predicts an unacceptably low value for the baryon asymmetry. All these problems can be overcome in suitable grand unified axion models with an intermediate mass scale of about 10 to the 11th power to 10 to the 12th power GeV. An example based on the gauge group SO(10) is presented. Among other things, it predicts that the axions comprise the 'dark' mass in the universe, and that there exists a galactic monopole flux of 10 to the -8th power to 10 to the -7th power/sq cm/yr. Other topics that are briefly discussed include proton decay, family symmetry, neutrino masses and the gauge hierarchy problem.

Shafi, Q.↗

NASA NTRS1983

Rotor-vortex interaction noise

A theoretical and experimental study is carried out to develop a first-principles analysis for predicting noise generated by helicopter main-rotor shed vortices interacting with the tail rotor. The generalized prediction procedure calls for a knowledge of the incident vortex velocity field, the rotor geometry, and the rotor operating conditions. The analysis encompasses compressibility effects and chordwise and spanwise noncompactness and treats oblique intersections with the blade planform. In assessing the theory, a model rotor experiment which isolates the blade-vortex interaction noise from other rotor noise mechanisms is conducted. An isolated tip vortex, generated by an upstream semispan airfoil, is convected into the model rotor, and acoustic spectra, pressure signatures, and directivity are measured. Ingestion of the vortex by the rotor is experimentally observed to generate harmonic noise and impulsive waveforms.

Schlinker, R. H.↗

NASA NTRS1984

Intermediate energy proton stopping power for hydrogen molecules and monoatomic helium gas

Stopping power in the intermediate energy region (100 keV to 1 MeV) was investigated, based on the work of Lindhard and Winther, and on the local plasma model. The theory is applied to calculate stopping power of hydrogen molecules and helium gas for protons of energy ranging from 100 keV to 2.5 MeV. Agreement with the experimental data is found to be within 10 percent.

Xu, Y. J.↗

NASA NTRS1984

Intermediate energy proton stopping power for hydrogen molecules and monoatomic helium gas

Xu, Y. J.↗