Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “coupling constant”

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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Coupled Aerodynamic and Structural Sensitivity Analysis of a High-Speed Civil Transport

An objective of the High Performance Computing and Communication Program at the NASA Langley Research Center is to demonstrate multidisciplinary shape and sizing optimization of a complete aerospace vehicle configuration by using high-fidelity, finite-element structural analysis and computational fluid dynamics aerodynamic analysis. In a previous study, a multi-disciplinary analysis system for a high-speed civil transport was formulated to integrate a set of existing discipline analysis codes, some of them computationally intensive, This paper is an extension of the previous study, in which the sensitivity analysis for the coupled aerodynamic and structural analysis problem is formulated and implemented. Uncoupled stress sensitivities computed with a constant load vector in a commercial finite element analysis code are compared to coupled aeroelastic sensitivities computed by finite differences. The computational expense of these sensitivity calculation methods is discussed.

Mason, B. H.↗
NASA NTRS1981

Effect of gravity on coupled convective and interfacial instabilities during directional solidification

Instabilities occurring during the directional constant-rate solidification of a dilute solution of tin in lead are investigated as a function of gravity with particular emphasis on small constant gravitational accelerations. Two types of instabilities have been identified: (1) convective type that corresponds to long wavelengths, and (2) morphological type that corresponds to short wavelengths. These instabilities are coupled but while the convective instabilities depend strongly on gravity, the morphological instabilities are practically independent of gravity. For low velocities, the convective instabilities occur at much lower solute concentrations than the morphological instabilities, whereas at high velocities the reverse is true.

Coriell, S. R.↗
NASA NTRS1980

Integrated optic waveguide devices

Integrated optic waveguide circuits with a phase bias and modulator on the same chip were designed, fabricated, and tested for use in a fiber-optic rotation sensor (gyro) under development. Single mode fiber-optic pigtails were permanently coupled to the four ports of the chip. The switch format was based on coherent coupling between waveguides formed in Z-cut LiNbO3. The control of the coupling was achieved by electro-optically varying the phase propagation constants of each guide. Fiber-to-chip interfacing required the development of appropriate fixturing and manipulation techniques to achieve the close tolerance needed for high coupling efficiency between a fiber with an approximately 5 micron m core and a channel guide with a roughly 2 micron m by 5 micron m cross section. Switch and chip performance at 0.85 micron m is discussed as well as potential improvements related to insertion loss reduction, switching voltages, and suppression of Li2O out-diffusion.

Ramer, O. G.↗
NASA NTRS1994

Constant current loop impedance measuring system that is immune to the effects of parasitic impedances

A constant current loop measuring system is provided for measuring a characteristic of an environment. The system comprises a first impedance positionable in the environment, a second impedance coupled in series with said first impedance and a parasitic impedance electrically coupled to the first and second impedances. A current generating device, electrically coupled in series with the first and second impedances, provides a constant current through the first and second impedances to produce first and second voltages across the first and second impedances, respectively, and a parasitic voltage across the parasitic impedance. A high impedance voltage measuring device measures a voltage difference between the first and second voltages independent of the parasitic voltage to produce a characteristic voltage representative of the characteristic of the environment.

Anderson, Karl F.↗
NASA NTRS1974

Evaluation of atomic constants for optical radiation, volume 1

Atomic constants for optical radiation are discussed which include transition probabilities, line strengths, and oscillator strengths for both dipole and quadrupole transitions, as well as the associated matrix elements needed for line broadening calculations. Atomic constants were computed for a wide selection of elements and lines. An existing computer program was used, with modifications to include, in an approximate manner, the effect of equivalent electrons, and to enable reordering and restructuring of the output for publication. This program is suitable for fast, low cost computation of the optical constants, using the Coulomb approximation formalism for LS coupling.

Kylstra, C. D.↗
NASA NTRS1980

A line parameter list for the nu2 and nu4 bands of /C-12/H4 and /C-13/H4, extended to J-prime = 25 and its application to planetary atmospheres

Line parameters (transition frequencies, line strengths, line widths, ground state energies and quantum identifications) for the nu2 and nu4 bands of (C-12)H4 and (C-13)H4 have been calculated for J-prime equal to or less than 25 using the simultaneous coupled fitting procedure of Gray and Robiette. Molecular constants for the nu2 band of (C-13)H4 were estimated from isotopic shifts from (C-12)H4 values. Agreement with laboratory spectra, where available, is always well within 1 kayser over the entire spectral range covered by the list. The most serious problem in comparison with laboratory data is the omission of lines belonging to 'hot' bands in this spectral region. This list is valuable in remote sensing problems for sorting out lines of trace species from weak methane lines and for determining the atmospheric opacity in relatively transparent spectral regions. Applications of the parameter list are demonstrated for remote sounding of the Jovian atmosphere.

Orton, G. S.↗
NASA NTRS1981

Parameterization of linear wave chemical transport in planetary atmospheres by eddy diffusion

Two-dimensional transport by linear waves is parameterized by wave velocity and temperature correlations and nonconservative properties of the atmosphere in a residual Eulerian framework. Explicit expressions derived for the eddy tracer flux vector are written in eddy diffusion tensor form, but it is demonstrated that strong coupling of chemistry and temperature through the rate constants, as is the case for ozone, requires additional terms proportional to the mixing ratio and not to its gradient. A variety of limiting cases are discussed. In the residual Eulerian framework the K(yz), K(zy) components are nonzero for a nonconservative atmosphere and/or a reactive tracer. Tracers have common transport coefficients in the limit where their chemistry is negligible in comparison to transience. It is shown that the usual one-dimensional vertical eddy diffusion continuity equation is rigorously valid only when the temperature dependence of the rate constants is negligible and the tracer has strong vertical stratification relative to its horizontal variability.

Strobel, D. F.↗
NASA NTRS1987

The influence of gravitoinertial force level on oculomotor and perceptual responses to Coriolis, cross-coupling stimulation

The goal of the present experiment was to determine whether gravitoinertial force magnitude influences oculomotor and perceptual responses to Coriolis cross-coupling stimulation. Blindfolded subjects who were rotating at constant velocity were asked to make standardized head movements during the free-fall and high-force phases of parabolic flight, and the characteristics of their horizontal nystagmus and the magnitude of their experienced self-motion were measured. Both responses were less intense in the free-fall periods than in the high-force periods. These findings suggest that the response to semicircular canal stimulation depends on the background level of gravitoinertial force.

Dizio, Paul↗
NASA NTRS1995

A Correlated Ab Initio Study of Linear Carbon-Chain Radicals C(sub n)H (n=2-7)

Linear carbon-chain radicals C(sub n) H for n = 2-7 have been studied with correlation consistent valence and core-valence basis sets and the coupled cluster method RCCSD(T). Equilibrium structures, rotational constants, and dipole moments are reported and compared with available experimental data. The ground state of the even-n series changes from 2Sigma(+) to 2Pi as the chain is extended. For C4H, the 2Sigma(+) state was found to lie only 72 cm(exp -1) below the 2Pi state in the estimated complete basis set limit for valence correlation. The C2H(-) and C3H(-) anions have also been characterized.

Woon, David E.↗
NASA NTRS2001

On Interpreting the Photoelectron Spectra of MgO

The (sup 2)Sigma(+) and (sup 2)Pi states of MgO(-) and the (sup 1)Sigma(+), (sup 1)Pi, and (sup 3)Pi states of MgO are studied using the averaged coupled-pair functional (ACPF) approach. The computed spectroscopic constants are in good agreement with the available experimental data. The computed Franck-Condon factors and photodetachment overlaps are compared with experiment.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1995

A correlated ab initio study of linear carbon-chain radicals CnH (n = 2-7)

Linear carbon-chain radicals CnH for n = 2-7 have been studied with correlation consistent valence and core-valence basis sets and the coupled cluster method RCCSD(T). Equilibrium structures, rotational constants, and dipole moments are reported and compared with available experimental data. The ground state of the even-n series changes from 2 sigma+ to 2 pi as the chain is extended. For C4H, the 2 sigma+ state was found to lie only 72 cm-1 below the 2 pi state in the estimated complete basis set limit for valence correlation. The C2H- and C3H- anions have also been characterized.

NASA Discipline Exobiology↗
NASA NTRS1988

On-orbit parametric identification methodology

On-orbit system identification (ID) of large space systems is essential for various reasons. For example, the complex composite structure of such systems cannot be ground-tested; their structural dynamic characteristics must be known accurately in order to accomplish active control. Furthermore, such capability can be used to characterize/identify various disturbances. The identification process is consisted of four principal elements: (1) modeling, (2) the estimation algorithm, (3) input system, and (4) measurement system. These elements are highly correlated and all togerher determine the success of the identification problem. Accurate modeling of large space systems is the most important element of the identification process. Large flexible structures are non-linear and infinite dimensional systems with highly coupled parameters and low frequency packed modes. In addition, these systems are subject to stochastic and time-varying disturbances, they have structural parameters which can vary due to on-orbit assembly deployment, and operations. These systems are generally; however, represented by constant coefficient, finite order differential equations. The non-linearities, coupling and noise effects are also often neglected. Moreover, identification experiment designs which lead to highly complex optimization problems usually require the simultaneous choice of ID algorithm, sensor, and actuator type and placement. On-orbit bandwidth and power restrictions on excitation, limited data window, and restrictions on sensor/actuator type, placement and number, has led to practical questions of implementations.

Hadaegh, Fred Y.↗
NASA NTRS1981

Nutation damping in a dual-spin spacecraft

A dual-spin spacecraft having a momentum wheel spinning relative to a platform to provide bias momentum utilizes cross products of inertia (POI) existing in the platform between the spinning axis and the transverse axes to achieve nutation damping. When the platform is rotating or is displaced from a reference the cross products of inertia are also rotating or are displaced causing thereby degradation of the optimum nutation damping time constant. Two or more phase shifting networks are provided to be sequentially coupled into a control loop to shift nutation signals to effect optimum nutation damping at selected positions of the rotating or displaced platform without substantial nutation damping time constant degradation.

Phillips, Kevin J.↗
NASA NTRS1961

Cross-Sectional Deformations of Monocoque Beams and Their Effects on the Natural Vibration Frequencies

The variational principle, differential equations, and boundary conditions governing the cross-sectional distortions due to inertia loading of a two-dimensional model of a thin monocoque wing are shown. A theoretical analysis of this simplified model is made in order to determine the nature of the coupling between the cross-sectional modes and the spanwise deformation modes. General solutions are obtained in finite-difference form for arbitrary cross sections and an exact solution is presented for a parabolic-arc cross section of constant cover thickness. The application of these results in evaluating the coupled frequencies of the actual structure is discussed. Frequencies evaluated for a parabolic-arc monocoque beam show good agreement with experimental values.

Thomson, Robert G.↗
NASA NTRS1977

Twin-capacitive shaft angle encoder with analog output signal

A precision capacitive shaft encoder providing a dc signal corresponding to the angular position of a shaft is described. Two variable capacitances are coupled in tandem by a rotatable shaft. Each capacitor has a capacitance that varies linearly with a change in the angular position of the shaft. The sum of the two capacitances is always constant for any angular position of the shaft. Each capacitance is alternately coupled to a reference dc voltage and a discharge circuit. The capacitances are electrically coupled in series and the charge periodically acquired at the junction of the capacitance is a function of the position of the shaft. An error-compensating voltage is imposed on the junction when the capacitances are coupled to the reference voltages. The junction is coupled to sample-and-hold apparatus provided with a error-correcting circuit.

Hruby, R. J.↗
NASA NTRS1985

Flap-Lag-Torsion Stability in Forward Flight

An aeroelastic stability of three-degree flap-lag-torsion blade in forward flight is examined. Quasisteady aerodynamics with a dynamic inflow model is used. The nonlinear time dependent periodic blade response is calculated using an iterative procedure based on Floquet theory. The periodic perturbation equations are solved for stability using Floquet transition matrix theory as well as constant coefficient approximation in the fixed reference frame. Results are presented for both stiff-inplane and soft-inplane blade configurations. The effects of several parameters on blade stability are examined, including structural coupling, pitch-flap and pitch-lag coupling, torsion stiffness, steady inflow distribution, dynamic inflow, blade response solution and constant coefficient approximation.

Panda, B.↗
NASA NTRS2006

Monitoring Temperatures of Tires Using Luminescent Materials

A method of noncontact, optical monitoring of the surface temperature of a tire has been devised to enable the use of local temperature rise as an indication of potential or impending failures. The method involves the use of temperature-sensitive paint (or filler): Temperature-sensitive luminescent dye molecules or other luminescent particles are incorporated into a thin, flexible material coating the tire surface of interest. (Alternatively, in principle, the luminescent material could be incorporated directly into the tire rubber, though this approach has not yet been tested.) The coated surface is illuminated with shorter-wavelength light to excite longer-wavelength luminescence, which is observed by use of a charge-coupled-device camera or a photodetector (see Figure 1). If temporally constant illumination is used, then the temperature can be deduced from the known temperature dependence of the intensity response of the luminescence. If pulsed illumination is used, then the temperature can be deduced from the known temperature dependence of the time or frequency response of the luminescence. If sinusoidally varying illumination is used, then the temperature can be deduced from the known temperature dependence of the phase response of the luminescence. Unlike a prior method of monitoring the temperature at a fixed spot on a tire by use of a thermocouple, this method is not restricted to one spot and can, therefore, yield information on the spatial distribution of temperature: in particular, it enables the discovery of newly forming hot spots where damage may be starting. Also unlike in the thermocouple method, the measurements in this method are not vulnerable to breakage of wires in repeated flexing of the tire. Moreover, unlike in another method in which infrared radiation is monitored as an indication of surface temperature, the luminescence measurements in this method are not significantly affected by changes in infrared emissivity. This method has been demonstrated in application to the outside surface of a tire (see Figure 2), using both constant and pulsed light sources for illumination and cooled, slow-scan, gated CCD cameras for detection. For observing the temperature of the inside surface of a tire (this has not yet been done), it would probably be necessary to use fiber optics and/or windows for coupling excitation light into, and coupling luminescence out of, the interior volume.

Bencic, Timothy J↗
NASA NTRS1978

On the coupled nature of atmospheric phenomena

The interactions that take place in the stratosphere and the troposphere which are important to the maintenance of the chemical, dynamic, and thermal state and of the middle atmosphere, and which may be important in the determination of the state of the lower atmosphere are reviewed. Examples of these interactions due to either natural or anthropogenic processes are discussed, and promising areas for future research are indicated. Specific topics include: (1) coupling between temperature and chemistry via temperature dependent rate constants; (2) the effect of latitudinal temperature variations on zonal winds; (3) the effect of clouds, surface albedo, and the lower atmosphere on stratospheric chemistry due to the scattering and reflection of solar radiation; (4) the effect of trace constituents on thermal structure and thermal balance; (5) the effect of the stratosphere on tropospheric climate; (6) the effect of solar UV variability on stratospheric chemistry and temperature; and (7) the effect of trace constituents on stratospheric dynamics.

Callis, L. B.↗