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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Interactions of coupled acoustic and vortical instability

In the past, the acoustic combustion instability was studied independently of the hydrodynamic instability induced by vortex motions. This paper is intended to combine the two different sources of energy everywhere within the spatial domain and determine the effect of one upon the other. This can be achieved by calculating the mean flow velocities and vorticities and their fluctuating parts of velocities and vortices, as well as the fluctuating pressure. The Orr-Sommerfeld equation is utilized to determine the wavenumbers and unsteady stream functions from which vortically coupled acoustic instability growth constants are calculated. This process demonstrates that there are two different frequencies, acoustic and hydrodynamic, various combinations of which contribute to either damping or amplification. It is found that stability boundaries for coupled acoustic and vortical oscillations are somewhat similar to the classical hydrodynamic stability boundaries, but they occur in the form of multiple islands.

Chung, T. J.↗
NASA NTRS1986

AH-1G flight vibration correlation using NASTRAN and the C81 rotor/airframe coupled analysis

Analytical results are presented bearing on the accuracy of state-of-the-art NASTRAN FEM modeling techniques and rotor/airframe coupling methods for the prediction of flight vibrations; these results have been studied by NASA and industry experts in order to ensure scientific control of the analysis/correlation exercise. The rotor loads predicted by the dynamically coupled rotor/airframe analysis showed good agreement between calculated and experimental blade loads, as did the predominant excitation frequency vibration levels predicted by NASTRAN.

Dompka, R. V.↗
NASA NTRS1986

Thermal shaft effects on load-carrying capacity of a fully coupled, variable-properties cryogenic journal bearing

The purpose of this work was to perform a rather complete analysis for a cryogenic (oxygen) journal bearing. The Reynolds equation required coupling and simultaneous solution with the fluid energy equation. To correctly account for the changes in the fluid viscosity, the fluid energy equation was coupled with the shaft and bearing heat conduction energy equations. The effects of pressure and temperature on the density, viscosity, and load-carrying capacity were further discussed as analysis parameters, with respect to relative eccentricity and the angular velocity. The isothermal fluid case and the adiabatic fluid case represented the limiting boundaries. The discussion was further extrapolated to study the Sommerfeld number dependency on the fluid Nusselt number and its consequence on possible total loss of load-carrying capacity and/or seizure (catastrophic failure).

Braun, M. J.↗
NASA NTRS1986

Three-wave coupling coefficient in a drifting bi-Maxwellian plasma

A general electrostatic coupling coefficient which satisfies the Manley-Rowe relations is used to derive an explicit expression for the resonant three-wave coupling coefficient between electrostatic normal modes of a uniformly magnetized, infinite, homogeneous plasma with species described by drifting bi-Maxwellian distribution functions. The limit of this expression is taken when the phase velocities of the three waves are much larger than a species thermal speed, and also when the phase velocities are much smaller than the thermal speed. These are fluid limits and are applicable to the three-wave interaction between some low-frequency electrostatic waves, such as ion acoustic and ion cyclotron modes, in a plasma where T(e) is much greater than T(i).

Bergmann, Rachelle↗
NASA NTRS1986

Solar wind-magnetosphere coupling; Proceedings of the Chapman Conference, California Institute of Technology, Pasadena, Feb. 12-15, 1985

Various papers on the coupling of the solar wind with the earth's magnetosphere are presented. The topics addressed include: geomagnetic indices and statistical methods; solar wind and magnetospheric processes, including solar wind control of the magnetosphere, dayside interaction, and solar wind disturbances and magnetospheric response; the electrodynamics of magnetosphere-ionosphere coupling, including electric fields and currents and auroras and auroral precipitation; and solar wind control of the nightside magnetosphere.

Kamide, Y.↗
NASA NTRS1987

Optical emission from coupled surface plasmons

Surface plasmons on opposite sides of a thin metal film surrounded by identical dielectrics interact to form coupled surface plasmons (CSP's). Corrugation of the metal film permits interaction of the CSP's with the radiation field. This paper reports the observation of optical emission from CSP's excited by the near-field coupling of molecules adjacent to a corrugated thin metal film embedded in photoresist.

Gruhlke, R. W.↗
NASA NTRS1987

Extension of a semi-implicit shock-capturing algorithm for 3-D fully coupled, chemically reacting flows in generalized coordinates

A semiimplicit high-resolution shock-capturing method for multidimensional systems of hyperbolic conservation laws with stiff source terms has been developed by Yee and Shinn (1987). The goal of this work is to extend this method to solve the three-dimensional fully coupled Navier-Stokes equations for a hypersonic chemically reacting flow in generalized coordinates. In this formulation, the global continuity equation was replaced by all the species continuity equations. The shock-capturing technique is a second-order-accurate, symmetric total-variation-diminishing method which accounts fully and directly for the coupling among the fluid and all the species. To verify the current approach, it was implemented into an existing computer code which contained the MacCormack method. Test results for a five-species reacting flow are shown to be oscillation-free around the shock, and the time spent per iteration only doubles when compared to the result using classical way of supplying numerical dissipation. The extra computation is more than justified by the elimination of spurious oscillation and nonlinear instability associated with the classical shock-capturing schemes in computing hypersonic reacting flows.

Shinn, J. L.↗
NASA NTRS1987

Spectral-domain analysis of single and coupled cylindrical striplines

A spectral-domain technique for finding the characteristic impedances of a single cylindrical stripline and a coupled pair of cylindrical striplines is presented. Assuming a charge distribution on the strip, the variational expression for the line capacitance for single cylindrical stripline is derived. Good agreement with published results is obtained. The cylindrical coupled strip and microstrip lines are also analyzed and a comparison with their planar counterparts is made.

Deshpande, Manohar D.↗
NASA NTRS1987

Indirect measurement of N-14 quadrupolar coupling for NH3 intercalated in potassium graphite

A method for indirect measurement of the nuclear quadrupolar coupling was developed and applied to NH3 molecules in the graphite intercalation compound K(NH3)4.3C24, which has a layered structure with alternating carbon and intercalant layers. Three triplets were observed in the H-1 NMR spectra of the compound. The value of the N-14 quadrupolar coupling constant of NH3 (3.7 MHz), determined indirectly from the H-1 NMR spectra, was intermediate between the gas value of 4.1 MHz and the solid-state value of 3.2 MHz. The method was also used to deduce the (H-1)-(H-1) and (N-14)-(H-1) dipolar interactions, the H-1 chemical shifts, and the molecular orientations and motions of NH3.

Tsang, T.↗
NASA NTRS1984

Coupled convective instabilities at crystal-melt interfaces

The stability of the parallel flow between a vertical crystal-melt interface and a vertical wall held at a temperature above the melting point of the crystal is analyzed for Prandtl numbers, P, ranging from 0.01 to 100. Three modes of instability occur: (1) a buoyant mode, (2) a shear mode, and (3) a coupled crystal-melt mode. The buoyant and shear modes are similar to those that occur for flow between two vertical rigid walls held at different temperatures. For Prandtl numbers greater than approximately two, the coupled crystal-melt mode occurs at a lower Grashof number than the other two modes. Specific results are given for succinonitrile (P = 22.8) and lead (P = 0.0225). These calculations and similar calculations for a cylindrical geometry were motivated by and are in general agreement with recent experiments on succinonitrile.

Coriell, S. R.↗
NASA NTRS1988

Rotary Fluid Coupling

Rotary coupling for heat-transfer fluid contains four lines for vapor and four corresponding liquid-return lines. This one allows unlimited rotation and does not have to be rewound to prevent damage to hoses. Fluid coupled with minimal leakage between stationary housing and inner rotating shaft.

Zentner, Ron↗
NASA NTRS1988

Pressure-Sealing Optical Coupling

Light signals passed out of high-pressure cryogenic environment. Optical coupling passes signals in fiber-optic channels across pressure-and-temperature barrier. Coupling made in different configurations and modified to suit requirements of different cryogenic instrumentation systems.

Irvin, Timothy B.↗
NASA NTRS1988

Contactless Coupling For Power And Data

Experimental flat-plate coupling transmits digital data signals and electrical power across small gap between two modules. Split transformer and optoelectronic components transmit electrical power and digital signals across small gap. Coupling concept useful substitute for electrical connectors in equipment assembled by robots, remote manipulators, or humans working in protective clothing or otherwise restricted in dexterity. Offers higher reliability due to one overall alignment mechanism as opposed to multiple pin/socket alignment requirements.

Moody, John C.↗
NASA NTRS1987

Studies of pressure-velocity coupling schemes for analysis of incompressible and compressible flows

Two pressure-velocity coupling schemes, both of which solve the fully implicit discretized equations governing the flow of fluids were examined, and the capability of performing large Reynolds number, low Mach number compressible flow calculations were assessed. The semi-implicit iterative SIMPLE algorithm is extended to handle transient compressible flow calculations. This extension takes into account a strong coupling between the pressure and temperature through a correction procedure, based on the equations of state. Results obtained from the extended SIMPLE algorithm are then compared to similar results obtained from the non-iterative PISO algorithm. Both time-dependent and steady state calculations were performed using an axisymmetric 2:1 pipe expansion geometry and laminar flow conditions corresponding to Reynolds number of 1000 and Mach number of 2.0. For calculations simulating a time-dependent compression/expansion process, both schemes exhibit transient features in excellent agreement with each other, and moreover, the PISO method shows a significant computational time reduction of 60 percent over the SIMPLE scheme, regardless of the time step size or grid size employed. The effects of numerical diffusion are shown to be significant in these calculations. For steady state compressible flows, however, the SIMPLE algorithm displays increasing computational efficiency over the PISO method as the time step sizes employed to reach steady state conditions are decreased.

Burgreen, Gregory Wayne↗
NASA NTRS1988

Coupled bending-torsion steady-state response of pretwisted, nonuniform rotating beams using a transfer-matrix method

Using the Newtonian method, the equations of motion are developed for the coupled bending-torsion steady-state response of beams rotating at constant angular velocity in a fixed plane. The resulting equations are valid to first order strain-displacement relationships for a long beam with all other nonlinear terms retained. In addition, the equations are valid for beams with the mass centroidal axis offset (eccentric) from the elastic axis, nonuniform mass and section properties, and variable twist. The solution of these coupled, nonlinear, nonhomogeneous, differential equations is obtained by modifying a Hunter linear second-order transfer-matrix solution procedure to solve the nonlinear differential equations and programming the solution for a desk-top personal computer. The modified transfer-matrix method was verified by comparing the solution for a rotating beam with a geometric, nonlinear, finite-element computer code solution; and for a simple rotating beam problem, the modified method demonstrated a significant advantage over the finite-element solution in accuracy, ease of solution, and actual computer processing time required to effect a solution.

Gray, Carl E., Jr.↗
NASA NTRS1987

Spatial light modulation by beam coupling in GaAs crystals

The first demonstration of spatial light modulation in GaAs using the photorefractive effect is reported. A special configuration was employed in which polarization rotation created by beam coupling was utilized. The ability to obtain these results despite a small coupling gain coefficient demonstrates the usefulness of the polarization technique presented here for optical processing with GaAs crystals.

Cheng, Li-Jen↗
NASA NTRS1987

Characteristics of inhomogeneous coupled cylindrical striplines

Using conformal transformation, closed-form expressions for the even and odd mode impedances of inhomogeneous coupled cylindrical striplines are presented. It is shown that the analysis can be extended for the calculation of characteristics of coupled cylindrical microstrip lines. The analysis can also be extended to reveal the effects of warping due to environmental changes on an otherwise planar structure.

Reddy, C. J.↗
NASA NTRS1987

IOS and ECS line coupling calculation for the CO-He system - Influence on the vibration-rotation band shapes

Line coupling coefficients resulting from rotational excitation of CO perturbed by He are computed within the infinite order sudden approximation (IOSA) and within the energy corrected sudden approximation (ECSA). The influence of this line coupling on the 1-0 CO-He vibration-rotation band shape is then computed for the case of weakly overlapping lines in the 292-78 K temperature range. The IOS and ECS results differ only at 78 K by a weak amount at high frequencies. Comparison with an additive superposition of Lorentzian lines shows strong modifications in the troughs between the lines. These calculated modifications are in excellent quantitative agreement with recent experimental data for all the temperatures considered. The applicability of previous approaches to CO-He system, based on either the strong collision model or exponential energy gap law, is also discussed.

Boissoles, J.↗