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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Tau approximation techniques for identification of coefficients in parabolic PDE

A variant of the Tau method, called the weak Tau method, is developed on the basis of the weak form of the PDE for use in least-squares parameter estimation; also presented is a suitable abstract convergence framework. The emphasis is on the theoretical framework that allows treatment of the weak Tau method when it is applied to a wide class of inverse problems, including those for diffusion-advection equations, the Fokker-Planck model for population dynamics, and damped beam equations. Extensive numerical testing of the weak Tau method has demonstrated that it compares quite favorably with existing methods.

Banks, H. T.↗
NASA NTRS1991

Sinc-Galerkin estimation of diffusivity in parabolic problems

A fully Sinc-Galerkin method for the numerical recovery of spatially varying diffusion coefficients in linear partial differential equations is presented. Because the parameter recovery problems are inherently ill-posed, an output error criterion in conjunction with Tikhonov regularization is used to formulate them as infinite-dimensional minimization problems. The forward problems are discretized with a sinc basis in both the spatial and temporal domains thus yielding an approximate solution which displays an exponential convergence rate and is valid on the infinite time interval. The minimization problems are then solved via a quasi-Newton/trust region algorithm. The L-curve technique for determining an approximate value of the regularization parameter is briefly discussed, and numerical examples are given which show the applicability of the method both for problems with noise-free data as well as for those whose data contains white noise.

Smith, Ralph C.↗
NASA NTRS1992

Parabolized reduced Navier-Stokes computational techniques

A review is presented of methods in which composite or reduced Navier-Stokes (RNS) equations are treated with a pressure-gradient-based flux-vector splitting. The methods are similar to large Re asymptotic formulations, and streamwise diffusion terms are ignored in favor of an explicit deferred corrector based on higher-order diffusion terms. The methods can be used for 2D and 3D supersonic flows in which the effects of real gas are incorporated. Several examples of the procedure are given, and subsonic and supersonic flows are handled well with relaxation procedures that incorporate multigrid acceleration. Effective solutions are described for problems ranging from incompressible flows and supersonic flows to sharp shocks and reverse-flow capturing.

Rubin, Stanley G.↗
NASA NTRS1993

Materials science on parabolic aircraft: The FY 1987-1989 KC-135 microgravity test program

This document covers research results from the KC-135 Materials Science Program managed by MSFC for the period FY87 through FY89. It follows the previous NASA Technical Memorandum for FY84-86 published in August 1988. This volume contains over 30 reports grouped into eight subject areas covering acceleration levels, space flight hardware, transport and interfacial studies, thermodynamics, containerless processing, welding, melt/crucible interactions, and directional solidification. The KC-135 materials science experiments during FY87-89 accomplished direct science, preparation for space flight experiments, and justification for new experiments in orbit.

Curreri, Peter A.↗
NASA NTRS1991

Acute hemodynamic response to weightlessness during parabolic flight

The effect of a short exposure to weightlessness on hemodynamic parameters of humans was investigated in seven subjects flown aboard the KC-135 aircraft. Particular attention is given to the relationships among various hemodynamic responses to hypergravic and hypogravic states, observed for four different postures: semisupine, supine, standing, and sitting. Results are presented on changes in the thoracic fluid index, heart rate, cardiac index, and the coefficient of variation of the R-R intervals. High values of the coefficient of variation were found at the onset of 0-G, suggesting that vagal cardiac neural activity increases in all positions except supine (where a small decrease was registered).

Mukai, Chiaki N.↗