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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Viscous-inviscid interaction and local grid refinement via truncation error injection

A methodology is presented which makes it possible to decouple a complex problem having multiple disparate length scales into problems of single length scale so that they can be solved more efficiently on a computer. The method is applied to a viscous transonic flow over an airfoil. It is found that accurate prediction of the flow over an airfoil can be obtained by solving the Euler equations on a relatively coarse global grid with viscous effects computed separately on a boundary-layer type grid and injected into the global grid solution as a combination of vorticity and trucation error.

Goble, Brian D.↗
NASA NTRS1989

A few remarks concerning several refined theories of anisotropic composite laminated plates

An analysis and comparison of several shear deformable bending theories of composite laminated anisotropic plates currently encountered in the field literature are given in this paper. Although apparently different, it is shown in a unitary way, that these theories constitute in fact only different formulations of a single theory, generically designated to as the moderately thick plate theory. Their connection with the first order transverse shear deformation theory is also emphasized and some conclusions concerning its shortcomings and field applicability are presented.

Librescu, L.↗
NASA NTRS1990

Additional measurements and a refined analysis of the millimeter- and submillimeter-wave spectrum of methanol

A total of 414 previously unobserved millimeter- and submillimeter-wave transitions of (C-12)H3OH through J = 10 and v(t) = 2 are assigned. These data and previous measured spectral transitions are combined and fitted by a modified internal axis method (IAM) treatment in which the A and E substates are treated separately and a wide variety of new rotational-torsional interaction terms are employed. The modified IAM treatment reduces the overall rms deviation of the fits to the level of experimental accuracy. The resultant spectroscopic constants allow for the accurate prediction of 569 additional transitions through J = 12 or less.

Anderson, Todd↗
NASA NTRS1989

Development and refinement of test bed simulations

Lewis Research Center of NASA, with support from Rocketdyne, has engaged in a nonreal-time computer simulation effort for the Space Station Freedom Electric Power System (EPS). EASYS, a simulation package, is used as the primary tool for this activity. Early in the design of the EPS, two test beds were set up at Lewis. The Integrated Test Bed (ITB) that combines and upgrades these test beds is in the planning stage. The test beds are designed to functionally represent many of the components of the EPS and their interconnections. The simulation effort is primarily directed towards these test beds. Model verification is performed using test bed data.

Dravid, N. V.↗
NASA NTRS1991

Computation Of Flow In A Turbine Stage On A Refined Grid

Finer grid yields more accurate results. Report describes numerical simulation of flow in axial-turbine stage, showing interactions between rotor- and stator-airfoil rows. Complements earlier three-dimensional, time-accurate Navier-Stokes numerical simulation.

Madavan, N. K.↗
NASA NTRS1989

TOPEX microwave radiometer system calibration - Refining the SMMR heritage

A modified version of the Scanning multichannel Microwave Radiometer (SMMR) will be used for wet tropospheric path-delay corrections to the TOPEX/POSEIDON radar altimeter measurements. A number of the sources of calibration problems encountered by SMMR onboard the Seasat and Nimbus-7 platforms have been identified, and appropriate corrections have been attempted. Calibration hardware corrections include a more representative modeling of the microwave losses and reflections, and a reduction in the thermal gradients expected across this hardware through the use of radomes and sun shades and the choice of pertinent orbit parameters. Antenna calibration corrections include a postlaunch fine tuning of the antenna pattern correction algorithm to accommodate small errors in the prelaunch antenna pattern measurements. This is accomplished by overpasses of ground-based, upward-looking water vapor radiometers. An absolute calibration accuracy of 1.0 K or less is anticipated.

Ruf, Christopher S.↗
NASA NTRS1991

Light scattering by nonspherical particles - A refinement to the coupled-dipole method

In the coupled-dipole method, an arbitrary particle is modeled as an array of N polarizable subunits, each of which gives rise to only electric dipole radiation. The Clausius-Mosotti relation is widely used to calculate the polarizability of the subunits that correspond to the dielectric function of the particle that the array represents. The Clausius-Mosotti relation is replaced here with an exact expression for the electric dipole polarizability, and improvement is found in extinction calculations for spheres as compared with Mie theory. Near a Froehlich frequency the coupled-dipole method yields extinction cross sections for spheres and spheroids that compare favorably with the continuous distribution of ellipsoids method and measured values.

Dungey, Clifton E.↗
NASA NTRS1990

On refined theories of composite laminates

A review of the developments in the displacement-based theories of plates is presented. It is shown that many of the third-order theories reported in the literature are based on the same or equivalent displacement field, and thus lead to the same results. A strain-consistent third-order theory is presented, which contains most existing third-order plate theories as special cases. The layer-wise laminate plate theory proposed is also reviewed. The accuracy of the theories is evaluated by comparing the numerical solutions with those of the three-dimensional elasticity theory.

Reddy, J. N.↗
NASA NTRS1991

Interface conditions for domain decomposition with radical grid refinement

Interface conditions for coupling the domains in a physically motivated domain decomposition method are discussed. The domain decomposition is based on an asymptotic-induced method for the numerical solution of hyperbolic conservation laws with small viscosity. The method consists of multiple stages. The first stage is to obtain a first approximation using a first-order method, such as the Godunov scheme. Subsequent stages of the method involve solving internal-layer problem via a domain decomposition. The method is derived and justified via singular perturbation techniques.

Scroggs, Jeffrey S.↗
NASA NTRS1992

Impeller tandem blade study with grid embedding for local grid refinement

Flow non-uniformity at the discharge of high power density impellers can result in significant unsteady interactions between impeller blades and downstream diffuser vanes. These interactions result in degradation of both performance and pump reliability. The MSFC Pump Technology Team has recognized the importance of resolving this problem and has thus initiated the development and testing of a high head coefficient impeller. One of the primary goals of this program is to improve impeller performance and discharge flow uniformity. The objective of the present work is complimentary. Flow uniformity and performance gains were sought through the application of a tandem blade arrangement. The approach adopted was to numerically establish flow characteristics at the impeller discharge for the baseline MSFC impeller and then parametrically evaluate tandem blade configurations. A tandem design was sought that improves both impeller performance and discharge uniformity. The Navier-Stokes solver AEROVISC was used to conduct the study. Grid embedding is used to resolve local gradients while attempting to minimize model size. Initial results indicate that significant gains in flow uniformity can be achieved through the tandem blade concept and that blade clocking rather than slot location is the primary driver for flow uniformity.

Bache, George↗
NASA NTRS1992

Iterative refinement scheduling

We present a heuristics-based approach to deep space mission scheduling which is modeled on the approach used by expert human schedulers in producing schedules for planetary encounters. New chronological evaluation techniques are used to focus the search by using information gained during the scheduling process to locate, classify, and resolve regions of conflict. Our approach is based on the assumption that during the construction of a schedule there exist several disjunct temporal regions where the demand for one resource type or a single temporal constraint dominates (bottleneck regions). If the scheduler can identify these regions and classify them based on their dominant constraint, then the scheduler can select the scheduling heuristic.

Biefeld, Eric↗
NASA NTRS1992

Refining the granulite suite

Early studies of rocks retrieved from the Moon during the Apollo missions defined a group of rocks as granulites or 'granulitic impactites'. This included rocks with cataclastic, granulitic, and poikilitic or poikiloblastic textures. Petrographic studies indicate that the textures of 'granulitic breccias' are significantly varied so as to redefine the granulitic suite into at least two distinct groups. The first group consists of rocks that have true granulitic textures: polygonal to rounded, equant grains that are annealed, and have triple junctions with small dispersions from the average 120 degrees. The second group of rocks have poikilitic or poikiloblastic textures, with subhedral to euhedral plagioclase and/or olivine grains enclosed in pyroxene oikocrysts. In some instances, the relationship between the minerals resembles an orthocumulate texture. Rocks previously thought of as granulites may have formed in more than one way. These formation mechanisms are briefly discussed.

Taylor, G. Jeffrey↗
NASA NTRS1993

A comparison of refined models for flexible subassemblies

Interactions between structure response and control of large flexible space systems have challenged current modeling techniques and have prompted development of new techniques for model improvement. Due to the geometric complexity of envisioned large flexible space structures, finite element models (FEM's) will be used to predict the dynamic characteristics of structural components. It is widely accepted that these models must be experimentally 'validated' before their acceptance as the basis for final design analysis. However, predictions of modal properties (natural frequencies, mode shapes, and damping ratios) are often in error when compared to those obtained from Experimental Modal Analysis (EMA). Recent research efforts have resulted in the development of algorithmic approaches for model improvement, also referred to as system or structure identification.

Smith, Suzanne Weaver↗
NASA NTRS1993

Refinements on the pinhole camera measurements of the LDEF attitude

The results from the University of Alabama in Huntsville (UAH) pinhole camera were reanalyzed to include the effects of corotation of the atmosphere with the Earth as well as satellite oscillation. Previous results from the instrument showed that the satellite had stable attitude offsets in yaw of 8.0 deg and 1.0 deg in pitch; these offsets are unchanged by the present analysis. The primary impact zone of oxygen, i.e., the directly exposed spot on a silver detector, had a ratio of major to minor axes equal to 1.05, which was interpreted as being caused by a small oscillation of plus or minus 0.35 degrees (with precision plus or minus 0.15 degrees). The present analysis shows that the observed effect can largely be accounted for by atmospheric corotation, but that an additional oscillation in yaw of the order of a degree cannot be excluded. The sensitivity of the pinhole camera to satellite oscillations is shown to decrease nonlinearly with decreasing magnitude of the oscillation and to vary inversely with the gas temperature.

Peters, Palmer N.↗
NASA NTRS1991

Passive range sensor refinement using texture and segmentation

Electrooptical sensors provide a covert way of computing range during helicopter flight. The optical flow-based computation of range provides range information only in certain distinguishable parts of the image. The regions where range information is available can be increased by performing texture analysis and object segmentation in the image. This paper reviews some of the literature on texture segmentation methods with a view towards applying them to images containing both man-made and natural objects at varying ranges. Two algorithmic approaches are given and their application to a real image is demonstrated. Results indicate that it will be necessary to combine several different texture measures and methods in a hierarchical way in order to achieve an object segmentation which is useful in enhancing range information.

Sridhar, Banavar↗
NASA NTRS1992

Refinement of Magellan radiometric correction using range centroid estimation

The Magellan (MGN) synthetic aperture radar (SAR) processing radiometric compensation algorithm is described, and the effective pointing error caused by the terrain is examined. It is shown how the range centroid can be computed from spacecraft ancillary data with an accurate topographic model. In cases where such data are not available, a technique is presented to estimate the range centroid from the coherent radar echoes. This technique is demonstrated using MGN SAR data.

Cheng, T.↗