Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Surface structure”

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 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Nonequilibrium effects for hypersonic transitional flows

Presented are the results of numerical simulations of hypersonic flow about blunt cones and hemispherical nose configurations for reentry velocities of 7.5 and 10 km/s. Cone half angles 0, 5, and 10 deg are considered at zero angle of incidence; however, the focus is for the 5 deg cone. The body size and altitude ranges considered (70 to 110 km) are such that the flow is in the transitional regime. Translational, thermodynamic, and chemical nonequilibrium effects are considered in the numerical simulation by utilizing the direct simulation Monte Carlo (DSMC) method of Bird. The DSMC results are compared with those obtained with viscous shock-layer and Navier-Stokes methods. Comparisons between the DSMC and continuum calculations show the altitude range where differences in flowfield structure and surface quantities become significant. The current calculations show that the binary scaling similitude provides a means of correlating the blunt body surface quantities in the hypersonic, transitional regime. Furthermore, for the higher velocity entry conditions, the results highlight some of the concerns in the application of multitemperature continuum formulations, particularly the use of some proposed functional relations for the chemical rate constants under thermodynamic nonequilibrium conditions.

Moss, James N.↗
NASA NTRS1986

Numerical simulations of rarefied reentry flows

A review of recent calculations obtained with Bird's direct simulation Monte Carlo (DSMC) method is presented for the transitional flowfield encountered at reentry conditions. Consequently, the emphasis is the real-gas effects resulting from a highly energetic nonequilibrium flow. The DSMC calculations for both wide-angle and slender bodies are compared with continuum calculations. The wide-angle body calculations simulate the windward nose of the Shuttle Orbiter and projected aeroassisted orbital transfer vehicles. For the slender, blunted configurations, both two-dimensional and axisymmetric results are presented. Comparisons between the DSMC and continuum calculations show the altitude range where differences in flowfield structure and surface quantities become significant.

Moss, James N.↗
NASA NTRS1987

Measuring ocean waves from space; Proceedings of the Symposium, Johns Hopkins University, Laurel, MD, Apr. 15-17, 1986

Papers are presented on ocean-wave prediction; the quasi-universal form of the spectra of wind-generated gravity waves at different stages of their development; the limitations of the spectral measurements and observations of the group structure of surface waves; the effect of swell on the growth of wind wave; operational wave forecasting; ocean-wave models, and seakeeping using directional wave spectra. Consideration is given to microwave measurements of the ocean-wave directional spectra; SIR research; estimating wave energy spectra from SAR imagery, with the radar ocean-wave spectrometer, and SIR-B; the wave-measurement capabilities of the surface contour radar and the airborne oceanographic lidar; and SIR-B ocean-wave enhancement with fast-Fourier transform techniques. Topics discussed include wave-current interaction; the design and applicability of Spectrasat; the need for a global wave monitoring system; the age and source of ocean swell observed in Hurricane Josephine; and the use of satellite technology for insulin treatment.

Beal, Robert C.↗
NASA NTRS1986

Direct simulation of hypersonic transitional flow

A review of recent calculations obtained with Bird's direct simulation Monte Carlo (DSMC) method are presented for the transitional flowfield encountered at reentry conditions. Consequently, the emphasis is to simulate the real-gas effects resulting from a highly energetic nonequilibrium flow. The DSMC calculations for both wide-angle and slender bodies are compared with experimental and continuum calculations. The wide angle body calculations simulate the widward nose of the Shuttle Orbiter and projected aeroassisted orbital transfer vehicles. For the slender, blunted configurations, both two-dimensional and axisymmetric results are presented. Comparisons between the DSMC and continuum calculations show the altitude range where differences in flowfield structure and surface quantities become significant.

Moss, J. N.↗
NASA NTRS1988

Direct simulation of AFE forebody and wake flow with thermal radiation

Calculated results for the flowfield structure and surface quantities are presented for an axisymmetric representation of an aeroassist flight experiment vehicle. The direct simulation Monte Carlo (DSMC) method is used to perform the calculations, since the flow is highly nonequilibrium about the vehicle during both the compression and expansion phases. The body configuration is an elliptically blunt nose followed by a skirt with a circular radius and an afterbody. Freestream conditions correspond to a single point along the entry trajectory at an altitude of 90 km and a velocity of 9.9 km/s. The calculations account for nonequilibrium in the translational and internal modes, dissociation, ionization, and thermal radiation. The degree of dissociation is large, but the maximum ionization is only about 2 percent by mole fraction. The bluntforebody flow experiences a high degree of thermal nonequilibrium in which the translational temperature is generally greater than the internal temperature. However, as the flow expands about the aerobrake skirt and afterbody, the internal temperature is generally greater than the translational temperature.

Moss, James N.↗
NASA NTRS1989

Near-field testing of the 15-meter hoop-column antenna

A 15-m-diameter antenna was tested to verify that dimensional tolerances for acceptable performance could be achieved and to verify structural, electromagnetic, and mechanical performance predictions. This antenna utilized the hoop column structure, a gold plated molybdenum mesh reflector, and 96 control cables to adjust the reflector conformance with a paraboloid. The dimensional conformance of the antenna structure and surface was measured with metric camera and theodolites. Near field pattern data were used to assess the electromagnetic performance at five frequencies from 2.225 to 11.6 GHz. The reflector surface was adjusted to greatly improve electromagnetic performance with a finite element model and the surface measurements. Measurement results show that antenna surface figure and adjustments and electromagnetic patterns agree well with predictions.

Schroeder, Lyle C.↗
NASA NTRS1989

Controlled method of reducing electrophoretic mobility of various substances

A method of reducing electrophoretic mobility of macromolecules, particles, cells, and the like is provided. The method comprises interacting the particles or cells with a polymer-linked affinity compound composed of: a hydrophilic neutral polymer such as polyethylene glycol, and an affinity component consisting of a hydrophobic compound such as a fatty acid ester, an immunocompound such as an antibody or active fragment thereof or simular macromolecule, or other ligands. The reduction of electrophoretic mobility achieved is directly proportional to the concentration of the polymer-linked affinity compound employed, and the mobility reduction obtainable is up to 100 percent for particular particles and cells. The present invention is advantageous in that analytical electrophoretic separation can not be achieved for macromolecules, particles, and cells whose native surface charge structure had prevented them from being separated by normal electrophoretic means. Depending on the affinity component utilized, separation can be achieved on the basis of specific/irreversible, specific/reversible, semi-specific/reversible, relatively nonspecific/reversible, or relatively nonspecific/irreversible ligand-substance interactions. The present method is also advantageous in that it can be used in a variety of standard laboratory electrophoresis equipment.

Vanalstine, James M.↗
NASA NTRS1988

Controls of CO2 sources and sinks in the earth scale surface ocean - Temperature and nutrients

Several regions in the ocean in which disequilibrium persists on an annual avarage between CO2 in the surface water and the overlying atmosphere were examined using various models in which CO2 does cycle in a steady state at which sources (ocean outgassing) and sinks (ingassing) are in balance. The relative values of the surface temperature and surface nutrients, the two major contributors to the CO2 source and/or sink properties, are determined. Results from models with two ocean surfaces indicate that the sink in the north Atlantic and the sources in the equatorial Atlantic and Pacific are all dominated by the global temperature patterns. Results from ocean models with three surface zones show that, in the equatorial Pacific, the temperature control is responsible for over 50 percent (and, possibly, for almost 70 percent) of the CO2 outgassing, with the balance coming from the earth scale surface nutrient structure.

Volk, Tyler↗
NASA NTRS1988

Lunar rated fasteners

A catalog of fasteners is presented for a variety of applications to be used in a lunar environment. The fastening applications targeted include: covers, panels, hatches, bearings, wheels, gears, pulleys, anchors for the lunar surface and structural fasteners (general duty preloadable). The robotic installation and removal of each fastener is presented along with a discussion of failure modes. Structural performance data is tabulated for various configurations. Potential materials for the space environment are presented along with recommendations of appropriate solid film lubricants. Three original fastener designs were found suitable for the lunar environment. A structural analysis is presented for each original design.

Gupton, Lindsey↗
NASA NTRS1989

Direct simulation of AFE forebody and wake flow with thermal radiation

Calculated results for the flowfield structure and surface quantities are presented for an axisymmetric representation of an aeroassist flight experiment vehicle. The direct simulation Monte Carlo (DSMC) method is used to perform the calculations, since the flow is highly nonequilibrium about the vehicle during both the compression and expansion phases. The body configuration is an elliptically blunt nose followed by a skirt with a circular radius and an afterbody. Freestream conditions correspond to a single point along the entry trajectory at an altitude of 90 km and a velocity of 9.9 km/s. The calculations account for nonequilibrium in the translational and internal modes, dissociation, ionization, and thermal radiation. The degree of dissociation is large, but the maximum ionization is only about 2 percent by mole fraction. The blunt forebody flow experiences a high degree of thermal nonequilibrium in which the translational temperature is generally greater than the internal temperature. However, as the flow expands about the aerobrake skirt and afterbody, the internal temperature is generally greater than the translational temperature.

Moss, James N.↗
NASA NTRS1991

Study of balloon and thermal control material degradation aboard LDEF

The initial results of analysis performed on a number of polymeric materials which were exposed aboard the Long Duration Exposure Facility (LDEF) are discussed. These materials include two typical high altitude balloon films (a polyester and a polyethylene) and silver-backed Teflon from thermal control blanket samples. The techniques used for characterizing changes in mechanical properties, chemical structure and surface morphology include Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy, and dynamic mechanical analysis.

Letton, Alan↗
NASA NTRS1991

Double face sealing device

A double face sealing device is disclosed for mounting between two surfaces to provide an air-tight and fluid-tight seal between a closure member bearing one of the surfaces and a structure or housing bearing the other surface which extends around the opening or hatchway to be closed. The double face sealing device includes a plurality of sections or segments mounted to one of the surfaces, each having a main body portion, a pair of outwardly extending and diverging, cantilever, spring arms, and a pair of inwardly extending and diverging, cantilever, spring arms, an elastomeric cover on the distal, free ends of the outwardly extending and diverging spring arms, and an elastomeric cover on the distal, free, ends of the outwardly extending and diverging spring arms, and an elastomeric cover on the distal, free ends of the inwardly extending and diverging spring arms. The double face sealing device has application or use in all environments requiring a seal, but is particularly useful to seal openings or hatchways between compartments of spacecraft or aircraft.

Weddendorf, Bruce↗
NASA NTRS1990

Flow computations for the Space Shuttle in ascent mode using thin-layer Navier-Stokes equations

The application of CFD techniques to the Space Shuttle ascent environment was aggressively undertaken in the wake of the Challenger accident in order to secure a major new source of aerodynamic information for both the nominal and mission-abort conditions, using Cray 2 and Cray YMP supercomputers. Due to the integrated vehicle's complexity, the 'chimera' composite grid approach, in which an overset body-conforming grid is used to represent each geometric component as well as special flow regions, was employed for the discretization process. Calculation results exhibit general agreement in both flow structure and surface pressure with the available wind tunnel and flight-test results.

Martin, F. W., Jr.↗
NASA NTRS1990

White dwarf evolution - Cradle-to-grave constraints via pulsation

White dwarf evolution, particularly in the early phases, is not very strongly constrained by observation. Fortunately, white dwarfs undergo nonradial pulsation in three distinct regions of the H-R diagram. These pulsations provide accurate masses, surface compositional structure and rotation velocities, and help constrain other important physical properties. We demonstrate the application of the tools of stellar seismology to white dwarf evolution using the hot white dwarf star PG 1159-035 and the cool DAV (or ZZ Ceti) stars as examples. From pulsation studies, significant challenges to the theory of white dwarf evolution emerge.

Kawaler, Steven D.↗
NASA NTRS1991

Hypersonic rarefied flow about a compression corner - DSMC simulation and experiment

The phenomena of shock/boundary-layer interactions and flow separation are investigated using both computational and experimental methods for low-density hypersonic flow about two-dimensional compression corners. The numerical calculations are made with the direct simulation Monte Carlo (DSMC) method. Experimental measurements provide information concerning the flowfield structure and surface flow patterns by means of gas glow discharge and oil flow pictures, respectively. Comparison of the two data sets provides a qualitative basis for assessing the ability of the DSMC method to describe such flows.

Moss, James N.↗
NASA NTRS1991

Hypersonic rarefied flow about a delta wing - Direct simulation and comparison with experiment

Three-dimensional simulations of hypersonic rarefied flow about a delta wing are made using the direct simulation Monte Carlo (DSMC) method of Bird, and the results of the computations are compared with recent experimental data obtained in a vacuum wind tunnel at the DLR in Gottingen, Germany. The present study considers Mach 8.89 nitrogen flow for a range of conditions that include Knudsen numbers of 0.016 to 3.505 for an incidence angle of 30 deg, and angles of incidence of 15 to 60 deg for a constant Knudsen number of 0.389. The calculations provide details concerning the flowfield structure and surface quantities. Comparisons between the calculations and the available experimental measurements are made for aerodynamic and overall heat-transfer coefficients and recovery temperature. The agreement between the measured and calculated data are very good, well within the estimated measurement uncertainty. Comparisons are also made with modified Newtonian and free-molecule theories.

Celenligil, M. C.↗
NASA NTRS1992

Conductive Bands Diminish Electrostatic Discharges

Electrostatic discharges on surfaces covered with electrically insulating paints reduced by connecting edges of painted surfaces to electrical grounds with band of conductive material. Prevents charge build up on paint which eventually arcs to conductive surface, damaging structures and equipment.

Leung, Philip L.↗
NASA NTRS1991

The application of differential roughness to mitigate friction and wear

By definition, differential roughness occurs where the surface roughness of one region is distinctly different from that of an adjacent region. Differential roughness may occur on a sliding surface when the structure of an area of the surface is modified relative to the original material. Differential roughness may be used to effect a film thickness change so as to cause hydrodynamic or hydrostatic lubrication effects just as if the surfaces were machined. The advantage of differential roughness is that the effective offset of film thickness continues to exist even if there is gross wear. One can effect film thickness changes which are smaller than can be made directly. Furthermore, asperity tip load support is the same over both the high roughness and small roughness regions. The potential uses for differential roughness are seals, bearings, and pumps. Some examples are presented.

Lebeck, Alan O.↗