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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Progressive impact cratering

Most cratering experiments are designed to study the effects of a single hypervelocity impact into a target of uniform properties. Experiments involving multiple impacts are usually limited to low velocity projectiles and unconsolidated target materials. Gault described saturation cratering in an unconsolidated target. Quaide and Oberbeck studied crater forms produced by hypervelocity impact into layered targets. Several investigators have modeled the generation of either a regolith or megaregolith by repeated impact on planetary surfaces. Studies now in progress examine changes in crater morphology and target properties by repeated impact into an initially consolidated target. Current studies employ low velocity projectiles (2 g at 0.5 km/sec) and consolidated salt targets. Records of crater size, morphology, and accumulated ejecta thickness are maintained as impacts collect on the surface.

Dehon, R. A.↗
NASA NTRS1983

Effects of wind on turbofan engines in outdoor static test stands

Wind can affect measured thrust and can cause turbofan engine speed to fluctuate during outdoor testing. Techniques used at an outdoor test stand at NASA Lewis Research Center to make testing easier and faster and to improve data repeatability include using an inflow control device (ICD) to make fan speed steadier, taking many raw data samples for better averaging, and correcting thrust for wind direction and speed. Data from engine tests are presented to show that the techniques improve repeatability of thrust and airflow measurements under various wind conditions. Previously announced in STAR as N83-34945

Mcardle, J. G.↗
NASA NTRS1983

Apparatus for continuous, fast, and precise measurements of position and velocity of a small spherical particle

The position and velocity of optically levitated glass spheres (radii 10-20 microns) movng in a gas are measured accurately, rapidly, and continuously using a high-speed rotating polygon mirror. The experimental technique developed here has repeatable position accuracies better than 20 microns. Each measurement takes less than 1 microsec and can be repeated every 100 microsec. The position of the levitated glass spheres can be manipulated accurately by modulating the laser power with an acoustic optic modulator. The technique provides a fast and accurate method to study general particle dynamics in a fluid.

Venkataraman, T. S.↗
NASA NTRS1984

Internal waves in the Gulf of California - Observations from a spaceborne radar

Pronounced signatures of internal waves were detected repeatedly in the Gulf of California by the Seasat synthetic aperture radar (SAR). A series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area. It was found that the number of observed wave groups was highly correlated with the strength of the local tides: the maximum number occurred during spring tides and the minimum number occurred during neap tides, indicating that the internal waves were tidally forced. Most of the wave activity was found to the north of 28 deg N where the tides were the strongest in the Gulf. The application of a simple, nonlinear internal wave model to the observations indicated that the peak-to-peak amplitude of the observed waves was about 50 m with an uncertainty of a factor of 2. The estimated upper bound for the rate of the loss of tidal energy to internal waves was about 5 x 10 to the 15th erg/s, representing only 10 percent of the rate of the dissipation of the dominant M2 tide in the Gulf.

Fu, L.-L.↗
NASA NTRS1984

One-impulse targeting strategy for longitudinal drift control of geosynchronous spacecraft subject to tesseral harmonics and luni-solar gravity perturbations

Kamel's (1973) East-West Stationkeeping Analysis is extended and an algorithm is presented that targets the geosynchronous spacecraft to the ideal initial conditions starting from any given relative longitude deviation within a given tolerance deadband in order to repeat the ideal longitudinal drift cycle that results in the longest possible period of time between maneuvers. The motion description takes into account the perturbations introduced by earth's tesseral harmonics and by the luni-solar gravity, assuming a near-circular orbit that requires only the control of orbital energy to repeat the ideal drift cycle via a single impulsive velocity change. The location of the maneuver along the orbit is such that the post-Delta-V eccentricity is always minimized.

Kechichian, J. A.↗
NASA NTRS1984

Altimetry, Orbits and Tides

The nature of the orbit error and its effect on the sea surface heights calculated with satellite altimetry are explained. The elementary concepts of celestial mechanics required to follow a general discussion of the problem are included. Consideration of errors in the orbits of satellites with precisely repeating ground tracks (SEASAT, TOPEX, ERS-1, POSEIDON, amongst past and future altimeter satellites) are detailed. The theoretical conclusions are illustrated with the numerical results of computer simulations. The nature of the errors in this type of orbits is such that this error can be filtered out by using height differences along repeating (overlapping) passes. This makes them particularly valuable for the study and monitoring of changes in the sea surface, such as tides. Elements of tidal theory, showing how these principles can be combined with those pertinent to the orbit error to make direct maps of the tides using altimetry are presented.

Colombo, O. L.↗
NASA NTRS1984

The capacity of digital links in tandem

The present investigation is concerned with the error control strategy used in connection with digital data networks, taking into account the capacity of the end-to-end channel. It is assumed that the only source of noise is Gaussian and that bandwidth limitation on capacity can be ignored. Attention is given to L links in tandem with binary repeaters, the asymptotic capacity with a large number of links, some alternative repeater strategies, and approaches for lowering the bit error probability. Numerical results are presented, taking into consideration capacity versus link error probability for various numbers of links.

Posner, E. C.↗
NASA NTRS1986

Laser Cutting of Thin Nickel Bellows

Laser cutting technique produces narrow, precise, fast, and repeatable cuts in thin nickel-allow bellows material. Laser cutting operation uses intense focused beam to melt material and assisting gas to force melted material through part thickness, creating void. When part rotated or moved longitudinally, melting and material removal continuous and creates narrow, fast, precise, and repeatable cut. Technique used to produce cuts of specified depths less than material thickness. Avoids distortion, dents, and nicks produced in delicate materials during lathe trimming operations, which require high cutting-tool pressure and holding-fixture forces.

Butler, C. L.↗
NASA NTRS1986

Continuous Removal of Coal-Gasification Residue

Continuous-flow hopper processes solid residue from coal gasification, converting it from ashes, cinders, and clinkers to particles size of sand granules. Unit does not require repeated depressurization of lockhopper to admit and release materials. Therefore consumes less energy. Because unit has no airlock valves opened and closed repeatedly on hot, abrasive particles, subjected to lesser wear. Coal-gasification residue flows slowly through pressure-letdown device. Material enters and leaves continuously. Cleanout door on each pressure-letdown chamber allows access for maintenance and emergencies.

Collins, Earl R., Jr.↗
NASA NTRS1986

Improved Orifice Plate for Spray Gun

Erratic spray pattern of commercial spray gun changed to repeatable one by simple redesign of two parts. In modified spray gun orifice plate and polytetrafluoroethylene bushing redesigned to assure centering and alignment with nozzle. Such improvement useful in many industrial applications requiring repeatable spray patterns. Might include spraying of foam insulation, paint, other protective coatings, detergents, abrasives, adhesives, process chemicals, or fuels. Unmodified spray gun produces erratic spray because lateral misalignment between orifice plate and nozzle.

Cunningham, W.↗
NASA NTRS1986

Evaluation of a standard test method for total hemispherical emittance of surfaces from 293K to 1673K

Emittance tests were made on samples of Rene' 41, Haynes 188, and Inconel 625 superalloy metals in an evaluation of a standard test method for determining total hemispherical emittances of surfaces from 293 K to 1673 K. The intent of this evaluation was to address any problems encountered, check repeatability of measured emittances, and gain experience in use of the test procedure. Five test specimens were fabricated to prescribe test dimensions and surfaces cleaned of oil and residue. Three of these specimens were without oxidized surfaces and two with oxidized surfaces. The oxidized specimens were Rene' 41 and Haynes 188. The tests were conducted in a vacuum where the samples were resistance-heated to various temperature levels ranging from 503 K to 1293 K. The calculated results for emittance, in the worst case, were repeatable to a maximum spread to + or - 4% from the mean of five sets of plotted data for each specimen.

Compton, E. C.↗
NASA NTRS1986

Linearized traveling wave amplifier with hard limiter characteristics

A dynamic velocity taper is provided for a traveling wave tube with increased linearity to avoid intermodulation of signals being amplified. In a traveling wave tube, the slow wave structure is a helix including a sever. A dynamic velocity taper is provided by gradually reducing the spacing between the repeating elements of the slow wave structure which are the windings of the helix. The reduction which takes place coincides with the ouput point of helix. The spacing between the repeating elements of the slow wave structure is ideally at an exponential rate because the curve increases the point of maximum efficiency and power, at an exponential rate. A coupled cavity traveling wave tube having cavities is shown. The space between apertured discs is gradually reduced from 0.1% to 5% at an exponential rate. Output power (or efficiency) versus input power for a commercial tube is shown.

Kosmahl, H. G.↗
NASA NTRS1985

Mesospheric winds observed by the Kyoto meteor radar

The Kyoto meteor radar has been operated almost continuously from May 1983. By using a large amount of radar data, seasonal variations of mean winds, planetary waves and atmospheric tides can be delinated. Seasonal and latitudinal variation of tidally corrected mean winds including Kyoto observations have been examined in comparison with the CIRA 1972 model. A power spectral density of the zonal wind field for 60 days of data is formed from an autocorrelation function with a maximum time lag of 30 days. A quasi-2-day oscillation was evident in the period from June to September, and seems to be repeated in 1983 and 1983. It had large amplitudes in June and July and became weak in August; then it was again amplified in September. In summer months, the period of the wave was indicated as 2.2 days, and it became shorter in September. At Kyoto (35 deg N), the diurnal tide is the main component of atmospheric tides. The monthly mean amplitude of the eastward component of diurnal tide is plotted for the period from May 1983 to September 1984. It was clearly amplified in summer months at around 92 to 96 km altitudes. This feature was repeated in two successive years except for the maximum amplitude which exceeded 40 m/sec and 30 m/sec in 1983 and 1984, respectively.

Tsuda, T.↗
NASA NTRS1986

Time-domain sensitivity enhancement in pulsed Pb-TDL gas monitors

A Pb-salt tunable diode laser (TDL) has found many applications in the field of atmospheric gas analysis. Its continuous tunablility and fine spectral purity in the mid infrared region are outstanding from other lasers. The only shortcoming is that it requires cryogenic operating temperatures, though, it is improved year by year towards the room temperature operation. A repeated pulse operation of Pb salt diode lasers is possible with a thermoelectric cooling device, which allows an instrument a portable geometry disusing a heavy, bulky and power consuming mechanical refrigerator. A derivative spectrometry was exploiting the quick tunability of Pb salt diode lasers, though they are continuous wave (cw) operated with refrigerator or liquid nitrogen so far. A new system for derivative spectrometry with a pulsed diode laser will extend its field of applications because of reduced weights and size of measuring instruments. A preliminary results is shown that demonstrates the feasibility of an attempt to implement the derivative spectrmetry with repeatedly pulse driven diode lasers. Atmospheric methane was measured with 8 ppm/m sensitivity. Further results of parametric optimization for the best signal to noise ratios under any given device characteristics as well as for available real devices is given.

Koga, R.↗
NASA NTRS1986

Multi-path peristaltic pump

The instant invention is directed to a peristaltic pump for critical laboratory or hospital applications requiring precise flow rates over an extended period of time. Within the cylindrical barrel pump housing is a single-piece, molded, elastometric, cylindrical liner with a multiplicity of flattened helical channels created therein from one end of the liner to the other. Three cylindrical rollers rotate about the center axis of the pump around the inside surface of the liner selectively compressing the liner, and hence the helical channels between the rollers and the barrel housing, creating a pumping action by forcing trapped fluid in the helical channels axially from one end of the liner to the opposite end. The novelty of the invention appears to lie in the provision of the special liner with multiple helical channels as the pumping chamber, rather than the standard single elastomeric tubing which is squeezed repeatedly by rollers to move the liquid through a typical peristaltic pump. Large, repeated deflections on the standard tubing causes a permanent set in the tubing, thus either changing the flow rate, or requiring a new section of tubing to be positioned in the pump head. Further, this configuration minimizes the amount of outflow pulsation which is characteristic of a typical single tubing peristaltic pump.

Chandler, Joseph A.↗
NASA NTRS1987

On the eigenvalue and eigenvector derivatives of a general matrix

The existence of differentiable eigenvalues and eigenvectors for a general matrix is addressed. The eigenspace which contains differentiable eigenvectors is determined and computed by using the concept of subspace intersection in conjunction with the singular value decomposition algorithm. The differentiable eigenvectors associated with repeated eigenvalues should be simultaneously the eigenvectors of the general matrix and its corresponding sensitivity matrix. Furthermore, the derivatives for differentiable eigenvectors associated with repeated eigenvalues can be computed using higher order derivatives of the matrix, whereas the corresponding eigenvalue derivatives are the eigenvalues of the sensitivity matrix.

Juang, Jer-Nan↗
NASA NTRS1986

Observations of fatigue crack growth rate and closure behavior in 7475-T731 aluminum under variable amplitude loading

Simultaneous measures of fatigue crack propagation rate and crack closure were taken from 7475-T731 aluminum alloy center cracked tensile specimens under variable amplitude loading conditions. Results indicate the presence of load interaction in a variety of repeated variable amplitude loading blocks. Load interaction results in retardation of the propagation rate for most loading blocks examined in the study. Closure did not explain observed delay behavior associated with high stress ratio and single peak overloads. Primary influences on the crack opening stress intensity level include the maximum stress intensity of the repeated loading block, the minimum stress intensity of the block, and the number of fatigue cycles between overloads of the block.

Turner, Charles C.↗
NASA NTRS1987

Semi-2-interpenetrating networks of high temperature systems

A semi-2-interpenetrating network of improved qualities which is prepared by combining a linear polymer and a cross-linkable oligomer having identical repeating units is developed. Polymers have been combined in the past into interpenetrating networks in order to gain useful properties from the combination of materials. However, previous semi-interpenetrating networks have only been formed using polymers having different repeating units. This method provides a semi-2-interpenetrating network of improved strength, adhesion, and processability.

Egli, Annmarie O.↗