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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

An empirical analysis of the quantitative effect of data when fitting quadratic and cubic polynomials

A study is made of the extent to which the size of the sample affects the accuracy of a quadratic or a cubic polynomial approximation of an experimentally observed quantity, and the trend with regard to improvement in the accuracy of the approximation as a function of sample size is established. The task is made possible through a simulated analysis carried out by the Monte Carlo method in which data are simulated by using several transcendental or algebraic functions as models. Contaminated data of varying amounts are fitted to either quadratic or cubic polynomials, and the behavior of the mean-squared error of the residual variance is determined as a function of sample size. Results indicate that the effect of the size of the sample is significant only for relatively small sizes and diminishes drastically for moderate and large amounts of experimental data.

Canavos, G. C.↗
NASA NTRS1974

Ar-40/Ar-39 chronology and cosmic ray exposure ages of the Apollo 15 samples

The Ar-40*/Ar-39* thermal release patterns of igneous soil fragments, rake basalts, and large crystalline rocks are by and large well defined. Shock deformations of up to moderate intensities have no observable effects on the Ar-40*/Ar-39* release patterns. Neither do the Ar-40* diffusion losses have any relationship with the shock intensities. The peak of the magnetic activity in Palus Putredinis occurred at 3.33 plus or minus 0.02 Gy, lava flows continuing up to 3.13 Gy but at much reduced intensity. No correlation between the crystallization ages and the petrographic rock types was observed. The cosmic ray exposure gas indicate a mature regolith around the Hadley Rille-Apennine Front region. The exposure ages of the Apollo 15 samples cannot reliably be used to obtain the time of prominent cratering events at this site.

Husain, L.↗
NASA NTRS1974

Test results from the Langley high Reynolds number cryogenic transonic tunnel

NASA has recently developed and proof tested a pilot cryogenic transonic pressure tunnel. In addition to providing an attractive method for obtaining high Reynolds number results at moderate aerodynamic loadings and tunnel power, this unique facility enables the independent determination of the effects of Reynolds number, Mach number, and aeroelasticity. The proof-of-concept experimental and theoretical studies are briefly reviewed. Experimental results are included which indicate pressure distributions for a two-dimensional airfoil and strain-gage balance characteristics for a three-dimensional delta wing model.

Ray, E. J.↗
NASA NTRS1974

Strengthening silicon carbide by quenching

Quenching was used to form compressive surface layers in hot-pressed silicon carbide. The presence of the compressive stresses was verified by slotted rod tests. The slotted rod tip deflection was retained at temperatures to at least 1380 C, showing that the stresses are not relieved immediately at elevated temperatures. The flexural strength and impact resistance of specimens quenched from moderate temperatures (2000 C) were increased. Frequently, specimens quenched from higher temperatures were weakened by thermal shock damage.

Gruver, R. M.↗
NASA NTRS1974

Electron beam fluorescence system to measure gas density in impulse facilities

Very rapid measurements, ranging from a few microsecond to milliseconds in duration, characterize studies made in shock regions or behind them. A system to measure gas density under such conditions in a 15.24-cm (6-in.) expansion tube is described. The basic elements are an electron beam of moderate energy and high current capability, an optical detector, and the associated electronics and data readout equipment. A heated-cathode electron gun, capable of pulsed operation and delivering up to 200 milliamperes current, provides the source of electrons. Optics include a simple collector lens, aperture, collimator lens, filters, and a photomultiplier tube. The photomultiplier output signal was recorded by means of photographed oscilloscope traces for pulsed beam operation.

Hoppe, J. C.↗
NASA NTRS1974

Equatorial ionospheric absorption during half a solar cycle /1964-1970/

An extensive series of vertical incidence absorption measurements made at an equatorial station is analyzed in detail to provide information which will lead to a better understanding of the lower ionosphere. A quantitative empirical relationship is derived between absorption and 1-8 A solar flux for moderate levels of solar activity. It is shown that the threshold flux for D-region modification, at a solar zenith angle of 10 deg, is approximately 0.0005 erg per sq cm per sec. Attention is drawn to the incidence of days of high absorption even in the absence of solar X-ray activity. Available evidence points to variability of the order of 10-40 per cent in the intensity of the solar Lyman-alpha radiation as the most likely cause of these unusual, though infrequent, enhancements in absorption.

Gnanalingam, S.↗
NASA NTRS1974

Plasma wave turbulence at distant crossings of the plasma sheet boundaries and the neutral sheet

The orbit of IMP 7 frequently takes the spacecraft across the neutral sheet in the geomagnetic tail at a downstream distance of about 35 earth radii. This preliminary report discusses the detection of strong low-frequency electromagnetic signals and moderate electrostatic noise enhancements near local midnight. Data used were obtained during a substorm period on Oct. 28, 1972, when there were multiple crossings of the neutral sheet and the boundary of the plasma sheet.

Scarf, F. L.↗
NASA NTRS1974

The prebiotic synthesis of deoxythymidine oligonucleotides

Deoxythymidine 5 prime-triphosphate in the presence of deoxythymidine 5 prime-phosphate, cyanamide and 4-amino-5-imidazole carboxamide polymerizes under drying conditions at moderate temperatures (60 to 90 C) to yield oligonucleotides of up to four units in length. Enzymatic analysis indicated that the majority of these oligomers contained natural 3 prime-5 prime phosphodiester bonds. This reaction offers a possible method for the formation of deoxyoligonucleotides under primitive earth conditions.

Stephen-Sherwood, E.↗
NASA NTRS1975

Curable polyphosphazenes

Class of polyphosphazene polymers can be cured at moderate temperatures by action of moisture. In addition, polymers maintain flexibility when exposed to low temperatures.

Reynard, K. A.↗
NASA NTRS1974

Techniques for Improving the Stability of Soft Inplane Hingeless Rotors

The influence of basic parameters that govern flap lag stability of hingeless rotor blades in hover is reviewed, and potential methods are studied for improving the lead lag damping of soft inplane configurations for low thrust conditions. These conditions are relevant for ground and air resonance stability of coupled rotor body dynamic systems. Results indicate that the isolated rotor blade lead lag damping can be usefully increased by a combination of flap lag elastic coupling and pitch lag coupling. For a typical soft inplane configuration, 6% of critical damping can be obtained for moderate pitch lag coupling. For large values of the coupling parameters, the lead lag frequency is substantially reduced at high pitch angles and airfoil stall effects also reduce the lead lag damping.

Ormiston, R. A.↗
NASA NTRS1974

Heat pipe manufacturing study

Heat pipe manufacturing methods are examined with the goal of establishing cost effective procedures that will ultimately result in cheaper more reliable heat pipes. Those methods which are commonly used by all heat pipe manufacturers have been considered, including: (1) envelope and wick cleaning, (2) end closure and welding, (3) mechanical verification, (4) evacuation and charging, (5) working fluid purity, and (6) charge tube pinch off. The study is limited to moderate temperature aluminum and stainless steel heat pipes with ammonia, Freon-21 and methanol working fluids. Review and evaluation of available manufacturers techniques and procedures together with the results of specific manufacturing oriented tests have yielded a set of recommended cost-effective specifications which can be used by all manufacturers.

Edelstein, F.↗
NASA NTRS1974

Atmospheric response to variations in sea surface temperature

An extended range prediction experiment was performed with the GISS atmospheric model on a global data to test the sensitivity of the model to sea surface temperature (SST) variation over a two-week forecast period. The use of an initial observed SST field in place of the climatological monthly mean sea temperatures for surface flux calculations in the model was found to have a significant effect on the predicted precipitation over the ocean, with enhanced convection computed over areas where moderately large warm SST anomalies are found. However, there was no detectable positive effect of the SST anomaly field on forecast quality. The influence of the SST anomalies on the daily predicted fields of pressure and geopotential is relatively insignificant up to about one week compared with the growth of prediction error, and is no greater over a two-week period than that resulting from random errors in the initial meteorological state. The 14-day average fields of sea level pressure and 500-mb height predicted by the model, appear to be similarly insensitive to anomalies of sea surface temperature.

Spar, J.↗
NASA NTRS1974

Three-dimensional flow in transonic axial compressor blade rows

Recent developments in the three-dimensional aerodynamic theory of inviscid flow in transonic axial compressors are reviewed. Emphasis is placed on the newly completed lifting surface theory of a transonic ducted rotor. The relationship between the lifting surface theory and axisymmetric through-theories of turbomachines is illustrated; a few examples of the additional information obtainable from the new theory are then given. Quasi-two-dimensional cascade theory can also be extracted from the present analysis and the relevance of cascade theory to the actual three-dimensional problem assessed. Details are reported elsewhere, but some of the qualitative conclusions are discussed here. Even moderate departure from uniform spanwise loading of the rotor blades, for example, leads to a rather profound influence of the downstream wakes, suggesting the need for considerable care in applying cascade data on a direct quasi-two-dimensional basis.

Mccune, J. E.↗
NASA NTRS1974

Physical effects in cavitating flows

The microscopic and macroscopic aspects of the physical effects of cavitating flows are discussed. The microscopic features are related to the properties of nuclei in liquids and to the moderate tensile strengths which are usually encountered in flows. The macroscopic features are concerned with the growth of vapor or gaseous cavities from a small initial size and with their eventual collapse. Mathematical models are developed to analyze the characteristics of: (1) tensile strength in liquids, (2) growth of vapor bubbles, and (3) collapse of vapor bubbles.

Plesset, M. S.↗
NASA NTRS1974

Effect of treated length on performance of full scale turbofan inlet noise suppressors

Two inlet noise suppressors containing wall treatment plus three treated rings were tested on a fan in an outdoor noise facility. Sound power attenuations were measured for three treated lengths of each suppressor. The noise reduction from the segment of liner closest to the fan, which contained a segment of wall treatment downstream of the splitter rings, was greater than the reduction from either of the other segments. The decibel attenuations of the ringed liner segments were linear with liner length as predicted by theory. The acoustic attenuation of the wall treatment was considerably greater than expected for available theory. This inordinate effectiveness of the wall treatment strongly suggests the possibility of using no-ring inlet suppressors when the required noise reduction is moderate. The decibel attenuations were higher than predicted above 2000 hertz, and the two suppressors behaved similarly despite the prediction of different behavior.

Dittmar, J. H.↗
NASA NTRS1974

An experimental study of the effect of treated length on fan inlet noise suppressors

The effect of length of acoustic treatment was studied on a full scale fan using two different inlets. Analysis of the data revealed that measured suppression varied linearly with the length of the ringed liner segments as anticipated. Further analysis indicated that the wall only portion of the treatment was substantially more effective than anticipated, suggesting that, if only moderate suppression is needed, wall only treatment may suffice. The two inlets behaved similarly. Introduction of a hard exhaust splitter into the configuration resulted in a noise increase at certain frequencies.

Dittmar, J. H.↗
NASA NTRS1974

Reduction of acoustic disturbances in the test section of supersonic wind tunnels by laminarizing their nozzle and test section wall boundary layers by means of suction

The feasibility of quiet, suction laminarized, high Reynolds number (Re) supersonic wind tunnel nozzles was studied. According to nozzle wall boundary layer development and stability studies, relatively weak area suction can prevent amplified nozzle wall TS (Tollmien-Schlichting) boundary layer oscillations. Stronger suction is needed in and shortly upstream of the supersonic concave curvature nozzle area to avoid transition due to amplified TG (Taylor-Goertler) vortices. To control TG instability, moderately rapid and slow expansion nozzles require smaller total suction rates than rapid expansion nozzles, at the cost of larger nozzle length Re and increased TS disturbances. Test section mean flow irregularities can be minimized with suction through longitudinal or highly swept slots (swept behind local Mach cone) as well as finely perforated surfaces. Longitudinal slot suction is optimized when the suction-induced crossflow velocity increases linearly with surface distance from the slot attachment line toward the slot (through suitable slot geometry). Suction in supersonic blowdown tunnels may be operated by one or several individual vacuum spheres.

Pfenninger, W.↗
NASA NTRS1974

Nonlinear equations of motion for the elastic bending and torsion of twisted nonuniform rotor blades

The equations of motion are developed by two complementary methods, Hamilton's principle and the Newtonian method. The resulting equations are valid to second order for long, straight, slender, homogeneous, isotropic beams undergoing moderate displacements. The ordering scheme is based on the restriction that squares of the bending slopes, the torsion deformation, and the chord/radius and thickness/radius ratios are negligible with respect to unity. All remaining nonlinear terms are retained. The equations are valid for beams with mass centroid axis and area centroid (tension) axis offsets from the elastic axis, nonuniform mass and stiffness section properties, variable pretwist, and a small precone angle. The strain-displacement relations are developed from an exact transformation between the deformed and undeformed coordinate systems. These nonlinear relations form an important contribution to the final equations. Several nonlinear structural and inertial terms in the final equations are identified that can substantially influence the aeroelastic stability and response of hingeless helicopter rotor blades.

Hodges, D. H.↗