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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Elastic constants for superplastically formed/diffusion-bonded corrugated sandwich core

Formulas and associated graphs for evaluating the effective elastic constants for a superplastically formed/diffusion bonded (SPF/DB) corrugated sandwich core, are presented. A comparison of structural stiffnesses of the sandwich core and a honeycomb core under conditions of equal sandwich core density was made. The stiffness in the thickness direction of the optimum SPF/DB corrugated core (that is, triangular truss core) is lower than that of the honeycomb core, and that the former has higher transverse shear stiffness than the latter.

Ko, W. L.↗
NASA NTRS1980

Upper limits for the rate constant for the reaction Br + H2O2 yields HB2 + HO2

Upper limits for the rate constant for the reaction Br + H2O2 yields HBr + HO2 have been measured over the temperature range 298 to 417 K in a discharge flow system using a mass spectrometer as a detector. Results are k sub 1 less than 1.5 x 10 to the -15th power cu cm/s at 298 K and k sub 1 less than 3.0 x 10 to the -15th power cu cm/s at 417 K, respectively. The implication to stratospheric chemistry is discussed.

Leu, M.-T.↗
NASA NTRS1980

Solution of Euler's Equations of Motion and Eulerian Angles for near symmetric rigid bodies subject to constant moments

Analytic expressions are found for Euler's Equations of Motion and for the Eulerian Angles for both symmetric and near symmetric rigid bodies under the influence of arbitrary constant body-fixed torques. These solutions provide the body-fixed angular velocities and the attitude of the body, respectively, as functions of time. They are of special interest in applications to spinning spacecraft (such as the Galileo Spacecraft to be launched in 1984) because they include the effect of time-varying spin rate. Thus they can be applied to spin-up and spin-down maneuvers as well as to error analysis for thruster misalignments. The solutions are given for arbitrary initial conditions in terms of Fresnel, Sine and Cosine Integrals. Numerical integration of the governing differential equations has verified that the approximate analytic solutions are very accurate in many physical situations of interest.

Longuski, J. M.↗
NASA NTRS1981

On variable hydrostatic transmission for road vehicles, powered by supply of fluid at constant pressure

Various hydrostatic power transmission systems for automotive applications with power supply at constant pressure and unrestricted flow and with a Volvo Flygmotor variable displacement motor as the principal unit were investigated. Two most promising concepts were analyzed in detail and their main components optimized for minimum power loss at the EPA Urban Driving Cycle. The best fuel consumption is less than 10 lit. per 100 kM for a 1542 kG vehicle with a hydrostatic motor and a two speed gear box in series (braking power not recovered). Realistic system pressure affects the fuel consumption just slightly, but the package volume/weight drastically. Back pressure increases losses significantly. Special attention was paid to description of the behavior and modeling of the losses of variable displacement hydrostatic machines.

Magi, M.↗
NASA NTRS1980

Theoretical microwave spectral constants for C3H/+/ and C4H/+/

A number of linear conjugated carbon chain molecules have been observed in the interstellar gas. It has been suggested that ion molecule chemistry schemes may explain the formation of these compounds. In the present paper, theoretical bond lengths and rotation constants are obtained for C3H(+) and C4H(+). Calculations for C3 are used to assess the accuracy of the former. Recent results for C2H(+) are examined.

Wilson, S.↗
NASA NTRS1981

Comparison of radiative-convective models with constant and pressure-dependent lapse rates

One of the most commonly used models for studying climatic processes is the convective adjustment radiation model. In current radiation models, stable temperature profiles are maintained with a convective adjustment in which the temperature lapse rate is set equal to a critical lapse rate whenever the computed lapse rates exceed the critical value. First introduced by Manabe and Strickler (1964), a variety of convective adjustment models are now in use. It is pointed out that on a global scale, moist adiabatic processes, and thus moist adiabatic lapse rates, approximate the atmospheric temperature profile. Comparisons of profiles from a one-dimensional-radiative-convective model have been made using the conventional 6.5 K/km as the critical lapse rate and the pressure-dependent moist adiabatic lapse rates. For a clear sky and a single effective cloud the surface temperatures are 1 to 3 K higher with the constant 6.5 K/km critical lapse rate.

Hummel, J. R.↗
NASA NTRS1981

Analysis of the tensile stress-strain behavior of elastomers at constant strain rates. I - Criteria for separability of the time and strain effects

A theoretical analysis of the tensile stress-strain relation of elastomers at constant strain rate is presented which shows that the time and the stress effect are separable if the experimental time scale coincides with a segment of the relaxation modulus that can be described by a single power law. It is also shown that time-strain separability is valid if the strain function is linearly proportional to the Cauchy strain, and that when time-strain separability holds, two strain-dependent quantities can be obtained experimentally. In the case where time and strain effect are not separable, superposition can be achieved only by using temperature and strain-dependent shift factors.

Hong, S. D.↗
NASA NTRS1981

Radiation balances and the solar constant

The radiometric concepts are defined in order to consider various types of radiation balances and relate them to the diabetic form of the energy balance. Variability in space and time of the components of the radiation field are presented. A specific concept for sweeping which is tailored to the requirements is proposed. Finally, after establishing the truncated character of the present knowledge of the radiation balance. The results of the last observations of the solar constant are given. Ground and satellite measurement techniques are discussed.

Crommelynck, D.↗
NASA NTRS1981

Variations of the Solar Constant

The variations in data received from rocket-borne and balloon-borne instruments are discussed. Indirect techniques to measure and monitor the solar constant are presented. Emphasis is placed on the correlation of data from the Solar Maximum Mission and the Nimbus 7 satellites.

Sofia, S.↗
NASA NTRS1981

Change in the solar constant between 1968 and 1978

Solar irradiance measurements made from a balloon on January 27, 1978 and February 10, 1980 show a change of 0.4% over similar measurements made in 1968. This change is greater than the uncertainty of the measurement and is felt to be the result of a change in the solar constant.

Kosters, J. J.↗
NASA NTRS1982

Constant magnification optical tracking system

A constant magnification optical tracking system for continuously tracking of a moving object is described. In the tracking system, a traveling objective lens maintains a fixed relationship with an object to be optically tracked. The objective lens was chosen to provide a collimated light beam oriented in the direction of travel of the moving object. A reflective surface is attached to the traveling objective lens for reflecting an image of the moving object. The object to be tracked is a free-falling object which is located at the focal point of the objective lens for at least a portion of its free-fall path. A motor and control means is provided for mantaining the traveling objective lens in a fixed relationship relative to the free-falling object, thereby keeping the free-falling object at the focal point and centered on the axis of the traveling objective lens throughout its entire free-fall path.

Frazer, R. E.↗
NASA NTRS1982

Rate constant for the reaction NH2 + NO from 216 to 480 K

The absolute rate constant was measured by the technique of flash photolysis-laser induced fluorescence (FP-LIF). NH2 radicals were produced by the flash photolysis of ammonia and the fluorescent NH2 photons were measured by multiscaling techniques. At each temperature, the results were independent of variations in total pressure, and flash intensity. The results are compared with previous determinations using the techniques of mass spectrometry, absorption spectroscopy, laser absorption spectroscopy, and laser induced fluorescence. The implications of the results are discussed with regard to combustion, post combustion, and atmospheric chemistry. The results are also discussed theoretically.

Stief, L. J.↗
NASA NTRS1981

Absolute rate constant of the reaction OH + HO2 yields H2O + O2

The absolute rate constant of the reaction OH + HO2 yields H2O + O2 was determined by using the discharge-flow resonance fluorescence technique at 299 K and 1-torr total pressure. Pseudo-first-order conditions were used with HO2 concentrations in large excess over OH. Secondary reactions of atomic oxygen and atomic hydrogen were shown not to interfere under the conditions used. The result is (6.4 plus or minus 1.5) x 10 to the -11th cu cm/molecule s where the error limits are twice the standard deviation. The overall experimental error is estimated to be plus or minus 30%.

Keyser, L. F.↗
NASA NTRS1982

The /A 1 Sigma +/ - /X 1 Sigma +/ system of the isotopic lithium hydrides - The molecular constants, potential energy curves, and their adiabatic corrections

The molecular constants and their adiabatic corrections have been determined for the (A 1 Sigma +) - (X 1 Sigma +) system of the isotopic lithium hydrides: (Li-6)H, (Li-7)H, (Li-6)D, and (Li-7)D. Using a fully quantum mechanical variational method, the potential energy curves (IPA potentials) are determined. Extending the variational method, we have obtained for the first time adiabatic corrections of potential energy curves from isotopic spectroscopic data. A significant difference between the potential energy curves of the lithium hydrides and the lithium deuterides has been observed. When Li-6 was replaced by Li-7, a significant difference was only observed for the (A 1 Sigma +) state, but not for the (X 1 Sigma +) state.

Vidal, C. R.↗
NASA NTRS1983

Constant-temperature hot-wire anemometer practice in supersonic flows. I - The normal wire

The performance of a constant-temperature normal hot-wire in a supersonic flow is critically examined. It is shown that this instrument is inherently unsuitable for measuring turbulent temperature correlations because of the highly nonlinear response to temperature fluctuations, particularly at low overheat ratios. The instrument is therefore limited to measurements of mean and fluctuating mass-flow rates. Suitable calibration procedures, as well as the limits on spatial and temporal resolution are discussed, and corrections for mean stagnation temperature changes are suggested.

Smits, A. J.↗
NASA NTRS1983

Constant-temperature hot-wire anemometer practice in supersonic flows. II - The inclined wire

The performance of a constant-temperature inclined hot-wire in a supersonic flow is critically examined. It is shown that calibration techniques applicable to subsonic flow, such as the cosine cooling law cannot be used when the flow is supersonic. Calibration and measurement procedures appropriate to supersonic flow are suggested, together with the possible limits on their validity. Experimental results for different wires indicate that the sensitivities do not seem to depend on flow direction according to any simple correlation. When the sensitivity exhibits a strong dependence on flow direction, the wire should be discarded to avoid errors due to nonlinear effects.

Smits, A. J.↗
NASA NTRS1983

Relative rate constants for the reactions of atomic oxygen with HO2 anad OH radicals

Relative rate constants for the reactions O + HO2 - OH + O2 (1) and O + OH - H + O2 (2) were obtained by using the discharge-flow resonance fluorescence technique at 2 torr total pressure and 299 K. HO2 radicals were generated by reacting atomic hydrogen with an excess of O2. Quasi-steady-state concentrations of OH and HO2 were established in the presence of excess atomic oxygen. Observed concentration ratios, namely the ratio of the OH concentration to the HO2 concentration, resulted in a value of 1.7 + or 0.2 for k1/k2. The error limits are twice the standard deviation obtained from the data analysis. Overall experimental error is estimated to be + or - 25 percent. This result confirms earlier direct measurements of k1 and k2 which required knowledge of absolute radical or atomic oxygen concentrations.

Keyser, L. F.↗