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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Upper Atmosphere Research Satellite attitude disturbances during shadow entry and exit

The Upper Atmosphere Research Satellite (UARS), as with the Landsat-4 and Landsat-5 spacecraft, experiences large attitude disturbances when entering and exiting the Earth's shadow. Previous investigations have provided some evidence linking these disturbances to rapid bending of the solar array but have also raised questions. For example, the magnitudes of the roll attitude disturbances have shown an unmolested asymmetry, and the timing of the disturbances at sunrise appears to disagree with the modeled timing. A better understanding of this phenomenon is important in assessing the implications for UARS science gathering and for future mission design analysis. To this end, UARS attitude, sensor, and actuator data are used to evaluate the disturbances as they vary with solar beta angle and solar array drive angle. The attitude data are examined during specific periods of interest, such as the month in which the solar array was parked in its high-noon position, and are also tracked from the beginning of the mission to determine any trends that may result from changing mass properties due to cryogen boiloff and propellant usage. Attitude rate and torque profiles are derived from inertial reference until data and related to the disturbances seen in the attitude data. The timing of the disturbances with respect to spacecraft sunset and sunrise is characterized to allow event predictions. Stability during the disturbances is discussed in terms of science instrument requirements. Finally, the results are compared with the behavior predicted by models that are based on solar array bending.

Lambertson, M.↗
NASA NTRS2014

Multi-Scale Computational Modeling of Two-Phased Metal Using GMC Method

A multi-scale computational model for determining plastic behavior in two-phased CMSX-4 Ni-based superalloys is developed on a finite element analysis (FEA) framework employing crystal plasticity constitutive model that can capture the microstructural scale stress field. The generalized method of cells (GMC) micromechanics model is used for homogenizing the local field quantities. At first, GMC as stand-alone is validated by analyzing a repeating unit cell (RUC) as a two-phased sample with 72.9% volume fraction of gamma'-precipitate in the gamma-matrix phase and comparing the results with those predicted by finite element analysis (FEA) models incorporating the same crystal plasticity constitutive model. The global stress-strain behavior and the local field quantity distributions predicted by GMC demonstrated good agreement with FEA. High computational saving, at the expense of some accuracy in the components of local tensor field quantities, was obtained with GMC. Finally, the capability of the developed multi-scale model linking FEA and GMC to solve real life sized structures is demonstrated by analyzing an engine disc component and determining the microstructural scale details of the field quantities.

nickel alloys↗
NASA NTRS1992

Reasoning about energy in qualitative simulation

While possible behaviors of a mechanism that are consistent with an incomplete state of knowledge can be predicted through qualitative modeling and simulation, spurious behaviors corresponding to no solution of any ordinary differential equation consistent with the model may be generated. The present method for energy-related reasoning eliminates an important source of spurious behaviors, as demonstrated by its application to a nonlinear, proportional-integral controlled. It is shown that such qualitative properties of such a system as stability and zero-offset control are captured by the simulation.

Fouche, Pierre↗
NASA NTRSDate not supplied

Testing of ACC-6 Carbon-Carbon at High Strain Rates and High Temperatures

Some materials, such as steel, titanium, and tungsten, have a yield stress that depends on the strain rate, and actually are stronger at high rates of load or deformation. The increase in strength is relevant; and if not taken into account, the computer models will not match the experimental behavior observed in typical shock loading, ordnance, or ballistic tests. For higher velocity (hypervelocity impacts), an equation of state that accounts for non-linearities and temperature in the pressure-volume relation, may also be needed. This rate-dependent behavior of the strength has also been observed in some composite materials. Southwest Research Institute® (SwRI®) has started an internal research effort to measure and better model the behavior of materials, in particular carbon/carbon composites like ACC-6, at ultra-high temperatures for both static and high rates of deformation. The ultimate objective is to obtain reliable computer models of carbon/carbon material under hypersonic flight conditions, hypervelocity impacts, shock-loading situations such as booster-vehicle separation, and munition operation events. SwRI® has successfully modeled in the past ballistic impact on other composites, namely S-2 glass/epoxy, Kevlar/resin, polyethylene fibers/resin, and carbon fiber composites. This presentation will show test results relevant to the strength properties of the ACC-6 C/C material which were measured at quasistatic, medium, and the moderately high strain rates (~103 s—1) achievable in a conventional Split Hopkinson bar apparatus. Some of the tests were performed at both high-rates and high temperatures typical of hypersonic flight, something that, to the authors’ knowledge, has never been published in the past for this particular material. The test method will be presented, as well as the comparison of the stress-strain curves for the different temperatures and strain-rates of interest. A discussion of how the results can be used in the typical hydrocodes of interest will be included.

carbon/carbon↗
NASA NTRS1992

The viscoelastic characterization of polymer materials exposed to the low-Earth orbit environment

Recent accomplishments in our research efforts have included the successful measurement of the thermal mechanical properties of polymer materials exposed to the low-earth orbit environment. In particular, viscoelastic properties were recorded using the Rheometrics Solids Analyzer (RSA 2). Dynamic moduli (E', the storage component of the elastic modulus, and E'', the loss component of the elastic modulus) were recorded over three decades of frequency (0.1 to 100 rad/sec) for temperatures ranging from -150 to 150 C. Although this temperature range extends beyond the typical use range of the materials, measurements in this region are necessary in the development of complete viscoelastic constitutive models. The experimental results were used to provide the stress relaxation and creep compliance performance characteristics through viscoelastic correspondence principles. Our results quantify the differences between exposed and control polymer specimens. The characterization is specifically designed to elucidate a constitutive model that accurately predicts the change in behavior of these materials due to exposure. The constitutive model for viscoelastic behavior reflects the level of strain, the rate of strain, and the history of strain as well as the thermal history of the material.

Strganac, Thomas↗
NASA NTRS1997

Isolated Fluid Oxygen Drop Behavior in Fluid Hydrogen at Rocket Chamber Pressures

A model has been developed for the behavior of an isolated fluid drop of a single compound immersed into another compound in finite, quiescent surroundings at supercritical conditions. The model is based upon fluctuation theory which accounts for both Soret and Dufour effects in the calculation of the transport matrix relating molar and heat fluxes to the transport properties and the thermodynamic variables.

Fluid↗
NASA NTRS1973

Pollution monitoring in Lake Champlain using ERTS-1 imagery

The author has identified the following significant results. Band 4 imagery of April 7 and 25 show contrasting pollution effects due to seasonal and discharge variations. The pollution plume emanating from the International Paper Co. mill just north of Fort Ticonderoga was first detected on October 10 ERTS-1 imagery and now has been documented during spring high lake level conditions. The plume was observed extending further to the north and east than under low water conditions of October 10. This northward extension reflects a stronger northward current flow expected in the turbid southern leg of Lake Champlain. The extensive plume of April 25 represents full plant operation while the April 5 scene shows some plume traces directly over the submerged diffuser, discharge pipe representing minimal discharge during weekend plant operation. The ERTS-1 documentation will be used in developing a model of plume behavior under varying environmental conditions and will hopefully serve to assist in a major resource decision pending at U.S. Supreme Court level.

Lind, A. O.↗
NASA NTRS1973

Gravity-gradient dynamics experiments performed in orbit utilizing the Radio Astronomy Explorer (RAE-1) spacecraft

Six dynamic experiments were performed in earth orbit utilizing the RAE spacecraft in order to test the accuracy of the mathematical model of RAE dynamics. The spacecraft consisted of four flexible antenna booms, mounted on a rigid cylindrical spacecraft hub at center, for measuring radio emissions from extraterrestrial sources. Attitude control of the gravity stabilized spacecraft was tested by using damper clamping, single lower leading boom operations, and double lower boom operations. Results and conclusions of the in-orbit dynamic experiments proved the accuracy of the analytic techniques used to model RAE dynamical behavior.

Walden, H.↗
NASA NTRS1973

Solar wind and substorm-related changes in the lobes of the geomagnetic tail

The relationship of the geomagnetic tail lobe energy density to solar wind dynamic pressure, the north-south component of the interplanetary magnetic field, and substorm expansion onsets is investigated. Enhanced lobe energy densities are observed to follow both southward turnings of the interplanetary magnetic field and solar wind dynamic pressure increases. An empirical relationship is developed relating the tail lobe magnetic energy density to the solar wind dynamic pressure by using data obtained when the interplanetary field was northward. Localized, off-center, or multiple-onset substorm expansion phases are shown to have little effect on the lobe magnetic field. A positive correlation is found between magnetosphere-wide substorm expansions and decreases in the lobe energy density. The positive correlation of the energy density with both the solar wind dynamic pressure and a southward interplanetary magnetic field and the positive correlation between magnetospheric substorm activity and lobe energy density decreases are demonstrated to be consistent with a phenomenological model of substorm behavior.

Caan, M. N.↗