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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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Splattered metal produced by welding can be easily removed from inaccessible areas by method resembling ball milling. Hard steel balls are vibrated inside welded unit so that they "scrub away" excess metal on interior side of weld joint.
Variations in the composition of the regolith due to irradiation by the solar wind are examined by categorizing the exposure history recorded in each sample. The history can be defined by two parameters: the duration of solar wind exposure (maturity) and a measure of how long the exposure took place (antiquity). Three partially successful methods for determining antiquity are described: the regolith contains small amounts of unsupported, trapped radiogenic noble gases, the most common being Ar-40. Assuming relatively prompt outgassing of the lunar interior, the amount of Ar-40 implanted per unit time should be proportional to the lunar content of K-40, and thus should have decayed exponentially over the lifetime of the moon. Normalization to constant exposure duration is achieved by taking the ratio Ar-40/Ar-36 in trapped gas, Ar-36 being an efficiently trapped solar wind species. The second method involves the interaction between galactic cosmic rays and lunar material producing certain spallogenic nuclides which may be analyzed in terms of a cosmic ray exposure age. The third method deals with the fact that there is a general tendency for depth within a core to be related to time deposition; two variants of this method are presented.
Bartky's method for the numerical evluation of integrals of the complete elliptic type is modified to improve its accuracy. The resulting modified method is then applied to integrals involving complex arithmetic which map the upper half of one plane onto either the interior or exterior of round-nosed wedges. These solutions have engineering applications to such problems as the design of magnets and the flow of fluids in and around corners.
The physics of the flow interaction between swirl and secondary flow was studied in duct bends relevant to the design of advanced aircraft nozzle systems. Both laminar and turbulent subsonic flows were investigated in generic duct bends for different amounts of swirl. The flow calculations are based on an economical three-dimensional spatial marching method employed in an existing computer code (PEPSIG). The computational method and code were extended to allow azimuthal periodicity and solutions in which the polar coordinate singularity occurs in the interior of the flow field. These extensions are needed to address swirling flow and twisted centerlines arising in out-of-plane bends. It was found that appropriate amounts of swirl can reduce total pressure loss relative to nonswirling cases. This conclusion was found to be insensitive to computational mesh.
A method for determining the turbulent diffusivity tensor is proposed which has application to problems such as the mixing in the interior of the sun for the solar neutrino problem, the chemical evolution of the galaxy, and grain sedimentation on the primitive solar nebula. A model for determining the turbulent energy spectral function, the eddy decorrelation rate, and the growth rate of the underlying instability is discussed. Good agreement is obtained between the present values for the coefficient of turbulent diffusivity and those obtained from both numerical simulation studies and laboratory data on shear turbulence.
A contact-less method for determining transport critical current density and flux penetration depth in bulk superconductor material. A compressor having a hollow interior and a plunger for selectively reducing the free space area for distribution of the magnetic flux therein are formed of superconductor material. Analytical relationships, based upon the critical state model, Maxwell's equations and geometrical relationships define transport critical current density and flux penetration depth in terms of the initial trapped magnetic flux density and the ratio between initial and final magnetic flux densities whereby data may be reliably determined by means of the simple test apparatus for evaluating the current density and flux penetration depth.
Modal testing of a vibro-acoustic test article referred to as the Aluminum Testbed Cylinder (ATC) has provided frequency response data for the development of validated numerical models of complex structures for interior noise prediction and control. The ATC is an all aluminum, ring and stringer stiffened cylinder, 12 feet in length and 4 feet in diameter. The cylinder was designed to represent typical aircraft construction. Modal tests were conducted for several different configurations of the cylinder assembly under ambient and pressurized conditions. The purpose of this paper is to present results from dynamic testing of different ATC configurations using two modal analysis software methods: Eigensystem Realization Algorithm (ERA) and MTS IDEAS Polyreference method. The paper compares results from the two analysis methods as well as the results from various test configurations. The effects of pressurization on the modal characteristics are discussed.
The research accomplished during this period is briefly summarized. The interior radiances within an optically deep absorbing medium scattering according to the Haze L phase function is discussed along with a method for calculating the radiance and color of the twilight sky. The application of the matrix operator method to calculations of radiance, polarization, and ellipticity of the radiation scattered from homogeneous layers scattering is reported. Reports, and publications are listed.
Two- and three-dimensional, viscous blunt body flows with planar impinging shocks are computed using an explicit, time-dependent, finite-difference method to solve the complete set of Navier-Stokes equations. The bow shock is treated as a discontinuity, while all interior shock layer detail such as shear layers, shock waves, jets and the wall boundary layer are automatically captured in the solution. Numerical results are presented for cases in which planar shock waves of different strengths and orientations are allowed to impinge on the flow field surroundings an infinite cylinder resulting in two- and three-dimensional shock interference patterns. The numerical results are compared with experiment.
A technique for noise calculation on the basis of vortex flow models is described. The 'reflection principle' is first extended to the whole class of potential flows which may be solved by the method of images. This allows the sound radiation to be computed solely through a volume integral over both the exterior and interior of any surfaces which may be present. The source distribution is then rewritten in terms of the vorticity within the flow which yields a highly computationally efficient formulation of the aeroacoustic theory. Several examples of such noise calculations are included.
A numerical solution of flow and heat transfer characteristics is obtained by the finite analytic method for a two dimensional laminar channel flow over a two-dimensional square cavity. The finite analytic method utilizes the local analytic solution in a small element of the problem region to form the algebraic equation relating an interior nodal value with its surrounding nodal values. Stable and rapidly converged solutions were obtained for Reynolds numbers ranging to 1000 and Prandtl number to 10. Streamfunction, vorticity and temperature profiles are solved. Local and mean Nusselt number are given. It is found that the separation streamlines between the cavity and channel flow are concave into the cavity at low Reynolds number and convex at high Reynolds number (Re greater than 100) and for square cavity the mean Nusselt number may be approximately correlated with Peclet number as Nu(m) = 0.365 Pe exp 0.2.
The variable solar magnetic activity known as the 11-year solar cycle has the longest history of solar observations. These cycles dramatically affect conditions in the heliosphere and the Earth's space environment. Our current understanding of the physical processes that make up global solar dynamics and the dynamo that generates the magnetic fields is sketchy, resulting in unrealistic descriptions in theoretical and numerical models of the solar cycles. The absence of long-term observations of solar interior dynamics and photospheric magnetic fields hinders development of accurate dynamo models and their calibration. In such situations, mathematical data assimilation methods provide an optimal approach for combining the available observational data and their uncertainties with theoretical models in order to estimate the state of the solar dynamo and predict future cycles. In this presentation, we will discuss the implementation and performance of an Ensemble Kalman Filter data assimilation method based on the Parker migratory dynamo model, complemented by the equation of magnetic helicity conservation and longterm sunspot data series. This approach has allowed us to reproduce the general properties of solar cycles and has already demonstrated a good predictive capability for the current cycle, 24. We will discuss further development of this approach, which includes a more sophisticated dynamo model, synoptic magnetogram data, and employs the DART Data Assimilation Research Testbed.
Volcanic surfaces are common and varied throughout the terrestrial planets. Remote spectroscopy is often the only method for determining surface chemistry and mineralogy of such provinces, and is thus critical for understanding petrologic processes and constraining planetary interior evolution and chemistry. Natural volcanic systems exhibit variability in magmatic chemical evolution, crystallinity, oxidation, and eruption-related alteration (e.g. hydrothermal). The extent to which spectroscopy can identify these characteristics alongside each other is thus a key question for interpreting volcanic processes from orbit. While the effects of each of these on visible/near infrared (VNIR) and thermal infrared (TIR) spectra of igneous rocks has been studied separately to varying degrees, their combined spectral effects (and interpretability of such spectra) are understudied.
Trends and transitions in the growing season MODerate resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) time-series at 250-m resolution were analyzed for the period from 2000 to 2018 to understand recent patterns of vegetation change in ecosystems of the Yukon River basin in interior Alaska. Statistical analysis of changes in the NDVI time series was conducted using the "Breaks for Additive Seasonal and Trend" method (BFAST). This structural change analysis indicated that NDVI breakpoints and negative 18-yr trends in vegetation greenness over the years since 2000 could be explained in large part by the impacts of severe wildfires, commonly affecting shrubland and forested ecosystems at relatively low elevations (< 300 m).
Techniques used to explain the nature of the optical effects of clouds on the light produced by lightning include a Monte Carlo simulation, an equivalent medium approach, and methods based on Boltzmann transport theory. A cuboidal cloud has been considered using transform methods and a diffusion approximation. Many simplifying assumptions have been used by authors to make this problem tractable. In this report, the cloud will have a spherical shape and its interior will consist of a uniform distribution of identical spherical water droplets. The source will be modeled as a Hertz dipole, electric or magnetic, inside or outside the cloud. An impulsive source is used. Superposition may be employed to obtain a sinusoid within an envelope which describes a lightning event. The problem is investigated by transforming to the frequency domain, obtaining Green's functions, and then using the Cagniard-DeHoop method to symbolically recover the time domain solution.
The noise effects programs objective is to develop aircraft noise criteria and noise reduction methods for achieving greater community and passenger acceptance of air transportation systems. The approach consists of laboratory tests to subjectively evaluate the properties of aircraft-generated noise that are responsible for causing annoyance and field surveys to study the broader problems of community and passenger acceptability. The program is organized into two major thrusts: community acceptance and passenger acceptance. The community acceptance includes subjective response studies of single and multiple aircraft overflights as well as longer term community noise exposure. Emphasis is on the development of units and indices which accurately quantify annoyance. The passenger acceptance program includes studies to determine acceptably levels of interior noise and vibration for speech intelligibility and comfort of crew and passengers. Selected results from several recent studies are presented to indicate the nature, scope, and methods of the research program.
Several studies relative to high pressure cosmochemistry of major planetary interiors are summarized. The behavior of gas-ice mixtures at very high pressures, studies of the phase diagram of (NH3) sub x (H2O) sub 1-x at pressures to 5GPa and temperatures from 240 to 370 K, single crystal growth of ammonia dihydrate at room temperature in order to determine their structures by x-ray diffraction, spectroscopy of chemical reactions during shock compression in order to evaluate how the reactions affect the interpretation of equation of state data obtained by shock methods, and temperature and x-ray diffraction measurements made on resistively heated wire in diamond anvil cells in order to obtain phase and structural data relevant to the interiors of terrestrial planets are among the studies discussed.
The comparative computational efficiencies of the finite element (FEM), boundary element (BEM), and hybrid boundary element-finite element (HBFEM) analysis techniques are evaluated for representative bounded domain interior and unbounded domain exterior problems in elastostatics. Computational efficiency is carefully defined in this study as the computer time required to attain a specified level of solution accuracy. The study found the FEM superior to the BEM for the interior problem, while the reverse was true for the exterior problem. The hybrid analysis technique was found to be comparable or superior to both the FEM and BEM for both the interior and exterior problems.