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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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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

T RI M E ++: Multi-threaded triangular meshing in two dimensions

We present T RI M E ++, a multi-threaded software library designed for generating two-dimensional meshes for intricate geometric shapes using the Delaunay triangulation. Multi-threaded parallel computing is implemented throughout the meshing procedure, making it suitable for fast generation of large-scale meshes. Three iterative meshing algorithms are implemented: the DistMesh algorithm, the centroidal Voronoi diagram meshing, and a hybrid of the two. We compare the performance of the three meshing methods in T RI M E ++, and show that the hybrid method retains the advantages of the other two. The software library achieves significant parallel speedup when generating large-scale meshes containing between 10 4 to 10 7 points. T RI M E ++ can handle complicated geometries and generates adaptive meshes of high quality.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1975

Apparatus description and data analysis of a radiometric technique for measurements of spectral and total normal emittance

The development of a radiometric technique for determining the spectral and total normal emittance of materials heated to temperatures of 800, 1100, and 1300 K by direct comparison with National Bureau of Standards (NBS) reference specimens is discussed. Emittances are measured over the spectral range of 1 to 15 microns and are statistically compared with NBS reference specimens. Results are included for NBS reference specimens, Rene 41, alundum, zirconia, AISI type 321 stainless steel, nickel 201, and a space-shuttle reusable surface insulation.

Edwards, S. F.↗
NASA NTRS1989

Wentzel-Kramers-Brillouin method in the Bargmann representation

It is demonstrated that the Bargmann representation of quantum mechanics is ideally suited for semiclassical analysis, using as an example the WKB method applied to the bound-state problem in a single well of one degree of freedom. For the harmonic oscillator, this WKB method trivially gives the exact eigenfunctions in addition to the exact eigenvalues. For an anharmonic well, a self-consistent variational choice of the representation greatly improves the accuracy of the semiclassical ground state. Also, a simple change of scale illuminates the relationship of semiclassical versus linear perturbative expansions, allowing a variety of multidimensional extensions.

Voros, A.↗
NASA NTRS2016

Wave Telescope Technique for MMS Magnetometer

Multipoint measurements are a powerful method in studying wavefields in space plasmas.The wave telescope technique is tested against magnetic field fluctuations in the terrestrial magnetosheath measured by the four Magnetospheric Multiscale (MMS) spacecraft on a spatial scale of about 20 km.The dispersion relation diagram and the wave vector distribution are determined for the first time in the ion-kinetic range. Moreover, the dispersion relation diagram is determined in a proxy plasma restframe by regarding the low-frequency dispersion relation as a Doppler relation and compensating for the apparent phase velocity. Fluctuations are highly compressible, and the wave vectors have an angle of about 60 from the mean magnetic field. We interpret that the measured fluctuations represent akinetic-drift mirror mode in the magnetosheath which is dispersive and in a turbulent state accompanied by a sideband formation.

Magnetometer↗
NASA NTRS2016

Electron Scale Structures and Magnetic Reconnection Signatures in the Turbulent Magnetosheath

Collisionless space plasma turbulence can generate reconnecting thin current sheets as suggested by recent results of numerical magnetohydrodynamic simulations. The Magnetospheric Multiscale (MMS) mission provides the first serious opportunity to verify whether small ion-electron-scale reconnection, generated by turbulence, resembles the reconnection events frequently observed in the magnetotail or at the magnetopause. Here we investigate field and particle observations obtained by the MMS fleet in the turbulent terrestrial magnetosheath behind quasi-parallel bow shock geometry. We observe multiple small-scale current sheets during the event and present a detailed look of one of the detected structures. The emergence of thin current sheets can lead to electron scale structures. Within these structures, we see signatures of ion demagnetization, electron jets, electron heating, and agyrotropy suggesting that MMS spacecraft observe reconnection at these scales.

Yordanova, E.↗