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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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Fluid dynamical analysis for idealized reactors system with spherical symmetry determines the effect which the destructive component of a nuclear accident produces on primary containment structures. Steel strands surrounding the reactor cavity in the biological shield exhibit plastic deformation to achieve the energy absorption.
Confirmation of Barston's (1964) conclusions regarding the underlying mechanism of the Herlofson paradox by examining in detail several analytically tractable cases of delta-function and sinusoidal excitation. The effects of collisions and nonzero electron temperature in determining the steady state fields and dissipation are considered. Energy absorption without dissipation in plasmas is shown to be analogous to that occurring after application of a signal to a network of lossless resonant circuits. This analogy is pursued and is extended to cover Landau damping in a warm homogeneous plasma in which the resonating elements are the electron streams making up the velocity distribution. Some of the practical consequences of resonant absorption are discussed, together with a number of paradoxical plasma phenomena which can also be elucidated by considering a superposition of normal modes rather than a single Fourier component.
During the past thirty years, a tremendous amount of research was done on the development of crazing in polymers. The phenomenon of crazing was recognized as an unusual deformation behavior associated with a process of molecular orientation in a solid to resist failure. The craze absorbs a fairly large amount of energy during the crazing process. When a craze does occur the surrounding bulk material is usually stretched to several hundred percent of its original dimension and creates a new phase. The total energy absorbed by a craze during the crazing process in creep was calculated analytically with the help of some experimental measurements. A comparison of the energy absorption by the new phase and that by the original bulk uncrazed medium is made.
Materials to absorb impact energy of spacecraft during landing
Energy absorbing characteristics of crushable aluminum structures in space environment
Casting and compression testing of cellular aluminum alloys for applications requiring kinetic energy dissipation
Variable energy gamma ray production, neutron sources, and scintillation dosimeters
The forward and vertical impact stability of a composite honeycomb Deployable Energy Absorber (DEA) was evaluated during a full-scale crash test of an MD-500 helicopter at NASA Langley?s Landing and Impact Research Facility. The lower skin of the helicopter was retrofitted with DEA components to protect the airframe subfloor upon impact and to mitigate loads transmitted to Anthropomorphic Test Device (ATD) occupants. To facilitate the design of the DEA for this test, an analytical study was conducted using LS-DYNA(Registered TradeMark) to evaluate the performance of a shell-based DEA incorporating different angular cell orientations as well as simultaneous vertical and forward impact conditions. By conducting this study, guidance was provided in obtaining an optimum design for the DEA that would dissipate the kinetic energy of the airframe while maintaining forward and vertical impact stability.
Forty-one composite aircraft subfloor intersection specimens were tested to determine the effects of geometry and material on the energy absorbing behavior, failure characteristics, and post-crush structural integrity of the specimens. The intersections were constructed of twelve ply + or - 45 sub 6 laminates of either Kevlar 49/934 or AS-4/934 graphite-epoxy in heights of 4, 8, and 12 inches. The geometry of the specimens varied in the designs of the intersection attachment angle. Four different geometries were tested.
As a precursor to future manned missions to the moon, an inexpensive, unmanned vehicle that could carry small, scientific payloads to the lunar surface was studied by NASA. The vehicle, called the Common Lunar Lander, required extremely optimized structural systems to increase the potential payload mass. A lightweight energy-absorbing system (LAGFEAS), which also acts as a landing load-limiter was designed to help achieve this optimized structure. Since the versatile and easily tailored system is a load-limiter, it allowed for the structure to be designed independently of the ever-changing landing energy predictions. This paper describes the LAGFEAS system and preliminary verification testing performed at NASA's Johnson Space Center for the Common Lunar Lander program.
Time-dependent density functional theory (TDDFT) combined with range-separated hybrid (RSH) functionals and a tuned range-separation parameter γ offers a computationally economical approach for high-throughput excited- state property predictions. The γ-tuning procedure in the gas phase is well established. However, no agreement on the best γ- tuning procedure has been made when considering the solvent effect with implicit solvent models like the polarizable continuum model (PCM). To answer that question, this study created a diverse dataset with 937 molecules with experimental solutionphase UV/vis absorption spectra. Three γ-tuning methods, the gasphase γ-tuning (GPγT), the partial vertical γ-tuning (PVγT), and the strict vertical γ-tuning (SVγT), were evaluated for the ωPBEh functional over the entire dataset. Additional benchmarks are done for the optimally tuned screened range-separated hybrid combined with the PCM approach (SRSH-PCM) and the solvation-mediated tuning procedure (sol-med-OT). Our findings revealed that the optimal γ-values obtained by the PVγT and the SVγT are significantly smaller than the GPγT. This trend holds consistently across all molecules in our dataset, and we explained the origin of this phenomenon. TDDFT calculations with PVγTand SVγT-tuned γ-values and default global Fock exchange fraction achieve superior performance compared to those using GPγTtuned or default γ and slightly outperform SRSH-PCM and sol-med-OT with similar or lesser computational cost. Furthermore, we found that the smaller γ-values from SVγT captured the expected 1/(εR) asymptotic behavior in the solution phase, resulting in accurate prediction of solution-phase CT excitations, consistent with the screened asymptote behavior encoded in SRSH-PCM. These results show that SVγT is the best scheme for high-throughput UV/vis absorption spectrum calculations using the ωPBEh functional from a data-driven perspective.
Heat transfer in stagnation-point laminar boundary layer with mass injection and absorption of incident radiation
Measurement of radiation dosage from spatial gamma rays
Reimaging system efficiently uses incident light and overcomes previous imaging detector problems. Optical system collects reflected and focal plane transmitted light and redirects it so it again impinges on focal plane in register with original image. Reimaging unabsorbed light increases light absorption and detector use probability.
The stress distributions around individual fibers in a unidirectional boron/aluminum composite material subjected to axial and transverse loadings are being studied utilizing a generalized plane strain finite element analysis. This micromechanics analysis was modified to permit the analysis of longitudinal sections, and also to incorporate crack initiation and propagation. The analysis fully models the elastoplastic response of the aluminum matrix, as well as temperature dependent material properties and thermal stress effects. The micromechanics analysis modifications are described, and numerical results are given for both longitudinal and transverse models loaded into the inelastic range, to first failure. Included are initially cracked fiber models.
The crack initiation and crack propagation capability was extended to the previously developed generalized plane strain, finite element micromechanics analysis. Also, an axisymmetric analysis was developed, which contains all of the general features of the plane analysis, including elastoplastic material behavior, temperature-dependent material properties, and crack propagation. These analyses were used to generate various example problems demonstrating the inelastic response of, and crack initiation and propagation in, a boron/aluminum composite.
Results of experiments designed to demonstrate spectrally selective absorption in dielectric waveguides on semiconductor substrates are reported. These experiments were conducted with three waveguides formed by sputtering films of PSK2 glass onto silicon-oxide layers grown on silicon substrates. The three waveguide samples were studied at 633 and 532 nm. The samples differed only in the thickness of the silicon-oxide layer, specifically 256 nm, 506 nm, and 740 nm. Agreement between theoretical predictions and measurements of propagation constants (mode angles) of the six or seven modes supported by these samples was excellent. However, the loss measurements were inconclusive because of high scattering losses in the structures fabricated (in excess of 10 dB/cm). Theoretical calculations indicated that the power distribution among all the modes supported by these structures will reach its steady state value after a propagation length of only 1 mm. Accordingly, the measured loss rates were found to be almost independent of which mode was initially excited. The excellent agreement between theory and experiment leads to the conclusion that low loss waveguides confirm the predicted loss rates.
Simplified procedures for determining the qualitative effect a variable has on structural response of a composite tube are very useful in both preliminary design as well as in providing insight into the general response. An analysis procedure is presented that can be used to determine the qualitative change in the sustained crushing load due to a change in specimen material properties or geometry. The analysis procedure is similar in form to the equation for the buckling load of a column on an elastic foundation.