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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Dynamic behavior of the Bering Glacier-Bagley icefield system during a surge, and other measurements of Alaskan glaciers with ERS SAR imagery

ERS-1 synthetic aperture radar (SAR) imagery was employed for the measurement of the dynamics of the Bagley icefield during a major surge in 1993-1994, the measurement of ice velocities on the Malaspina piedmont glacier during a quiescent phase between surges, and for mapping the snow lines and the position of the terminus of Nabesna glacier on Mount Wrangell (a 4317 m andesitic shield volcano) in the heavily glacierized Saint Elias and Wrangell Mountains of Alaska. An overview and summary of results is given. The methods used include interferometry, cross-correlation of sequential images, and digitization of boundaries using terrain-corrected SAR imagery.

Lingle, Craig S.↗
NASA NTRS1998

Measurement of Interfacial Undercooling in a Dilute Pb-Sn Alloy Near the Regime of Morphological Instability

The solid/liquid (s/1) interfacial Seebeck technique was used to measure interfacial undercooling in a Pb-1 wt.% Sn alloy. For plane front solidification an undercooling in the range of 0.54-0.57C was recorded. However, for growth velocities between 6 to 15 micron/s the undercooling, increased with increase in velocity. 'Tbis is in contradiction to the theoretical predictions based on growth at the extremum condition. A modified analytical expression was developed based on the maro,,inal stability criterion to predict undercooling for growth velocities immediately over the limit of morphological stability. Between 6 to 15 microns/s the trend predicted by this modified expression is in qualitative agreement with the experimental results. This model is more consistent with the analysis of Venugopal and Kirkaldy which states that the extremum condition criterion is not applicable in the marginal stability regime. At higher growth velocities between 20 and 50 microns/s where stable cellular growth is expected the undercooling, decreased with increase in velocity. The predictions of Burden and Hunt based on extremum criterion agree reasonably well with the experimental results in this velocity range. Finally, the importance of non-equilibrium phase diagram parameters such as partition coefficient and liquidus slope were also evaluated using the experimental undercooling results obtained in this investigation.

Sen, S.↗
NASA NTRS2000

Differential Phase Mode with the Keck Interferometer

We describe the differential phase mode of the Keck Interferometer. The scientific goal of this mode is the direct detection and spectroscopic characterization of hot, Jupiter mass planets. We describe the differential phase effect, the basic observational mode, and the expected differential phase signatures for the extrasolar planets discovered through radial velocity searches.

Akeson, Rachel↗
NASA NTRS1997

The Onset of the Madden-Julian Oscillation Within an Aquaplanet Model

A series of numerical experiments using a two-level atmospheric general circulation model (AGCM) were performed for the purpose of investigating the coupling between sea surface temperature (SST) profile and the onset of the Madden-Julian Oscillation (MJO). The AGCM was modified to run as an aquaplane with all seasonal forcing removed. SST distributions based on the New Global Sea-Ice and Sea Surface Temperature (GISST) Data Set for 1903-1994 were generated then modified to vary the north-south gradient and tropical temperatures. It was found that the MJO signal did not depend on the SST temperature gradients but rather on the absolute temperature of the equatorial region, EOF analysis revealed that the SST distribution which generated the strongest MJO signal produced a periodic fluctuation in velocity potential at the 250 millibar level with a phase speed of 15 m/s, and a periodicity of 30 days which falls within the shortest limit of observed oscillations. This distribution also possessed the coolest equatorial SSTs which suggests that increased stability in the atmosphere favors the occurrence of organized MJO propagation.

Colon, Edward↗
NASA NTRS2003

Planar Particle Imaging and Doppler Velocimetry System and Method

A planar velocity measurement system (100) is operative to measure all three velocity components of a flowing fluid (106) across an illuminated plane (108) using only a single line of sight. The fluid flow is seeded with small particles which accurately follow the flow field fluctuations. The seeded flow field is illuminated with pulsed laser light source (102) and the positions of the particles in the flow are recorded on CCD cameras (122,124). The in-plane velocities are measured by determining the in-plane particle displacements. The out-of-plane velocity component is determined by measuring the Doppler shift of the light scattered by the particles. Both gas and liquid velocities can be measured, as well as two-phase flows.

Wernet, Mark P.↗
NASA NTRS2020

Motivations and Preliminary Design for Mid-Air Deployment of a Science Rotorcraft on Mars

Mid-Air Deployment (MAD) of a rotorcraft during Entry, Descent and Landing (EDL) on Mars eliminates the need to carry a propulsion or airbag landing system. This reduces the total mass inside the aeroshell by more than 100 kg, aeroshell complexity, and likely the risk and cost associated to the mission. Moreover, the lighter entry mass enables landing in the Martian highlands, at elevations inaccessible to current EDL technologies. This paper proposes a novel MAD concept for a Mars helicopter. We suggest a minimum science payload package to perform relevant science in the highlands. A variant of the Ingenuity helicopter is proposed to provide increased deceleration during MAD, and enough lift to fly the science payload in the highlands. We show in simulation that the lighter aeroshell results in lower terminal velocity (30 m/s) at the end of the parachute phase of the EDL, and at higher altitudes than other approaches. After discussing the aerodynamics, controls, guidance and mechanical challenges associated to deploying at such speed, we propose a backshell architecture that addresses them to release the helicopter in the safest conditions. Finally, we implemented the helicopter model and aerodynamic descent perturbations in the JPL Dynamics and Real-Time Simulation (DARTS) framework. Preliminary performance evaluation indicate landing and helicopter operations can be achieved up to +5 km MOLA.

Rapin, William↗
DOE OSTI2017

High-gain thompson-scattering X-ray free-electron laser by time-synchronic laterally tilted optical wave

An improved optical undulator for use in connection with free electron radiation sources is provided. A tilt is introduced between phase fronts of an optical pulse and the pulse front. Two such pulses in a counter-propagating geometry overlap to create a standing wave pattern. A line focus is used to increase the intensity of this standing wave pattern. An electron beam is aligned with the line focus. The relative angle between pulse front and phase fronts is adjusted such that there is a velocity match between the electron beam and the overlapping optical pulses along the line focus. This allows one to provide a long interaction length using short and intense optical pulses, thereby greatly increasing the radiation output from the electron beam as it passes through this optical undulator.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Multi-scale simulations of wind farm performance with complex terrain and weather events

Predicting the response of wind farms to local weather is necessary for optimal design and operation. In this work, simulation and analysis of a frontal passage through a utility scale wind farm is achieved for the first time using a seamless multi-scale modeling approach. A generalized actuator disk (GAD) wind turbine model is used to represent turbine wakes, and results are compared to novel radar observations during the frontal passage. The Weather Research and Forecasting (WRF) model is employed with a nested grid setup that allows for coupling between multi-scale atmospheric conditions and turbine response. Starting with mesoscale forcing, the atmosphere is dynamically downscaled to the region of interest, where the interaction between turbulent flows and individual wind turbines is simulated with the GAD at10 m resolution. Several improvements are made to the GAD model to mimic realistic turbine operation, including a yawing capability and a power output calculation. Ultimately, the model is able to capture both the dynamics of the frontal passage and the turbine response; predictions show good agreement with observed turbine wake structure, velocity deficit, and power output after accounting for a phase shift in the mesoscale forcing. This study demonstrates the utility of the WRF-GAD framework for simulating wind farm performance under complex atmospheric conditions.

17 WIND ENERGY↗
DOE OSTI2020

Characterization of Spall in Hard Rock from Observations and Simulations of the Source Physics Experiment Phase I

In this work, spall signals from the Source Physics Experiments are presented, analyzed, and modeled for insight to the explosion source. The observed signal is similar in nature to nearby historical nuclear explosions, and the surface force-time history or velocity can be interpreted with the same model. We use the models for peak spall velocity, spalled mass, and spall depth and radius derived from historical nuclear explosions to parameterize the physical force-time history model from Stump (1985) and show that this parameterized model can be used for spall prediction. The spall signal is also investigated with a numerical continuum model that incorporates gravity. Peak velocity and dwell time are well predicted, and the multiple slap-down phases are captured if one includes a weak near-surface layer similar to the geologic observation.

58 GEOSCIENCES↗
DOE OSTI2015

Measurement of the Stopping Power of Water for Carbon Ions Using Inverted Doppler Shift Attenuation

Carbon ion therapy has gained importance in cancer treatment due to its locally well confined dose distribution, but there is a significant lack of experimental data which is needed for dose calculations and estimation of biological damage. Since tissue is mainly comprised of water, the energy-dependent stopping power of water is the critical measure. Importantly, previous data gathered from experiments with light ions has been limited to water vapour and ice and neglected water in its liquid phase. Additionally, theoretical models regarding the stopping power cannot yet describe the complex charge transfer interactions of the projectile at velocities in the range of the mean velocity of the valence electrons of the traversed medium. There are also discrepancies in the amount of phase effects concerning water and water vapour cross sections. Despite its importance there exists no experimental data for the stopping power of water for carbon ions in the energy region between 1 MeV and 5 MeV. This may be due to the short track length of carbon ions which makes traditional transmission experiments unfeasible. Therefore a project was launched to measure the stopping power of liquid water for carbon ions in the vicinity of the Bragg peak which corresponds to the energy regime of the maximum stopping power. For this measurement the inverted Doppler shift attenuation method was used. This uses the gamma quanta emitted from excited carbon nuclei which are produced by means of the {sup 12}C(α,α'){sup 12}C* reaction. The recorded γ-spectra contain the information of the projectiles velocity at the time they decay to their ground state and an internal clock provided by the exponential decay law. The deceleration of the projectile is directly connected to the stopping power which can be determined with this method as a function of the projectiles kinetic energy. Further measurements have been carried out to improve the experimental method. The setup and the preliminary results of this study will be presented. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Modeling of melting and erosion in high velocity microparticle impacts

High velocity collisions can cause melting, a situation involving elasticity, plasticity, and phase transformations in tandem, which is very challenging for mechanical modeling. Here, this paper advances the use of smoothed particle hydrodynamics (SPH) simulations for this complex situation, investigating stainless steel microspheres impacting a tin substrate. After extensive validation against a range of mechanical and geometrical measurements of experimental impacts, the model provides a detailed, quantitative view of melt volume production over a broad range of impact velocities. It also enables direct decomposition of the impact energy partitioning, including analysis of the energy absorbed by plasticity in the impactor, the system kinetic energy, and the adiabatic heating of the substrate in addition to the melting itself. Since these quantities are not available experimentally, SPH modeling substantially enhances the quantitative understanding of such impacts. Finally, the model speaks to the phase characteristics of the ejecta formed during impact, confirming the experimental inference that the ejected material likely contains a significant fraction of solid material.

Constitutive modeling↗
DOE OSTI2025

Elasticity of davemaoite as a primary contributor to lower-mantle heterogeneities

Geophysical detection of subducted mid–ocean ridge basalt (MORB) in the lower mantle is hindered by uncertainties in the elasticity of Fe,Al,Mg,Ti–bearing davemaoite, a key MORB component. Using Brillouin spectroscopy and x-ray diffraction, we determined the elasticity of a Ca 0.906(1) Fe 2+ 0.027(1) Fe 3+ 0.042(1) Mg 0.033(1) Al 0.072(1) Ti 0.020(1) Si 0.912(1) O 3 davemaoite up to 113 gigapascals and 2294 K. Here, we found that it exhibited a shear wave velocity 10 to 20% slower than end-member davemaoite, making it the slowest phase among major lower-mantle minerals. Our models show that MORB, containing 20 to 25 volume percent davemaoite, potentially contributes to large low-shear-velocity provinces (LLSVPs), whereas a cumulate layer enriched in davemaoite crystallized from basal magma ocean may comprise ultralow-velocity zones (ULVZs). Davemaoite’s ability to host incompatible and heat-producing elements possibly links LLSVPs and ULVZs to mantle plume initiation and geochemical signatures of ocean island basalts.

Zhou, Wen-Yi [Texas A & M Univ., College Station, ↗
NASA NTRS1991

Phase space distribution of halo particles and detection of WIMPS

We calculate the velocity distribution of halo particles using realistic models for the density profiles of the Galactic disk, spheroid, and halo components. We get the resulting velocity distribution, which is different from the Maxwellian distribution of isothermal halo. We investigate the consequences concerning the time averaged count rate and the amplitude of the annual modulation in WIMPS detection experiments. Compared to the previous estimate based on the Maxwellian distribution, the time averaged count rate is up to 40 percent larger. On the other hand, the amplitude of the annual modulation is up to a factor of two larger.

Ryu, Dongsu↗
NASA NTRS2008

A Synthetic Quadrature Phase Detector/Demodulator for Fourier Transform Transform Spectrometers

A method is developed to demodulate (velocity correct) Fourier transform spectrometer (FTS) data that is taken with an analog to digital converter that digitizes equally spaced in time. This method makes it possible to use simple low cost, high resolution audio digitizers to record high quality data without the need for an event timer or quadrature laser hardware, and makes it possible to use a metrology laser of any wavelength. The reduced parts count and simplicity implementation makes it an attractive alternative in space based applications when compared to previous methods such as the Brault algorithm.

Campbell, Joel↗
DOE OSTI2013

Ion velocities in direct current arc plasma generated from compound cathodes

Arc plasma from Ti-C, Ti-Al, and Ti-Si cathodes was characterized with respect to charge-state-resolved ion energy. The evaluated peak velocities of different ion species in plasma generated from a compound cathode were found to be equal and independent on ion mass. Therefore, measured difference in kinetic energies can be inferred from the difference in ion mass, with no dependence on ion charge state. The latter is consistent with previous work. These findings can be explained by plasma quasineutrality, ion acceleration by pressure gradients, and electron-ion coupling. Increasing the C concentration in Ti-C cathodes resulted in increasing average and peak ion energies for all ion species. This effect can be explained by the “cohesive energy rule,” where material and phases of higher cohesive energy generally result in increasing energies (velocities). This is also consistent with the here obtained peak velocities around 1.37, 1.42, and 1.55 (10{sup 4} m/s) for ions from Ti{sub 0.84}Al{sub 0.16}, Ti{sub 0.90}Si{sub 0.10}, and Ti{sub 0.90}C{sub 0.10} cathodes, respectively.

36 MATERIALS SCIENCE↗
NASA NTRS1994

On the Behavior of Three-dimensional Wave Packets in Viscously Spreading Mixing Layers

We consider analytically the evolution of a three-dimensional wave packet generated by an impulsive source in a mixing layer. The base flow is assumed to be spreading due to viscous diffusion. The analysis is restricted to small disturbances (linearized theory). A suitable high-frequency ansatz is used to describe the packet; the key elements of this description are a complex phase and a wave action density. It is found that the product of this density and an infinitesimal material volume convecting at the local group velocity is not conserved: there is a continuous interaction between the base flow and the wave action. This interaction is determined by suitable mode-weighted averages of the second and fourth derivatives of the base-flow velocity profile. Although there is some tendency for the dominant wave number in the packet to shift from the most unstable value toward the neutral value, this shift is quite moderate. In practice, wave packets do not become locally neutral in a diverging base flow (as do instability modes), therefore, they are expected to grow more suddenly than pure instability modes and do not develop critical layers. The group velocity is complex; the full significance of this is realized by analytically continuing the equations for the phase and wave action into a complex domain. The implications of this analytic continuation are discussed vis-a-vis the secondary instabilities of the packet: very small scale perturbations on the phase can grow very rapidly initially, but saturate later because most of the energy in these perturbations is convected away by the group velocity. This remark, as well as the one regarding critical layers, has consequences for the nonlinear theories.

Balsa, Thomas F.↗
DOE OSTI2013

PERICENTER PASSAGE OF THE GAS CLOUD G2 IN THE GALACTIC CENTER

We have further followed the evolution of the orbital and physical properties of G2, the object currently falling toward the massive black hole in the Galactic Center on a near-radial orbit. New, very sensitive data were taken in 2013 April with NACO and SINFONI at the ESO VLT. The ''head'' of G2 continues to be stretched ever further along the orbit in position-velocity space. A fraction of its emission appears to be already emerging on the blueshifted side of the orbit, past pericenter approach. Ionized gas in the head is now stretched over more than 15,000 Schwarzschild radii R{sub S} around the pericenter of the orbit, at Almost-Equal-To 2000 R{sub S} Almost-Equal-To 20 light hours from the black hole. The pericenter passage of G2 will be a process stretching over a period of at least one year. The Brackett-{gamma} luminosity of the head has been constant over the past nine years, to within {+-}25%, as have the line ratios Brackett-{gamma}/Paschen-{alpha} and Brackett-{gamma}/Helium-I. We do not see any significant evidence for deviations of G2's dynamical evolution due to hydrodynamical interactions with the hot gas around the black hole from a ballistic orbit of an initially compact cloud with moderate velocity dispersion. The constant luminosity and the increasingly stretched appearance of the head of G2 in the position-velocity plane, without a central peak, is not consistent with several proposed models with continuous gas release from an initially bound zone around a faint star on the same orbit as G2.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

SDSS-IV MaNGA: Unveiling Galaxy Interaction by Merger Stages with Machine Learning

We use machine-learning techniques to classify galaxy merger stages, which can unveil physical processes that drive the star formation and active galactic nucleus (AGN) activities during galaxy interaction. The sample contains 4690 galaxies from the integral field spectroscopy survey SDSS-IV MaNGA and can be separated into 1060 merging galaxies and 3630 nonmerging or unclassified galaxies. For the merger sample, there are 468, 125, 293, and 174 galaxies (1) in the incoming pair phase, (2) in the first pericentric passage phase, (3) approaching or just passing the apocenter, and (4) in the final coalescence phase or post-mergers. With the information of projected separation, line-of-sight velocity difference, Sloan Digital Sky Survey (SDSS) gri images, and MaNGA Hα velocity map, we are able to classify the mergers and their stages with good precision, which is the most important score to identify interacting galaxies. For the two-phase classification (binary; nonmerger and merger), the performance can be high (precision > 0.90) with LGBMClassifier . We find that sample size can be increased by rotation, so the five-phase classification (nonmerger, and merger stages 1, 2, 3, and 4) can also be good (precision > 0.85). The most important features come from SDSS gri images. The contribution from the MaNGA Hα velocity map, projected separation, and line-of-sight velocity difference can further improve the performance by 0%–20%. In other words, the image and the velocity information are sufficient to capture important features of galaxy interactions, and our results can apply to all the MaNGA data, as well as future all-sky surveys.

79 ASTRONOMY AND ASTROPHYSICS↗