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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

A Nonlinear Dynamic Subscale Model for Partially Resolved Numerical Simulation (PRNS)/Very Large Eddy Simulation (VLES) of Internal Non-Reacting Flows

A brief introduction of the temporal filter based partially resolved numerical simulation/very large eddy simulation approach (PRNS/VLES) and its distinct features are presented. A nonlinear dynamic subscale model and its advantages over the linear subscale eddy viscosity model are described. In addition, a guideline for conducting a PRNS/VLES simulation is provided. Results are presented for three turbulent internal flows. The first one is the turbulent pipe flow at low and high Reynolds numbers to illustrate the basic features of PRNS/VLES; the second one is the swirling turbulent flow in a LM6000 single injector to further demonstrate the differences in the calculated flow fields resulting from the nonlinear model versus the pure eddy viscosity model; the third one is a more complex turbulent flow generated in a single-element lean direct injection (LDI) combustor, the calculated result has demonstrated that the current PRNS/VLES approach is capable of capturing the dynamically important, unsteady turbulent structures while using a relatively coarse grid.

Shih, Tsan-Hsing↗
NASA NTRS2010

Neutral Atom Diffusion in a Partially Ionized Prominence Plasma

The support of solar prominences is normally described in terms of a magnetic force on the prominence plasma that balances the solar gravitational force. Because the prominence plasma is only partially ionized. it is necessary to consider in addition the support of the neutral component of the prominence plasma. This support is accomplished through a frictional interaction between the neutral and ionized components of the plasma, and its efficacy depends strongly on the degree of ionization of the plasma. More specifically, the frictional force is proportional to the relative flow of neutral and ion species, and for a sufficiently weakly ionized plasma, this flow must be relatively large to produce a frictional force that balances gravity. A large relative flow, of course, implies significant draining of neutral particles from the prominence. We evaluate the importance of this draining effect for a hydrogen-helium plasma, and consider the observational evidence for cross-field diffusion of neutral prominence material,

Gilbert, Holly↗
NASA NTRS2010

A New Method for Interfacing Unsuited Subjects to Overhead Suspension Partial Gravity Simulators

The purpose of performing unsuited testing as part of a reduced gravity extravehicular (EVA) suited human performance research program is to define baseline performance. These results are then coupled with suited test results to evaluate how the suit system affects human performance at reduced gravity. The primary drawback to this approach is that previous studies used notably different systems to interface suited and unsuited subjects to overhead-suspension, partial-gravity simulators. A spreader bar (SB) assembly previously used for unsuited tests allowed limited pitch and roll of the subject, whereas the gimbal for suited tests allowed more pitch and roll, although the mass distribution led to large moments of inertia in the yaw axis. It is hypothesized that use of the same methods for offload of both unsuited and suited subjects is needed to make meaningful comparisons. A new gimbal (GIM) was designed with the idea that it could function with both suited and unsuited subjects. GIM was designed to minimize mass and moments of inertia and to be adjustable to co-locate the 3 axes of rotation with the subject s center of gravity. OBJECTIVE: To evaluate human performance differences between SB and GIM. METHODS: Ten unsuited subjects were off-loaded to 1/6-g using both interfaces. Subjects completed tasks including overground and treadmill ambulation, picking up objects, shoveling, postural stability, range of motion testing, and recovery from the kneeling and prone positions. Metabolic, biomechanical, and/or subjective data were collected based on task. RESULTS: Initial analyses suggest that subjects completed all tasks with lower levels of compensation and a more terrestrial approach to movement when suspended via GIM. With SB, subjects were not able to fall or get into a prone position and had increased difficulty both retrieving objects off the floor and with overground ambulation, especially at gait initiation, because they were unable to bend their torso. GIM shows promise as a new method.

Norcross, Jason R.↗
NASA NTRS2010

Oxidation of SiC/BN/SiC Composites in Reduced Oxygen Partial Pressures

SiC fiber-reinforced SiC composites with a BN interphase are proposed for use as leading edge structures of hypersonic vehicles. The durability of these materials under hypersonic flight conditions is therefore of interest. Thermogravimetric analysis was used to characterize the oxidation kinetics of both the constituent fibers and composite coupons at four temperatures: 816, 1149, 1343, and 1538 C (1500, 2100, 2450, and 2800 F) and in oxygen partial pressures between 5% and 0.1% (balance argon) at 1 atm total pressure. One edge of the coupons was ground off so the effects of oxygen ingress into the composite could be monitored by post-test SEM and EDS. Additional characterization of the oxidation products was conducted by XPS and TOF-SIMS. Under most conditions, the BN oxidized rapidly, leading to the formation of borosilicate glass. Rapid initial oxidation followed by volatilization of boria lead to protective oxide formation and further oxidation was slow. At 1538C in 5% oxygen, both the fibers and coupons exhibited borosilicate glass formation and bubbling. At 1538C in 0.1% oxygen, active oxidation of both the fibers and the composites was observed leading to rapid SiC degradation. BN oxidation at 1538C in 0.1% oxygen was not significant.

Opila, Elizabeth J.↗
NASA NTRS2006

Fluid Dynamics Assessment of the VPCAR Water Recovery System in Partial and Microgravity

The Vapor Phase Catalytic Ammonia Removal (VPCAR) system is being developed to recycle water for future NASA Exploration Missions. Testing was recently conducted on NASA s C-9B Reduced Gravity Aircraft to determine the microgravity performance of a key component of the VPCAR water recovery system. Six flights were conducted to evaluate the fluid dynamics of the Wiped-Film Rotating Disk (WFRD) distillation component of the VPCAR system in microgravity, focusing on the water delivery method. The experiments utilized a simplified system to study the process of forming a thin film on a disk similar to that in the evaporator section of VPCAR. Fluid issues are present with the current configuration, and the initial alternative configurations were only partial successful in microgravity operation. The underlying causes of these issues are understood, and new alternatives are being designed to rectify the problems.

Niederhaus, Charles↗
NASA NTRS2011

Measuring Parameters of Massive Black Hole Binaries with Partially Aligned Spins

The future space-based gravitational wave detector LISA will be able to measure parameters of coalescing massive black hole binaries, often to extremely high accuracy. Previous work has demonstrated that the black hole spins can have a strong impact on the accuracy of parameter measurement. Relativistic spin-induced precession modulates the waveform in a manner which can break degeneracies between parameters, in principle significantly improving how well they are measured. Recent studies have indicated, however, that spin precession may be weak for an important subset of astrophysical binary black holes: those in which the spins are aligned due to interactions with gas. In this paper, we examine how well a binary's parameters can be measured when its spins are partially aligned and compare results using waveforms that include higher post-Newtonian harmonics to those that are truncated at leading quadrupole order. We find that the weakened precession can substantially degrade parameter estimation, particularly for the "extrinsic" parameters sky position and distance. Absent higher harmonics, LISA typically localizes the sky position of a nearly aligned binary about an order of magnitude less accurately than one for which the spin orientations are random. Our knowledge of a source's sky position will thus be worst for the gas-rich systems which are most likely to produce electromagnetic counterparts. Fortunately, higher harmonics of the waveform can make up for this degradation. By including harmonics beyond the quadrupole in our waveform model, we find that the accuracy with which most of the binary's parameters are measured can be substantially improved. In some cases, the improvement is such that they are measured almost as well as when the binary spins are randomly aligned.

Lang, Ryan N.↗
NASA NTRS2011

A New Method for Interfacing Unsuited Subjects to Overhead Suspension Partial Gravity Simulators

The purpose of performing unsuited testing as part of a reduced gravity extravehicular (EVA) suited human performance research program is to define baseline performance. These results are then coupled with suited test results to evaluate how the suit system affects human performance at reduced gravity. The primary drawback to this approach is that previous studies used notably different systems to interface suited and unsuited subjects to overhead-suspension, partial-gravity simulators. A spreader bar (SB) assembly previously used for unsuited tests allowed limited pitch and roll of the subject, whereas the gimbal for suited tests allowed more pitch and roll, although the mass distribution led to large moments of inertia in the yaw axis. It is hypothesized that use of the same methods for offload of both unsuited and suited subjects is needed to make meaningful comparisons. A new gimbal (GIM) was designed with the idea that it could function with both suited and unsuited subjects. GIM was designed to minimize mass and moments of inertia and to be adjustable to co-locate the 3 axes of rotation with the subject s center of gravity. OBJECTIVE: To evaluate human performance differences between SB and GIM. METHODS: Ten unsuited subjects were offloaded to 1/6-g using both interfaces. Subjects completed tasks including overground and treadmill ambulation, picking up objects, shoveling, postural stability, range of motion testing, and recovery from the kneeling and prone positions. Metabolic, biomechanical, and/or subjective data were collected based on task. RESULTS: Initial analyses suggest that subjects completed all tasks with lower levels of compensation and a more terrestrial approach to movement when suspended via GIM. With SB, subjects were not able to fall or get into a prone position and had increased difficulty both retrieving objects off the floor and with overground ambulation, especially at gait initiation, because they were unable to bend their torso. GIM shows promise as a new method.

Norcross, Jason↗
NASA NTRS2005

Hygrometer for Detecting Water in Partially Enclosed Volumes

A portable hygrometer has been devised to implement a pre-existing technique for detecting water trapped in partially enclosed volumes that may be difficult to reach and cannot be examined directly. The technique is based on the fact that eventually the air in such a volume becomes saturated or nearly so. The technique is straightforward: One measures the relative humidity and temperature of both the ambient air and a sample of air from the enclosed volume. If the relative humidity of the sample is significantly greater than that of the ambient air and/or if the sample is at or close to the dew point, then it can be concluded that water is trapped in the volume. Of course, the success of this technique depends on the existence of an access hole through which one can withdraw some air from the enclosed volume.

Youngquist, Robert C.↗
NASA NTRS2012

Analysis of the Pressure Rise in a Partially Filled Liquid Tank in Microgravity with Low Wall Heat Flux and Simultaneous Boiling and Condensation

Experiments performed with Freon 113 in the space shuttle have shown that in a pro- cess of very slow heating, high liquid superheats can be sustained for a long period in microgravity. In a closed system explosive vaporization of superheated liquid resulted in pressure spikes of varying magnitudes. In this paper, we analyze the pressure rise in a partially lled closed tank in which a large vapor bubble (i.e., ullage) is initially present, and the liquid is subjected to a low wall heat ux. The liquid layer adjacent to the wall becomes superheated until the temperature for nucleation of the bubbles (or the incipience of boiling) is achieved. In the absence of the gravity-induced convection large quantities of superheated liquid can accumulate over time near the heated surface. Once the incipience temperature is attained, explosive boiling occurs and the vapor bubbles that are produced on the heater surface tend to quickly raise the tank pressure. The liquid-vapor saturation temperature increases as well. These two e ects tend to induce condensation of the large ullage bubble that is initially present, and tends to mitigate the tank pressure rise. As a result, the tank pressure is predicted to rise sharply, attain a maximum, and subsequently decay slowly. The predicted pressure rise is compared with experimental results obtained in the microgravity environments of the space shuttle for Freon 113. The analysis is appli- cable, in general to heating of liquid in closed containers in microgravity and to cryogenic fuel tanks, in particular where small heat leaks into the tank are unavoidable.

Hasan, Mohammad M.↗
NASA NTRS2013

The 0.5-2.22 micrometer Scattered Light Spectrum of the Disk around TW Hya: Detection of a Partially Filled Disk Gap at 80 AU*

We present a 0.5-2.2 micrometer scattered light spectrum of the circumstellar disk around TW Hya from a combination of spatially resolved Hubble Space Telescope STIS spectroscopy and NICMOS coronagraphic images of the disk. We investigate the morphology of the disk at distances greater than 40 AU over this wide range of wavelengths, and identify the presence of a depression in surface brightness at approximately 80 AU that could be caused by a gap in the disk. Additionally, we quantify the surface brightness, azimuthal symmetry, and spectral character of the disk as a function of radius. Our analysis shows that the scattering efficiency of the dust is largely neutral to blue over the observed wavelengths. We model the disk as a steady α-disk with an ad hoc gap structure. The thermal properties of the disk are selfconsistently calculated using a three-dimensional radiative transfer code that uses ray tracing to model the heating of the disk interior and scattered light images. We find a good fit to the data over a wide range of distances from the star if we use a model disk with a partially filled gap of 30% depth at 80 AU and with a self-similar truncation knee at 100 AU. The origin of the gap is unclear, but it could arise from a transition in the nature of the disk's dust composition or the presence of a planetary companion. Based on scalings to previous hydrodynamic simulations of gap-opening criteria for embedded proto-planets, we estimate that a planetary companion forming the gap could have a mass between 6 and 28 solar mass.

radiative transfer↗
NASA NTRS2014

Partial Automated Alignment and Integration System

The present invention is a Partial Automated Alignment and Integration System (PAAIS) used to automate the alignment and integration of space vehicle components. A PAAIS includes ground support apparatuses, a track assembly with a plurality of energy-emitting components and an energy-receiving component containing a plurality of energy-receiving surfaces. Communication components and processors allow communication and feedback through PAAIS.

Kelley, Gary Wayne↗
NASA NTRS2014

Partial Arc Curvilinear Direct Drive Servomotor

A partial arc servomotor assembly having a curvilinear U-channel with two parallel rare earth permanent magnet plates facing each other and a pivoted ironless three phase coil armature winding moves between the plates. An encoder read head is fixed to a mounting plate above the coil armature winding and a curvilinear encoder scale is curved to be co-axis with the curvilinear U-channel permanent magnet track formed by the permanent magnet plates. Driven by a set of miniaturized power electronics devices closely looped with a positioning feedback encoder, the angular position and velocity of the pivoted payload is programmable and precisely controlled.

Sun, Xiuhong↗
NASA NTRS2016

A Mission Concept to Study Multigenerational Mammalian Reproduction in Partial Gravity

A team at NASA Langley Research Center conducted a study during which a conceptual space mission was designed. In this study, rodents are used as human analogs to gather biological and systems data in a relevant environment applicable to future settlements on Mars. The mission concept uniquely addresses the combined effects of long-durations (one-year or greater), autonomous and robotic operations, and biological responses to partial gravity with an emphasis on reproduction. The objectives of this study were to 1) understand challenges associated with designing an artificial gravity habitat that supports the reproduction and maturation of a large animal colony, 2) identify mission architectures and operational concepts to transport and maintain such a facility, and 3) identify fundamental science considerations for mammalian reproduction studies to inform vehicle design. A model demonstration unit was developed to visualize and test certain design concepts that resulted from these considerations. Three versions of this demonstration unit were built over the course of the study, each taking into account lessons learned from the previous version. This paper presents the updated baseline mission and spacecraft design concepts to achieve these objectives, with a specific emphasis on updates since publication in previous works. Analyses of the integrated system trades among the elements which make up the conceptual vehicle are described to address overall feasibility and identify potential integrated design opportunities. The latest iteration of the habitat robotics design and a conceptual design example for autonomous care of crew and systems are also presented. Finally, the conclusion of this conceptual design study, necessary future analyses to enable such a facility, and comments upon other applications of a similar exploration-focused research facilities are addressed.

Rodgers, Erica M.↗
NASA NTRS2017

Centrifuge in Free Fall: Combustion at Partial Gravity

A centrifuge apparatus is developed to study the effect of variable acceleration levels in a drop tower environment. It consists of a large rotating chamber, within which the experiment is conducted. NASA Glenn Research Center 5.18-second Zero-Gravity Facility drop tests were successfully conducted at rotation rates up to 1 RPS with no measurable effect on the overall Zero-Gravity drop bus. Arbitrary simulated gravity levels from zero to 1-g (at a radius of rotation 30 cm) were produced. A simple combustion experiment was used to exercise the capabilities of the centrifuge. A total of 23 drops burning a simulated candle with heptane and ethanol fuel were performed. The effect of gravity level (rotation rate) and Coriolis force on the flames was observed. Flames became longer, narrower, and brighter as gravity increased. The Coriolis force tended to tilt the flames to one side, as expected, especially as the rotation rate was increased. The Zero-Gravity Centrifuge can be a useful tool for other researchers interested in the effects of arbitrary partial gravity on experiments, especially as NASA embarks on future missions which may be conducted in non-Earth gravity.

microgravity↗
NASA NTRS2019

Partially Chloritized Smectites: Analogues of Smectites at Gale Crater, Mars

Characterizing the structure and composition of phyllosilicates is important for interpreting the aqueous history of Mars and identifying potential habitable environments. Smectites and chlorites are the most dominant clay types on Mars, and there is evidence of the presence of smectite/chlorite intergrades. Smectite has been detected at Gale Crater, Mars, via orbital observations and in-situ measurements, in abundances up to approximately 25 weight percentage of bulk rock. John Klein (JK) and Cumberland (CB) were analyzed by the Chemistry and Mineralogy (CheMin) and Samples Analysis at Mars (SAM) evolved gas analysis experiment (EGA) instruments, onboard Mars Science Laboratory (MSL), Curiosity, to distinguish clay mineralogy. John Klein has a collapsed 2:1 smectite with a d-spacing of 10 Angstroms, whereas Cumberland smectite did not fully collapse and has a d-spacing of approximately 13.2 Angstroms. It has been suggested that partial chloritization or ‘pillaring’ could be responsible for the expanded Cumberland smectite because pillaring inhibits the collapse of smectites down to 10 Angstrom, even under the desiccating conditions on the martian surface. Clay minerals have been detected in ancient fluvio-lacustrine rocks throughout Curiosity’s traverse and catalog the changes of the lake water chemistry and diagenetic conditions at Gale Crater, Mars. Investigating clay minerals is important for identifying them on the Martian surface, in particular as Curiosity proceeds into the upcoming Clay-bearing Unit.

Tu, V. M.↗
NASA NTRS2019

The Moon's Deep Interior: A Hotbed for Seismicity and the Question of Partial Melt

Terrestrial planets all share a common structural framework (crust, mantle, core) which is developed very shortly after formation and which determines subsequent evolution. The Moon formed under very unique circumstances. Interior properties provide constraints on formation and evolution models, and possible indicators of an early dynamo for magnetic field generation: Layering, Composition, Seismic velocity & density, Presence of partial melt, Core state. Constraints on these properties arise from geophysical observations: Geodetic parameters, Lunar laser ranging, Gravity field, Magnetic induction, Heat flow, Seismology.

Weber, Renee↗
NASA NTRS2019

Modeling Mg II During Solar Flares. I. Partial Frequency Redistribution, Opacity, and Coronal Irradiation

The Interface Region Imaging Spectrograph has routinely observed the flaring Mg II near-ultraviolet (NUV) spectrum, offering excellent diagnostic potential and a window into the location of energy deposition. A number of studies have forward-modeled both the general properties of these lines and specific flare observations. Generally these have forward-modeled radiation via post-processing of snapshots from hydrodynamic flare simulations through radiation transfer codes. There has, however, not been a study of how the physics included in these radiation transport codes affects the solution. A baseline setup for forward-modeling Mg II in flares is presented and contrasted with approaches that add or remove complexity. It is shown for Mg II that (1) partial frequency distribution (PRD) is still required during flare simulations despite the increased densities; (2) using full angle-dependent PRD affects the solution but takes significantly longer to process a snapshot; (3) including Mg I in non-LTE (NLTE) results in negligible differences to the Mg II lines but does affect the NUV quasi-continuum; (4) only hydrogen and Mg II need to be included in NLTE; (5) ideally the nonequilibrium hydrogen populations, with nonthermal collisional rates, should be used rather than the statistical equilibrium populations; (6) an atom consisting of only the ground state, h and k upper levels, and continuum level is insufficient to model the resonance lines; and (7) irradiation from a hot, dense flaring transition region can affect the formation of Mg II. We discuss modifications to the RH code allowing straightforward inclusion of the transition region and coronal irradiation in flares.

Kerr, Graham S.↗
NASA NTRS2020

CFD Predictions of Soot & CO Emissions Generated by a Partially-Fueled 9-Element Lean-Direct Injection Combustor

A study was undertaken to investigate the CO & soot emissions generated by a partially-fueled 9- element LDI (Lean-Direct Injection) combustor configuration operating in the idle range of jet engine conditions. In order to perform the CFD analysis, several existing soot/chemistry models were implemented into the OpenNCC (Open National Combustion Code). The calculations were based on a Reynolds-Averaged Navier Stokes (RANS) simulation with standard k-epsilon turbulence model, a 62- species jet-a/air chemistry, a 2-equation soot model, & a Lagrangian spray solver. A separate transport equation was solved for all individual species involved in jet-a/air combustion. In the test LDI configuration we examined, only five of the nine injectors were fueled with the major pilot injector operating at an equivalence ratio of near one and the other four main injectors operating at an equivalence ratio near 0.55. The calculations helped to identify several reasons behind the soot & CO formation in different regions of the combustor. The predicted results were compared with the reported experimental data on soot mass concentration (SMC) & emissions index of CO (EICO). The experimental results showed that an increase in either T3 and/or F/A ratio lead to a reduction in both EICO & SMC. The predicted results were found to be in reasonable agreement. However, the predicted EICO differed substantially in one test condition associated with higher F/A ratio.

Raju, M. S.↗