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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Intraocular Pressure Dynamics in Microgravity and Terrestrial Analogues: A Systematic Review and Qualitative Analysis

Spaceflight-Associated Neuro-ocular Syndrome (SANS) presents risk to expeditionary spaceflight. Related ocular findings carry poorly understood pathophysiology, including relationship to intraocular pressure (IOP) dynamics in microgravity. The study objectives were to conduct a systematic literature review and pool available IOP data from terrestrial microgravity analogs plus published spaceflight measures for comparison and qualitative analysis.

Elkhatib, Wiaam↗
DOE OSTI2018

An exploration of pressure dynamics using differential equations defined on a fractal geometry

Pressure tests have been used to understand the behavior of naturally fractured reservoirs (NFRs) by establishing parameters such as permeability, connectivity of fractures, system compressibility, fracture network parameters, and others associated with the physical properties of the reservoir. The complex fracture network of a NFR produces anomalous fluid flow, which is shown by the pressure behavior at the well. A plausible model to explain this behavior is to assume that it arises from a fractal fracture system. However, to estimate the parameters that define this fractal fracture system, fluid flow models based on the modification of Darcy’s law are used. On the other hand, in this work, a fractal structure with known fractal dimension: Sierpinski gasket (SG) is proposed. The objective of this work is to solve numerically the diffusion equation on SG, and establish a comparison with flow models used in the oil industry to investigate the fractality assumption. This study is focused on the qualitative behavior of the solution of the diffusion equation defined on a SG supported by the Kigami’s theory of differential equations on fractals.

42 ENGINEERING↗
NASA NTRS2001

Demodulation System for Fiber Optic Bragg Grating Dynamic Pressure Sensing

Fiber optic Bragg gratings have been used for years to measure quasi-static phenomena. In aircraft engine applications there is a need to measure dynamic signals such as variable pressures. In order to monitor these pressures a detection system with broad dynamic range is needed. This paper describes an interferometric demodulator that was developed and optimized for this particular application. The signal to noise ratio was maximized through temporal coherence analysis. The demodulator was incorporated in a laboratory system that simulates conditions to be measured. Several pressure sensor configurations incorporating a fiber optic Bragg grating were also explored. The results of the experiments are reported in this paper.

Lekki, John D.↗
DOE OSTI2013

Gas kinematics on giant molecular cloud scales in M51 with PAWS: Cloud stabilization through dynamical pressure

We use the high spatial and spectral resolution of the PAWS CO(1-0) survey of the inner 9 kpc of the iconic spiral galaxy M51 to examine the effects of gas streaming motions on the star-forming properties of individual giant molecular clouds (GMCs). We compare our view of gas flows in M51—which arise due to departures from axisymmetry in the gravitational potential (i.e., the nuclear bar and spiral arms)—with the global pattern of star formation as traced by Hα and 24 μm emission. We find that the dynamical environment of GMCs strongly affects their ability to form stars, in the sense that GMCs situated in regions with large streaming motions can be stabilized, while similarly massive GMCs in regions without streaming go on to efficiently form stars. We argue that this is the result of reduced surface pressure felt by clouds embedded in an ambient medium undergoing large streaming motions, which prevent collapse. Indeed, the variation in gas depletion time expected based on the observed streaming motions throughout the disk of M51 quantitatively agrees with the variation in the observed gas depletion time scale. The example of M51 shows that streaming motions, triggered by gravitational instabilities in the form of bars and spiral arms, can alter the star formation law; this can explain the variation in gas depletion time among galaxies with different masses and morphologies. In particular, we can explain the long gas depletion times in spiral galaxies compared with dwarf galaxies and starbursts. We suggest that adding a dynamical pressure term to the canonical free-fall time produces a single star formation law that can be applied to all star-forming regions and galaxies across cosmic time.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Development of a dynamic pressure calibration technique

The report deals with work continuing on the development of a method of producing sinusoidally varying pressures of at least 34 kPa zero-to-peak with amplitude variations within plus or minus 5% up to 2 kHz for the dynamic calibration of pressure transducers. Sinusoidally varying pressures of 34 kPa zero-to-peak were produced between 40 Hz and 750 Hz by vibrating a 10-cm column of a dimethyl siloxane liquid at 36gn zero-to-peak. Damping of the liquid column was accomplished by packing the fixture tube with a number of smaller diameter tubes.

Vezzetti, C. F.↗
NASA NTRS1998

Intracranial pressure dynamics during simulated microgravity using a new noninvasive ultrasonic technique

It is believed that intracranial pressure (ICP) may be elevated in microgravity because a fluid shift toward the head occurs due to loss of gravitational blood pressures. Elevated ICP may contribute to space adaptation syndrome, because as widely observed in clinical settings, elevated ICP causes headache, nausea, and projectile vomiting, which are similar to symptoms of space adaptation syndrome. However, the hypothesis that ICP is altered in microgravity is difficult to test because of the invasiveness of currently-available techniques. We have developed a new ultrasonic technique, which allows us to record ICP waveforms noninvasively. The present study was designed to understand postural effects on ICP and assess the feasibility of our new device in future flight experiments.

NASA Center ARC↗
DOE OSTI2019

Ultra-High Pressure Dynamic Compression of Geological Materials

Dynamic-compression experiments on geological materials are important for understanding the composition and physical state of the deep interior of the Earth and other planets. These experiments also provide insights into impact processes relevant to planetary formation and evolution. Recently, new techniques for dynamic compression using high-powered lasers and pulsed-power systems have been developed. These methods allow for compression on timescales ranging from nanoseconds to microseconds and can often achieve substantially higher pressure than earlier gas-gun-based loading techniques. The capability to produce shockless (i.e., ramp) compression provides access to new regimes of pressure–temperature space and new diagnostics allow for a more detailed understanding of the structure and physical properties of materials under dynamic loading. This review summarizes these recent advances, focusing on results for geological materials at ultra-high pressures above 200 GPa. Implications for the structure and dynamics of planetary interiors are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Mechanical and optical response of [100] lithium fluoride to multi-megabar dynamic pressures

An understanding of the mechanical and optical properties of lithium fluoride (LiF) is essential to its use as a transparent tamper and window for dynamic materials experiments. In order to improve models for this material, we applied iterative Lagrangian analysis to ten independent sets of data from magnetically driven planar shockless compression experiments on single crystal [100] LiF to pressures as high as 350 GPa. We found that the compression response disagreed with a prevalent tabular equation of state for LiF that is commonly used to interpret shockless compression experiments. We also present complementary data from ab initio calculations performed using the diffusion quantum Monte Carlo method. The agreement between these two data sets lends confidence to our interpretation. In order to aid in future experimental analysis, we have modified the tabular equation of state to match the new data. We have also extended knowledge of the optical properties of LiF via shock-compression and shockless compression experiments, refining the transmissibility limit, measuring the refractive index to ~300 GPa, and confirming the nonlinear dependence of the refractive index on density. Lastly, we present a new model for the refractive index of LiF that includes temperature dependence and describe a procedure for correcting apparent velocity to true velocity for dynamic compression experiments.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Radiation pressure dynamics in planetary exospheres - A 'natural' framework

Exospheric theory is reformulated to provide for the analysis of dynamical underpinning of exospheric features. The formulation is based on the parabolic-cylindrical separability of the Hamiltonian that describes particle motions in the combined fields of planetary gravity and solar radiation pressure. An approximate solution for trajectory evolution in terms of orbital elements is derived and the role of the exopause in the tail phenomenon is discussed. Also, an expression is obtained for the bound constituent atom densities at outer planetocoronal positions along the planet-sun axis for the case of an evaporative, uniform exobase. This expression is used to estimate midnight density enhancements as a function of radial distance for the terrestrial planets.

Bishop, James↗
DOE OSTI2018

Absorber Cooling Circuits Dynamic Pressure Study

The flow rates through the flange/stick absorber cooling circuit and the crotch absorber cooling circuit should not exceed 2 GPM. The purpose of this document is to define the scope and present the results of the NSLSII absorber circuit water cooling pressure test. This report also provides flow capacities for each type of absorber cooling circuit in accordance with the required header pressure differential and other cooling system design parameters.

43 PARTICLE ACCELERATORS↗
NASA NTRS1964

New anemometer has fast response, measures dynamic pressure directly

A simple anemometer having a fast response to high frequency wind fluctuations by direct measurement of two drag-force components in orthogonal planes is described. It may be used to determine wind profiles to extensive heights and would be helpful in takeoff and landing of light planes.

Lynch, J. W.↗
NASA NTRS1966

Colloidal suspension simulates linear dynamic pressure profile

Missile nose fairings immersed in colloidal suspension prepared with various specific gravities simulate pressure profiles very similar to those encountered during reentry. Stress and deflection conditions similar to those expected during atmospheric reentry are thus attained in the laboratory.

Mc Cann, R. J.↗