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Results for “WAVE REFLECTION”

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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Composite Material Property Nondestructive Characterization Using Obliquely Insonified Ultrasonic Waves

The analysis of reflected ultrasonic waves induced by oblique insonification of composite materials is a powerful tool for providing informations about defects and material properties. A device was developed to manipulate a pair of transmitting and receiving transducers at vrious angles of wave incidence and propagation with the fiber orientation.

Non-Destructive Evaluation Composites Mechanical P↗
NASA NTRS2007

Sources of and Remedies for Removing Unwanted Reflections in Millimeter Wave Images of Complex SOFI-Covered Structures

In the recent years, continuous-wave (CW) near-field and lens-focused millimeter wave imaging systems have been effectively. used to demonstrate their utility for producing high-resolution images of metallic structures covered with spray on foam insulation (SOFI) such as the space shuttle external tank. These systems have produced images with a spatial resolution of approximately 2 mm at a frequency of 150 GHz, and can easily interrogate thin as well as thick SOFI (> 9") enabling detection and evaluation of flaws such as voids, disbands, delaminations and corrosion. These systems are relatively simple, inexpensive, easy-to-use, require little to no signal processing of the raw data, on-site friendly, real-time and small. However, for some specific structures a certain interference pattern may be superimposed on the produced images. Generally, this occurs when the SOFI surface is at a relatively significant angle with respect to the surface of the substrate (or other sub-structures) on which it is sprayed. Consequently, the reflection from the surface of the SOFI and that from the substrate (or sub-structure) coherently combine into an interference pattern as the SOFI surface is scanned. There are methods by which the influence of this unwanted interference can be reduced, such as the incorporation of an incidence angle and the proper use of signal polarization. This paper presents the basics of this problem and describes the use of the methods for reducing this unwanted influence through several specific examples. A discussion on how the use of a swept-frequency or pulsed method may also alleviate this problem is also presented.

Khakovsky, S.↗
DOE OSTI2020

High-pressure ignition delay time measurements of a four-component gasoline surrogate and its high-level blends with ethanol and methyl acetate

Ignition delay times of a gasoline surrogate (iso-octane/toluene/n-heptane/1-hexene at 55/25/15/5% by liquid volume, developed in McCormick et al. 2017) with high-level bioblendstock-gasoline surrogate blends (50% and 85% biofuel by liquid volume of each ethanol and methyl acetate) were collected behind reflected shock waves. Post-reflected-shock temperatures ranged from 968 to 1361 K at pressures of about 4, 10, 25, and 50 atm. Data were collected for real fuel–air mixtures at fuel lean and stoichiometric conditions (φ = 0.5, 1.0) with focus on the more-practical, fuel-lean conditions. Ignition delay times were measured from OH* chemiluminescence around 307 nm using an endwall diagnostic. The RON and MON of the surrogate were 90.3 and 84.7, respectively. Ethanol was chosen due to its wide use in flex-fuel vehicles and availability, while also providing an increased octane rating. Methyl acetate was chosen for its especially high octane rating to investigate the effect of an extreme case. To validate the gasoline surrogate, the data are compared to real gasoline (RD387) and several gasoline surrogate experiments from the literature. Using the wide range of pressures studied, the gasoline surrogate’s pressure dependence was quantified to account for test-to-test variations using regression analysis. Similarly, a global correlation for gasoline and its surrogates was developed using all available data from the literature. Two modern chemical kinetics models targeting gasoline and its surrogates are compared to the ignition delay time measurements. These new high-pressure, high-bioblendstock concentration tests provide required chemical kinetic data for optimizing fuel and engine design.

42 ENGINEERING↗
DOE OSTI2022

The Challenges of Modeling Defect Behavior and Plasticity across Spatial and Temporal Scales: A Case Study of Metal Bilayer Impact

Atomistic molecular dynamics (MD) and a microstructural dislocation density-based crystalline plasticity (DCP) framework were used together across time scales varying from picoseconds to nanoseconds and length scales spanning from angstroms to micrometers to model a buried copper–nickel interface subjected to high strain rates. The nucleation and evolution of defects, such as dislocations and stacking faults, as well as large inelastic strain accumulations and wave-induced stress reflections were physically represented in both approaches. Both methods showed similar qualitative behavior, such as defects originating along the impactor edges, a dominance of Shockley partial dislocations, and non-continuous dislocation distributions across the buried interface. The favorable comparison between methods justifies assumptions used in both, to model phenomena, such as the nucleation and interactions of single defects and partials with reflected tensile waves, based on MD predictions, which are consistent with the evolution of perfect and partial dislocation densities as predicted by DCP. This substantiates how the nanoscale as modeled by MD is representative of microstructural behavior as modeled by DCP.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Multiply reflected standing Alfven waves in the Io torus - Pioneer 10 observations

Observations from the Voyager 1 pass by the Io flux tube strongly suggest that large amplitude standing Alfven waves are generated as Jovian plasma flows past Io. It has recently been proposed by Gurnett and Goertz (1981) that this Io generated standing Alfven wave system extends an appreciable way around the Io L-shell. Observations are presented here of magnetic perturbations found in the Pioneer 10 record as it crossed the Io L-shell. The field perturbations are found to be qualitatively consistent with the passage of the spacecraft through a standing Alfven wave pattern. The observations suggest an Alfven Mach number of 0.03, which is 1/5 the value inferred from Voyager 1 observations. This implies a lower plasma density at the time of the flyby of Pioneer 10.

Walker, R.↗