Tech Briefs

High-Pressure, Reduced-Kinetics Mechanism for N-Hexadecane Oxidation

NASA’s Jet Propulsion Laboratory, Pasadena, California Combustion of realistic fuels is described by thousands of reactions involving thousands of species. Coupling these detailed chemical mechanisms with turbulence simulations is completely impractical because there is no computer powerful enough to solve the resulting equations.

Posted in: Information Sciences, Electronics & Computers, Briefs

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Method of Error Floor Mitigation in Low-Density Parity-Check Codes

NASA’s Jet Propulsion Laboratory, Pasadena, California Low-density parity-check (LDPC) codes often suffer from an “error floor” in which increasing signal-to-noise ratios do not lead to substantially better error rate performance. Error floors of LDPC codes are often not an inherent problem of the code design, but rather, a limitation of the standard decoding algorithms.

Posted in: Information Sciences, Electronics & Computers, Briefs

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X-Ray Flaw Size Parameter for POD Studies

Lyndon B. Johnson Space Center, Houston, Texas Nondestructive evaluation (NDE) method capability is determined by a statistical flaw detection study called probability of detection (POD) study. In many instances, the NDE flaw detectability is given as a flaw size such as crack length. The flaw is either a crack or behaving like a crack in terms of affecting the structural integrity of the material. Although the crack size relates to structural integrity of the part, it may not be the only factor that affects the flaw detectability for most NDE methods. Crack length, depth, and opening may relate differently to the flaw detectability. Part surface roughness and cleanliness may affect the flaw detectability. The proposed flaw size parameter and the computer application described here give an alternative approach to conduct the POD studies and apply results of the POD study to reliably detect small flaws through better assessment of effect of interaction between various geometric parameters.

Posted in: Information Sciences, Electronics & Computers, Briefs

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Large Eddy Simulation Composition Equations for Two-Phase Fully Multicomponent Turbulent Flows

The composition probability density function moment variables are based on a new type of filter. NASA’s Jet Propulsion Laboratory, Pasadena, California Liquid sprays are commonly used to inject fuels into combustion devices, making it important to study multicomponent (MC) two-phase flows in order to reveal their physics. “Multicomponent” is the terminology describing all fuels that are combinations of a myriad of species. Single-component simulations lack a detailed representation of the complex composition and reaction mechanisms of realistic fuels, which can contain hundreds to thousands of species. Some species may be responsible for fuel ignition, other species may be the initiators of soot formation, and yet others may be involved in surface corrosion, all of which demonstrates the importance of being able to track the multitude of species.

Posted in: Information Sciences, Electronics & Computers, Briefs

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Scheduling Targeted and Mapping Observations with State, Resource, and Timing Constraints

NASA’s Jet Propulsion Laboratory, Pasadena, California This innovation creates observations of both targeted geographical regions of interest and general mapping observations, while respecting spacecraft constraints such as data volume, observation timing, visibility, lighting, season, and science priorities. This tool, therefore, addresses both geometric and state/timing/resource constraints by using a grid-based approach. These set covering constraints are then incorporated into a greedy optimization scheduling algorithm that incorporates operations constraints to generate feasible schedules. The resultant tool generates schedules of hundreds of observations per week out of potentially thousands of observations.

Posted in: Information Sciences, Electronics & Computers, Briefs

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Processing COSMIC/FORMOSAT-3 Data for Slant Total Electron Content Measurements

New leveling algorithm uses GPS multipath signals to provide an improved leveling of ionospheric measurements. NASA’s Jet Propulsion Laboratory, Pasadena, California The COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) mission has GPS (Global Positioning System) radio occultation dual-band receivers onboard. The received signals slice through the ionosphere, layer by layer, in much the same way as peeling off the layers of an onion. In order to use GPS signals for ionospheric measurements, they must be edited, phase leveled, and the hardware biases removed. The leveling algorithm used for ground-based GPS receivers is inadequate for space-based receivers due to substantially different multipath characteristics.

Posted in: Test & Measurement, Briefs

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Gridded Atmosphere Products from GPS Radio Occultation Measurements with Bayesian Interpolation Technique

NASA’s Jet Propulsion Laboratory, Pasadena, California GPS radio occultation measurements are vital for climate monitoring and atmospheric temperature change detection. However, the data are irregularly distributed in space and time, which makes it inconvenient for many applications.

Posted in: Test & Measurement, Software, Briefs

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