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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.

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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.

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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: Briefs, TSP, Electronics & Computers

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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.

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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.

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Safety Analysis of Conflict Prevention Algorithms

This algorithm provides guidance maneuvers to avoid conflict in air traffic management systems. Langley Research Center, Hampton, Virginia Different types of information are used to help aircraft maintain separation standards. At the lowest level, information is needed to indicate if separation standards will be violated in the near future, called a conflict. Once a conflict is detected, then conflict resolution information may be used to create a new path in which there is no conflict. Most future airspace concepts propose using computer algorithms to produce this information. Both conflict detection and resolution algorithms usually work in a pair-wise fashion: the ownership aircraft and one other aircraft. In situations where traffic density is low, this pair-wise assumption does not significantly impact operations. However, when traffic density is high, resolving one conflict may result in new near-term conflicts called secondary conflicts. These secondary conflicts may be nearer (in time) than the original conflict being addressed, so, the safety of the aircraft depends on avoiding these conflicts.

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CT-CURS: Unwrapping/Re-slicing Software for Cylindrical Objects Inspected Using Computed Tomography

This method provides 10¥ greater ability to resolve flaws in cylindrical CT data. John H. Glenn Research Center, Cleveland, Ohio Ultra-thin-wall metallic cylinders are extremely difficult to analyze for flaws from top-view X-ray computed tomography (CT) slices and volume renderings. A protocol has been developed using software to unwrap and re-slice the ultra-thinwall cylinder CT data into 2D sheets from the exterior to the interior of the cylinder. This method is based on interior and exterior surface edge detection, and under proper conditions, is fully automated and requires no input from the user except proper voxel dimension from the CT experiment and wall thickness of the part. By performing this transformation to a series of 2D sheets, and utilizing a local contrast expansion method in which each sheet is automatically contrast expanded between its minimum and maximum gray values, the flaws “pop out” at the inspector. This software has allowed NASA to extend the in-house world-class micro-computed tomography method for 10x better flaw resolution for cylindrical structures.

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