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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 NTRS2006

Using Plates To Represent Fillets in Finite-Element Modeling

A method that involves the use of fictitious plate elements denoted b ridge plates has been developed for representing the stiffnesses of fillets in finiteelement calculations of deflections, stresses, and strains in structures. The bridge plates of the present method are re duced-order models of fillets that do not yield accurate stresses wi thin fillets but do make it possible to accurately calculate the dyna mic characteristics of the structure and to approximate the effects of fillets on stresses and strains elsewhere in a structure that con tains the fillets

Brown, Andrew↗
NASA NTRS2010

Suzaku Observes Weak Flares from IGRJ17391-3021 Representing a Common Low-Activity State in this SFXT

We present an analysis of a 37-ks observation of the supergiant fast X-ray transient (SFXT) IGRJ17391 -3021 (=XTEJ1739-302) gathered with Suzaku. The source evolved from quiescence to a low-activity level culminating in three weak flares lasting approx.3 ks each in which the peak luminosity is only a factor of 5 times that of the pre-flare luminosity. The minimum observed luminosity was 1.3 x 10(exp 33) erg/s (d/2.7 kpc)(exp 2) in the 0.5-10 keV range. The weak flares are accompanied by significant changes in the spectral parameters including a column density (N(sub H) = (4.1(+0.4/-0.5)) x 10(exp 22)/sq cm) that is approx.2-9 times the absorption measured during quiescence. Accretion of obscuring clumps of stellar wind material can explain both the small flares and the increase in NH. Placing this observation in the context of the recent Swift monitoring campaign, we find that weak-flaring episodes, or at least epochs of enhanced activity just above the quiescent level but well below the moderately bright or high-luminosity outbursts, represent more than 60+/-5% of all observations in the 0.5-10keV energy range making this the most common state in the emission behavior of IGRJ17391 -3021.

Bodaghee, A.↗
NASA NTRS2012

Design of a Representative Low Earth Orbit Satellite to Improve Existing Debris Models

This paper summarizes the process and methodologies used in the design of a small-satellite, DebriSat, that represents materials and construction methods used in modern day Low Earth Orbit (LEO) satellites. This satellite will be used in a future hypervelocity impact test with the overall purpose to investigate the physical characteristics of modern LEO satellites after an on-orbit collision. The major ground-based satellite impact experiment used by DoD and NASA in their development of satellite breakup models was conducted in 1992. The target used for that experiment was a Navy Transit satellite (~40 cm, 35 kg) fabricated in the 1960 s. Modern satellites are very different in materials and construction techniques from a satellite built 40 years ago. Therefore, there is a need to conduct a similar experiment using a modern target satellite to improve the fidelity of the satellite breakup models. The design of DebriSat will focus on designing and building a next-generation satellite to more accurately portray modern satellites. The design of DebriSat included a comprehensive study of historical LEO satellite designs and missions within the past 15 years for satellites ranging from 10 kg to 5000 kg. This study identified modern trends in hardware, material, and construction practices utilized in recent LEO missions, and helped direct the design of DebriSat.

Clark, S.↗
NASA NTRS2016

Acoustic Characterization and Prediction of Representative, Small-Scale Rotary-Wing Unmanned Aircraft System Components

In this study, hover performance and acoustic measurements are taken on two different isolated rotors representative of small-scale rotary-wing unmanned aircraft systems (UAS) for a range of rotation rates. Each rotor system consists of two fixed-pitch blades powered by a brushless motor. For nearly the same thrust condition, significant differences in overall sound pressure level (OASPL), up to 8 dB, and directivity were observed between the two rotor systems. Differences are shown to be in part attributed to different rotor tip speeds, along with increased broadband and motor noise levels. In addition to acoustic measurements, aeroacoustic predictions were implemented in order to better understand the noise content of the rotor systems. Numerical aerodynamic predictions were computed using the unsteady Reynoldsaveraged Navier Stokes code OVERFLOW2 on one of the isolated rotors, while analytical predictions were computed using the Propeller Analysis System of the Aircraft NOise Prediction Program (ANOPP-PAS) on the two rotor configurations. Preliminary semi-empirical frequency domain broadband noise predictions were also carried out based on airfoil self-noise theory in a rotational reference frame. The prediction techniques further supported trends identified in the experimental data analysis. The brushless motors were observed to be important noise contributors and warrant further investigation. It is believed that UAS acoustic prediction capabilities must consider both rotor and motor components as part of a combined noise-generating system.

Zawodny, Nikolas S.↗
NASA NTRS2016

Tool for Generation of MAC/GMC Representative Unit Cell for CMC/PMC Analysis

This document describes a recently developed analysis tool that enhances the resident capabilities of the Micromechanics Analysis Code with the Generalized Method of Cells (MAC/GMC) 4.0. This tool is especially useful in analyzing ceramic matrix composites (CMCs), where higher fidelity with improved accuracy of local response is needed. The tool, however, can be used for analyzing polymer matrix composites (PMCs) as well. MAC/GMC 4.0 is a composite material and laminate analysis software developed at NASA Glenn Research Center. The software package has been built around the concept of the generalized method of cells (GMC). The computer code is developed with a user friendly framework, along with a library of local inelastic, damage, and failure models. Further, application of simulated thermomechanical loading, generation of output results, and selection of architectures to represent the composite material have been automated to increase the user friendliness, as well as to make it more robust in terms of input preparation and code execution. Finally, classical lamination theory has been implemented within the software, wherein GMC is used to model the composite material response of each ply. Thus, the full range of GMC composite material capabilities is available for analysis of arbitrary laminate configurations as well. The primary focus of the current effort is to provide a graphical user interface (GUI) capability that generates a number of different user-defined repeating unit cells (RUCs). In addition, the code has provisions for generation of a MAC/GMC-compatible input text file that can be merged with any MAC/GMC input file tailored to analyze composite materials. Although the primary intention was to address the three different constituents and phases that are usually present in CMCs-namely, fibers, matrix, and interphase-it can be easily modified to address two-phase polymer matrix composite (PMC) materials where an interphase is absent. Currently, the tool capability includes generation of RUCs for square packing, hexagonal packing, and random fiber packing as well as RUCs based on actual composite micrographs. All these options have the fibers modeled as having a circular cross-sectional area. In addition, a simplified version of RUC is provided where the fibers are treated as having a square cross section and are distributed randomly. This RUC facilitates a speedy analysis using the higher fidelity version of GMC known as HFGMC. The first four mentioned options above support uniform subcell discretization. The last one has variable subcell sizes due to the primary intention of keeping the RUC size to a minimum to gain the speed ups using the higher fidelity version of MAC. The code is implemented within the MATLAB (The Mathworks, Inc., Natick, MA) developmental framework; however, a standalone application that does not need a priori MATLAB installation is also created with the aid of the MATLAB compiler.

Materials Engineering↗
NASA NTRS2018

Probabilistic Sensitivity Analyses Incorporating Surrogate Models for the Structural Response of a Representative Inflatable Space Structure

This study concentrates on results from probabilistic analysis and numerical simulation tools to identify parameter sensitivities and assess surrogate model suitability for a novel inflatable airlock concept, specifically the Non-Axisymmetric Inflatable Pressure Structure (NAIPS) under NASA's Minimalistic Advanced Softgoods Hatch (MASH) Program. The current studies extended the demonstration of probabilistic analysis tools to identify parameter sensitivities by: incorporating nonlinear material load-strain property curves and orthotropic representation of the fabric; and exploring the use of surrogate models to facilitate rapid evaluations as new information becomes available, as well as enable optimizations. The airlock model has been simplified to focus on the end dome section. Brief overviews of the finite element model and associated surrogate models are provided along with the probabilistic sensitivity analysis approaches. Responses of interest include the sensitivities of various loads in the structural elements of the NAIPS to material properties, cord lengths, inflation pressure and friction between softgoods components. The use of surrogate models was explored to facilitate rapid sensitivity evaluations as parameter ranges change. The completion of the sensitivity studies improved understanding of the dependence of load responses to several uncertain parameters and confidence in the ability to use surrogate models to represent the finite element simulations.

Lyle, Karen H.↗
NASA NTRS2016

A Representative Application of a Layered Interface Modeling Pattern

Model-based systems engineering (MBSE) is intended to improve how systems engineering is performed compared with a more traditional document-based approach by effectively using models to analyze, specify, design, and verify systems. The OMG Systems Modeling Language (OMG SysML™) enables the practice of MBSE by providing a robust and expressive language for representing systems.

Shames, Peter M.↗
NASA NTRSDate not supplied

Computational Prediction of Broadband Noise from a Representative Unmanned Aerial System Rotor

This work details the application of a lattice-Boltzmann method–very-large-eddy simulation (LBM-VLES) employed by the software suite, PowerFLOW. This LBM-VLES simulation predicted the aeroacoustic noise emanating from a representative, small unmanned aircraft system rotor, namely, the DJI-9450 in a hover condition. Predicted total aerodynamic loading as well as 2D aerodynamic loading along discrete spanwise sections of a rotor blade were compared to lower fidelity predictions and experimental results acquired in the Structural Acoustic Loads and Transmission anechoic chamber facility at the NASA Langley Research Center. The total acoustic spectra were decomposed into tonal and broadband components, which showed that broadband noise was a dominant contributor above 1 kHz for this rotor. These data were then compared to experimentally acquired data, showing good agreement up to approximately 11 kHz. Above 11 kHz, however, a grid sensitivity study showed dependency of the highest resolvable frequency on the spatial resolution of the computational domain, explaining the roll off in predicted data. Individual broadband noise sources were further investigated by calculating one-third octave sound pressure levels of the unsteady pressure fluctuations acting on the rotor, providing evidence that blade self-noise was the prominent noise source. Using these results, blade wake interaction noise was seen to be negligible for this particular rotor, which was further validated by calculating blade vortex miss distances and comparing to theory.

Christopher S. Thurman↗
NASA NTRS2022

AgMIP Regional Integrated Assessment of Agricultural Systems in Nioro, Senegal: Representative Agricultural Pathways, Climate, Crop and Economic Datasets

This paper describes the datasets that were used to implement an AgMIP Regional Integrated Assessment for the Nioro region of Senegal to assess the potential impacts of climate change on the principal agricultural system in the Senegal peanut basin and to assess adaptations of that system to climate change under current as well as future climate and socio-economic conditions. This dataset includes the Representative Agricultural Pathways developed for Nioro from 2000-2050; the climate data that were used to implement crop yield simulations; the data that were used to parameterize the DSSAT and APSIM crop models, including historical climate data and future climate scenarios; and the data that were used to parameterize the Tradeoff Analysis Model for Multi-dimensional Impact Assessment (TOAMD) economic simulation model, as well as simulated model outputs.

AgMIP↗
NASA NTRS2020

BDDs for Representing Data in Runtime Verification

A BDD (Boolean Decision Diagram) is a data structure for the compact representation of a Boolean function. It is equipped with efficient algorithms for minimization and for applying Boolean operators. The use of BDDs for representing Boolean functions, combined with symbolic algorithms, facilitated a leap in the capability of model checking for the verification of systems with a huge number of states. Recently BDDs were considered as an efficient representation of data for Runtime Verification (RV). We review here the basic theory of BDDs and summarize their use in model checking and specifically in runtime verification.

Peled, Doron↗
NASA NTRSDate not supplied

Lunar Dust Tolerance Testing of Representative Seals for Lunar Surface Hatch Seals

The Moon’s surface creates a uniquely challenging environment for mechanisms and materials. Electrostatic adhesion combined with a jagged particulate morphology makes lunar dust particularly destructive to the components and sub-systems of lunar surface assets. One component that will be acutely impacted by lunar dust is seals, particularly those on the hatches which will be opened and closed to allow extravehicular activities (EVA) and on docking systems that will connect surface assets and spacecraft together. Lunar dust on these seals can create leak paths for the pressurized atmosphere of a surface asset to escape. Quantifying the level of lunar dust contamination that is allowable for seals is of paramount importance for mission planners and asset designers. This paper covers dust tolerance testing that was conducted on representative hatch seals with the Uniform Dust Deposition System (UDDS) at NASA Glenn Research Center [1]. Sub scale (≈30 cm diameter) versions of seals for the Orion docking hatch and NASA Docking System (NDS were coated evenly with varying amounts of lunar dust simulant to evaluate its effect on seals leak rates. The resulting leak rate results from these flight-proven seal design can help planners and designers construct robust missions and products

N. Jimenez↗
NASA NTRSDate not supplied

Deriving representative size distributions from UW OPC data for SAGE II extinction measurements

For the purposes of studying the impacts of aerosols on the chemistry and climate of the atmosphere, size distribution information has been inferred from extinction measurements for decades. Using the measurements from the University of Wyoming balloon-borne optical particle counter experiment we have derived representative size distributions at SAGE II channel wavelengths. These are bimodal lognormal size distributions grouped into bins of 525 to 1020 nm extinction ratio. Future work will include expanding this analysis to SAGE III’s channels and considering the effect of a absorbing channel in the IR would have.

Aerosol↗
NASA NTRS2023

Low-Cost Testing in Representative Lunar Regolith Environment

Rapid prototyping and testing are key enablers of iterative designs common in early technology research and development. Testing in a dusty environment is critical to prepare the Cryogenic Magnetic Coupler for lunar operations. To enable early and iterative testing of dust mitigation concepts, a low-cost, low-fidelity representative lunar regolith environment was developed at the National Aeronautics and Space Administration (NASA) Armstrong Flight Research Center (Edwards, California). Based on preliminary testing with this test setup, a similar setup may be of interest to universities and other entities looking to develop the capability to safely test relatively small-scale components with lunar regolith simulant. The development of this lunar regolith test chamber and results from preliminary testing are presented in this paper. Also discussed are further development strategies for the potential improvement of this setup.

Scott Stebbins↗
NASA NTRSDate not supplied

Deriving Representative Size Distributions From UW OPC Data for Sage II Extinction Measurements

For the purposes of studying the impacts of aerosols on the chemistry and climate of the atmosphere, size distribution information has been inferred from extinction measurements for decades. Using the measurements from the University of Wyoming balloon-borne optical particle counter experiment we have derived representative size distributions at SAGE II channel wavelengths. These are bimodal lognormal size distributions grouped into bins of 525 to 1020 nm extinction ratio. However there exists fundamental limitations to the information that can be derived from SAGE measurements. Future work will include expanding this analysis to SAGE III’s channels and considering the effect of a absorbing channel in the IR would have.

Aerosol↗
NASA NTRSDate not supplied

Deriving Representative Size Distributions From UW OPC Data for Sage II Extinction Measurements

For the purposes of studying the impacts of aerosols on the chemistry and climate of the atmosphere, size distribution information has been inferred from extinction measurements for decades. Using the measurements from the University of Wyoming balloon-borne optical particle counter experiment we have derived representative size distributions at SAGE II channel wavelengths. These are bimodal lognormal size distributions grouped into bins of 525 to 1020 nm extinction ratio. However there exists fundamental limitations to the information that can be derived from SAGE measurements. Future work will include expanding this analysis to SAGE III’s channels and considering the effect of a absorbing channel in the IR would have.

Aerosol↗
NASA NTRSDate not supplied

Development of a Combined Cohesive and Virtual Crack-Closure Technique Approach to Represent R-Curves

Resistance curve (R-curve) effects due to fiber bridging, crack migration, and other blunting mechanisms are common in composite laminates. These mechanisms can dramatically increase the resistance to crack propagation but can be challenging to simulate. Delamination with R-curves can be analyzed using cohesive zone modeling (CZM) or the virtual crack closure technique (VCCT). Large fracture process zones can be simulated with CZM, but they require highly refined meshes. Coarser meshes can be used with VCCT, but this method is only applicable to small fracture process zones with R-curves defined as functions of position. Therefore, a technique with the computational efficiency of VCCT and the natural ability of cohesive elements to represent large fracture process zones is desirable. An approach is proposed that starts as a CZM in which the cohesive traction separation law (TSL) is separated into high-strength (HS) and low-strength (LS) components. The HS part, which is responsible for the mesh requirements of the CZM analysis, is replaced by VCCT. The combined method is evaluated by analyzing the response of double cantilevered beam specimens. Two specimen layup configurations, [0/90/90/0] 3s and [0/90/90/0] 9s , are evaluated. The R-curve response from each configuration is determined and applied to the constitutive properties of models built with CZM and with VCCT. The results and computational efficiency of the CZM, VCCT, and combined approaches are compared. The results are indicative that a combined cohesive/VCCT approach can enable progressive failure analyses to retain the computational efficiency of VCCT with the ability of the cohesive elements to capture R-curve effects.

Virtual Crack-Closure Technique↗
NASA NTRSDate not supplied

Effects of Natural Variability on the Use of Standard Deviation to Represent Measurement Uncertainties in Atmospheric Composition Studies

Measurement uncertainty is defined as a “non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand”. It is most common that the uncertainties of GAW hourly measurements, such as greenhouse gas measurements, are reported as standard deviations derived from individual sampling at a higher time resolution (e.g., 1 min). In contrast, the uncertainties of GAW measurements of reactive gases and aerosol properties are reported in percentiles covering the same probability. A quick look at hourly CO 2 data from Cape Grim, Australia yielded some interesting findings: the hourly standard deviation is, on average, more than a factor of 10 higher for the measurements under non-background conditions (over 50% observations), while the difference in average CO 2 amount fraction was less than 2 ppm. The dramatic contrast cannot be explained by the difference in measurement uncertainties, but can largely be attributed the natural variability, or episodic ambient CO 2 variation reflecting changes in meteorological conditions or emissions. These initial findings motivated a more in-depth analysis of the ground-based measurements of trace gases and aerosol properties. This analysis will be using continuous 1 min ground site observations to construct time averaged statistical indicators to evaluate whether the standard deviation is adequate to represent the dispersion, especially under marked influence by natural variability. The suitability of this representation can be determined by examining the difference between the standard deviation and percentiles encompassing the same probability. We will examine time intervals of 1 hour, 3 hours, and 24 hours, with the latter time intervals chosen to match those commonly used in model assessments. We will also investigate how natural variability can alter the probability distribution of the measurands and how adequate the quadrature propagation of uncertainties is under these conditions. The results will include several trace gases (e.g., CO 2 , CO, O 3 , and NO 2 ) with a range of measurement techniques (e.g., PANDORA, in situ), atmospheric lifetimes, and aerosol properties (e.g. scattering coefficient). The findings from this analysis should provide some useful feedback on the best practices for uncertainty reporting.

Measurement Uncertainty↗