Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “quantitative structure”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Boiler Tube Corrosion Characterization with a Scanning Thermal Line

Wall thinning due to corrosion in utility boiler water wall tubing is a significant operational concern for boiler operators. Historically, conventional ultrasonics has been used for inspection of these tubes. Unfortunately, ultrasonic inspection is very manpower intense and slow. Therefore, thickness measurements are typically taken over a relatively small percentage of the total boiler wall and statistical analysis is used to determine the overall condition of the boiler tubing. Other inspection techniques, such as electromagnetic acoustic transducer (EMAT), have recently been evaluated, however they provide only a qualitative evaluation - identifying areas or spots where corrosion has significantly reduced the wall thickness. NASA Langley Research Center, in cooperation with ThermTech Services, has developed a thermal NDE technique designed to quantitatively measure the wall thickness and thus determine the amount of material thinning present in steel boiler tubing. The technique involves the movement of a thermal line source across the outer surface of the tubing followed by an infrared imager at a fixed distance behind the line source. Quantitative images of the material loss due to corrosion are reconstructed from measurements of the induced surface temperature variations. This paper will present a discussion of the development of the thermal imaging system as well as the techniques used to reconstruct images of flaws. The application of the thermal line source coupled with the analysis technique represents a significant improvement in the inspection speed and accuracy for large structures such as boiler water walls. A theoretical basis for the technique will be presented to establish the quantitative nature of the technique. Further, a dynamic calibration system will be presented for the technique that allows the extraction of thickness information from the temperature data. Additionally, the results of the application of this technology to actual water wall tubing samples and in-situ inspections will be presented.

Cramer, K. Elliott↗
NASA NTRS2001

Scalar Measurements and Analysis of Helium Jets in Earth Gravity and Microgravity using Rainbow Schlieren Deflectometry

Recent experiments have shown that low-density gas jets injected into a high-density gas undergo an instability mode leading to highly periodic oscillations in the flow field. The transition from laminar to turbulent flow in these jets is abrupt, without a gradual change in scales. Although this type of instability at high Richardson numbers has been attributed to buoyancy, direct physical evidence was not acquired through experiments. In this study, several experiments were conducted in Earth gravity and microgravity to acquire qualitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The operating parameters of this study included the tube inside diameter, the jet Reynolds number, and the jet Richardson number. Tubes with inside diameters of 19.05 mm and 31.75 mm were used in the experiments conducted in the drop tower. The jet flow was analyzed using quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and the resulting helium mole fraction obtained from color schlieren images taken at 60 Hz. Three sets of experimental data with respect to three schlieren fields of view were acquired for each tube. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. The global jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low-density jet was buoyancy-induced. This study provides quantitative details of temporal flow evolution as the experiments undergo change in gravity in the drop tower.

Yep, Tze Wing↗
NASA NTRS2005

Probabilisitc Geobiological Classification Using Elemental Abundance Distributions and Lossless Image Compression in Recent and Modern Organisms

Last year we presented techniques for the detection of fossils during robotic missions to Mars using both structural and chemical signatures[Storrie-Lombardi and Hoover, 2004]. Analyses included lossless compression of photographic images to estimate the relative complexity of a putative fossil compared to the rock matrix [Corsetti and Storrie-Lombardi, 2003] and elemental abundance distributions to provide mineralogical classification of the rock matrix [Storrie-Lombardi and Fisk, 2004]. We presented a classification strategy employing two exploratory classification algorithms (Principal Component Analysis and Hierarchical Cluster Analysis) and non-linear stochastic neural network to produce a Bayesian estimate of classification accuracy. We now present an extension of our previous experiments exploring putative fossil forms morphologically resembling cyanobacteria discovered in the Orgueil meteorite. Elemental abundances (C6, N7, O8, Na11, Mg12, Ai13, Si14, P15, S16, Cl17, K19, Ca20, Fe26) obtained for both extant cyanobacteria and fossil trilobites produce signatures readily distinguishing them from meteorite targets. When compared to elemental abundance signatures for extant cyanobacteria Orgueil structures exhibit decreased abundances for C6, N7, Na11, All3, P15, Cl17, K19, Ca20 and increases in Mg12, S16, Fe26. Diatoms and silicified portions of cyanobacterial sheaths exhibiting high levels of silicon and correspondingly low levels of carbon cluster more closely with terrestrial fossils than with extant cyanobacteria. Compression indices verify that variations in random and redundant textural patterns between perceived forms and the background matrix contribute significantly to morphological visual identification. The results provide a quantitative probabilistic methodology for discriminating putatitive fossils from the surrounding rock matrix and &om extant organisms using both structural and chemical information. The techniques described appear applicable to the geobiological analysis of meteoritic samples or in situ exploration of the Mars regolith. Keywords: cyanobacteria, microfossils, Mars, elemental abundances, complexity analysis, multifactor analysis, principal component analysis, hierarchical cluster analysis, artificial neural networks, paleo-biosignatures

Storrie-Lombardi, Michael C.↗
NASA NTRSDate not supplied

Predicting Char Yield of High-Temperature Resins

A simulation technique has been developed for predicting the char yield of organic resins during high-temperature processing. In silico methods can aid in the screening of new advanced materials for a number of important properties, but no chemistry-sensitive protocol currently exists for predicting the important experimental value of char yield. The proposed method utilizes a reactive force field (ReaxFF) to model the chemical transformation of precursor monomers into carbonized structures during three processing stages: ramp-up to pyrolysis temperatures (~3000 K), pyrolysis, and quenching. Achieving good agreement with experimental char yields requires continuous removal of small by-product molecules to mimic outgassing, and the application of high pressure to encourage the formation of a dense, glassy network. Six different resin chemistries were investigated: an ethynyl, a phenylethynyl, a cyanate ester, a phthalonitrile, acrylonitrile, and adamantane. These candidates represent a diverse group of precursors with respect to initial cyclic content, presence of heteroatoms, and types of reactive groups. The protocol developed accurately predicts the relative char yield between the investigated chemistries and provides quantitative agreement with experimental values, especially for high char yield resins. Several simulated properties of the carbonized structures are compared with experimental results, including outgassing products, morphology of the final chemical configurations, cyclic content, and mechanical properties.

polymer simulations, molecular dynamics↗
NASA NTRS1996

Dextroamphetamine: a pharmacologic countermeasure for space motion sickness and orthostatic dysfunction

Dextroamphetamine has potential as a pharmacologic agent for the alleviation of two common health effects associated with microgravity. As an adjuvant to Space Motion Sickness (SMS) medication, dextroamphetamine can enhance treatment efficacy by reducing undesirable Central Nervous System (CNS) side effects of SMS medications. Secondly, dextroamphetamine may be useful for the prevention of symptoms of post-mission orthostatic intolerance caused by cardiovascular deconditioning during spaceflight. There is interest in developing an intranasal delivery form of dextroamphetanmine for use as a countermeasure in microgravity conditions. Development of this dosage form will require an analytical detection method with sensitivity in the low ng range (1 to 100 ng/mL). During the 1995 Summer Faculty Fellowship Program, two analytical methods were developed and evaluated for their suitability as quantitative procedures for dextroamphetamine in studies of product stability, bioavailability assessment, and pharmacokinetic evaluation. In developing some of the analytical methods, beta-phenylethylamine, a primary amine structurally similar to dextroamphetamine, was used. The first analytical procedure to be evaluated involved hexane extraction and subsequent fluorescamine labeling of beta-phenylethylamine. The second analytical procedure to be evaluated involved quantitation of dextroamphetamine by an Enzyme-Linked ImmunoSorbent Assay (ELISA).

Snow, L. Dale↗
NASA NTRS2000

Thermographic Imaging of Material Loss in Boiler Water-Wall Tubing by Application of Scanning Line Source

Localized wall thinning due to corrosion in utility boiler water-wall tubing is a significant inspection concern for boiler operators. Historically, conventional ultrasonics has been used for inspection of these tubes. This technique has proven to be very manpower and time intensive. This has resulted in a spot check approach to inspections, documenting thickness measurements over a relatively small percentage of the total boiler wall area. NASA Langley Research Center has developed a thermal NDE technique designed to image and quantitatively characterize the amount of material thinning present in steel tubing. The technique involves the movement of a thermal line source across the outer surface of the tubing followed by an infrared imager at a fixed distance behind the line source. Quantitative images of the material loss due to corrosion are reconstructed from measurements of the induced surface temperature variations. This paper will present a discussion of the development of the thermal imaging system as well as the techniques used to reconstruct images of flaws. The application of the thermal line source coupled with the analysis technique represents a significant improvement in the inspection speed for large structures such as boiler water-walls. A theoretical basis for the technique will be presented which explains the quantitative nature of the technique. Further, a dynamic calibration system will be presented for the technique that allows the extraction of thickness information from the temperature data. Additionally, the results of applying this technology to actual water-wall tubing samples and in situ inspections will be presented.

Cramer, K. Elliott↗
NASA NTRS1989

The outer R Aquarii nebula - Comparison of 6 centimeter radio continuum and Balmer line emission

The 6 cm radio continuum structure of the R Aquarii outer nebula is compared with CCD imagery of H-alpha and H-beta line emission. It is shown that the 6 cm VLA imagery is morphologically similar and quantitatively related spatially to Balmer line imagery. There is negligible interstellar or circumstellar absorption along the line of sight to the outer nebula. The 6 cm structure of the outer nebula is consistent with thermal bremsstrahlung emission by a hot, optically thin gas. Spectra of the outer R Aquarii nebula are suggestive of shock-wave heating. The approximate equality of mass loss and radiative cooling suggests that the system's wind is probably enough to power the outer nebula and may account for its long-term persistence.

Hollis, J. M.↗
NASA NTRS2001

Quantitative risk assessment system (QRAS)

A quantitative risk assessment system (QRAS) builds a risk model of a system for which risk of failure is being assessed, then analyzes the risk of the system corresponding to the risk model. The QRAS performs sensitivity analysis of the risk model by altering fundamental components and quantifications built into the risk model, then re-analyzes the risk of the system using the modifications. More particularly, the risk model is built by building a hierarchy, creating a mission timeline, quantifying failure modes, and building/editing event sequence diagrams. Multiplicities, dependencies, and redundancies of the system are included in the risk model. For analysis runs, a fixed baseline is first constructed and stored. This baseline contains the lowest level scenarios, preserved in event tree structure. The analysis runs, at any level of the hierarchy and below, access this baseline for risk quantitative computation as well as ranking of particular risks. A standalone Tool Box capability exists, allowing the user to store application programs within QRAS.

Weinstock, Robert M↗
NASA NTRS1998

A Novel Ultrasonic Method for Characterizing Microstructural Gradients in Tubular Structures

Ultrasonic velocity and time-of-flight (TOF) imaging that uses back surface reflections to gage volumetric material quality is highly suited for quantitative characterization of microstructural gradients including those due to pore fraction, density, fiber fraction, and chemical composition variations. However, a weakness of conventional pulse echo ultrasonic velocity and TOF imaging is that the image shows the effects of thickness as well as microstructural variations, unless the part is uniformly thick. This limits this imaging method's usefulness in practical applications. Prior studies have described a pulse echo TOF based ultrasonic imaging method that requires using a single transducer in combination with a reflector plate placed behind samples which, eliminates the effect of thickness variation in the image. In those studies, this method was successful at isolating ultrasonic variations due to material in plate like samples of silicon nitride, metal matrix composite, and polymer matrix composite. In this study, the method is engineered for inspection of more complex shaped structures- those having (hollow) tubular or curved geometry. The experimental inspection technique and results are described as applied to a polymer matrix composite "proof of concept" tube that contains machined patches of various depths and an as manufactured monolithic silicon nitride ceramic tube that might be used in "real world" applications.

Roth, Don J.↗
NASA NTRS1973

The turbulence structure in the plane two-stream mixing layer.

Experimental data on the turbulent structure of free shear layers is examined in incompressible air streams. Both single-point and two-point data are used to examine the large coherent structure of the mixing layer. The use of spatial scales to define this large structure is explored. Application of these scales to modeling of free shear layers to show the similarity of such flows is demonstrated. Comparison of the statistical structure with observations from shadowgraph displays of plane shear layer flows shows good qualitative and quantitative agreement.

Jones, B. G.↗
NASA NTRS1979

X-ray diffraction studies of shocked lunar analogs

The X-ray diffraction experiments on shocked rock and mineral analogs of particular significance to lunar geology are described. Materials naturally shocked by meteorite impact, nuclear-shocked, or artificially shocked in a flat plate accelerator were utilized. Four areas were outlined for investigation: powder diffractometer studies of shocked single crystal silicate minerals (quartz, orthoclase, oligoclase, pyroxene), powder diffractometer studies of shocked polycrystalline monomineralic samples (dunite), Debye-Scherrer studies of single grains of shocked granodiorite, and powder diffractometer studies of shocked whole rock samples. Quantitative interpretation of peak shock pressures experienced by materials found in lunar or terrestrial impact structures is presented.

Hanss, R. E.↗
NASA NTRS1986

Quantitative thermal diffusivity measurements of composites

A remote radiometric technique for making quantitative thermal diffusivity measurements is described. The technique was designed to make assessments of the structural integrity of large composite parts, such as wings, and can be performed at field sites. In the measurement technique, a CO2 laser beam is scanned using two orthogonal servo-controlled deflecting mirrors. An infrared imager, whose scanning mirrors oscillate in the vertical and the horizontal directions, is used as the detector. The analysis technique used to extract the diffusivity from these images is based on a thin infinite plate assumption, which requires waiting a given period of time for the temperature to equilibrate throughout the thickness of the sample. The technique is shown to be accurate to within two percent for values of the order of those for composite diffusivities, and to be insensitive to convection losses.

Heath, D. M.↗
NASA NTRS1987

Theoretical approaches to metal chemistry

Theoretical calculations on metals ranging from very accurate ab initio studies of diatomic and triatomic systems to model studies of larger clusters are presented. Recent improvements in the representation of one-particle and n-particle spaces have made possible the prediction that Al2 has a 3Pi(u) ground state, even though the 3Sigma(-)g state lies within 200/cm. Results suggest that cluster geometry varies dramatically with cluster size, and that rather large clusters are required before the bulk structure becomes optimal. Al cluster studies show that three-body terms are needed for quantitative agreement with ab initio calculations.

Bauschlicher, Charles W.↗
NASA NTRS1994

Testing and analysis of flat and curved panels with multiple cracks

An experimental and analytical investigation of multiple cracking in various types of test specimens is described in this paper. The testing phase is comprised of a flat unstiffened panel series and curved stiffened and unstiffened panel series. The test specimens contained various configurations for initial damage. Static loading was applied to these specimens until ultimate failure, while loads and crack propagation were recorded. This data provides the basis for developing and validating methodologies for predicting linkup of multiple cracks, progression to failure, and overall residual strength. The results from twelve flat coupon and ten full scale curved panel tests are presented. In addition, an engineering analysis procedure was developed to predict multiple crack linkup. Reasonable agreement was found between predictions and actual test results for linkup and residual strength for both flat and curved panels. The results indicate that an engineering analysis approach has the potential to quantitatively assess the effect of multiple cracks in the arrest capability of an aircraft fuselage structure.

Broek, David↗
NASA NTRS1994

Development of a Model Following Control Law for Inflight Simulation and Flight Controls Research

The U.S. Army and NASA are currently developing the Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL) at the Ames Research Center. RASCAL, shown in Figure 1, is a UH-60, which is being modified in a phased development program to have a research fly-by-wire flight control system, and an advanced navigation research platform. An important part of the flight controls and handling qualities research on RASCAL will be an FCS design for the aircraft to achieve high bandwidth control responses and disturbance rejection characteristics. Initially, body states will be used as feedbacks, but research into the use of rotor states will also be considered in later stages to maximize agility and maneuverability. In addition to supporting flight controls research, this FCS design will serve as the inflight simulation control law to support basic handling qualities, guidance, and displays research. Research in high bandwidth controls laws is motivated by the desire to improve the handling qualities in aggressive maneuvering and in severely degraded weather conditions. Naturally, these advantages will also improve the quality of the model following, thereby improving the inflight simulation capabilities of the research vehicle. High bandwidth in the control laws provides tighter tracking allowing for higher response bandwidths which can meet handling qualities requirements for aggressive maneuvering. System sensitivity is also reduced preventing variations in the response from the vehicle due to changing flight conditions. In addition, improved gust rejection will result from this reduced sensitivity. The gust rejection coupled with a highly stable system will make more precise maneuvering and pointing possible in severely degraded weather conditions. The difficulty in achieving higher bandwidths from the control laws in the feedback and in the responses arises from the complexity of the models that are needed to produce a satisfactory design. In this case, high quality models that include rotor dynamics in a physically meaningful context must be available. A non-physical accounting of the rotor, such as lumping the effect as a time delay, is not likely to produce the desired results. High order simulation models based on first principals are satisfactory for the initial design phase in order to work out the control law design concept and get an initial set of gains. These models, however, have known deficiencies, which must be resolved in the final control law design. The error in the pitch-roll cross coupling is one notable deficiency that even sophisticated rotorcraft models including complex wake aerodynamics have yet to capture successfully. This error must be accounted for to achieve the desired decoupling. The approach to design the proposed inflight simulation control law is based on using a combination of simulation and identified models. The linear and nonlinear higher order models were used to develop an explicit model following control structure. This structure was developed to accommodate the design of control laws compliant to many of the quantitative requirements in ADS-33C. Furthermore, it also allows for control law research using rotor-state feedback and other design methodologies such as Quantitative Feedback and H-Infinity. Final gain selection will be based on higher order identified models which include rotor degrees of freedom.

Takahashi, Mark↗
NASA NTRS1996

In Situ Mineralogical Analysis of Planetary Materials Using X-Ray Diffraction and X-Ray Fluorescence

Remote observations of Mars have led scientists to believe that its early climate was similar to that of the early Earth, having had abundant liquid water and a dense atmosphere. One of the most fascinating questions of recent times is whether simple bacterial life developed on Mars (as it did on the Earth) during this early element period. Analyses of SNC meteorites have broadened considerably our knowledge of the chemistry of certain types of Martian rocks, underscoring the tantalizing possibility of early hydrothermal systems and even of ancient bacterial life. Detailed analyses of SNC meteorites in Terrestrial laboratories utilize the most sophisticated organic, isotopic and microscopic techniques in existence. Indeed; it is unlikely that the key biogenic indicators used in McKay et al (ibid) could be identified by a remote instrument on the surface of Mars. As a result, it is probable that any robotic search for evidence of an ancient Martian biosphere will have as its focus the identification of key minerals in likely host rocks rather than the direct detection of organic or isotopic biomarkers. Even on a sample return mission, mineralogical screening will be utilized to choose the most likely candidate rocks. X-ray diffraction (XRD) is the only technique that can provide a direct determination of the crystal structures of the phases present within a sample. When many different crystalline phases are present, quantitative analysis is better constrained if used in conjunction with a determination of elemental composition, obtainable by X-ray fluorescence (XRF) using the same X-ray source as for XRD. For planetary surface analysis, a remote instrument combining XRD and XRF could be used for mineralogical characterization of both soils and rocks. We are designing a remote XRD/XRF instrument with this objective in mind. The instrument concept pays specific attention to constraints in sample preparation, weight, volume, power, etc. Based on the geometry of a pinhole camera (transmission geometry, flat two-dimensional detector perpendicular to the direct beam), the instrument (which we call CHEMIN, for Chemistry and Mineralogy) uses an X-ray sensitive CCD detector which will allow concurrent positional and energy-dispersive analysis of collected photons. Thus XRF (energy) and XRD (geometry) analysis of transmitted X-rays will be performed at the same time. Tests performed with single minerals and simple mixtures give promising results. Refinements of the prototype promise interpretable results on complex samples.

Sarrazin, P.↗
NASA NTRS2004

A 3D Convective Model for the Jovian Wind Bands

In an earlier paper, we proposed that Jupiter's alternating wind bands are a manifestation of the global interaction between rotation and convection in a shallow layer. The model, however, was obtained from linearization of the 2D equations of motions. At HKUST/Hong Kong, we are now trying to study this problem by rigorous numerical simulation. Using a three-dimensional spectral numerical code, we compute models for the outermost layer of Jupiter's convective envelope. Two cases have been studied. In one the atmospheric pressure varies from 1 to 23 bar, and in the other from 1 to 115 bar. The physical parameters (internal energy flux, rotation rate) are chosen to be close to those expected, but solar heating, chemistry, as well as dynamical influences from deeper layers are ignored. The models generate wind field patterns that contain alternating jet streams with resemblance to the Jovian bands. Instantaneous values of the mean zonal flow at the equator reach 80 m/sec. Yet the mean meridional flows are less than 1% of such value. The meridional temperature profile at the cloud top level also shows a double hump structure of a few degrees (as observed) in the subtropics. Though there is not complete quantitative agreement (caused perhaps by neglected effects like solar radiation), these models demonstrate, in principle, the feasibility of generating a Jovian type wind pattern through the interaction of fast rotation and convection in a thin shell.

Mayr, H. G.↗
NASA NTRS2017

Validation Process for LEWICE by Use of a Navier-Stokes Solver

A research project is underway at NASA Glenn to produce computer software that can accurately predict ice growth under any meteorological conditions for any aircraft surface. This report will present results from the latest LEWICE release, version 3.5. This program differs from previous releases in its ability to model mixed phase and ice crystal conditions such as those encountered inside an engine. It also has expanded capability to use structured grids and a new capability to use results from unstructured grid flow solvers. A quantitative comparison of the results against a database of ice shapes that have been generated in the NASA Glenn Icing Research Tunnel (IRT) has also been performed. This paper will extend the comparison of ice shapes between LEWICE 3.5 and experimental data from a previous paper. Comparisons of lift and drag are made between experimentally collected data from experimentally obtained ice shapes and simulated (CFD) data on simulated (LEWICE) ice shapes. Comparisons are also made between experimentally collected and simulated performance data on select experimental ice shapes to ensure the CFD solver, FUN3D, is valid within the flight regime. The results show that the predicted results are within the accuracy limits of the experimental data for the majority of cases.

large-eddy simulations↗