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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

The Path Resistance Method for Bounding the Smallest Nontrivial Eigenvalue of a Laplacian

We introduce the path resistance method for lower bounds on the smallest nontrivial eigenvalue of the Laplacian matrix of a graph. The method is based on viewing the graph in terms of electrical circuits; it uses clique embeddings to produce lower bounds on lambda(sub 2) and star embeddings to produce lower bounds on the smallest Rayleigh quotient when there is a zero Dirichlet boundary condition. The method assigns priorities to the paths in the embedding; we show that, for an unweighted tree T, using uniform priorities for a clique embedding produces a lower bound on lambda(sub 2) that is off by at most an 0(log diameter(T)) factor. We show that the best bounds this method can produce for clique embeddings are the same as for a related method that uses clique embeddings and edge lengths to produce bounds.

Guattery, Stephen↗
NASA NTRS1938

A method of rapidly estimating the position of the laminar separation point

A method is described of rapidly estimating the position of the laminar separation point from the given pressure distribution along a body; the method is applicable to a fairly wide variety of cases. The laminar separation point is found by the von Karman-Millikan method for a series of velocity distributions along a flat plate, which consist of a region of uniform velocity followed by a region of uniform decreased velocity. It is shown that such a velocity distribution can frequently replace the actual velocity distribution along a body insofar as the effects on laminar separation are concerned. An example of the application of the method is given by using it to calculate the position of the laminar separation point on the NACA 0012 airfoil section at zero lift. The agreement between the position of the separation point calculated according to the present method and that found from more elaborate computations is very good.

Von Doenhoff, Albert E↗
DOE OSTI2015

Wet-chemical systems and methods for producing black silicon substrates

A wet-chemical method of producing a black silicon substrate. The method comprising soaking single crystalline silicon wafers in a predetermined volume of a diluted inorganic compound solution. The substrate is combined with an etchant solution that forms a uniform noble metal nanoparticle induced Black Etch of the silicon wafer, resulting in a nanoparticle that is kinetically stabilized. The method comprising combining with an etchant solution having equal volumes acetonitrile/acetic acid:hydrofluoric acid:hydrogen peroxide.

14 SOLAR ENERGY↗
NASA NTRS2002

Force Evaluation in the Lattice Boltzmann Method Involving Curved Geometry

The present work investigates two approaches for force evaluation in the lattice Boltzmann equation: the momentum- exchange method and the stress-integration method on the surface of a body. The boundary condition for the particle distribution functions on curved geometries is handled with second order accuracy based on our recent works. The stress-integration method is computationally laborious for two-dimensional flows and in general difficult to implement for three-dimensional flows, while the momentum-exchange method is reliable, accurate, and easy to implement for both two-dimensional and three-dimensional flows. Several test cases are selected to evaluate the present methods, including: (i) two-dimensional pressure-driven channel flow; (ii) two-dimensional uniform flow past a column of cylinders; (iii) two-dimensional flow past a cylinder asymmetrically placed in a channel (with vortex shedding); (iv) three-dimensional pressure-driven flow in a circular pipe; and (v) three-dimensional flow past a sphere. The drag evaluated by using the momentum-exchange method agrees well with the exact or other published results.

Mei, Renwei↗
NASA NTRS1946

Stress Analysis of Columns and Beam Columns by the Photoelastic Method

Principles of similarity and other factors in the design of models for photoelastic testing are discussed. Some approximate theoretical equations, useful in the analysis of results obtained from photoelastic tests are derived. Examples of the use of photoelastic techniques and the analysis of results as applied to uniform and tapered beam columns, circular rings, and statically indeterminate frames, are given. It is concluded that this method is an effective tool for the analysis of structures in which column action is present, particularly in tapered beam columns, and in statically indeterminate structures in which the distribution of loads in the structures is influenced by bending moments due to axial loads in one or more members.

BEAM-COLUMNS - STRESSES↗
DOE OSTI2026

Uniformity, performance, and durability of roll-to-roll-coated iridium oxide electrolyzer catalyst layers

This work investigates the use of roll-to-roll coating methods for the production of iridium oxide catalyst layers for proton exchange membrane water electrolyzers. Catalyst layers were produced using two coating methods: slot die and gravure. By varying the solids content of the catalyst ink and coating process variables loadings between 0.08 and 0.64 mg Ir cm −2 were prepared with relatively high spatial uniformity. However, at loadings below 0.2 mg Ir cm −2 microscopy reveals voids in the catalyst layer due to similar length scales of catalyst agglomerates and overall layer thickness. Electrochemical testing shows that these voids do not impact initial membrane electrode assembly performance but lead to increased performance losses after potential cycling compared to spray coated catalyst layers.

08 HYDROGEN↗
DOE OSTI2022

Correlation energy of the uniform electron gas determined by ground-state conditional probability density functional theory

Conditional-probability density functional theory (CP-DFT) is a formally exact method for finding correlation energies from Kohn-Sham DFT without evaluating an explicit energy functional. We present details on how to generate accurate exchange-correlation energies for the ground-state uniform gas. We also use the exchange hole in a CP antiparallel spin calculation to extract the high-density limit. We give a highly accurate analytic solution to the Thomas-Fermi model for this problem, showing its performance relative to Kohn-Sham and may be useful at high temperatures. We explore several approximations to the CP potential. Furthermore, results are compared to accurate parameterizations for both exchange-correlation energies and holes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

A Geostatistical Study in Support of CO 2 Storage in Deep Saline Aquifers of the Shenhua CCS Project, Ordos Basin, China

The Shenhua Carbon Capture and Storage (CCS) project at the Shenbei Slope injection site in North Yulin is the first 100,000 ton-per-year scale CCS pilot project in China with an injection operation lasting nearly 3 years. In this study, we investigate various geostatistical methods and their impact on the respective geologic models on which simulation is performed to understand the phenomena observed during 3 years of Shenhua CCS operations. Although there was a brief period of wellhead pressure increase at the injection well, it unexpectedly dropped for most of the time. Another interesting observation showed that the majority of CO 2 gas injection was received by the topmost sandstone Liujiagou formation instead of the basement limestone Majiagou formation, which was predicted to have much more injectivity and storage capacity. Based on the current geostatistical methods and available data, 3 steps of reservoir modeling and flow simulation are carried out and they go from having homogeneous property models to incorporating standard 2-point geostatistical methods to using object-based models. The layer-cake models generate a rather uniform plume shape and increased pressure response. Meanwhile, two-point statistical models add more complexity to the size and shape of CO 2 plume, however are not capable of reproducing the pressure decline behavior. These results demonstrate homogeneous and 2-point geostatistical models are inadequate in interpreting subsurface heterogeneity, both due to their method and data limitations. Further work is being done with object-based models to produce a system of meandering rivers based on the geological concept of Shenhua injection site. This will help offset the data limitation and bring our model closer to geologic reality.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRSDate not supplied

Derivation of Effective Properties Based on Porous Scale Simulations Using Filtering Techniques

This study presents a method for derivation of effective properties at the interface and in-depth of porous materials. The method defines a Representative Elementary Volume (REV) and applies filtering techniques to computer effective properties such as porosity and flow quantities, such as velocity and pressure. The script, developed to process the data was tested on the VTK type files that contain the mesh information and the flow solution. The method allows to choose between two types of filters, such as cellular and top-hat and define the size of the REV and number of samples along the domain. Extraction of the REV from the domain is performed to exact boundaries requested for the user. This is done using a triangulation technique and cutting through the cells to comply to the requested boundaries of the volume. The method can be applied to both structured and unstructured meshes. Filtering the material porosity and flow quantities involves integration of the numerical data. The algorithm provides three integration methods, such as Riemann sum, Monte Carlo and Quadrature rule to perform the integration. The Monte-Carlo technique permits the use of either uniform or linearly spaced distribution of points. The Quadrature rule is currently applicable to tetrahedral element types. The Monte Carlo and Quadrature rule methods require interpolation of the flow quantities at the sample points. For interpolation, two methods were tested and are readily available, Gaussian interpolation and re-sampling. It has been shown that re-sampling method has better consistency and acceptable accuracy in interpolation of the data. The algorithm was written in Python language and uses a number of modules. The major module besides numpy is PyVista. It is used to process the computational domain, clip the REV and interpolate the data. Quadrature rule integration was performed using a quadpy module. ParaView software was used externally to convert the flow solution to the VTK (or more specifically VTU) format. Integration of ParaView in the same environment with PyVista encountered problems and could not be implemented in this work. The developed algorithm is expected to be applicable to unstructured meshes and more complex porous structures as soon as the data can be passed in VTK type format. With the report is provided Python script for filtering the solution and a Matlab script for simple generation and processing of 2-D and 3-D porous channel geometries. The two scripts don't communicate.

Alexsander Zibitsker↗
NASA NTRS1988

Compressibility effects on flow friction in a fully developed pipe flow

A method was evolved to account for the effects of compressibility in flows through long circular pipes of uniform diameter. Velocity and density variations across the flow cross section were approximated by profile shapes recommended for a flow past flat plates. The wall of the pipe was assumed to have attained an adiabatic condition. An integral method was used to obtain solutions for the governing equations of flow. The method was then used to analyze the detailed pressure measurements made in a long pipe for flow of air at different flow rate settings. Flow friction values derived from these pressure measurements were compared with the standard incompressible pipe flow data available in existing literature.

Murthy, Sreedhara V.↗
DOE OSTI2019

Parallel-In-Time Multigrid with Adaptive Spatial Coarsening for The Linear Advection and Inviscid Burgers Equations

We apply a multigrid reduction-in-time (MGRIT) algorithm to hyperbolic partial differential equations in one spatial dimension. This study is motivated by the observation that sequential time-stepping is a computational bottleneck when attempting to implement highly concurrent algorithms; thus parallel-in-time methods are desirable. MGRIT adds parallelism by using a hierarchy of successively coarser temporal levels to accelerate the solution on the finest level. In the case of explicit time-stepping, spatial coarsening is a suitable approach to ensure that stability conditions are satisfied on all levels, and it may be useful for implicit time-stepping by producing cheaper multigrid cycles. Unfortunately, uniform spatial coarsening results in extremely slow convergence when the wave speed is near zero, even if only locally. We present an adaptive spatial coarsening strategy that addresses this issue for the variable coefficient linear advection equation and the inviscid Burgers equation using first-order explicit or implicit time-stepping methods. Serial numerical results show this method offers significant improvements over uniform coarsening and is convergent for the inviscid Burgers equation with and without shocks. Parallel scaling tests on up to 128K cores indicate that run-time improvements over serial time-stepping strategies are possible when spatial parallelism alone saturates, and that scalability is robust for oscillatory solutions which change on the scale of the grid spacing.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Chemical copatterning strategies using azlactone-based block copolymers

Interfaces can be modified with azlactone-functional polymers in order to manipulate the chemical surface reactivity. Azlactone groups are highly reactive toward amine, thiol, and alcohol nucleophiles, providing a versatile coupling chemistry for secondary surface modification. Azlactone-based surface polymers have been explored in numerous applications, including chemical and biological capture, sensing, and cell culture. These applications often require that the polymer is copatterned within a chemically or biologically inert background; however, common fabrication methods degrade azlactone groups during processing steps or result in polymer films with poorly controlled thicknesses. Here, the authors develop fabrication strategies using parylene lift-off and interface-directed assembly methods to generate microscale patterns of azlactone-based block copolymer in chemically or biologically inert backgrounds. The functionality of azlactone groups was preserved during fabrication, and patterned films appeared as uniform, 80–120 nm brushlike films. The authors also develop a patterning approach that uses a novel microcontact stamping method to generate cross-linked, three-dimensional structures of azlactone-based polymers with controllable, microscale thicknesses. The authors identify the benefits of each approach and expect these polymers and patterning strategies to provide a versatile toolbox for developing synthetic interfaces with tuned chemical and physical features for sensing, cell culture, or material capture applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Low-Temperature Carburization of AL-6XN Enabled by Provisional Passivation

Employing AISI-AL-6XN as example, we introduce a new method of surface activation for low-temperature carburization. This method consists of two steps: (i) removing the passivating surface oxide and a potentially existing severely plastically deformed surface layer (Beilby layer) by aqueous (liquid) hydrochloric acid, and (ii) immersion in ethanol and subsequent drying in nitrogen. Upon carburization with a gas mixture of acetylene, hydrogen, and nitrogen, this new method of surface activation enables the formation of a fully developed “case”, i.e., a uniform solid solution of interstitial carbon in austenite with carbon fractions up to 0.20 near the alloy surface. The underlying mechanism of surface activation is shown to involve the formation of a provisional passivating layer. It consists of chlorides or ethoxides that are insoluble in ethanol. It prevents the reformation of the regular Cr-rich passivating oxide layer and is readily removed upon heating and exposure to the carburizing gas. As the new activation method is quicker, more effective, and less destructive to furnace hardware than activation with hot gaseous hydrochloric acid that is currently applied in industrial manufacturing, it may have considerable technological impact.

Li, Zhen (ORCID:000000017245400X)↗
DOE OSTI2022

Spectroscopic Investigation of Catalyst Inks and Thin Films Toward the Development of Ionomer Quality Control

As the production of polymer electrolyte fuel cells expands, novel quality control methods must be invented or adapted in order to support expected rates of production. Ensuring the quality of deposited catalyst layers is an essential step in the fuel cell manufacturing process, as the efficiency of a fuel cell is reliant on the catalyst layer being uniform at both the target platinum loading and the target ionomer content. Implementing a quality control method that is sensitive to these aspects is imperative, as wasting precious metals and other catalyst materials is expensive, and represents a potential barrier to entry into the field for manufacturers experimenting with novel deposition processes. In this work, we analyzed catalyst inks to determine if their ionomer content could be quantized spectroscopically. Attenuated total reflection (ATR) Fourier transform infrared spectroscopic technique was investigated producing a signal proportional to the ionomer content. ATR spectroscopy was able to quantitatively differentiate samples in which the ionomer to carbon mass ratio (I/C) varied between 0.9 and 3.0. The I/C ratio was correlated to the measured ATR signal near the CF 2 vibrational bands located between 1100 cm −1 and 1400 cm −1 . The experimental results obtained constitute a step toward the development of novel quality control methodologies for catalyst inks utilized by the fuel cell industry.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2019

Highly Stable Oxygen Electrodes Enabled by Catalyst Redistribution through an In Situ Electrochemical Method

Here, in this work, for the first time an in situ electrochemical pretreatment approach to fabricate a highly reversible oxygen electrode with redistributed ultrafine RuO 2 catalysts on a carbon nanotube (CNT) matrix is reported. The optimally pretreated RuO 2 /CNT oxygen electrodes demonstrate an extremely stable cycling life, 800 times with non-Li metal anode, under a capacity-limited protocol of 800 mAh g −1 in an ether-based electrolyte in an O 2 environment. The highly stable activity of ultrafine RuO 2 catalysts in oxygen reduction and evolution processes originates from the synergetic effect of greatly reduced size of catalyst (<2 nm) and uniform redistribution of catalyst particles after the in situ electrochemical pretreatment process. The pretreatment method discovered in this work can not only significantly enhance the activity/efficiency of the catalysts used for air electrodes but can also be widely applied to other electro-catalysis systems.

25 ENERGY STORAGE↗
DOE OSTI2022

Metrics for Intercomparison of Remapping Algorithms (MIRA) protocol applied to Earth system models

Abstract. Strongly coupled nonlinear phenomena such as those described by Earth system models (ESMs) are composed of multiple component models with independent mesh topologies and scalable numerical solvers. A common operation in ESMs is to remap or interpolate component solution fields defined on their computational mesh to another mesh with a different combinatorial structure and decomposition, e.g., from the atmosphere to the ocean, during the temporal integration of the coupled system. Several remapping schemes are currently in use or available for ESMs. However, a unified approach to compare the properties of these different schemes has not been attempted previously. We present a rigorous methodology for the evaluation and intercomparison of remapping methods through an independently implemented suite of metrics that measure the ability of a method to adhere to constraints such as grid independence, monotonicity, global conservation, and local extrema or feature preservation. A comprehensive set of numerical evaluations is conducted based on a progression of scalar fields from idealized and smooth to more general climate data with strong discontinuities and strict bounds. We examine four remapping algorithms with distinct design approaches, namely ESMF Regrid (Hill et al., 2004), TempestRemap (Ullrich and Taylor, 2015), generalized moving least squares (GMLS) (Trask and Kuberry, 2020) with post-processing filters, and WLS-ENOR (Li et al., 2020). By repeated iterative application of the high-order remapping methods to the test fields, we verify the accuracy of each scheme in terms of their observed convergence order for smooth data and determine the bounded error propagation using challenging, realistic field data on both uniform and regionally refined mesh cases. In addition to retaining high-order accuracy under idealized conditions, the methods also demonstrate robust remapping performance when dealing with non-smooth data. There is a failure to maintain monotonicity in the traditional L2-minimization approaches used in ESMF and TempestRemap, in contrast to stable recovery through nonlinear filters used in both meshless GMLS and hybrid mesh-based WLS-ENOR schemes. Local feature preservation analysis indicates that high-order methods perform better than low-order dissipative schemes for all test cases. The behavior of these remappers remains consistent when applied on regionally refined meshes, indicating mesh-invariant implementations. The MIRA intercomparison protocol proposed in this paper and the detailed comparison of the four algorithms demonstrate that the new schemes, namely GMLS and WLS-ENOR, are competitive compared to standard conservative minimization methods requiring computation of mesh intersections. The work presented in this paper provides a foundation that can be extended to include complex field definitions, realistic mesh topologies, and spectral element discretizations, thereby allowing for a more complete analysis of production-ready remapping packages.

58 GEOSCIENCES↗
DOE OSTI2017

Characterizing bonding patterns in diradicals and triradicals by density-based wave function analysis: A uniform approach

Density-based wave function analysis enables unambiguous comparisons of electronic structure computed by different methods and removes ambiguity of orbital choices. Here, we use this tool to investigate the performance of different spin-flip methods for several prototypical diradicals and triradicals. In contrast to previous calibration studies that focused on energy gaps between high and low spin-states, we focus on the properties of the underlying wave functions, such as the number of effectively unpaired electrons. Comparison of different density functional and wave function theory results provides insight into the performance of the different methods when applied to strongly correlated systems such as polyradicals. We also show that canonical molecular orbitals for species like large copper-containing diradicals fail to correctly represent the underlying electronic structure due to highly non-Koopmans character, while density-based analysis of the same wave function delivers a clear picture of bonding pattern.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1988

Essentially non-oscillatory shock capturing methods applied to turbulence amplification in shock wave calculations

ENO (essentially non-oscillatory) schemes can provide uniformly high order accuracy right up to discontinuities while keeping sharp, essentially non-oscillatory shock transitions. Recently, an efficient implementation of ENO schemes was obtained based on fluxes and TVD Runge-Kutta time discretizations. The resulting code is very simple to program for multi-dimensions. ENO schemes are especially suitable for computing problems with both discontinuities and fine structures in smooth regions, such as shock interaction with turbulence, for which results for 1-D and 2-D Euler equations are presented. Much better resolution is observed by using third order ENO schemes than by using second order TVD schemes for such problems.

Osher, Stanley↗