Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “reversible computation”

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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

E × B flow driven electron temperature bifurcation in a closed slot divertor with ion B × ∇ B away from the X-point in the DIII-D tokamak

An electron temperature bifurcation is observed in the small angle slot divertor, which has been developed to enhance neutral cooling across the divertor target by coupling a closed slot structure with appropriate target shaping. Experiments in the DIII-D tokamak and associated SOLPS-ITER modeling with full drifts find a strong interplay between drifts and divertor geometry on divertor dissipation. The coupling of divertor geometry and drift flows can strongly affect the path towards divertor detachment onset as the plasma density is raised. With the strike point on the inner slanted surface and ion B × ∇B away from the magnetic X-point, bifurcative transitions were observed with sharp decrease of T e towards detachment onset both experimentally and computationally. This differs from the situation for the open divertor where the T e cliff was only observed for ion B × ∇B towards the X-point. SOLPS-ITER modeling with full drifts demonstrates that the magnitude of the E × B drift flow is comparable with the main plasma flow. The reversal of both the poloidal and radial E × B flows near the strike point leads to rapid density accumulation right near the separatrix, which results in bifurcative step transition of divertor conditions with cold plasma across the entire divertor target plate. Furthermore, these results indicate that the interplay between geometry and drifts should be fully taken into account in future fusion reactor divertor designs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Electronic structure and anomalous Hall effect in the ferromagnetic 3d-5d superlattice SrMnO3/SrIrO3

The electronic structure and the anomalous Hall effect (AHE) at the recently grown 3 d - 5 d superlattice structure (SrMnO 3 ) 1 / (SrIrO 3 ) 1 are investigated theoretically using model and density-functional calculations. The observed ferromagnetism for the SMO layer, which becomes electron doped because of the charge transfer across the interface, is explained to be due to the Anderson-Hasegawa double exchange, while the SIO side becomes ferromagnetic due to the proximity effect and the Nagaoka physics of a hole-doped system. The broken time-reversal symmetry and the strong spin-orbit coupling in SIO provide the two essential ingredients for the AHE, which we describe within a square lattice model of d-orbitals relevant for the present structure. The model correctly predicts the order of magnitude of the anomalous Hall conductivity (AHC), which is computed using the Kubo formula. The density-functional results for the AHC are in good agreement with the experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A Low Mach Number Model for Moist Atmospheric Flows

A low Mach number model for moist atmospheric flows is introduced that accurately incorporates reversible moist processes in flows whose features of interest occur on advective rather than acoustic time scales. Total water is used as a prognostic variable, so that water vapor and liquid water are diagnostically recovered as needed from an exact Clausius–Clapeyron formula for moist thermodynamics. Low Mach number models can be computationally more efficient than a fully compressible model, but the low Mach number formulation introduces additional mathematical and computational complexity because of the divergence constraint imposed on the velocity field. Here in this paper, latent heat release is accounted for in the source term of the constraint by estimating the rate of phase change based on the time variation of saturated water vapor subject to the thermodynamic equilibrium constraint. Finally, the authors numerically assess the validity of the low Mach number approximation for moist atmospheric flows by contrasting the low Mach number solution to reference solutions computed with a fully compressible formulation for a variety of test problems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Mechanism of Catalytic O2 Reduction by Iron Tetraphenylporphyrin

The catalytic reduction of O2 to H2O is important for energy transduction in both synthetic and natural systems. Herein, we report a kinetic study of O2 reduction catalyzed by iron tetraphenylporphyrin in N,N-dimethylformamide using decamethylferrocene as a soluble reductant and para-toluenesulfonic acid (pTsOH) as the proton source. Reduction of the ferric porphyrin, [FeIII(TPP)]+ , forms the ferrous porphyrin, FeII(TPP), which binds O2 reversibly to form the ferric-superoxide porphyrin complex, FeIII(TPP)(O2 •?). The temperature dependence of both the electron transfer and O2 binding equilibrium constants have been determined. Kinetic studies over a range of concentrations and temperatures show that the catalyst resting state changes during the course of each catalytic run, necessitating the use of global kinetic modeling to extract rate constants and kinetic barriers. The rate-determining step in oxygen reduction is protonation of FeIII(TPP)(O2•?) by pTsOH, which proceeds with a substantial kinetic barrier. Computational studies indicate that this barrier for proton transfer arises from an unfavorable pre-association of the proton donor with the superoxide adduct and a transition state that requires significant desolvation of the proton donor. Together, these results are the first example of oxygen reduction by iron tetraphenylporphyrin where the pre-equilibria between ferric, ferrous, and ferric-superoxide intermediates have been quantified under catalytic conditions. This work gives a generalizable model for the mechanism of iron porphyrin-catalyzed ORR and provides an unusually complete mechanistic study of an ORR reaction. More broadly, this study also highlights the kinetic challenges for proton transfer to catalytic intermediates in organic media.

Pegis, Michael L.↗
DOE OSTI2024

Mapping Composition Evolution through Synthesis, Purification, and Depolymerization of Random Heteropolymers

Random heteropolymers (RHPs) consisting of three or more comonomers have been routinely used to synthesize functional materials. While increasing the monomer variety diversifies the side-chain chemistry, this substantially expands the sequence space and leads to ensemble-level sequence heterogeneity. Most studies have relied on monomer composition and simulated sequences to design RHPs, but the questions remain unanswered regarding heterogeneities within each RHP ensemble and how closely these simulated sequences reflect the experimental outcomes. Here, we quantitatively mapped out the evolution of monomer compositions in four-monomer-based RHPs throughout a design-synthesis-purification-depolymerization process. By adopting a Jaacks method, we first determined 12 reactivity ratios directly from quaternary methacrylate RAFT copolymerization experiments to account for the influences of competitive monomer addition and the reversible activation/deactivation equilibria. The reliability of in silico analysis was affirmed by a quantitative agreement (<4% difference) between the simulated RHP compositions and the experimental results. Furthermore, we mapped out the conformation distribution within each ensemble in different solvents as a function of monomer chemistry, composition, and segmental characteristics via high-throughput computation based on self-consistent field theory (SCFT). These comprehensive studies confirmed monomer composition as a viable design parameter to engineer RHP-based functional materials as long as the reactivity ratios are accurately determined and the livingness of RHP synthesis is ensured.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Continuum model for chiral induced spin selectivity in helical molecules

A minimal model is exactly solved for electron spin transport on a helix. Electron transport is assumed to be supported by well oriented p{sub z} type orbitals on base molecules forming a staircase of definite chirality. In a tight binding interpretation, the spin-orbit coupling (SOC) opens up an effective π{sub z} − π{sub z} coupling via interbase p{sub x,y} − p{sub z} hopping, introducing spin coupled transport. The resulting continuum model spectrum shows two Kramers doublet transport channels with a gap proportional to the SOC. Each doubly degenerate channel satisfies time reversal symmetry; nevertheless, a bias chooses a transport direction and thus selects for spin orientation. The model predicts (i) which spin orientation is selected depending on chirality and bias, (ii) changes in spin preference as a function of input Fermi level and (iii) back-scattering suppression protected by the SO gap. We compute the spin current with a definite helicity and find it to be proportional to the torsion of the chiral structure and the non-adiabatic Aharonov-Anandan phase. To describe room temperature transport, we assume that the total transmission is the result of a product of coherent steps.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Decoupled Fréchet kernels based on a fractional viscoacoustic wave equation

We formulate the Fréchet kernel computation using the adjoint-state method based on a fractional viscoacoustic wave equation. We first numerically prove that both the 1/2- and the 3/2-order fractional Laplacian operators are self-adjoint. Using this property, we show that the adjoint wave propagator preserves the dispersion and compensates the amplitude, while the time-reversed adjoint wave propagator behaves identically as the forward propagator with the same dispersion and dissipation characters. Without introducing rheological mechanisms, this formulation adopts an explicit Q parameterization, which avoids the implicit Q in the conventional viscoacoustic/viscoelastic full waveform inversion (Q-FWI). In addition, because of the decoupling of operators in the wave equation, the viscoacoustic Fréchet kernel is separated into three distinct contributions with clear physical meanings: lossless propagation, dispersion, and dissipation. Here, we find that the lossless propagation kernel dominates the velocity kernel, while the dissipation kernel dominates the attenuation kernel over the dispersion kernel.

58 GEOSCIENCES↗
NASA NTRS1992

Eno-Osher schemes for Euler equations

The combination of the Osher approximate Riemann solver for the Euler equations and various ENO schemes is discussed for one-dimensional flow. The three basic approaches, viz. the ENO scheme using primitive variable reconstruction, either with Cauchy-Kowalewski procedure for time integration or the TVD Runge-Kutta scheme, and the flux-ENO method are tested on different shock tube cases. The shock tube cases were chosen to present a serious challenge to the ENO schemes in order to test their ability to capture flow discontinuities, such as shocks. Also the effect of the ordering of the eigen values, viz. natural or reversed ordering, in the Osher scheme is investigated. The ENO schemes are tested up to fifth order accuracy in space and time. The ENO-Osher scheme using the Cauchy-Kowalewski procedure for time integration is found to be the most accurate and robust compared with the other methods and is also computationally efficient. The tests showed that the ENO schemes perform reasonably well, but have problems in cases where two discontinuities are close together. In that case there are not enough points in the smooth part of the flow to create a non-oscillatory interpolation.

Vandervegt, Jacobus J.↗
NASA NTRS2003

Carbon-Nitrogen-Oxygen Line Radiation and the X-ray Bowen Fluorescence Mechanism in Optically Thick, Highly Ionized Media

Radiative transfer effects due to overlapping X-ray lines in a high-temperature, optically thick, highly ionized medium are investigated. One particular example, in which the O VIII Lyalpha doublet (2(sup 2) P(sub 1/2,3/2)-1(sup 2) S(sub 1/2) coincides in frequency with the N VII Lyzeta lines (7(sup 2) P(sub 1/2,3/2)-1(sup 2) S(sub 1/2) is studied in detail to illustrate the effects on the properties of the emergent line spectrum. We solve the radiative transfer equation to study the energy transport of resonance-line radiation in a static, infinite, plane-parallel geometry, which is used to compute the destruction/escape probabilities for each of the lines for various total optical thicknesses of the medium, as well as destruction probabilities by sources of underlying photoelectric opacity. It is found that a large fraction of the O vIII Lyalpha line radiation can be destroyed by N VII, which can result in a reversal of the O VIII Lyalpha/N VII Lyalpha line intensity ratio similar to what may be seen under nonsolar abundances. Photoelectric absorption by ionized carbon and nitrogen can also subsequently increase the emission-line intensities of these ions. We show that line ratios, which are directly proportional to the abundance ratios in optically thin plasmas, are not good indicators of the true CNO abundances. Conversely, global spectral modeling that assumes optically thin conditions may yield incorrect abundance estimates when compared with observations, especially if the optical depth is large. Other potentially important overlapping lines and continua in the X-ray band are also identified, and their possible relevance to recent high-resolution spectroscopic observations with Chandra and XMM-Newton are briefly discussed.

Sako, Masao↗
DOE OSTI2026

Assessing the Accuracy of Property Model Predictions for Cost Optimization of Desalination Technologies

Accurate modeling of seawater thermophysical and thermodynamic properties is critical for optimizing desalination processes. This study compares three seawater property models, a Reaktoro multicomponent model, the thermophysical seawater properties library from the Massachusetts Institute of Technology, and a simplified sodium chloride model, in the context of levelized cost of water (LCOW) minimization for reverse osmosis (RO) and mechanical vapor compression systems. Process simulations and cost optimizations reveal that although all three models yield comparable LCOW and specific energy consumption (SEC) estimates under baseline conditions, deviations among their predictions increase with salinity. Relative differences in LCOW and SEC reach up to 6% and 8%, respectively. RO results show greater variability due to differences in osmotic pressure predictions, which affect pressure constraints at high recoveries. Computational performance varies substantially; specifically, Reaktoro simulations are up to 28 times slower than empirical models due to their detailed equilibrium calculations. These results suggest that empirical models offer acceptable accuracy for routine desalination process design, while Reaktoro provides advantages in scenarios requiring detailed speciation, such as scaling or pH adjustment studies. These findings underscore the importance of selecting appropriate property models based on the modeling objective of desalination applications and motivate future work integrating thermodynamic rigor with empirical efficiency.

Physical and chemical properties↗
DOE OSTI2019

DiaMonD: An Integrated Multifaceted Approach to Mathematics at the Interfaces of Data, Models, and Decisions

For many problems in computational science and engineering, the so-called forward problem—solution of the underlying mathematical model to yield output quantities of interest, given input parameters—is difficult enough for frontier complex models, which are often characterized by coupled multiphysics and possibly stochastic behavior over a wide range of length and time scales. However, we face the need to move beyond the forward problem, to address what is often the ultimate goal of CS&E: decision making. This requires us to tackle a spectrum of mathematical problems that subsume, and are thus even more difficult than, the forward problem. First, given experimental data, we wish to estimate unknown parameters characterizing a model of a natural or engineered system by solving an inverse problem. Second, we seek the optimal configuration of the system (or experiments) by solving an optimal design problem. Third, the optimal operation of the system must be determined by solving an optimal control problem. And fourth, we must quantify uncertainties as they propagate through all of the preceding problems, from data to model inference to prediction and finally to optimal design and control. Optimal mathematical methods and algorithms for such end-to-end, data-to-decisions modeling and simulation of complex problems—requiring integrated solution of forward, inverse, optimization, and UQ problems for large, multiphysics, multiscale models—entails challenges of the highest order, while also presenting great opportunities for applied mathematics research. Unfortunately, research on forward, inverse, optimization, and UQ problems has all-too-often progressed in isolation. This has led to mathematical methods that perform well when considering the forward simulation in isolation, but are prohibitive or suboptimal or unstable when combined with other methods within the framework of inversion, optimization, or UQ. The reverse is also true: general-purpose methods developed within the inversion, optimization, and UQ fields often become prohibitive when applied to complex CS&E problems since they do not exploit their structure.

58 GEOSCIENCES↗
DOE OSTI2020

Ultrahigh coulombic efficiency electrolyte enables Li||SPAN batteries with superior cycling performance

Raising the coulombic efficiency of lithium metal anode cycling is the deciding step in realizing long-life rechargeable lithium batteries. Here, we designed a highly concentrated salt/ether electrolyte diluted in a fluorinated ether: 1.8 M LiFSI in DEE/BTFE (diethyl ether/bis(2,2,2-trifluoroethyl)ether), which realized an average coulombic efficiency of 99.37% at 0.5 mA cm -2 and 1 mAh cm -2 for more than 900 cycles. This electrolyte also maintained a record coulombic efficiency of 98.7% at 10 mA cm -2 , indicative of its ability to provide fast-charging with high cathode loadings. Morphological studies reveal dense, dendrite free Li depositions after prolonged cycling, while surface analyses confirmed the formation of a robust LiF-rich SEI layer on the cycled Li surface. Moreover, we discovered that this ether-based electrolyte is highly compatible with the low-cost, high-capacity SPAN (Sulfurized polyacrylonitrile) cathode, where the constructed Li||SPAN cell exhibited reversible cathode capacity of 579 mAh g -1 and no capacity decay after 1200 cycles. A cell where a high areal loading SPAN electrode (>3.5 mAh cm -2 ) is paired with only onefold excess Li was constructed and cycled at 1.75 mA cm -2 , maintaining a coulombic efficiency of 99.30% for the lithium metal. Computational simulations revealed that at saturation, the Li-FSI complex forms contact ion pairs, with a first solvation shell comprising DEE molecules, and a second solvation shell with a mix of DEE/BTFE. This study provides a path to enable high energy density Li||SPAN batteries with stable cycling.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Control of monodomain polymer-stabilized cuboidal nanocrystals of chiral nematics by confinement.

Liquid crystals are important components of optical technologies. Cuboidal crystals consisting of chiral liquid crystals-the so-called blue phases (BPs), are of particular interest due to their crystalline structures and fast response times, but it is critical that control be gained over their phase behavior as well as the underlying dislocations and grain boundaries that arise in such systems. Blue phases exhibit cubic crystalline symmetries with lattice parameters in the 100 nm range and a network of disclination lines that can be polymerized to widen the range of temperatures over which they occur. Here, we introduce the concept of strain-controlled polymerization of BPs under confinement, which enables formation of strain-correlated stabilized morphologies that, under some circumstances, can adopt perfect single-crystal monodomain structures and undergo reversible crystal-to-crystal transformations, even if their disclination lines are polymerized. We have used super-resolution laser confocal microscopy to reveal the periodic structure and the lattice planes of the strain and polymerization stabilized BPs in 3D real space. Our experimental observations are supported and interpreted by relying on theory and computational simulations in terms of a free energy functional for a tensorial order parameter. Simulations are used to determine the orientation of the lattice planes unambiguously. The findings presented here offer opportunities for engineering optical devices based on single-crystal, polymer-stabilized BPs whose inherent liquid nature, fast dynamics, and long-range crystalline order can be fully exploited.

confinement↗
DOE OSTI2014

Integrated two-cylinder liquid piston Stirling engine

Heat engines utilizing the Stirling cycle may run on low temperature differentials with the capacity to function at high efficiency due to their near-reversible operation. However, current approaches to building Stirling engines are laborious and costly. Typically the components are assembled by hand and additional components require a corresponding increase in manufacturing complexity, akin to electronics before the integrated circuit. We present a simple and integrated approach to fabricating Stirling engines with precisely designed cylinders. We utilize computer aided design and one-step, planar machining to form all components of the engine. The engine utilizes liquid pistons and displacers to harness useful work from heat absorption and rejection. As a proof of principle of the integrated design, a two-cylinder engine is produced and characterized and liquid pumping is demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Prestack reverse time migration for 3D marine reflection seismic data

Prestack reverse time migration (RTM) is a method for imaging the subsurface using the inner product of wavefield extrapolation in shot domain and in receiver domain. It is well known that RTM is better for preserving amplitudes and phases than other prestack migrations. Since 3D seismic data is huge data volume and it needs heavy computing works, it requires parallel computing in order to have a meaningful depth image of the 3D subsurface. We implemented a parallelized version of 3D RTM for prestack depth migration. The results of numerical example for 3D SEG/EAGE salt model showed good agreement with the original geological model. We applied RTM to offshore 3D seismic reflection data. The study area is 12 × 25 km with 120 survey lines. Shot and receiver spacing is 25 m and 12.5 m. The line spacing is 100 m. Shot gathers were preprocessed to enhance signal to noise ratio and velocity model was calculated from conventional stack velocity. Both of them were used to obtain 3D image using RTM. The results show reasonable subsurface image.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1987

Performance of a three-dimensional Navier-Stokes code on CYBER 205 for high-speed juncture flows

A vectorized 3D Navier-Stokes code has been implemented on CYBER 205 for solving the supersonic laminar flow over a swept fin/flat plate junction. The code extends MacCormack's predictor-corrector finite volume scheme to a generalized coordinate system in a locally one dimensional time split fashion. A systematic parametric study is conducted to examine the effect of fin sweep on the computed flow field. Calculated results for the pressure distribution on the flat plate and fin leading edge are compared with the experimental measurements of a right angle blunt fin/flat plate junction. The decrease in the extent of the separated flow region and peak pressure on the fin leading edge, and weakening of the two reversed supersonic zones with increase in fin sweep have been clearly observed in the numerical simulation.

Lakshmanan, B.↗
NASA NTRS1995

Three-dimensional transient flow of spin-up in a filled cylinder with oblique gravity force

Three-dimensional transient flow profiles of spin-up in a fully liquid filled cylinder from rest with gravity acceleration at various direction are numerically simulated and studied. Particular interests are concentrated on the development of temporary reverse flow zones and Ekman layer right after the impulsive start of spin-up from rest, and decay before the flow reaching to the solid rotation. Relationship of these flow developments and differences in the Reynolds numbers of the flow and its size selection of grid points concerning the numerical instabilities of flow computations are also discussed. In addition to the gravitational acceleration along the axial direction of the cylindrical container, a series of complicated flow profiles accompanied by three-dimensional transient flows with oblique gravitational acceleration has been studies.

Hung, R. J.↗
DOE OSTI2025

TGCM: (T)rait, (G)ene, and (C)rop Growth (M)odel Directed Targeted Gene Characterization in Sorghum (Final Technical Report)

Understanding which genes control important crop traits could help scientists develop better bioenergy and food crops more efficiently. However, plant genomes contain tens of thousands of genes, and testing each one individually is expensive and time-consuming. This project developed computational tools to predict which genes are most likely to matter, allowing researchers to focus their efforts where they will have the greatest impact. This project developed and validated integrated approaches combining machine learning, quantitative genetics, and crop growth modeling to improve the efficiency of functional gene characterization in sorghum (Sorghum bicolor), a critical bioenergy and food security crop. The research addressed a fundamental challenge in plant biology: the majority of genes in plant genomes lack experimentally validated functions, making it difficult to prioritize which genes to study using resource-intensive reverse genetics approaches.

60 APPLIED LIFE SCIENCES↗