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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Computational Molecular Simulation of the Oxidative Adsorption of Ferrous Iron at the Hematite (001)-Water Interface

The interaction of Fe(II) with ferric oxide/oxyhydroxide phases is central to the biogeochemical redox chemistry of iron. Molecular simulation techniques were employed to determine the mechanisms and quantify the rates of Fe(II) oxidative adsorption at the hematite (001)-water interface. Molecular dynamics potential of mean force calculations of Fe(II) adsorbing on the hematite surface revealed the presence of three free energy minima corresponding to Fe(II) adsorbed in an outersphere complex, a monodentate innersphere complex, and a tridentate innersphere complex. The free energy barrier for adsorption from the outersphere position to the monodentate innersphere site was calculated to be similar to the activation enthalpy for water exchange around aqueous Fe(II). Adsorption at both innersphere sites was predicted to be unfavorable unless accompanied by release of protons. Molecular dynamics umbrella sampling simulations and ab initio cluster calculations were performed to determine the rates of electron transfer from Fe(II) adsorbed as an innersphere and outersphere complex. The electron transfer rates were calculated to range from 10^-4 to 10^2 s-1, depending on the adsorption site and the potential parameter set, and were generally slower than those obtained in the bulk hematite lattice. The most reliable estimate of the rate of electron transfer from Fe(II) adsorbed as an outersphere complex to lattice Fe(III) was commensurate with the rate of adsorption as an innersphere complex suggesting that adsorption does not necessarily need to precede oxidation.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Behavior of nanoporous thermal barrier coatings under cyclic thermal loading. Computer-aided simulation

The work presents the development of new algorithms for calculating the fraction of thermal energy dissipated during the irradiation on the inner surface of pores. On the basis of these algorithms, the simulation of heat transfer in three-layered systems was carried out taking into account the dissipation of thermal energy in specimens having different porosity. We have performed quantitative estimates of the portion of dissipating thermal energy and its influence on the distribution of thermal stresses in thermal barrier coating systems. It was demonstrated that the presence of pores with a large internal surface area in the intermediate layer material enables two-fold decrease of the internal thermal stresses.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Sandia National Laboratories Advanced Simulation and Computing (ASC) Appraisal Method for the Implementation of the ASC Software Quality Engineering Practices (V.2.0)

This document provides a guide to the process of conducting software appraisals under the Sandia National Laboratories (SNL) ASC Program. The goal of this document is to describe a common methodology for planning, conducting, and reporting results of software appraisals thereby enabling: 1) Identification of improvements in implementation of the software quality engineering (SQE) practices identified in the ASC Software Quality Plan across the ASC Program against objective baselines. 2) Feedback from project teams on SQE opportunities for improvement. 3) Identification of strengths and opportunities for improvement for individual project teams. 4) Guidance to the ASC Program on the focus of future SQE activities. Document contents include process descriptions, templates to promote consistent conduct of appraisals, and an explanation of the relationship of this procedure to the SNL ASC software program. The activities described by this document are under the oversight of SNL ASC Program Director and SNL ASC Program Manager.

42 ENGINEERING↗
DOE OSTI2025

Technical Report on Subsurface Monitoring of the Brady Hot Spring Geothermal Site, Nevada, based upon Full Waveform Inversion

Abilities to accurately characterize the subsurface in a geothermal setting is key to assess and support production. An important element of geothermal reservoir monitoring is also the ability to investigate fluid transport within fracture network. This report focuses on improving subsurface imaging and monitoring in geothermal settings using full waveform inversion based on the adjoint method and time-lapse imaging. To assess our method, we rely on a dense seismic dataset collected in 2016 at the Brady Hot Springs geothermal site in Nevada for the DOE-funded project Poroelastic Tomography by Adjoint Inverse Modeling of Data from Seismology, Geodesy, and Hydrology. This dataset captures subsurface changes across four stages of geothermal power plant operations, which involve varying rates of fluid injection and extraction. Two velocity models were previously derived from this dataset using different methods: one based on travel times and another on sweep interferometry. Our first step is to refine these models using adjoint tomography, which has been applied successfully at global and regional-scales but is less common at the reservoir-scale. Two approaches are then explored for time-lapse analysis: directly comparing refined tomographic models from different stages or backpropagating waveform differences relative to a baseline tomographic model. The main take away is that both approaches highlight similar reservoir behaviors, but the latter approach is more computationally effective in capturing small-scale changes in subsurface properties. For this work, we leverage the use of Salvus (www.mondaic.com), an end-to-end seismic imaging solution, relying on the spectral element method to compute forward and adjoint simulations, and developed by Mondaic Ltd. It includes integrated workflow management that handles waveform and metadata, launches simulations, computes waveform misfits and adjoint sources, and iterates for model updates by nonlinear optimization.

15 GEOTHERMAL ENERGY↗
NASA NTRS1972

Functional requirements for design of the Space Ultrareliable Modular Computer (SUMC) system simulator

The functional requirements for the design of an interpretive simulator for the space ultrareliable modular computer (SUMC) are presented. A review of applicable existing computer simulations is included along with constraints on the SUMC simulator functional design. Input requirements, output requirements, and language requirements for the simulator are discussed in terms of a SUMC configuration which may vary according to the application.

Curran, R. T.↗
NASA NTRS1978

Transient response to three-phase faults on a wind turbine generator

In order to obtain a measure of its responses to short circuits a large horizontal axis wind turbine generator was modeled and its performance was simulated on a digital computer. Simulation of short circuit faults on the synchronous alternator of a wind turbine generator, without resort to the classical assumptions generally made for that analysis, indicates that maximum clearing times for the system tied to an infinite bus are longer than the typical clearing times for equivalent capacity conventional machines. Also, maximum clearing times are independent of tower shadow and wind shear. Variation of circuit conditions produce the modifications in the transient response predicted by analysis.

Gilbert, L. J.↗
NASA NTRS1982

Computer program for a four-cylinder-Stirling-engine controls simulation

A four cylinder Stirling engine, transient engine simulation computer program is presented. The program is intended for controls analysis. The associated engine model was simplified to shorten computer calculation time. The model includes engine mechanical drive dynamics and vehicle load effects. The computer program also includes subroutines that allow: (1) acceleration of the engine by addition of hydrogen to the system, and (2) braking of the engine by short circuiting of the working spaces. Subroutines to calculate degraded engine performance (e.g., due to piston ring and piston rod leakage) are provided. Input data required to run the program are described and flow charts are provided. The program is modular to allow easy modification of individual routines. Examples of steady state and transient results are presented.

Daniels, C. J.↗
NASA NTRS1988

Modified hybrid control of robot manipulators for high precision assembly operations

This paper is concerned with applications of robot manipulators in high precision assembly tasks that can be successfully performed by employing a hybrid control scheme that independently controls force and position. A traditional hybrid control scheme is implemented in Cartesian space. In the modified hybrid control scheme introduced in this paper, the error driven control signals are expressed in joint space. This paper studies the implementation of the modified hybrid control scheme on a two-degree-of-freedom robot manipulator with a closed-kinematic chain mechanism. The performance of the traditional and modified hybrid control schemes is comparatively evaluated by computer simulation in terms of computation time and accuracy for several study cases.

Nguyen, Charles C.↗
NASA NTRS1988

Development of automation and robotics for space via computer graphic simulation methods

A robot simulation system, has been developed to perform automation and robotics system design studies. The system uses a procedure-oriented solid modeling language to produce a model of the robotic mechanism. The simulator generates the kinematics, inverse kinematics, dynamics, control, and real-time graphic simulations needed to evaluate the performance of the model. Simulation examples are presented, including simulation of the Space Station and the design of telerobotics for the Orbital Maneuvering Vehicle.

Fernandez, Ken↗
NASA NTRS1990

Computational flow simulation of liquid oxygen in a SSME preburner injector element LOX post

Liquid oxygen (LOX) is simulated as an incompressible flow through a Space Shuttle main engine fuel preburner injector element LOX post for the full range of operating conditions. Axial profiles of axial velocity and static pressure are presented. For each operating condition analyzed, the minimum pressure downstream of the orifice is compared to the vapor pressure to determine if cavitation could occur. Flow visualization is provided by velocity vectors and stream function contours. The results indicate that the minimum pressure is too high for cavitation to occur. To establish confidence in the CFD analysis, the simulation is repeated with water flow through a superscaled LOX post and compared with experimental results. The agreement between calculated and experimental results is very good.

Rocker, Marvin↗