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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Computational Fluid Dynamics Simulation of Lignocellulosic Biomass Transport in a Compression-Screw Feeder

There is continued interest in lignocellulosic biomass feedstocks for producing power, heat, and transportation liquid fuels in order to increase energy diversification and security. However, there are a few problems associated with the biomass production that must be resolved before biorefineries are considered economical. One of these problematic operations is the process of feeding biomass to reactor systems. Compression-screw feeders have been widely used as a way to fulfill this purpose. However, due to variability of feedstock properties and its complex challenges, production plants operate at less than 50% of their design capacity due to process upsets along with mechanical wear and failure. The objective of this study is to numerically investigate the screw-feeder operation and performance for various biomass physical properties and under different operating conditions. Therefore, the findings from this study will reduce the number of physical experiments needed to improve the plant design.

09 BIOMASS FUELS↗
DOE OSTI2019

Dynamic simulation and techno-economic analysis of a concentrated solar power (CSP) plant hybridized with both thermal energy storage and natural gas

The addition of thermal energy storage and natural gas as a complementary energy source improves the flexibility, reliability, and value of concentrated solar power (CSP) plants. Nevertheless, due to the transient nature of solar energy, transitions from solar-only mode and natural-gas mode to hybrid solar-natural gas mode is quite challenging, especially when the plant is equipped with thermal storage. Thus, it is important to develop proper dynamic modeling and control schemes to accurately simulate such transitions. The objective of this study is to address this subject by demonstrating a dynamic model with reliable control schemes for a highly integrated hybrid parabolic trough-natural gas plant equipped with thermal energy storage. The specific goal is to study the dynamics of adding thermal storage to the hybrid plant. It is found that the developed control schemes assist smooth transitions between different operational modes and effective utilization of thermal storage and natural gas to maintain steady power production and steam mass flow rates under different solar conditions. The results demonstrate that the integration of storage regulates power production by solar energy and natural gas during the day time. It also enables an increase in the solar fraction of the hybrid plant while it causes a small decrease in thermodynamic efficiency. The analysis shows that the hybrid plant with the storage has a substantially lower specific CO 2 emission (0.320 tonne/MWh) than single natural gas plant (0.413 tonne/MWh) although it has a higher levelized cost of electricity (86.32/MWh against 74.92/MWh). The hybrid plant with storage demonstrates a promising potential for reliable and clean production of electricity, although research and development should be conducted to lower its cost.

03 NATURAL GAS↗
NASA NTRS2018

Aladyn - Adaptive Neural Network Molecular Dynamics Simulation Code: Computational Materials Mini-Application

This report provides an overview and commands description of the Computational Materials mini-application, Aladyn. Aladyn is a simple molecular dynamics code written in FORTRAN 2008, which is designed to demonstrate the use of adaptive neural networks (ANNs) in atomistic simulations. The role of ANNs is to reproduce the very complex energy landscape resulting from the atomic interactions in materials with the accuracy of quantum mechanics-based energy calculations. The ANN is trained on a large set of atomic structures calculated using the density functional theory (DFT) method. The Aladyn code is being released to serve as a training testbed for students and professors in academia to explore possible optimization algorithms for parallel computing on multicore central processing unit (CPU) computers or computers utilizing many core architectures based on graphic processing units (GPUs). The effort is related to the High Performance Computing Incubator (HPCI) project at NASA Langley Research Center.

Yamakov, Vesselin I.↗
DOE OSTI2016

Development of a thermal neutron scattering law for polyethylene using molecular dynamics simulations

Polyethylene is an organic polymer that has been used as a neutron moderator and reflector material in various assemblies designed to perform critical and subcritical experiments. Neutrons that are produced within an assembly containing polyethylene will interact with its various atomic components (especially hydrogen) to slow down and eventually reach thermal energies. In this work, the thermal neutron scattering cross sections are generated in support of criticality safety analysis of neutronic assemblies that utilize polyethylene. Polyethylene is composed of ethylene (C{sub 2}H{sub 4}) monomers that are attached in long molecular chains producing the polymer structure. The principle neutron scatterer in this material is hydrogen. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Assessment of structural, thermal, and mechanical properties of portlandite through molecular dynamics simulations

The structural, thermal, and mechanical properties of portlandite, the primary solid phase of ordinary hydrated cement paste, are investigated using the molecular dynamics method. To understand the effects of temperature on the structural properties of portlandite, the coefficients of thermal expansion of portlandite are determined in the current study and validated with what reported from the experimental tests. The atomic structure of portlandite equilibrated at various temperatures is then subjected to uniaxial tensile strains in the three orthogonal directions and the stress-strain curves are developed. Based on the obtained results, the effect of the direction of straining on the mechanical properties of portlandite is investigated in detail. Structural damage analysis is performed to reveal the failure mechanisms in different directions. The energies of the fractured surfaces are calculated in different directions and compared to those of the ideal surfaces available in the literature. The key mechanical properties, including tensile strength, Young's modulus, and fracture strain, are extracted from the stress-strain curves. The sensitivity of the obtained mechanical properties to temperature and strain rate is then explored in a systematic way. This leads to valuable information on how the structural and mechanical properties of portlandite are affected under various exposure conditions and loading rates. - Graphical abstract: Fracture mechanism of portlandite under uniaxial strain in the z-direction. - Highlights: • The structural, thermal, and mechanical properties of portlandite are investigated. • The coefficients of thermal expansion are determined. • The stress-strain relationships are studied in three orthogonal directions. • The effects of temperature and strain rate on mechanical properties are examined. • The plastic energy required for fracture in the crystalline structure is reported.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Computational fluid dynamics simulations of a binary particle bed in a riser-based carbon stripper for chemical looping combustion

Chemical-looping combustion (CLC) is a next generation combustion technology that shows great promise as a solution for the need of high-efficiency low-cost carbon capture from fossil fueled power plants. In this paper, numerical simulations are conducted of a binary particle bed associated with a coal-direct CLC system consisting of coal (represented by plastic beads) and oxygen carrier particles and validated against an experimental riser-based carbon stripper. The detailed particle dynamics and solid-gas and solid-solid interactions are investigated using the Lagrangian particle-tracking approach known as the discrete element method coupled with the computational fluid dynamics solution for the flow field. The simulation results of the fluidization behavior and the separation ratio of the particles are in excellent agreement with the experiment. In conclusion, a credible simulation of a binary particle bed is of particular importance for understanding the details of the fluidization behavior; the baseline simulation established in this work can be used as a tool for designing and optimizing the performance of such systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Particlization in fluid dynamical simulations of heavy-ion collisions: The IS3D module

The IS3D particlization module simulates the emission of hadrons from heavy-ion collisions via Monte-Carlo sampling of the Cooper–Frye formula which converts fluid dynamical information into local phase-space distributions for hadrons. The code package includes multiple choices for the non-equilibrium correction to these distribution functions: the 14-moment approximation, first-order Chapman–Enskog expansion, and two types of modified equilibrium distributions. This makes it possible to explore to what extent heavy-ion experimental data are sensitive to different choices for δf n , presently the main source of theoretical uncertainty in the particlization stage. Here, we validate our particle sampler with a high degree of precision by generating several million hadron emission events from a longitudinally boost-invariant hypersurface and comparing the event-averaged particle spectra and space–time distributions to the Cooper–Frye formula.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRSDate not supplied

Application and use of Multi Body Dynamic Simulations for In Space Mechanisms

The Thermal and Mechanical Analysis Branch of the Space System Department (ES22) is actively growing and expanding a new mechanical analysis capability. In recent years, there has been an increase in the demand for Multi Body Dynamics (MBD) analysis to support small ESPA ring size spacecraft, cubesats, lunar surface operations and large spacecraft with complex operations or deployables. Requirements can be balanced for both needs to ensure mechanism is verified for launch. Multi-body dynamics is the study of multiple rigid or flexible bodies that are linked together or are in contact and the associated kinematics and dynamics of the system. The typical outputs include performance information, loads, and deflections of mechanical systems. They routinely support the development of robotic mechanisms, deployment mechanisms, landing simulations, control systems, and conops planning.

Multi Body Dynamics Analysis↗
DOE OSTI2017

Determining Atomistic SAXS Models of Tri-Ubiquitin Chains from Bayesian Analysis of Accelerated Molecular Dynamics Simulations

Small-angle X-ray scattering (SAXS) has become an increasingly popular technique for characterizing the solution ensemble of flexible biomolecules. However, data resulting from SAXS is typically low-dimensional and is therefore difficult to interpret without additional structural knowledge. In theory, molecular dynamics (MD) trajectories can provide this information, but conventional simulations rarely sample the complete ensemble. Here, we demonstrate that accelerated MD simulations can be used to produce higher quality models in shorter time scales than standard simulations, and we present an iterative Bayesian Monte Carlo method that is able to identify multistate ensembles without overfitting. This methodology is applied to several ubiquitin trimers to demonstrate the effect of linkage type on the solution states of the signaling protein. Here, we observe that the linkage site directly affects the solution flexibility of the trimer and theorize that this difference in plasticity contributes to their disparate roles in vivo.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Effect of Mg and Ni impurities on tritium diffusion in lithium ceramics through cluster dynamics simulations

This study investigates the impact of Mg and Ni doping on tritium diffusion in LiAlO 2 and LiAl 5 O 8 ceramics, that are used in tritium-producing burnable absorber rods (TPBARs). Utilizing Centipede simulations across a broad temperature range (500 K to 1250 K), we explore the interplay between defect dynamics, cluster formation, and tritium mobility. In LiAlO 2 , Mg doping significantly enhances tritium diffusivity by increasing tritium interstitial concentrations and diffusion coefficients of key species, thereby doubling the overall tritium diffusivity. Ni doping, while shifting the dominant defect to Li vacancies, maintains high tritium mobility due to the low binding energy of Li vacancy-tritium complexes, which ensures effective tritium migration. In LiAl 5 O 8 , Mg and Ni doping results in a slight reduction in the diffusion coefficients of key species, yet the dramatic increase in tritium interstitial concentrations compensates, leading to a net small increase in tritium diffusivity. In conclusion, the findings highlight the critical role of defects in tritium transport and the effect of Mg and Ni defects on the performance of these ceramics in demanding nuclear environments.

Cluster dynamics↗
DOE OSTI2020

Exploring non-adiabaticity to CO reduction reaction through ab initio molecular dynamics simulation

Non-adiabatic chemical reaction refers to the electronic excitation during reactions. This effect cannot be modeled by the ground-state Born-Oppenheimer molecular dynamics (BO-MD), where the electronic structure is at the ground state for every step of ions' movement. Although the non-adiabatic effect has been explored extensively in gas phase reactions, its role in electrochemical reactions, such as water splitting and CO 2 reduction, in electrolyte has been rarely explored. On the other hand, electrochemical reactions usually involve electron transport; thus, a non-adiabatic process can naturally play a significant role. In this work, using one-step CO 2 reduction as an example, we investigated the role of the non-adiabatic effect in the reaction. The reaction barriers were computed by adiabatic BO-MD and non-adiabatic real-time time dependent density functional theory (rt-TDDFT). We found that by including the non-adiabatic effect, rt-TDDFT could increase the reaction barrier up to 6% compared to the BO-MD calculated barrier when the solvent model is used to represent water. Simulations were carried out using explicit water molecules around the reaction site under different overpotentials, and similar non-adiabatic effects were found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Predicting the structural basis of targeted protein degradation by integrating molecular dynamics simulations with structural mass spectrometry

Targeted protein degradation (TPD) is a promising approach in drug discovery for degrading proteins implicated in diseases. A key step in this process is the formation of a ternary complex where a heterobifunctional molecule induces proximity of an E3 ligase to a protein of interest (POI), thus facilitating ubiquitin transfer to the POI. In this work, we characterize 3 steps in the TPD process. (1) We simulate the ternary complex formation of SMARCA2 bromodomain and VHL E3 ligase by combining hydrogen-deuterium exchange mass spectrometry with weighted ensemble molecular dynamics (MD). (2) We characterize the conformational heterogeneity of the ternary complex using Hamiltonian replica exchange simulations and small-angle X-ray scattering. (3) We assess the ubiquitination of the POI in the context of the full Cullin-RING Ligase, confirming experimental ubiquitinomics results. Differences in degradation efficiency can be explained by the proximity of lysine residues on the POI relative to ubiquitin.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1990

Simulated dynamic response of a servovalve controlled hydraulic actuator

A general purpose math model of a servovalve controlled hydraulic actuator system is derived. The system consists of a linear actuator with unequal piston areas, a single stage servovalve, a gas charged hydraulic accumulator, and the interconnecting piping. The state equations are integrated using the Advanced Continuous Simulation Language (ACSL) for determining the system's dynamic response characteristics. Using this generalized hydraulic actuator system model, response characteristics were determined for various servovalve commands.

Babcock, Dale A.↗
NASA NTRS1975

Computer program system for dynamic simulation and stability analysis of passive and actively controlled spacecraft. Volume 1. Theory

A theoretical development and associated digital computer program system is presented. The dynamic system (spacecraft) is modeled as an assembly of rigid and/or flexible bodies not necessarily in a topological tree configuration. The computer program system may be used to investigate total system dynamic characteristics including interaction effects between rigid and/or flexible bodies, control systems, and a wide range of environmental loadings. Additionally, the program system may be used for design of attitude control systems and for evaluation of total dynamic system performance including time domain response and frequency domain stability analyses. Volume 1 presents the theoretical developments including a description of the physical system, the equations of dynamic equilibrium, discussion of kinematics and system topology, a complete treatment of momentum wheel coupling, and a discussion of gravity gradient and environmental effects. Volume 2, is a program users' guide and includes a description of the overall digital program code, individual subroutines and a description of required program input and generated program output. Volume 3 presents the results of selected demonstration problems that illustrate all program system capabilities.

Bodley, C. S.↗
DOE OSTI2017

Development of reactive force fields using ab initio molecular dynamics simulation minimally biased to experimental data

Incorporation of quantum mechanical electronic structure data is necessary to properly capture the physics of many chemical processes. Proton hopping in water, which involves rearrangement of chemical and hydrogen bonds, is one such example of an inherently quantum mechanical process. Standard ab initio molecular dynamics (AIMD) methods, however, do not yet accurately predict the structure of water and are therefore less than optimal for developing force fields. We have instead utilized here a recently developed method which minimally biases AIMD simulations to match limited experimental data to develop novel multiscale reactive molecular dynamics (MS-RMD) force fields by using relative entropy minimization. In this paper, we present two new MS-RMD models using such a parameterization: one which employs water with harmonic internal vibrations and another which uses anharmonic water. We show that the newly developed MS-RMD models very closely reproduce the solvation structure of the hydrated excess proton in the target AIMD data. We also find that the use of anharmonic water increases proton hopping, thereby increasing the proton diffusion constant.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Insights into the Reactivity of Brookite TiO 2 Nanorods in Liquid Water from Ab Initio Molecular Dynamics Simulations

Brookite TiO 2 , a rare natural polymorph of TiO 2 , has been reported to be an excellent photocatalyst for the production of hydrogen from water and aqueous alcohol solutions, especially when it is reduced and synthesized in the form of nanorods. Here, we investigate the reactivity of stoichiometric and reduced brookite nanorods in liquid water using ab initio molecular dynamics and hybrid density functional theory calculations. Our simulations show a much higher water dissociation fraction on reduced nanorods than on stoichiometric ones, with an accumulation of the resulting bridging hydroxyls (O br H) and terminal hydroxyls (Ti –OH) on different facets of the nanorod. ObrH groups accumulate preferentially on low-energy (210) facets, where they are stabilized by adjacent reduced Ti (Ti 3+ ) sites, while Ti –OH groups prefer to form at the four-fold coordinated Ti atoms on high-energy (010) facets. This hydroxylation pattern also favors the spatial localization of excited holes on the (010) facets. This coupling between water-induced surface chemistry and charge separation underpins the enhanced photocatalytic activity of brookite nanorods, providing useful information for the design of more efficient TiO2-based nanostructures for solar-driven hydrogen evolution.

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

Dynamic Simulation of a Sub-Critical Coal Fired Power Plant

In order to address the demanding operating conditions for remaining coal-fired power plants, a dynamic model and a suite of tools have been developed for studying load cycling and to find optimization opportunities. A sub-critical steam cycle power plant was modeled in a flow-sheet modeling tool, APROS™. The model represented the firing system, economizer, evaporator, superheat, and reheat systems. Four loads from 100% TMCR to 25% TMCR were calibrated and tested such that low-to-high cycling could be studied. The model was run through various load cycles; one of which is presented here. This modeling is a prototype for general use in developing cutting edge controls products and for maximizing economic, low-emissions, and efficient operation of the existing coal power fleet.

Braun, Timothy↗