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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Hydrogeologic Setting and Groundwater Contaminant Conceptual Model, Los Alamos National Laboratory - 18681

Our understanding of the complex hydrogeologic setting at Los Alamos National Laboratory (LANL) has evolved significantly over the previous decade. The semi-arid, high-desert setting consists of generally dry drainages in canyons that head either in uplands to the west of the Laboratory or on the high mountain-front plateau where the Laboratory is spread across approximately 40 square miles. Some canyon drainages have spatially limited reaches with perennial surface water from natural runoff and spring sources and/or from permitted effluent sources. The Rio Grande rift basin-fill stratigraphy includes primary volcanic deposits from pyroclastic eruptions and intermediate composition lava flows, and fluvial and alluvial fan deposits. Highly complex and spatially variable stratigraphy governs the occurrences of three groundwater zones: shallow 'alluvial groundwater', deep perched groundwater, and a thick 'regional' aquifer that is the water supply for the community of Los Alamos and the Laboratory. The current understanding of the hydrogeologic framework was greatly expanded as part of a site hydrogeologic characterization program completed in 2005. Higher resolution information exists in area where more detailed groundwater characterization has been conducted to support specific project objectives. A conceptual model for occurrences of contaminants in each of the three groundwater zones is governed by four factors: contaminant solubility/mobility, the mass of historical release, presence of a continuous hydraulic driver, and 'breakthrough' geology, defined as geology conducive to infiltration of shallow groundwater to deeper groundwater zones. The Laboratory's operations were historically somewhat spatially partitioned. Most of the radionuclide work (and historical releases) was conducted in the northern portion of the Laboratory, high explosives work has taken place exclusively in the southwestern portion, and treated sanitary effluent was released at a limited number of outfalls. Historical material disposal areas (MDAs) are dispersed throughout the Laboratory, and active MDAs are all located on a single dry mesa at the eastern part of the Laboratory. Evidence exists of transport of anthropogenic constituents to the regional aquifer. However, years of groundwater characterization have identified only two cases for which all the key factors were present and a complete contaminant pathway to the regional aquifer has resulted in contamination at levels above an applicable standard. Hexavalent chromium contamination associated with historical use as a corrosion inhibitor in a power plant is present beneath Mortandad Canyon, and RDX contamination associated with high-explosives machining is present beneath Canon de Valle. Each of those project areas have refined conceptual and numerical models that address contaminant migration pathways, spatial extent of perched-intermediate groundwater, mass balance, and fate and transport within the regional aquifer. No known contamination is present in the regional aquifer associated with MDAs, and interestingly, much of the Laboratory's groundwater background dataset is from wells located beneath active MDAs. A comprehensive groundwater monitoring program is in place to track the evolution of chromium and RDX contamination, and to identify any other constituents that may be attributable to historical LANL operations. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

The Challenges of Air Monitoring at a Soil Remediation Project in a Suburban Setting - 20448

Air monitoring during soil excavation at a chemically and radiologically impacted site in a suburban setting presents unique challenges. Site activities were conducted in a manner that minimized the release of airborne particulates of concern, principally radionuclides of concern (ROC). Dust and air monitoring were performed to ensure the public was not being exposed to the soil contaminants. The project team collected representative air and dust data while being mindful to not impose on the lives of residents in the area. Due to the close proximity to the public, there was a high level of oversight from the client and regulatory agencies. The challenges involved with air sampling at this soil remediation site located in a suburban setting included the number of contaminants, the ranges of risks and hazards presented by the contaminants and the method of remediation, the concerns of the regulators and the public, and the perception of risk from the public. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Two-phase Flow Regime Transition Study using Level-Set Method

In Boiling Water Reactors (BWRs) the coolant exiting the core often has void fractions as high as 50%, resulting in high gas volume fraction two-phase flow regimes, such as annular or churn-turbulent flow. As the coolant boils along the subchannels it will experience flow regime transitions from bubbly to slug, slug to churn, and, finally, churn to annular. While these transition points are known to occur as a higher void develops along the flow path, the driving physics of the transition phenomenon is not well understood. Currently, experiment based correlations are the most reliable method for predicting where in the core the flow regime transitions will occur. However, experimentally, it's ever difficult to observe the details of the two-phase flow at prototypical pressures/temperatures, or, as with high fidelity experiments, the conditions differ from those in a reactor. Being able to predict these flow regime transitions is critical to safe and efficient reactor operations as well as maintaining fuel rod integrity by avoiding dryout. The characterization of flow regimes has been extensively studied, producing a wide set of flow regime maps based on characteristic parameters such as vapor and liquid superficial velocity, time dependent pressure drop, interfacial area density, etc. While these studies are useful in predicting the flow regime for certain geometry and flow conditions, they do not provide a universal predictive capability for any geometry under any conditions. Additionally, it is difficult to achieve reactor realistic pressure and temperature conditions in experiments. Direct Numerical Simulation (DNS) coupled with Interface Tracking Methods (ITMs) becomes advantageous in this case because the simulations are not limited by the material properties or to the real world conditions. DNS allows for analysis of flows that would be impossible to achieve, or observe in detail, experimentally. The finite element based DNS code, PHASTA (parallel, hierarchic, higher-order accurate, adaptive, stabilized transient analysis flow solver), used in this work utilizes the level set ITM and has been previously shown to properly resolve bubbly, slug, and annular flows, but not transitions between the two-phase flow regimes. The present work uses PHASTA to analyze flow in a pipe for various void fractions and superficial velocities. Flow regime transitions were induced to demonstrate the transient behavior of this phenomenon. With the unique advanced analysis capabilities developed in PHASTA that allow for individual bubble tracking, it becomes possible to extract new localized information about the flow behavior that is currently not attainable from experiments. The potential of this capability is to uncover the underlying physics of the flow regime transition phenomenon. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2024

Federated Machine Learning-Based Anomaly Detection System for Synchrophasor Network Using Heterogeneous Data Sets: Preprint

Synchrophasor technology is widely deployed in the energy management system to monitor the grid health at micro level and perform necessary corrective actions in real time; however, integrated phasor devices and data aggregators are exposed to several cybersecurity threats. This paper proposes a federated ML(FML)-based ADS to detect several data integrity attacks in the synchrophasor network. The proposed approach integrates the horizontal FML technique and consists of substation-based local models and a control center-based global model. The proposed methodology includes training local models using heterogeneous data sets that include network and grid information and updating the global model through multiple iterations by sharing model gradients. Finally, the trained global model is applied to identify cyberattacks, normal operation, and physical events. To validate the proof of concept, we used synthetic data sets generated by Mississippi State University and Oak Ridge National Laboratory for training and testing the classification models using the National Renewable Energy Laboratory's high performance computing resources. Our experimental results, computed through several performance measures, reveal that the proposed approach shows consistent performance during the binary, three-class, and multiclass classifications while ensuring privacy of synchrophasor data.

anomaly detection system↗
DOE OSTI2025

A hereditary integral, transient network approach to modeling permanent set and viscoelastic response in polymers

An efficient numerical framework is presented for modeling viscoelasticity and permanent set of polymers. It is based on the hereditary integral form of transient network theory, in which polymer chains belong to distinct networks each with different natural equilibrium states. Chains continually detach from previously formed networks and reattach to new networks in a state of zero stress. The free energy of these networks is given in terms of the deformation gradient relative to the configuration at which the network was born . A decomposition of the kernel for various free energies allows for a recurrence relationship to be established, bypassing the need to integrate over all time history. The technique is established for both highly compressible and nearly incompressible materials through the use of neo-Hookean, Blatz–Ko, Yeoh, and Ogden-Hill material models. Multiple examples are presented showing the ability to handle rate-dependent response and residual strains under complex loading histories.

Finite element method↗
DOE OSTI2026

An efficient level set method for tracking many materials

Here, we present an efficient level set method to track an arbitrary number of materials. The algorithm is optimal in the sense that it only needs to store a single unsigned distance-like function and a single integer indicator function, independent of the number of materials or distinct regions being tracked. Furthermore, for smooth velocity fields and smooth interface shape, arbitrarily high order solutions can be demonstrated. For interfaces that are or become kinked, the solution is limited to second-order convergence rates in the L 1 norm and first-order in the L ∞ norm.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

A level set approach for the computational study of a yield stress fluid filling a thin mold

Many important engineering and scientific applications such as cement slurries, foams, crude oil, and granular avalanches involve the concept of yield stress. Therefore, modeling yield stress fluids in different flow configurations, including the accurate prediction of the yield surface, is important. In this paper, we present a computational model based on the finite element method to study the flow of yield stress fluids in a thin mold and compare the results with data from flow visualization experiments. Here, we use the level set method to describe the interface between the filling fluid and air. We use polypropylene glycol as a model Newtonian fluid and Carbopol for the model yield stress fluid, as the Carbopol solution demonstrates yielding without thixotropy. To describe the yielding and shear-thinning behavior, we use a generalized Newtonian constitutive equation with a Bingham–Carreau–Yasuda form. We compare the results obtained from the mold filling experiments with the results from the three-dimensional (3D) model and from a reduced-order Hele-Shaw (HS) model that is two-dimensional, including the effect of shear-thinning along the thin direction only approximately. We show that both the 3D and the HS model can capture the experimental meniscus shape reasonably well for all the fluids considered at three different flow rates. This indicates that the shape evolution is insensitive to the dimensionality of the model. However, the viscosity and yield surfaces predicted by the 3D and HS models are different. The HS model underestimates the high viscosity and unyielded regions compared to the estimation by the 3D model.

42 ENGINEERING↗
DOE OSTI2015

Accelerating the Convergence of Replica Exchange Simulations Using Gibbs Sampling and Adaptive Temperature Sets

We recently introduced a novel replica-exchange scheme in which an individual replica can sample from states encountered by other replicas at any previous time by way of a global configuration database, enabling the fast propagation of relevant states through the whole ensemble of replicas. This mechanism depends on the knowledge of global thermodynamic functions which are measured during the simulation and not coupled to the heat bath temperatures driving the individual simulations. Therefore, this setup also allows for a continuous adaptation of the temperature set. In this paper, we will review the new scheme and demonstrate its capability. The method is particularly useful for the fast and reliable estimation of the microcanonical temperature T (U) or, equivalently, of the density of states g(U) over a wide range of energies.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Dynamic homotopy and landscape dynamical set topology in quantum control

We examine the topology of the subset of controls taking a given initial state to a given final state in quantum control, where 'state' may mean a pure state Double-Vertical-Line {psi}>, an ensemble density matrix {rho}, or a unitary propagator U(0, T). The analysis consists in showing that the endpoint map acting on control space is a Hurewicz fibration for a large class of affine control systems with vector controls. Exploiting the resulting fibration sequence and the long exact sequence of basepoint-preserving homotopy classes of maps, we show that the indicated subset of controls is homotopy equivalent to the loopspace of the state manifold. This not only allows us to understand the connectedness of 'dynamical sets' realized as preimages of subsets of the state space through this endpoint map, but also provides a wealth of additional topological information about such subsets of control space.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

An efficient basis set representation for calculating electrons in molecules

The method of McCurdy, Baertschy, and Rescigno, is generalised to obtain a straightforward, surprisingly accurate, and scalable numerical representation for calculating the electronic wave functions of molecules. It uses a basis set of product sinc functions arrayed on a Cartesian grid, and yields 1 kcal/mol precision for valence transition energies with a grid resolution of approximately 0.1 bohr. The Coulomb matrix elements are replaced with matrix elements obtained from the kinetic energy operator. A resolution-of-the-identity approximation renders the primitive one- and two-electron matrix elements diagonal; in other words, the Coulomb operator is local with respect to the grid indices. The calculation of contracted two-electron matrix elements among orbitals requires only O( N log (N)) multiplication operations, not O( N 4 ), where N is the number of basis functions; N = n 3 on cubic grids. The representation not only is numerically expedient, but also produces energies and properties superior to those calculated variationally. Absolute energies, absorption cross sections, transition energies, and ionisation potentials are reported for 1- (He + , H + 2 ), 2- (H 2 , He), 10- (CH 4 ), and 56-electron (C 8 H 8 ) systems.

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

Atomic forces from Dirac-Kohn-Sham equations: Implementation in flexible (APW+lo/LAPW)+LO basis set

The atomic forces formulation based on the Dirac-Kohn-Sham equation and the flexible (APW+lo/LAPW)+LO basis set is presented here. The formulation was implemented in the code FlapwMBPT and allows a user to easily switch between different basis functions of the augmentation type (APW or LAPW) and between different kind of local orbitals. Similar to the work (Phys.Rev.B 91 (2015) 035105), the implementation takes into account small discontinuities of the wave functions, density, and potential at the muffin-tin sphere boundaries. Applications to the materials with strong relativistic effects, such as $\alpha$-Uranium, PuCoGa$_{5}$, and FePt, demonstrate robustness of the method. The comparison of the calculated forces with the ones obtained by numerical differentiation of free energy shows close agreement with deviations about 0.1% or less.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Setting the scale for the CLS 2 + 1 flavor ensembles

Here, we present measurements of a combination of the decay constants of the light pseudoscalar mesons and the gradient flow scale t 0 , which allow us to set the scale of the lattices generated by CLS with 2 + 1 flavors of nonperturbatively improved Wilson fermions. Furthermore, we correct for mistunings of the quark masses by measuring the derivatives of observables with respect to the bare quark masses.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Distributed-Memory Fast Maximal Independent Set

The Maximal Independent Set (MIS) graph problem arises in many applications such as computer vision, information theory, molecular biology, and process scheduling. The growing scale of MIS problems suggests the use of distributed-memory hardware as a cost-effective approach to providing necessary compute and memory resources. Luby proposed four randomized algorithms to solve the MIS problem. All those algorithms are designed focusing on shared-memory machines and are analyzed using the PRAM model. These algorithms do not have direct efficient distributed-memory implementations. In this paper, we extend two of Luby’s seminal MIS algorithms, “Luby(A)” and “Luby(B),” to distributed-memory execution, and we evaluate their performance. We compare our results with the “Filtered MIS” implementation in the Combinatorial BLAS library for two types of synthetic graph inputs.

distributed memory parallel↗
DOE OSTI2022

Reduced Switching Frequency Finite Control Set Model Predictive Control (FCS-MPC) for DFIG

An enhanced Finite Control Set Model Predictive Control (FCS-MPC) strategy with a two-step prediction horizon for a Doubly-Fed Induction Generator (DFIG) is the focus of this paper. The DFIG and RL filter's discrete-time model is used in the proposed control scheme for a two-step prediction horizon of rotor and filter currents for the converter's eight possible switching states. Afterward, the control algorithm selects the ideal switching state, which minimizes currents' objective function. The proposed control scheme does not require a modulation stage for internal controllers. We use Lagrange extrapolations to predict the dynamic changes in currents. The switching frequency reduction is achieved by integrating an optimization constraint in the algorithm's cost function. Furthermore, the Total Harmonic Distortion level of currents is kept below 5%, according to IEEE Std 519-14. Obtained results reveal that the switching frequency of the DFIG converters is considerably reduced without losing control; it is reduced by 13.89KHz for the Grid Side Converter (GSC) and by 1.78KHz for the Rotor Side Converter (RSC).

doubly-fed induction generator↗
DOE OSTI2018

The Pacific Marine Energy Center - South Energy Test Site (PMEC-SETS)

The overall goal of this project was to build on existing progress to establish the Pacific Marine Energy Center South Energy Test Site (PMEC-SETS) as the nation's first fully permitted test site for wave energy converter arrays. Specifically, it plays an essential role in reducing levelized cost of energy for the wave energy industry by providing both the facility and resources to address the challenges of cost reduction.

16 TIDAL AND WAVE POWER↗