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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 1,279 records · Page 71
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DOE OSTI2017

Galactic Angular Momentum in Cosmological Zoom-in Simulations. I. Disk and Bulge Components and the Galaxy–Halo Connection

We investigate the angular momentum evolution of four disk galaxies residing in Milky-Way–sized halos formed in cosmological zoom-in simulations with various sub-grid physics and merging histories. We decompose these galaxies, kinematically and photometrically, into their disk and bulge components. The simulated galaxies and their components lie on the observed sequences in the j {sub *}–M {sub *} diagram, relating the specific angular momentum and mass of the stellar component. We find that galaxies in low-density environments follow the relation j{sub ∗} ∝ M{sub ∗}{sup α} past major mergers, with α∼0.6 in the case of strong feedback, when bulge-to-disk ratios are relatively constant, and α∼1.4 in the other cases, when secular processes operate on shorter timescales. We compute the retention factors (i.e., the ratio of the specific angular momenta of stars and dark matter) for both disks and bulges and show that they vary relatively slowly after averaging over numerous but brief fluctuations. For disks, the retention factors are usually close to unity, while for bulges, they are a few times smaller. Our simulations therefore indicate that galaxies and their halos grow in a quasi-homologous way.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Circumbinary Disk Scenario for the Negative Orbital-period Derivative of the Ultra-compact X-Ray Binary 4U 1820-303

It is generally thought that an ultra-compact X-ray Binary is composed of a neutron star and a helium white dwarf donor star. As one of the most compact binaries, 4U 1820-303 in globular cluster NGC 6624 was predicted to have an orbital period of P-dot /P∼1.1×10{sup −7} yr{sup −1} if the mass transfer is fully driven by gravitational radiation. However, recent analysis of 16 year data from Rossi X-ray Timing Explorer and other historical records has yielded a negative orbital-period derivative in the past 35 years. In this work, we propose an evolutionary circumbinary (CB) disk model to account for this anomalous orbital-period derivative. 4U 1820-30 is known to undergo superburst events caused by runaway thermal nuclear burning on the neutron star. We assume that, for a small fraction of the superbursts, part of the ejected material may form a CB disk around the binary. If the recurrence time of such superbursts is ∼10,000 year and ∼10% of the ejected mass feeds a CB disk, the abrupt angular-momentum loss causes a temporary orbital shrink, and the donor’s radius and its Roche lobe radius do not keep in step. Driven by mass transfer and angular-momentum loss, the binary would adjust its orbital parameters to recover a new stable stage. Based on theoretical analysis and numerical simulation, we find that the required feed mass at the CB disk is approximately ∼10{sup −8} M {sub ⊙}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

GASP. IV. A Muse View of Extreme Ram-pressure-stripping in the Plane of the Sky: The Case of Jellyfish Galaxy JO204

In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP) survey, we present the characterization of JO204, a jellyfish galaxy in A957, a relatively low-mass cluster with M=4.4×10{sup 14} M{sub ⊙}. This galaxy shows a tail of ionized gas that extends up to 30 kpc from the main body in the opposite direction of the cluster center. No gas emission is detected in the galaxy outer disk, suggesting that gas-stripping is proceeding outside-in. The stellar component is distributed as a regular disk galaxy; the stellar kinematics shows a symmetric rotation curve with a maximum radial velocity of 200 km s{sup −1} out to 20 kpc from the galaxy center. The radial velocity of the gas component in the central part of the disk follows the distribution of the stellar component; the gas kinematics in the tail retains the rotation of the galaxy disk, indicating that JO204 is moving at high speed in the intracluster medium. Both the emission and radial-velocity maps of the gas and stellar components indicate ram-pressure as the most likely primary mechanism for gas-stripping, as expected given that JO204 is close to the cluster center and it is likely at the first infall in the cluster. The spatially resolved star formation history of JO204 provides evidence that the onset of ram-pressure-stripping occurred in the last 500 Myr, quenching the star formation activity in the outer disk, where the gas has been already completely stripped. Our conclusions are supported by a set of hydrodynamic simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Formation and Reconnection of Three-dimensional Current Sheets with a Guide Field in the Solar Corona

We analyze a series of three-dimensional magnetohydrodynamic numerical simulations of magnetic reconnection in a model solar corona to study the effect of the guide-field component on quasi-steady-state interchange reconnection in a pseudostreamer arcade configuration. This work extends the analysis of Edmondson et al. by quantifying the mass density enhancement coherency scale in the current sheet associated with magnetic island formation during the nonlinear phase of plasmoid-unstable reconnection. We compare the results of four simulations of a zero, weak, moderate, and a strong guide field, B{sub GF}/B{sub 0}={0.0,0.1,0.5,1.0}, to quantify the plasmoid density enhancement’s longitudinal and transverse coherency scales as a function of the guide-field strength. We derive these coherency scales from autocorrelation and wavelet analyses, and demonstrate how these scales may be used to interpret the density enhancement fluctuation’s Fourier power spectra in terms of a structure formation range, an energy continuation range, and an inertial range—each population with a distinct spectral slope. We discuss the simulation results in the context of solar and heliospheric observations of pseudostreamer solar wind outflow and possible signatures of reconnection-generated structure.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Teleoperation for Nuclear Applications Considering Communication Delay and Uncertainty - 18205

Teleoperation in remote environment is of great interest in robotics. Advancement in communication technology has enabled safe execution of complex and life threatening tasks in network environment in teleoperation. Using bilateral teleoperation, the operator receives force feedback from the slave which provides an interactive feel of forces and smoother coordination. However, time delay across the communication link in sending the command signal from the master to the slave may cause instability to the system. In this research, we use the continuous pole placement method to address the time delay problem in teleoperation. Compared to approximation based and prediction based methods, this method shows improved robustness. Simulations and experiments show a stable and well synchronized control. (authors)

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

Subcritical Benchmark of the BeRP Ball Reflected by Tungsten

In September 2012, eight subcritical configurations were measured with the clad a-phase plutonium sphere known as the Beryllium-Reflected Plutonium (BeRP) ball at the National Criticality Experiments Research Center (NCERC). The configurations had varying tungsten thicknesses including: 0 (bare), 0.5, 1.0, 1.5, 2.0, 2.5, 2.75, and 3.0 inches. Measurements were conducted to provide subcritical benchmark data. This work includes measured and simulated results from the International Handbook of Evaluated Criticality Safety Benchmark Experiments (ICSBEP) evaluation. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Nuclear Power Plant Control Room Modernization - Simulation Based Design

As many plants age and equipment modifications are implemented, the industry has the opportunity to address the issue of control room obsolescence through technology application and enhanced engineering techniques using existing systems. This paper addresses the practice of Simulation Based Design (SBD) for control room modernization driven by plant modifications and upgrades.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Effects of Boron and Graphite Uncertainty in Fuel for TREAT Simulations

As a result of the accident at Fukushima, the United States has made a concerted effort to develop fuel with enhanced accident tolerance for the current fleet of reactors. In 2012 Congress laid out a schedule for the development of accident tolerant fuel (ATF), the goal of which is to test in a commercial reactor by 2022. Idaho National Lab's (INL) Transient Reactor Test Facility (TREAT) is one of the locations that will be performing ATF testing and is scheduled for restart in 2018. TREAT was built to subject fuel to conditions ranging from mild transients to severe reactor accidents. However, typically a number of pre-test calibrations are required before evaluation of fuel can begin, which is costly and time consuming. Advanced modeling techniques and current computational capacity make full core TREAT simulations possible, with the goal of such simulations to understand the pre-test core and minimize the number of required calibrations. But, in order to simulate TREAT with a high degree of precision the reactor materials and geometry must also be modeled with a high degree of precision. This paper examines how uncertainty in the reported values of boron and graphite have an effect on simulations of TREAT.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Initiation of fission chains during delayed criticality accidents - 14366

We present the simulation of the waiting time probability distribution before a prescribed reaction rate in a delayed supercritical system. The Kolmogorov backward equations for the count number probability distribution taking into account the delayed neutron precursors are solved within the time dependent point model framework. The initiation of fission chains is also studied using analog Monte-Carlo simulations of the prompt neutrons and delayed neutron precursors population. The fission rate is calculated for comparison with deterministic simulations. Numerical results are presented using both deterministic and Monte-Carlo calculations to study the effect of the source strength and reactivity level. (authors)

42 ENGINEERING↗
DOE OSTI2019

Topological Structures in Unconventional Scenario for 2D Cuprates

Numerous experimental data point to cuprates as d-d charge transfer unstable systems whose description implies the inclusion of the three many-electron valence states CuO{sub 4}{sup 7−,6−,5−} (nominally Cu{sup 1+,2+,3+}) on an equal footing as a well-defined charge triplet. We introduce a minimal model to describe the charge degree of freedom in cuprates with the on-site Hilbert space reduced to only the three states and make use of the S = 1 pseudospin formalism. The formalism constitutes a powerful method to study complex phenomena in interacting quantum systems characterized by the coexistence and competition of various ordered states. Overall, such a framework provides a simple and systematic methodology to predict and discover new kinds of orders. In particular, the pseudospin formalism provides the most effective way to describe different topological structures, in particular, due to a possibility of a geometrical two-vector description of the on-site states. We introduce and analyze effective pseudospin Hamiltonian with on-site and inter-site charge correlations, two types of a correlated one-particle transfer and two-particle, or the composite boson transfer. The latter is of a principal importance for the HTSC perspectives. The 2D S = 1 pseudospin system is prone to a creation of different topological structures, which form topologically protected inhomogeneous distributions of the eight local S = 1 pseudospin order parameters. We present a short overview of localized topological structures, typical for S = 1 (pseudo)spin systems, focusing on unexpected antiphase domain walls in parent cuprates and so-called quadrupole skyrmion, which are believed to be candidates for a topological charge excitation in parent or underdoped cuprates. Puzzlingly, these unconventional structures can be characterized by an uniform distribution of the mean on-site charge, that makes these invisible for X-rays. Quasi-classical approximation and computer simulation are applied to analyze localized topological defects and evolution of the domain structures in “negative-U” model under charge order-superfluid phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Analysis of Plane-Parallel Electron Beam Propagation in Different Media by Numerical Simulation Methods

Simulation by the Monte Carlo method is widely used to calculate the character of ionizing radiation interaction with substance. A wide variety of programs based on the given method allows users to choose the most suitable package for solving computational problems. In turn, it is important to know exactly restrictions of numerical systems to avoid gross errors. Results of estimation of the feasibility of application of the program PCLab (Computer Laboratory, version 9.9) for numerical simulation of the electron energy distribution absorbed in beryllium, aluminum, gold, and water for industrial, research, and clinical beams are presented. The data obtained using programs ITS and Geant4 being the most popular software packages for solving the given problems and the program PCLab are presented in the graphic form. A comparison and an analysis of the results obtained demonstrate the feasibility of application of the program PCLab for simulation of the absorbed energy distribution and dose of electrons in various materials for energies in the range 1–20 MeV.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Connecting the dots: Semi-analytical and random walk numerical solutions of the diffusion–reaction equation with stochastic initial conditions

We study a system with bimolecular irreversible kinetic reaction A+B→∅ where the underlying transport of reactants is governed by diffusion, and the local reaction term is given by the law of mass action. We consider the case where the initial concentrations are given in terms of an average and a white noise perturbation. Our goal is to solve the diffusion–reaction equation which governs the system, and we tackle it with both analytical and numerical approaches. To obtain an analytical solution, we develop the equations of moments and solve them approximately. To obtain a numerical solution, we develop a grid-less Monte Carlo particle tracking approach, where diffusion is modeled by a random walk of the particles, and reaction is modeled by annihilation of particles. The probability of annihilation is derived analytically from the particles' co-location probability. We rigorously derive the relationship between the initial number of particles in the system and the amplitude of white noise represented by that number. This enables us to compare the particle simulations and the approximate analytical solution and offer an explanation of the late time discrepancies. - Graphical abstract:.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

A stochastic thermostat algorithm for coarse-grained thermomechanical modeling of large-scale soft matters: Theory and application to microfilaments

As all-atom molecular dynamics method is limited by its enormous computational cost, various coarse-grained strategies have been developed to extend the length scale of soft matters in the modeling of mechanical behaviors. However, the classical thermostat algorithm in highly coarse-grained molecular dynamics method would underestimate the thermodynamic behaviors of soft matters (e.g. microfilaments in cells), which can weaken the ability of materials to overcome local energy traps in granular modeling. Based on all-atom molecular dynamics modeling of microfilament fragments (G-actin clusters), a new stochastic thermostat algorithm is developed to retain the representation of thermodynamic properties of microfilaments at extra coarse-grained level. The accuracy of this stochastic thermostat algorithm is validated by all-atom MD simulation. This new stochastic thermostat algorithm provides an efficient way to investigate the thermomechanical properties of large-scale soft matters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Accelerating population balance-Monte Carlo simulation for coagulation dynamics from the Markov jump model, stochastic algorithm and GPU parallel computing

This paper proposes a comprehensive framework for accelerating population balance-Monte Carlo (PBMC) simulation of particle coagulation dynamics. By combining Markov jump model, weighted majorant kernel and GPU (graphics processing unit) parallel computing, a significant gain in computational efficiency is achieved. The Markov jump model constructs a coagulation-rule matrix of differentially-weighted simulation particles, so as to capture the time evolution of particle size distribution with low statistical noise over the full size range and as far as possible to reduce the number of time loopings. Here three coagulation rules are highlighted and it is found that constructing appropriate coagulation rule provides a route to attain the compromise between accuracy and cost of PBMC methods. Further, in order to avoid double looping over all simulation particles when considering the two-particle events (typically, particle coagulation), the weighted majorant kernel is introduced to estimate the maximum coagulation rates being used for acceptance–rejection processes by single-looping over all particles, and meanwhile the mean time-step of coagulation event is estimated by summing the coagulation kernels of rejected and accepted particle pairs. The computational load of these fast differentially-weighted PBMC simulations (based on the Markov jump model) is reduced greatly to be proportional to the number of simulation particles in a zero-dimensional system (single cell). Finally, for a spatially inhomogeneous multi-dimensional (multi-cell) simulation, the proposed fast PBMC is performed in each cell, and multiple cells are parallel processed by multi-cores on a GPU that can implement the massively threaded data-parallel tasks to obtain remarkable speedup ratio (comparing with CPU computation, the speedup ratio of GPU parallel computing is as high as 200 in a case of 100 cells with 10 000 simulation particles per cell). These accelerating approaches of PBMC are demonstrated in a physically realistic Brownian coagulation case. The computational accuracy is validated with benchmark solution of discrete-sectional method. The simulation results show that the comprehensive approach can attain very favorable improvement in cost without sacrificing computational accuracy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Multiscale Universal Interface: A concurrent framework for coupling heterogeneous solvers

Graphical abstract: - Abstract: Concurrently coupled numerical simulations using heterogeneous solvers are powerful tools for modeling multiscale phenomena. However, major modifications to existing codes are often required to enable such simulations, posing significant difficulties in practice. In this paper we present a C++ library, i.e. the Multiscale Universal Interface (MUI), which is capable of facilitating the coupling effort for a wide range of multiscale simulations. The library adopts a header-only form with minimal external dependency and hence can be easily dropped into existing codes. A data sampler concept is introduced, combined with a hybrid dynamic/static typing mechanism, to create an easily customizable framework for solver-independent data interpretation. The library integrates MPI MPMD support and an asynchronous communication protocol to handle inter-solver information exchange irrespective of the solvers' own MPI awareness. Template metaprogramming is heavily employed to simultaneously improve runtime performance and code flexibility. We validated the library by solving three different multiscale problems, which also serve to demonstrate the flexibility of the framework in handling heterogeneous models and solvers. In the first example, a Couette flow was simulated using two concurrently coupled Smoothed Particle Hydrodynamics (SPH) simulations of different spatial resolutions. In the second example, we coupled the deterministic SPH method with the stochastic Dissipative Particle Dynamics (DPD) method to study the effect of surface grafting on the hydrodynamics properties on the surface. In the third example, we consider conjugate heat transfer between a solid domain and a fluid domain by coupling the particle-based energy-conserving DPD (eDPD) method with the Finite Element Method (FEM)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Extension of moment projection method to the fragmentation process

The method of moments is a simple but efficient method of solving the population balance equation which describes particle dynamics. Recently, the moment projection method (MPM) was proposed and validated for particle inception, coagulation, growth and, more importantly, shrinkage; here the method is extended to include the fragmentation process. The performance of MPM is tested for 13 different test cases for different fragmentation kernels, fragment distribution functions and initial conditions. Comparisons are made with the quadrature method of moments (QMOM), hybrid method of moments (HMOM) and a high-precision stochastic solution calculated using the established direct simulation algorithm (DSA) and advantages of MPM are drawn.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Note: A real-time beam current density meter

We have developed a real-time beam current density meter for charged particle beams. It measures the mean current density by collimating a uniform and large diameter primary beam. The suppression of the secondary electrons and the deflection of the beam were simulated, and it was tested with a 105 keV Ar{sup 7+} ion beam.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Double shock front formation in cylindrical radiative blast waves produced by laser irradiation of krypton gas

Radiative blast waves were created by irradiating a krypton cluster source from a supersonic jet with a high intensity femtosecond laser pulse. It was found that the radiation from the shock surface is absorbed in the optically thick upstream medium creating a radiative heat wave that travels supersonically ahead of the main shock. As the blast wave propagates into the heated medium, it slows and loses energy, and the radiative heat wave also slows down. When the radiative heat wave slows down to the transonic regime, a secondary shock in the ionization precursor is produced. This paper presents experimental data characterizing both the initial and secondary shocks and numerical simulations to analyze the double-shock dynamics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗