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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Effects of Different Closure Choices in Core-collapse Supernova Simulations

The two-moment method is widely used to approximate the full neutrino transport equation in core-collapse supernova (CCSN) simulations, and different closures lead to subtle differences in the simulation results. In this paper, we compare the effects of closure choices on various physical quantities in 1D and 2D time-dependent CCSN simulations with our multigroup radiation hydrodynamics code FORNAX. We find that choices of the third-order closure relations influence the time-dependent simulations only slightly. Choices of the second-order closure relation have larger consequences than choices of the third-order closure, but these are still small compared to the remaining variations due to ambiguities in some physical inputs such as the nuclear equation of state. We also find that deviations in Eddington factors are not monotonically related to deviations in physical quantities, which means that simply comparing the Eddington factors does not inform one concerning which closure is better.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1976

A study of fatigue crack closure using electric potential and compliance techniques

Compared are closure data produced on the same specimen by the crack tip compliance gage and electric potential techniques. Experiments on 7075-T651 aluminum center cracked panels produced equivalent results on closure using the two techniques. The results also indicated that closure is a function of stress ratio, specimen thickness and maximum applied stress intensity. Maximum stress intensity had a strong effect on closure in the range of applied stresses used. This dependence of closure on specimen thickness and maximum stress intensity accounts for many of the discrepencies in closure behavior reported in the literature.

Clarke, C. K.↗
NASA NTRS1976

Remarks on the construction of a second-order closure description of turbulent reacting flows

In this paper an attempt is made to illustrate how second-order closure techniques might be used to make detailed calculations of turbulent diffusion flames. Two of the problems of closure that are peculiar to turbulent chemically reacting flows are discussed in some detail. These are the problem of computing in a consistent way all the correlations of fluctuations in scalar quantities needed for closure and the problem of the generation of turbulence by chemical reactions. Tentative closure models are put forward for both of these problems. Although the closure model for fluctuations in scalar quantities can, to a certain extent, be checked against idealized numerical examples for which exact solutions are known, the validity of both the closure models proposed here must, in the end, be determined by detailed comparison of computed results with experimental data.

DONALDSON C. DUP.↗
NASA NTRS1985

A comparison of three algebraic stress closures for combustor flow calculations

A comparison is made of the performance of two locally nonequilibrium and one equilibrium algebraic stress closures in calculating combustor flows. Effects of four different pressure-strain models on these closure models are also analyzed. The results show that the pressure-strain models have a much greater influence on the calculated mean velocity and turbulence field than the algebraic stress closures, and that the best mean strain model for the pressure-strain terms is that proposed by Launder, Reece and Rodi (1975). However, the equilibrium algebraic stress closure with the Rotta return-to-isotropy model (1951) for the pressure-strain terms gives as good a correlation with measurements as when the Launder et al. mean strain model is included in the pressure-strain model. Finally, comparison of the calculations with the standard k-epsilon closure results show that the algebraic stress closures are better suited for simple turbulent flow calculations.

Nikjooy, M.↗
NASA NTRS1991

Near-wall turbine closure for curved flows

At present, turbulence closures for curved flows only account for curvature effects in the fully turbulent region where the Reynolds number is large. The justification is that, near a wall, viscous effects dominate and curvature effects are only of secondary importance. Recent direct simulation data show that this assumption is not valid, even for simple two-dimensional fully developed turbulent curved channel flows. This paper presents an approach to develop a near-wall turbulence closure for wall-bounded curved flows. The curved channel direct simulation data is used as a guide to held develop such a closure. The proposed closure has the unique property of approaching conventional high-Reynolds-number Reynolds-stress closures far away from the wall. Hence, curvature effects in both the near-wall and the fully turbulent parts of the flow are accounted for properly. Validations of the closure are carried out with a set of low-Reynolds-number simulation data and with experimental measurements at high Reynolds number. Good agreement is obtained in both cases; in particular, the anisotropic behavior of the normal stresses and the shear stress behavior near the convex and concave walls.

So, R. M. C.↗
NASA NTRS1999

Ocean Turbulence: Two-Point Closure Model Momentum, Heat and Salt Vertical Diffusivities in the Presence of Shear - Paper 3

In papers 1 and 2 we have presented the results of the most updated 1-point closure model for the turbulent vertical diffusivities of momentum, heat and salt, K(sub m,h,s). In this paper, we derive the analytic expressions for K(sub m,h,s) using a new 2-point closure model that has recently been developed and successfully tested against some approx. 80 turbulence statistics for different flows. The new model has no free parameters. The expressions for K(sub m, h. s) are analytical functions of two stability parameters: the Turner number R(sub rho) (salinity gradient/temperature gradient) and the Richardson number R(sub i) (temperature gradient/shear). The turbulent kinetic energy K and its rate of dissipation may be taken local or non-local (K-epsilon model). Contrary to all previous models that to describe turbulent mixing below the mixed layer (ML) have adopted three adjustable "background diffusivities" for momentum. heat and salt, we propose a model that avoids such adjustable diffusivities. We assume that below the ML, K(sub m,h,s) have the same functional dependence on R(sub i) and R(sub rho) derived from the turbulence model. However, in order to compute R(sub i) below the ML, we use data of vertical shear due to wave-breaking measured by Gargett et al. (1981). The procedure frees the model from adjustable background diffusivities and indeed we use the same model throughout the entire vertical extent of the ocean. Using the new K(sub m,h, s), we run an O-GCM and present a variety of results that we compare with Levitus and the KPP model. Since the traditional 1-point (used in papers 1 and 2) and the new 2-point closure models used here represent different modeling philosophies and procedures, testing them in an O-GCM is indispensable. The basic motivation is to show that the new 2-point closure model gives results that are overall superior to the 1-point closure in spite of the fact that the latter rely on several adjustable parameters while the new 2-point closure has none. After the extensive comparisons presented in papers 1 and 2, we conclude that the new model presented here is overall superior for it not only is parameter free but also 2 because is part of a more general turbulence model that has been previously successfully tested on a wide variety of other types of turbulent flows.

Canuto, V. M.↗
NASA NTRS2003

Modeling the Interactions Between Multiple Crack Closure Mechanisms at Threshold

A fatigue crack closure model is developed that includes interactions between the three closure mechanisms most likely to occur at threshold; plasticity, roughness, and oxide. This model, herein referred to as the CROP model (for Closure, Roughness, Oxide, and Plasticity), also includes the effects of out-of plane cracking and multi-axial loading. These features make the CROP closure model uniquely suited for, but not limited to, threshold applications. Rough cracks are idealized here as two-dimensional sawtooths, whose geometry induces mixed-mode crack- tip stresses. Continuum mechanics and crack-tip dislocation concepts are combined to relate crack face displacements to crack-tip loads. Geometric criteria are used to determine closure loads from crack-face displacements. Finite element results, used to verify model predictions, provide critical information about the locations where crack closure occurs.

Newman, John A.↗
NASA NTRS1989

Quick actuating closure

A quick actuating closure for a pressure vessel 80 in which a wedge ring 30 with a conical outer surface 31 is moved forward to force shear blocks 40, with conical inner surfaces 41, radially outward to lock an end closure plug 70 within an opening 81 in the pressure vessel 80. A seal ring 60 and a preload ramp 50 sit between the shear blocks 40 and the end closure plug 70 to provide a backup sealing capability. Conical surfaces 44 and 55 of the preload ramp 50 and the shear blocks 40 interact to force the seal ring 60 into shoulders 73 and 85 in the end closure plug 70 and opening 81 to form a tight seal. The end closure plug 70 is unlocked by moving the wedge ring 30 rearward, which causes T-bars 32 of the wedge ring 30 riding within T -slots 42 of the shear blocks 40 to force them radially inward. The end closure plug 70 is then removed, allowing access to the interior of the pressure vessel 80.

White, III, Dorsey E.↗
DOE OSTI2015

Leaning the tank closure process at the Savannah River Site - 15515

The Savannah River Site liquid waste system consists of multiple facilities that safely receive and store legacy radioactive waste prior to treatment and disposition. The liquid radioactive waste is stored in large underground tanks. The waste inventory currently stored in these tanks is a complex mixture of insoluble metal hydroxide solids and soluble salt supernate. The high-level (radioactive) portion of the waste is vitrified into a glass waste form, while the low-level waste is immobilized into a cementitious grout waste form called salt-stone. Once the waste is retrieved and processed, the tanks are closed. The closure process includes; waste removal, characterizing residuals, isolating the tank systems, and stabilizing the tank with tailored grout formulations. The core of Lean is to eliminate waste or non-value added steps from processes to maximize customer value. From the perspective of the customer, 'value' is defined as any action or process for which a customer would willingly pay. In this case our product is to safely and efficiently remove waste from the underground storage tanks and demonstrate operational closure to the State of South Carolina. Savannah River Remediation (SRR) initiated the use of the Lean process in late 2013 and identified the Tank Closure process as one of the targeted areas to improve. The first step in the Lean process is to 'map' out the value stream and identify areas where non-value added steps are present and then prioritize Rapid Improvement Events (RIE). Based on this mapping process, there were a number of areas that SRR determined warranted further evaluation for improvements, including; standard equipment design, characterization, standard work packages, regulatory documentation, tank characterization, structural evaluations, engineering documentation and equipment re-use. This paper focuses on the application of the Lean process at SRR and more specifically, effective application to the Tank Closure Process. This paper discusses the value stream mapping process for Tank Closures, as well as, summarizes the RIEs and demonstrate the realized benefits. Benefits can come in a variety of forms, from schedule compression to decreased costs. Through the Lean process we have been able to identify close to $10 M in savings over the life cycle of the tank closure process and a 4 year schedule compression. Cost and schedule savings are used to accomplish further risk reduction efforts. In addition to hard benefits, there are also soft benefits. These soft benefits are a result of the process itself and help drive improved efficiencies through better communication with key stakeholders, such as regulators and customers. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Safety Classification and Design Rules for Structures, Systems and Components in a Near Surface Disposal Facility-Post Closure Phase - 19716

Canadian Nuclear Laboratories (CNL) is developing a Near Surface Disposal Facility (NSDF) to be constructed at its Chalk River Laboratories (CRL) site. In general, a NSDF is a facility for radioactive waste disposal, under an engineered cover, located at or within a few meters of the earth's surface. The NSDF will establish a safe, local and permanent means for the disposal of low level radioactive waste. The NSDF is intended to dispose historic waste currently in interim storage as well as waste arising from building decommissioning and environmental remediation activities. The NSDF is to be composed of engineered containment mound, waste water treatment plant and other supporting facilities and infrastructures that are needed to preserve radioactive waste. The NSDF life cycle will comprise two distinct phases: pre closure and post closure. The pre closure phase involves construction, operation and closure activities. The post closure phase includes institutional control and post-institutional control to ensure long term safety and radiological acceptability of the disposal facility. As part of the evolving activities for the NSDF project, a process is developed in accordance with Canadian regulations and International Atomic Energy Agency (IAEA) principles to classify systems that comprise NSDF for safe operation, long term safety of the disposal facility and the protection of workers, the public and the environment. This paper describes the methodology developed to classify Structures, Systems and Components (SSCs) important to safety in post closure phase and determine their design rules. The design rules are the relevant codes, standards and proven engineering practices that should be applied, as appropriate, to the design of SSCs to meet the applicable design requirements. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Understanding the consequences of hypothetical post-closure transient criticality in a geological disposal facility - 14439

Radioactive Waste Management (RWM) is responsible for implementing geological disposal of the UK's higher-activity radioactive wastes. These wastes include significant quantities of fissile nuclides and, therefore, demonstration of criticality safety for the wastes under disposal conditions forms an important component of RWM's disposal system safety case. At the time of disposal all waste packages will be safely sub-critical. Containment provided by the engineered barrier system of a geological disposal facility (GDF) will ensure that criticality is not possible for some time after disposal. However, as waste packages degrade, fissile and other materials may be mobilised, which could affect the potential for criticality. Although the likelihood of a critical configuration developing is demonstrably low, it cannot be assumed to be zero over long post-closure timescales. The UK environment agencies' Guidance on Requirements for Authorisation for a GDF includes a specific requirement to consider the consequences of hypothetical 'what-if' post-closure criticality. RWM has undertaken a programme of research to model and understand the consequences of hypothetical post-closure criticality events. Initially focused on the scenario of fissile material relocation and accumulation following intermediate level waste (ILW) disposal, two bespoke computer models were developed. The quasi-steady-state (QSS) model considered critical systems maintained by accumulation of fissile materials where the temperature feedback remains negative throughout the transient. The rapid transient model (RTM) considered systems with positive temperature feedback. The QSS model development included a successful comparison with the Oklo natural reactors. With a requirement to consider post-closure criticality for a wider range of potential waste types under different illustrative disposal concepts, the initial transient criticality models had some limitations. For the QSS model this was the assumption of fixed geometry, while the complex functional inputs required in the RTM were not readily available for different materials. For the QSS model this paper describes the model development to allow changing volume; this has enabled its application to 'what-if' scenarios of flooding within a spent fuel waste package and the slumping of a stack of ILW packages. For rapid transient criticality this paper explains how the development of a simpler 'bounding approach' model to complement the RTM has enabled transient criticality analysis for a wider range of host materials. The role of this research in demonstrating post-closure criticality safety of a GDF in the UK is presented in a companion paper which also draws on the results of a parallel research project to demonstrate that the likelihood of post-closure criticality is low. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

Second Order Closures for the Radiative Transfer Equation: Some Are Unstable

The largest existing simulations of cosmic reionization model radiative transfer with moment methods that require a closure relation. The two most commonly used closure relations are M1 and OTVET; both close the moment hierarchy at the first moment. We explore the properties of a higher, second-order closure. We show that direct generalizations of M1 and OTVET to one higher order are physically unstable - i.e., the closure equations themselves result in unstable solutions, not just their numerical implementation. In fact, a generalization of OTVET to any order higher than the first one is unstable. We are also able to show that any local (i.e., depending only on the local moments of the radiation field, like M1) second-order closure that depends only on the radiation intensity and radiation flux, but does not explicitly depend on the radiation pressure, is physically unstable. This result restricts the choice of possible second-order closure relations.

Gnedin, Nickolay Y. [Fermilab; Chicago U., Astron.↗
DOE OSTI2017

Efficient algorithms and implementations of entropy-based moment closures for rarefied gases

We present efficient algorithms and implementations of the 35-moment system equipped with the maximum-entropy closure in the context of rarefied gases. While closures based on the principle of entropy maximization have been shown to yield very promising results for moderately rarefied gas flows, the computational cost of these closures is in general much higher than for closure theories with explicit closed-form expressions of the closing fluxes, such as Grad's classical closure. Following a similar approach as Garrett et al. (2015) , we investigate efficient implementations of the computationally expensive numerical quadrature method used for the moment evaluations of the maximum-entropy distribution by exploiting its inherent fine-grained parallelism with the parallelism offered by multi-core processors and graphics cards. We show that using a single graphics card as an accelerator allows speed-ups of two orders of magnitude when compared to a serial CPU implementation. To accelerate the time-to-solution for steady-state problems, we propose a new semi-implicit time discretization scheme. The resulting nonlinear system of equations is solved with a Newton type method in the Lagrange multipliers of the dual optimization problem in order to reduce the computational cost. Additionally, fully explicit time-stepping schemes of first and second order accuracy are presented. We investigate the accuracy and efficiency of the numerical schemes for several numerical test cases, including a steady-state shock-structure problem.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Structure-preserving neural networks for the regularized entropy-based closure of a linear, kinetic, radiative transport equation

The main challenge of large-scale numerical simulation of radiation transport is the high memory and computation time requirements of discretization methods for kinetic equations. In this work, we derive and investigate a neural network-based approximation to the entropy-based closure method to accurately compute the solution of the multi-dimensional moment system with a low memory footprint and competitive computational time. We extend methods developed for the standard entropy-based closure to the regularized entropy-based closures. The main idea is to interpret structure-preserving neural network approximations of the regularized entropy-based closure as a two-stage approximation to the original entropy-based closure. We conduct a numerical analysis of this approximation and investigate optimal parameter choices. Our numerical experiments demonstrate that the method has a much lower memory footprint than traditional methods with competitive computation times and simulation accuracy. The code and all trained networks are provided on GitHub.

entropy closure↗
DOE OSTI2025

Flux-Closure Domain Structures in Ferroelectric K 0.5 Na 0.5 NbO 3 Thin Films

Topological domain structures in ferroelectric materials have garnered increasing attention due to their intriguing physical properties and promising applications. While most existing topological structures in ferroelectric perovskite oxides originate from tetragonal or rhombohedral bulk phases, much less is understood about their counterparts in orthorhombic ferroelectrics. Here, in this work, we employ ferroelectric K 0.5 Na 0.5 NbO 3 (KNN) thin films as a model system and leverage phase-field simulations to theoretically predict the static structures and dynamic behaviors of three types of flux-closure domain configurations: in-plane (Type-I), out-of-plane (Type-II), and superdomain (Type-III) flux-closure structures. We systematically investigate the effects of finite size, misfit strains, and electrical boundary conditions on the formation and switching of these topological structures. For the Type-I structure, size reduction or small misfit strain facilitates a transition of the flux-closure pattern to polar vortices. Type-II structures emerge under open-circuit electrical boundary conditions of the film, forming at the junctions of specific domain walls with the film surface or the film–substrate interface. The formation mechanisms of these two flux-closure structures are rationalized from an energy perspective. We demonstrated switching capabilities of Type-II and Type-III structures by obtaining polarization–electric field hysteresis loops. Our simulations also reveal a reversible electric-field-induced transition between the orthorhombic and rhombohedral ferroelectric phases with a checkerboard domain pattern, during which the integrity of the flux-closure structure is preserved. These findings provide theoretical insights and practical guidance for identifying and manipulating topological structures in low-symmetry ferroelectrics, paving the way for developing energy-efficient microelectronic devices based on topological structures.

P-E loop↗
DOE OSTI2023

A New Hybrid Mass-Flux/High-Order Turbulence Closure for Ocean Vertical Mixing

While various parameterizations of vertical turbulent fluxes at different levels of complexity have been proposed, each has its own limitations. For example, simple first-order closure schemes such as the K-Profile Parameterization (KPP) lack energetic constraints; two-equation models $k-ε$ like directly solve an equation for the turbulent kinetic energy but do not account for non-diffusive fluxes, and high-order closures that include the high-order transport terms are computationally expensive. To address these, we extend the Assumed-Distribution Higher-Order Closure (ADC) framework originally proposed for the atmospheric boundary layer and apply it to the ocean surface boundary layer. By assuming a probability distribution function relationship between the vertical velocity and tracers, all second-order and higher-order moments are exactly constructed and turbulence closure is achieved in the ADC scheme. In addition, this ADC parameterization has full energetic constraints and includes non-diffusive fluxes without the computational cost of a full higher-order closure scheme. We have tested the ADC scheme against a combination of large eddy simulation (LES), KPP, and $k-ε$ for surface buoyancy-driven convective mixing and found that the ADC scheme is robust with different vertical resolutions and compares well to the LES results.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Closure theory for high-collisionality multi-ion plasmas

A general formalism is developed to construct and solve a system of linearized moment equations for parallel and perpendicular closures in high-collisionality plasmas. It is applicable for multiple ion species with arbitrary masses, temperatures, charges, and densities. The convergence of closure coefficients is evaluated by increasing the number of moments from 2 to 32 for scalar, vector, and rank-2 tensor moments. As an example, the complete set of closure coefficients for a deuterium-carbon plasma over the entire Hall parameter range is presented. Furthermore, the closure coefficients at various temperature ratios show that the one-temperature closure coefficients can differ significantly from the two-temperature coefficients.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Closure Report for Corrective Action Unit 548: Areas 9, 10, 18, 19, and 20 Housekeeping Sites, Nevada National Security Site, Nevada

This Closure Report (CR) documents closure activities for Corrective Action Unit (CAU) 548, Areas 9, 10, 18, 19, and 20 Housekeeping Sites, and complies with the Federal Facility Agreement and Consent Order (FFACO) that was agreed to by the State of Nevada; the U.S. Department of Energy (DOE), Environmental Management; the U.S. Department of Defense; and DOE, Legacy Management (FFACO, 1996 as amended). CAU 548 consists of the following Corrective Action Sites (CASs), located in Areas 9, 10, 12, 18, 19, and 20 of the Nevada National Security Site: · CAS 09-99-02, Material Piles (2) · CAS 09-99-04, Wax, Paraffin · CAS 09-99-05, Asbestos, Vermiculite · CAS 09-99-07, Tar Spill · CAS 10-22-02, Drums · CAS 10-22-05, Gas Block · CAS 10-22-07, Gas Block · CAS 10-22-34, Drum · CAS 10-22-38, Drum; Cable · CAS 12-99-04, Epoxy Tar Spill · CAS 12-99-08, Cement Spill · CAS 18-14-01, Transformers (3) · CAS 19-22-01, Drums · CAS 19-22-11, Gas Block (2) · CAS 19-44-01, Fuel Spill · CAS 20-22-07, Drums (2) · CAS 20-22-09, Drums (3) · CAS 20-22-14, Drums (2) · CAS 20-22-16, Drums (2) · CAS 20-24-09, Battery Closure activities began in July 2011 and were completed in December 2011 and included removal and disposal of material piles, spills, sanitary debris, a lead acid battery, lead and steel shot, and stained soil. Activities were conducted according to the Sectored Clean-up Work Plan for Housekeeping Category Waste Sites (U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office [NNSA/NSO], 2003). Closure activities generated sanitary waste, hydrocarbon waste, low-level waste, hazardous waste, and mixed waste. Some wastes exceeded land disposal limits and required offsite treatment prior to disposal. Other wastes met land disposal restrictions and were disposed in appropriate onsite or offsite landfills. NNSA/NSO requests the following: · A Notice of Completion from the Nevada Division of Environmental Protection to NNSA/NSO for closure of CAU 548 · The transfer of CAU 548 from Appendix III to Appendix IV, Closed Corrective Action Units, of the FFACO

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗