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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A Mathematical Model for Prediction of Carbon Concentration During RH Refining Process

A mathematical model was developed to predict the carbon concentration during RH refining process. Three reaction sites such as the free surface, inner sites of the molten steel in vacuum chamber, and the bubble surface were considered. The decarburization at inner sites of the molten steel in vacuum chamber was dominant at the initial stage, and then subsequently, it was dominated by the free surface and bubble surface. The decarburization rate constant was also evaluated.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Numerical Simulation of the Three-Phase Flow of a Bubble Interacting with the Steel–Slag Interface During the Secondary Refining Process

Gas stirring is an effective method for the secondary refining process of steel. The microphenomena among the phases of an argon bubble floating in steel and motion across the steel–slag interface were simulated and discussed with a sharp interface tracking method. A water-model experiment was set to validate the numerical model, and the experimental results showed agreement with the numerical model. A critical size for bubbles to pass the interface was found using the model.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Al{sub 2}O{sub 3} Level in CaO-SiO{sub 2}-MgO-Al{sub 2}O{sub 3} Refining Slags on Slag/Magnesia-Doloma Refractory Interactions

The influence of the Al{sub 2}O{sub 3} level in CaO-SiO{sub 2}-MgO-Al{sub 2}O{sub 3} (CSMA) stainless steel refining slags on the degradation of magnesia-doloma refractories was investigated through static refractory finger corrosion tests. The tests were performed at 1620 °C under Ar atmosphere, using slags with Al{sub 2}O{sub 3} contents of 5, 10, and 20 wt pct, respectively. The results indicate that the formation of 2CaO·SiO{sub 2} at the slag/refractory interface was suppressed by increasing the Al{sub 2}O{sub 3} content to 20 wt pct, thereby changing the corrosion mechanism from an indirect dissolution to a direct dissolution of CaO and MgO from the refractories. The increased solubility limit of MgO by the Al{sub 2}O{sub 3}-rich CSMA slags results in an overall higher corrosion rate of the MgO-doloma refractory.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Nucleation and Grain Refinement of 7A04 Aluminum Alloy Under a Low-Power Electromagnetic Pulse

The effects of a low-power electromagnetic pulse on the grain size and cooling curve of high-strength aluminum alloy 7A04 were investigated for various pulse duty cycles. This electromagnetic pulse treatment was found to effectively produce fine grains with globular crystals and a uniform microstructure for pulse duty cycles between 20 and 40%. The key factors that affected grain refinement under the electromagnetic pulse included the electromagnetic energy and the conversion frequency between B and E. The nucleation rate increased as the nucleation period was extended. A new kinetic condition of magnetic nucleation was explored by decreasing the critical Gibbs free energy in the electromagnetic pulse, which was more sensitive under low undercooling. In addition, the crystal orientation was controlled in such a solidification environment.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ultrafine Grain Refinement and Superplasticity of Ti-55 Alloy Obtained by Hydrogen Absorption and Desorption

Hydrogen absorption and desorption treatment consists of two processes for near α-phase Ti-55 titanium alloy: (1) hydrogenation with different contents and (2) hydrogen desorption by vacuum annealing at 700 °C and with pressure less than 10{sup −4}Pa for 2 h. Equiaxed ultrafine-grained structure with a grain size range between 0.5 and 1 μm has been obtained. Compared with as-received alloy, the grain size of fully dehydrogenated specimen is reduced by ten times. The grain refinement mainly results from α{sub H} ↔ β{sub H} transformation and accompanied recrystallization. The optimum superplastic temperature of Ti-55 alloy is reduced by about 150 °C, which arises from more grain boundary area and higher proportion of extremely deformable β phase in the ultrafine-grained alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Grain Refinement of Co-Cr-Mo-C Through Plastic Deformation Followed by Reversion of Lamellar Eutectoid Structure

Small plastic straining was combined with a two-step heat treatment to obtain grain refinement of the Co-28Cr-6Mo-0.33C alloy. The solution-treated specimens were furnace cooled to room temperature, obtaining partially transformed pearlite at grain boundaries. Afterward, the specimens were compressed up to 10% of engineering strain, followed by aging at 850 °C that contributed to the decomposition of the austenite phase into a lamellar eutectoid structure (α + M{sub 23}C{sub 6}). The full lamellar structure was then reverse-treated at temperatures from 1000 to 1237 °C, where the austenite phase was stable. The reversion treatment led to the nucleation of a fine-grained austenitic structure (with average size of 48.23 ± 21.30 μm—i.e., about 1/10 of its initial average size) at the lamellar eutectoid structure. Compression tests carried out on reverse-transformed samples showed better mechanical properties compared to those of the samples tested before reversing transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation on Equal-Channel Angular Pressing-Induced Grain Refinement in an Aluminum Matrix Composite Reinforced with Al-Cu-Ti Metallic Glass Particles

In the present study, a homogeneous ultrafine grain structure composite consisting of metallic glass particles reinforcements was developed by equal-channel angular pressing (ECAP) process. The microstructure of composite was characterized using x-ray diffraction (XRD), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. The uniaxial compression test was used to determine the mechanical properties. The mechanisms of grain refinement during ECAP process were discussed based on the microstructural evolutions. A composite was successfully produced after four passes of ECAP, having an average grain size of 610 nm and compressive yield strength of 242 MPa. Also, the yield strength of composite after each pass was quantitatively estimated by considering all the effective strengthening mechanism. The findings showed that the dislocations strengthening mechanism with contribution of more than 50% plays a major role in strengthening the composite. There was a negligible gap between the experimental and theoretical values of yield strength for all ECAP pass numbers.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Microstructure Refinement on Hardness Homogeneity of Aluminum Alloy 1100 Processed by Accumulative Roll Bonding

This work examines the effect of grain refinement via accumulative roll bonding (ARB) on the homogeneity of microstructure and hardness through the thickness of commercially pure aluminum AA1100 sheets. The use of 7 cycles of ARB was shown to produce homogeneous ultrafine-grained microstructure, reducing the grain size to 0.46 and 1.03 µm in normal direction and rolling direction, respectively. Examination by electron backscattered diffraction indicates that continuous dynamic recrystallization was the main mechanism for the formation of submicron equiaxed grains bounded with high-angle grain boundaries (HAGBs). The fraction of HAGBs increased gradually reaching a maximum of 71.6% after 7 cycles. Through-thickness hardness measurements using Vickers and nanoindentation tests show an increase from 43.5 Hv (0.85 GPa) for as-received sample to 63 Hv (1.1 GPa) after 7 cycles. The heterogeneity in hardness through the thickness of the as-received material was shown to restrain the evolution of uniform hardness across the sheet thickness with increasing ARB cycles. Tensile tests showed that the tensile strength is increased to 250 MPa, which is about 2 times its initial value. Owing to the high stacking fault energy of AA1100, strong dynamic recovery occurred with increasing ARB strain which was balanced with the strain hardening property of the material. This resulted in plastic instability at small strains and thus early necking during the tensile test.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The effects of sequential hydrothermal-mechanical refining pretreatment on cellulose structure changes and sugar recoveries

The recalcitrance of lignocellulosic biomass necessitates an efficient pretreatment protocol for operating a successful cellulosic biorefinery. It is critical to improve cellulose accessibility for hydrolysis and fermentation by altering the plant cell wall’s physical structure and chemical composition. Sequential hydrothermal-mechanical refining pretreatment (HMR) allows efficient recovery of cellulosic sugars without utilizing any hazardous chemicals. HMR has been successfully applied to Liberty switchgrass, a bioenergy cultivar released by the USDA, and now it is being applied to oilcane, a recently developed transgenic sugarcane variety engineered to accumulate lipids in its vegetative tissues. Sugar yields of oilcane bagasse (OCB) and switchgrass (SG) treated with HMR are 96.4% and 75.4%, respectively. This study sought to correlate cellulosic sugar yields with structural changes within the cell wall caused by HMR on two distinct bioenergy crops. Simon’s staining technique for the specific surface area analysis showed that HMR increased the specific surface area of pretreated biomass residues by 80–112%. In addition, ATR-FTIR was performed to determine the effects of HMR on physical structures based on the total crystallinity index (TCI) and hydrogen bonding intensity (HBI). Irrespective of biomass type, HMR decreased the initial crystalline cellulose contents of untreated biomass residues by 3.5% and reduced TCI and HBI by 7–13%. Here, the study found that sugar yields were negatively correlated to reducing values of hydrogen bonding intensity, crystalline cellulose content, and total crystallinity index.

09 BIOMASS FUELS↗
DOE OSTI2025

A staged deep learning approach to spatial refinement in 3D temporal atmospheric transport

High-resolution spatiotemporal simulations effectively capture the complexities of atmospheric plume dispersion in complex terrain. However, their high computational cost makes them impractical for applications requiring rapid responses or iterative processes, such as optimization, uncertainty quantification, or inverse modeling. To address this challenge, this work introduces the Dual-Stage Temporal Three-dimensional UNet Super-resolution (DST3D-UNet-SR) model, a highly efficient deep learning model for plume dispersion predictions. DST3D-UNet-SR is composed of two sequential modules: the temporal module (TM), which predicts the transient evolution of a plume in complex terrain from low-resolution temporal data, and the spatial refinement module (SRM), which subsequently enhances the spatial resolution of the TM predictions. We train DST3D-UNet-SR using a comprehensive dataset derived from high-resolution large eddy simulations (LES) of plume transport. We propose the DST3D-UNet-SR model to significantly accelerate LES of three-dimensional (3D) plume dispersion by three orders of magnitude. Additionally, the model demonstrates the ability to dynamically adapt to evolving conditions through the incorporation of new observational data, substantially improving prediction accuracy in high-concentration regions near the source.

3D temporal sequences↗
DOE OSTI2015

A freestream-preserving fourth-order finite-volume method in mapped coordinates with adaptive-mesh refinement

We present a fourth-order accurate finite-volume method for solving time-dependent hyperbolic systems of conservation laws on mapped grids that are adaptively refined in space and time. Some novel considerations for formulating the semi-discrete system of equations in computational space are combined with detailed mechanisms for accommodating the adapting grids. Furthermore, these considerations ensure that conservation is maintained and that the divergence of a constant vector field is always zero (freestream-preservation property). The solution in time is advanced with a fourth-order Runge-Kutta method. A series of tests verifies that the expected accuracy is achieved in smooth flows and the solution of a Mach reflection problem demonstrates the effectiveness of the algorithm in resolving strong discontinuities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Multilayered triangular and quadrilateral flat shell elements based on the Refined Zigzag Theory

The paper presents a class of C 0 -continuous, flat shell elements based on the Refined Zigzag Theory (RZT) for the analysis of multilayered and curved composite and sandwich structures. In this study, the use of the interdependent interpolation strategy allows eliminating the shear-locking phenomenon and introducing the drilling rotation necessary to complete the set of classical nodal degrees of freedom (three displacements and three rotations). Additional kinematic variables are present in RZT, the zigzag rotations around the in-plane axes that measure the normal distortion typical of multilayered structures. An additional “drilling” zigzag rotation is therefore included among the nodal degrees of freedom in order to properly model curved and built-up structures. A stabilization procedure is adopted to suppress spurious zero-energy modes. A three-node triangular and a four-node quadrilateral flat shell element are formulated with 9 degrees of freedom per node. Example problems involving flat and curved multilayered structures are presented and discussed in order to assess the accuracy and convergence properties of the presented elements. Both static response predictions and free vibrations analyses are considered and the comparison is made with analytic RZT solutions, high-fidelity 3D finite element models and FSDT-based flat shell elements.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Columnar to equiaxed transition and grain refinement of cast CrCoNi medium-entropy alloy by microalloying with titanium and carbon

Thermomechanical processing has been used to control the grain size/shape of the equiatomic CrCoNi medium-entropy alloy (MEA) and obtain excellent strength and ductility. However, in the cast state, the alloy has coarse columnar grains with average widths and lengths of approximately 120 and 1000 μm, respectively, resulting in inferior mechanical properties. To overcome this deficiency, we microalloyed with Ti and C and successfully changed the grain shape (from columnar to equiaxed) and refined the grain size. The degree to which the microstructure changes depends on the amount of Ti and C added, with the best results obtained at 0.4 at.% each. In the optimal alloy [(CrCoNi) 99.2 Ti 0.4 C 0.4 ], the as-cast grains were nearly equiaxed with a uniform size of ~75 μm. Associated with this change in grain shape/size was a significant improvement of yield strength, ultimate tensile strength and elongation to fracture at both 293 and 77 K. Finally, the columnar to equiaxed transition is attributed to the strong mutual affinity of C and Ti, which leads to their build-up ahead of the solid-liquid interface and, in turn, to enhanced constitutional undercooling.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A new re-redistribution scheme for weighted state redistribution with adaptive mesh refinement

State redistribution (SRD) is a recently developed technique for stabilizing cut cells that result from finite-volume embedded boundary methods. SRD has been successfully applied to a variety of compressible and incompressible flow problems. When used in conjunction with adaptive mesh refinement (AMR), additional steps are needed to preserve the accuracy and conservation properties of the solution if the embedded boundary is not restricted to a single level of the mesh hierarchy. In this work, we extend the weighted state redistribution algorithm to cases where cut cells live at or near a coarse-fine interface within the domain. Here, we present numerical results that demonstrate that the algorithm is conservative when the coarse-fine interface intersects the embedded boundary. Additionally we compare the numerical solution of the Sod shock tube problem in an inclined cylinder with the analytic solution, and we compare the simulation of a shock hitting a cylindrical obstacle with experimental data. Finally we demonstrate the methodology for simulation of the multicomponent compressible Navier-Stokes equations in a piston-bowl geometry, and discuss the computational efficiency gained by not requiring the entire embedded boundary to be defined at the finest level.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Dominant balance-based adaptive mesh refinement for incompressible fluid flows

This work introduces a novel adaptive mesh refinement (AMR) method that utilizes dominant balance analysis (DBA) for efficient and accurate grid adaptation in computational fluid dynamics (CFD) simulations. The proposed method leverages a Gaussian mixture model (GMM) to classify grid cells into active and passive regions based on the dominant physical interactions within the equation space. By modeling truncation error probabilistically from discretized terms, the method identifies regions of high interaction where numerical accuracy is most sensitive to resolution. Unlike traditional AMR strategies, this approach does not rely on heuristic-based sensors or user-defined thresholds, providing a fully automated and problem-independent framework for AMR. Applied to the incompressible Navier-Stokes equations for steady and unsteady flow past a cylinder, the DBA-based AMR method achieves comparable accuracy to high-resolution grids while reducing computational costs by up to 70 %. The validation highlights the method’s effectiveness in capturing complex flow features while minimizing grid cells, directing computational resources toward regions with the most critical dynamics. This modular and scalable strategy is adaptable to a wide range of applications, presenting a promising tool for efficient high-fidelity simulations in CFD and other multiphysics domains.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

A constitutive model incorporating grain refinement strengthening on metallic alloys

Surface nano-crystallization techniques have been recently developed as one of the most efficient ways to optimize materials’ structure, and therefore develop the local and global mechanical behavior as to increase strength without compromising ductility. Here, in this work, we present a constitutive model incorporating grain refinement hardening to simulate the nano-crystallization technique, specifically, surface mechanical attrition treatment. The computation is implemented using user-defined VUMAT subroutines. As an example of its application, a geometry model with full coverage of random impacts are employed. The results show that the model has rather precise predictability of grain size evolution during plastic deformation. The readily embedded with a computational code of material dynamics enables this novel model to be a promising tool to study the dynamic evolution of microstructures under plastic deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High resolution numerical simulations of methane pool fires using adaptive mesh refinement

The ability to accurately predict the structure and dynamics of pool fires using computational simulations is of great interest in a wide variety of applications, including accidental and wildland fires. However, the presence of physical processes spanning a broad range of spatial and temporal scales poses a significant challenge for simulations of such fires, particularly at conditions near the transition between laminar and turbulent flow. Here, in this study, we examine the transition to turbulence in methane pool fires using high-resolution simulations with multi-step finite rate chemistry, where adaptive mesh refinement (AMR) is used to directly resolve small-scale flow phenomena. We perform three simulations of methane pool fires, each with increasing diameter, corresponding to increasing inlet Reynolds and Richardson numbers. As the diameter increases, the flow transitions from organized vortex roll-up via the puffing instability to much more chaotic mixing associated with finger formation along the shear layer and core collapse near the inlet. These effects combine to create additional mixing close to the inlet, thereby enhancing fuel consumption and causing more rapid acceleration of the fluid above the pool. We also make comparisons between the transition to turbulence and core collapse in the present pool fires and in inert helium plumes, which are often used as surrogates for the study of buoyant reacting flows.

42 ENGINEERING↗
DOE OSTI2025

E3SM‐Arctic: Regionally Refined Coupled Model for Advanced Understanding of Arctic Systems Interactions

Earth system models are essential tools for climate projections, but coarse resolutions limit regional accuracy, especially in the Arctic. Regionally refined meshes (RRMs) enhance resolution in key areas while maintaining computational efficiency. This paper provides an overview of the United States (U.S.) Department of Energy's (DOE's) Energy Exascale Earth System Model version 2.1 with an Arctic RRM, hereafter referred to as E3SMv2.1-Arctic, for the atmosphere (25 km), land (25 km), and ocean/ice (10 km) components. We evaluate the atmospheric component and its interactions with land, ocean, and cryosphere by comparing the RRM (E3SM2.1-Arctic) historical simulations (1950–2014) with the uniform low-resolution (LR) counterpart, reanalysis products, and observational data sets. The RRM generally reduces biases in the LR model, improving simulations of Arctic large-scale mean fields, such as precipitation, atmospheric circulation, clouds, atmospheric river frequency, and sea ice thickness. However, it introduces a seasonally dependent surface air temperature bias, reducing the LR cold bias in summer but enhancing the LR warm bias in winter, which contributes to the underestimated winter sea ice area and volume. Radiative feedback analysis shows similar climate feedback strengths in both model configurations, with the RRM exhibiting a more positive surface albedo feedback and contributing to a stronger surface warming than LR. These findings underscore the importance of high-resolution modeling for advancing our understanding of Arctic climate changes and their broader global impacts, although some persistent biases appear to be independent of model resolution at 10–100 km scales.

Energy Exascale Earth System Model (E3SM)↗