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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Transient Rheological Behavior of Semisolid SEED-Processed 7075 Aluminum Alloys in Rapid Compression

The transient rheological behavior and microstructure evolution of semisolid SEED-processed 7075 aluminum alloys were studied using the rapid compression tests. The effects of the TiB{sub 2} grain refinement on the grain morphology and size of semisolid slurries were investigated. Results indicated that the grain refiner could reduce the grain size and improve the globularity of α-Al grains. The grain-refined alloy can be easily deformed at a wide range of solid contents (0.42 to 0.53 Fs), in which the deformation level appears to be independent from the solid content. Under the transient state, the apparent viscosity decreased with increasing shear rate to a minimum value and followed by an increase as the shear rate decreased. The apparent viscosity of the base alloy exhibited a dependency on the solid content, while the apparent viscosity of the grain-refined alloy in the decreasing or increasing shear rate periods was not substantially influenced by the solid content. The viscosity as a function of applied shear rate can be described using the power law viscosity model. The differences in the flow behavior index (n) and the consistency index (k) for two alloys were discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Modeling Approach for Time-Dependent Geometry Applied to Transient Heat Transfer of Aluminum Electrolysis Cells

The thermal balance of aluminum electrolysis cells (AEC) have to be rigorously controlled in order to improve the efficiency and sustainability of this industrial process. A new modeling strategy is developed to consider the displacements of solid bodies and moving boundaries in finite element models. The transient thermal-electric modeling of the AEC demonstrates the effect of an increase in operating voltage on both the anode cover and the side ledge. With higher heat generation, the anode cover deteriorates and the side ledge thickness decreases. Since the anode cover is characterized by irreversible transformations, the top heat dissipation remains higher even when the operating voltage comes back to its typical value. For the first time, the transient temperature and electric fields throughout the anode life are simulated and validated by industrial measurements. The modeling predictions have been validated from instrumented anodes and manual measurements, all performed on operating AEC.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Control of High-Temperature Static and Transient Thermomechanical Behavior of SiMo Ductile Iron by Al Alloying

Abstract Silicon and molybdenum ( SiMo ) ductile iron is commonly used for exhaust manifolds because these components experience thermal cycling in oxidizing environment, which requires resistance to fatigue during transient thermomechanical loads. Previous studies have demonstrated that alloying elements, such as Al , to SiMo ductile iron reduces the amount of surface degradation during static high-temperature exposure. However, deterioration of sphericity of the graphite nodules and a decrease in ductility could affect the tendency of cracking during thermal cycling. In this article, the effect of Al alloying on static and transient thermomechanical behavior of SiMo ductile iron was investigated to optimize the amount of Al alloying. A thermodynamic approach was used to confirm the effect of the Al alloying on the phase transformations in two SiMo cast irons, alloyed by 1.8% Al and 3% Al . These two alloys were cast in a laboratory along with the baseline SiMo ductile iron. Several experimental methods were used to evaluate the dimensional stability, physical properties, static oxidation, and failure resistance during constrained thermal cycling testing to compare their high-temperature capability. Experimental results verified that Al alloying increases the temperature range and decreases volume change during eutectoid transformation, which together with enhancement of oxidation protection improved the dimensional stability. Thermocycling tests showed that the number of cycles to failure depends on the amount of Al alloying and the applied high-temperature exposure during each cycle. SEM/EDX, high-resolution TEM and µCT analysis were used to verify the mechanism resulting from the Al alloying protection. It was shown that an optimal level of Al alloying for balancing oxidation and thermal cracking resistance depends on thermomechanical conditions of application.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Prospects for observing and localizing gravitational-wave transients with Advanced LIGO, Advanced Virgo and KAGRA

We present possible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals, and study the capability of the network to determine the sky location of the source. We report our findings for gravitational-wave transients, with particular focus on gravitational-wave signals from the inspiral of binary neutron star systems, which are the most promising targets for multi-messenger astronomy. The ability to localize the sources of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and 90% credible regions can be as large as thousands of square degrees when only two sensitive detectors are operational. Determining the sky position of a significant fraction of detected signals to areas of 5– 20 deg 2 requires at least three detectors of sensitivity within a factor of ~2 of each other and with a broad frequency bandwidth. When all detectors, including KAGRA and the third LIGO detector in India, reach design sensitivity, a significant fraction of gravitational-wave signals will be localized to a few square degrees by gravitational-wave observations alone.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Effects of transient fission gas release on rod balloon burst behavior during a loss-of-coolant accident

The US nuclear energy industry is investigating strategies to increase the reactor operating cycle to 24 months, which would result in rod average burnups exceeding the current limit of 62 GWd/tU. To support this goal, multiphysics simulations tools and methodologies are being developed to predict the effects of this change during transient events such as loss-of-coolant accidents (LOCAs). In this work, two cladding burst correlations were used to predict cladding failure. Here, these were coupled with three transient fission gas release (tFGR) models and were implemented in the BISON fuel performance code to quantify any changes in cladding burst behavior during a large-break LOCA. First, a simple linear model was used to perform a sensitivity analysis of a single fuel rod. Second, a tFGR model available in BISON was applied to 281 fuel rods throughout the core. The third model examined was an empirical correlation based on data from the literature.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2026

Transient Multiphysics Simulations with Pin Power Reconstruction in the Griffin Reactor Physics Code

This work introduces the pin power reconstruction capability available in the Griffin reactor physics code. This capability is implemented in an unstructured mesh framework, and the methods introduced are applied to the 2D SIMBA reactor core, which has assemblies and pins arranged in a hexagonal lattice. Since this reactor has a non-Cartesian geometry and also operates in the thermal spectrum, a general approach to pin power reconstruction is adopted, where SPH-based equivalence is leveraged to preserve assembly-wise reaction rates, while computing full-core form functions to preserve pin-wise fission production rates within the fuel pins of the reactor core. In a 2D microreactor benchmark problem, this pin power reconstruction approach was shown to reproduce pin powers compared to the Serpent2 Monte Carlo code for fixed temperature conditions and control drum rotation angles, yielding a core-wide RMS error level of 0.6\% and a maximum absolute pin error of 2.3\%. In addition, a tabulated library of multigroup cross sections, SPH factors, and form functions was generated to demonstrate the applicability of pin power reconstruction to a thermal feedback problem. Finally, a control drum transient was successfully simulated, showcasing the application of pin power reconstruction in a transient multiphysics feedback problem.

97 - MATHEMATICS AND COMPUTING↗
DOE OSTI2018

GhoT of the GhoT/GhoS toxin/antitoxin system damages lipid membranes by forming transient pores

Highlights: • Determined that toxin GhoT disrupts membranes by forming transient pores. • Determined that membrane charge affects the activity of GhoT. • Determined through molecular dynamic simulations why GhoT F38R is inactive. GhoT is a bacterial toxin of the type V toxin/antitoxin system that allows Escherichia coli to reduce its metabolism in response to oxidative and bile stress. GhoT functions by increasing membrane permeability and reducing both ATP levels and the proton motive force. However, how GhoT damages the inner membrane has not been elucidated. Here we investigated how GhoT damages membranes by studying its interaction with lipid bilayers and determined that GhoT does not cause macroscopic disruption of the lipid bilayer to increase membrane permeability to the dye carboxyfluorescein. Using circular dichroism, we found that GhoT forms an alpha helical structure in lipid bilayers that agrees with the structure predicted by the I-TASSER protein structure prediction program. The structure generated using I-TASSER was used to conduct coarse-grained molecular dynamics simulations, which indicate that GhoT damages the cell membrane, as a multimer, by forming transient transmembrane pores.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Transient receptor potential ankyrin 1 channels are involved in spontaneous peptide hormone release from astrocytes

Highlights: • TRPA1 regulates spontaneous calcium signals in astrocytes. • Astrocytes spontaneously release gliotransmitters. • Spontaneous gliotransmitter release is modulated by TRPA1 channels. Astrocytes, a large population of glial cells, detect neurotransmitters and respond by increasing intracellular Ca{sup 2+} concentration ([Ca{sup 2+}]{sub i}) and releasing chemical molecules called gliotransmitters. Recently discovered Ca{sup 2+} influx through transient receptor potential ankyrin 1 (TRPA1) channels is reported to cause spontaneous [Ca{sup 2+}]{sub i} increase in astrocytes. While several physiological functions of TRPA1-mediated spontaneous Ca{sup 2+} signal have been revealed, relation with gliotransmitter release, especially peptide hormone exocytosis is largely unknown. We therefore explored the [Ca{sup 2+}]{sub i} and exocytosis dynamics in rat astrocyte cell line C6 cells and primary astrocytes. TRPA1-mediated spontaneous [Ca{sup 2+}]{sub i} transients were observed in both C6 cells and primary astrocytes. Total internal reflection fluorescence microscopy revealed that Venus-tagged brain-derived neurotrophic factor and neuropeptide Y were released spontaneously from astrocytes. Activation of TRPA1 channels enhanced the frequency of peptide hormone exocytosis, and inhibition of TRPA1 channels decreased the number of peptide hormone exocytosis. These results suggest that TRPA1-mediated spontaneous [Ca{sup 2+}]{sub i} increase modulates the spontaneous release of peptide hormones from astrocytes.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Mechanistic pathways and role of oxygen in oxidative coupling of methane derived from transient kinetic studies

Oxidative coupling of methane (OCM) is a promising industrial process to upgrade natural gas to high value chemicals. In this study, Temporal Analysis of Products (TAP) and steady-state experiments were conducted to distinguish how the composition of surface and gas phase oxygen influence mechanistic details of the selective conversion of CH 4 to C 2 H 4 over the Mn-Na 2 WO 4 /SiO 2 catalyst. The results from TAP studies indicate that methane activation on this catalyst proceeds predominantly via a short-lived, transient surface oxygen species and there is a competition for this species to form either CO or methyl radicals on the surface. This active species has a total lifetime of 3 s and is identified to have a dioxygen (e.g. O 2 2- or O 2 -) form. We show that the concentration of the transient surface oxygen species significantly impacts the OCM performance. Oxygen attributed to the catalyst lattice (in a singular form e.g., O - ), is found to activate methane to a lesser degree, but exclusively forms CO 2 . Evidence for these surface pathways for methyl radical, CO and CO 2 formation identified by TAP are also validated through steady-state experiments. Finally, by distinguishing different catalyst oxygen species and their role in selective/nonselective pathways, important screening criteria have been identified for the advancement of superior catalyst formulations.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Statistical distributions for transient transport

Here, this paper introduces the use of statistical distributions based on transport differential equations for clear distinction of transport modes within transient kinetic experiments. More specifically, novel techniques are developed for the transient data obtained through the Temporal Analysis of Products (TAP) reactor and are applicable to experiments where pulse response into a gas flow is used. The methodology allows distinguishing between two domains of diffusion transport in heterogeneous catalytic systems, i.e., Knudsen and non-Knudsen diffusion, using statistical fingerprints, and finding the transition domain. Two distribution parameters were obtained that directly result in coefficients that correspond to the concentration and the rate of transport. Using a linear relationship between the rate and concentration coefficients, Knudsen diffusion is revealed when the rate of transport is constant and non-Knudsen diffusion is confirmed when the rate of transport coefficient is a function of the concentration coefficient. As a result, accurate transport information can be extracted from experimental data even in the presence of comprising instrument drift or noise particularly when analyzing higher pressure pulse responses with complex transport. This enables more direct investigation of experiments influenced by gas-phase reactions.

TAP reactor↗
DOE OSTI2018

Transient performance of MED processes with different feed configurations

Four different configurations of Multi-Effect-Desalination (MED): backward feed (BF), forward feed (FF), parallel feed (PF) and parallel/cross feed (PCF) are modeled in steady and dynamic operation to examine the behavior of these configurations under transient operation. Adding thermal vapor compressor (TVC) unit with the last effect of parallel/cross configuration is also studied and compared to the other configurations to show the advantage of this type of integration. The transient operation is achieved by applying ramp changes (disturbances) in the main input parameters that include steam flow rate at the heat source and cooling seawater temperature and flow rate at the heat sink. Steady state results indicate that parallel/cross feed has a relatively better performance characteristic than the other feed configurations regarding Gain Output Ratio (GOR) and specific heat consumption (SHC). Adding TVC unit to the parallel/cross feed achieves the lowest water production cost. Dynamic results show that MED-TVC with parallel/cross feed has the fastest response while backward feed and forward feed have the slower response to the applied disturbances. In the case of heat source disturbance, MED plants operating in the backward feed arrangement may be exposed to shut down due to the significant increase in brine level for the first effect. The MED-TVC process is susceptible to the heat sink disturbances compared to the PCF and other configurations. Also, changes in input parameters lead to the highest reduction in GOR for the MED-TVC process compared to the different configurations, especially for cooling seawater temperature. The highest reduction in brine level occurs in MED-TVC for a disturbance in the cooling seawater flow rate and may lead to MED-TVC evaporator drying condition. Hence, MED-TVC will require a reliable control system to avoid this type of plant operational disturbance.

42 ENGINEERING↗
DOE OSTI2025

Nuclear microreactor transient and load-following control with deep reinforcement learning

The economic feasibility of nuclear microreactors will depend on minimizing operating costs through advancements in autonomous control, especially when these microreactors are operating alongside other types of energy systems (e.g., renewable energy). This study explores the application of deep reinforcement learning (RL) for real-time drum control in microreactors, exploring performance in regard to load-following scenarios. By leveraging a point kinetics model with thermal and xenon feedback, we first establish a baseline using a single-output RL agent, then compare it against a traditional proportional–integral–derivative (PID) controller. This study demonstrates that RL controllers, including both single- and multi-agent RL (MARL) frameworks, can achieve similar or even superior load-following performance as traditional PID control across a range of load-following scenarios. In short transients, the RL agent was able to reduce the tracking error rate in comparison to PID by one half to one third. Over extended 300-minute load-following scenarios in which xenon feedback becomes a dominant factor, PID maintained better accuracy, but RL still remained within a 1% error margin despite being trained only on short-duration scenarios. This highlights RL’s strong ability to generalize and extrapolate to longer, more complex transients, affording substantial reductions in training costs and reduced overfitting. Furthermore, when control was extended to multiple drums, MARL enabled independent drum control as well as maintained reactor symmetry constraints without sacrificing performance---an objective that standard single-agent RL could not learn. We also found that, as increasing levels of Gaussian noise were added to the power measurements, the RL controllers were able to maintain lower error rates than PID, and to do so with at least 10% and upwards of 150% less control effort. These findings illustrate RL's potential for autonomous nuclear reactor control, laying the groundwork for future integration into high-fidelity simulations and experimental validation efforts.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2018

Direct measurement of building transient and residual drift using an optical sensor system

Interstory drift (ID) is a key response parameter for buildings subjected to lateral loads and is used to define performance-based limit states, allowable deformations and damage states in a number of seismic design codes and standards. Here, an ability to rapidly and accurately measure both transient and residual ID during an earthquake would provide important observables for understanding the seismic demands and post-earthquake condition of a building. Accurate retrieval of ID from accelerometer-based instrumentation systems can be very challenging, if not impossible, as a result of instrumentation limitations and the post-processing associated with strong motion accelerometer data. This is particularly true for the case in which residual drifts occur during inelastic building response. In the study presented herein, a newly developed optical sensor system, designed specifically for directly measuring both transient and residual ID, was experimentally evaluated through shake table testing and computational simulations. The ability of the sensor to accurately measure ID is demonstrated and key operational considerations for sensor system deployment are examined through a model-based investigation.

42 ENGINEERING↗
DOE OSTI2018

Geodetic measurements and numerical models of transient deformation at Raft River geothermal field, Idaho, USA

Here, we perform synthetic aperture radar interferometry using data acquired between 2004 and 2016 by the Envisat, and ALOS-2 satellite missions to measure transient deformation at the Raft River geothermal field in Cassia County in Southern Idaho where geothermal production began in late 2007. Time-series analysis of multiple interferometric pairs indicates uplift at an exponentially decaying rate, over an ~8 km-by-5 km area centered near three injection wells that recycle produced brine. Similarly, subsidence at an exponentially decaying rate is observed in a 4 km-by-4 km area west of the production wells. These two signatures stay in the same location in all of the well-correlated Envisat interferometric pairs spanning the time interval between 2007 and 2010. The boundary separating the uplifting and subsiding areas is associated with the steeply dipping Bridge fault zone. Using two-dimensional numerical models, we explore first-order, bi-directional coupling between hydrological and mechanical processes. Our results suggest that: (i) most of the deformation occurs due to pore pressure changes following the start of geothermal production, (ii) the rate of deformation decays to zero over a time scale on the order of ~5 years as the system reaches steady state, and (iii) a reservoir-scale permeability of the order of ~1E–14 m 2 is required to explain the transient deformation.

15 GEOTHERMAL ENERGY↗
DOE OSTI2019

Comparison of steady and transient flow boiling critical heat flux for FeCrAl accident tolerant fuel cladding alloy, Zircaloy, and Inconel

Steady and transient (with a heating rate of 685?/s) internal-flow CHF (Critical Heat Flux) experiments were conducted under atmospheric pressure at a fixed inlet temperature (40? or 60?) and mass flow (300kg/m 2 s) on Fe-13Cr-6Al alloy, Inconel 600 and Zircaloy-4 tube samples. Multiple experiments were repeated on the same specimen to investigate the effect of surface characteristic changes (i.e., roughness, wettability, and oxide scale morphology) on the occurrence of CHF. Despite notable changes of wettability, roughness, and oxide layer characteristics on samples that had already been subjected to CHF, measured flow CHF remained unchanged throughout repeated experiments for tested materials. This demonstrates that the surface effects on flow CHF are limited in the test conditions. In the steady-state flow boiling condition, Fe-13Cr-6Al alloy demonstrated a 22% and 14% increase in CHF compared to Zircaloy-4 and Inconel 600, respectively. Compared to the 2006 Groeneveld CHF lookup table, Fe-13Cr-6Al alloy gives a 13% increase in the tested flow boiling condition. Material properties are considered primarily responsible for the observed CHF differences among the tested materials. The surface thermal economy parameter $\frac{(pc_p)^{3/2}}{\sqrt{k}}$ is proposed as an explanation for the observed CHF differences; this parameter is related to material’s ability to avoid an irreversible dry spot formation. The apparent disagreement of Zircaloy-4 CHF with both the look up table predictions and Inconel 600 shows the limitation of departure of nuclate boiling (DNB) evaluations that do not consider cladding materials. The transient Fe-13Cr-6Al CHF is 39% and 23% higher than the lookup table prediction and the steady-state condition experimental result, respectively.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

A multi-dimensional dataset for two-phase instability in low pressure natural circulation based on direct transient local measurement

Thermal hydraulic instability can challenge the control and the safety of nuclear reactors. This experimental research captures and investigates the instability in a low-pressure (1–10 atmospheres) natural circulation loop with an adiabatic chimney installed above the heated section. Direct transient local measurement of two-phase flow is performed at multiple axial locations along the flow channel with thermocouples and conductivity probes traversed by customized high-precision mechanisms. Based on the periodicity of oscillations, a post-processing method is proposed to align the data captured non-simultaneously to reconstruct the instability behavior in one representative period. The averaging operation over multiple oscillation cycles is performed to reduce the random errors. Cyclic phenomena are clearly demonstrated by the post-processed data, and rapid void fraction change induced by the flashing is observed to be significant in the driving mechanism for low pressure oscillations. Parametric effects of inlet subcooling, heat flux, inlet flow restriction and system pressure are studied within the experiment range, and qualitative results are explained and compared with existing literature. The ratio between the oscillation period and the travelling time of the fluid particle through the test section is compared with the theoretical value for the density wave oscillation. The new dataset contains directly measured transient multi-dimensional two-phase data along the flow channel for natural circulation under density wave oscillations. The generated dataset is valuable for the validation of system analysis codes and CFD codes in the simulation of natural circulation phenomena and dynamic two-phase flow.

42 ENGINEERING↗
DOE OSTI2024

Reduced-dimension Bayesian optimization for model calibration of transient vapor compression cycles

Development and calibration of first-principles dynamic models of vapor compression cycles (VCCs) is of critical importance for applications that include control design and fault detection and diagnostics. Nevertheless, the inherent complexity of models that are represented by large systems of differential–algebraic equations leads to significant challenges for model calibration processes that utilize classical gradient-based methods. Bayesian optimization (BO) is a sample-efficient and gradient-free approach using a probabilistic surrogate model and optimal search over a feasible parameter space. Despite the benefits of BO in reducing computational costs, challenges remain in dealing with a high-dimensional calibration task resulting from a large set of parameters that have significant impacts on system behavior and need to be calibrated simultaneously. This paper presents a reduced-dimension BO framework for calibrating transient VCCs models where the calibration space is projected to a low-dimensional subspace for accelerating convergence of the solution algorithm and consequently reducing the number of transient simulations. The proposed approach was demonstrated via two case studies associated with different VCC applications where 10 parameters were calibrated in each case using laboratory measurements. The reduced-dimension BO framework only required 1 / 8 th of the iterations associated with a standard BO method that deals with high-dimensional calibration parameters for converged solutions and yielded comparable accuracy. Furthermore, both calibrated models revealed significant accuracy improvements compared to uncalibrated models.

Ma, Jiacheng↗
DOE OSTI2020

An explicit scheme to enforce charge conservation in transient Particle-in-Cell simulations with Maxwell-Boltzmann electrons

The Maxwell-Boltzmann electron model is a very popular approximation of the electronic behavior in electrostatic plasmas, adopted in all cases where the electron dynamics is governed only by a balance between electric and pressure forces. In such a model, the electron dynamics is reduced to solving for a nonlinear Poisson problem together with an additional expression enforcing charge conservation. In this work we derive an expression of charge conservation which can be conveniently applied to explicit schemes to update the reference Boltzmann density, particularly useful when simulating plasma sheaths. The scheme can be equally applied to both steady-state and transient problems. Two examples are shown, a steady-state plasma sheath, and a radio-frequency magnetic presheath. Our proposed scheme allows to enforce global charge conservation locally in time, and can thus be applied to the simulation of transient phenomena.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗