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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

SOHO Ultraviolet Coronagraph Spectrometer (UVCS) Mission Operations and Data Analysis

The scientific goal of UVCS is to obtain detailed empirical descriptions of the extended solar corona as it evolves from a period of minimum activity to maximum and to use these descriptions to identify and understand the physical processes responsible for coronal heating, solar wind acceleration, coronal mass ejections (CME's), and the phenomena that establish the plasma properties of the solar wind as measured by the CELIAS/SOHO experiment. We must observe a wide range of conditions (e.g., heating rate, impulsive mass ejections, magnetic field opening) in order to choose among competing theoretical explanations of the observed coronal structures and dynamics. During the first year of scientific observations (1 April 1996 through 31 March 1997), the LTVCS made the first extensive ultraviolet spectroscopic observations above the base of the solar corona. Those observations revealed extremely high most probable speeds along the line of sight for O(5+) in polar coronal holes above 2 solar radii from sun center and smaller such speeds for H(0) and protons. Doppler dimming and pumping diagnostics indicated that O(5+) and H(0) I reached supersonic outflow velocities within 2 solar radii. The observations appeared to be consistent with O95+) heating and direct momentum transfer by high frequency MHD waves through ion cyclotron resonance. Equatorial streamers were found to appear much different when observed in O VI, Fe XII and Mg X than when observed in H I Lyman-alpha or visible light. This led G. Noci to suggest that the elemental abundance of O, Fe, and Mg are lower in the dark center region of the O VI streamer image than it is in the brighter outer legs of the streamer. The O VI line ratio indicated a much smaller outflow speed in streamers than in the surrounding coronal holes. Spectroscopic observations of CME's in June and December 1996 showed large Doppler shifts indicating macroscopic flows of up to 200 km/s transverse to the apparent motion of the CME. The December event displayed factor of 500 intensity increases in H I Lyman lines and bright emissions in cool ion lines like C III 977 A indicating that the origin of some of the gas was a prominence. UVCS also observed two comets, several stars and interplanetary hydrogen. In the current reporting period, the initial results were published and detailed analyses including self consistent empirical models were developed. The research results were reported, published or submitted/accepted for publication. New observations were made to uncover additional information about the surprising results of the first year and other new observations revealed more surprises. A UVCS Tutorial was developed to familiarize potential users of UVCS data with the data products, analysis techniques and coronal models needed to analyze the data.

Kohl, John L.↗
NASA NTRS2014

New Worlds / New Horizons Science with an X-ray Astrophysics Probe

In 2013 NASA commenced a design study for an X-ray Astrophysics Probe to address the X-ray science goals and program prioritizations of the Decadal Survey New World New Horizons (NWNH) with a cost cap of approximately $1B. Both the NWNH report and 2011 NASA X-ray mission concept study found that high-resolution X-ray spectroscopy performed with an X-ray microcalorimeter would enable the most highly rated NWNH X-ray science. Here we highlight some potential science topics, namely: 1) a direct, strong-field test of General Relativity via the study of accretion onto black holes through relativistic broadened Fe lines and their reverberation in response to changing hard X-ray continuum, 2) understanding the evolution of galaxies and clusters by mapping temperatures, abundances and dynamics in hot gas, 3) revealing the physics of accretion onto stellar-mass black holes from companion stars and the equation of state of neutron stars through timing studies and time-resolved spectroscopy of X-ray binaries and 4) feedback from AGN and star formation shown in galaxy-scale winds and jets. In addition to these high-priority goals, an X-ray astrophysics probe would be a general-purpose observatory that will result in invaluable data for other NWNH topics such as stellar astrophysics, protostars and their impact on protoplanetary systems, X-ray spectroscopy of transient phenomena such as high-z gamma-ray bursts and tidal capture of stars by massive black holes, and searches for dark matter decay.

Smith, Randall K.↗
DOE OSTI2025

Dynamic motion trajectory control with nanoradian accuracy for multi-element X-ray optical systems via laser interferometry

The past decades have witnessed the development of new X-ray beam sources with brightness growing at a rate surpassing Moore’s law. Current and upcoming diffraction limited and fully coherent X-ray beam sources, including multi-bend achromat based synchrotron sources and high repetition rate X-ray free electron lasers, puts increasingly stringent requirements on stability and accuracy of X-ray optics systems. Parasitic motion errors at sub-micro radian scale in beam transport and beam conditioning optics can lead to significant loss of coherence and brightness delivered from source to experiment. To address this challenge, we incorporated optical metrology based on interferometric length and angle sensing and real-time correction as part of the X-ray optics motion control system. A prototype X-ray optics system was constructed following the optical layout of a tunable X-ray cavity. On-line interferometric metrology enabled dynamical feedback to a motion control system to track and compensate for motion errors. The system achieved sub-microradian scale performance, as multiple optical elements are synchronously and continuously adjusted. This first proof of principle measurement demonstrated both the potential and necessity of incorporating optical metrology as part of the motion control architecture for large scale X-ray optical systems such as monochromators, delay lines, and in particular, X-ray cavity systems to enable the next generation cavity-based X-ray free electron lasers.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Transition state redox during dynamical processes in semiconductors and insulators

Activation barriers associated with ion diffusion and chemical reactions are vital to understand and predict a wide range of phenomena, such as material growth, ion transport, and catalysis. In the calculation of activation barriers for non-redox processes in semiconductors and insulators, it has been widely assumed that the charge state remains fixed to that of the initial electronic ground state throughout a dynamical process. In this work, we demonstrate that this assumption is generally inaccurate and that a rate-limiting transition state can have a different charge state from the initial ground state. This phenomenon can significantly lower the activation barrier of a dynamical process that depends strongly on charge state, such as carbon vacancy diffusion in 4H-SiC. With inclusion of such transition state redox, the activation barrier varies continuously with Fermi level, in contrast to the step-line feature predicted by the traditional fixed-charge assumption. In this study, a straightforward approach to include the transition state redox effect is provided, the typical situations where the effect plays a significant role are identified, and the relevant electron dynamics are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Denial of Service Attack Detection via Differential Analysis of Generalized Entropy Progressions

Denial-of-Service (DoS) attacks are one the most common and consequential cyber attacks in computer networks. While existing research offers a plethora of detection methods, the issue of achieving scalability, a low false positive rate, and high detection accuracy remains open. In this work, we address this problem by developing a differential method based on generalized entropy progression. In this method, named as DoDGE, we continuously fit the line of best fit to the entropy progression of destination addresses and check if the derivative, that is, the slope of this line is less than the negative of the dynamically computed standard deviation of the derivatives. Furthermore, to distinguish from flash events, we leverage the symmetry that when a flash event occurs, the derivative of the entropy progression of source addresses is positive. With this design, we omit the usage of the thresholds and the results with five real-world network traffic datasets confirm that DoDGE outperforms threshold-based DoS attack detection by two orders of magnitude in terms of false positives on average. When compared to ten machine learning (ML) models, DoDGE achieves a balanced accuracy of 99%, while the average balanced accuracy for the ML models is 52%. Moreover, the results show that DoDGE successfully differentiates between a flash event and a DoS attack. Furthermore, since the main computation cost of DoDGE is the entropy computation, which is linear in the volume of the unit-time network flow, uses integer only operations, and works on a small fraction of the total flow, it is lightweight and scalable.

Cybersecurity, wireless communication↗
DOE OSTI2018

Final Report on CFD and Thermal-Mechanical Stress Analysis of PWR Surge Line under Transient Condition Thermal Stratification and an Evolutionary Cyclic Plasticity Based Transformative Fatigue Evaluation Approach without Using S~N Curve: Rev. 1

This report presents an evolutionary cyclic plasticity based transformative approach for fatigue evaluation of safety critical components. This approach is generic which can be used not only for the present generation light water reactor components (which is our focus) but also for advanced reactor components. The approach is based on the fundamental concept of time-evolution of progressive fatigue damage rather than the end-of-life data based conventional S~N curve approaches. Series of fatigue tests on 316 stainless steel uniaxial specimens were conducted under strain-controlled and stress-controlled cyclic loading in two different environment such as in-air at 300 °C and PWR coolant water condition at 300 °C. Material models are developed to capture the uniaxial test data and are subsequently programmed into commercially available ABAQUS code to transform the uniaxial material behavior to multiaxial loading domain. The developed evolutionary cyclic-plasticity approach is verified by both analytical and 3D-FE modeling of uniaxial fatigue test specimens. Results show that the developed material models can capture the time-dependence of material hardening and softening with great accuracy. In addition, results show that the material models not only can capture the material behavior under constant amplitude loading but also can capture the load-sequence effect under variable and random amplitude loading. The ANL developed approach is one of its kind, which shows first in the fatigue research community that fatigue evaluation of a component (in our case verified for laboratory scale fatigue test specimens with great accuracy) can be performed for its entire fatigue life, including the hardening and softening behavior, without using a conventional S~N curve based approach. Additionally results are presented related to fatigue evaluation of real reactor components such as of a pressurized water reactor (PWR) surge line (SL), under upset transient conditions. SLs of PWR experience complex thermal stratification due to the mixing of differential temperature flow from hot leg and pressurizer. A detailed parametric study of thermal stratification in SL is performed through both standalone computational fluid dynamics (CFD) analysis and fluid-structure-interaction based coupled CFD and heat transfer analysis. Results show that the mass flow rate in SL substantially affects the extent of its thermal stratification. The resulting thermal boundaries conditioned are used as inputs for thermal-mechanical stress analysis and component level fatigue evaluation. Fatigue evaluation of SL pipe under example loading conditions was performed using the above-mentioned evolutionary-plasticity based approach and ASME code (for in-air life) and NUREG-6909 (for PWR environment life) based approaches. Results show that the evolutionary plasticity based approach estimate substantially different life compared to the conventional ASME based approach. To show the entirety of the proposed evolutionary fatigue-modeling framework, this report includes the results presented in semi-annual March report (ANL/LWRS-17/01). Sections 2-5 of March report are directly included as Sections 2-5 in this report, without any significant changes. However, Sections 6-9 of this report present the work performed during March-September of 2017. Whereas, Sections 1 and 10 present the organization of this report and the summary and future work, respectively. This report (ANL/LWRS-17/03 Rev. 1) is a slightly revised version of the earlier published report (ANL/LWRS-17/03). In this revised version, some of the results and associated discussion have been corrected/updated.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2001

Laser Powered Launch Vehicle Performance Analyses

The purpose of this study is to establish the technical ground for modeling the physics of laser powered pulse detonation phenomenon. Laser powered propulsion systems involve complex fluid dynamics, thermodynamics and radiative transfer processes. Successful predictions of the performance of laser powered launch vehicle concepts depend on the sophisticate models that reflects the underlying flow physics including the laser ray tracing the focusing, inverse Bremsstrahlung (IB) effects, finite-rate air chemistry, thermal non-equilibrium, plasma radiation and detonation wave propagation, etc. The proposed work will extend the base-line numerical model to an efficient design analysis tool. The proposed model is suitable for 3-D analysis using parallel computing methods.

Chen, Yen-Sen↗
DOE OSTI2012

Dynamic modeling of a single-stage downward firing, entrained flow gasifier

The gasifier is the heart of the integrated gasification combined cycle (IGCC), a technology that has emerged as an attractive alternative to conventional coal-fired power plant technology due to its higher efficiency and cleaner environmental performance especially with the option of CO{sub 2} capture and sequestration. Understanding the optimal performance of the gasifier is therefore paramount for the efficient operation of IGCC power plants. Numerous gasifier models of varying complexity have been developed to study the various aspects of gasifier performance. These range from simple one-dimensional (1D) process-type models to rigorous higher order 2-3D models based on computational fluid dynamics (CFD). Whereas high-fidelity CFD models can accurately predict most key aspects of gasifier performance, they are computationally expensive and typically take hours to days to execute on high-performance computers. Therefore, faster 1D partial differential equation (PDE)-based models are required for use in dynamic simulation studies, control system analysis, and training applications. A number of 1D gasifier models can be found in the literature, but most are steady-state models that have limited application in the practical operation of the gasifier. As a result, 1D PDE-based dynamic models are needed to further study and predict gasifier performance under a wide variety of process conditions and disturbances. In the current study, a 1D transient model of a single-stage downward-fired GE/Texaco-type entrained-flow gasifier has been developed. The model comprises mass, momentum and energy balances for the gas and solid phases. The model considers the initial gasification processes of water evaporation and coal devolatilization. In addition, the key heterogeneous and homogeneous chemical reactions have been modeled. The resulting time-dependent PDE model is solved using the well-known method of lines approach in Aspen Custom Modeler®, whereby the PDEs in the spatial domain are discretized and the resulting differential algebraic equations (DAEs) are then integrated over time using a dynamic integrator. The dynamic response results of the gasifier performance parameters to certain disturbances commonly encountered during practical operation are presented. These disturbances include ramp and step changes to input variables such as coal flow rate, oxygen-to-coal ratio and water-to-coal ratio among others. Comparison of model predictions to available dynamic data will also be discussed.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2012

MODEL FOR ALFVEN WAVE TURBULENCE IN SOLAR CORONAL LOOPS: HEATING RATE PROFILES AND TEMPERATURE FLUCTUATIONS

It has been suggested that the solar corona may be heated by dissipation of Alfven waves that propagate up from the solar photosphere. According to this theory, counterpropagating Alfven waves are subject to nonlinear interactions that lead to turbulent decay of the waves and heating of the chromospheric and coronal plasma. To test this theory, better models for the dynamics of Alfven waves in coronal loops are required. In this paper, we consider wave heating in an active region observed with the Solar Dynamics Observatory in 2010 May. First a three-dimensional (3D) magnetic model of the region is constructed, and ten magnetic field lines that match observed coronal loops are selected. For each loop we construct a 3D magnetohydrodynamic model of the Alfven waves near the selected field line. The waves are assumed to be generated by footpoint motions inside the kilogauss magnetic flux elements at the two ends of the loop. Based on such models, we predict the spatial and temporal profiles of the heating along the selected loops. We also estimate the temperature fluctuations resulting from such heating. We find that the Alfven wave turbulence model can reproduce the observed characteristics of the hotter loops in the active region core, but the loops at the periphery of the region have large expansion factors and are predicted to be thermally unstable.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

EXPLORING MAGNETIC FIELD STRUCTURE IN STAR-FORMING CORES WITH POLARIZATION OF THERMAL DUST EMISSION

The configuration and evolution of the magnetic field in star-forming cores are investigated in order to directly compare simulations and observations. We prepare four different initial clouds having different magnetic field strengths and rotation rates, in which magnetic field lines are aligned/misaligned with the rotation axis. First, we calculate the evolution of such clouds from the prestellar stage until long after protostar formation. Then, we calculate the polarization of thermal dust emission expected from the simulation data. We create polarization maps with arbitrary viewing angles and compare them with observations. Using this procedure, we confirmed that the polarization distribution projected on the celestial plane strongly depends on the viewing angle of the cloud. Thus, by comparing the observations with the polarization map predicted by the simulations, we can roughly determine the angle between the direction of the global magnetic field and the line of sight. The configuration of the polarization vectors also depends on the viewing angle. We find that an hourglass configuration of magnetic field lines is not always realized in a collapsing cloud when the global magnetic field is misaligned with the cloud rotation axis. Depending on the viewing angle, an S-shaped configuration of the magnetic field (or the polarization vectors) appears early in the protostellar accretion phase. This indicates that not only the magnetic field but also the cloud rotation affects the dynamical evolution of such a cloud. In addition, by comparing the simulated polarization with actual observations, we can estimate properties of the host cloud such as the evolutionary stage, magnetic field strength, and rotation rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Engineering the fracture resistance of 2H-transition metal dichalcogenides using vacancies: An in-silico investigation based on HRTEM images

Vacancy engineering of 2H-transition metal dichalcogenides (2H-TMDs) has recently attracted great attention due to its potential to fine-tune the phonon and opto-electric properties of these materials. From a mechanical perspective, this symmetry-breaking process typically reduces the overall crack resistance of the material and adversely affects its reliability. However, vacancies can trigger the formation of heterogeneous phases that synergistically improve fracture properties. In this study, using MoSe2 as an example, we characterize the types and density of vacancies that can emerge under electron irradiation and quantify their effect on fracture. Molecular dynamic (MD) simulations, employing a re-parameterized Tersoff potential capable of accurately capturing bond dissociation and structural phase changes, reveal that isolated transition metal monovacancies or chalcogenide divacancies tend to arrest the crack tip and hence enhance the monolayer toughness. In contrast, isolated chalcogenide monovacancies do not significantly affect toughness. The investigation further reveals that selenium vacancy lines, formed by high electron dose rates, alter the crack propagating direction and lead to multiple crack kinking. Using atomic displacements and virial stresses together with a continuum mapping, displacement, strain, and stress fields are computed to extract mechanistic information, e.g., conditions for crack kinking and size effects in fracture events. The study also reveals the potential of specific defect patterns, “vacancy engineering,” to improve the toughness of 2H-TMDs materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Application of the Generic Electronics for Time Projection Chamber ($\mathrm{GET}$) readout system for heavy Radioactive isotope collision experiments

Here we have implemented the Generic Electronics for Time Projection Chamber (GET) in a SAMURAI Pion Reconstruction and Ion-Tracker (SπRIT) readout system for heavy radioactive ion collision experiments at RIKEN-RIBF. The SπRIT experiment is designed for heavy ion collision experiments with radioactive ion beams, where a Time Projection Chamber (TPC) with 12096 pixelized readout pads is employed as the main device. Since the TPC is located on the beam line, the readout electronics must handle small signals from pions as well as very large signals from beam or large fragment particles. Operation of the GET electronics during experiment functioned well using 270 time-bucket readout with 25 MHz sampling at an event Data acquisition (DAQ) rate of 60 Hz. Using the slope information of acquired signals it is possible to extend the dynamic range of dE/dx information compared to using the peak height information. However, huge signals arising from energetic δ-rays produced by un-interacted projectiles induce dead channels, which can be recovered after 70 μs on average.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

A particle finite element-based model for droplet spreading analysis

Here, a particle finite element method-based model is proposed to analyze droplet dynamics problems, particularly droplet spreading on solid substrates (wetting). The model uses an updated Lagrangian framework to formulate the governing equations of the liquid. The curvature of the liquid surface is tracked accurately using a deforming boundary mesh. In order to predict the spreading rate of the droplet on the solid substrate and track the corresponding contact angle evolution, dissipative forces at the contact line are included in the formulation in addition to the Navier-slip boundary conditions at the solid–liquid interface. The inclusion of these boundary conditions makes it possible to account for the induced Young’s stress at the contact line and for the viscous dissipation along the solid–liquid interfacial region. These are found to be essential to obtain a mesh-independent physical solution. The temporal evolution of the contact angle and the contact line velocity of the proposed model are compared with spreading droplets and micro-sessile droplet injection experiments and are shown to be in good agreement.

42 ENGINEERING↗
NASA NTRS1982

Adaptive identification for the dynamics of large space structures

A new approach for identifying the dynamics of large space structures using noisy measurements is presented. In this approach, a modal system description is avoided and, hence, the a priori specification of model order. Instead, the system's order is recursively determined on-line, along with its parameters, using recursive lattice filters which are widely used in adaptive signal processing. The order determination is carried out based on statistical hypothesis testing theory. The approach is illustrated for the problem of identifying the structural dynamic characteristics of a free-free beam. Results on the effectiveness and accuracy of the identification scheme with respect to noise levels, sampling rates, and data window sizes are presented

Sundararajan, N.↗
NASA NTRS1983

Direct coronal heating from dissipation of magnetic field

The visible corona of the Sun appears to be heated by direct dissipation of magnetic fields. The magnetic fields in the visible corona are tied at both ends to the photosphere where the active convection continually rotates and shuffles the footpoints in a random pattern. The twisting and wrapping of flux tubes about each other produce magnetic neutral sheets in a state of dynamical nonequilibrium such that the current sheets become increasingly concentrated with the passage of time. Dissipation of the high current densities takes place regardless of the high electrical conductivity of the fluid. The convection on the feet of the lines of force at the surface of the Sun goes directly (within a matter of 10 to 20 hours) into heat in the corona. The rate of doing work seems adequate to supply the necessary 10 to the 7th power ergs/square cm. sec for the active corona.

Parker, E. N.↗
NASA NTRS2012

Spatially-Resolved HST GRISM Spectroscopy of a Lensed Emission Line Galaxy at Z to approximately 1

We take advantage of gravitational lensing amplification by Abell 1689 (z=0.187) to undertake the first space-based census of emission line galaxies (ELGs) in the field of a massive lensing cluster. Forty-three ELGs are identified to a flux of i(sub 775)=27.3 via slitless grism spectroscopy. One ELG (at z=0.7895) is very bright owing to lensing magnification by a factor of approx = 4.5. Several Balmer emission lines detected from ground-based follow-up spectroscopy signal the onset of a major starburst for this low-mass galaxy (M(sub star) approx = 2 x 10(exp 9)Solar Mass) with a high specific star formation rate (approx = 20/ Gyr). From the blue emission lines we measure a gas-phase oxygen abundance consistent with solar (12+log(O /H)=8.8 +/- O.2). We break the continuous line-emitting region of this giant arc into seven approx 1 kpc bins (intrinsic size) and measure a variety of metallicity dependent line ratios. A weak trend of increasing metal fraction is seen toward the dynamical center of the galaxy. Interestingly, the metal line ratios in a region offset from the center by -lkpc have a placement on the blue HI! region excitation diagram with f([OIII]/ f(H-Beta) and f([NeIII/ f(H-Beta) that can be fit by an AGN. This asymmetrical AGN-like behavior is interpreted as a product of shocks in the direction of the galaxy's extended tail, possibly instigated by a recent galaxy interaction.

Frye, Brenda L.↗
DOE OSTI2023

Measurements and Prediction of Ash Deposition in a Cyclone-Fired Boiler Operating under Variable Load Conditions

Measurements of ash deposition rates were made between the secondary superheater and reheater sections of a 450 MW cyclone-fired lignite boiler as the operational load varied from 33 to 100%. Significant reductions in deposition rates with a decrease in operational load were observed. To uncover the causative mechanisms behind these observations, operational data from the power plant were used to carry out computational fluid dynamic (CFD) simulations of the boiler. After ascertaining that the gas temperatures and velocities at various sections within the boiler were being represented adequately, decoupled simulations of the ash deposition process on the deposit probe were carried out using a finely resolved boundary layer mesh. Fly ash particle size distribution (PSD) and its concentration for the decoupled calculations were determined from stand-alone cyclone barrel simulations. The ash partitioning (mass %) between the fly ash and slag was found to be ~50:50, which was in line with previous field observations, and it did not vary significantly across different cyclone loads. The predicted PSD of the deposit ash was concentrated in the size range 10–30 microns, which was in agreement with cross-sectional images of the deposit obtained from the measurements. At lower loads, sharp variations in the deposition rates were predicted in the gas temperature range 950–1150 K. The particle kinetic energy—particle viscosity-based capture methodology utilized in this study in conjunction with appropriate ash compositions, ash viscosity models and gas temperature estimates can help estimate slagging propensities at different loads reasonably well in these systems.

Krishnamoorthy, Gautham (ORCID:0000000255205092)↗
DOE OSTI2011

Study of the Power Supply Ripple Effect on teh Dynamics at SPEAR

For long term stability analysis time variation of tunes is important. We have proposed and tested a technique for measuring the magnitude of this variation. This was made possible by using tune extraction algorithms that require small number of turns thus giving an instantaneous tune of the machine. In this paper we demonstrate the measured effect of the tune modulation with 60 Hz power supplies ripple, power line interference from SLAC linac operating at 30 Hz repetition rate, and nonperiodic variation.

43 PARTICLE ACCELERATORS↗