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All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Convective mixing in vertically-layered porous media: The linear regime and the onset of convection

In this paper, we study the effect of permeability heterogeneity on the stability of gravitationally unstable, transient, diffusive boundary layers in porous media. Permeability is taken to vary periodically in the horizontal plane normal to the direction of gravity. In contrast to the situation for vertical permeability variation, the horizontal perturbation structures are multimodal. We therefore use a two-dimensional quasi-steady eigenvalue analysis as well as a complementary initial value problem to investigate the stability behavior in the linear regime, until the onset of convection. We find that thick permeability layers enhance instability compared with thin layers when heterogeneity is increased. On the contrary, for thin layers the instability is weakened progressively with increasing heterogeneity to the extent that the corresponding homogeneous case is more unstable. For high levels of heterogeneity, we find that a small change in the permeability field results in large variations in the onset time of convection, similar to the instability event in the linear regime. However, this trend does not persist unconditionally because of the reorientation of vorticity pairs due to the interaction of evolving perturbation structures with heterogeneity. Consequently, an earlier onset of instability does not necessarily imply an earlier onset of convection. A resonant amplification of instability is observed within the linear regime when the dominant perturbation mode is equal to half the wavenumber of permeability variation. On the other hand, a substantial damping occurs when the perturbation mode is equal to the harmonic and sub-harmonic components of the permeability wavenumber. Finally, the phenomenon of such harmonic interactions influences both the onset of instability as well as the onset of convection.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Forward and reverse transfer function model synthesis

A process for synthesizing a mathematical model for a linear mechanical system using the forward and reverse Fourier transform functions is described. The differential equation for a system model is given. The Bode conversion of the differential equation, and the frequency and time-domain optimization matching of the model to the forward and reverse transform functions using the geometric simplex method of Nelder and Mead (1965) are examined. The effect of the window function on the linear mechanical system is analyzed. The model is applied to two examples; in one the signal damps down before the end of the time window and in the second the signal has significant energy at the end of the time window.

Houghton, J. R.↗
DOE OSTI2014

Short-period pulsar oscillations following a glitch

Following a glitch, the crust and magnetized plasma in the outer core of a neutron star are believed to rapidly establish a state of co-rotation within a few seconds by process analogous to classical Ekman pumping. However, in ideal magnetohydrodynamics, a final state of co-rotation is inconsistent with conservation of energy of the system. We demonstrate that, after the Ekman-like spin up is completed, magneto-inertial waves continue to propagate throughout the star, exciting torsional oscillations in the crust and plasma. The crust oscillation is irregular and quasi-periodic, with a dominant frequency of the order of seconds. Crust oscillations commence after an Alfvén crossing time, approximately half a minute at the magnetic pole, and are subsequently damped by the electron viscosity over approximately an hour. In rapidly rotating stars, the magneto-inertial spectrum in the core approaches a continuum, and crust oscillations are damped by resonant absorption analogous to quasi-periodic oscillations in magnetars. The oscillations predicted are unlikely to be observed in timing data from existing radio telescopes, but may be visible to next generation telescope arrays.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Thermomechanical and sequential stress performance of photovoltaic backsheets

Photovoltaic backsheet technology is utilized to protect the interior components of solar modules from environmental stress as well as provide electrical insulation to the module. The growing demand for solar energy and longer module service life requirements have brought backsheet performance into focus. Despite being a protective packaging material, many backsheets have exhibited failure in the field, limiting the performance and service life of entire modules. Most backsheets consist of multiple polymeric layers laminated together using adhesives. A new backsheet, with a high performance polyamide structure, has been developed as the solution to module failure. Primarily, it contains a unique polyamide-ionomer alloy targeted at improved weather resistance. In this study, several photovoltaic industry standard backsheets, and the novel polyamide compositions of multilayered backsheets fabricated from the coextrusion process, were examined using thermomechanical analysis (TMA). The coefficient of thermal expansion (CTE) for entire backsheets and their constituent layers was used to model the thermomechanical behavior of various backsheet constructions. Subsequently, thermal cycling was performed in the TMA to examine the intrinsic thermal behavior of the backsheets. Thermal cycling in the TMA indicates the resilience and dimensional stability in the coextruded structures as opposed to the laminated structures. Lastly, results from a Module Accelerated Sequential Testing (MAST), are included to show the mechanical integrity of these backsheets after sequential exposure to stressors including damp heat, ultra-violet (UV) light radiation, and thermal cycling. The laminate backsheets deteriorated extensively after sequential exposure to these stressors, while the novel coextruded structures retained their physical properties.

14 SOLAR ENERGY↗
DOE OSTI2015

ON THE ORIGIN AND PHYSICS OF GAMMA FLARES IN CRAB NEBULA

We consider parametric generation of electrostatic waves in the magnetosphere of the pulsar PSR0531. The suggested mechanism allows us to convert the pulsar rotational energy into the energy of Langmuir waves. The maximum growth rate is achieved in the “superluminal” area, where the phase velocity of perturbations exceeds the speed of light. Therefore, electromagnetic waves do not damp on particles. Instead, they create plasmon condensate, which is carried out outside of the pulsar magnetosphere and reaches the Crab Nebula. It is shown that the transfer of the energy of the plasmon condensate from the light cylinder to the active region of the nebula happens practically without losses. Unlike the plasma of the magnetosphere, the one of the nebula contains ions, i.e., it may sustain modulation instability, that leads to the collapse of the Langmuir condensate. Langmuir wave collapse, in turn, leads to the acceleration of the distribution function particles. Furthermore, the processes that lead to self-trapping of the synchrotron radiation are discussed. The self-trapping results in the growth of the radiation intensity, which manifests itself observationally as a flare. The condition for the self-trapping onset is derived, showing that if the phenomenon takes place at 100 MeV, then it does not happen at lower (or higher) energies. This specific kind of higher-/lower-energy cutoff could explain why when we observe the flare at 100 MeV that no enhanced emission is observed at lower/higher energies!.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2015

A Numerical and Experimental Study of Coflow Laminar Diffusion Flames: Effects of Gravity and Inlet Velocity

In this work, the influence of gravity, fuel dilution, and inlet velocity on the structure, stabilization, and sooting behavior of laminar coflow methane-air diffusion flames was investigated both computationally and experimentally. A series of flames measured in the Structure and Liftoff in Combustion Experiment (SLICE) was assessed numerically under microgravity and normal gravity conditions with the fuel stream CH4 mole fraction ranging from 0.4 to 1.0. Computationally, the MC-Smooth vorticity-velocity formulation of the governing equations was employed to describe the reactive gaseous mixture; the soot evolution process was considered as a classical aerosol dynamics problem and was represented by the sectional aerosol equations. Since each flame is axisymmetric, a two-dimensional computational domain was employed, where the grid on the axisymmetric domain was a nonuniform tensor product mesh. The governing equations and boundary conditions were discretized on the mesh by a nine-point finite difference stencil, with the convective terms approximated by a monotonic upwind scheme and all other derivatives approximated by centered differences. The resulting set of fully coupled, strongly nonlinear equations was solved simultaneously using a damped, modified Newton's method and a nested Bi-CGSTAB linear algebra solver. Experimentally, the flame shape, size, lift-off height, and soot temperature were determined by flame emission images recorded by a digital camera, and the soot volume fraction was quantified through an absolute light calibration using a thermocouple. For a broad spectrum of flames in microgravity and normal gravity, the computed and measured flame quantities (e.g., temperature profile, flame shape, lift-off height, and soot volume fraction) were first compared to assess the accuracy of the numerical model. After its validity was established, the influence of gravity, fuel dilution, and inlet velocity on the structure, stabilization, and sooting tendency of laminar coflow methane-air diffusion flames was explored further by examining quantities derived from the computational results.

microgravity↗
NASA NTRS2009

International Space Station Solar Alpha Rotary Joint Failure Analysis: The Materials and Processes Perspective

This paper summarizes the on-orbit structural dynamic data and the related modal analysis, model validation and correlation performed for the ISS configurations spanning ISS Stage 12A. The objective of this analysis is to validate and correlate analytical models used to verify the ISS critical interface dynamic loads and improve its fatigue life prediction. On-Orbit dynamic responses were measured during the ISS configurations throughout ISS Stage 12A by the two main ISS instrumentation systems; Internal Wireless Instrumentation System (IWIS) and the Structural Dynamic Measurement System (SDMS). These nominal on-orbit events include Russian vehicle docking and undockings. Also, the ISS photogrammetric system recorded the movements of the 2A and 4A solar arrays during a modified ISS maneuver. Modal analyses were performed on the measured data to extract modal parameters including frequency, damping and mode shapes. Correlation and comparisons between the test and analytical frequencies and mode shapes were performed to assess the accuracy of the analytical models for the ISS configurations under consideration.

Dasgupta, Rajib↗
DOE OSTI2011

Final Technical Report - Recovery Act: Organic Coatings as Encapsulants for Low Cost, High Performance PV Modules

The objective of this project was to evaluate the feasibility of utilizing PPG's commercial organic coatings systems as efficient, modernized encapsulants for low cost, high performance, thin film photovoltaic modules. Our hypothesis was that the combination of an anticorrosive coating with a more traditional barrier topcoat would mitigate many electrochemical processes that are now responsible for the significant portion of photovoltaic (PV) failures, thereby nullifying the extremely high moisture barrier requirements of currently used encapsulation technology. Nine commercially available metal primer coatings and six commercially available top coatings were selected for screening. Twenty-one different primer/top coat combinations were evaluated. The primer coatings were shown to be the major contributor to corrosion inhibition, adhesion, and barrier properties. Two primer coatings and one top coating were downselected for testing on specially-fabricated test modules. The coated test modules passed initial current leakage and insulation testing. Damp Heat testing of control modules showed visible corrosion to the bus bar metal, whereas the coated modules showed none. One of the primer/top coat combinations retained solar power performance after Damp Heat testing despite showing some delamination at the EVA/solar cell interface. Thermal Cycling and Humidity Freeze testing resulted in only one test module retaining its power performance. Failure modes depended on the particular primer/top coating combination used. Overall, this study demonstrated that a relatively thin primer/top coating has the potential to replace the potting film and backsheet in crystalline silicon-based photovoltaic modules. Positive signals were received from commercially available coatings developed for applications having performance requirements different from those required for photovoltaic modules. It is likely that future work to redesign and customize these coatings would result in a coating system meeting the requirements for photovoltaic module encapsulation.

14 SOLAR ENERGY↗
DOE OSTI2026

Tandem Photovoltaics Core Program Final Technical Report

The Tandem Photovoltaics Core Program was a multi-year initiative aimed at advancing hybrid tandem solar cell technologies to enhance solar module efficiency beyond the limits of single junction devices. This project focused on the development, testing, and scaling of prototype photovoltaic devices, with the goal of achieving commercial relevance and driving industry adoption. The work was divided into three tasks: 1) Comparative Analysis of Tandem Technologies: This task focused on quantifying energy yield under real-world conditions and assessing economic viability of tandems relative to silicon-based modules. The project's modeling framework incorporated performance data, cost of materials, and manufacturing process impacts to optimize tandem designs 2) Tandem Integration and Prototyping: In this task, we developed innovative tandem designs by combining metal halide perovskite (MHP) top cells and silicon (Si) bottom cells. The project focuses on both mechanical integration and direct deposition techniques to enable compatibility with commercially relevant Si technologies, such as passivated contact or PERC cells. 3) Scale-up and Reliability: This task addressed the challenges of large-area fabrication by developing scalable deposition methods and robust interconnection schemes for tandems. The project looked at different accelerated testing such as thermal cycling, damp heat exposure, and potential induced degradation, to ensure long-term stability of devices in field conditions. Tandem solar cells can greatly increase module efficiency beyond conventional single junction (SJ) devices, which are approaching their theoretical limit. There are many ways to fabricate a tandem cell or module in terms of materials used, configuration, and terminal connection. This SETO core project focused critical factors in enabling tandems to enter the market, including hardware integration, technoeconomic analysis (TEA), and energy yield analysis. We focused on MHP/Si hybrid tandem solar cells and modules as a model system for their versatility in module design comparisons, providing valuable insights for other tandem options. While champion cells with areas <1cm2 are regularly demonstrated by groups around the world, it is significantly more challenging to translate these advances into modules, and fewer institutions and companies are working at the module level. This project addressed questions about module fabrication, testing, and reliability that are hard to answer without actually fabricating prototypes. We also performed analysis and road-mapping activities to understand the potential for a wider variety of tandems, including all-perovskite tandems fabricated in collaboration with the Perovskite PV core program. Detailed technical results from this project are described for each task in Section 7.

14 SOLAR ENERGY↗
DOE OSTI2026

Cyclotron breaking: a mechanism for parallel ion cyclotron waves to heat the fast solar wind

The Parker Solar Probe mission has observed near-continuous power in parallel ion cyclotron waves (PICWs) in the young, fast solar wind. These waves are unlikely to be directly produced by the turbulent cascade and are likely born of a local instability; yet, they are observed to both cool – and heat – the plasma. We propose that these observations can be self-consistently explained as the natural consequence of PICWs propagating in the inhomogeneous solar wind after they have been driven unstable. In this work, we argue that strong proton heating by a turbulent cascade of oblique ICWs will result in PICWs being driven unstable in a process known as quasi-linear focusing. Because the power in the turbulent cascade is concentrated at scales above the turbulent transition region, PICWs will be driven unstable within a range of wavenumbers parallel to the background magnetic field, 𝑘 ∥ , that is bounded from above by 𝑘$^{∗}_{∥P}$, corresponding to the start of the transition region. As unstable PICWs propagate away from the Sun to regions of lower proton density, their 𝑘 ∥ , multiplied by the proton inertial length 𝑑 p , increases. Eventually, 𝑘$^{∗}_{∥P}$ of the PICWs becomes larger than 𝑘$^{∗}_{∥P}$⁢𝑑 p and the waves damp, heating the solar wind. We call this effect ‘cyclotron breaking’, in analogy with ocean waves breaking on the shore. We then discuss the testable predictions of the theory, including a distinct heating signature in which PICWs cool fast protons and heat slow protons at any given heliocentric distance 𝑟. Finally, we conjecture that cyclotron breaking can lead to net heating by PICWs if the power emitted as PICWs decreases sufficiently rapidly with 𝑟 that local emission of PICWs is overwhelmed by the local damping of PICWs generated closer to the Sun.

plasma heating↗
DOE OSTI2016

RICH KOZAI–LIDOV DYNAMICS IN AN INITIALLY THIN AND ECCENTRIC STELLAR DISK AROUND A SUPERMASSIVE BLACK HOLE

There is growing evidence of star formation in the vicinity of supermassive black holes (SMBHs) in galactic nuclei. A viable scenario for this process assumes infall of a massive gas cloud toward the SMBH and subsequent formation of a dense accretion disk, which gives birth to the young stars. Numerical hydrodynamical models indicate that this star formation process is rather fast and precedes full circularization of the accretion flow, i.e., the new stars are born on elliptic orbits. By means of direct numerical N -body modeling, we show in this paper that the nonzero eccentricity of the stellar disks around the SMBH leads to an onset of various types of the Kozai–Lidov oscillations of a non-negligible subset of individual orbits in the disk, showing a remarkable robustness of this classical mechanism. Among others, we demonstrate that under certain circumstances, the presence of an additional spherical cluster (which is generally known to damp Kozai–Lidov oscillations) may trigger such oscillations as a result of affecting the internal flow of the angular momentum through the disk. We conclude that the Kozai–Lidov oscillations are capable of substantially modifying the initial structure of the disk (its thickness and distribution of eccentricities, in particular).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

>24% screen printed Cu contacted n-TOPCon solar cells with successful implementation of LECO process

In this paper, we report the successful fabrication of >24.0 % efficiency n-TOPCon Si solar cells with screen-printed, fire-through Cu contact to n-TOPCon on the rear side and Ag contacted boron emitter on the front side by implementing optimized firing and LECO conditions. The highest efficiency (24.3%) Cu contacted n-TOPCon cell in this study showed excellent cell performance parameters with V oc >730 mV, J sc of 41.1 mA/cm 2 and FF of 80.8%, resulting in an absolute efficiency gap of 0.2% between Cu-contacted and fully Ag contacted n-TOPCon cells (24.5%). The mini-module fabricated with the Cu contacted n-TOPCon cell showed excellent reliability and durability of open-circuit voltage (V oc ), pseudo fill factor (pFF) and efficiency after prolonged damp-heat tests. Such high efficiency screen printed Cu contacted n-TOPCon cells provide unique opportunity to replace very expensive Ag contact on n-TOPCon with cheaper screen printable Cu metal pastes.

14 SOLAR ENERGY↗
DOE OSTI2015

Deformation and Failure Mechanisms of Shape Memory Alloys

The goal of this research was to understand the fundamental mechanics that drive the deformation and failure of shape memory alloys (SMAs). SMAs are difficult materials to characterize because of the complex phase transformations that give rise to their unique properties, including shape memory and superelasticity. These phase transformations occur across multiple length scales (one example being the martensite-austenite twinning that underlies macroscopic strain localization) and result in a large hysteresis. In order to optimize the use of this hysteretic behavior in energy storage and damping applications, we must first have a quantitative understanding of this transformation behavior. Prior results on shape memory alloys have been largely qualitative (i.e., mapping phase transformations through cracked oxide coatings or surface morphology). The PI developed and utilized new approaches to provide a quantitative, full-field characterization of phase transformation, conducting a comprehensive suite of experiments across multiple length scales and tying these results to theoretical and computational analysis. The research funded by this award utilized new combinations of scanning electron microscopy, diffraction, digital image correlation, and custom testing equipment and procedures to study phase transformation processes at a wide range of length scales, with a focus at small length scales with spatial resolution on the order of 1 nanometer. These experiments probe the basic connections between length scales during phase transformation. In addition to the insights gained on the fundamental mechanisms driving transformations in shape memory alloys, the unique experimental methodologies developed under this award are applicable to a wide range of solid-to-solid phase transformations and other strain localization mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2011

A Solid-State Nanosecond Beam Kicker Modulator Based on the DSRD Switch

A fast solid-state beam kicker modulator is under development at the SLAC National Accelerator Laboratory. The program goal is to develop a modulator that will deliver 4 ns, {+-}5 kV pulses to the ATF2 damping ring beam extraction kicker. The kicker is a 50 {Omega}, bipolar strip line, 60 cm long, fed at the downstream end and terminated at the upstream end. The bunch spacing in the ring is 5.6 ns, bunches are removed from the back end of the train, and there is a gap of 103.6 ns before the next train. The modulator design is based on an opening switch topology that uses Drift Step Recovery Diodes as the opening switches. The design and results of the modulator development are discussed. There are many applications that benefit from very fast high power switching. However, at MW power levels and nanosecond time scales, solid state options are limited. One option, the Drift Step Recovery Diode (DSRD) has been demonstrated as capable of blocking thousands of volts and switching in nanosecond to sub-nanosecond ranges. When used as an opening switch, the DSRD exhibits a very fast turn off transient. The process is described in detail by its pioneers in [5,6]. In essence, charge is pumped into and then extracted from the DSRD under pulsed conditions. The turn off transient occurs precisely when the pumped charge is equal to the extracted charge and the DSRD is switched off. At the SLAC National Accelerator Laboratory, a DSRD is being used as an opening switch in the development of a fast kicker modulator. The modulator is designed to create {+-}5kV pulses with <1ns rise and fall time on a 50{Omega} strip line kicker. As is common in beam optics, the absence of power in the kicker before and after the pulse is very important. The entire {+-}5kV kicker modulator is composed of two identical 5kV pulsing circuits, each with its own DSRD component. This paper describes the modulator topology and the status of tests on one of the two 5kV pulse circuits.

43 PARTICLE ACCELERATORS↗
NASA NTRS1988

Longitudinal long-period dynamics of aerospace craft

Linear analyses are performed to examine the generic aspects of aerospace vehicle longitudinal long-period or trajectory modes of motion. The influence of Mach number, dynamic pressure, thrust-to-drag ratio, and propulsion system thrust laws on the longitudinal trajectory modes is presented in terms of phugoid frequency and damping and height mode stability. The results of these analyses are compared to flying qualities requirements where possible, and potential deficiencies in both the vehicle and the criteria are noted. A preliminary look at possible augmentation schemes to improve potential deficiencies is also presented. Interpretation of the practical consequences of the results is aided by typical time histories. Results indicate that propulsion system characteristics are the dominant influence on the longitudinal long-period flight dynamics of hypersonic aerospace craft. However, straightforward augmentation systems demonstrated the potential to accommodate these influences if the effects are included in the design process. These efforts may be hampered by a lack of design criteria for hypersonic aircraft.

Berry, Donald T.↗
DOE OSTI2024

Paper #50 Preliminary Sizing of Active Magnetic Bearings for sCO2 Waste-Heat Recovery Application

The team of Southwest Research Institute (SwRI) and GE Vernova (GE) is executing a project developing conceptual designs of high-temperature active magnetic bearings (AMBs) for sCO2 machinery applications. The goals of the project are to develop conceptual designs for radial and thrust AMBs capable of operating in sCO2 environments up to 1000°F. A waste-heat recovery (WHR) application with hermetic machinery is used as a reference case to apply AMBs. This application was previously investigated to compare hermetic machinery enabled by process-lubricated bearings and high-speed motors/generators with traditional machinery configurations using oil-lubricated bearings, gearboxes, and grid-frequency electric machines. In this paper, AMBs are sized for the WHR application machinery. Load capacity estimates are made using first-principle-derived formulas that consider operation at elevated temperatures. Estimates of linearized AMB system coefficients are also made to aid future controller development. Rotor models are developed that account for AMB rotor geometry and housing space requirements. Rotordynamics studies are performed to identify reasonable target values for closed-loop AMB stiffness and closed-loop AMB damping. These target values will be used in future control studies.

Lipham, Robert↗
DOE OSTI2023

Delineating magnetization dynamics in solution-processed doped yttrium iron garnet thin films

Here, in this work, thin films of ruthenium-doped and cerium-doped yttrium iron garnet were deposited on silicon using solgel chemistry. Doped YIG could be produced in phase pure form up to a precursor stoichiometry of Y 3 Ru 0.1 Fe 4.9 O 12 and Ce 0.7 Y 2.3 Fe 5 O 12 . Both dopants significantly increase the coercivity and anisotropy field of the materials either due to domain wall pinning or increased spin–orbit coupling from the dopant. To delineate these two effects, the dynamic magnetic properties were studied using strip line ferromagnetic resonance (FMR). The FMR linewidth was separated into intrinsic loss and inhomogeneous line broadening. Inhomogeneous line broadening was found to dominate the magnetic losses in all the films likely due to magnon scattering off grain boundaries, but the Gilbert damping remained fairly low. By comparing the two dopants, it was found that Gilbert damping increased more in Ce:YIG films than in Ru:YIG films. This finding was corroborated by changes in the anisotropy field of the films, indicating a larger contribution from spin–orbit coupling from cerium than from ruthenium. Surprisingly, while magnetic loss globally increased with higher substitution, adding a small amount of dopant actually reduced the inhomogeneous line broadening in both sets of films. This was corroborated by crystallite size. The damping in Ru:YIG also decreased with a small amount of the dopant, which has been predicted by Kittel for doped garnets. Thus, it follows that there is an ideal doping regime where solgel YIG can be doped at low levels without increasing magnetic loss.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The evolution dynamical processes of Ural blocking through the lens of local finite-amplitude wave activity budget analysis

Understanding the formation and evolution mechanisms of Ural blocking (UB) is of great importance for the prediction of UB and relevant extremes in east Asia. Using the 6-hourly ERA-Interim reanalysis data, this study quantifies the conservative and nonconservative processes in the lifecycle of UB through the lens of the hybrid Eulerian-Lagrangian local finite-amplitude wave activity (LWA) diagnostics. It is found that (i) as a wave activity source, eddy heat flux works to not only initiate the UB, but also prevent the wave activity of the blocking from dispersing downstream---the key characteristic of blocking; (ii) both the wave propagation and wave advection mechanisms are indispensable for the evolution of UB, playing a tug-of-war on the downstream development of wave activity; (iii) Throughout the lifespan of UB, diabatic heating provides the most important damping mechanism for the wave activity both upstream and downstream; and (IV) irreversible PV mixing appears to compensate the eddy PV flux during the wave breaking stage of blocking.

Blocking, wave activity, eddy-mean flow interactio↗