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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 433 records · Page 24

All sources NASA NTRS DOE OSTI

DOE OSTI2020

Setting operating points for circuits in an integrated circuit chip using an integrated voltage regulator power loss model

An apparatus includes an integrated circuit chip with a set of circuits having two or more subsets of circuits; an external voltage regulator separate from the integrated circuit chip; two or more integrated voltage regulators on the integrated circuit chip that each provide an input voltage to a respective subset of the circuits; and a controller. The controller determines, using an integrated voltage regulator power loss model, an electrical power loss for the integrated voltage regulators for a first combination of operating points for the subsets of the circuits. The controller then determines, based on the electrical power loss, a second combination of operating points for the subsets of the circuits that includes an adjustment to an operating point for at least one of the subsets of the circuits that compensates for an electrical power loss of the corresponding integrated voltage regulator. The controller sets an operating point of each of the subsets of the circuits based on the second combination of operating points.

42 ENGINEERING↗

DOE OSTI2021

Geometrical defect detection for additive manufacturing with machine learning models

This study proposed a scheme based on Machine Learning (ML) models to detect geometric defects of additively manufactured objects. The ML models are trained with synthetic 3D point clouds with defects and then applied to detect defects in actual production. Using synthetic 3D point clouds rather than experimental data could save a huge amount of training time and costs associated with many prints for each design. Besides distance differences of individual points between source and target point clouds, this scheme uses a new concept called “patch” to capture macro-level information about nearby points for ML training and implementation. Numerical comparisons of prediction results on experimental data with different shapes showed that the proposed scheme outperformed the existing Z-difference method in the literature. Five ML methods (Bagging of Trees, Gradient Boosting, Random Forest, K-nearest Neighbors and Linear Supported Vector Machine) were compared under various conditions, such as different point cloud densities and defect sizes. Bagging and Random Forest were found the two best models regarding predictability; and the right patch size was found to be at 20. The proposed ML-based scheme is applicable to in-situ defect detection during additive manufacturing with the aid of a proper 3D data acquisition system.

Additive manufacturing↗

DOE OSTI2023

Interpolation Methods to Enable Fast and Accurate EMT Simulation of PV Inverters

In this paper, interpolation methods to enable fast simulation of photovoltaic (PV) inverters are proposed. The interpolation methods are based on the event-driven interpolating method that can be introduced in the simulation model to run the model at a higher timestep while maintaining accuracy. The proposed methods are tested on a neutral point clamp (NPC) converter and a two-level converter (2LC) that are typically used in large-scale PV plants. The interpolation methods are integrated into the NPC and 2LC simulation models in PSCAD/Fortran and RSCAD C platforms. These models are tested at different simulation timesteps in off-line and real-time simulation platforms PSCAD and RSCAD respectively.

Marthi, Phani Ratna Vanamali↗

DOE OSTI2024

Revealing the landscape of globally color-dual multi-loop integrands

Abstract We report on progress in understanding how to construct color-dual multi-loop amplitudes. First we identify a cubic theory, semi-abelian Yang-Mills, that unifies many of the color-dual theories studied in the literature, and provides a prescriptive approach for constructingD-dimensional color-dual numerators through one-loop directly from Feynman rules. By a simple weight counting argument, this approach does not further generalize to two-loops. As a first step in understanding the two-loop challenge, we use aD-dimensional color-dual bootstrap to successfully construct globally color-duallocaltwo-loop four-point nonlinear sigma model (NLSM) numerators. The double-copy of these NLSM numerators with themselves, pure Yang-Mills, and$$\mathcal{N}$$= 4 super-Yang-Mills correctly reproduce the known unitarity constructed integrands of special Galileons, Born-Infeld theory, and Dirac-Born-Infeld-Volkov-Akulov theory, respectively. Applying our bootstrap to two-loop four-point pure Yang-Mills, we exhaustively search the space of local numerators and find that it fails to satisfy global color-kinematics duality, completing a search previously initiated in the literature. We pinpoint the failure to the bowtie unitarity cut, and discuss a path forward towards non-local construction of color-dual integrands at generic loop order.

Physics↗

NASA NTRS2017

Performance of the Widely-Used CFD Code OVERFLOW on the Pleides Supercomputer

Computational performance studies were made for NASA's widely used Computational Fluid Dynamics code OVERFLOW on the Pleiades Supercomputer. Two test cases were considered: a full launch vehicle with a grid of 286 million points and a full rotorcraft model with a grid of 614 million points. Computations using up to 8000 cores were run on Sandy Bridge and Ivy Bridge nodes. Performance was monitored using times reported in the day files from the Portable Batch System utility. Results for two grid topologies are presented and compared in detail. Observations and suggestions for future work are made.

Widely Used↗

NASA NTRS2007

Small Scale Response and Modeling of Periodically Forced Turbulence

The response of the small scales of isotropic turbulence to periodic large scale forcing is studied using two-point closures. The frequency response of the turbulent kinetic energy and dissipation rate, and the phase shifts between production, energy and dissipation are determined as functions of Reynolds number. It is observed that the amplitude and phase of the dissipation exhibit nontrivial frequency and Reynolds number dependence that reveals a filtering effect of the energy cascade. Perturbation analysis is applied to understand this behavior which is shown to depend on distant interactions between widely separated scales of motion. Finally, the extent to which finite dimensional models (standard two-equation models and various generalizations) can reproduce the observed behavior is discussed.

Bos, Wouter↗

DOE OSTI2022

Cyber-Attack Detection for Active Neutral Point Clamped (ANPC) Photovoltaic (PV) Converter using Kalman Filter

With the upgrading of communication technology, cyber threats to power converters are increasing. In this paper, a model-based cyber-attack detection methodology is proposed for the interleaved Active neutral point clamped (ANPC) Photovoltaic (PV) converter. The proposed methodology identifies cyber-attacks using two estimations based on the Kalman filter and the state-space model of the ANPC PV converter. The residual between the two estimations is analyzed from a statistical perspective. Based on the Cumulative Sum (CUSUM) Control Chart, the standard errors shift of the residual is used to identify cyber-attacks. Besides, to validate the feasibility of the proposed methodology, several conditions are considered in the simulation, including white noise in the sensor, irradiance variation, and cyber-attacks in the PV converter. Furthermore, the simulation result demonstrates the proposed method can identify cyber-attacks in the ANPC PV converter.

14 SOLAR ENERGY↗

NASA NTRS2012

Modeling of Aerobrake Ballute Stagnation Point Temperature and Heat Transfer to Inflation Gas

A trailing Ballute drag device concept for spacecraft aerocapture is considered. A thermal model for calculation of the Ballute membrane temperature and the inflation gas temperature is developed. An algorithm capturing the most salient features of the concept is implemented. In conjunction with the thermal model, trajectory calculations for two candidate missions, Titan Explorer and Neptune Orbiter missions, are used to estimate the stagnation point temperature and the inflation gas temperature. Radiation from both sides of the membrane at the stagnation point and conduction to the inflating gas is included. The results showed that the radiation from the membrane and to a much lesser extent conduction to the inflating gas, are likely to be the controlling heat transfer mechanisms and that the increase in gas temperature due to aerodynamic heating is of secondary importance.

Bahrami, Parviz A.↗

DOE OSTI2018

Logarithmic Finite-Size Correction in Non-neutral Two-Component Plasma on Sphere

We consider a general two-component plasma of classical pointlike charges +e (e is say the elementary charge) and −Ze (valency Z=1,2,…), living on the surface of a sphere of radius R. The system is in thermal equilibrium at the inverse temperature β, in the stability region against collapse of oppositely charged particle pairs βe{sup 2}<2/Z. We study the effect of the system excess charge Qe on the finite-size expansion of the (dimensionless) grand potential βΩ. By combining the stereographic projection of the sphere onto an infinite plane, the linear response theory and the planar results for the second moments of the species density correlation functions we show that for any βe{sup 2}<2/Z the large-R expansion of the grand potential is of the form βΩ∼A{sub V}R{sup 2}+[χ/6−β(Qe){sup 2}/2]ln R, where A{sub V} is the non-universal coefficient of the volume (bulk) part and the Euler number of the sphere χ=2. The same formula, containing also a non-universal surface term proportional to R, was obtained previously for the disc domain (χ=1), in the case of the symmetric (Z=1) two-component plasma at the collapse point βe{sup 2}=2 and the jellium model (Z→0) of identical e-charges in a fixed neutralizing background charge density at any coupling βe{sup 2} being an even integer. Our result thus indicates that the prefactor to the logarithmic finite-size expansion does not depend on the composition of the Coulomb fluid and its non-universal part −β(Qe){sup 2}/2 is independent of the geometry of the confining domain.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

Cosmological constraints on Λ(α)CDM models with time-varying fine structure constant

We study the Λ(α)CDM models with Λ(α) being a function of the time-varying fine structure constant α. We give a close look at the constraints on two specific Λ(α)CDM models with one and two model parameters, respectively, based on the cosmological observational measurements along with 313 data points for the time-varying α. We find that the model parameters are constrained to be around 10{sup −4}, which are similar to the results discussed previously but more accurately.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Robust d x 2 - y 2 -wave superconductivity of infinite-layer nickelates

Motivated by the recent observation of superconductivity in strontium-doped NdNiO 2 , we study the superconducting instabilities in this system from various vantage points. Starting with first-principles calculations, we construct two distinct tight-binding models, a simpler single-orbital as well as a three-orbital model, both of which capture the key low-energy degrees of freedom to varying degrees of accuracy. We study superconductivity in both models using the random phase approximation. We then analyze the problem at stronger coupling, and study the dominant pairing instability in the associated t-J model limit. Finally, in all instances, the dominant pairing tendency is in the d x 2 -y 2 channel, analogous to the cuprate superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Ab initio based examination of the kinetics and thermodynamics of oxygen in Fe-Cr alloys

The behavior of oxygen in Fe-Cr binary alloys is important to understand for a variety of applications including fuel cell interconnects and nuclear energy systems. In this work, we performed an ab initio investigation of the binding of oxygen in the entire compositional range of Fe-Cr at minima and saddles. This database was subsequently used to parametrize concentration-dependent local cluster expansions which were utilized to examine the kinetics of oxygen transport in the alloy and the thermodynamics of the system. The behavior of oxygen in the alloy system was investigated using our cluster expansion model and a convex hull diagram was recorded. The most favorable composition for the incorporation of oxygen was found to occur at 70% Cr. The dependence of the oxygen solution energy on the Cr occupation of the nearest neighbor shells was carefully characterized. It was determined that the third nearest neighbor Cr occupation was unfavorable and that, generally speaking, the first and second nearest neighbor shell Cr occupation was favored with a few exceptions. Kinetic Monte Carlo models at dilute oxygen levels were performed using two models [a kinetically resolved activation (kRA) model and a cluster expansion model for the saddle points]. The models qualitatively agreed with the observed trends in the literature which reported a decrease in diffusivity at dilute Cr levels, but the models predicted different behaviors beyond the dilute Cr limit. Finally, using grand canonical Monte Carlo, we further examined the thermodynamics of oxygen incorporation into the alloy. Furthermore, our results offer new insight into the behavior of oxygen in Fe-Cr alloys that have ramifications on the early stages of the corrosive behavior of the material.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Topological and nodal superconductor kagome magnesium triboride

Recently the kagome compounds have inspired enormous interest and made some great progress such as in the field of superconductivity and topology. Here we predict a different kagome magnesium triboride (Mg⁢B 3 ) superconductor with a calculated T c ~ 12.2K and T c ~ 15.4 K by external stress, the potentially highest among the reported diverse kagome-type superconductors. We reveal its various exotic physical properties including the van Hove singularity, flat-band, multiple Dirac points, and nontrivial topology. The system can be described by a two-band model with highly anisotropic superconducting gaps on Fermi surfaces. Its topological and nodal superconducting nature is unveiled by a recently developed symmetry indicators method. In conclusion, our results suggest that Mg⁢B 3 can be a new platform to study exotic physics in the kagome structure, and pave a way to seek for more superconductors and topological materials with XY 3 -type kagome lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Dynamic Mode Decomposition for Compressive System Identification

Dynamic mode decomposition has emerged as a leading technique to identify spatiotemporal coherent structures from high-dimensional data, benefiting from a strong connection to nonlinear dynamical systems via the Koopman operator. In this work, we integrate and unify two recent innovations that extend DMD to systems with actuation [Proctor et al., 2016] and systems with heavily subsampled measurements [Brunton et al., 2015]. When combined, these methods yield a novel framework for compressive system identification [code is publicly available at: https://github.com/zhbai/cDMDc]. It is possible to identify a low-order model from limited input-output data and reconstruct the associated full-state dynamic modes with compressed sensing, adding interpretability to the state of the reduced-order model. Moreover, when full-state data is available, it is possible to dramatically accelerate downstream computations by first compressing the data. We demonstrate this unified framework on two model systems, investigating the effects of sensor noise, different types of measurements (e.g., point sensors, Gaussian random projections, etc.), compression ratios, and different choices of actuation (e.g., localized, broadband, etc.). In the first example, we explore this architecture on a test system with known low-rank dynamics and an artificially inflated state dimension. The second example consists of a real-world engineering application given by the fluid flow past a pitching airfoil at low Reynolds number. This example provides a challenging and realistic test-case for the proposed method, and results demonstrate that the dominant coherent structures are well characterized despite actuation and heavily subsampled data.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS1980

Analytical study of twin-jet shielding development of a 3-dimensional model

The solution for a point source impinging on a cylinder of heated flow is presented. The indefinite integral is solved approximately using a saddle of point method. Comparison of the three-dimensional model to a previously obtained two-dimensional model of twin jet noise indicate the the approximate solution of the integral is valid. The model was analyzed to differentiate among the mechanims of shielding. Zone in which diffraction and transmission dominate are identified. The model was found to compare to experimental shielding results.

Gerhold, C. H.↗

NASA NTRS1983

Staffing implications of software productivity models

The attributes of software project staffing and productivity implied by equating the effects of two popular software models in a small neighborhood of a given effort-duration point are investigated. The first model presupposes that organizational productivity decreases as a function of the project staff size due to interfacing and intercommunication. The second, the so-called software equation, relates the product size to effort and duration through a power law tradeoff formula. The conclusions that may be reached by assuming that both of these describe project behavior, the former as a global phenomenon and the latter as a localized effect in a small neighborhood of a given effort duration point, are that (1) there is a calculable maximum effective staff level, which, if exceeded, reduces the project production rate, (2) there is a calculable maximum extent to which effort and time may be traded effectively, (3) it becomes ineffective in a practical sense to expend more than an additional 25 to 50% of resources in order to reduce delivery time, and (4) the team production efficiency can be computed directly from the staff level, the slope of the intercommunication loss function, and the ratio of exponents in the software equation.

Tausworthe, R. C.↗

NASA NTRS1985

A computational model for a regenerator

This paper concerns a numerical model of a regenerator running at very low temperatures. The model consists of the usual three equations for a compressible fluid with an additional equation for a matrix temperature. The main difficulty with the model is the very low Mach number (approximately 1.E-3). The divergence of the velocity is not small, the pressure divergence is small, and the pressure fluctuation in time is not small. An asymptotic expansion based on the bounded derivative method of Kreiss is used to give a reduced model which eliminates acoustic waves. The velocity is then determined by a two-point boundary value problem which does not contain a time derivative. The solution obtained from the reduced system is compared with the numerical solution of the original system.

Gary, J.↗

NASA NTRS1987

The dynamics and control of large flexible space structures X, part 1

The effect of delay in the control system input on the stability of a continuously acting controller which is designed without considering the delay is studied. The stability analysis of a second order plant is studied analytically and verified numerically. For this example it is found that the system becomes unstable for a delay which is equivalent to only 16 percent of its natural period of motion. It is also observed that even a small amount of natural damping in the system can increase the amount of delay that can be tolerated before the onset of instability. The delay problem is formulated in the discrete time domain and an analysis procedure suggested. The maximum principle from optimal control theory is applied to minimize the time required for the slewing of a general rigid spacecraft. The slewing motion need not be restricted to a single axis maneuver. The minimum slewing time is calculated based on a quasi-linearization algorithm for the resulting two point boundary value problem. Numerical examples based on the rigidized in-orbit model of the SCOLE also include the more general reflector line-of-sight slewing maneuvers.

Bainum, Peter M.↗