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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

On a new algorithm for time step integration of nonlinear systems

A new implicit algorithm for time step integration of finite element structural dynamic equations is presented. Convergence, stability and numerical damping properties are discussed. Due to the way nonlinear structural behavior is taken into account, the algorithm is expected to compare favorably with existing ones. Some simple numerical results are presented. A related explicit algorithm is also derived and shortly discussed.

Anderheggen, E.↗
NASA NTRS2006

The Complete Spectral Catalog of Bright BATSE Gamma-Ray Bursts

We present a systematic spectral analysis of 350 bright Gamma-Ray Bursts (GRBs) observed by the Burst and Transient Source Experiment (BATSE; approx. 30 keV - 2 MeV; including 17 short GRBs) with high energy and time resolution. Our sample was selected from the complete set of 2704 BATSE GRBs based on their energy fluence or peak photon flux values to assure good statistics. To obtain well-constrained, model-unbiased spectral parameters, a set of various photon models is used to fit each spectrum, and internal characteristics of each model are also investigated. A thorough analysis has been performed on 342 time-integrated and 8459 time-resolved burst spectra, and the effects of integration times in determining the spectral parameters are explored. The analysis results presented here provide the most detailed perspective of spectral aspects of the GRB prompt emission to date. Using the results, we study correlations among spectral parameters and spectral evolutions. The results of all spectral fits are available electronically in FITS format, from the High-Energy Astrophysics Science Archive Research Center (HEASARC).

Kaneko, Yuki↗
NASA NTRS2002

Pulmonary venous flow determinants of left atrial pressure under different loading conditions in a chronic animal model with mitral regurgitation

BACKGROUND: The aim of our study was to quantitatively compare the changes and correlations between pulmonary venous flow variables and mean left atrial pressure (mLAP) under different loading conditions in animals with chronic mitral regurgitation (MR) and without MR. METHODS: A total of 85 hemodynamic conditions were studied in 22 sheep, 12 without MR as control (NO-MR group) and 10 with MR (MR group). We obtained pulmonary venous flow systolic velocity (Sv) and diastolic velocity (Dv), Sv and Dv time integrals, their ratios (Sv/Dv and Sv/Dv time integral), mLAP, left ventricular end-diastolic pressure, and MR stroke volume. We also measured left atrial a, x, v, and y pressures and calculated the difference between v and y pressures. RESULTS: Average MR stroke volume was 10.6 +/- 4.3 mL/beat. There were good correlations between Sv (r = -0.64 and r = -0.59, P <.01), Sv/Dv (r = -0.62 and r = -0.74, P <.01), and mLAP in the MR and NO-MR groups, respectively. Correlations were also observed between Dv time integral (r = 0.61 and r = 0.57, P <.01) and left ventricular end-diastolic pressure in the MR and NO-MR groups. In velocity variables, Sv (r = -0.79, P <.001) was the best predictor of mLAP in both groups. The sensitivity and specificity of Sv = 0 in predicting mLAP 15 mm Hg or greater were 86% and 85%, respectively. CONCLUSION: Pulmonary venous flow variables correlated well with mLAP under altered loading conditions in the MR and NO-MR groups. They may be applied clinically as substitutes for invasively acquired indexes of mLAP to assess left atrial and left ventricular functional status.

Pulmonary Veins/physiopathology↗
DOE OSTI2021

National Opacity Program: Analysis of Opacity-relevant X-ray Emission Spectra (Milestone Report ID 7121)

We have produced high energy density iron plasmas at temperatures above 1 keV and electron densities exceeding 1023 cm -3 (~ 1 g/cm 3 ) using the Orion laser at the Atomic Weapons Establishment. These plasmas were created by irradiating 50 µm diameter layered targets with frequency doubled (λ = 527 nm), 1 ps laser pulses focused to a 100 µm diameter producing an irradiance of ~ 2 x 10 18 W/cm 2 . The buried layer targets consist of 160 nm iron sulfide (FeS), 60 nm potassium chloride (KCl), and 15 nm carbon. The combined layers are tamped on both sides with 3 µm of parylene-N. The x-ray emission from the plasma was measured using two time-resolved, and four time-integrated Bragg crystal spectrometers, as well as one time-integrated imaging system. One time-resolved x-ray spectrometer measured emission from L-shell transitions in highly charged iron, the other from K-shell transitions in helium-like S 14+ and hydrogen-like S 15+ . The time-integrated spectrometers are intensity-calibrated and measured emission from K-shell transitions in sulfur, potassium, chlorine, and both K-shell and L-shell transitions in iron. The density and temperature of the plasma were determined by modeling the x-ray spectra using different spectral and hydrodynamic modeling packages. A brief overview of the uncertainties associated with the measurements and models are presented. We also give an overview of our 1-D HYDRA-DCA radiation-hydrodynamics model and improvements for future work. Our results aid in assessing experimental uncertainties associated with plasma uniformity and with x-ray emission employed as diagnostics in opacity experiments at temperatures and densities not achievable elsewhere and represent a significant step in creating and diagnosing plasmas near LTE. These results are summarized as part of the completion requirements for milestone 7121

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

The action-integral and energy to explode short gold wires in ambient air

This paper is about electrically induced explosions of short (1 mm) and thin (38 μm diameter) gold bridgewires in ambient air and contrasts this behavior with that observed for longer wires in a vacuum used in applications such as Z-pinch systems. The action-integral (the time integral of the wire current squared) and energy-to-burst are measured using high current discharge systems. It is found that in contrast to some reports, the action-integral to burst is not a constant for a specific wire geometry and material but, instead, is a function of the rate of current change in the wire around the time of burst and the related metric of the current flux at burst. Furthermore, it is found that the accuracy of the constant action-integral to burst approximation is dependent on the discharge system used. Short gold wires such as these have relevancy to exploding bridgewire detonators.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRSDate not supplied

Picosecond Clock Synchronization Across A 7-Node Metropolitan Scale Quantum Network

Quantum networking protocols relying on interference and precise time-of-flight measurements require high precision clock synchronization. This study describes the design, implementation, and characterization of two optical time transfer methods in a metropolitan-scale quantum networking research testbed. The first technique called active electronic stabilization (ELSTAB), was able to achieve sub-picosecond time deviation (TDEV) at integration times between 1 s and 105s over multiple different fiber lengths of both underground and aerial deployed fiber. The second technique, White Rabbit-Precision Time Protocol (WR-PTP), was able to achieve 10-picosecond TDEV’s over similar fiber lengths at comparable integration times. Environmental fluctuations affected the stability of clock synchronization over deployed fiber. These fluctuations resulted in path delay gradients, chromatic dispersion, polarization drift, and optical power variations. The results from this study will inform future work in the development of compensation methods essential for enabling experimental research in developing practical quantum networking protocols.

synchronization↗
DOE OSTI2015

A new approach to calculate charge carrier transport mobility in organic molecular crystals from imaginary time path integral simulations

We present a new non-perturbative method to calculate the charge carrier mobility using the imaginary time path integral approach, which is based on the Kubo formula for the conductivity, and a saddle point approximation to perform the analytic continuation. The new method is first tested using a benchmark calculation from the numerical exact hierarchical equations of motion method. Imaginary time path integral Monte Carlo simulations are then performed to explore the temperature dependence of charge carrier delocalization and mobility in organic molecular crystals (OMCs) within the Holstein and Holstein-Peierls models. The effects of nonlocal electron-phonon interaction on mobility in different charge transport regimes are also investigated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Numerical coupling of aerosol emissions, dry removal, and turbulent mixing in the E3SM Atmosphere Model version 1 (EAMv1) – Part 2: A semi-discrete error analysis framework for assessing coupling schemes

Abstract. Part 1 (Wan et al., 2024) of this study discusses the motivation and empirical evaluation of a revision to the aerosol-related numerical process coupling in the atmosphere component of the Energy Exascale Earth System Model version 1 (EAMv1) to address the previously reported issue of strong sensitivity of the simulated dust aerosol lifetime and dry removal rate to the model's vertical resolution. This paper complements that empirical justification of the revised scheme with a mathematical justification leveraging a semi-discrete analysis framework for assessing the splitting error of process coupling methods. The framework distinguishes the error due to numerical splitting from the error due to the time integration method(s) used for each individual process. Such a distinction results in a framework that provides an intuitive understanding of the causes of the splitting error. The application of this framework to the dust life cycle in EAMv1 confirms (i) that the original EAMv1 scheme artificially strengthens the effect of dry removal processes and (ii) that the revised splitting reduces that artificial strengthening. While the error analysis framework is presented in the context of the dust life cycle in EAMv1, the framework can be broadly leveraged to evaluate process coupling schemes, both in other physical problems and for any number of processes. This framework will be particularly powerful when the various process implementations support a variety of time integration approaches. Whereas traditional local truncation error approaches require separate consideration of each combination of time integration methods, this framework enables evaluation of coupling schemes independent of particular time integration approaches for each process while still allowing for the incorporation of these specific time integration errors if so desired. The framework also explains how the splitting error terms result from (i) the integration of individual processes in isolation from other processes and (ii) the choices of input state and time step size for the isolated integration of processes. Such a perspective has the potential for the rapid development of alternative coupling approaches that utilize knowledge both about the desired accuracy and about the computational costs of individual processes.

58 GEOSCIENCES↗
DOE OSTI2019

Bridge-bursting and the action-integral in exploding bridge-wire (EBW) detonators

Methods of simulating the electrical characteristics of exploding bridge-wire detonators using only inert materials are reported. Specifically, it is found that both pressed finely powdered sucrose (confectioners sugar) and 3 µm aluminum oxide powder match the signals measured in a real EBW detonator with PETN fill. The exact pressing density of the inert powder is found not to affect to the measured electrical signals. Additionally, the action-integral (the time integral of bridge current squared) and energy-to-burst are measured for the same gold bridge design with several capacitor discharge units at different charge voltages and inductances as well as pseudo-constant current fireset made from charged coaxial-cables. It is found that in contrast to some reports, the action-integral to burst is not a constant for a specific bridge geometry and material, but instead is a function of the rate of current change in the bridge around the time of burst. This is explained by the confining effects of bridge-wire inertia affecting the rapid expansion of the bridge around burst time and hence the dynamic resistance.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Preconditioned conjugate-gradient methods for low-speed flow calculations

An investigation is conducted into the viability of using a generalized Conjugate Gradient-like method as an iterative solver to obtain steady-state solutions of very low-speed fluid flow problems. Low-speed flow at Mach 0.1 over a backward-facing step is chosen as a representative test problem. The unsteady form of the two dimensional, compressible Navier-Stokes equations is integrated in time using discrete time-steps. The Navier-Stokes equations are cast in an implicit, upwind finite-volume, flux split formulation. The new iterative solver is used to solve a linear system of equations at each step of the time-integration. Preconditioning techniques are used with the new solver to enhance the stability and convergence rate of the solver and are found to be critical to the overall success of the solver. A study of various preconditioners reveals that a preconditioner based on the Lower-Upper Successive Symmetric Over-Relaxation iterative scheme is more efficient than a preconditioner based on Incomplete L-U factorizations of the iteration matrix. The performance of the new preconditioned solver is compared with a conventional Line Gauss-Seidel Relaxation (LGSR) solver. Overall speed-up factors of 28 (in terms of global time-steps required to converge to a steady-state solution) and 20 (in terms of total CPU time on one processor of a CRAY-YMP) are found in favor of the new preconditioned solver, when compared with the LGSR solver.

Ajmani, Kumud↗
NASA NTRS1993

Preconditioned Conjugate Gradient methods for low speed flow calculations

An investigation is conducted into the viability of using a generalized Conjugate Gradient-like method as an iterative solver to obtain steady-state solutions of very low-speed fluid flow problems. Low-speed flow at Mach 0.1 over a backward-facing step is chosen as a representative test problem. The unsteady form of the two dimensional, compressible Navier-Stokes equations are integrated in time using discrete time-steps. The Navier-Stokes equations are cast in an implicit, upwind finite-volume, flux split formulation. The new iterative solver is used to solve a linear system of equations at each step of the time-integration. Preconditioning techniques are used with the new solver to enhance the stability and the convergence rate of the solver and are found to be critical to the overall success of the solver. A study of various preconditioners reveals that a preconditioner based on the lower-upper (L-U)-successive symmetric over-relaxation iterative scheme is more efficient than a preconditioner based on incomplete L-U factorizations of the iteration matrix. The performance of the new preconditioned solver is compared with a conventional line Gauss-Seidel relaxation (LGSR) solver. Overall speed-up factors of 28 (in terms of global time-steps required to converge to a steady-state solution) and 20 (in terms of total CPU time on one processor of a CRAY-YMP) are found in favor of the new preconditioned solver, when compared with the LGSR solver.

Ajmani, Kumud↗
DOE OSTI2021

Three-dimensional reconstruction of neutron, gamma-ray, and x-ray sources using a cylindrical-harmonics expansion

Inertial confinement fusion capsule implosions produce neutron, gamma-ray, and x-ray emission, which are recorded by a variety of detectors, both time integrated and time resolved, to determine the performance of the implosion. Further, two-dimensional emission images from multiple directions can now be combined to infer three-dimensional structures in the implosion, such as the distribution of thermonuclear fuel density, carbon ablator, and impurities. Because of the cost and complexity of the imaging systems, however, only a few measurements can be made, so reconstructions of the source must be made from a limited number of views. Here, a cylindrical-harmonics decomposition technique to reconstruct the three-dimensional object from two views in the same symmetry plane is presented. In the limit of zero order, this method recovers the Abel inversion method. The detailed algorithms used for this characterization and the resulting reconstructed neutron source from an experiment collected at the National Ignition Facility are presented.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

High‐order methods for low Reynolds number flows around moving obstacles based on universal meshes

Summary We propose a family of methods for simulating two‐dimensional incompressible, low Reynolds number flow around a moving obstacle whose motion is prescribed. The methods make use of a universal mesh: a fixed background mesh that adapts to the geometry of the immersed obstacle at all times by adjusting a few elements in the neighborhood of the obstacle's boundary. The resulting mesh provides a conforming triangulation of the fluid domain over which discretizations of any desired order of accuracy in space and time can be constructed using standard finite element spaces together with off‐the‐shelf time integrators. We demonstrate the approach by using Taylor‐Hood elements to approximate the fluid velocity and pressure. To integrate in time, we consider implicit Runge‐Kutta schemes as well as a fractional step scheme. We illustrate the methods and study their convergence numerically via examples that involve flow around obstacles that undergo prescribed deformations. Copyright © 2015 John Wiley & Sons, Ltd.

Gawlik, Evan S.↗
DOE OSTI2026

Efficient and flexible multirate temporal adaptivity

In this work we present two new families of multirate time step adaptivity controllers, that are designed to work with embedded multirate infinitesimal (MRI) time integration methods for adapting time steps when solving problems with multiple time scales. We compare these controllers against competing approaches on two benchmark problems, showing that the proposed methods offer dramatically improved performance and flexibility. The combination of embedded MRI methods and the proposed controllers enable adaptive simulations of problems with a potentially arbitrary number of time scales, achieving high accuracy while maintaining low computational cost. Additionally, we introduce a new set of embeddings for the family of explicit multirate exponential Runge–Kutta (MERK) methods of orders 2 through 5, resulting in the first-ever fifth-order embedded MRI method. Finally, we compare the performance of a wide range of embedded MRI methods on our benchmark problems to provide guidance on how to select an appropriate MRI method and multirate controller.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Hydrogen plasma dynamics in the spherical theta pinch plasma target for heavy ion stripping

Due to the superior ability of dense and highly ionised plasmas to ionise penetrating heavy ion beams to degrees beyond those reachable by common gas strippers, many experiments have been performed to find suitable plasma generators for this application. In the field of gas discharges, mainly z-pinch devices have been investigated so far, which are known to be limited by the nonlinear focusing effects of the plasma columns sustaining current and by electrode erosion. The spherical theta pinch has therefore been proposed as a substitution for the z-pinch, promising progress by inductive rather than capacitive coupling and displacement of the outer magnetic field by the dense, diamagnetic discharge plasma. As yet mainly experiments with argon/hydrogen mixture gas have been performed, which is not suitable for the application as a plasma stripper, this paper describes the first detailed analysis of the plasma parameters and dynamics of a hydrogen plasma created by the spherical theta pinch. These include the time integrated and time resolved electron density, the dynamics of the plasma in the discharge vessel, the comparison with the argon dominated plasma, and an outlook to reachable characteristics with similar devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Staggered solution procedures for multibody dynamics simulation

The numerical solution procedure for multibody dynamics (MBD) systems is termed a staggered MBD solution procedure that solves the generalized coordinates in a separate module from that for the constraint force. This requires a reformulation of the constraint conditions so that the constraint forces can also be integrated in time. A major advantage of such a partitioned solution procedure is that additional analysis capabilities such as active controller and design optimization modules can be easily interfaced without embedding them into a monolithic program. After introducing the basic equations of motion for MBD system in the second section, Section 3 briefly reviews some constraint handling techniques and introduces the staggered stabilized technique for the solution of the constraint forces as independent variables. The numerical direct time integration of the equations of motion is described in Section 4. As accurate damping treatment is important for the dynamics of space structures, we have employed the central difference method and the mid-point form of the trapezoidal rule since they engender no numerical damping. This is in contrast to the current practice in dynamic simulations of ground vehicles by employing a set of backward difference formulas. First, the equations of motion are partitioned according to the translational and the rotational coordinates. This sets the stage for an efficient treatment of the rotational motions via the singularity-free Euler parameters. The resulting partitioned equations of motion are then integrated via a two-stage explicit stabilized algorithm for updating both the translational coordinates and angular velocities. Once the angular velocities are obtained, the angular orientations are updated via the mid-point implicit formula employing the Euler parameters. When the two algorithms, namely, the two-stage explicit algorithm for the generalized coordinates and the implicit staggered procedure for the constraint Lagrange multipliers, are brought together in a staggered manner, they constitute a staggered explicit-implicit procedure which is summarized in Section 5. Section 6 presents some example problems and discussions concerning several salient features of the staggered MBD solution procedure are offered in Section 7.

Park, K. C.↗
NASA NTRS1994

Numerical Simulations of Self-Focused Pulses Using the Nonlinear Maxwell Equations

This paper will present results in computational nonlinear optics. An algorithm will be described that solves the full vector nonlinear Maxwell's equations exactly without the approximations that are currently made. Present methods solve a reduced scalar wave equation, namely the nonlinear Schrodinger equation, and neglect the optical carrier. Also, results will be shown of calculations of 2-D electromagnetic nonlinear waves computed by directly integrating in time the nonlinear vector Maxwell's equations. The results will include simulations of 'light bullet' like pulses. Here diffraction and dispersion will be counteracted by nonlinear effects. The time integration efficiently implements linear and nonlinear convolutions for the electric polarization, and can take into account such quantum effects as Kerr and Raman interactions. The present approach is robust and should permit modeling 2-D and 3-D optical soliton propagation, scattering, and switching directly from the full-vector Maxwell's equations. Abstract of a proposed paper for presentation at the meeting NONLINEAR OPTICS: Materials, Fundamentals, and Applications, Hyatt Regency Waikaloa, Waikaloa, Hawaii, July 24-29, 1994, Cosponsored by IEEE/Lasers and Electro-Optics Society and Optical Society of America

Goorjian, Peter M.↗
NASA NTRS2013

Inductive Pulsed Plasma Thruster Development and Testing at NASA-MSFC

THE inductive pulsed plasma thruster (IPPT) is an electrodeless space propulsion device where a capacitor is charged to an initial voltage and then discharged producing a high current pulse through a coil. The field produced by this pulse ionizes propellant, inductively driving current in a plasma located near the face of the coil. Once the plasma is formed it can be accelerated and expelled at a high exhaust velocity by the electromagnetic Lorentz body force arising from the interaction of the induced plasma current and the magnetic field produced by the current in the coil. In the present work, we present a summary of the IPPT research and development conducted at NASA's Marshall Space Flight Center (MSFC). As a higher-power, still relatively low readiness level system, there are many issues associated with the eventual deployment and use of the IPPT as a primary propulsion system on spacecraft that remain to be addressed. The present program aimed to fabricate and test hardware to explore how these issues could be addressed. The following specific areas were addressed within the program and will be discussed within this paper. a) Conical theta-pinch IPPT geometry thruster configuration. b) Repetition-rate multi-kW thruster pulsing. c) Long-lifetime pulsed gas valve. d) Fast pulsed gas valve driver and controller. e) High-voltage, repetitive capacitor charging power processing unit. During the course of testing, a number of specific tests were conducted, including several that, to our knowledge, have either never been previously conducted (such as multi-KW repetition-rate operation) or have not been performed since the early 1990s (direct IPPT thrust measurements).2 Conical theta-pinch IPPT thrust stand measurements are presented in Fig. 1 while various time-integrated and time

Polzin, Kurt A.↗