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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Differentiable Multiphysics Codes: A Breakthrough Technology for Simulation and Computing

This document summarizes the findings of a strategic planning exercise commissioned by the Weapons Simulation and Computing, Computational Physics (WSC/CP) program at the Lawrence Livermore National Laboratory (LLNL) in FY24. During the year, the committee met with multiple stakeholder communities to gather input, opinions, suggestions and concerns which have been incorporated throughout this document. The key findings from this exercise are summarized: • The development of multiphysics modelling and simulation (mod/sim) codes and software technologies, their deployment on exascale compute platforms, and their broad adoption across the NNSA is a major success of the Advanced Simulation and Computing (ASC) program and the Exascale Computing Project (ECP). Sustained investment in these core technologies is essential. • Today’s state of the art involves running ensembles of O(100K) simulations to perform uncertainty quantification (UQ) and design studies using multiple statistical methods such as Bayesian optimization to understand sensitivities of our models and explore parameterized design spaces. Even with exascale computing, we are practically limited to O(10) parameters in these studies since the number of simulations required to sample the space scales exponentially with the number of design parameters. • The data from these simulation ensembles is increasingly being used to train machine learned (ML) surrogates (or reduced order models, ROMs) which can then be used for optimization or real time design exploration. However, the trained surrogates are still limited in the number of parameters they can represent due to the sampling limitations previously noted. • Augmenting our suite of integrated multiphysics simulation codes, both current and emerging, with the ability to compute gradients (solution derivatives) of arbitrary simulation outputs with respect to (some or all) simulation inputs would be a breakthrough technology, opening the door to a new era of efficient and automated inverse design based on verified and validated mod/sim capabilities. • This capability, which we refer to as differentiable multiphysics codes (DMCs), would revolutionize both UQ and optimization studies by breaking the curse of dimensionality that presently limits our “gradient-free” ensemble based computing approach. A similar breakthrough occurred in the AI/ML community once the ability to compute gradients of arbitrary loss functions using back-propagation became commonplace. Gradient information from the multiphysics codes can also be used to dramatically improve the efficiency and scale of training of ML/ROM surrogates for rapid assessments. • Achieving this in our suite of codes will be a grand challenge, similar to the amount of effort that was required to transition from CPU to GPU computing. It will require buy-in from the entire WSC/CP program and beyond, including all integrated codes, physics and engineering models, third-party library dependencies and performance portability abstractions. It will also require investment in research and development of numerical methods for computing adjoints of coupled physics across multiple adaptively refined moving meshes and of stochastic (Monte Carlo) and mesh free (SPH) methods. • New software and numerical techniques, largely pioneered by the AI/ML community, make this feasible. Chief among these is automatic differentiation (AD), the ability to employ AD at point-wise locations in a physics calculation (instead of traditional black-box approaches) and the ability to perform “back-propagation in time” (or reverse mode AD) for non-linear partial differential equations (PDEs). Fundamentally, the conclusion of this strategic planning exercise is that the time is right to undertake a large scale effort in WSC, centered on the existing integrated codes, to continue the natural evolution of mod/sim in the age of AI/ML. Instead of attempting to replace mod/sim with purely data driven AI/ML models, we believe the key to success is to integrate AI/ML by building on top of the decades of hard-won knowledge and the verified/validated multiphysics modelling capability that is the hallmark of the ASC program.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2016

Documenting the NASA Armstrong Flight Research Center Oblate Earth Simulation Equations of Motion and Integration Algorithm

A desire for more complete documentation of the National Aeronautics and Space Administration (NASA) Armstrong Flight Research Center (AFRC), Edwards, California legacy code used in the core simulation has led to this e ort to fully document the oblate Earth six-degree-of-freedom equations of motion and integration algorithm. The authors of this report have taken much of the earlier work of the simulation engineering group and used it as a jumping-o point for this report. The largest addition this report makes is that each element of the equations of motion is traced back to first principles and at no point is the reader forced to take an equation on faith alone. There are no discoveries of previously unknown principles contained in this report; this report is a collection and presentation of textbook principles. The value of this report is that those textbook principles are herein documented in standard nomenclature that matches the form of the computer code DERIVC. Previous handwritten notes are much of the backbone of this work, however, in almost every area, derivations are explicitly shown to assure the reader that the equations which make up the oblate Earth version of the computer routine, DERIVC, are correct.

integrators↗
DOE OSTI2020

Corrigendum: Thermal dynamics in the flux-coordinate independent turbulence code GRILLIX

Here, we have discovered that one of the original articles findings, that the actual choice of the dimensionless parameter χ ∥i0 for the ion heat conductivity seemed to play no role for the simulation results, was not physical. Instead, due to a mistake in the handling of input parameters, χ ∥i0 was actually not used in the code – the dimensionless electron heat conductivity χ ∥e0 was used instead.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Late Prompt Fission Gamma Rays from 235 U(n,f) and 252 Cf(sf)

Two measurements of fission γ rays were performed with the DANCE and NEUANCE arrays using the reactions 235 U(n, f) and 252 Cf(sf). Utilizing the fast time response of the detectors and a method for estimating the accidental background, we obtained the energy spectrum of the late prompt fission γ rays as a function of the time since fission. The experimental results are compared with predictions of the code CGMF folded with GEANT4 simulations of the detector response.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

The diphoton $$q_T$$ spectrum at N$$^3$$LL$$^\prime $$ + NNLO

Abstract We present a $$q_T$$ q T -resummed calculation of diphoton production at order N $$^3$$ 3 LL $$^\prime $$ ′ + NNLO. To reach the primed level of accuracy we have implemented the recently published three-loop $${\mathcal {O}}(\alpha _s^3)$$ O ( α s 3 ) virtual corrections in the $$q\bar{q}$$ q q ¯ channel and the three-loop transverse momentum dependent beam functions and combined them with the existing infrastructure of , a code performing resummation at order N $${}^3$$ 3 LL. While the primed predictions are parametrically not more accurate, one typically observes from lower orders and other processes that they are the dominant effect of the next order. We include in both the $$q\bar{q}$$ q q ¯ and loop-induced gg channel the hard contributions consistently together at order $$\alpha _s^3$$ α s 3 and find that the resummed $$q\bar{q}$$ q q ¯ channel without matching stabilizes indeed. Due to large matching corrections and large contributions and uncertainties from the gg channel, the overall improvements are small though. We furthermore study the effect of hybrid-cone photon isolation and hard-scale choice on our fully matched results to describe the ATLAS $$\text {8}$$ 8 TeV data and find that the hybrid-cone isolation worsens agreement at small $$q_T$$ q T compared to smooth-cone isolation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1983

Computer simulation of auroral kilometric radiation

An investigation is carried out of the linear amplification and nonlinear saturation of electromagnetic waves associated with two components of electrons consisting of a cold Maxwellian background and a weakly relativistic population of electrons possessing a loss-cone distribution. The goal is to understand the mechanism responsible for the production of auroral kilometric radiation (AKR). A relativistic 1-2/2 dimensional electromagnetic particle simulation code is used in studying an initial value problem modeling the AKR source region. The simulation makes it possible to follow the growth of all modes of radiation, including the ordinary mode (O-mode), slow extraordinary mode (Z-mode), whistler mode and fast extraordinary mode (X-mode), past the point of saturation.

Wagner, J. S.↗
NASA NTRS1985

Computation of flow regimes in parameter space for the AGCE

This report describes the results of a small study program in support of the design studies for NASA's proposed Atmospheric General Circulation Experiment (AGCE). The proposed experiment will model the atmosphere using a hemispherical layer of a dielectric fluid such as silicone oil, heated at the equator, and with a large radial AC electric field producing a temperature-dependent radial body force similar to radial gravity. The effect of terrestrial gravity on the experiment can be eliminated by doing the experiment in space flight. The author developed a series of three computer models to support these design studies. The first two calculate axisymmetric solutions and their stability to small non-axisymmetric perturbations. The third computes three-dimensional solutions. These codes allow the option of solving problems in a cylindrical geometry as well as a rather generally defined spherical layer.

Roberts, G. O.↗
NASA NTRS1988

The Basic Aerodynamics Research Tunnel - A facility dedicated to code validation

Computational fluid dynamics code validation requirements are discussed together with the need for close interaction between experiment and code development. Code validation experiments require a great deal of data and for the experiments to be successful, a highly-productive research facility is required. A description is provided of the NASA Langley Basic Aerodynamics Research Tunnel (BART); especially the instrumentation and experimental techniques that make the facility ideally suited to code validation experiments. Results are presented from recent tests which illustrate the techniques used in BART.

Sellers, William L., III↗
NASA NTRS1989

Local intensity adaptive image coding

The objective of preprocessing for machine vision is to extract intrinsic target properties. The most important properties ordinarily are structure and reflectance. Illumination in space, however, is a significant problem as the extreme range of light intensity, stretching from deep shadow to highly reflective surfaces in direct sunlight, impairs the effectiveness of standard approaches to machine vision. To overcome this critical constraint, an image coding scheme is being investigated which combines local intensity adaptivity, image enhancement, and data compression. It is very effective under the highly variant illumination that can exist within a single frame or field of view, and it is very robust to noise at low illuminations. Some of the theory and salient features of the coding scheme are reviewed. Its performance is characterized in a simulated space application, the research and development activities are described.

Huck, Friedrich O.↗
NASA NTRS1990

Solar flare gamma-ray line shapes

A computer code has been developed which is used to calculate ab initio the laboratory shapes and energy shifts of gamma-ray lines from (C-12)(p, gamma/4.438/)p-prime(C-12) and (O-16)(p, gamma/6.129/)p-prime(O-16) reactions and to calculate the expected shapes of these lines from solar flares. The sensitivity of observable solar flare gamma-ray line shapes to the directionality of the incident particles is investigated for several projectile angular distributions. Shapes of the carbon and oxygen lines are calculated assuming realistic proton energy spectra for particles in circular orbits at the mirror points of magnetic loops, for particle beams directed downward into the photosphere, and for isotropic particle distributions. Line shapes for flare sites near the center of the sun and on the limb are shown for both thin-target and thick-target interaction models.

Werntz, C.↗
NASA NTRS1993

Numerical simulations of the superdetonative ram accelerator combusting flow field

The effects of projectile canting and fins on the ram accelerator combusting flowfield and the possible cause of the ram accelerator unstart are investigated by performing axisymmetric, two-dimensional, and three-dimensional calculations. Calculations are performed using the INCA code for solving Navier-Stokes equations and a guasi-global combustion model of Westbrook and Dryer (1981, 1984), which includes N2 and nine reacting species (CH4, CO, CO2, H2, H, O2, O, OH, and H2O), which are allowed to undergo a 12-step reaction. It is found that, without canting, interactions between the fins, boundary layers, and combustion fronts are insufficient to unstart the projectile at superdetonative velocities. With canting, the projectile will unstart at flow conditions where it appears to accelerate without canting. Unstart occurs at some critical canting angle. It is also found that three-dimensionality plays an important role in the overall combustion process.

Soetrisno, Moeljo↗
NASA NTRS1994

Direct numerical simulation of incompressible axisymmetric flows

In the present work, we propose to conduct direct numerical simulations (DNS) of incompressible turbulent axisymmetric jets and wakes. The objectives of the study are to understand the fundamental behavior of axisymmetric jets and wakes, which are perhaps the most technologically relevant free shear flows (e.g. combuster injectors, propulsion jet). Among the data to be generated are various statistical quantities of importance in turbulence modeling, like the mean velocity, turbulent stresses, and all the terms in the Reynolds-stress balance equations. In addition, we will be interested in the evolution of large-scale structures that are common in free shear flow. The axisymmetric jet or wake is also a good problem in which to try the newly developed b-spline numerical method. Using b-splines as interpolating functions in the non-periodic direction offers many advantages. B-splines have local support, which leads to sparse matrices that can be efficiently stored and solved. Also, they offer spectral-like accuracy that are C(exp O-1) continuous, where O is the order of the spline used; this means that derivatives of the velocity such as the vorticity are smoothly and accurately represented. For purposes of validation against existing results, the present code will also be able to simulate internal flows (ones that require a no-slip boundary condition). Implementation of no-slip boundary condition is trivial in the context of the b-splines.

Loulou, Patrick↗
NASA NTRS1996

Performance of NASA Equation Solvers on Computational Mechanics Applications

This paper describes the performance of a new family of NASA-developed equation solvers used for large-scale (i.e. 551,705 equations) structural analysis. To minimize computer time and memory, the solvers are divided by application and matrix characteristics (sparse/dense, real/complex, symmetric/nonsymmetric, size: in-core/out of core) and exploit the hardware features of current and future computers. In this paper, the equation solvers, which are written in FORTRAN, and are therefore easily transportable, are shown to be faster than specialized computer library routines utilizing assembly code. Twenty NASA structural benchmark models with NASA solver timings reside on World Wide Web with a challenge to beat them.

Storaasli, Olaf O.↗
NASA NTRS1994

Lagrangian Transport Calculations Using UARS Data. Part I: Passive Tracers

The transport of passive tracers observed by UARS has been simulated using computed trajectories of thousands of air parcels initialized on a three-dimensional stratospheric grid. These trajectories are calculated in isentropic coordinates using horizontal winds provided by the United Kingdom Meteorological Office data assimilation system and vertical (cross-isentropic) velocities computed using a fast radiation code.

UARS computed trajectories↗
NASA NTRS2006

Rapid Aeroelastic Analysis of Blade Flutter in Turbomachines

The LINFLUX-AE computer code predicts flutter and forced responses of blades and vanes in turbomachines under subsonic, transonic, and supersonic flow conditions. The code solves the Euler equations of unsteady flow in a blade passage under the assumption that the blades vibrate harmonically at small amplitudes. The steady-state nonlinear Euler equations are solved by a separate program, then equations for unsteady flow components are obtained through linearization around the steady-state solution. A structural-dynamics analysis (see figure) is performed to determine the frequencies and mode shapes of blade vibrations, a preprocessor interpolates mode shapes from the structural-dynamics mesh onto the LINFLUX computational-fluid-dynamics mesh, and an interface code is used to convert the steady-state flow solution to a form required by LINFLUX. Then LINFLUX solves the linearized equations in the frequency domain to calculate the unsteady aerodynamic pressure distribution for a given vibration mode, frequency, and interblade phase angle. A post-processor uses the unsteady pressures to calculate generalized aerodynamic forces, response amplitudes, and eigenvalues (which determine the flutter frequency and damping). In comparison with the TURBO-AE aeroelastic-analysis code, which solves the equations in the time domain, LINFLUX-AE is 6 to 7 times faster.

Trudell, J. J.↗
NASA NTRS2021

JPSS-1 ATMS Post-launch Active Geolocation Analysis

A NOAA-20 (N20) ATMS active geolocation test was performed around Jan. 2018 with 24 pre-selected coastline crossing scenes. After comprehensive analysis of ATMS stare data and the corresponding VIIRS data, the ATMS pitch, roll and yaw pointing angle errors are found from the nadir perpendicular, the nadir oblique shallow angle, and the off-nadir perpendicular coastline crossing data, respectively. In this study, we first determine the ATMS radiometric coastline crossing time by using the ATMS radiometric count data. Since the coastline can be located anywhere within one ATMS FOV from the passive (regular scanning) geolocation data, depending on the scan starting time, it is not a valid assumption for the inflection point being the same as the coastline location. Consequently, using the passive geolocation data to validate the sensor’s on-orbit pointing angle performance is limited. After finding the ATMS radiometric coastline crossing time from the ATMS data, we compare it with the VIIRS effective time stamp (see main text). Specifically the VIIRS M3, M4 & M5 (true color) & M15 and M16 bands (thermal) data have a much smaller footprint size. Using the differences of the ATMS and VIIRS (effective) coastlines crossing times, the N20 ATMS pitch, roll and yaw pointing angle errors are found to be -0.09o, -0.24o and 0.28o, respectively. To determine ATMS geolocation properly, these on-orbit pointing errors need to be corrected, adding to the ATMS SDR Processing Coefficient Table, and passed on to the operational geolocation processing code.

Active Geolocation↗
NASA NTRSDate not supplied

Towards a Third-Order Accurate, Second-Derivative-Free, Shock-Capturing Finite-Volume Method for Hypersonic Flows on Tetrahedral Grids

In this paper, we report progress in the development of a third-order accurate, second-derivative-free, shock-capturing finite-volume solver for three-dimensional unstructured grids. The method is economical in the sense that the computation and storage of second derivatives are not required for third-order accuracy. It is based on point-valued numerical solutions stored at cells, gradients computed and stored at nodes, and an efficient projected-derivative formula that eliminates the need for second derivatives in a quadratic solution interpolation. The projected-derivative formula is also used to eliminate second derivatives from a high-order flux quadrature formula, so that it can be implemented conveniently in the form of a numerical flux at a face center plus a correction term. Similarly, a high-order source quadrature formula can also be implemented in the form of a cell-center point evaluation plus a similar correction term. These features make it relatively straightforward to extend an existing second-order finite-volume code to third-order. This paper reports progress of implementing the method in the NASA VULCAN-CFD code and discusses the implementation of a high-order accurate limiter for shock capturing.

Weighted Least-Squares↗