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Results for “IMplicit/EXplicit (IMEX)”

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 OSTI2010

A Second Order JFNK-based IMEX Method for Single and Multi-phase Flows

Abstract We present a second order time accurate IMplicit/EXplicit (IMEX) method for solving single and multi-phase flow problems. The algorithm consists of a combination of an explicit and an implicit blocks. The explicit block solves the non-stiff parts of the governing system whereas the implicit block operates on the stiff terms. In our self-conisstent IMEX implementation, the explicit part is always executed inside the implicit block as part of the nonlinear functions evaluation making use of the Jacobian-freeNewton Krylov (JFNK) method [7]. This leads to an implicitly balanced algorithm in that all non-linearities due to the coupling of different time terms are consistently converged. In this paper, we present computational results when this IMEX strategy is applied to single/multi-phase incompressible flow models. Samet

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Towards an IMEX Monolithic ALE Method with Integrated UQ for Multiphysics Shock-hydro

A number of critical science, engineering and advanced technology applications require predictive analysis of complex shock-hydrodynamics of fluid/solid materials with possible electromagnetic interaction. The physical mechanisms include wave-phenomena, material-transport, diffusion, chemical reactions, and electromagnetics. The highly nonlinear multiple-time and length-scale response of these mechanisms include discontinuities formed from shocks, contact surfaces, and complex tabular equations-of-state (EOS). Current dominant computational solution strategies use ad-hoc combinations of operator- splitting, semi-implicit, and explicit time-integration methods and decoupled nonlinear-solvers. While these approaches have enabled progress in forward simulation, the inherited mathematical structure has not provided stability, accuracy and efficiency to resolve all the dynamical time-scales of interest, nor has it enabled integrated fast sensitivity analysis and uncertainty quantification (UQ). This draft report describes initial progress towards developing a new multiphysics shock-hydro capability that is intended to be more robust, mathematically well-structured and can readily be combined with advanced higher-order implicit/explicit (IMEX) time integration and efficient adjoint-enhanced uncertainty quantification (UQ) techniques.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

A Second Order Self-Consistent IMEX Method for Radiation Hydrodynamics

We present a second order non-linearly consistent implicit/explicit (methods that use com- bination of implicit/explicit discretizations are often referred to as IMEX (IMplicit/EXplicit) methods [2,1,3]) time integration technique for solving radiation hydrodynamics problems. The idea is to hybridize an implicit and an explicit discretization in a nonlinearly consis- tent way in order to achieve second order time convergent calculations. In this scope, the hydrodynamics equations are discretized explicitly making use of the capability of well- understood explicit schemes. On the other hand , the radiation diffusion part is solved implicitly. In the view of the non-linearly consistent IMEX method, the hydrodynamics equations are solved as part of the non-linear function evaluation within the framework of the Jacobian-Free Newton Krylov (JFNK) method [16,14]. This is to avoid order reductions in time convergence due to the operator splitting. We present results from several test prob- lems in order to validate the numerical order of the scheme. For each test, we established second order time convergence.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2010

A Fully Second Order Implicit/Explicit Time Integration Technique for Hydrodynamics Plus Nonlinear Heat Conduction Problems

We present a second order non-linearly consistent implicit/explicit time integration tech¬nique for solving hydrodynamics coupled with nonlinear heat conduction problems. The idea is to hybridize an implicit and an explicit discretization in a nonlinearly consistent way in order to achieve second order time convergent calculations. In this scope, the hydrody¬namics equations are discretized explicitly making use of the capability of well-understood explicit schemes. On the other hand , the nonlinear heat conduction is solved implicitly. Such methods are often referred to as IMEX methods [2,1,3]. The Jacobian-Free Newton Krylov (JFNK) method (e.g, [10,9]) is applied to the problem in such a way as to render a nonlinearly iterated IMEX method. We solve three test problems in order to validate the nu-merical order of the scheme. For each test, we established second order time convergence. We support these numerical results with a Modi?ed Equation Analysis (MEA) [23,22]. The set of equations studied here constitute a base model for radiation hydrodynamics.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗