51 research outputs found

    A Decentralized Parallelization-in-Time Approach with Parareal

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    With steadily increasing parallelism for high-performance architectures, simulations requiring a good strong scalability are prone to be limited in scalability with standard spatial-decomposition strategies at a certain amount of parallel processors. This can be a show-stopper if the simulation results have to be computed with wallclock time restrictions (e.g.\,for weather forecasts) or as fast as possible (e.g. for urgent computing). Here, the time-dimension is the only one left for parallelization and we focus on Parareal as one particular parallelization-in-time method. We discuss a software approach for making Parareal parallelization transparent for application developers, hence allowing fast prototyping for Parareal. Further, we introduce a decentralized Parareal which results in autonomous simulation instances which only require communicating with the previous and next simulation instances, hence with strong locality for communication. This concept is evaluated by a prototypical solver for the rotational shallow-water equations which we use as a representative black-box solver

    Parareal in time 3D numerical solver for the LWR Benchmark neutron diffusion transient model

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    We present a parareal in time algorithm for the simulation of neutron diffusion transient model. The method is made efficient by means of a coarse solver defined with large time steps and steady control rods model. Using finite element for the space discretization, our implementation provides a good scalability of the algorithm. Numerical results show the efficiency of the parareal method on large light water reactor transient model corresponding to the Langenbuch-Maurer-Werner (LMW) benchmark [1]

    Time Parallel Gravitational Collapse Simulation

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    This article demonstrates the applicability of the parallel-in-time method Parareal to the numerical solution of the Einstein gravity equations for the spherical collapse of a massless scalar eld. To account for the shrinking of the spatial domain in time, a tailored load balancing scheme is proposed and compared to load balancing based on number of time steps alone. The performance of Parareal is studied for both the sub-critical and black hole case; our experiments show that Parareal generates substantial speedup and, in the super-critical regime, can reproduce Choptuik's black hole mass scaling law

    The parareal in time algorithm applied to the kinetic neutron diffusion equation

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    International audienceIn the framework of nuclear core calculations, the development of efficient tools to run neutron kinetic computations is a field of current active research. While such calculations are crucial for security assessment and the study of new reactor concepts, they present several mathematical and computational issues that still need to be overcome. The exact model (kinetic transport equation) is indeed far too expensive to be simulated for these purposes and different simplifications (multi group diffusion approximation) have led to more tractable numerical simulations. Nevertheless, on real geometries and despite the use of domain decomposition enabling accelerations of the simulations thanks to parallel architectures, there is still need for improvements for applications on regular basis. In this context, the purpose of this work is to investigate the implementation of the parareal in time algorithm within an industrial solver called MINOS developed at C.E.A

    MINARET or the quest towards the use of time-dependent neutron transport solvers for nuclear core calculations on a regular basis

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    International audienceThe present paper deals with the resolution of the time-dependent neutron transport equation that is involved in the field of nuclear safety studies. Through the presentation of the newly implemented kinetic module in the MINARET solver [24] (developed at CEA in the framework of the APOLLO3\registered project), we aim first of all at presenting a brief and comprehensive overview of the most widespread resolution techniques employed nowadays in neutron transport industrial codes. Given that the main obstacle in the use of this type of accurate solver on a regular basis relies in the long computing times, MINARET has been used in the present work as a support to rigorously quantify the efficiency of the most common sequential and parallel acceleration techniques that are currently used in this field. An important part of the paper will be devoted to study the performances of an acceleration method that has never been considered before in the resolution of this equation, which is the parallelization of the time variable. In this regard, the parareal in time algorithm (a domain decomposition method for the time variable, [20]) has been implemented to explore its potentialities in this particular application
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