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Multilevel Monte Carlo Methods for Elliptic Problems with Applications to Radioactive Waste Disposal

椭圆问题的多级蒙特卡罗方法及其在放射性废物处置中的应用

基本信息

批准号：
EP/H051503/1
负责人：
Robert Scheichl
金额：
$ 33.43万
依托单位：
University of Bath
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FH051503%2F1
关键词：
Multilevel Monte Carlo Methods Elliptic

项目摘要

We propose to carry out fundamental mathematical research into efficient methods for problems with uncertain parameters and apply them to radioactive waste disposal.The UK Government's policy on nuclear power states that it is a proven low-carbon technology for generating electricity and should form part of the UK's future energy supply. Energy companies will be allowed to build new nuclear power stations provided sufficient progress is made on the radioactive waste issue. In common with other nations, geological disposal is the UK's preferred option for dealing with radioactive waste in the long term. Making a safety case for geological disposal is a major scientific undertaking. National and international research programmes have produced a good understanding of the mechanisms by which radionuclides might return to the human environment and of their consequences once there. One of the outstanding challenges is how to deal with the uncertainties inherent in geological systems and in the evolution of a repository over long time periods and this is at the heart of the proposed research.The main mechanism whereby radionuclides might return to the environment, in the event that they escape from the repository, is transport by groundwater flowing in rocks underground. The mathematical equations that model this flow are well understood, but in order to solve them and to predict the transport of radionuclides the permeability and porosity of the rocks must be specified everywhere around the repository. It is only feasible to measure these quantities at relatively few locations. The values elsewhere have to be inferred and this, inevitably, gives rise to uncertainty. In early performance assessments, relatively rudimentary approaches to treating these uncertainties were used, primarily due to the computational cost. Since then, there have been considerable advances in computer hardware and in the mathematical field of uncertainty quantification. One of the most common approaches to quantify uncertainty is to use probabilistic techniques. This means that the coefficients within the flow equations will be modelled as random fields, leading to partial differential equations with random coefficients (stochastic PDEs), and solving these is much harder and more computationally demanding than their deterministic equivalents. Many fast converging techniques for stochastic PDEs have recently emerged, which are applicable when the uncertainty can be approximated well with a small number of stochastic parameters. However, evidence from field data is such that in repository safety cases much larger numbers of stochastic parameters will be required to capture the uncertainty in the system. Only Monte Carlo (MC) sampling and averaging methods are currently feasible in this case, and the relatively slow rate of convergence of these methods is a major issue.In the work proposed here we will develop and analyse a new and exciting approach to accelerate the convergence of MC simulations for stochastic PDEs. The multilevel MC approach combines multigrid ideas for deterministic PDEs with the classical MC method. The dramatic savings in computational cost which we predict for this approach stem from the fact that most of the work can be done on computationally cheap coarse spatial grids. Only very few samples have to be computed on finer grids to obtain the necessary spatial accuracy. This method has already been applied (by one of the PIs), with great success, to stochastic ordinary differential equations in mathematical finance. In this project we will extend the technique to PDEs, developing the analysis of the method required, and apply the technique to realistic models of groundwater flow relevant to radioactive waste repository assessments. The potential impact for future work on radioactive waste disposal and also for other areas where uncertainty quantification plays a major role (e.g. carbon capture and storage) is considerable.

我们建议开展基础数学研究，为不确定参数的问题提供有效的方法，并将其应用于放射性废物处理。英国政府的核电政策指出，核电是一种经过验证的低碳发电技术，应成为英国未来能源供应的一部分。如果在放射性废物问题上取得足够的进展，能源公司将被允许建造新的核电站。与其他国家一样，地质处置是英国长期处理放射性废物的首选方案。为地质处置提供安全理由是一项重大的科学任务。国家和国际研究方案使人们对放射性核素可能返回人类环境的机制及其返回后的后果有了很好的了解。突出的挑战之一是如何处理地质系统和处置库长期演变过程中固有的不确定性，这是拟议研究的核心，放射性核素在从处置库逃逸后可能返回环境的主要机制是通过地下水在地下岩石中的流动进行迁移。模拟这种流动的数学方程很容易理解，但为了求解这些方程并预测放射性核素的迁移，必须指定处置库周围各处岩石的渗透性和孔隙度。只有在相对较少的地点测量这些量才是可行的。其他地方的价值必须推断出来，这不可避免地会产生不确定性。在早期的性能评估中，主要由于计算成本的原因，使用了相对初级的方法来处理这些不确定性。从那时起，计算机硬件和不确定性量化的数学领域取得了长足的进步。量化不确定性的最常见方法之一是使用概率技术。这意味着流动方程中的系数将被建模为随机场，导致具有随机系数的偏微分方程（随机偏微分方程），并且求解这些方程比其确定性等价物更困难，计算量更大。随机偏微分方程的快速收敛技术是近年来出现的，当不确定性可以用少量的随机参数很好地近似时，这些技术是适用的。然而，来自现场数据的证据是这样的，在处置库安全的情况下，将需要大量的随机参数来捕捉系统中的不确定性。只有Monte Carlo（MC）采样和平均方法是目前可行的，在这种情况下，这些方法的收敛速度相对较慢是一个主要问题，在这里提出的工作，我们将开发和分析一个新的和令人兴奋的方法来加速随机偏微分方程的MC模拟收敛。多层次MC方法结合了多重网格思想的确定性偏微分方程与经典MC方法。我们预测这种方法的计算成本的显着节省源于这样一个事实，即大部分的工作可以在计算上便宜的粗空间网格。只有极少数的样本必须计算更精细的网格，以获得必要的空间精度。这种方法已经被应用（由一个PI），并取得了巨大的成功，随机常微分方程在数学金融。在这个项目中，我们将技术扩展到偏微分方程，开发所需的方法的分析，并将该技术应用于现实的地下水流模型相关的放射性废物处置库的评估。对放射性废物处置的未来工作以及对不确定性量化发挥主要作用的其他领域（如碳捕获和储存）的潜在影响是相当大的。