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arXiv 2309.14031math.NAcs.NA
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相空间迭代求解器

Phase-space iterative solvers

Gaëtan Cortes, Nur Cristian Sangiorgio, Joaquin Garcia-Suarez

AI总结:

本文提出相空间迭代法(PSIs),通过在物理容许集与材料容许集之间交替投影求解小应变非线性弹性边值问题,并展示了其相对于牛顿-拉夫森方法的优势及处理神经网络本构定律的能力。

摘要:

我们引入了一种用于求解小应变非线性弹性问题的迭代方法,称为“相空间迭代法”(Phase-Space Iterations,简称 PSIs)。该方法受数据驱动计算力学近期工作的启发,后者利用与网格相关联的“相空间”概念重新表述了连续介质力学的经典边值问题。该相空间是一个抽象度量空间,其坐标由应变和应力分量索引,离散化物体的每个可能状态对应一个点。随后定义两个子集:一个是由满足平衡条件的点组成的仿射空间,称为“物理容许集”;另一个是包含满足本构定律的点的“材料容许集”。求解边值问题等价于找到这两个子域的交集。在线弹性情形下,这可以通过求解一组线性方程来实现;然而当材料非线性介入时,情况不再如此,必须采用迭代求解方法。我们的迭代方法是将点交替地从一个集合投影到另一个集合,直至收敛。为评估该方法性能,我们借鉴了“交替投影法”和“凸集投影法”,二者在解的存在性条件和收敛性保证方面具有坚实的数学基础。我们利用这一基础分析了最简单的情形,并建立了几何收敛速率。我们还展示了一个实际算例,以说明相空间迭代法相较于经典牛顿-拉夫森方法(非线性连续介质力学中常用的工具)的优势。最后,还展示了该方法处理基于神经网络的本构定律的能力。

英文摘要:

We introduce an iterative method to solve problems in small-strain non-linear elasticity, termed ``Phase-Space Iterations'' (PSIs). The method is inspired by recent work in data-driven computational mechanics, which reformulated the classic boundary value problem of continuum mechanics using the concept of ''phase space'' associated with a mesh. The latter is an abstract metric space, whose coordinates are indexed by strains and stress components, where each possible state of the discretized body corresponds to a point. Two subsets are then defined: an affine space termed ``physically-admissible set'' made up by those points that satisfy equilibrium and a ``materially-admissible set'' containing points that satisfy the constitutive law. Solving the boundary-value problem amounts to finding the intersection between these two subdomains. In the linear-elastic setting, this can be achieved through the solution of a set of linear equations; when material non-linearity enters the picture, such is not the case anymore and iterative solution approaches are necessary. Our iterative method consists on projecting points alternatively from one set to the other, until convergence. To evaluate the performance of the method, we draw inspiration from the ''method of alternative projections'' and the ''method of projections onto convex sets'', both of which have a robust mathematical foundation in terms of conditions for the existence of solutions and guarantees convergence. This foundation is leveraged to analyze the simplest case and to establish a geometric convergence rate. We also present a realistic case to illustrate PSIs' strengths when compared to the classic Newton-Raphson method, the usual tool of choice in non-linear continuum mechanics. Finally, its aptitude to deal with constitutive laws based on neural network is also showcased.

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