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arXiv 0802.2820math-phmath.MP
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拉格朗日和哈密顿双尺度约化

Lagrangian and Hamiltonian two-scale reduction

Johannes Giannoulis, Michael Herrmann, Alexander Mielke

摘要:

研究高维Hamilton系统的微观结构,在大的时空尺度上确定描述某些有效动力学的简化宏观模型是一个重要而具有挑战性的问题。本文讨论如何从微观系统导出合理的宏观拉氏和哈密顿结构的问题。在第一部分中,我们开发了一个一般的方法来解决这个问题,通过考虑非正则哈密顿结构的切丛。这种方法可以应用于所有的哈密尔顿格(或哈密尔顿偏微分方程),并涉及三个构建模块:(i)嵌入的微观系统,(ii)一个可逆的双尺度变换编码的空间和时间的底层标度,(iii)一个基本的模型约简,是基于一致性扩展的原则。在第二部分中,我们改进了约化方法,推导出了原子链的各种约化PDE模型。简化的方程要么与长波长运动有关,要么描述振荡微结构的宏观调制。

英文摘要:

Studying high-dimensional Hamiltonian systems with microstructure, it is an important and challenging problem to identify reduced macroscopic models that describe some effective dynamics on large spatial and temporal scales. This paper concerns the question how reasonable macroscopic Lagrangian and Hamiltonian structures can by derived from the microscopic system. In the first part we develop a general approach to this problem by considering non-canonical Hamiltonian structures on the tangent bundle. This approach can be applied to all Hamiltonian lattices (or Hamiltonian PDEs) and involves three building blocks: (i) the embedding of the microscopic system, (ii) an invertible two-scale transformation that encodes the underlying scaling of space and time, (iii) an elementary model reduction that is based on a Principle of Consistent Expansions. In the second part we exemplify the reduction approach and derive various reduced PDE models for the atomic chain. The reduced equations are either related to long wave-length motion or describe the macroscopic modulation of an oscillatory microstructure.

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