论文标题

使用机器学习揭示湍流的状态空间

Revealing the state space of turbulence using machine learning

论文作者

Page, Jacob, Brenner, Michael P., Kerswell, Rich R.

论文摘要

尽管湍流的复杂性明显复杂,但确定对基本动力学系统的简单描述仍然是一个基本挑战。如Hopf在1948年所设想的那样,使用一些有效的表示,捕获了相位空间中不稳定状态(简单不变解决方案)中的湍流如何蜿蜒而行,尽管在识别这些状态方面存在固有的困难,但仍具有最佳希望。在这里,我们通过证明深卷积自动编码器可以识别出二维湍流的低维表示,朝着这一目标迈出了重要一步,这些表示与表征湍流吸引子的简单不变解决方案密切相关。为了确定这一点,我们开发了潜在的傅立叶分析,该分析将嵌入到一组正交的潜在傅立叶模式中分解为分解成类似于简单不变解决方案的物理有意义的模式。通过分析湍流的kolmogorov流(大规模强制的2D圆环流动流),在$ re = 40 $中,突出了这种方法的实用性,在此,在间歇性爆发之间,该流量位于不稳定状态的附近,并且尺寸很低。对单个潜在傅立叶波数的投影揭示了简单的不变解决方案,以一种系统的方式组织了静态和破裂的动力学,无法访问以前的方法。

Despite the apparent complexity of turbulent flow, identifying a simpler description of the underlying dynamical system remains a fundamental challenge. Capturing how the turbulent flow meanders amongst unstable states (simple invariant solutions) in phase space, as envisaged by Hopf in 1948, using some efficient representation offers the best hope of doing this, despite the inherent difficulty in identifying these states. Here, we make a significant step towards this goal by demonstrating that deep convolutional autoencoders can identify low-dimensional representations of two-dimensional turbulence which are closely associated with the simple invariant solutions characterizing the turbulent attractor. To establish this, we develop latent Fourier analysis that decomposes the flow embedding into a set of orthogonal latent Fourier modes which decode into physically meaningful patterns resembling simple invariant solutions. The utility of this approach is highlighted by analysing turbulent Kolmogorov flow (flow on a 2D torus forced at large scale) at $Re=40$ where, in between intermittent bursts, the flow resides in the neighbourhood of an unstable state and is very low dimensional. Projections onto individual latent Fourier wavenumbers reveal the simple invariant solutions organising both the quiescent and bursting dynamics in a systematic way inaccessible to previous approaches.

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