Structure-preserving Lift & Learn: Scientific machine learning for nonlinear conservative partial differential equations

TL;DR

This paper introduces a structure-preserving machine learning method called Lift & Learn for creating reduced-order models of nonlinear PDEs with conservation laws, ensuring physical fidelity and computational efficiency.

Contribution

It develops a hybrid energy-quadratization approach that derives quadratic reduced models analytically, preserving the structure and conservation laws of the original PDEs.

Findings

The method accurately models nonlinear PDEs like wave and Klein-Gordon equations.

Quadratic reduced models are computationally efficient and respect physical laws.

The approach is competitive with state-of-the-art methods in accuracy and efficiency.

Abstract

This work presents structure-preserving Lift & Learn, a scientific machine learning method that employs lifting variable transformations to learn structure-preserving reduced-order models for nonlinear partial differential equations (PDEs) with conservation laws. We propose a hybrid learning approach based on a recently developed energy-quadratization strategy that uses knowledge of the nonlinearity at the PDE level to derive an equivalent quadratic lifted system with quadratic system energy. The lifted dynamics obtained via energy quadratization are linear in the old variables, making model learning very effective in the lifted setting. Based on the lifted quadratic PDE model form, the proposed method derives quadratic reduced terms analytically and then uses those derived terms to formulate a constrained optimization problem to learn the remaining linear reduced operators in a structure-preserving way. The proposed hybrid learning approach yields computationally efficient quadratic reduced-order models that respect the underlying physics of the high-dimensional problem. We demonstrate the generalizability of quadratic models learned via the proposed structure-preserving Lift & Learn method through three numerical examples: the one-dimensional wave equation with exponential nonlinearity, the two-dimensional sine-Gordon equation, and the two-dimensional Klein-Gordon-Zakharov equations. The numerical results show that the proposed learning approach is competitive with the state-of-the-art structure-preserving data-driven model reduction method in terms of both accuracy and computational efficiency.