Nonlinear finite element analysis of solids and structures by M.A. Crisfield

Abstract : It is shown that Galerkin's procedure is always available for twice continuously differentiable periodic differential systems if a periodic solution is restricted to an isolated periodic solution. This gives an explicit condition for applying Galerkin's procedure and reveals the wide applicability of Galerkin's procedure to general nonlinear periodic differential systems. The proof of this result is based on existence theorems which are derived from idea contained in Newton's iterative method. The relationship of Galerkin's procedure to the method of averaging is also discussed. Finally the paper exemplifies Galerkin's procedure with a certain nonlinear equation. (Author)

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Galerkin's Procedure for Nonlinear Periodic Systems (関数方程式の近似解法研究会報告集)

A quadratic manifold for model order reduction of nonlinear structural dynamics

This paper aims at reviewing nonlinear methods for model order reduction in structures with geometric nonlinearity, with a special emphasis on the techniques based on invariant manifold theory. Nonlinear methods differ from linear-based techniques by their use of a nonlinear mapping instead of adding new vectors to enlarge the projection basis. Invariant manifolds have been first introduced in vibration theory within the context of nonlinear normal modes and have been initially computed from the modal basis, using either a graph representation or a normal form approach to compute mappings and reduced dynamics. These developments are first recalled following a historical perspective, where the main applications were first oriented toward structural models that can be expressed thanks to partial differential equations. They are then replaced in the more general context of the parametrisation of invariant manifold that allows unifying the approaches. Then, the specific case of structures discretised with the finite element method is addressed. Implicit condensation, giving rise to a projection onto a stress manifold, and modal derivatives, used in the framework of the quadratic manifold, are first reviewed. Finally, recent developments allowing direct computation of reduced-order models relying on invariant manifolds theory are detailed. Applicative examples are shown and the extension of the methods to deal with further complications are reviewed. Finally, open problems and future directions are highlighted.

Model order reduction methods for geometrically nonlinear structures: a review of nonlinear techniques

Exact nonlinear model reduction for a von Kármán beam: Slow-fast decomposition and spectral submanifolds

Generalization of quadratic manifolds for reduced order modeling of nonlinear structural dynamics

Model reduction to spectral submanifolds and forced-response calculation in high-dimensional mechanical systems.

Invariant manifolds are important constructs for the quantitative and qualitative understanding of nonlinear phenomena in dynamical systems. In nonlinear damped mechanical systems, for instance, spectral submanifolds have emerged as useful tools for the computation of forced response curves, backbone curves, detached resonance curves (isolas) via exact reduced-order models. For conservative nonlinear mechanical systems, Lyapunov subcenter manifolds and their reduced dynamics provide a way to identify nonlinear amplitude–frequency relationships in the form of conservative backbone curves. Despite these powerful predictions offered by invariant manifolds, their use has largely been limited to low-dimensional academic examples. This is because several challenges render their computation unfeasible for realistic engineering structures described by finite element models. In this work, we address these computational challenges and develop methods for computing invariant manifolds and their reduced dynamics in very high-dimensional nonlinear systems arising from spatial discretization of the governing partial differential equations. We illustrate our computational algorithms on finite element models of mechanical structures that range from a simple beam containing tens of degrees of freedom to an aircraft wing containing more than a hundred–thousand degrees of freedom.

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Shobhit Jain

Papers

A quadratic manifold for model order reduction of nonlinear structural dynamics

Exact nonlinear model reduction for a von Kármán beam: Slow-fast decomposition and spectral submanifolds

Generalization of quadratic manifolds for reduced order modeling of nonlinear structural dynamics

Model reduction to spectral submanifolds and forced-response calculation in high-dimensional mechanical systems.

How to compute invariant manifolds and their reduced dynamics in high-dimensional finite element models