Importance and effectiveness of representing the shapes of Cosserat rods and framed curves as paths in the special Euclidean algebra

TL;DR

This paper explores how representing Cosserat rod shapes as paths in the special Euclidean algebra provides an intrinsic, efficient, and invariant way to analyze their geometry and mechanics, improving numerical schemes.

Contribution

It introduces a novel intrinsic representation of Cosserat rod shapes as paths in the special Euclidean algebra, enhancing geometric understanding and computational methods.

Findings

Shape representation is invariant under isometries.

Discretization schemes avoid strain reconstruction.

Full placement can be reconstructed from shape and a cross section.

Abstract

We discuss how the shape of a special Cosserat rod can be represented as a path in the special Euclidean algebra. By shape we mean all those geometric features that are invariant under isometries of the three-dimensional ambient space. The representation of the shape as a path in the special Euclidean algebra is intrinsic to the description of the mechanical properties of a rod, since it is given directly in terms of the strain fields that stimulate the elastic response of special Cosserat rods. Moreover, such a representation leads naturally to discretization schemes that avoid the need for the expensive reconstruction of the strains from the discretized placement and for interpolation procedures which introduce some arbitrariness in popular numerical schemes. Given the shape of a rod and the positioning of one of its cross sections, the full placement in the ambient space can be uniquely reconstructed and described by means of a base curve endowed with a material frame. By viewing a geometric curve as a rod with degenerate point-like cross sections, we highlight the essential difference between rods and framed curves, and clarify why the family of relatively parallel adapted frames is not suitable for describing the mechanics of rods but is the appropriate tool for dealing with the geometry of curves.