Geometrically Explicit Cosserat-Rod Modeling with Piecewise Linear Strain for Complex Rod Systems

Abstract: This paper presents a geometrically explicit formulation for Cosserat rods that unifies configuration-space and strain-based representations within a single modeling framework. The proposed method uses nodal configurations on the Lie group SE(3) as generalized coordinates, while internal strains are reconstructed via a piecewise-linear parameterization. This hybrid design preserves the geometric rigor of Lie-group formulations and retains the locality, simplicity, and computational efficiency characteristic of strain-parameterized rod models. The formulation naturally avoids shear and membrane locking without additional stabilization techniques, and it accommodates arbitrary rod networks, closed-loop architectures, and gridshell-like structures through element-wise assembly. A Riemannian Newton solver is further developed to solve the equilibrium equations directly on SE(3), providing rapid convergence and consistent treatment of rotations. Numerical examples demonstrate that the method achieves high accuracy with only a few elements and generalizes seamlessly from single rods to complex multi-rod systems. These properties highlight the potential of the proposed formulation as a fast, robust, and scalable simulation tool for slender mechanisms and compliant structures.