Strain Tensors in the Absolute Nodal Coordinate and the Floating Frame of Reference Formulation

Abstract

The floating frame of reference (FFR) formulation and the absolute nodal coordinate(ANC) formulation are often used for the modeling of multibody systems. In the presentwork, a reduced strain model is derived for the ANC formulation which is equivalent tothe (small strain) FFR formulation. The reduced strain model is based on a co-rotatedreference configuration and the deformation is assumed to be small with respect to thisconfiguration. This configuration is described by a translation vector and a rotation matrix which are both determined from the motion of the body with respect to its fixedreference. The ANC formulation with reduced strain leads to a constant mass matrix. The stiffness matrix consists of two parts: The most significant part depends on the small-strain stiffness matrix of the body in the fixed reference configuration which is rotated by the rotation matrix and the second part is small and nonlinearly depending on the strain tensor. Both formulations represent displacements and deformations differently but lead to exactly thesame results in the case of equivalent floating reference configurations. Different aspects of both formulations are shown in a 2D example problem of a rotating hinged plate. A detailed description of the modeling in both cases as well as numerical results are presented.