History of Flexible Bodies in Adams

The first attempt to automatically interface with Finite Element Method (FEM) software was in a product called Adams FEA. In Adams FEA the FEM software used Guyan Reduction to automatically condense the entire set of FEM degrees of freedom (DOF) to a reduced number of DOF.

In the Guyan reduction method, a set of user-defined primary nodes are retained and the remaining set of secondary nodes are removed by condensation. Only stiffness properties are considered during the condensation, and inertia coupling of primary and secondary nodes are ignored. This is why Guyan reduction is sometimes referred to as static condensation.

Guyan reduction condenses the large, sparse FEM mass and stiffness matrices down to a small, dense pair of matrices, with respect to the Primary DOF.

The challenge in Adams FEA was to represent the Primary nodes using PART elements and an NFORCE element. While the condensed stiffness could be captured correctly by the NFORCE, the dense, condensed mass matrix from the Guyan reduction did not always lend itself to being represented by an “equivalent” lumped mass matrix.

The goals of matching:

could not always be met. Adams FEA was difficult to use successfully and did not win favor with Adams customers.

In 1996 an alternative modal flexibility method was introduced in a product called Adams Flex. Rather than being based on Adams primitives like PART and NFORCE elements, Adams Flex introduced a new inertia element, the FLEX_BODY.