Validation of current state frequency based substructuring technology for the characterisation of steering gear-vehicle interaction

This paper presents a validation study of several experimental Frequency Based Substructuring (FBS) techniques that were developed recently. Advances in the techniques up to 2009 were already applied and validated using the rear axle differential - vehicle interaction as a test case. Since then several advances were achieved by various researchers, such as the Modal Constraints for Fixtures and Subsystems (MCFS) and the method of Equivalent Multi-Point Connections (EMPC). So far these advances have been tested on relatively simple academic problems. This validation study is conducted at BMW and focuses on the complex interaction between the steering gear and the vehicle. First, the response of the vehicle is obtained experimentally while a simple substitute beam is installed in place of the steering gear. This beam is then decoupled and replaced numerically by the actual steering gear using Frequency Response Functions (FRF) obtained from finite element models. The whole procedure of decoupling and coupling is evaluated by comparison with a validation measurement. Different to the MCFS method, the decoupling and coupling is performed using Lagrange Multiplier FBS instead of component mode synthesis. This paper also presents a different derivation for the virtual point transformation that extends and generalises the EMPC method.