Structure-borne Vehicle Analysis using a Hybrid Finite Element Method

The hybrid FEA method combines the conventional FEA method with the energy FEA (EFEA) for computing the structural vibration in vehicle structures when the excitation is applied on the load bearing stiff structural members. Conventional FEA models are employed for modeling the behavior of the stiff members in the vehicle. In order to account for the effect of the flexible members in the FEA analysis, appropriate damping and spring/mass elements are introduced at the connections between stiff and flexible members. Computing properly the values of these damping and spring/mass elements is important for the overall accuracy of the computations. Utilizing in these computations the analytical solutions for the driving point impedance of infinite or semi-infinite members introduces significant approximations. Alternatively, a component mode synthesis method applied to analytical modal solutions can be employed for determining the driving point conductance at joints between stiff and flexible members and for defining the dynamic properties of the flexible members when analyzing the stiff components. Once the vibration of the stiff members and the amount of power dissipated at the damping elements has been identified, an EFEA analysis is performed in order to determine the amount of vibrational energy in the flexible members. The hybrid FEA is used for analyzing a full vehicle structure and the results are compared to test data. The impact on the results from the values used for representing the dynamic characteristics of the flexible members in the FEA part of the calculations is also examined and presented.