Achieving targeted global modes (torsion, vertical bending and lateral bending) is one of the main enablers in meeting desired NVH performance characteristics of a new vehicle program.
The torsion mode of next generation Land Rover - Freelander was lagging behind its target while the development cycle was quite progressed beyond underbody freeze. There was a challenge to recover more than 8 Hz in BIW torsion mode. A combination of Nastran Sol 200 (design sensitivity and optimization) and iterative process was adopted to demonstrate how the mode could be recovered with optimum mass penalty to the program.
The paper states the existing modal status when this work was taken up. Next it elucidates design sensitivity/optimization module outcome which identifies sensitive areas to improve torsion mode. Then it describes how feasible design solutions were developed while iterating using Nastran Sol 103 modal analysis, based on the outcome of above sensitivity/optimization analyses, to converge to the specified target. Pictures of all design enablers are shown with mass penalty associated and performance gained mentioned along-with them. The final status when the target was achieved is outlined.
Appropriate conclusions have been made to highlight major enablers affecting the vehicle torsion mode and the effective vehicle areas to address for torsion mode recovery.