Modal Methodology for the Simulation and Optimisation of the Free-Layer Damping Treatment of a Car Body

The cost and weight reduction requirements in automotive applications are very important targets in the design of a new car. For this reason all the components of the vehicle have to be optimised, and the design of the damping material layout has to be deeply analysed in order to have a good NVH performance with the minimum of weight and cost. A tool for the optimisation of the damping material layout has been implemented and tested; the need to explore the entire design space with a big number of variables suggested the use of a genetic multi-objective algorithm for the optimisation. These algorithms require a large number of calculations and the solution of the complete NVH model would be too expensive in terms of computation time. For this reason, a new software tool has been developed based on the simulation of the damping material treatments by means of an auxiliary mass and stiffness matrix to be added to the baseline modal base; using this procedure the required time for the simulation of each damping material layout configuration is reduced to a few minutes, allowing to exploit the genetic algorithm capability to efficiently explore the design space. As a result, some configurations with an important weight reduction or a much better acoustic performance have been found. This method has been verified on a simple Aluminium box in order to verify all the assumptions and to test the effectiveness in predicting the vibration levels of plates with free layer damping added to it.