Application of the concept of acoustic influence coefficients for the optimization of a vehicle roof

To improve the acoustic behaviour of vehicles is an increasing challenge for every car manufacturer. The sound pressure at the drivers ear due to an arbitrary excitation of the structure can be calculated by a harmonic analysis first of the structure and then of the fluid. Using the concept of influence coefficients one has to carry out the harmonic analysis of the fluid only once to determine the sound pressure at the drivers ear. If the influence coefficients are available one has to solve an easy algebraic relation instead of a full harmonic analysis. This requires that geometry modifications are small compared with the acoustic wave lengths. So, the computational expenditure is mainly confined to the harmonic analysis of the structure. In this paper, the principal way of carrying out an optimization of a vehicle body is presented for the example of a vehicle roof. The parametric geometry based model of the roof is time harmonically excited. All other parts of the body are considered to remain rigid. Admittance boundary conditions are included. Results are presented for different loads and frequency domains, for limited and for unlimited permissible variations of the geometry and for different modal dampings.