Acoustic problems such as a high sound radiation can arise later in the development process, e.g.,,due to a change of a component. Usually, at this stage, it is uneconomic to completely redesign the,product’s geometry, rather, it is better to implement small, locally limited modifications. In the case,of thin-walled structures it is common to apply damping patches to the finished product in order to,reduce the unwanted vibrations that occur and, thus, the radiated sound. The aim of this work is to,develop modification rules for dealing with acoustic problems of thin-walled structures. Using these,rules, the structures themselves can be modified during the development process in order to prevent unwanted vibrations from appearing at all. These rules are intended to indicate at which positions small modifications in the form of additional mass and/or stiffness result in a considerable reduction of the sound radiation. It would also be possible to include additional damping patches for a further noise reduction. There are two approaches that appear promising to derive such modification rules. Both are analyzed in this work, using the finite element method (FEM) – first on a plate and then for validation on a trunk floor panel (basic models).

The first approach chosen is the analysis of the structural intensity (STI), which is the energy flow of structure-borne sound. There have been STI analysis approaches found in recent literature that exhibit a large potential for low-noise construction. The aim is to identify connections between the STI and the sound radiation, in order to derive modification rules. To do this, scalar quantities are first set up in order to reduce the information density and, thus, to characterize the STI vector fields and then correlated with the sound radiation. On the basis of the established correlations and including research results from the literature, a hypothesis for a modification rule is posed and tested.

As for the second approach, it is practical to systematically examine the relationship between the position of a modification and the resulting sound radiation. First, the position of a localized modification is gradually varied on the two basis models of the plate and the trunk floor panel, in order to build up a model basis each. Then, the relationships between the positions and the resulting equivalent radiated sound power (ERP) are visualized by means of so-called ERP scalar fields. In order to develop the modification rules, it will subsequently be examined whether the ERP scalar fields can be used as "maps" to locate meaningful positions for larger and, therefore, more effective sound-reducing modifications. Lastly, it will be examined how the ERP scalar fields can be approximated by structural quantities of the basic models themselves and, thus, be directly predicted, without the effort of building up the model bases.

The investigations show that the sound radiation of structures can indeed be evaluated by means of some scalar quantities derived from the STI analysis. Furthermore, the systematic analysis of the relationship between the position of modifications and the resulting sound radiation can be used to develop modification rules for sound reduction, which are then successfully validated experimentally as well as numerically. For the first time, it is possible to specifically determine where on a structure a small increase of mass and/or stiffness considerably reduces the sound radiation either during the development process or during alterations to the finished product. Moreover, the second approach presented is suitable for the use as a method for developing further modification rules by means of a systematic investigation of other modification types such as a removal of material.