Sound radiation of complex mode shapes

• Applicant: Professor Dr.-Ing. Michael Sinapius
• Subject Area: Acoustics
• Term: from 2014 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 256895788

The effective suppression of noise pollution requires the precise knowledge of the noise generating sources. Nowadays a profound and consolidated basic knowledge on vibroacoustics exists. Sources of noise are mainly characterized by vibration amplitude, spectral content, and frequency dependent radiation capability. The latter was investigated in detail in terms of structural mode shapes because the dynamic response of structures is determined by mode shapes. The related research is mainly based on the assumption of homogenously distributed structural damping and simple boundary conditions which simplifies the underlying differential equations. Then the related eigenproblem yields real normal modes. This assumption is valid for many applications and delivers sufficiently accurate results. However, the increasing application of high performance light weight structures made from fiber reinforced plastics simultaneously increase the acoustic requirements and, in consequence measures for acoustic damping. The latter are located at critical structural points for weight-saving reasons which violates the assumption of homogenously distributed structural damping. Consequently the structural resonances are determined by modes of complex shapes, i.e. forward waves instead of standing waves. Boundary condition may cause these complex mode shapes as well. The existence of complex modes raises the question of their influence on sound radiation.The basic hypothesis of the project is that the grade of complexity of complex mode shapes caused by non-proportional damping has a significant influence on the sound radiation below the coincidence frequency. The sound radiation characteristics should by describable by a complex radiation coefficient. The project will systematically investigate the relation between the mode shape complexity and the sound radiation.

• DFG Programme: Research Grants
• Participating Person: Professor Dr.-Ing. Hans Peter Monner