Development and validation of a universally valid measurement method for the determination of the structural internsity based on 3D laser vibrometry

• Applicant: Professor Dr.-Ing. Joachim Bös
• Subject Area: Acoustics
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 325274371

The goal of this research project is the development of a universally valid and manageable measurement method for the structural intensity (STI) of thin-walled real parts and structures based on 3D laser vibrometry. The STI describes the energy flow of structure borne sound within a vibrating structure. It provides the necessary information on the paths of the energy flow, which can be visualized and from which design measures for noise and vibration reduction can be systematically deduced. The STI is generally calculated from the product of the mechanical stress tensor and the velocity vector, but it can also be calculated from the internal force variables known from engineering mechanics (normal and shear forces, moments) and the velocities.In the literature several approaches can be found for the derivation of the vibrational quantities inside shell and beam structures from quantities measured at their outer surface. This project intends to enable a simultaneous measurement of the separate portions of the STI originating from in-plane vibrations (normal forces) and out-of-plane vibrations (shear forces and moments). In this way, results of numerical simulations, which will also be carried out, can be validated, and noise and vibration reduction measures can be designed efficiently and specifically for the dominant portion of the local structure borne sound transfer. 3D scanning laser vibrometers enable the simultaneous measurement of all vibrational quantities (including in-plane quantities) and also the simultaneous measurement of the vibrational quantities normal to the surface in various spatial directions, which makes the STI measurement suitable for curved beam and shell structures.Besides the measurement of all relevant vibrational quantities required for the metrological determination of the STI (applied to several test structures with increasing complexity), the calculation of the spatial derivatives of these vibrational quantities is another important aspect. The approaches that can be found in the literature have not been applied yet to curved structures or for the determination of the in-plane portions of the STI. Thus, it is necessary to analyze these methods with respect to their applicability for curved structures and, if necessary, to enhance them. Out-of-plane vibrations exhibit significantly higher amplitudes for real, curved structures than in-plane vibrations. Generally, their ratio depends on the direction of the vibration excitation as well and, thus, is not known a priori. When both vibrations are measured simultaneously, a lower signal-to-noise ratio can be expected for the in-plane vibrations due to the recording level. Therefore, the aspect of signal filtering particularly for the in-plane vibrations is of utmost importance for a precise STI analysis. This is why a filtering method is to be developed that is not only suitable for the out-of-plane vibrations, but also for the in-plane vibrations.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Tobias Melz