VIRTualization of Experimental facilities in structural aCoustics by wall pressure syntHesis – VIRTECH

Sustainable transports require the use of lightweight structures to improve their energy efficiency. New materials (steel with very high strength, polymeric materials, hybrid polymer / metal or organo-mineral, biocomposites etc ...) are both very rigid and lightweight, with the drawback of poor acoustic performance. Improvement requires very expensive in-situ tests, especially in the case of turbulent boundary layer noise. Manufacturers must revolutionize their characterization and measurement protocols to transpose their knowledge from metallic materials to these new technologies. Currently available experimental facilities are very expensive, have a heavy carbon footprint and do not allow mastering all the physical parameters (noise, field temperature, homogeneity, etc.). The reproducibility of measurements can then be questioned, making it difficult to compare different technology solutions. It is therefore of considerable interest to have a tool usable in production, in order to reproduce random excitations characteristics and to evaluate systems with a high accuracy. The VIRTECH project brings an approach and tools for pressure field synthesis for integrating acoustic feature in new materials, replacing in-situ campaigns, significantly reducing costs without compromising realism. Under the terms "pressure fields synthesis" are grouped experimental methods (and optionally computational) that reproduce a pressure field complying with prescribed properties (homogeneity of the field, temporal and spatial correlations) using reproduction sound systems (speakers, mobile sources). These methods can be used in real-time or in a later post-processing step. Applications are as varied as characterization of acoustic performance, studies on aging or resistance in extreme conditions or even for sound quality applications. Potentially, the "field synthesis" could be used to test systematically strategic parts (in aeronautics or space activities in particular) directly on the assembly line. The project will address the following issues:
(1) the identification of useful components of the acoustic field by direct measurements (using an antenna of MEMS microphones), by indirect measurement by observing the vibro-acoustic behavior of the tested structure and by analysis of a numerical modeling of the pressure field. These analyzes will be coupled with a perceptive study for a comprehensive assessment of the filtering process of the exciting pressure field.
(2) optimization of a network of sources and its management to synthesize a pressure field having the characteristics of a diffuse field or a turbulent boundary layer by leveraging the filtering phenomena observed previously. The optimization will focus on various criteria: speed of implementation, spatial resolution, error sensitivity, cost, reproducibility.
(3) The confrontation between the obtained results and those obtained by standard test means including direct measures of the generated field and perceptual studies. Finally, the capacity of these alternative means will be illustrated with applications on "vibro-acoustic metrology" or "real-time quality control test bench"