Réponse acoustique non-linéaire de métamatériaux compacts soumis à des niveaux d’excitation sonore élevés, modélisation par une approche masse-ressort

Abstract

The absorption of sound at low frequencies by compact materials remains a challenge. Conventional porous materials (e.g. : foams) and resonators (e.g. : perforated plate backed by cavity) require significant thicknesses, of the order of magnitude of the wavelength to be treated. The volumes available for acoustic solutions are often limited, as in the case of helicopter tail rotor fairings. For this type of problem, resonant structured materials are interesting solutions. They are effective at wavelengths far greater than their thickness. However, they are sensitive to their environment, particularly to sound excitation levels. The main objective of this thesis is to analyze the behavior and develop compact structured materials for acoustic treatment of sound at low frequencies, subjected to low to high levels of sound excitation. To meet this objective, the results of the thesis are presented in four chapters, three of which are scientific papers. The first paper focuses on the study of the behavior of structured materials for low acoustic excitation levels (<110 dB). The proposed structured material consists of a periodic array of air pores spaced by annular Helmholtz resonators. To analyze its behavior, a mass-spring model was developed. By solving the eigenvalue problem, mode frequencies (absorption peak frequencies) and deformations were determined. This model compares well with experimental and numerical (finite element) simulation results. The second paper looks at the losses added by high acoustic levels in the reference material composed of a compact array of perforated plates. An estimate of these losses was determined by studying the resistivity to air flow over a material composed of a periodic array of air pores spaced by thin air cavities. A computational fluid dynamics study showed that losses dominate in the first pore and estimated a coefficient associated with these losses. In the third paper, the mass-spring model was adapted from the Forchheimer parameter to predict the sound absorption of the reference material at high levels. The model is validated with measurements at sound levels up to 140 dB. The last chapter is interested in the non-linear behavior of acoustic black holes : compact array of air pores with decreasing cross-section along the material thickness spaced by thin air cavities. The mass-spring model has been adapted to this geometry and validated by measurements. Sensitivity to high sound excitation levels was analyzed for different profiles of decreasing pore cross-section.

Date	16 Oct 2024
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Thomas Dupont (Supervisor) & Raymond Panneton (Co-supervisor)