Vibroacoustic analysis of a coupled Helmholtz resonator in a liquid medium

Doktorsko delo obravnava sklopljen Helmholtzov resonator v kapljevinskem mediju v nizkofrekvenčnem območju. Sklopljen vibroakustičen problem zajema interakcijo med fluidom in strukturo ter interakcijo med akustičnimi votlinami. Za popis interakcije med prožnim Helmholtzovim resonatorjem in akustično votlino je razvit analitičen model s pristopom modalnega sklapljanja. Pri tem je napoved odziva tlačnega polja ob nezveznih prehodih geometrije izboljšana na podlagi nove formulacije izginjajočih valov. Predlagan model je razširjen z lastno dinamiko sklopljene plošče za upoštevanje interakcije med strukturo in zunanjim akustičnim poljem. Nadalje so v model implementirani mehanizmi disipacije v fluidu in strukturno dušenje. Za namen eksperimentalne validacije je zasnovana impedančna cev za merjenje disipacije v kapljevinskem mediju v nizkofrekvenčnem območju ter razvita metodologija za identifikacijo zvočne hitrosti in atenuacije. Absorpcijski koeficienti testnih Helmholtzovih resonatorjev izkazujejo dobro ujemanje med modelom in meritvami. Napoved odziva s predlaganim modelom je bolj točna od analize MKE.Doctoral thesis focuses on the analysis of the coupled Helmholtz resonator in a liquid medium in the low-frequency range. The coupled vibroacoustic problem includes fluid-structure interaction and coupling of acoustic cavities. Based on the modal-interaction approach an analytical model is developed for the coupled system of an flexible Helmholtz resonator and an acoustic cavity. Improved representation of the pressure response at the geometric discontinuities is achieved with new formulation of the evanescent waves. Hydroelastic vibration of the elastic plate is included in the proposed model to account for the interaction between the structure and the free acoustic field. Furthermore, mechanisms of the acoustic losses and structural damping are implemented. For the purpose of the experimental validation, an impedance tube for the low-frequency dissipation measurements in the liquid medium is designed and methods for the identification of the sound velocity and attenuation are developed. The absorption coefficients of the test Helmholtz resonators show good agreement between the model and the measurements. The proposed model gives more accurate results than the FEM analysis