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Streszczenie:
Prediction of the acoustic performance of 3D printed materials is investigated at normal and grazing incidence. A direct numerical (microscopic) simulation that solves the full set of Navier-Stokes equations is used as a reference. It is compared with a macroscopic approach in which the material is represented by an equivalent fluid. The materials have a periodic microstructure, consisting either of a single network of spherical or cubic cavities connected by cylindrical channels or of a double-nested network. The samples are printed using the stereolithography technique and are tested using an impedance tube and a duct test bench. For single network geometries, the results of sound absorption at normal and grazing incidence predicted using the equivalent fluid approach are in good agreement with those obtained by the microscopic approach. Comparisons with impedance tube measurements confirm that both approaches can accurately predict the absorption coefficient of the samples. For the in-duct liner configuration, the transmission loss measurements and predictions show similar evolution with frequency change, despite the discrepancy in amplitude. For the double network geometry, the equivalent fluid approach cannot exactly reproduce the results obtained with the direct numerical simulation. Finally, while the predictions with the microscopic approach provide a good match with the impedance tube measurements, only a poor agreement is obtained using the duct testing bench.

Słowa kluczowe:
Acoustic absorber, 3D printing, Duct, Multiscale approach

Streszczenie:
The paper presents theoretical and experimental studies on the original multi-resonant sound-absorbing material. A representative geometry of the material contains several channels (disjoint pore networks) of contrasting tortuosity. For the assumed material thickness, one can estimate the quarter-wavelength resonance frequency of each channel based on its tortuosity. The proposed estimate is sufficiently accurate or can be systematically adjusted to eliminate the predictable error. It can therefore be used to design a very effective sound-absorbing layer by tuning the resonance frequencies. This is because the sound absorption peaks for such a layer backed by a rigid wall occur at the resonant frequencies. The tuning is performer by tailoring the shape of the channels to obtain contrasting tortuosities that should distribute their corresponding resonant frequencies over the desired, wide frequency range. In this way, broadband absorption can be achieved. An additional goal of tailoring the channels is to fit them tightly inside the representative space of the material while maintaining their separation. In the proposed material design, all shapes and characteristic sizes are suitable for additive manufacturing, so a sample of the material was 3D printed. It was tested in an impedance tube for sound absorption to validate the theoretical results.

Słowa kluczowe:
Sound absorption, Separated pore networks, Quarter-wavelength resonances, Acoustic metamaterials