Computational and experimental studies of resonance sound-absorbing multilayer structures
The paper considers a developed mathematical model of adjusting multi-layer sound-absorbing structures in order to get the set absorption frequencies based on experimental frequency results of single-layer sound-absorbing structures. Mesh samples which are actually Helmholtz resonators are considered as sound-absorbing structures that have resonant sound absorption. Resonant frequency of a single-layer or mesh type with different geometrical parameters is defined by the acoustic device "Interferometer". Combining such one-layer sound-absorbing structures and piling it into a multilayer structure leads to the increase of sound absorbing spectral range and of sound absorption coefficient. Mathematical model of the acoustic system in multilayer resonance sound-absorbing structures is built based on acoustomechanical analogue with resonant system, where the number of freedom degrees complies with the number of sound absorbing structures. The model helps to find the characteristics of sound-absorbing structures adjusted to the set ratio of resonance frequencies. Resonant frequencies of multilayer sound-absorbing structures are analytically determined by means of resonance frequencies of single-layer cellular sound-absorbing structures on the basis of the mathematical model developed for the oscillatory system with several degrees of freedom. Experimental verification of the calculation results showed that the difference between the experimental and calculated resonance frequencies of sound-absorbing structures is not more than 3 %. Thus, the proposed computational and experimental technique is experimentally confirmed, and geometrical parameters of the resonant cellular aggregate to create multilayer cellular sound-absorbing structures which can be used in the construction of aircraft engines is created.