A numerical investigation of damping in fuzzy oscillators with poroelastic coating attached to a host structure

Abstract

This paper analyzes efficacy of fuzzy oscillators combined with poroelastic coatings to reduce low frequency vibrations. The authors had previously shown that the poroelastic interactions across contact interfaces are tunable for broadband rate-independent damping. As a follow-up to that work, dynamic analyses are conducted on a host structure interacting with multiple fuzzy oscillators through contact interfaces across poro/viscoelastic coatings. Contact interactions are modeled by Fractional Zener Models. As viscoelastic coating material, hevea rubber is chosen because of its exceptionally high damping characteristics (i.e., highest loss tangent). For the poroelastic coating, relaxed and unrelaxed compliances as well as maximum damping capacity are assumed as identical to the viscoelastic rubber coating. In the first step, the dominant vibration mode of a host structure is modeled as a single degree-of-freedom system. The modal frequency of the host structure is first assumed to match peak relaxation frequency of the viscoelastic coating (220 kHz). Then, the modal frequency is reduced to lower frequencies (20,100 and 200 Hz). In the next step of the analysis, the investigation is extended to a host structure modeled as a two degree of freedom system. Results show that, if relaxation frequencies of the viscoelastic and poroelastic materials are close to the modal frequency of the host structure, the vibration suppression performances of both coatings are similar. However, poroelastic coating outperforms the viscoelastic coating at lower modal frequencies due to its tunable dynamic relaxation properties. Viscoelastic coating, in contrast, responds as a spring, and loses its damping capacity away from its peak relaxation frequency. To explore the best possible performance of the poroelastic coatings for low frequency damping, an optimization routine is adopted, and optimal number of fuzzy oscillators with optimally distributed mass and frequency properties is found. Results promise up to ∼35 dB vibration reduction around the structural modes for the single degree of freedom systems. For two degree of freedom system, vibration reduction level is predicted up to ∼27 dB reduction for the first mode and ∼15 dB for the second mode.