Sound Insulation of Flow-Permeable Biomimetic Honeycomb Structures with Helmholtz Resonators

Lawrence, Jassper (2025) Sound Insulation of Flow-Permeable Biomimetic Honeycomb Structures with Helmholtz Resonators. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

This research is proposed to address the challenge of sound attenuation without obstructing fluid flowby exploring biomimetic hierarchical honeycomb core designs integrated with Helmholtz resonators(HR). The scope of this study is narrowed to developing an acoustically effective, lightweight ventilated structure with enhanced mechanical properties. The core of this research involves two novel conceptual designs: one incorporating tubular hierarchical elements and another featuring hexagonal hierarchical elements at the vertex of the honeycomb unit cell, both of which are sandwiched between two perforated plates and integrated with Helmholtz resonators. The proposed designs aim to enhance sound transmission loss (STL), especially in the low frequency region, where lightweight strucutres such as honeycomb structures with perforated faceplates performpoorly. With context to the methodology, experimental impedance tube test and numerical simulations in ANSYS were performed to validate the proposed designs. Model verification was also done to ensure the simulation conducted had appropriate boundary conditions and mesh quality. By successfully implementing these biomimetic hierarchical designs enhanced with Helmholtz resonators, it can be useful in applications that need high strength, fluid flow and superior acoustic performance, such as machinery enclosures, railway interiors and in HVAC ducts. The experimental validation revealed that the general trend had high correlation in the frequency ranges of 200Hz to 400Hz and 1100Hz to 1400Hz but the peaks due to the Helmholtz resonators obtained numerically could not be observed. Numerically, the HBEP model achieved a mean STL improvement of over 14.299dB and the HSSH1 design with an improvement of 13.47dB over the baseline model while experimentally, the HBEP and HSSH1 models showed improvements in the mean STL with values of 12.46dB and 11.42dB respectively highlighting its superior acoustic performance on average compared to the baseline model. For a more thorough analysis into the discrepancies, the overall error and averaged STL difference was computed. The computed overall errors for the baseline model, HBEP model and HSSH1 model were 74.55%, 46.2% and 46.4% respectively while the averaged STL difference between the experiment and simulation obtained were 3.16dB, 6.69dB and 6.23dB respectively. The large discrepancies were attributed to several reasons such as the non-planar wave effects, viscous effects, air leakage, differences in boundary conditions used in the experiment and simulation and the limitations in the sample fabrication process. Hence, since the overall trend showed a high correlation with the exception of the TL peaks due to the Helmholtz resonator, the results are said to be validated. In short, the proposed flow permeable biomimetic hierarchical honeycomb designs with Helmholtz resonators showed a significant improvement over the traditional perforated honeycomb sandwich structure but the experimental results could not accurately capture the transmission loss peaks due to the Helmholtz resonators obtained numerically which were attributed to the aforementioned factors.