Session: 01-02-01: Passive, Semi-Active, and Active Noise and Vibration Control

Paper Number: 120117

120117 - Inverse Modeling of Porous Noise Absorbers With Triply Periodic Minimal Surface Architectures 

Porous structures, due to their array of beneficial properties, are widely favored in various industrial applications. Over the decades, researchers have extensively studied these properties and devised numerous models to characterize them. In acoustics, models such as Johnson-Champoux-Allard (JCA), Johnson-Champoux-Allard-Lafarge (JCAL), and Johnson-Champoux-Allard-Pride-Lafarge (JCAPL) have been developed to describe the sound absorption behavior of porous absorbers. In the JCA formulation, the acoustic behavior of the fluid region is expressed as a function of five bulk properties: open porosity, tortuosity, static airflow resistivity, viscous characteristic length, and thermal characteristic length. These properties can either be directly measured through experimental methods or derived from impedance tube measurements using inverse characterization methods.

In this study, we investigate the use of the JCA formulation to model the acoustical behavior of 3D printed porous absorbers with triply periodic minimal surface (TPMS) architectures. We focus our attention on two, surface based TPMS structures: Gyroids and Diamonds. The models are designed using an implicit, field-based modeling approach. The relative densities of the models are varied by altering the wall thickness of the TPMS unit cells while maintaining a uniform cell size of 3mm throughout the study for consistency. The modeled samples are then 3D printed using the stereolithographic (SLA) resin-based printing method and their sound absorption characteristics are measured using the conventional normal-impedance impedance tube technique.  Using the measured transfer function, we obtain the reflection coefficient, absorption coefficient, and the surface impedance of each sample. A print quality analysis is conducted to identify the sample defects occurring during the fabrication process.

Finally, we model their acoustical behavior using the JCA formulation. To obtain the transport properties of each sample, we use the inverse characterization method built into the commercially available software FOAM-X. The inverse characterization method is a numerical curve fitting technique to match the modeled curve to the experimental absorption curve by varying the five transport properties. The reflection coefficient, absorption coefficient, and the normalized surface impedance of each sample are tabulated over the frequency range and are used as the inputs for the inverse characterization process. To increase the computational accuracy of the model, the measured porosity of each sample is also used as an input; the porosity of each sample is calculated using their respective weights and the cured resin density. After obtaining the transport properties, the predicted absorption curves are compared to the experimental results. Results show that the proposed model can robustly predict the normal incidence absorption behavior for all samples. Further, we use the finite element software Nova FEM to investigate stepwise RD gradient configurations that have potentially greater absorption characteristics compared to the uniform RD configurations. Our results show that this workflow may be utilized to tailor porous absorbers to accomplish superior absorption results in industrial acoustical applications.

Presenting Author: Janith Godakawela Michigan Technological University

Presenting Author Biography: Janith Godakawela is currently a graduate research assistant in the Mechanical Engineering - Engineering Mechanics department at Michigan Tech. He is pursuing his PhD with a focus on the use of additive manufacturing techniques for noise control and reduction applications.

Authors:

Janith Godakawela Michigan Technological University
Bhisham Sharma Michigan Technological University