Degree Candidacy: Master of Science in Mechanical Engineering
Date: Thursday, May 8, 2014
Time: 9:00 AM
Location: 215 EIB
Advisor: Dr. Lonnie Thompson
Committee Members: Dr. Gang Li and Dr. Joshua Summers
Title: Acoustic scattering and radiation response of circular hexagonal and auxetic honeycomb shell structures
Sandwich panels with honeycomb cores are used in many engineering applications because of their high strength to weight ratio, vibration isolation and sound transmission loss characteristics. Previous studies indicate that such sandwich structures with auxetic honeycomb cores (negative in-plane Poisson’s ratio) can have a higher sound transmission loss compared to a regular hexagonal honeycomb core structure. In this study, sound scattering and acoustic radiation characteristics of sandwich structures with hexagonal and auxetic cores arranged in a circular pattern interacting with exterior acoustic domains of both air and water have been investigated using finite element analysis.
A novel in-plane honeycomb geometry is developed which provides for a gradual decrease in radial cell size and whole number of circumferential cells to generate a uniform distribution of cells in the circular shell. Adding more circumferential cells, enables outer honeycomb edges to approach a circular arc and provides a comparison between the circular honeycomb and a solid elastic cylinder shell with the same mass. Natural frequencies of the different shell structures in-vacuo have been extracted in the analysis range of 0-2000 Hz. It is observed that auxetic honeycomb has lower natural frequencies compared to regular honeycomb for the same mass indicating that the auxetic is more flexible.
The acoustic scattering and radiation performance in terms of target strength (TS) defined as the magnitude of reflected/scattered wave pressure relative to the magnitude of the incident plane wave pressure is measured both on the scattering surface and far-field at both the back and front scattering point were studied in both air and water. In the case of interaction with air in the exterior acoustic region, the radiation response shows prominent resonance peaks at the in-vacuo natural frequencies of the elastic structures as expected. Results show that there are significant differences in target strength between the auxetic and regular honeycomb and elastic solid circular shell structures studied, with relative TS performance between the different shells depending on the frequency of the incident wave and the acoustic domain used.