Finite element modeling of the low-frequency sound speed of seagrass leaves

Abstract

Previous investigations related to acoustic propagation through seagrass have shown that sound waves are sensitive to the gas contained within seagrass tissue as well as free bubbles produced by photosynthesis. The acoustical effects include reduced low-frequency sound speed and increased sound attenuation. The effects are more pronounced when the density of vegetation is higher as well as during daylight hours when sunlight-driven photosynthesis occurs. However, the application of mathematical models to describe these phenomena have been limited to effective medium models for water containing spherical gas bubbles. These approaches neglect both the effects of elastic properties of seagrass tissue as well as the shape of the aspherical gas bodies constrained within the plant. In this work, a finite element model of an acoustic resonator containing seawater and seagrass blades was developed to explain previously published measurements. Themodel utilizes independently measured values of the elastic propertiesof seagrass tissue and microscopic cross-section imagery of the gas volumes contained within the seagrass tissue. These results represent a step towards defining an appropriate effective medium model for acoustic propagation through seagrass tissue. [Work supported by ARL:UT IR&D and ONR.]