UC San Diego

Anthropogenic sound in the ocean, such as sonar, has been related to mass strandings of marine life, in particular the Cuvier's beaked whale (Ziphius cavirostris). Since opportunities to study behavioral responses are limited, furthering our knowledge of whales through simulation has become a well adopted process. To simulate sound reception, the Ziphius ear complex was implemented as a three dimensional finite element model with two mechanisms that enable hearing; pressure loading from surrounding soft tissues and bone conduction from skull vibration. The numerical formulation was summarized to demonstrate an assumed-strain technique using nodally integrated continuum elements (NICE) for a forced harmonic vibration problem.

This work focuses on obtaining hearing responses using both mechanisms in conjunction with each other, while also looking into the effects of each mechanism individually. Mesh refinement with surface and volume smoothing reveals variations of simulated auditory response for the two loading mechanisms considered. Effects of the amplitudes and phase shifts, used in loading, along with material damping were reviewed for cases of only one mechanism applied at a time, then with both mechanisms active together.

A synthetic audiogram was generated from the stapes velocity transfer function (SVTF) based on relative displacement of the hearing structure. Results found here provide insight on the auditory sensitivity of the Cuvier's beaked whale and its ability to capture sound in the known range of mid-frequency sonar. Since this marine mammal has mass strandings heavily linked to sonar activity, this work allows for an understanding of the whale's hearing over a given range of frequencies.