18 - Computational Simulation and Evaluation of Blast Induced Impulse Noise Effect

Abstract Text: Recent data from heavy weapons training environments suggest that protection of the ear canal alone may not be sufficient to protect the Warfighter from impulse noise (over 140 dB) induced hearing loss and cognitive performance degradation. The typical consequence of impulse noise exposure includes hearing loss, tinnitus, dizziness and headache that could lead to reduced situational awareness, and potentially lethal mistakes on the battlefield. The objective of this work is to elucidate the possible auditory pathways of impulse noise, gain insight into the fundamental mechanism of blast induced hearing loss and explore material and design solutions to protect the Warfighter from repeated impulse noise effects.
We have developed a corresponding head finite element (FE) model to simulate the biomechanical response of ear to blast induced impulse noise. The key components of the model were derived from MRI images, detailed geometric representation and material models for bones, tissues and fluids in the auditory organ. The head-ear FE model incorporated major ear structural components with NRL high-fidelity head model by utilizing the local mesh refinement. The loading conditions were derived from notional weapons firing and/or explosive incidents, and used to characterize the biomechanical effects in the ear. We have also developed a reduced-order model to analyze the dynamic behavior of inner ear when subjected to the skull vibration stimulated by the impulse noise. The cochlea model was calibrated by using frequency response data from the literature.
We have also designed and fabricated a new anthropomorphic, biofidelic head surrogate with acoustic and pressure sensors in the auditory organs to quantify the pressure wave and noise propagation in the inner ear, and compared with other measurements to calibrate the surrogate system. We then used this instrumented head in weapons training and breaching exercise environments to assess the effects of impulse noise propagation into both the inner ear and the brain through the skull, soft tissue and the ear canal. By measuring the impulse noise induced pressure change in the fluid-filled inner ear, we identified the bone conduction pathway and the possible disruption outcomes to inner ear organs (cochlea and vestibular).
The simulation results showed the sound transmission difference between bone conduction and air conduction pathways. We also compared the pressure responses in the brain and the inner ear with experimental data. Based on the simulated vibration of the basilar membrane, we established the relationship between the impulse noise and the auditory risk probability of inner ear.

Keywords: head and ear computational models, blast, impulse noise, bone conduction