A High Fidelity Computational Method for Flow-Tissue Interaction in Biological Flows

Abstract

Flow induced vibration and deformation are phenomena that routinely occur in biological systems including cardiovascular dynamics, phonation and biological locomotion, and computational modeling of such phenomena remains a challenge. The biophysics of phonation (which refers to the production of sound in the larynx) in particular is primarily driven by a highly coupled interaction between glottal aerodynamics and vocal fold tissue. In the current work, we have developed a coupled 3D immersed-boundary finite-element method (IBFEM) for modeling the interaction of fluid with biological structures (tissue) and applied this method to investigate the biophysics of phonation. In this method, the NavierStokes equations for fluid flow are solved using a sharp interface immersed boundary method (IBM). The elastrodynamic equations for the tissue are solved using a finite--element method which is coupled with the IBM solver. The results are analyzed to gain an insight into the glottal jet aerodynamics as well as the dynamics and deformation of the vocal folds. Results show that self--sustained vibrations can be achieved for the modeled vocal fold. I. Introduction HONATION is a complex biological phenomenon which results from a highly coupled biomechanical interaction between glottal aerodynamics and vocal fold tissue vibration. The vocal folds are driven by transglottal pressure drop and vibrate mostly at a single frequency which is very close to one of the modal frequencies of the vocal folds. This frequency is the fundamental phonation frequency and decides the pitch of speech. Also a pulsatile transitional/turbulent jet is formed by the pressure drop and the moving wall of the vocal folds. The coupling of this jet with a very complicated human airway produces a complex flow field. The pulsatile jet flow and flow vortices are sound source and determine the voice quality. Due to the high complexity of human airway lumen geometric shape and nonlinearity of the coupling between airway flow aerodynamics and vocal fold vibration, modeling this problem is an immense challenge. Early studies have employed the lumped mass vocal folds model coupled with the Bernoulli equation 5 . Despite its simplicity, these models were able to demonstrate sustained vocal fold vibration and pulsatile flows. However, lumped mass models cannot precisely predict continuum system behavior 8 and flow models based on the Bernoulli equation provide no information on development of the glottal jet. Hence more sophisticated models have been used for the airflow as well as the vocal fold modeling. The lumped model has been coupled with Naiver-Stokes equations 4 . The results show that the glottal jet has a strong asymmetry which also has been observed through experiments 6