Biao Geng

A finite element study on the cause of vocal fold vertical stiffness variation

A finite element method based numerical indentation technique was used to quantify the effect of the material stiffness variation and the subglottal convergence angle of the vocal fold on the vertical stiffness difference of the medial surface. It was found that the vertical stiffness difference increased with the increasing subglottal angle, and it tended to saturate beyond a subglottal angle of about 50°. The material stiffness variation could be as important as the subglottal angle depending on the actual material properties.

The effect of wing flexibility on sound generation of flapping wings

In this study, the unsteady flow and acoustic characteristics of a three-dimensional (3D) flapping wing model of a Tibicen linnei cicada in forward-flight are numerically investigated. A single cicada wing is modelled as a membrane with a prescribed motion reconstructed from high-speed videos of a live insect. The numerical solution takes a hydrodynamic/acoustic splitting approach: the flow field is solved with an incompressible Navier-Stokes flow solver based on an immersed boundary method, and the acoustic field is solved with linearized perturbed compressible equations. The 3D simulation allows for the examination of both the directivity and frequency compositions of the flapping wing sound in a full space. Along with the flexible wing model, a rigid wing model that is extracted from real motion is also simulated to investigate the effects of wing flexibility. The simulation results show that the flapping sound is directional; the dominant frequency varies around the wing. The first and second frequency harmonics show different radiation patterns in the rigid and flexible wing cases, which are demonstrated to be highly associated with wing kinematics and loadings. Furthermore, the rotation and deformation in the flexible wing is found to help lower the sound strength in all directions.

The effect of vocal fold vertical stiffness variation on voice production.

A parametric study was conducted using the numerical technique that coupled a three-dimensional continuum vocal fold model with a one-dimensional Bernoulli flow model to investigate the effect of vocal fold vertical stiffness variation on voice production. Vertical stiffness gradient was defined as the ratio of the inferior-superior stiffness difference to the mean stiffness and was introduced in the cover layer. The results showed that increasing the vertical stiffness gradient would increase the peak flow rate and sound intensity and decrease the open quotient and threshold pressure. The effect was found to be more prominent at low subglottal pressures. The underlying mechanism might be that the reduced stiffness at the superior aspect of the vocal fold would allow a larger lateral displacement and result in a larger vibration. Increasing the vertical stiffness gradient was also found to increase the vertical phase difference and glottal divergent angle during the vocal fold vibration. Meanwhile, increasing the vertical stiffness variation only slightly increased the mean flow rate, which is important to maintaining the speech time between breaths.

High-fidelity image-based computer modeling of voice production—From muscle contraction to flow-structure-acoustics interaction

This study aims to develop a high-fidelity computer model of voice production which can employ the image-based realistic three-dimensional geometries of larynges and simulate the complex mechanical process of voice production and control, from muscle contraction to flow-structure-acoustics interactions. Such a model will advance our understanding of the relationship between muscle contraction, vocal fold posturing, vocal fold vibration, and final voice outcome, which has important clinical implications for voice management, training, and treatment. The key components of the model include a sharp-interface-immersed-boundary-method based impressible flow model, a finite-element method based nonlinear structural dynamics model and a hydrodynamics/acoustics splitting method based acoustics model. A Hill-based contractile model is coupled in the finite element analysis to capture the active response of vocal fold tissues, and a fiber-reinforced model is employed for the passive response. A series of validations have been performed. The coupled Hill-based model and fiber-reinforced model demonstrated a good agreement with literature experimental data for dynamics, concurrent tissue stimulation, and stretching. The flow-structure-acoustics interaction model was validated with excised canine experiments using realistic geometric and material properties. The simulations showed a good agreement on the fundamental frequency, vocal fold maximum divergent angle, flow rate, and intraglottal velocity and pressure fields.This study aims to develop a high-fidelity computer model of voice production which can employ the image-based realistic three-dimensional geometries of larynges and simulate the complex mechanical process of voice production and control, from muscle contraction to flow-structure-acoustics interactions. Such a model will advance our understanding of the relationship between muscle contraction, vocal fold posturing, vocal fold vibration, and final voice outcome, which has important clinical implications for voice management, training, and treatment. The key components of the model include a sharp-interface-immersed-boundary-method based impressible flow model, a finite-element method based nonlinear structural dynamics model and a hydrodynamics/acoustics splitting method based acoustics model. A Hill-based contractile model is coupled in the finite element analysis to capture the active response of vocal fold tissues, and a fiber-reinforced model is employed for the passive response. A series of validation...