Experimental validation of a three-dimensional reduced-order continuum model of phonation

2018

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The goal of this study is to identify vocal fold conditions that produce irregular vocal fold vibration and the underlying physical mechanisms. Using a three-dimensional computational model of phonation, parametric simulations are performed with co-variations in vocal fold geometry, stiffness, and vocal tract shape. For each simulation, the cycle-to-cycle variations in the amplitude and period of the glottal area function are calculated, based on which the voice is classified into three types corresponding to regular, quasi-steady or subharmonic, and chaotic phonation. The results show that vocal folds with a large medial surface vertical thickness and low transverse stiffness are more likely to exhibit irregular vocal fold vibration when tightly approximated and subject to high subglottal pressure. Transition from regular vocal fold vibration to vocal instabilities is often accompanied by energy redistribution among the first few vocal fold eigenmodes, presumably due to nonlinear interaction between eigenmodes during vocal fold contact. The presence of a vocal tract may suppress such contact-related vocal instabilities, but also induce new instabilities, particularly for less constricted vocal fold conditions, almost doubling the number of vocal fold conditions producing irregular vibration.

Section: A Computational Model and Simulation Conditionsmentioning

confidence: 80%

Vocal instabilities in a three-dimensional body-cover phonation model

2018

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“…The subglottal pressure is varied from 0.05 to 2.4 kPa, in 18 steps, as in Zhang (2016). The range of vocal fold stiffness is selected to encompass ranges used in previous numerical studies (e.g., Alipour et al, 2000;Berry et al, 1994). Three values of the transverse Young's modulus E t are considered: 1, 2, and 4 kPa.…”

Section: A Numerical Model and Simulation Conditionsmentioning

confidence: 99%

Effect of vocal fold stiffness on voice production in a three-dimensional body-cover phonation model

2017

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Although stiffness conditions in the multi-layered vocal folds are generally considered to have a large impact on voice production, their specific role in controlling vocal fold vibration and voice acoustics is unclear. Using a three-dimensional body-cover continuum model of phonation, this study shows that changes in vocal fold stiffness have a large effect on F0 and the means and amplitudes of the glottal area and flow rate. However, varying vocal fold stiffness, particularly along the anterior-posterior direction, has a much smaller effect on the closed quotient, vertical phase difference, and the spectral shape of the output acoustics, which are more effectively controlled by changes in the vertical thickness of the medial surface. These results suggest that although changes in vocal fold stiffness are often correlated with production of different voice types, there is no direct cause-effect relation between vocal fold stiffness and voice types, and the correlation may simply result from the fact that both vocal fold stiffness and geometry are regulated by the same set of laryngeal muscles. These results also suggest the possibility of developing reduced-order models of phonation in which the vocal fold is simplified to a one-layer structure.

“…Zhang (2015Zhang ( , 2017. Despite these simplifications, our previous studies using similar computational models have been able to reproduce experimental observations on voice production by unsteady glottal flow (Zhang et al, 2002), phonation threshold pressure and frequency in a two-layer silicone vocal fold model (Farahani and Zhang, 2016), and vocal fold vibration patterns in different vibratory regimes and transitions between regimes (Zhang and Luu, 2012).…”

Section: A Computational Model and Simulation Conditionsmentioning

confidence: 91%

Vocal fold contact pressure in a three-dimensional body-cover phonation model

2019

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The goal of this study is to identify vocal fold geometric and mechanical conditions that are likely to produce large contact pressure and thus high risk of vocal fold injury. Using a three-dimensional computational model of phonation, parametric simulations are performed with co-variations in vocal fold geometry and stiffness, with and without a vocal tract. For each simulation, the peak contact pressure is calculated. The results show that the subglottal pressure and the transverse stiffness of the vocal folds in the coronal plane have the largest and most consistent effect on the peak contact pressure, indicating the importance of maintaining a balance between the subglottal pressure and transverse stiffness to avoiding vocal fold injury. The presence of a vocal tract generally increases the peak contact pressure, particularly for an open-mouth vocal tract configuration. While a low degree of vocal fold approximation significantly reduces vocal fold contact pressure, for conditions of moderate and tight vocal fold approximation changes in vocal fold approximation may increase or decrease the peak contact pressure. The effects of the medial surface thickness and vocal fold stiffness along the anterior−posterior direction are similarly inconsistent and vary depending on other control parameters and the vocal tract configuration.