## 4 Conclusions  
This study presents a comprehensive investigation of voice production using a subject-specific model that incorporates realistic geometries and ambient domain. By employing patient-specific geometries, we demonstrate the feasibility of using such simulations for clinical applications, potentially offering more accurate representations of physiological conditions. We employed direct numerical simulation of flow-structure interaction based on compressible Navier-Stokes equations to examine the glottal flow rate, vocal fold dynamics, and acoustics. Our baseline model effectively captured essential physiological parameters. The characteristics of the glottal flow rate waveform, including the mean and peak flow rates and skewness quotient, along with the glottal area waveform parameters such as fundamental frequency and the open quotient, all fell within established physiological ranges. Additionally, the realistic vocal fold model accurately recreated the convergent-divergent pattern, which is crucial for efficient phonation. Our acoustic analysis also identified the first four formant frequencies of the airway tract with reasonable accuracy when compared to experimental data, further validating our model's ability to simulate complex vocal tract acoustics. We extended our study to explore the effects of subglottic stenosis (SGS) on voice production using realistic geometries. Our findings reveal a relationship between SGS severity and various aspects of phonation. Up to 75% SGS severity, we observed no significant changes in glottal flow, vocal fold vibration, or acoustics. At 90% SGS severity, glottal flow was notably impacted, with decreases in the mean and peak flow rates, skewness quotient, and maximum flow declination rate (MFDR). While vocal fold vibration remained largely unchanged, we detected slight alterations in the energies of the Proper Orthogonal Decomposition (POD) modes. The acoustic field exhibited minor decreases in sound pressure level and vocal efficiency. At 96% SGS severity, we noted accelerated declines in glottal flow dynamics and acoustic parameters. Vocal fold dynamics were significantly affected, showing decreases in the mean and peak glottal areas and open quotient, along with an increase in fundamental frequency. POD analysis revealed that the most substantial change in vocal fold vibration occurred in the second mode shape at this severity. It is also noteworthy that while our patient-specific model captures anatomical details and variability with high fidelity, our results suggest that these subtleties do not introduce significant changes in model outputs, especially at lower SGS severities. However, in cases of advanced stenosis (e.g., 90% or 96% obstruction), the effects of patient-specific details in geometry become more evident to accurately capture the progression of aerodynamic and acoustic changes. Our analysis of the underlying mechanisms revealed that flow resistance--particularly the interaction between resistances at the subglottic stenosis (SGS) and the vocal folds--plays a crucial role in determining the onset and extent of changes in voice production. We found that the ratio of glottal to stenosis area significantly impacts voice production in severe cases. Our study suggested that the pressure drop across the vocal folds, rather than flow resistance alone, is a key factor in altering vocal fold vibration patterns. This was especially evident in the 96% SGS case, where a significant pressure drop led to substantial changes in vocal fold dynamics. Our findings demonstrated that while flow changes may occur at lower severities, significant alterations in vocal fold dynamics manifest only at very high stenosis levels. These insights confirm that the effects of SGS on the glottal flow rate, vocal fold dynamics, and acoustics are negligible for Grade I and II stenosis (up to 70% obstruction), while higher grades produce increasingly significant impacts that may require treatment.