Numerical Simulation of Fluid–Structure Interaction Problems with Applications to Flow in Vocal Folds - Fluid-Structure Interaction and Biomedical Applications - page 382

Fig. 5.33 Computational domain at time t D 0 with a finite element mesh and the description of
its size: L I D 50 mm, L g D 15:4 mm, L O D 94:6 mm, H D 16 mm. The width of the channel
in the narrowest part is 1:6 mm

Fig. 5.34 Allocation of the sensors

which show the displacements d x and d y of the sensor points on the vocal folds
surface (marked in Fig. 5.34 ) in the horizontal and vertical directions, respectively.
Moreover, the fluid pressure fluctuations in the middle of the gap as well as the
Fourier analysis of the signals are shown here. The vocal folds vibrations are not
fully symmetric due to the “Coanda effect” (a flapping jet—see [ 57 ]) and are
composed of the fundamental horizontal mode of vibration with the corresponding
frequency 113 Hz and by the higher vertical mode with the frequency 439 Hz.
The increase of vertical vibrations due to the aeroelastic instability of the system
results in a fast decrease of the glottal gap. At about t D 0:2s, when the gap
is nearly closed, the fluid mesh deformation in this region is too high and the
numerical simulation stopped. The dominant peak at 439 Hz in the spectrum of
the pressure signal corresponds well to the vertical oscillations of the glottal gap,
while the influence of the lower frequency 113 Hz associated with the horizontal
vocal folds motion is in the pressure fluctuations negligible. The modelled flow-
induced instability of the vocal folds is called phonation onset followed in reality
by a complete closing of the glottis and consequently by the vocal folds collisions
producing a source acoustic signal for voicing.