A Canonical Biomechanical Vocal Fold Model

The present article aimed at constructing a canonical geometry of the human vocal fold (VF) from subject-specific image slice data. A computer-aided design approach automated the model construction. A subject-specific geometry available in literature, three abstractions (which successively diminished in geometric detail) derived from it, and a widely used quasi two-dimensional VF model geometry were used to create computational models. The first three natural frequencies of the models were used to characterize their mechanical response. These frequencies were determined for a representative range of tissue biomechanical properties, accounting for underlying VF histology. Compared with the subject-specific geometry model (baseline), a higher degree of abstraction was found to always correspond to a larger deviation in model frequency (up to 50% in the relevant range of tissue biomechanical properties). The model we deemed canonical was optimally abstracted, in that it significantly simplified the VF geometry compared with the baseline geometry but can be recalibrated in a consistent manner to match the baseline response. Models providing only a marginally higher degree of abstraction were found to have significant deviation in predicted frequency response. The quasi two-dimensional model presented an extreme situation: it could not be recalibrated for its frequency response to match the subject-specific model. This deficiency was attributed to complex support conditions at anterior-posterior extremities of the VFs, accentuated by further issues introduced through the tissue biomechanical properties. In creating canonical models by leveraging advances in clinical imaging techniques, the automated design procedure makes VF modeling based on subject-specific geometry more realizable

Contactless pressing of a sheet

The paper summarizes the results of several numerical flow simulations of force influence of air flows on the treated paper sheet to get a contactless fixing of the treated material during its passage through the machine and to prevent the contact of the sheet with the structural elements in the surroundings

CFD simulation of flow-induced vibration of an elastically supported airfoil

Flow-induced vibration of lifting or control surfaces in aircraft may lead to catastrophic consequences. Under certain circumstances, the interaction between the airflow and the elastic structure may lead to instability with energy transferred from the airflow to the structure and with exponentially increasing amplitudes of the structure. In the current work, a CFD simulation of an elastically supported NACA0015 airfoil with two degrees of freedom (pitch and plunge) coupled with 2D incompressible airflow is presented. The geometry of the airfoil, mass, moment of inertia, location of the centroid, linear and torsional stiffness was matched to properties of a physical airfoil model used for wind-tunnel measurements. The simulations were run within the OpenFOAM computational package. The results of the CFD simulations were compared with the experimental data

Matematické a fyzikální modelování prouděním vyvolaného kmitání lidských hlasivek

the pressure and velocity fields in coronal plane along the vibrating vocal folds were studied using a finite element mathematical model. The shapes of the vocal folds were specified according to data measured on excised human larynges in phonation position. The mathematical model of the flow is based on 2D incompressible Navier-Stokes equations adapted to deal with the time-variable shape of the domain, caused by vocal fold vibration. The numerical simulations allow to observe closely various flow features related to phonation - flow separation in the glottis, Coanda effect or vortex shedding

Matematické modelování interakce tekutiny a tělesa v problematice lidských hlasivek

In the paper numerical results from a mathematical model of human vocal folds are compared with experimental data obtained from measurements on a maquette of vocal folds, which consisted of a silicone element vibrating in a channel conveying air

Evaluation of Interferograms of Unsteady Subsonic Airflow Past a Fluttering Airfoil

The paper reports on time-resolved interferometric measurements of unsteady ow elds around a uttering NACA0015 airfoil. A mechanical model with two degrees of freedom (pitch and plunge) has been designed and tested in a high-speed subsonic wind tunnel. Aeroelastic instability of the classical utter and dynamic stall type has been observed in the Mach number range M = 0.2 - 0.5. The interferograms were recorded using a Mach-Zehnder interferometer and a high-speed camera. An in-house software IFGPro was developed for the postprocessing and evaluation of the interferogram sequences, yielding pressure distribution, lift and drag force on the airfoil

Computational aeroacoustics of human phonation

The current paper presents a CFD model of flow past vibrating vocal folds coupled to an acoustic solver, which calculates the sound sources from the flow field in a hybrid approach. The CFD model is based on the numerical solution of 3D Navier-Stokes equations on a time-dependent domain, solved by cell-centered finite volume method. To capture the fine turbulent scales important for the acoustic source calculations, the equations are discretized and solved on large computational meshes up to 3.2M elements. The CFD simulations were run in parallel using domain decomposition method and OpenMPI implementation of the MPI standard. Aeroacoustic simulations are calculated in a separate step by Lighthill’s acoustic analogy, which determines the acoustic sources based on the fluid field. This is done with the research code CFS++ which employs the finite element method (FEM)

Interakce tělesa a tekutiny v lidských hlasivkách

Matematicko-fyzikální fakultaFaculty of Mathematics and Physic