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Article

Fluid-structure interaction simulation with relevance to snoring

Authors: Schickhofer, L., Dahlkild, A. A., Mihaescu, M
Document Type: Conference
Pubstate: Accepted
Journal: Svenska Mekanikdagar, Linköping, Sweden, June 10-12, 2015
Volume:   
Year: 2015

Abstract

The human upper respiratory tract is susceptible to abnormal airway obstructions that considerably influence the patient's quality of life. One of the most common airway disorders is the Obstructive Sleep Apnea Syndrome (OSAS) characterized by partial or total obstruction of the airway. Snoring is always associated with OSAS. It is caused by flow based excitation of the soft palate and uvula, which is a region of elastic, compliant tissue separating the nasal and oral cavities. The characterization of the involved tissues by constitutive models is a complex task, as they are nonlinear, viscoelastic, and heterogeneous. In-vivo measurements are often impossible or inaccurate, so that numerical assessment based on simplified geometries becomes an important option. Additionally, Computational Fluid Dynamics has gained increasing importance for the analysis of respiratory airway disorders, as well as planning of surgical treatment. Generally, a quantification of the effects of tissue properties on both the biomechanics of obstructions and the onset of tissue vibrations and resonance is desired. This is attempted here by simulating the fluid-structure interaction problem in an idealized confined flow-elastic filament interaction setup resembling the soft palate behavior during inhalation. The evaluation of the flow field enables an estimation of the critical parameters leading to vortex shedding and unsteady pressure loads at the filament trailing edge. If both the filament length and the Reynolds number are increased, the vortices tend to be shed with higher frequency. The displacement of the elastic filament is larger with increased Reynolds number, length of the filament, and reduced modulus of elasticity. For particular conditions (e.g. low Young's modulus) the filament can potentially couple with the flow to show resonance with significantly increased flow dislocation. This leads to strong pressure fluctuations and to sound generation similar to the typical snoring noise. It is shown that a longer filament may totally suppress the generation of the von Karman vortex street for certain lower Reynolds numbers (e.g. Re = 150). This suggests the existence of a critical length of the filament and a critical Reynolds number necessary for vibrations to occur. The present work will investigate this aspect since it has a potential impact on the surgical therapeutic measures targeting the soft palate region in patients with e.g. OSAS.