Snoring : a flow-structure interaction

• Main Author: Howell, Richard Martyn
• Published: University of Warwick 2006
• Subjects: 620.1064; TJ Mechanical engineering and machinery
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429746

A novel method for calculating the linear fluid-structure interaction of a cantilevered flexible surface centrally positioned in an ideal channel flow, incorporating the effects of vorticity shed downstream, is described. The perturbation pressure is modelled using a linearised boundary-element method. The flexible surface deflection is modelled using linearised one-dimensional beam theory. The shed vorticity is modelled using a linearised discrete vortex method. The computational model can therefore be used to conduct numerical experiments where no presupposition of the flexible surface deflection is made. This linear model can accurately capture the onset of instability in this fluid-structure system. The flexible surface is infinitely thin; the upper and lower sides of the surface can therefore be considered stream lines of the flow, with a step jump in pressure between them across the surface. The discontinuity of tangential velocity across the flexible surface generates lift. The flexible surface is therefore modelled by a distribution of vortex singularities with a Kutta condition applied at the surface’s trailing edge. The individual models of the flexible surface and the fluid velocity and vorticity, together with the action of the individual hydrodynamic pressure components created when the models are combined to form a single unsteady model, are validated via a series of numerical experiments and by quantitative comparison with an appropriate, previously developed computational model. Unique, highly detailed investigations into the ideal fluid-structure phenomena observed in numerical experiments conducted over a wide range of mass ratio and inlet velocity are documented. For the first time, detailed numerical investigation of the effect on this fluid-structure interaction of channel walls, a rigid central surface (upstream and adjacent to the flexible surface), unsteady mean flow, the variation of stiffness and damping properties along the flexible surface and the vorticity shed at the trailing edge of the flexible surface have been quantified. Calculations of the critical velocity show good correlation with other published work and examples of the possible application of the unsteady model to different physical fluid-structure phenomena are outlined. Of central importance is the application of the unsteady model to the investigation of the human snoring phenomenon. Further insight into the operation of two types of snore is made and a new type of snore is discovered, incorporating the effects of inhalation. The numerical experiments demonstrate that the location (on the flexible surface) of the destabilising phase shift between the flexible surface velocity and fluid pressure leading to instability change drastically for a small shift in mass ratio. Coupled with knowledge of further snore mechanisms from other published work, these results show the uniqueness of treatment required to provide effective surgical treatment to individual patients suffering from snoring; furthermore, this highlights the need for more realistic fluid-structure models to be created.