The effect of inertial inhomogeneity on the flutter of a cantilevered flexible plate

Howell, Richard; Lucey, Anthony D.; Pitman, Mark

doi:10.1016/j.jfluidstructs.2010.11.014

Cited by 13 publications

(4 citation statements)

References 18 publications

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“…The above counter-intuitive results-that locally decreasing the stiffness can lead to increased system stability-for short uvulae are paralleled in the studies of Howell et al (2009) and Howell et al (2011), at least for inviscid flow. The former demonstrated that localised stiffening can be destabilising while the latter demonstrated that inertial inhomogeneity can be either stabilising or destabilising depending on the location of the added mass and the length of the soft palate.…”

Section: Resultsmentioning

confidence: 80%

Modelling and simulation of fluid-structure interactions in human snoring

Elliott

Lucey

Eastwood

et al. 2011

Chan, F., Marinova, D. And Anderssen, R.S. (Eds) MODSIM2011, 19th International Congress on Modelling and Simulation.

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Snoring noise is generated by vibration of the soft tissues of the upper airway, principally those that form the back of the roof of the mouth (the soft palate) and its conical extension (the uvula). In addition to discord with bed partners, snorers are at much greater risk of obstructive sleep apnoea. This sleep-related breathing disorder is characterised by episodic upper airway obstruction with accompanying sleep disruption and consequent excessive daytime sleepiness, as well as an elevated risk of accidents and cardiovascular disease. The instability that leads to flow-induced oscillations characteristic of inspiratory snoring in the human upper airway may be modelled using a cantilevered flexible plate in a mean channel flow. However, the cantilever in existing models strictly only captures the dynamics of the uvula. In a more complete model, these dynamics will be augmented by their interaction with the motions of the soft palate-itself a flexible structure of higher effective stiffness-from which the uvula extends. To investigate how the elasticity of the soft palate affects uvula motion and their combined susceptibility to flow-induced oscillation a modification is made to the standard model. In a one-dimensional cantilevered flexible plate we allow thickness to vary as a function of length, thus effecting local changes in inertia and flexural rigidity. The overall cantilever therefore comprises a section representing the soft palate followed by a section of lower thickness that represents the uvula. The cantilever is attached to a rigid wall (hard palate) separating upper (nasal) and lower (oral) inlets of a rigid-walled channel (pharynx) conveying a viscous flow. This model is formulated using the open-source finite-element software library oomph-lib. A parametric study is performed in which the uvula-to-soft palate length and thickness ratios are varied whilst keeping their combined length constant. Results show that there is a critical uvula-length fraction that determines whether the uvula stabilises or destabilises the system. A relatively 'short' uvula swings out of phase with the soft palate and these oscillations are observed to decay; the mode shapes involved are not predicted by a uniform-thickness plate model. By contrast, if the uvula is relatively 'long' the flexible plate motion is isolated to the uvular section and the oscillations grow in amplitude, indicating a net energy transfer from fluid to structure. Increasing the thickness, hence inertia and flexural rigidity, of a 'short' uvula, e.g., by oedema, makes the fluid-structure system more unstable. In this case if the oedema were aggrevated by the vibratory mechanical insult then it would be self-sustaining and imply a bidirectional relationship between snoring and oedema of the uvula. Anatomical variability is common in the lengths of the soft palate and uvula which may make some people more susceptible than others to uvulopalatal snoring. Palatal surgery for snoring has proved highly variable in its effectiveness. Modelling of palata...

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Section: Resultsmentioning

confidence: 80%

Modelling and simulation of fluid-structure interactions in human snoring

Elliott

Lucey

Eastwood

et al. 2011

Chan, F., Marinova, D. And Anderssen, R.S. (Eds) MODSIM2011, 19th International Congress on Modelling and Simulation.

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“…One method to do this would be to use the approach of [15]: a line stiffening strip could be added through the axis of the wing/belt that increases the bending stiffness of the belt but does not increase the torsional stiffness; this is analogous to adding point masses, e.g. see [8]. To investigate oscillation amplitudes at and above the linear instability boundary i.e.…”

Section: Discussionmentioning

confidence: 99%

Crossflow fluid-structure instabilities in wind belts for energy harvesting

Taylor¹,

Wilson²,

Howell³

et al. 2020

Australasian Fluid Mechanics Conference (AFMC)

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Windbelt generators are an energy harvesting method that have viable uses for small-scale battery-charging applications for operation in low to medium wind speed conditions. The windbelt mechanism is a fluid-structure interaction (FSI) between airflow and a flexible belt, causing unstable vibration called aeroelastic flutter. The aim of this study is to understand the relationships between key parameters which will aid the future design of high efficiency windbelts. Experiments were conducted to test different length and chord rubber belts in a wind tunnel. It was found that the critical velocity of flutter onset and its frequency are a function of surface area and to a lesser extent belt pre-tension. In parallel, a novel linear FSI theoretical model that couples Theodorsen's method and Euler-Bernoulli beam theory was developed. The system is solved using a state-space method; thus we are assess the applicability of linear theory to predict the onset of non-linear limit-cycle flutter. The computational model captures the trends of the experimental data with varying quantitative accuracy and allows the identification of bending and torsional modes that couple to generate flutter. It is found that the model identifies either the bending or torsional mode that is unstable, the other coalescing mode is identified by examining the frequency space; it is the coupled bending mode that has the greatest influence on the flutter frequency. Better agreement for critical velocity is found at higher aspect ratios, demonstrating the over prediction of aerodynamic forces and absence of 3D effects at low aspect ratios in the Theodorsen method.

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“…Ihara and Watanabe, 1994;Carra et al, 2013;Arellano Castro et al, 2014). Fundamental problems, such as the stability and vibration modes of plates and beams acted upon by axial flows, have been considered previously by Taylor and Ohkusu (2000), Gluck et al (2001), Eloy et al (2008), Howell et al (2011), andTubaldi and. In addition, the non-linear behavior and coupled interactions of parallel plates confining axial flows have prompted complementary work due to their practical applications (e.g.…”

Section: Introductionmentioning

confidence: 99%