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Capillary-elastic instabilities with applications to airway closure.The lung is comprised of a network of bifurcating airway tubes which are coated with a thin viscous film. Often times, especially in the case of disease, the liquid film can form a mensicus which fills the whole tube, thus obstructing airflow. The formation of the liquid mensicus is due to capillary driven instabilities which can arise in the lining, causing the lining to close up. In addition, airflow can also be obstructed if the airway tube collapses in on itself. This occurs when the elastic forces of the tube are not large enough to sustain the negative fluid pressures inside the tube, and the tube collapses. More recently, we have been looking at means of preventing closure, for example, the effects of an oscillatory shear stress on the air-fluid interface.
Movies of closure simulations. Halpern, D. and Grotberg, J.B. Fluid-elastic instabilities of liquid lined flexible tubes: Airway closure. J. Fluid Mech. 244: 615-632, 1992. Halpern, D. and Grotberg, J.B. Surface-tension instabilities of liquid-lined elastic tubes. Contemporary Mathematics 141: 295-316, 1993, edited by A.Y. Cheer and C.P. van Dam. Halpern, D. and Grotberg, J.B. Surfactant effects on fluid elastic instabilities of liquid lined flexible tubes: a model of airway closure. J. Biomech. Eng. 115: 271-277, 1993. Cassidy, K.J, Halpern, D., Ressler, B.G. and Grotberg, J.B. Surfactant effects in model airway closure experiments. J. Applied Physiology 87: 415-427,1999. [Abstract] [Full Text] [PDF] Halpern, D., Moriarty, J.A. and Grotberg, J.B. (1999) Capillary-Elastic Instabilities with an Oscillatory Forcing Function. In IUTAM Symposium on Non-linear Singularities in Deformation and Flow. Editors, Durban, D. and Pearson, J.R.A, pp. 243-255. Publishers: Kluwer Academic, Dordrecht, The Netherlands. Halpern, D. and Grotberg, J.B. (2000) Oscillatory shear stress induced stabilization of thin film instabilities.In: IUTAM Symposium on Nonlinear Waves in Multiphase Flow.Editor, Chang, H.-C, Volume 57, pp. 33-43. Publishers: Kluwer Academic, Dordrecht, The Netherlands.< u2:p> Halpern, D. and Grotberg, J.B. Nonlinear Saturation of the Rayleigh instability in a liquid-lined tube due to oscillatory flow. J. Fluid Mech. 492: 251-270, 2003. Halpern, D., Fujioka, H. and Grotberg, J. B. The effect of viscoelasticity on the stability of a pulmonary airway liquid layer. Phys. Fluids 22, 011901, 2010. Bian, S., Tai, C.-F., Halpern, D., Zheng, Y. and Grotberg, J.B. Experimental Study of Flow Fields in an Airway Closure Model. J. Fluid Mech. 647, 391-402, 2010. Tai, C.-F., Bian, S., Halpern, D., Zheng, Y., Filoche, M. and Grotberg, J.B. Numerical Study of Flow Fields in an Airway Closure Model. J. Fluid Mech. 677, 483-502, 2011. |