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Brian McCary, Osman Basaran Basaran, Valeri Kolesnitchenko; Computational Fluidic Dynamics (CFD) modeling of a novel vitreous liquifier. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5925. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The geometry of the active liquification zone at the tip of a hypersonic vitreous liquefier has not been fully described. The concept of using the fluid traveling through a port to disrupt fluid in front of the port is not as intuitive as the use of a moving metal blade in guillotine vitrectomy cutters. The action takes place on a time and displacement scale that limits visualization of the action. We employed three computational fluidic dynamics (CFD) models to study the action near the tip, identify bounds on the active region and understand key characteristics to an accurate model.
Three different CFD models were created by two different teams with increasing sophistication. A linear acoustic COMSOL model was developed to identify the most active regions. A non-linear COMSOL model was developed to assess port flow in water. Finally, a proprietary non-linear model was developed to assess the impact of fluid viscosity. All models were done assuming closed spherical end 23 gage tips with round ports. Port ID, lumen ID and port structure were allowed to vary, with and without aspiration flow superimposed. Pressures, flows and strain rates were evaluated. Modeling challenges were identified.
The linear acoustic model predicted a 24 m/s port fluid velocity for a 483 um lumen and 152 um port at a 40 um stroke; the Comsol CFD predicted a 35 m/sec velocity under the same conditions, as did an unbounded vacuum swept-volume computational model. The proprietary model showed transient maximum strain rates in excess of 30 at the edge of the port for similar construction, which can vary with port shape. Dependencies of fluid flows on the design parameters were clearly identified.
Our results show that the region directly in front of the port is far more active than any other external region. The most active portion of this region can be bounded by a spherical volume no larger in diameter than the tip. The velocities in the port can be practically estimated from the geometry of the tip, but inertial effects must be considered when estimating the size of the active zone. Vacuum in the tip might create cyclical pressure release artifacts inside the tip at most tip amplitudes. Further modeling will be required to understand the impact of these artifacts and of aspiration flow on the peak port velocity.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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