Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session BB: Biofluid Dynamics IV: Aneurysm |
Hide Abstracts |
Chair: George Karniadakis, Brown University Room: Tampa Marriott Waterside Hotel and Marina Grand Salon F |
Sunday, November 19, 2006 11:00AM - 11:13AM |
BB.00001: A better understanding of the relevant mechanical parameters in the design of treatment techniques for cerebral aneurysms. Gador Canton, Paloma Mora, Christian Geindreau, Javier Rodriguez-Rodriguez, Juan C. Lasheras We have measured the effect of placing multiple stents across the neck of a 90\r{ }-bend sidewall cerebral aneurysm. A polycarbonate rigid model with a typical shape aneurysm arising from a 4-mm parent artery was used in order to avoid the influence of the deformation produced by the stent in the geometry of the complex parent artery-aneurysm. The characterization of the flow was done using DPIV. We measured both the kinetic energy and the circulation before and after the sequential placement of multiple stents. These measurements, complemented with a finite element method, were used to perform a parametric study to determine the optimum number of stents required to achieve the formation of a stable thrombus inside the aneurysmal sac for each specific geometrical configuration. [Preview Abstract] |
Sunday, November 19, 2006 11:13AM - 11:26AM |
BB.00002: Effects of the Transient Blood Flow-Wall Interaction on the Wall Stress Distribution in Abdominal Aortic Aneurysm (AAA) Rubing Tang, Christian Geindreau, Juan Lasheras Our static finite element analysis (FEA) of both idealized and real clinical models has shown that the maximum diameter and asymmetry have substantial influence on the AAA wall stress distribution. The thrombus inside the AAA was also found to reduce the magnitude of the wall stresses. To achieve a better understanding of the wall stress distribution in real AAAs, a dynamic FEA was also performed. We considered models, both symmetric and non-symmetric, in which the aorta is assumed isotropic with nonlinear material properties. For the limiting case of rigid walls, the evolution of the flow pattern and the wall shear stresses due to fluid flow at different stages of cardiac cycle predicted by our simulations are compared with experimental results obtained in in-vitro models. A good agreement is found between both results. Finally, we have extended the analysis to the physiologically correct case of deformable walls and characterized the transient effects on the wall stresses. [Preview Abstract] |
Sunday, November 19, 2006 11:26AM - 11:39AM |
BB.00003: Changes in wall shear stresses in abdominal aortic aneurysms with increasing wall stiffness Anne-Virginie Salsac, Miguel Fernandez During the growth of abdominal aortic aneurysms, local changes occur in the composition and structure of the diseased wall, resulting in its stiffening. A numerical simulation of the fluid structure interactions is performed in idealized models of aneurysms using a finite element method. A full coupling of the equations governing the pulsatile blood flow and the deformation of the compliant wall is undertaken. The effect of the progressive stiffening of the wall is analyzed at various stages in the growth of the aneurysm. Increasing the wall stiffness alters the distribution of wall shear stresses and leads to an increase in their magnitude. The wall compliance is shown to have a more pronounced effect on non-axisymmetric aneurysms, which sustain large displacements. The overall movement of the aneurysm models increases the three-dimensionality of the flow. [Preview Abstract] |
Sunday, November 19, 2006 11:39AM - 11:52AM |
BB.00004: A mechanical view on aneurisms Virginie Duclaux, Fran\c{c}ois Gallaire, Christophe Clanet Aneurisms form at bifurcations: Either before (aorta), either after (brain). They appear as a dilatation of the artery which increases in time and brakes when the local diameter becomes larger then few times the mean diameter. We model the artery as a cylindrical elastic membrane submitted to a pulsed flow. We first show that the artery either deforms locally, or globally. Both deformations are associated to the two different aneurisms locations. In a second step we show that above a critical diameter, the wave regime of the artery sweetches to an unstable deformation regime. We identify the parameters responsible for the instability and discuss their physiological counterparts. [Preview Abstract] |
Sunday, November 19, 2006 11:52AM - 12:05PM |
BB.00005: Treatment of Basilar Aneurysms with SMP Foams J.M. Ortega, J.N. Rodriguez, D.J. Maitland, T.S. Wilson, J. Hartman Researchers in the Medical Division at LLNL are currently developing a shape memory polymer (SMP) foam aneurysm treatment technique. This technique involves the catheter delivery of a compressed piece of SMP foam to an aneurysm.~ When the foam is heated by laser radiation from a diffusing fiber-optic element embedded within the catheter, the foam expands, filling the aneurysm volume.~ If proven successful, such a treatment alternative will provide clinicians the ability to not only isolate an aneurysm from the vascular system with one device, but also to customize the shape of the lumen beneath the aneurysm neck. Consequently, the flow patterns beneath the aneurysm neck could potentially be optimized to minimize the hemodynamic stresses on the lumen. In this computational study, multiple lumen shapes are simulated beneath the necks of several patient-specific basilar aneurysms. A comparison is made between the pre-treatment and post-treatment configurations, as well as with a conventional surgical clipping configuration. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. UCRL-ABS-222933. [Preview Abstract] |
Sunday, November 19, 2006 12:05PM - 12:18PM |
BB.00006: Experimental study of physiological flow in a cerebral saccular tip aneurysm William Tsai, Omer Savas, Jason Ortega, Duncan Maitland, David Saloner Allowed to grow unchecked, a cerebral aneurysm may hemorrhage, leading to possible brain damage or death. Preventive treatment can alleviate this risk. The research presented will focus on cerebral saccular aneurysms. Flow visualization and particle image velocimetry are used at physiological input flow conditions in a simplified model geometry of a basilar artery bifurcation with a tip aneurysm. The results show the formation of vortical structures at the neck which impinge near the fundus and travel along the walls of the aneurysm. The goal of this research is to aid in the development of the implementation of laser-activated shape memory polymer devices for treatment. Future work on this project includes fluid flow and temperature studies during and post treatment. [Preview Abstract] |
Sunday, November 19, 2006 12:18PM - 12:31PM |
BB.00007: DNS of flow in stenosed carotid artery Leopold Grinberg, Alexander Yakhot, George Karniadakis Direct numerical simulation (DNS) of a three-dimensional flow through a stenosed carotid artery has been performed. Onset of turbulence downstream of the occlusion has been observed. The developing turbulence is characterized by an alternating spatio-temporal transitional regime. The transition to turbulence occurs during the systolic phase approximately five throat-diameters downstream of the throat, while laminarization occurs during the diastolic phase. Transition in space is first enhanced and subsequently decays downstream. The wall shear stress increases in the stenosed internal carotid artery due to the vessel occlusion and as the result of turbulence. [Preview Abstract] |
Sunday, November 19, 2006 12:31PM - 12:44PM |
BB.00008: Instability and transition modes of pulsatile stenotic flow Hugh Blackburn, Spencer Sherwin Stability of pulsatile stenotic flow in an axisymmetric tube with a smooth 50\% diametral stenosis is examined using Floquet analysis and direct numerical simulation. Inflow is a linear combination of Hagen--Poiseuille flow and a single fluctuating harmonic, giving a peak-to-mean ratio of 1.75. The two controlled parameters are Reynolds number and reduced velocity (alternatively, Reynolds number and Womersley number). The main features of the axisymmetric flows are vortex rings that are blown out of the stenosis throat with each pulse, and a shear layer trailing in the wake of each vortex that becomes more extended as reduced velocities increase. Two primary three-dimensional instability modes associated with the vortex rings are found: an alternating vortex-ring-tilting mode that is the most unstable mode at high reduced velocites, and a pair of wavy-vortex-core (or Widnall) modes that dominate at lower reduced velocities. Both these global modes lead to localized turbulent bursts, and these move upstream with time so that asymptotically the bursts occur within a comparatively few diameters of the throat. In addition, the extended shear layers that trail behind the vortex rings at high reduced velocities are susceptible to axisymmetric convective instability, and it is found that this can interact with and promote the global vortex-tilting mode. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700