Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session PE: Biofluids X: General IV - Biomedical Flows |
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Chair: Joseph Bull, University of Michigan Room: 101E |
Tuesday, November 24, 2009 11:40AM - 11:53AM |
PE.00001: Scaling analysis of magnetic fluid hyperthermia Monrudee Liangruksa, Ranjan Ganguly, Ishwar K. Puri Magnetic fluids have been investigated for hyperthermia and thermoablation applications. These have advantages over traditional treatments in terms of localization of the therapy and less serious side effects. Herein, an analysis of bioheat transfer during magnetic fluid hyperthermia is performed. The results provide insight into the roles of dimensionless numbers in the bioheat equation and can lead to parameter optimization for in vitro and in vivo magnetic fluid hyperthermia experiments. In addition, a clinical efficacy index and a damage is provided for magnetic heating. [Preview Abstract] |
Tuesday, November 24, 2009 11:53AM - 12:06PM |
PE.00002: Effects of encapsulation elasticity on the stability of an encapsulated contrast microbubble for medical imaging and drug delivery Amit Katiyar, Kausik Sarkar Encapsulated microbubbles for ultrasound imaging show a shelf life of months while free bubbles, in aqueous medium, last for milliseconds. For microbubbles, with inelastic encapsulation, lifetime of hours is possible only at extremely low surface tension ($<$1 mN/m) or at extreme oversaturation. However, microbubbles with elastic encapsulation can resist dissolution. Analytical expressions involving saturation level, surface tension and interfacial dilatational elasticity are determined for attaining non-zero equilibrium radius for these microbubbles. All encapsulated bubbles dissolve in undersaturated medium. In a saturated medium, an encapsulated bubble is found to achieve a long-time stable radius when interfacial dilatational elasticity is larger than the equilibrium surface tension. For bubbles with interfacial dilatational elasticity smaller than the equilibrium surface tension, stable bubble of non-zero radius can be achieved only when the saturation level is greater than a critical value. Even if they initially contain a gas other than air, bubbles that reach a stable radius finally become air bubbles. The model is applied to an octafluoropropane filled lipid-coated 2.5 lm bubble. Effects of elasticity, shell permeability, initial mole fraction, initial radius and saturation level are discussed. [Preview Abstract] |
Tuesday, November 24, 2009 12:06PM - 12:19PM |
PE.00003: Analysis of Alternative Polling Strategies for Derivative-Free Optimization of the Fontan Surgery Weiguang Yang, Jeffrey Feinstein, Alison Marsden We have recently proposed a new design for the Fontan surgery, performed to treat children with severe heart defects. The new design replaces the traditional straight graft between the inferior vena cava and the pulmonary arteries, with a Y-shaped graft. In preliminary work, this design offered superior hemodynamic performance compared to designs used in current practice. Here, we optimize an idealized Y-graft design under a range of rest to exercise pulsatile flow conditions using the surrogate management framework (SMF) and mesh adaptive direct search (MADS). Constraints are added to the problem using a filter method. In particular, we assess and compare the performance of two recently developed polling strategies used in the SMF algorithm: LTMADS and OrthoMADS. Although LTMADS works well in many applications, it chooses the polling directions randomly and may result in large angles between poll directions. OrthoMADS generates deterministic and orthogonal polling directions, which avoids the drawbacks above while still producing a dense set of directions. Finally, we extend the SMF method to incorporate multiple objectives based on clinical outcome data for Fontan patients. [Preview Abstract] |
Tuesday, November 24, 2009 12:19PM - 12:32PM |
PE.00004: Optimal shape design for cardiovascular surgery applications in the presence of uncertainties: a stochastic derivative-free approach Sethuraman Sankaran, Jeffrey Feinstein, Alison Marsden In the field of cardiovascular medicine, predictive finite element simulations that compute the hemodynamics of blood flow, particle residence times, as well as shear stresses induced on arterial walls could aid in surgical intervention. These simulations lack accurate input data and are often polluted with uncertainties in model geometry, blood inlet velocities and outlet boundary conditions. We develop a robust design framework to optimize geometrical parameters in cardiovascular simulations that accounts for diverse sources of uncertainties. Stochastic cost functions are incorporated into the design framework using their lower order statistical moments. The adaptive stochastic collocation technique embedded within a derivative-free optimization technique is employed. Numerical examples representative of cardiovascular geometries, including robust design on various anastomoses is presented and the efficiency of the adaptive collocation algorithm is shown. [Preview Abstract] |
Tuesday, November 24, 2009 12:32PM - 12:45PM |
PE.00005: Image-Based Flow Modeling Seth Dillard, John Mousel, James Buchholz, H.S. Udaykumar A preliminary method has been developed to model complex moving boundaries interacting with fluids in two dimensions using video files. Image segmentation techniques are employed to generate sharp object interfaces which are cast as level sets embedded in a Cartesian flow domain. In this way, boundary evolution is effected directly through imagery rather than by way of functional approximation. Videos of an American eel swimming in a water tunnel apparatus and a guinea pig duodenum undergoing peristaltic contractions \textit{in vitro} serve as external and internal flow examples, which are evaluated for wake structure and mixing efficacy, respectively. [Preview Abstract] |
Tuesday, November 24, 2009 12:45PM - 12:58PM |
PE.00006: Flow visualization of sterile air flows in surgical environments James McNeill, Jean Hertzberg, Zhiqiang Zhai The current design of surgical environments uses laminar flow air diffusers, originally intended for clean room environments, to provide clean, low-turbulence ventilation air across the patient surgical wound and aseptic regions of the surgical staff. The objective of the current design is to minimize turbulence which increases mixing between the sterile air field and any non-sterile areas. Full-scale laboratory experiments using laser sheet illumination were conducted to investigate the interface between the sterile air field underneath the laminar flow diffusers and the non-sterile room air in the area surrounding the diffuser array. The shear layer between the sterile air and the room air resulted in turbulent mixing. In addition, the shear layer boundary angled towards the patient causing the migration of contaminants towards the aseptic region. Further research is being conducted to understand the impact of the free shear layer along the boundary of the laminar flow diffuser array on contaminant transport into the sterile region. [Preview Abstract] |
Tuesday, November 24, 2009 12:58PM - 1:11PM |
PE.00007: Particle Size, Magnetic Field, and Blood Velocity Effects on Particle Retention in Magnetic Drug Targeting Erica Cherry, Peter Maxim, John Eaton Magnetic drug targeting (MDT) is a promising cancer treatment technique in which magnetic drug particles are steered through the blood stream or held near a tumor site using external magnetic fields. A physics-based model of a general MDT system was developed with the goal of realizing the practical limitations of MDT when electromagnets are the source of the magnetic field. The simulation tracks magnetic particles subject to gravity, drag force, magnetic force, and hydrodynamic lift in specified flow fields and external magnetic field distributions. A model problem was analyzed to determine the effect of drug particle size, blood flow velocity, and magnetic field gradient strength on efficiency in holding particles stationary in a laminar Poiseuille flow modeling blood flow in a medium-sized artery. It was found that particle retention rate increased with increasing particle diameter and magnetic field gradient strength and decreased with increasing bulk flow velocity. The results suggest that MDT systems with electromagnets are unsuitable for use in small arteries because it is difficult to control particles smaller than about 20 microns in diameter. [Preview Abstract] |
Tuesday, November 24, 2009 1:11PM - 1:24PM |
PE.00008: Bubble Evolution During Acoustic Droplet Vaporization Adnan Qamar, Joseph Bull A first theoretical model of bubble evolution in Acoustic Droplet Vaporization (ADV) inside a circular microchannel is presented. This work is motivated by a novel gas embolotherapy technique, which is intended to treat cancers by occluding blood flow using gas bubbles. The intended therapy involves the injection of superheated Dodecafluoropentane (DDFP, C$_{5}$F$_{12}$, boiling point 29\r{ }C) droplets, each encapsulated in an albumin shell, into the blood stream. The blood circulation carries these droplets into the tumor region where high-intensity ultrasound is used to trigger ADV to form bubbles near the desired occlusion sites. The proposed model describes the rapid phase transition from highly superheated DDFP droplet to the vapor phase via a homogeneous nucleation within the DDFP droplet. For every time step the radial component of the Navier-Stokes equation is integrated from the nucleated bubble surface to the expanding boundary of the droplet with proper boundary conditions taking into account for the vaporization process. Further from the droplet boundary to the end of microchannel a modified unsteady Bernoulli equation with the head loss term is utilized. Close agreement with experimental data for all the acoustic parameters and different initial droplet sizes is obtained. The proposed model is expected to elucidate the role of different parameters involved in the complex ADV process. This work is supported by NIH grant R01EB006476. [Preview Abstract] |
Tuesday, November 24, 2009 1:24PM - 1:37PM |
PE.00009: Numerical Simulation of Cellular Blood Flow through a Rigid Artery Daniel Reasor, Jonathan Clausen, Cyrus Aidun In blood flow, red blood cells (RBCs), the most numerous constituent of blood, influence continuum-level measures by altering the suspension at microscopic scales. The presence of RBCs alters the stress and diffusion individual cells experience, which can influence cardiovascular diseases by affecting other cells present in blood like platelets and white blood cells. Simulations of blood at a cellular level provide a tool that allows exploration of both the rheology and the stress and diffusion of individual suspended cells. In this work, a hybrid lattice-Boltzmann/finite element method is used to simulate suspension flows characteristic of blood with deformable RBCs at realistic hematocrit values. We have shown the ability to simulate thousands deformable suspensions capturing non-Newtonian flow characteristics such as shear thinning, and the results agree well with experimental observations. Simulations through rigid arteries have been deformed with as many as 2500 RBCs. This work outlines results obtained for pressure-gradient driven blood flow through a rigid artery with 20\%, 30\%, 40\%, and 50\% hematocrit values. Results include the effect these deformable RBCs have on mean velocity, flow rate, radial variation of RBC concentration, and the effective viscosity for simulations at moderate to low cell capillary numbers, $Ca \leq 0.08$. [Preview Abstract] |
Tuesday, November 24, 2009 1:37PM - 1:50PM |
PE.00010: Computational analysis of an aortic valve jet Shawn C. Shadden, Matteo Astorino, Jean-Fr\'ed\'eric Gerbeau In this work we employ a coupled FSI scheme using an immersed boundary method to simulate flow through a realistic deformable, 3D aortic valve model. This data was used to compute Lagrangian coherent structures, which revealed flow separation from the valve leaflets during systole, and correspondingly, the boundary between the jet of ejected fluid and the regions of separated, recirculating flow. Advantages of computing LCS in multi-dimensional FSI models of the aortic valve are twofold. For one, the quality and effectiveness of existing clinical indices used to measure aortic jet size can be tested by taking advantage of the accurate measure of the jet area derived from LCS. Secondly, as an ultimate goal, a reliable computational framework for the assessment of the aortic valve stenosis could be developed. [Preview Abstract] |
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