Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session M25: Biofluids: Transport and Control |
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Chair: Amy Gao, MIT Room: 304 |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M25.00001: Modeling Self-Induced Effects is Important for Flow-Relative Control Amy Gao, Michael Triantafyllou For aquatic animals, self-generated stimulation has the potential to mask signals from external sources. Fish, which sense their near field using their lateral lines, have developed passive and active means of subtracting the flow signals generated by their self motions, which not only mask biologically relevant stimuli, but also render control deficient. While prior work in this field estimates the orientation of a vehicle as a linear function of the difference in pressure between opposite sides, we demonstrate that a high performance controller cannot operate using simply this linear relationship, because in a hydrodynamic environment, the external flow and the self-induced flow combine in a nonlinear way. A misinterpretation of the hydrodynamic interactions due to simplistic signal manipulation can be catastrophic, leading to instability or collision. Overall, we demonstrate the importance of model-based control in the underwater environment, and propose a robust controller which uses flow-relative feedback from a sensor inspired by the lateral line of fish. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M25.00002: Optimal Sensor Layouts in Underwater Locomotory Systems Brendan Colvert, Eva Kanso Retrieving and understanding global flow characteristics from local sensory measurements is a challenging but extremely relevant problem in fields such as defense, robotics, and biomimetics. It is an inverse problem in that the goal is to translate local information into global flow properties. In this talk we present techniques for optimization of sensory layouts within the context of an idealized underwater locomotory system. Using techniques from fluid mechanics and control theory, we show that, under certain conditions, local measurements can inform the submerged body about its orientation relative to the ambient flow, and allow it to recognize local properties of shear flows. We conclude by commenting on the relevance of these findings to underwater navigation in engineered systems and live organisms. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M25.00003: Sinusoidal Forcing of Interfacial Films Fayaz Rasheed, Aditya Raghunandan, Amir Hirsa, Juan Lopez Fluid transport, in vivo, is accomplished via pumping mechanisms of the heart and lungs, which results in biological fluids being subjected to oscillatory shear. Flow is known to influence biological macromolecules, but predicting the effect of shear is incomplete without also accounting for the influence of complex interfaces ubiquitous throughout the body. Here, we investigated the oscillatory response of the structure of aqueous interfacial films using a cylindrical knife edge viscometer. Vitamin ${K}_{1}$ was used as a model monolayer because its behaviour has been thoroughly quantified and it doesn't show any measurable hysteresis. The monolayer was subjected to sinusoidal forcing under varied conditions of surface concentrations, periodic frequencies, and knife edge amplitudes. Particle Image Velocimetry(PIV) data was collected using Brewster Angle Microscopy(BAM), revealing the influence of oscillatory interfacial shear stress on the monolayer. Insights were gained as to how the velocity profile dampens at specific distances from the knife edge contact depending on the amplitude, frequency, and concentration of Vitamin ${K}_{1}$. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M25.00004: Why are there no short circuits in the arterial network? Shyr-Shea Chang, Shenyinying Tu, Yu-Hsiu Liu, Van Savage, Sheng-Ping Hwang, Marcus Roper Efficient transport within vascular networks requires red blood cells be delivered at the same rate to each capillary, to ensure even oxygen supply throughout an organism. However, real vascular systems are massive networks in which distance from the heart to capillary vessels can vary over several orders of magnitude. Why are there no short-circuits? Why don't capillaries closer to the heart receive more red blood cells than farther capillaries? We used the trunk arterial network of a zebrafish embryo as a model for understanding the mechanisms underlying red blood cell partitioning within the microvasculature. Using mathematical modeling and experiments in living zebrafish we show that a tuned hydrodynamic feedback mechanism evenly splits red blood cells between trunk vessels. This key design feature comes at a cost to the overall efficiency of the network in that creating a uniform flux means that many red blood cells no longer travel through capillaries. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M25.00005: Modeling and Simulation of Cardiogenic Embolic Particle Transport to the Brain Debanjan Mukherjee, Neel Jani, Shawn C. Shadden Emboli are aggregates of cells, proteins, or fatty material, which travel along arteries distal to the point of their origin, and can potentially block blood flow to the brain, causing stroke. This is a prominent mechanism of stroke, accounting for about a third of all cases, with the heart being a prominent source of these emboli. This work presents our investigations towards developing numerical simulation frameworks for modeling the transport of embolic particles originating from the heart along the major arteries supplying the brain. The simulations are based on combining discrete particle method with image based computational fluid dynamics. Simulations of unsteady, pulsatile hemodynamics, and embolic particle transport within patient-specific geometries, with physiological boundary conditions, are presented. The analysis is focused on elucidating the distribution of particles, transport of particles in the head across the major cerebral arteries connected at the Circle of Willis, the role of hemodynamic variables on the particle trajectories, and the effect of considering one-way vs. two-way coupling methods for the particle-fluid momentum exchange. These investigations are aimed at advancing our understanding of embolic stroke using computational fluid dynamics techniques. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M25.00006: Three-dimentional simulation of flow-induced platelet activation in artificial heart valves Mohammadali Hedayat, Hafez Asgharzadeh, Iman Borazjani Since the advent of heart valve, several valve types such as mechanical and bio-prosthetic valves have been designed. Mechanical Heart Valves (MHV) are durable but suffer from thromboembolic complications that caused by shear-induced platelet activation near the valve region. Bio-prosthetic Heart Valves (BHV) are known for better hemodynamics. However, they usually have a short average life time. Realistic simulations of heart valves in combination with platelet activation models can lead to a better understanding of the potential risk of thrombus formation in such devices. In this study, an Eulerian approach is developed to calculate the platelet activation in three-dimensional simulations of flow through MHV and BHV using a parallel overset-curvilinear immersed boundary technique. A curvilinear body-fitted grid is used for the flow simulation through the anatomic aorta, while the sharp-interface immersed boundary method is used for simulation of the Left Ventricle (LV) with prescribed motion. In addition, dynamics of valves were calculated numerically using under-relaxed strong-coupling algorithm. Finally, the platelet activation results for BMV and MHV are compared with each other. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M25.00007: Platelets aggregation in pathological conditions: role of local shear rates and platelet activation delay time. He Li, Alireza Zarif Khalili Yazdani, George Karniadakis Platelets play an essential role in the initiation and formation of a thrombus, however their detailed motion in blood vessels with complex geometries, such as in the aneurysmal vessel or stenotic vessel in atherosclerosis, has not been studied systematically. Here, we perform spectral element simulations (NEKTAR code) to obtain the 3D flow field in blood vessel with cavities, and we apply the force coupling method (FCM) to simulate the motion of platelets in blood flow. Specifically, simulations of platelets are performed in a 0.25 mm diameter circular blood vessel with 1 mm length. Corresponding coarse-grained molecular dynamics simulations are employed to provide input to the NEKTAR-FCM code. Simulations are conducted at several different Reynolds numbers (Re). An ellipsoid-shaped cavity is selected to intersect with the middle part of the circular vessel to represent the aneurysmal part of the blood vessel. Based on the simulation results, we quantify how the platelets motion and aggregation in the blood vessel cavities depend on Re, platelet activation delay time, and the geometry of the cavities. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M25.00008: A simple numerical model for membrane oxygenation of an artificial lung machine Sai Nikhil Subraveti, P.S.T. Sai, Vinod Kumar Viswanathan Pillai, B.S.V. Patnaik Optimal design of membrane oxygenators will have far reaching ramification in the development of artificial heart-lung systems. In the present CFD study, we simulate the gas exchange between the venous blood and air that passes through the hollow fiber membranes on a benchmark device. The gas exchange between the tube side fluid and the shell side venous liquid is modeled by solving mass, momentum conservation equations. The fiber bundle was modelled as a porous block with a bundle porosity of 0.6. The resistance offered by the fiber bundle was estimated by the standard Ergun correlation. The present numerical simulations are validated against available benchmark data. The effect of bundle porosity, bundle size, Reynolds number, non-Newtonian constitutive relation, upstream velocity distribution etc. on the pressure drop, oxygen saturation levels etc. are investigated. To emulate the features of gas transfer past the alveoli, the effect of pulsatility on the membrane oxygenation is also investigated. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M25.00009: Three-dimensional flow and vorticity transport in idealized airway model from laminar to turbulent regimes Sahar Jalal, Tristan Van de Moortele, Andras Nemes, Azar Eslam Panaha, Filippo Coletti The presence and intensity of secondary flows formed by the inhaled air during respiration has important consequences for gas exchange and particle transport in the lungs. Here we focus on the formation and persistence of such secondary flows by experimentally studying the steady inspiration in an idealized airway model. The geometry consists of a symmetric planar double bifurcation that respects the geometrical proportions of the human bronchial tree. Physiologically relevant Reynolds numbers from 100 to 5000 are investigated, ranging from laminar to turbulent regimes. The time-averaged, three-dimensional velocity fields are obtained from Magnetic Resonance Imaging (MRI), providing detailed distributions of vorticity, circulation, and secondary flow strength. Information on the velocity fluctuations are obtained by Particle Image Velocimetry (PIV). The measurements highlight the effect of the Reynolds number on the momentum transport, flow partitioning at the bifurcations, strength and sense of rotation of the longitudinal vortices. A marked change in topology is found at a specific Reynolds number, above which the influence of the upstream flow prevails over the effect of the local geometry. Finally, turbulence and its role in the mean vorticity transport are also discussed. [Preview Abstract] |
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