Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session FQ: Japan-US Minisymposium on Bio-Fluid Dynamics |
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Chair: Stanley Berger Room: Hilton Chicago Stevens 2 |
Monday, November 21, 2005 8:00AM - 8:26AM |
FQ.00001: Lessons from dragonfly flight Z. Jane Wang I will describe two lessons we learned from analyzing dragonfly flight using computers and table-top experiments. Part I: The role of drag in insect flight. Airplanes and helicopters are airborne via aerodynamic lift, not drag. However, it is not a priori clear that insects use only lift to fly. We find that dragonfly uses mainly drag to hover, which explains an anomalous factor of four in previous estimates of dragonfly lift coefficients, where drag was assumed to be negligible. Moreover, we show that the use of drag for flight is efficient at insect size. This suggests a re-consideration of the hovering efficiency of flapping flight, which is no longer described by the lift to drag ratio. Part II. Fore-hind wing interaction in dragonfly flight. A distinctive feature of dragonflies is their use of two pairs of wings which are driven by separate direct muscles. Dragonflies can actively modulate the phase delay between fore-hind wings during different maneuver. We compute the Navier-Stokes equation around two wings following the motion measured from our tethered dragonfly experiments, and find an explanation of the advantage of counter-stroking during hovering. [Preview Abstract] |
Monday, November 21, 2005 8:26AM - 8:52AM |
FQ.00002: An integrated approach on free flight mechanisms in insects and birds. Hao Liu To provide an overall understanding of aerodynamic and dynamic mechanisms in flying insects and birds we have succeed in establishing a biology-inspired dynamic flight simulator, which is capable to mimic hovering, forward flight and quick-turn on a basis of modeling of realistic geometry and wing kinematics, and modeling of wing-body flight dynamics. Coupling of an in-house CFD solver and a newly developed flapping flight dynamic solver enables the free flight simulation with consideration of both wing-wing interaction and wing-body interaction, and hence a systematic and quantitative evaluation of aerodynamics and flight stability in realistic flying animals. We carried out a systematic computational study on the hovering-and forward-flight of a wing-body moth model and validated the numerical results by comparing with the force-and moment-measurements based on a robotic moth model. Our results indicate that the leading-edge vortex is a universal high-lift/thrust enhancement mechanism in animal flight; and both aerodynamic force and inertial force are important in lift/thrust generation and power requirement, in particular in flight maneuverability. [Preview Abstract] |
Monday, November 21, 2005 8:52AM - 9:18AM |
FQ.00003: Microcirculatory Dynamics at the Cellular Level Aleksander S. Popel Blood is a suspension of formed elements that occupy 40{\%} of the volume; the formed elements are red blood cells (RBC), white blood cells or leukocytes, and platelets. Microcirculation refers to the flow of blood and associated transport processes in the network of vessels with diameters 5 to 100 microns. In these vessels, the ratio of the vessel diameter to the characteristic RBC diameter ranges between approximately one and ten, which precludes using a continuum description of blood and necessitates consideration of the discrete nature of the suspension. The blood vessels are lined with endothelial cells that determine RBC, leukocyte and platelet interactions with the vascular wall. The mechanics of the interactions between cells and with the endothelium are governed by complex physico-chemical processes, e.g., RBC and platelet aggregation, receptor-mediated leukocyte adhesion to the endothelium, and interactions of circulating cells with the endothelial glycocalyx, a network of polysaccharides that project from the endothelial luminal surface. Significant advances have been made in elucidating the nature of these interactions, but a general theory of blood flow in microvessels has been beyond reach. A brief overview of the achievements of the theoretical and numerical studies on the subject will be presented and unresolved problems will be discussed. [Preview Abstract] |
Monday, November 21, 2005 9:18AM - 9:44AM |
FQ.00004: The Hemodynamic Effects of Blood Flow-Arterial Wall Interaction on Cerebral Aneurysms Marie Oshima Mechanical stresses such as wall shear induced by blood flow play an important role on cardiovascular diseases and cerebral disorders like arterioscleroses and cerebral aneurysm. In order to obtain a better understanding of mechanism of formation, growth, and rupture of cerebral aneurysm, this paper focuses on investigation of cerebral hemodynamics and its effects on aneurismal wall. The paper mainly consists of three parts. Since it is important to obtain the detailed information on the hemodynamic properties in the cerebral circulatory system, the first part discusses a large-scale hemodynamic simulation of the Cerebral Arterial Circle of Willis. The second part presents the simulation and in-vitro experiment of cerebral aneurysm with the consideration of blood flow-arterial wall interaction. Both simulations in the first and the second parts are conducted in a patient specific manner using medical images and also include modeling of boundary conditions to emulate realistic hemodynamic conditions. The present mathematical model, however, includes only macroscopic mechanical functions. Therefore, in the third part, the paper touches upon on future prospects in modeling of microscopic functions such as the effects of endothelial cells and multi physics functions such as physiological effects. [Preview Abstract] |
Monday, November 21, 2005 9:44AM - 10:10AM |
FQ.00005: \textbf{Hemodynamic Intervention of Cerebral Aneurysms} Hui Meng Cerebral aneurysm is a pathological vascular response to hemodynamic stimuli. Endovascular treatment of cerebral aneurysms essentially alters the blood flow to stop them from continued growth and eventual rupture. Compared to surgical clipping, endovascular methods are minimally invasive and hence rapidly gaining popularity. However, they are not always effective with risks of aneurysm regrowth and various complications. We aim at developing a Virtual Intervention (VI) platform that allows: patient-specific flow calculation and risk prediction as well as recommendation of tailored intervention based on quantitative analysis.~ This is a lofty goal requiring advancement in three areas of research: (1). Advancement of image-based CFD; (2) Understanding the biological/pathological responses of tissue to hemodynamic factors in the context of cerebral aneurysms; and (3) Capability of designing and testing patient-specific endovascular devices. We have established CFD methodologies based on anatomical geometry obtained from 3D angiographic or CT images. To study the effect of hemodynamics on aneurysm development, we have created a canine model of a vascular bifurcation anastomosis to provide the hemodynamic environment similar to those in CA. Vascular remodeling was studied using histology and compared against the flow fields obtained from CFD. It was found that an intimal pad, similar to those frequently seen clinically, developed at the flow impingement site, bordering with an area of `groove' characteristic of an early stage of aneurysm, where the micro environment exhibits an elevated wall shear stresses. To further address the molecular mechanisms of the flow-mediated aneurysm pathology, we are also developing in vitro cell culture systems to complement the in vivo study. Our current effort in endovascular device development focuses on novel stents that alters the aneurysmal flow to promote thrombotic occlusion as well as favorable remodeling. Realization of an effective VI platform requires a strong multi-disciplinary team of engineers, biologists and clinicians. [Preview Abstract] |
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