Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session S27: Biofluids: General III |
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Chair: Amy Lang, University of Alabama Room: Ballroom I |
Tuesday, November 22, 2011 3:05PM - 3:18PM |
S27.00001: Development of a Physiological Model for the Human Spine Michael Kvitnitsky, Siva Thangam The intervertebral disc in a human spine is a complex structure consisting of three distinct parts: the nucleus pulposus, the annulus fibrosus, and the cartilaginous end-plates. The Nucleus Pulposus is centrally located within the disc surrounded by annulus fibrosus. It consists of a loose network of fibers and cells in a proteoglycan gel, which merges indistinctly at its outer margin with the annulus fibrosus. A viscoelastic constitutive model is proposed for the nucleus pulposus of the human spine to facilitate the development of a flexible intervetebral device designed for application in the thoraco-lumbar region of the human spine during surgery. A novel experimental set up was designed to establish application limits of the design concept for different approaches in spinal surgery. Both static and fatigue mechanical tests based on the ASTM standards provided a basis for the comparison with some existing clinically successful spinal implants designed for similar applications. Also, these mechanical tests and in-vitro comparison with normal spine provided the application limits of this design in surgery to maintain physiologic functional performance at the affected spinal level. The model is used to investigate the effect of the various design parameters on the biomechanical environment of the spine segment. [Preview Abstract] |
Tuesday, November 22, 2011 3:18PM - 3:31PM |
S27.00002: Application of Control Volume Analysis to Cerebrospinal Fluid Dynamics Timothy Wei, Benjamin Cohen, Tomer Anor, Joseph Madsen Hydrocephalus is among the most common birth defects and may not be prevented nor cured. Afflicted individuals face serious issues, which at present are too complicated and not well enough understood to treat via systematic therapies. This talk outlines the framework and application of a control volume methodology to clinical Phase Contrast MRI data. Specifically, integral control volume analysis utilizes a fundamental, fluid dynamics methodology to quantify intracranial dynamics within a precise, direct, and physically meaningful framework. A chronically shunted, hydrocephalic patient in need of a revision procedure was used as an in vivo case study. Magnetic resonance velocity measurements within the patient's aqueduct were obtained in four biomedical state and were analyzed using the methods presented in this dissertation. Pressure force estimates were obtained, showing distinct differences in amplitude, phase, and waveform shape for different intracranial states within the same individual. Thoughts on the physiological and diagnostic research and development implications/opportunities will be presented. [Preview Abstract] |
Tuesday, November 22, 2011 3:31PM - 3:44PM |
S27.00003: Lessons learned from the jellyfish: Fluid transport at intermediate Reynolds numbers Janna Nawroth, John Dabiri Biologically inspired hydrodynamic propulsion and maneuvering strategies promise the advancement of medical implants and novel robotic tools. We have chosen juvenile jellyfish as a model system for investigating fluid dynamics and morphological properties underlying fluid transport by an elastic system at intermediate Reynolds numbers. Recently we have described how natural variations in viscous forces are balanced by changes in jellyfish body shape (phenotypic plasticity), to the effect of facilitating efficient body-fluid interaction. Complementing these studies in our live model organisms, we are also engaged in engineering a synthetic jellyfish, that is, a rhythmically actuated elastomer capable of generating efficient feeding and propulsion currents. The main challenges here are (1) to derive a body shape and deformation suitable for effective fluid transport under physiological fluid conditions, (2) to understand the mechanical properties of actuator and elastomer to derive a design capable of the desired deformation, (3) to establish adequate 3D kinematics of power and recovery stroke, and (4) to evaluate the performance of the design. [Preview Abstract] |
Tuesday, November 22, 2011 3:44PM - 3:57PM |
S27.00004: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2011 3:57PM - 4:10PM |
S27.00005: A flow separation study over a shortfin mako shark pectoral fin Michael Bradshaw, Amy Lang, Redha Wahidi, Drew Smith, Philip Motta Many animals possess performance enhancing mechanisms, such as the denticles found on the skin of the shortfin mako shark (\textit{Isurus oxyrinchus)}. The shortfin mako, one of the fastest sharks on the planet, is covered by small, tooth-like scales that vary in bristling capability. Previous biological findings have shown that the scales increase in flexibility from the leading to trailing edge over the pectoral fin. As this fin is a primary control surface, the scale bristling may provide a mechanism for separation control that leads to decreased drag and increased maneuverability. Such findings can potentially lead to the development of similar micro-scale mechanisms to improve the efficiency of aerospace design. A left pectoral fin (71 cm span) was tested in a water tunnel facility under static and dynamic conditions. Digital Particle Image Velocimetry (DPIV) was used to characterize the flow over the fin. Various angles of attack at two speeds were tested (Re of 44,500 and 68,000). Two chord-wise locations, approximately mid-span where three-dimensional effects were minimized, were viewed to analyze the flow. After the initial testing, the fin was painted to eliminate the effect of the scales and retested to observe flow separation. [Preview Abstract] |
Tuesday, November 22, 2011 4:10PM - 4:23PM |
S27.00006: A whisker sensor: role of geometry and boundary conditions Hendrik Hans, Pablo Valdivia y Alvarado, Dilip Thekoodan, Miao Jianmin, Michael Triantafyllou Harbor seal whiskers are currently being studied for their role in sensing and tracking of the fluid structures left in wakes. Seal whiskers are exposed to incoming flows and are subject to self-induced vibrations. The whisker's unusual geometry is thought to reduce these self-induced disturbances and facilitate a stable reference for wake sensing. An experimental platform was designed to measure flow-induced displacements and vibrations at the base of whisker-like models. Four different whisker-like models (scale: 3x) were towed at different speeds down a towing tank and base displacements in the direction of motion and in the perpendicular axis were measured. Each model incorporated a particular geometrical feature found in harbor seal whiskers. Three different visco-elastic supports were used to mimic various boundary conditions at the base of the whisker models. The effects of geometrical features and boundary conditions on measured base vibrations at three relevant Reynolds numbers are discussed. The material properties of a model's base influence its sensitivity. When compared to a circular cylinder model, whisker models show almost no sign of VIV. [Preview Abstract] |
Tuesday, November 22, 2011 4:23PM - 4:36PM |
S27.00007: Numerical Study of Seal Whisker Vibrations Gabriel Weymouth, Michael Triantafyllou Harbor seal whiskers are thought to play an active role in the identification and tracking of wakes left by potential prey. Further, it is believed that the whisker's geometry enhances it's effectiveness as a sensor on the moving seal by minimizing self-induced fluid/structure excitations. In this study multiple test sections are simulated with an immersed-boundary numerical method at Re=500 to determine the geometry's influence on lift, drag, and wake structures in a fixed configuration. The results confirm findings that the whisker geometry is responsible for order of magnitude reductions in the lift force on the whisker and show that the whisker diminishes the strength of organized flow structures in the wake. Furthermore, prescribed, self-induced, and upstream-flow-induced vibration tests are preformed to asses if the fixed configuration results of the whisker morphology translate to increased effectiveness for wake detection. [Preview Abstract] |
Tuesday, November 22, 2011 4:36PM - 4:49PM |
S27.00008: Harbor Seal Vibrissa Morphology Reduces Vortex-Induced Vibrations Heather Beem, Jason Dahl, Michael Triantafyllou Studies show that harbor seals are adept at tracking small movements in the water, such as those left in the wake of fish, by using their highly sensitive whiskers to detect fluid structures, even without auditory or visual cues. The present work investigates the intriguing claim that the unique morphology of the harbor seal whisker suppresses Vortex Induced Vibrations (VIV) [1]. This implies that the geometry is specialized to reduce the background noise caused by the whisker's own wake in the detection of the upstream target. Forces on a rigid whisker model (scale: 50x) being towed steadily down a water tank while experiencing imposed oscillations are measured. A range of frequencies and amplitudes are tested, the hydrodynamic lift coefficient in phase with velocity (C$_{L,v}$) is calculated for each, and values are combined in a contour plot. The region of positive C$_{L,v}$ peaks at an amplitude ratio of 0.1, indicating that the whisker's undulatory, asymmetric structure considerably reduces (but does not entirely suppress) regions where the structure experiences VIV in comparison with a standard cylinder, whose peak reaches an amplitude ratio of 0.8. \\[4pt] [1] W. Hanke, et al., ``Harbor seal vibrissa morphology suppresses vortex-induced vibrations,'' J. Exp. Biol., vol. 213, pp. 2665-72, 2010. [Preview Abstract] |
Tuesday, November 22, 2011 4:49PM - 5:02PM |
S27.00009: Rectification of pulsatile stress on soft tissues: a mechanism for normal-pressure hydrocephalus Shreyas Jalikop, Sascha Hilgenfeldt Hydrocephalus is a pathological condition of the brain that occurs when cerebrospinal fluid (CSF) accumulates excessively in the brain cavities, resulting in compression of the brain parenchyma. Counter-intuitively, normal-pressure hydrocephalus (NPH) does not show elevated pressure differences across the compressed parenchyma. We investigate the effects of nonlinear tissue mechanics and periodic driving in this system. The latter is due to the cardiac cycle, which provides significant intracranial pressure and volume flow rate fluctuations. Nonlinear rectification of the periodic driving within a model of fluid flow in poroelastic material can lead to compression or expansion of the parenchyma, and this effect does not rely on changes in the mean intracranial pressure. The rectification effects can occur gradually over several days, in agreement with clinical studies of NPH. [Preview Abstract] |
Tuesday, November 22, 2011 5:02PM - 5:15PM |
S27.00010: Modeling the population dynamics of phytoplankton in lacustrine ecosystems Terry Jo Leiterman Phytoplankton are microscopic plants, diverse in shape, and form the basis of aquatic ecosystems. Through both photosynthesis and respiration, they produce organic compounds and contribute notably to the Earth's carbon cycle, which make the population dynamics of phytoplankton important in discussions on climate change. In this talk, we introduce a model that predicts the vertical distribution of phytoplankton in freshwater lakes. The growth of phytoplankton is intimately connected to nutrient and light availability. Quantifying the growth due to light availability requires quantifying the seasonal settling velocity of the particles. Careful consideration is paid to the interaction between the forces of buoyancy, gravity, and drag. To accurately formulate settling velocity, the low Reynolds nature of the system is exploited and added to an experimental, laboratory component. The laboratory research is guided by the use of a sedimentation tank and a collection of vertical cylinders that allow the characterization of particle separation and settling velocity for sparse phytoplankton populations of both spherical and slender shape. [Preview Abstract] |
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