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 EB: Bio-Fluid Dynamics: New Areas |
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Chair: James Brasseur, Pennsylvania State University Room: Hilton Chicago Waldorf |
Sunday, November 20, 2005 4:10PM - 4:23PM |
EB.00001: Computation of particle detachment from floors due to human walking Basman Elhadidi, Ezzat Khalifa A computational model for detachment of fine particles due to the unsteady flow under a foot is developed. As the foot approaches the floor, fluid volume is displaced laterally as a wall jet from the perimeter of the contact area at high velocity and acceleration. Unsteady aerodynamic forces on particles attached to the floor are considered. Results show that the jet velocity is $\sim $40 m/s for a foot idealized as a 15 cm circular disk approaching the floor at 1 m/s with a final gap of 0.8 mm. This velocity is sufficient to detach small particles (1$\sim \mu $m). The flow accelerates at $\sim $400 m/s$^{2}$ which affects the detachment of larger sized particles ($\sim $100 $\mu $m). As the disk is brought to rest, the unsteady jet expands outwards, advecting a vortex ring closely attached to it. At the disk edge, a counter rotating vortex is generated by the sudden deceleration of the disk. Both vortices can play a role in entrainment of the suspended particles in the flowfield. Numerical studies also show that the maximum jet velocity is $\sim $20 m/s for a simplified foot immediately after heel contact in the stance phase of the gait. [Preview Abstract] |
Sunday, November 20, 2005 4:23PM - 4:36PM |
EB.00002: A computational and experimental investigation of the human thermal plume Brent Craven, Gary Settles The human thermal plume in a standard room environment, including thermal stratification, is studied. We measured the velocity field around a human volunteer using particle image velocimetry (PIV). These results are compared with those of a steady three-dimensional computational fluid dynamics (CFD) solution of the Reynolds-averaged Navier-Stokes equations (RANS) using the RNG k-$\varepsilon $ two-equation turbulence model. Although the CFD simulation employs a highly-simplified model of the human form, it nonetheless compares quite well with the PIV data in terms of the plume centerline velocity distribution with height, velocity profiles, and flow rates. The effect of thermal stratification in the room upon the human plume is examined by comparing the stratified results with those of an additional CFD plume simulation in a uniform-temperature room. The reduction in plume buoyancy due to temperature stratification has a significant effect on human plume behavior. [Preview Abstract] |
Sunday, November 20, 2005 4:36PM - 4:49PM |
EB.00003: On the Opening of Thick Walled Elastic Tubes: A Fluid-Structure Model for Acid Reflux Sudip Ghosh, James Brasseur, Peter Kahrilas A coupled fluid-structure mathematical model was developed to quantify rapid opening of thick-walled elastic tubes, a phenomenon underlying biological flows such as gastroesophageal reflux disease (GERD). The wall was modeled using non-linear finite deformation theory to predict space-time radial distention of an axisymmetric tube with luminal fluid flow. Anisotropic azimuthal and longitudinal muscle-induced stresses were incorporated, and interstitial material properties were assumed isotropic and linearly elastic. Fluid flow was modeled using lubrication theory with inertial correction. Opening and flow were driven by a specified inflow pressure and zero pressure gradient was specified at outflow. No-slip and surface force balance were applied at the fluid-wall interface. Viscoelasticity was modeled with \textit{ad hoc} damping and the evolution of the tube geometry was predicted at mid-layer. A potentially important discovery was made when applied to studies of initiation of opening with GERD: while material stiffness is of minor consequence, small changes in resting lumen distension ($\sim $2 mm diameter) may be a sensitive distinguishing feature of the disease. [Preview Abstract] |
Sunday, November 20, 2005 4:49PM - 5:02PM |
EB.00004: One Dimensional Models for Bubble Bursts on a Tear Film Surface M.C. Sostarecz, R.J. Braun, L.P. Cook Recent observations of the human tear film surface show bright spots that appear to be bubbles which are present as the eyelid opens. These bubbles move upward on the tear film surface in what is generally accepted to be a concentration gradient. Typically, the bubbles burst and disperse in a process that is strongly suggestive of surfactant spreading in a background flow. Using lubrication theory, we present one-dimensional models both with and without mean surface tension, together with the Marangoni effect for an insoluble surfactant. Solutions are computed numerically using an implementation of the method of lines with finite difference discretizations in space. The models explore the multiple time scales that appear to be present in the tear film relatively rapid surfactant spreading is followed by slow relaxation driven by surface tension. [Preview Abstract] |
Sunday, November 20, 2005 5:02PM - 5:15PM |
EB.00005: Two Dimensional Models for Bubble Bursts on the Tear Film Surface Richard Braun, Michael Sostarecz, L. Pamela Cook Recent observations of the human tear film surface show bright spots that appear to be bubbles which are present as the eyelid opens. These bubbles move upward on the tear film surface in a concentration gradient. Typically, the bubbles burst and disperse in a process that is strongly suggestive of surfactant spreading in a background flow. Using lubrication theory, we present two-dimensional models both with and without mean surface tension, together with the Marangoni effect for an insoluble surfactant. Solutions are computed numerically using an implementation of the method of lines with finite difference discretizations in space. The models explore the multiple time scales that appear to be present in the tear film. [Preview Abstract] |
Sunday, November 20, 2005 5:15PM - 5:28PM |
EB.00006: Growth and analysis of anaerobic wastewater methanogens using microfluidics Ben Steinhaus, Amy Shen, Lars Angenent A micro-bioreactor ($\mu $BR) with a total system volume of 5 $\mu $l was developed using microfluidics and used to study the anaerobic waste-water methanogen \textit{methanosaeta concilli}. The $\mu $BR was contained inside of an anaerobic chamber designed to be placed directly under an inverted light microscope while maintaining the reactor under a N$_{2}$/CO$_{2}$ gas mixture. Methanogens were cultured for periods of up to 3 months inside channels of varying width. The varying channel widths created varying fluid velocities and hence varying shear-rates inside the $\mu $BR. This allowed for direct study of the behavior and response of the anaerobe to varying shear-rates. After completion of the study, \textit{fluorescent in situ hybridization} (FISH) was performed directly inside the microchannels to allow for further analysis and identification of the methanogens. [Preview Abstract] |
Sunday, November 20, 2005 5:28PM - 5:41PM |
EB.00007: Protein crystallization on liquid surfaces: Forced versus natural crystallization A. Hirsa, A. Nejatbakhsh, G. Belfort, H. Liu Two-dimensional crystallization of proteins has recently been reported where streptavidin protein dissolved in the bulk liquid anchors to binding sites on a biotinylated lipid monolayer initially spread on the liquid surface. Thermodynamic aspects investigated include the effects of subphase buffer and pH, dilution of bulk protein and monolayer. Here, we investigate three possible avenues where flow can influence protein crystallization: i) change the initial state of monolayer, ii) advect dissolved protein to the interface, iii) apply direct hydrodynamic force on the crystals at the interface. The flow system consists of a stationary open cylinder driven by constant rotation of the floor, in the axisymmetric flow regime with inertia. Direct imaging of the interface illuminated by forward scattering of a laser was utilized to avoid labeling proteins for conventional fluorescence microscopy. These images provide greater detail than Brewster angle microscopy. Scientific motivation is to use flow to probe protein structure, and the application is to make designer protein thin-films, e.g. for biosensors. [Preview Abstract] |
Sunday, November 20, 2005 5:41PM - 5:54PM |
EB.00008: The Kinetics of Forisome Conformation Change Stephen Warmann, Amy Shen, William Pickard Forisomes are a newly discovered proteinaceous contractile element found in the phloem of legumes. These protein bodies show promise as a biological smart material. Forisomes contract anisotropically in response to pH variation or the presence of calcium ions. Possible applications of forisomes include micro-valves, micro-actuators, and other smart sensing activities where one may currently see materials such as synthetic hydrogels or shape memory alloys. In order to pursue forisome synthesis as a smart material and to understand the biological function of the forisome, a detailed understanding of its material properties is necessary. Our research in this area entails the study of the mechanical properties and surface interactions of forisomes. Here we present detailed conformational kinetics of forisomes from \textit{Vicia faba}, \textit{Glycine max}, and \textit{Canavalia gladiata}. The flow rate dependency of conformational kinetics within a microfluidic network is described. Computational fluid dynamic models of the phloem are presented. [Preview Abstract] |
Sunday, November 20, 2005 5:54PM - 6:07PM |
EB.00009: Using selective withdrawal to encapsulate pancreatic islets for immunoisolation Jason Wyman, Seda Kizilel, Ryan Skarbek, Xiangyang Zhao, Matthew Connors, Shannon Dillmore, William Murphy, Milan Mrksich, Marc Garfinkel, Sidney Nagel We apply selective-withdrawal for encapsulating insulin-producing pancreatic islets within thin poly(ethylene glycol) (PEG) coats. Islets placed in an aqueous PEG solution are drawn into the selective-withdrawal spout which then breaks up, leaving the islets surrounded by a thin, 20$\mu $m, polymer coat. These coats, whose thickness is independent of the size of the encapsulated islet, are photo-crosslinked to form hydrogel capsules. We can apply multiple coats of varying chemical composition. These coats provide a semi-permeable membrane which allows the islets to respond to changes in glucose concentration by producing insulin in a manner similar to that of unencapsulated islets. Furthermore, the hydrogel capsules exclude large molecules the size of the smallest antibodies. Our results suggest that this microencapsulation technique may be useful for the transplantation of islets for treatment of Type I diabetes. [Preview Abstract] |
Sunday, November 20, 2005 6:07PM - 6:20PM |
EB.00010: On the Misuse of the Laplace Law in Bio Fluid Dynamics Azam Thatte, James Brasseur The Laplace law is commonly applied in biomechanical analyses of blood vessels, lung alveoli, and the gastrointestinal tract, often without concern to assumptions that underlie its use. This ``law'' is a simple force balance applied across the wall of a static pressurized (\textit{$\Delta $P}) vessel \textit{for small thickness-to-radius ratio $\tau $/r}. However, the true thin-wall requirement is more severe than \textit{$\tau $/r} $<<$ 1. Furthermore, because the Laplace law estimates \textit{total} stress rather than \textit{deviatoric} stress, the common practice of evaluating material stiffness by plotting Laplace law stress against strain is, in principle, incorrect. To study the validity of the Laplace law in biomechanical applications, we solved exactly the model problem of an axisymmetric pressurized cylinder of arbitrary thickness, linearly elastic isotropic material, in steady state, with the no-load state (\textit{$\Delta $P} = 0) as the zero stress state. Vessel radii and all stresses (total, deviatoric, hydrostatic) are predicted as functions of \textit{$\Delta $P}. We find that the Laplace law is invalid for many biomechanical applications and that total stress is not an appropriate surrogate for deviatoric stress to evaluate stiffness. We propose a model for deviatoric stress that we argue should replace the Laplace law for many biomechanical applications. [Preview Abstract] |
Sunday, November 20, 2005 6:20PM - 6:33PM |
EB.00011: Dust Resuspension due to Idealized Foot Motion Ritesh Sheth, Caroline Braud, Hiroshi Higuchi, Mark Glauser, H Ezzat Khalifa The air quality is affected by amount and types of particulate contaminants that are suspended in the air. The resuspension phenomena occur through two mechanisms: mechanical, where kinetic energy is transferred through direct contact from an impacting body or a vibrating surface, and aerodynamic, where dust particles are resuspended by the flow disturbance generated by the body. In this presentation we focus on aerodynamic resuspension of particles caused by walking. The foot movement is idealized and is either towards or away from a floor without touching it. As a first approach, a 15 cm diameter disk having the equivalent area to that of a human foot is used. The ``foot'' movement is driven vertically by a linear servo motor that controls the velocity, acceleration, stroke and deceleration (a typical vertical velocity is 0.5-1.0 m/s). A thin layer of dust is spread on a table relative to which the disk is allowed to move up and down. Flow visualizations show that both the upward and downward movements of the disk play an important role in the dust resuspension. A clear effect of radial jet and vortex dynamics on the particle resuspension is observed during the downward motion. In the wake of the rising disk, the particles were entrained upwards as a starting ring vortex formed. Quantitative PIV measurements will be performed to help further analyze the flow structure of this flow configuration. [Preview Abstract] |
Sunday, November 20, 2005 6:33PM - 6:46PM |
EB.00012: Multi{\-}window PIV measurements around a breathing manikin David Marr, Ritesh Sheth, Mark Glauser, Hiroshi Higuchi The presented work includes multi{\-}scale measurements via a stereo article Image Velocimetry (PIV) system to view a pair of two{\-}component windows of dissimilar scale using a varied focal length. These measurements are taken in the breathing zone of an isothermal breathing manikin (from mouth) in an environmental chamber of average office cubicle dimensions without ventilation and are analogous to an oscillatory jet. From these phase{\-}averaged measurements, we can extract information concerning length scales, turbulence quantities and low dimensional information in order to both determine correlation between data at different length scales as well as continuing research in exposure assessment for the indoor environment. In this talk we will present these turbulence quantities and interpret their influence on the breathing zone. While the largest scale is that of the room itself, we find that the relevant spatial scales associated with the breathing zone are much lower in magnitude. In future experiments, we will expand the multi window PIV technique to include PIV window configured to obtain scales of order the cubicle simultaneously with those of the breathing zone. This will aid in our understanding of the combined impact of these multiple scales on occupant exposure in the indoor environment. [Preview Abstract] |
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