Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session MJ: Bio-Fluids: General III |
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Chair: Charles Eggleton, University of Maryland, Baltimore County Room: 102A |
Tuesday, November 25, 2008 8:00AM - 8:13AM |
MJ.00001: Temporal Patterns in Bivalve Excurrent Flow Under Varying Ambient Flow Conditions S.K. Delavan, D.R. Webster The predator-prey relationship between blue crabs (\textit{Callinectes sapidus}) and bivalve clams (\textit{Mercenaria mercenaria)} is mediated by the transport of metabolites released by the prey (clams) and transported downstream as a passive scalar. This study focuses on how the prey behavior contributes to the information available within the odorant plume. Clams may modify factors such as excurrent flux, flow unsteadiness, and siphon height and diameter. A Particle Image Velocimetry (PIV) system has been used to quantify the temporal patterns in the excurrent jet of the bivalve siphon under varying ambient flow conditions. According to a spectral analysis of siphon excurrent velocity time records, there is a low frequency periodic component that could contribute to the mixing of clam metabolites through the generation of persistent jet vorticies. Also, fractal analysis of the velocity time records shows that as the ambient velocity increases the excurrent velocity becomes more correlated and less random. These results suggest that for high ambient flow a low frequency periodicity may be sufficient to promote the mixing and dilution of metabolites. In contrast, for low ambient flow more random siphon excurrent velocity may be required to reduce the amount of information available to predators in the downstream odorant plume. [Preview Abstract] |
Tuesday, November 25, 2008 8:13AM - 8:26AM |
MJ.00002: Modeling Physiological Systems in the Human Body as Networks of Quasi-1D Fluid Flows Anne Staples Extensive research has been done on modeling human physiology. Most of this work has been aimed at developing detailed, three-dimensional models of specific components of physiological systems, such as a cell, a vein, a molecule, or a heart valve. While efforts such as these are invaluable to our understanding of human biology, if we were to construct a global model of human physiology with this level of detail, computing even a nanosecond in this computational being's life would certainly be prohibitively expensive. With this in mind, we derive the Pulsed Flow Equations, a set of coupled one-dimensional partial differential equations, specifically designed to capture two-dimensional viscous, transport, and other effects, and aimed at providing accurate and fast-to-compute global models for physiological systems represented as networks of quasi one-dimensional fluid flows. Our goal is to be able to perform faster-than-real time simulations of global processes in the human body on desktop computers. [Preview Abstract] |
Tuesday, November 25, 2008 8:26AM - 8:39AM |
MJ.00003: A computational reproduction of Murray's law using surrogate-based design optimization Alison Marsden Murray's law describes the optimal relationship between the radius of a parent and daughter blood vessel in a bifurcation. In his 1926 paper, Murray determined the optimal radius and angle via an analytical optimization problem in which the cost function was the sum of a pressure loss term and a metabolic cost term. In this work, we present a computational investigation of Murray's law using derivative-free optimization and a 3-D finite element Navier-Stokes solver. The optimization method relies on Kriging surrogates and mesh adaptive direct search (MADS). The bifurcation geometry is parameterized so that the parent and daughter radii and bifurcation angle are optimized simultaneously. This framework also avoids the need for a steady Poiseuille flow assumption, as in Murray's original work. We will present results using a range of metabolic parameter values, illustrating the trade-off between energy dissipation and vessel size. These results demonstrate that Murray's solution can be reproduced with a particular choice of metabolic parameter (Taber, Biophys J., 1998). In addition, we will explore the effect of using a pulsatile inflow condition on the optimal solution. Finally, we will discuss the potential for broad impact of optimization methods in a range of cardiovascular design problems. [Preview Abstract] |
Tuesday, November 25, 2008 8:39AM - 8:52AM |
MJ.00004: Parallel Adaptive Computation of Blood Flow in a 3D ``Whole'' Body Model M. Zhou, C.A. Figueroa, C.A. Taylor, O. Sahni, K.E. Jansen Accurate numerical simulations of vascular trauma require the consideration of a larger portion of the vasculature than previously considered, due to the systemic nature of the human body's response. A patient-specific 3D model composed of 78 connected arterial branches extending from the neck to the lower legs is constructed to effectively represent the entire body. Recently developed outflow boundary conditions that appropriately represent the downstream vasculature bed which is not included in the 3D computational domain are applied at 78 outlets. In this work, the pulsatile blood flow simulations are started on a fairly uniform, unstructured mesh that is subsequently adapted using a solution-based approach to efficiently resolve the flow features. The adapted mesh contains non-uniform, anisotropic elements resulting in resolution that conforms with the physical length scales present in the problem. The effects of the mesh resolution on the flow field are studied, specifically on relevant quantities of pressure, velocity and wall shear stress. [Preview Abstract] |
Tuesday, November 25, 2008 8:52AM - 9:05AM |
MJ.00005: Comparison of Newtonian and Non-Newtonian Fluid Flow in Biological Models Jennifer Gunderson, Arvind Santhanakrishnan, Nhi Nguyen, Laura Miller We will present results from a qualitative investigation of fluid flow in physical models of the endothelial surface layer and the embryonic heart. We compare both Newtonian and non-Newtonian fluids and observed the differences in flow dynamics over a range of Reynolds numbers. Flow through these models can be categorized using known properties of the fluid and power law approximations. Based on comparisons of these fluids, we are able to obtain a better understanding of how non-Newtonian properties might alter flow patterns and the resulting shear stress and pressure gradients. This can also provide insight into how biological flows influence embryonic cardiogenesis and mechanosensing in the endothelial surface layer. [Preview Abstract] |
Tuesday, November 25, 2008 9:05AM - 9:18AM |
MJ.00006: The Aerodynamics and Transport Phenomena of Canine Olfaction Brent Craven, Gary Settles, Eric Paterson A high-fidelity computational fluid dynamics (CFD) model of the canine nasal airway, developed from a 3-D reconstruction of high-resolution magnetic resonance imaging (MRI) scans, is used to study the aerodynamics of canine olfaction. Simulation results reveal that a unique olfactory airflow pattern exists within the canine nasal cavity during sniffing that is critical for efficient olfaction. The physics of olfactory mass transport are next considered via a reduced-order numerical model of multi-phase odorant transport in mucus-lined olfactory airways. Calculations show that this novel olfactory airflow pattern provides a crucial residence time for odorant absorption in the sensory region and promotes spatiotemporal fractionation of odorant mixtures along the olfactory epithelium. Consequently, the aerodynamics and transport phenomena of canine olfaction are highly-optimized for odorant transfer and olfactory discrimination, which may largely explain the high olfactory acuity of the canine. [Preview Abstract] |
Tuesday, November 25, 2008 9:18AM - 9:31AM |
MJ.00007: Implications of steady streaming flows inside fish ears Charlotte Kotas, Peter Rogers, Minami Yoda Fish ears can typically hear sounds ranging from 10 to 1000 Hz with particle motions as small as 0.1 nm and discriminate sound sources with angular separations of 10--20\r{ }. They consist of dense geometrically complex bodies, the otoliths, surrounded by endolymph and tissue. Under acoustic stimulation, the fluid and tissue oscillate with respect to the otolith; these movements are registered by the deflection of hair cells embedded in the tissue next to the otolith. Although the hair cells are assumed to move with the fluid, it is unknown which characteristics of this relative motion are relevant to fish hearing. In particular, the steady streaming, or time-independent flow generated by the relative motion, should contain acoustically relevant information. These flows were modeled using a 350{\%} scale model cod otolith immersed in a viscous fluid and oscillating sinusoidally in various orientations at frequencies of 8--24 Hz. Phase-locked particle pathline images of tracers suspended in the fluid were used to visualize the steady portion of the flow, which was quantified with particle-image velocimetry (PIV). The resulting steady flows at streaming Reynolds numbers of $O$(10$^{-1})$ or less depend on the oscillation frequency, amplitude and direction. [Preview Abstract] |
Tuesday, November 25, 2008 9:31AM - 9:44AM |
MJ.00008: Identification of \emph{critical} zones in the flow through prosthetic heart valves A. Lopez, R. Ledesma, R. Zenit, G. Pulos The hemodynamic properties of prosthetic heart valves can cause blood damage and platelet activation due to the non- physiological flow patterns. Blood recirculation and elevated shear stresses are believed to be responsible for these complications. The objective of this study is to identify and quantify the conditions for which recirculation and high stress zones appear. We have performed a comparative study between a mechanical monoleaflet and biological valve. In order to generate the flow conditions to test the prosthesis, we have built a hydraulic circuit which reproduces the human systemic circulation, on the basis of the Windkessel model. This model is based on an electrical analogy which consists of an arterial resistance and compliance. Using PIV 3D- Stereo measurements, taken downstream from the prosthetic heart valves, we have reconstructed the full phase-averaged tridimensional velocity field. Preliminary results show that critical zones are more prominent in mechanical prosthesis, indicating that valves made with bio-materials are less likely to produce blood trauma. This is in accordance with what is generally found in the literature. [Preview Abstract] |
Tuesday, November 25, 2008 9:44AM - 9:57AM |
MJ.00009: Propulsive Performance Comparison of a Steady and Unsteady Self-Propelled Swimmer Lydia Ruiz, John Dabiri Aquatic animals differ from typical engineering systems in their use of unsteady flow for locomotion. Researchers have long shown interest in designing devices that resemble their shape and propulsive behaviour. The purpose of this study is to make a direct, empirical comparison between biological and engineering propulsion systems. We designed an underwater vehicle that has the capability to produce either a steady or unsteady jet, akin to a squid and jellyfish, for propulsion while utilizing the same mechanical efficiency. The total efficiency is measured for both modes of propulsion. This avoids the need for direct measurement of propulsive efficiency and the associated use of quasi-steady models. Further analysis was conducted to investigate the importance of vortex ring formation during pulsation. The vehicle was attached to a force balance and the ratio of fluid overpressure to total impulse was measured as a function of dimensionless frequency during unsteady propulsion. [Preview Abstract] |
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