Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session A19: Bio: Fluid-Structure Interaction |
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Chair: Jeffrey Guasto, Tufts University Room: D136 |
Sunday, November 20, 2016 8:00AM - 8:13AM |
A19.00001: Non-invasive estimation of coral tentacle material properties using underwater PIV data Anne Staples, Shai Asher, Uri Shavit With corals worldwide currently undergoing a third global bleaching event, understanding a detailed picture of local coral colony flow transport processes is more crucial than ever. Many coral species invest energy in extending flexible organs such as tentacles, that extrude from the coral's soft tissue surface and are used in either a passive or active manner for feeding, competitor sensing and even egg release. The significant role of these organs in transport and mixing processes is just beginning to be understood. For example, \textit{Xeniidea}'s rhythmic pulsation of its tentacles has recently been shown to intensify mixing and enhance photosynthesis (Kremien et al., 2013). A critical part of modeling these tentacle-induced flows is obtaining measurements of the tentacles' material properties. Obtaining such measurements, however, is challenging, since the \textit{tentacle is expected to have significantly different material properties than a harvested specimen}. Here, we demonstrate a non-invasive, \textit{in situ} approach for estimating these material properties for\textit{ Favia favus} tentacles using underwater particle image velocimetry (PIV) data and tentacle-tracking data, along with structural dynamics models of the tentacles. In this data, 2.7x2 [cm$^{\mathrm{2}}$] 1392x1024 pixel images were collected at a rate of 5 Hz 7mm above the crest of two separate \textit{Favia Favus }colonies in Eilat, Israel. Using the data and models, we are able to estimate the Young's modulus for the tentacles, which is found to be a function of the wave frequency. [Preview Abstract] |
Sunday, November 20, 2016 8:13AM - 8:26AM |
A19.00002: Passive scalar transport to and from the surface of a Pocillopora coral colony Md Monir Hossain, Anne Staples Three-dimensional simulations of flow through a single \textit{Pocillopora} coral colony were performed to examine the interaction between the flow conditions and scalar transport near a coral colony. With corals currently undergoing a third global bleaching event, a fuller understanding of the transport of nutrients, weak temperature gradients, and other passive scalars to and from the coral polyp tissue is more important than ever. The complex geometry of a coral colony poses a significant challenge for numerical simulation. To simplify grid generation and minimize computational cost, the immersed boundary method was implemented. Large eddy simulation was chosen as the framework to capture the turbulent flow field in the range of realistic Reynolds numbers of 5,000 to 30,000 and turbulent Schmidt numbers of up to 1,000. Both uniform and oscillatory flows through the colony were investigated. Significant differences were found between the cases when the scalar originated at the edge of the flow domain and was transported into the colony, versus when the scalar originated on the surface of the colony and was transported away from the coral. The domain-to-colony transport rates were found to be orders of magnitude higher than the colony-to-domain rates. [Preview Abstract] |
Sunday, November 20, 2016 8:26AM - 8:39AM |
A19.00003: Utilizing Surface Sensors to Identify Wake Regimes Mengying Wang, Maziar S. Hemati Marine swimmers often exploit external flow structures to reduce locomotive effort. To achieve this advantage, these swimmers utilize mechanosensory organs on the surface of their bodies to detect hydrodynamic signals from the surrounding fluid, which can then be used to inform the control task. Recently, there has been a growing interest in developing similar flow sensing systems to achieve enhanced propulsive efficiency and maneuverability in human-engineered underwater vehicles. In particular, much attention has been given to the problem of wake sensing; however, these investigations have concentrated on a restricted class of wakes---i.e., K\'{a}rm\'{a}n-type vortex streets---whereas more complicated wake structures can arise in practice. In this talk, we will explore the possibility of identifying wake regimes through the use of surface sensors. Potential flow theory is adopted to simulate the interactions of various wakes with a fish-like body. Wakes in different dynamical regimes impart distinct hydrodynamic signatures on the body, which permits these regimes to be distinguished from one another in an automated fashion. Our results can provide guidance for improving flow sensing capabilities in human-engineered systems and hint at how marine swimmers may sense their hydrodynamic surroundings. [Preview Abstract] |
Sunday, November 20, 2016 8:39AM - 8:52AM |
A19.00004: Be together, not the same: Spatiotemporal organization of different cilia types generates distinct transport functions Janna Nawroth, Hanliang Guo, Edward Ruby, John Dabiri, Margaret McFall-Ngai, Eva Kanso Motile cilia are microscopic, hair-like structures on the cell surface that can sense and propel the extracellular fluid environment. Cilia are often thought to be limited to stereotypic morphologies, beat kinematics and non-discriminatory clearance functions, but we find that the spatiotemporal organization of different cilia types and beat behaviors can generate complex flow patterns and transport functions. Here, we present a case study in the Hawaiian bobtail squid where collective ciliary activity and resulting flow fields help recruit symbiont bacteria to the animal host. In particular, we demonstrate empirically and computationally how the squid's internal cilia act like a microfluidic device that actively filters the water for potential bacterial candidates and also provides a sheltered zone allowing for accumulation of mucus and bacteria into a biofilm. Moreover, in this sheltered zone, different cilia-driven flows enhance diffusion of biochemical signals, which could accelerate specific bacteria-host recognition. These results suggest that studying cilia activity on the population level might reveal a diverse range of biological transport and sensing functions. Moreover, understanding cilia as functional building blocks could inspire the design of ciliated robots and devices. [Preview Abstract] |
Sunday, November 20, 2016 8:52AM - 9:05AM |
A19.00005: Cilia induced cerebrospinal fluid flow in the third ventricle of brain Yong Wang, Christian Westendorf, Regina Faubel, Gregor Eichele, Eberhard Bodenschatz Cerebrospinal fluid (CSF) conveys many physiologically important signaling factors through the ventricles of the mammalian brain. The walls of the ventricles are covered with motile cilia that were thought to generate a laminar flow purely following the curvature of walls. However, we recently discovered that cilia of the ventral third ventricle (v3V) generate a complex flow network along the wall, leading to subdivision of the v3V. The contribution of such cilia induced flow to the overall three dimensional volume flow remains to be investigated by using numerical simulation, arguably the best approach for such investigations. The lattice Boltzmann method is used to study the CFS flow in a reconstructed geometry of the v3V. Simulation of CSF flow neglecting cilia in this geometry confirmed that the previous idea about pure confined flow does not reflect the reality observed in experiment. The experimentally recorded ciliary flow network along the wall was refined with the smoothed particle hydrodynamics and then adapted as boundary condition in simulation. We study the contribution of the ciliary network to overall CSF flow and identify site-specific delivery of CSF constituents with respect to the temporal changes. [Preview Abstract] |
Sunday, November 20, 2016 9:05AM - 9:18AM |
A19.00006: Laboratory model of inner ear mechano-transduction Ibrahim Mohammad, Srdjan Prodanovic, Danielle Laiacona, Jong-Hoon Nam, Douglas Kelley A sound wave entering the mammalian ear displaces cochlear fluid, which in turn displaces hair-like organelles called stereocilia that act as acoustic sensors. Their incredible sensitivity is poorly understood, and probably depends on pre-amplification via fluid-structure interaction. In this talk, I will show how our lab uses a laboratory model to simulate this biological system to study the viscous coupling between the vibrating structures, cochlear fluid, and stereocilia. I will present measurements of modeled stereocilia gain and phase difference over a range of frequencies. Recent numerical simulations show that the sensor behaves as a high-pass filter with a gain plateau. However, our results show a peak in the gain. Further, I will show how the length of stereocilia affects gain. [Preview Abstract] |
Sunday, November 20, 2016 9:18AM - 9:31AM |
A19.00007: Predator localization by sensory hairs in free-swimming arthropods Daisuke Takagi, Daniel K. Hartline Free-swimming arthropods such as copepods rely on minute deflections of cuticular hairs (or "setae") for local flow sensing that is needed to detect food and escape from predators. We present a simple hydrodynamic model to analyze how the location, speed, and size of an approaching distant predator can be inferred from local flow deformation alone. The model informs suitable strategies of escape from an imminent predatory attack. The sensory capabilities of aquatic arthropods could inspire the design of flow sensors in technological applications. [Preview Abstract] |
Sunday, November 20, 2016 9:31AM - 9:44AM |
A19.00008: Bioinspired sensory systems for local flow characterization Brendan Colvert, Kevin Chen, Eva Kanso Empirical evidence suggests that many aquatic organisms sense differential hydrodynamic signals.This sensory information is decoded to extract relevant flow properties. This task is challenging because it relies on local and partial measurements, whereas classical flow characterization methods depend on an external observer to reconstruct global flow fields. Here, we introduce a mathematical model in which a bioinspired sensory array measuring differences in local flow velocities characterizes the flow type and intensity. We linearize the flow field around the sensory array and express the velocity gradient tensor in terms of frame-independent parameters. We develop decoding algorithms that allow the sensory system to characterize the local flow and discuss the conditions under which this is possible. We apply this framework to the canonical problem of a circular cylinder in uniform flow, finding excellent agreement between sensed and actual properties. Our results imply that combining suitable velocity sensors with physics-based methods for decoding sensory measurements leads to a powerful approach for understanding and developing underwater sensory systems. [Preview Abstract] |
Sunday, November 20, 2016 9:44AM - 9:57AM |
A19.00009: Pulsating Soft Corals Shilpa Khatri, Roi Holzman, Laura Miller, Julia Samson, Uri Shavit Soft corals of the family Xeniidae have a pulsating motion, a behavior not observed in many other sessile organisms. We are studying how this behavior may give these corals a competitive advantage. We will present experimental data and computational simulations of the pulsations of the coral. Video data and kinematic analysis will be shown from the lab and the field. We will present direct numerical simulations of the pulsations of the coral and the resulting fluid flow by solving the Navier-Stokes equations coupled with the immersed boundary method. Furthermore, parameter sweeps studying the resulting fluid flow will be discussed. [Preview Abstract] |
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