Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session C27: Biological Fluid Dynamics: Swimming, Sensing, Navigating |
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Chair: Arvind Santhanakrishnan, Oklahoma State University Room: 609 |
Sunday, November 24, 2019 8:00AM - 8:13AM |
C27.00001: Development and validation of a bio-inspired, self-propelled metachronal swimming robot Arvind Santhanakrishnan, Mitchell Ford Metachronal swimming is a method of drag-based locomotion used by crustaceans such as krill, mysids, and shrimp. Studies of metachronal swimming can help in understanding ecologically important daily vertical migrations of these organisms and their hydrodynamic signaling mechanisms. We developed a robotic model (``krillbot'') and validated its performance using published data on Pacific and Antarctic krill. Dynamic scaling was used to design the krillbot body and test conditions. The krillbot was suspended in an 8-foot long tank filled with water-glycerin mixture, and was allowed to self-propel on an air bearing. Time-resolved PIV measurements during self-propulsion showed that interaction of shear layers of adjacent paddles resulted in the formation of a continuous jet moving in the caudoventral direction. Swimming speed and orientation of the jet varied with phase lag and paddling frequency. Displacement efficiency and Reynolds number based on swimming speed were found to fall within the range observed in freely swimming krill. [Preview Abstract] |
Sunday, November 24, 2019 8:13AM - 8:26AM |
C27.00002: Importance of appendage spacing in metachronal swimming Mitchell Ford, Arvind Santhanakrishnan Drag-based metachronal paddling of multiple appendages is a common swimming strategy used by numerous aquatic animals (such as copepods, krill, and comb jellies) across a wide range of Reynolds numbers. These organisms have been reported to have a narrow range of dimensionless appendage spacing (ratio of inter-appendage spacing to appendage length) between 1/5 and 2/3 (Murphy et al., Mar. Biol. 158, 2011). Small inter-appendage spacing could allow for synergistic interaction of shear layers formed by paddling of adjacent appendages, whereas large inter-appendage spacing could effectively isolate individual appendages from each other. Using a robotic metachronal swimming model (``krillbot''), we investigated the effects of varying appendage spacing on propulsive forces, swimming speed, and wake characteristics for appendage spacings both within and greater than the biological range. Swimming speed was found to increase both with closer spacing of paddling appendages and with increasing paddling frequency. PIV-based flow visualization results will be presented. [Preview Abstract] |
Sunday, November 24, 2019 8:26AM - 8:39AM |
C27.00003: Hydrodynamics of caridoid escape response in krill Angelica Connor, D. Adhikari, Devesh Ranjan, D.R. Webster Krill are shrimp-like crustaceans and are a keystone species in many deep-water food webs. Due to their abundance and sensitivity to changes in the environment, there are many studies on krill ecology. But, there is limited quantitative analysis of the hydrodynamics of their locomotion and biomechanics. The length of Antarctic krill can range 2-6 cm, and these animals typically swim in a low to intermediate Reynolds number (\textit{Re}) regime. The caridoid escape response, a maneuver unique to crustaceans, occurs when the animal performs a series of rapid abdominal flexions resulting in powerful backward strokes. For the first time, the propulsion behavior and flow disturbance of a caridoid escape response performed by an Antarctic krill (\textit{Euphausia} \textit{superba}) has been quantified. A high-speed tomographic Particle Image Velocimetry (tomo-PIV) system quantifies three-dimensional flow fields around a free swimming \textit{E. superba} and its wake. The specimen is roughly 3 cm in length and by using this tail flipping mechanism, it is able to accelerate backwards increasing its speed by 2 orders of magnitude in an interval of 0.025 s to a maximum speed of 25 cm/s. The data from these flow fields are used to calculate the changes in the velocity and vorticity field shedding light on both the flow behavior in this \textit{Re} regime and intricacies of the bio-locomotion of zooplankton. [Preview Abstract] |
Sunday, November 24, 2019 8:39AM - 8:52AM |
C27.00004: Can the copepod seta sense the hydrodynamic disturbance of prey entrained in the feeding current? Xinhui Shen, Marcos Marcos, Henry Fu The prey detection of feeding-current feeding copepods is achieved by beating their cephalic appendages to generate flow entrainment and utilizing their mechanoreceptional setae to sense the presence of the prey. The hydrodynamic characteristics of the copepod's feeding current have been extensively studied; however, there is little knowledge on if the copepod seta is capable of sensing the hydrodynamic disturbance of prey, or otherwise a direct contact of the setae and prey is required. Here we present a mechanical model to examine the deformation mechanics of the copepod setae when subjected to the flow disturbance of an inert particle entrained in the copepod's feeding current. We first determine the hydrodynamic characteristics of a copepod and beating stroke of its cephalic appendages through video analysis, and utilize the immersed boundary method to solve for the flow fields around the seta with and without the presence of the entrained prey. We then proceed to evaluate the setal deformation induced by such flows, and demonstrate that the flow disturbance induced by the entrained prey leads to a different setal deformation pattern, which may be sensed by the copepod. [Preview Abstract] |
Sunday, November 24, 2019 8:52AM - 9:05AM |
C27.00005: Non-axisymmetric flow and sensing around copepods Julian Hachmeister, Daisuke Takagi Microscopic organisms generate a variety of viscous flow fields which are critical for locomotion, feeding, and sensing. We report on a simplified model of the flow field generated by a feeding copepod while sinking, swimming and hovering. In each case, we compare the different flow fields and compute the strength of the hydromechanical signal due to any suspended particle. Among the three modes, hovering is most effective in bringing in a fresh supply of nutrients from its surroundings. Our study shows an approximate range in which a copepod may sense its prey and the role mechanical sensing plays in feeding. [Preview Abstract] |
Sunday, November 24, 2019 9:05AM - 9:18AM |
C27.00006: Numerical investigation of seal whiskers in distinguishing the patterns of wakes induced by moving objects with different shapes Geng Liu, Qian Xue, Xudong Zheng Phocid seals are able to use their whiskers (or vibrissae) to detect and track artificial and biogenic hydrodynamic trails. Well trained seals are even able to discriminate the size and shape of upstream moving objects through their wakes. The present study employs a one-way coupling model of flow-structure interaction (FSI) to investigate the hydrodynamic mechanism of the wake discrimination. The root mechanical signals of whisker arrays in the wakes induced by different moving objects are simulated and analyzed in detail. It is found that the signal patterns of whisker arrays are associated with the strength and the direction of the jets induced by the 3D vortices in the wake. The distinct signal patterns enable the seal to discriminate the shapes of upstream moving objects. In addition, a theoretical model is built to decoding the relationship between the location of the disturbance source and the sensed flow information. [Preview Abstract] |
Sunday, November 24, 2019 9:18AM - 9:31AM |
C27.00007: A 3D computational fluid dynamics study of the swimming of the larva of mosquito (Chironomus plumosus). Bowen Jin, Haoxiang Luo, Yang Ding The larva of Chironomus plumosus has a cylindrical body with a length about 14mm. Experiments have shown that it swims by periodically bending its body into a circle (the head and tail nearly in touch) and then unfolding it. However, the propulsion mechanism of the larva is not well understood. Here we use 3D computational fluid dynamics to simulate the swimming of the larva. According to the experimental observations of the movement pattern, the centerline curvature $\kappa $ is prescribed in the form of a sinusoid function. The rotational and translational velocities are obtained by coupling the body with the fluid. The simulation results show that the greatest force and thrust are generated on the head and tail during the unfolding stage. By adjusting the time fraction $\gamma $ of the unfolding stage, we find that both the swimming speed and the energetic efficiency increase with decreasing $\gamma $. However, the difference in swimming speed is only significant at intermediate Reynolds number (Re$\approx $1000). When Reynolds number increases (Re$\approx $3000) or decreases (Re$\approx $30), the difference in speed becomes smaller. Our study suggests that the kinematics of the larva of mosquito is specialized for swimming at intermediate Reynolds numbers. [Preview Abstract] |
Sunday, November 24, 2019 9:31AM - 9:44AM |
C27.00008: Elastic hoops jumping on water: drag-dominant model of water-jumping arthropods Han Bi Jeong, Eunjin Yang, Yunsuk Jeung, Juliette Amauger, Ho-Young Kim Some remarkable milli-scale organisms jump from the water surface using surface tension, such as the well-studied water strider. Larger arthropods, however, require a greater force to complete the same task. In the case of fishing spiders, a pressure drag, rather than capillary forces, is utilized to propel the spiders' bodies into a successful jump. Such a strategy is also discriminated from the unsteady added inertia effects employed by a basilisk lizard, a water-walking reptile. Here, we present a mathematical model of thin elastic hoops jumping on water, inspired by the fishing spider. A pre-deformed hoop coated with superhydrophobic particles floating on water shows similar dynamic conditions to that of the jumping mechanics of fishing spiders. When released, the water applies a force against the deforming hoop, dominantly in the form of drag, propelling the hoop into the air. By combining the vibration model of the elastic hoop and the time-varying drag forces induced by fluid motion, we accurately predict the trajectory and jump efficiency of the hoops. This work can be used to develop large-scale water-jumping robots and to understand the water-jumping mechanics of large semi-aquatic arthropods. [Preview Abstract] |
Sunday, November 24, 2019 9:44AM - 9:57AM |
C27.00009: Swimming and settlement of coral larvae on structured surfaces in unsteady shear flow Daniel Gysbers, Mark Levenstein, Gabriel Juarez The large and amazing structures that we know as coral reefs have humble beginnings as tiny ($<$1 mm) swimming organisms. Coral larvae must navigate the vast marine environment to locate a suitable surface where they will permanently settle on by responding to various chemical, biological, and physical cues. We present experimental results of coral larvae swimming and settlement on varying structured surfaces in unsteady shear flow. Our experiments use PTV of swimming larvae and PIV of unsteady shear flow in a U-shaped oscillatory flume to investigate the effect of hydrodynamic interactions between coral larvae and local flow structures generated by surface topology on settlement rates. [Preview Abstract] |
Sunday, November 24, 2019 9:57AM - 10:10AM |
C27.00010: Role of large-scale advection and small-scale turbulence on the vertical migration of gyrotactic swimmers Cristian Marchioli, Gaetano Sardina, Luca Brandt, Alfredo Soldati We use DNS-based Eulerian-Lagrangian simulations to investigate the dynamics of small gyrotactic swimmers in free-surface turbulence. Swimmers are characterized by different vertical stability: some realign with a characteristic time smaller than the Kolmogorov time scale, $\tau_K$, while others possess a re-orientation time longer than $\tau_K$. We cover one order of magnitude in the flow Reynolds number, and two orders of magnitude in the stability number, which measures bottom heaviness. We observe that large-scale advection dominates vertical motion when the stability number, scaled on the local Kolmogorov time scale, is above unity: This leads to enhanced migration towards the surface, particularly at low Reynolds number, when swimmers can rise through surface renewal motions that originate from the bottom-boundary turbulent bursts. Small-scale effects become important when the Kolmogorov-based stability number is below unity: Migration towards the surface is hindered, particularly at high Reynolds, when bottom-boundary bursts are less effective in bringing bulk fluid to the surface. We demonstrate that a Kolmogorov-based stability number around unity represents a threshold beyond which swimmer capability to reach the surface and form clusters saturates. [Preview Abstract] |
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