Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session G05: High Reynolds Number Swimming: Sensing and Navigation |
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Chair: Rajat Mittal, Johns Hopkins Room: 132 |
Sunday, November 20, 2022 3:00PM - 3:13PM |
G05.00001: Seal-vibrissa-inspired wavy cylinders vibrate in the wake of a flapping foil Joel W Newbolt, Yuanhang Zhu, Eric Handy-Cardenas, Xiaowei He, Kenneth Breuer Seals have been shown to use their vibrissae (facial whiskers) to sense wake flows that are even slower than 1 mm/s (Dehndhardt et al. 1998). This exquisite sensitivity has been associated with the special wavy shape of the vibrissae which reduces cross-stream forces in steady flows (Hanke et al. 2010). We want to know how this wavy shape contributes to vibrissa sensitivity to disturbed flows and what is the role of the mounting stiffness at the root of the vibrissa. Our experiments use scaled-up models of vibrissae, along with comparable circular and elliptical cylinders, in a water flume, where we measure the forces and water flows around them in both steady flows and wake flows. We test both stationary and oscillating vibrissae and determine stability boundaries for self-sustained flow-induced oscillations. We find that the vibrissae models in a steady flow experience reduced cross-stream forces compared to circular cylinders, while vibrissae models positioned in the wake of a flapping hydrofoil feel stronger cross-stream forces which can cause them to vibrate. This effect can help explain how seal vibrissae are able to detect and identify wake flows. |
Sunday, November 20, 2022 3:13PM - 3:26PM |
G05.00002: Reconstructing the pressure field around an undulating body using a physics-informed neural network Michael A Calicchia, Rui Ni, Rajat Mittal, Jung-Hee Seo Hydrodynamic pressure has often been used by fish and many other aquatic animals for detecting the surrounding environments and predators. Non-invasive methods of measuring the pressure signal on the surface of an undulating body is crucial for advancing our understanding of how fish react to the incoming flow. In this study, the authors propose a method for reconstructing the instantaneous pressure field around an undulating body by training a physics-informed neural network (PINN) on PIV data. We will show that the PINN is less sensitive to the spatio-temporal resolution of the velocity field measurements and provides a more accurate pressure reconstruction, particularly on the surface of the body, when compared to other methods that rely on directly integrating the pressure gradient field. With increased accuracy in the surface pressure prediction, this PINN method can be used as an accurate, invasive array of pressure sensors distributed over the entire fish body. |
Sunday, November 20, 2022 3:26PM - 3:39PM |
G05.00003: Learning egocentric navigation against adversarial flows Yusheng Jiao, Eva Kanso Underwater navigation in the presence of ever-changing flows is an essential yet challenging task for underwater autonomous vehicles. In nature, fish have evolved sensory feedback control strategies to take advantage of ambient flow structures. However, it is non-trivial for engineers to design equivalent control laws. Here we focus on two types of challenges in sensing: First, the vehicle has only access to flow information in its immediate surroundings, which discounts a path planning beforehand. Second, sensory cues are measured in the body frame of reference (egocentric) and they change with the vehicle's translation and rotation. I will present our progress in obtaining control policies via deep reinforcement learning for a swimmer to reach a target against the unsteady background flow. While ignorance of the geocentric reference frame makes it harder for the swimmer to identify the wake structures, this difficulty can be overcome by adding velocity gradients to the sensory cues. The successful egocentric policy performs better than the geocentric policy in terms of time efficiency and generalizability to untrained situations. I will conclude with discussions on how the control policies could be further improved with different sensing strategies. |
Sunday, November 20, 2022 3:39PM - 3:52PM |
G05.00004: Fish-Inspired Navigation via Flow Sensing in an Autonomous Robotic Swimmer Peter J Gunnarson, John O Dabiri Autonomous ocean-exploring robots are challenged with navigating efficiently through complex, time-varying flow fields and seeking out areas of interest without prior knowledge of their surroundings. Aquatic animals, however, regularly accomplish this feat with a variety of flow sensing techniques. For example, fish are hypothesized to navigate by sensing velocity gradients with their lateral lines. Inspired by this navigation strategy, we placed distributed pressure sensors on a palm-sized robotic swimmer to mimic the function of canal neuromasts found in the lateral line of fishes, and tasked the robot with navigating efficiently through fluid flows in a 20-foot-tall water tank. Equipped with a high-speed microcontroller, the robot utilizes deep reinforcement learning and trains a neural network onboard in real time to control its actions. Additionally, we investigated thermal plume tracking with our robot platform, which has applications in tracking hydrothermal plumes and bio-signatures in the ocean. |
Sunday, November 20, 2022 3:52PM - 4:05PM |
G05.00005: Slow and steady? The effect of flow over eel tile and its instabilities on eel kinematics Guglielmo Sonnino Sorisio, Andy Don, Jo Cable, Catherine Wilson Guiding elver towards fish passes and helping them migrate past sections of high velocity flow is a challenging problem. The European eel (Anguilla anguilla) has experienced a population decline due to migration barriers in rivers and this has contributed to them being included on the IUCN critically endangered list. Eel tiles are a potential solution to some of these issues and they have been shown to be an effective substrate for elver to negotiate other types of obstructions such as weirs and low head dams. This experimental study examined the effect of the tiles on the swimming behaviour in a an open channel flume. The eel behaviour was quantified and analysed to extract key parameters for passage and kinematics, and the flow field was analysed using 2D Particle Image Velocimetry (PIV). The tile protrusions produced lower velocities within and immediately above the protrusion layer where turbulent structures formed as a result of instabilities between layers of flow travelling at different speeds. This structure may have the ability to destabilise fish. The eels seemed to favour the low velocity zones offered by the protrusions, and their kinematics were analysed to find the effect of this modified flow on their gait. Overall these tiles could represent a low cost and effective solution to some of the problems facing eels and may also help other species. |
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