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 R19: Bio: Flapping |
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Chair: Matthew Melius, Portland State University Room: D136 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R19.00001: Giant larvaceans: biologically equivalent flapping flexible foils exhibit bending modes that enhance fluid transport Kakani Katija, Alana Sherman, Bruce Robison The midwater region of the ocean (below the euphotic zone and above the benthos) is one of the largest ecosystems on our planet, yet remains one of the least explored. Little-known marine organisms that inhabit midwater have developed life strategies that contribute to their evolutionary success, and may inspire engineering solutions for societally relevant challenges. A group of midwater organisms, known as giant larvaceans (genus \textit{Bathochordaeus}), beat their tails to drive food and particle-laden water through complex, mucus filtering structures to feed. Giant larvaceans, whose motion and kinematics resemble flapping flexible foils, range in size from 1 to 10 cm in length, and can be found between the surface and 400 m. Using remotely-operated vehicles and DeepPIV, an instrument that enables in situ particle image velocimetry (PIV) measurements, the filtration rates and kinematics of giant larvaceans were investigated. These measurements yielded filtration rates for giant larvaceans as high as 80 L/hr, which exceeds expected filtration rates by a factor of 2 when compared with other larvacean groups. Comparing tail kinematics between \textit{Bathochordeaus} and smaller larvaceans reveals differences in tail bending modes, where a hinge is present throughout the tail beat in giant larvaceans. Using laboratory PIV measurements with swimming animals and soft-bodied mechanical mimics, we reveal how these differences in tail kinematics can lead to enhanced fluid transport. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R19.00002: Mathematical modeling of flipping flaps and flinging fins in fluids Jeff Eldredge, Xuanhong An, Darwin Darakananda Inviscid vortex models have served for decades as tools for distilling the physics of lifting and propulsive systems. In large-amplitude motions or massively separated flows, they lose some of their appeal due to the large number of vortex elements required to capture such flows with reasonable fidelity. However, in recent work (and in another talk at this conference by Darakananda et al.), we have shown that computational economy and physical fidelity can both be retained in a vortex model by using a heterogeneous set of vortex elements: vortex sheets of limited extent to capture the early formation of a new vortex structure, and a set of discrete vortices that represent developing and full-formed coherent structures. In this talk, we focus on the use of this hybrid vortex model for predicting interactions with flexible structures. By utilizing structures composed from linked rigid bodies, we can readily distinguish local added mass and vortex contributions along the body. We will demonstrate the overall model on two problems: the self-propulsion of a flexible plate due to rapid rotation about a pivot at the leading edge, and the enhancement of lift by the controlled pivot of a trailing-edge flap. We also discuss the use of such a model as a component in a dynamical observer. [Preview Abstract] |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R19.00003: Force and Power Measurements of a Functionally-Graded Chordwise-Flexible Flapping Wing Durlav Mudbhari, Malcolm Erdogan, Keith Moored Flyers and swimmers flap their wings and fins to propel themselves efficiently over long distances. A key element to achieve their high performance is the flexibility of their appendages. While numerous studies have shown that homogeneously flexible wings can enhance force production and efficiency, animals actually have wings with varying flexural rigidity along their chord and span. The goal of this study is to understand and characterize the force production and energetics of functionally-graded, chordwise flexible wings. A flapping wing composed of a rigid and a flexible region, that define a chordwise gradient in flexural rigidity, is used to model functionally-graded materials. By varying the ratio of the lengths of the rigid to flexible regions, the flexural rigidity of the flexible region, and the flapping frequency, the thrust production of a functionally-graded wing is directly measured in a wind tunnel. A novel vacuum chamber apparatus is used in conjunction with the wind tunnel measurements to reliably measure the aerodynamic power input and the propulsive efficiency. Limited flow visualization is performed with particle image velocimetry in order to connect the force production and energetics of the partially-flexible wing with its generated flow structures. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R19.00004: Flapping Wings of an Inclined Stroke Angle: Experiments and Reduced-Order Models in Dual Aerial/Aquatic Flight Jacob Izraelevitz, Michael Triantafyllou, Miranda Kotidis Flapping wings in nature demonstrate a large force actuation envelope, with capabilities beyond the limits of static airfoil section coefficients. Puffins, guillemots, and other auks particularly showcase this mechanism, as they are able to both generate both enough thrust to swim and lift to fly, using the same wing, by changing the wing motion trajectory. The wing trajectory is therefore an additional design criterion to be optimized along with traditional aircraft parameters, and could possibly enable dual aerial/aquatic flight. We showcase finite aspect-ratio flapping wing experiments, dynamic similarity arguments, and reduced-order models for predicting the performance of flapping wings that carry out complex motion trajectories. [Preview Abstract] |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R19.00005: Flapping dynamics of a flexible propulsor near ground. Jaeha Ryu, Sung Goon Park, Boyoung Kim, Hyung Jin Sung The flapping motion of a flexible propulsor near the ground was simulated using the immersed boundary method. The hydrodynamic benefits of the propulsor near the ground were explored by varying the heaving frequency ($St)$ of the leading edge of the flexible propulsor. The propulsion near the ground had some advantages to generate thrust and propel faster than that away from the ground. The mode analysis and the flapping amplitude along the Lagrangian coordinate were examined to analyze the kinematics as a function of the ground proximity ($d)$ and the heaving frequency ($St)$. The trailing edge amplitude ($a_{tail} )$ and the net thrust ($\bar{{F}}_{x} )$ were influenced by the heaving frequency ($St)$ of the flexible propulsor. The hydrodynamic benefits of the flexible propulsor by the ground effect were discussed within the framework of dynamics and kinematics. The trailing edge amplitude presented the high-peak and the low-peak. Each peak showed distinct difference in terms of both the dynamics and the kinematics. The vortical structures in the wake were analyzed for different flapping conditions. [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R19.00006: Testing Momentum Enhancement of Ribbon Fin Based Propulsion Using a Robotic Model With an Adjustable Body Ian English, Oscar Curet Lighthill and Blake's 1990 momentum enhancement theory suggests there is a multiplicative propulsive effect linked to the ratio of body and fin heights in Gymnotiform and Balistiform swimmers, which propel themselves using multi-rayed undulating fins while keeping their bodies mostly rigid. Proof of such a momentum enhancement could have a profound effect on unmanned underwater vehicle design and shed light on the evolutionary advantage to body-fin ratios found in nature, shown as optimal for momentum enhancement in Lighthill and Blake's theory. A robotic ribbon fin with twelve independent fin rays, elastic fin membrane, and a body of adjustable height was developed specifically to experimentally test momentum enhancement. Thrust tests for various body heights were conducted in a recirculating flow tank at different flow speeds and fin flapping frequencies. When comparing thrust at different body heights, flow speeds, and frequencies to a 'no-body' thrust test case at each frequency and flow speed, data indicate there is no momentum enhancement factor due to the presence of a body on top of an undulating fin. This suggests that if there is a benefit to a specific ratio between body and fin height, it is not due to momentum enhancement. [Preview Abstract] |
Tuesday, November 22, 2016 2:48PM - 3:01PM |
R19.00007: The effect of traveling wave shapes in the maneuver control and efficiency of an underwater robot propelled by an undulating fin Hanlin Liu, Oscar Curet Effective control of propulsive undulating fins has the potential to enhance the maneuverability and efficiency of underwater vehicles allowing them to navigate in more complex environments. Aquatic animals using this type of propulsion are able to perform complex maneuvers by sending different traveling waves along one or multiple elongated fins. Recent work has investigated the propulsive forces, the hydrodynamics and the efficiency of an undulating ribbon fin. However, it is still not understood how different traveling wave shapes along the fin can be used to control the hydrodynamic forces and torques to perform different maneuvers. In this work, we study the effect of traveling wave shapes on the hydrodynamic forces and torques, swimming speed, maneuver control and propulsive performance of an underwater vehicle propelled by an undulating fin. The underwater robot propels by actuating a fin that is composed of sixteen independent rays interconnected with a flexible membrane. The hull contains all the electronics, batteries, motors and sensors. The underwater vehicle was tested in a water tank-flume facility. In a series of experiments, we measured the motion of the vessel and the power consumption for different traveling wave patterns. In addition, we measured the flow around the fin using Particle Image Velocimetry. We present the results concerning the power distribution along the fin, propulsive efficiency, free-swimming speed and pitch control based on different fin kinematics. [Preview Abstract] |
Tuesday, November 22, 2016 3:01PM - 3:14PM |
R19.00008: A bioinspired modular aquatic robot Phanindra Tallapragada, Beau Pollard Several bio inspired swimming robots exist which seek to emulate the morphology of fish and the flapping motion of the tail and fins or other appendages and body of aquatic creatures. The locomotion of such robots and the aquatic animals that they seek to emulate is determined to a large degree by the changes in the shape of the body, which produce periodic changes in the momentum of the body and the creation and interaction of the vorticity field in the fluid with the body. We demonstrate an underactuated robot which swims due to the periodic changes in the angular momentum of the robot effected by the motion of an internal rotor. The robot is modular, unactuated tail like segments can be easily added to the robot. These segments modulate the interaction of the body with the fluid to produce a variety of passive shape changes that can allow the robot to swim in different modes. [Preview Abstract] |
Tuesday, November 22, 2016 3:14PM - 3:27PM |
R19.00009: Unsteady Performance of Finite-Span Pitching Propulsors in Mixtures of Side-by-Side and In-Line Arrangements Melike Kurt, Keith Moored Birds, insects, and fish propel themselves by flapping their wings or oscillating their fins in unsteady motions. Many of these animals fly or swim in groups or collectives, typically described as flocks, swarms and schools. The three-dimensional steady flow interactions and the two dimensional unsteady flow interactions that occur in collectives are well characterized. However, the interactions that occur among three-dimensional unsteady propulsors remain relatively unexplored. The aim of the current study is to measure the forces acting on and the energetics of two finite-span pitching wings. The wings are arranged in mixtures of canonical in-line and side-by-side configurations while the phase delay between the pitching wings is varied. The thrust force, fluid-mediated interaction force between the wings and the propulsive efficiency are quantified. The three-dimensional interaction mechanisms are compared and contrasted with previously examined two-dimensional mechanisms. Stereoscopic particle image velocimetry is employed to characterize the three-dimensional flow structures along the span of the pitching wings. [Preview Abstract] |
Tuesday, November 22, 2016 3:27PM - 3:40PM |
R19.00010: An autonomous sperm-like propulsor in a quiescent flow Boyoung Kim, Sung Goon Park, Hyung Jin Sung Flapping motions of flexible fins are widespread in nature. Birds, fish, and insects use their wings, fins, or bodies to stay afloat and to advance forward in the surrounding fluids. It is important to understand the physics of the flapping motions to utilize them for the biomimetic machines. In the present study, we introduce a sperm-like propulsor that consists of a rigid head containing genetic information and a flapping flexible tail for propulsion. The head gives a sinusoidal torque to the leading edge of the tail, and the flexible tail flaps along the leading edge. In other words, the sperm-like propulsor is moved by an oscillating relative angle between the head and the leading edge of the tail. Unlike self-propelled heaving and pitching fins, the `autonomous' sperm-like propulsor has no prescribed motion or constraint referenced from outside coordinates. The penalty method and the immersed boundary method are used to solve the autonomous sperm-like propulsor in a quiescent flow. The cruising speed and the propulsive efficiency of the propulsor are explored as a function of the head size ($D$/$L)$, the pitching angle ($\theta_{0})$, the pitching frequency ($f)$, and the distance from the wall ($G$/$L)$. [Preview Abstract] |
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