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 D19: Bio: Swimming |
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Chair: David Daily, Naval Undersea Warfare Centre Room: D136 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D19.00001: Imaging Techniques for Dense 3D reconstruction of Swimming Aquatic Life using Multi-view Stereo David Daily, Jillian Kiser, Sarah McQueen Understanding the movement characteristics of how various species of fish swim is an important step to uncovering how they propel themselves through the water. Previous methods have focused on profile capture methods or sparse 3D manual feature point tracking. This research uses an array of 30 cameras to automatically track hundreds of points on a fish as they swim in 3D using multi-view stereo. Blacktip sharks, sting rays, puffer fish, turtles and more were imaged in collaboration with the National Aquarium in Baltimore, Maryland using the multi-view stereo technique. The processes for data collection, camera synchronization, feature point extraction, 3D reconstruction, 3D alignment, biological considerations, and lessons learned will be presented. Preliminary results of the 3D reconstructions will be shown and future research into mathematically characterizing various bio-locomotive maneuvers will be discussed. [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D19.00002: Fin-Body Interaction and its Hydrodynamic Benefits in Fish's Steady Swimming Geng Liu, Yan Ren, Haibo Dong, George Lauder In many past studies on fish swimming, the hydrodynamics of fish caudal fins were investigated separately. However, fish body inevitably interacts with the caudal fin since the fin flaps in the wake of the body during swimming. In this work, an integrated experimental and computational approach has been used to investigate hydrodynamic performance improvement and the vortex dynamics associated with the fin-body interactions of a jack fish in steady swimming. Realistic 3D jack fish geometry and the undulatory kinematics are reconstructed based on the output of a high-speed photogrammetry system. Hydrodynamic performance and wake structures are simulated by an in-house immersed-boundary-method flow solver. It is found that the body-fin interactions enhance the thrust production of the caudal fin by more than 30{\%} compared to that produced by an isolated caudal fin. Further analysis on the vortex dynamics has shown that the vortices shed from the posterior part of the fish body are captured by the leading edge portion of the caudal fin. This further enhances the strength of the leading-edge vortex attaching to the caudal fin and results in larger thrust production. This work reveals a potential performance enhancement mechanism in fish's steady swimming. [Preview Abstract] |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D19.00003: Simulating underwater propulsion using an immersed boundary method based open-source solver Utku Senturk, Arman Hemmati, Alexander J. Smits The performance of a newly developed Immersed Boundary Method (IBM) incorporated into a finite volume solver is examined using foam-extend-3.2. IBM uses a discrete forcing approach based on the weighted least squares interpolation to preserve the sharpness of the boundary, which decreases the computational complexity of the problem. Initially, four case studies with gradually increasing complexities are considered to verify the accuracy of the IBM approach. These include the flow past 2D stationary and transversely oscillating cylinders and 3D wake of stationary and pitching flat plates with aspect ratio 1.0 at Re=2000. The primary objective of this study, which is pursued by an ongoing simulation of the wake formed behind a pitching deformable 3D flat plate, is to investigate the underwater locomotion of a fish at Re=10000. The results of the IBM based solver are compared to the experimental results, which suggest that the force computations are accurate in general. Spurious oscillations in the forces are observed for problems with moving bodies which change based on spatial and temporal grid resolutions. Although it still has the full advantage of the main code features, the IBM-based solver in foam-extend-3.2 requires further development to be exploited for complex grids. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D19.00004: Wave number effect on the neuromechanical phase characteristics of fish undulatory locomotion Jialei Song, yang Ding, yong zhong, ruxu du For animals with undulatory locomotion, it has been discovered that ``neuromechical phase lags'' (NPL) is commonly utilized. That is, the wave of the muscle activation propagates faster than the wave of body bending, leading to an advancing phase of activation relative to the curvature forward the tail. Even though several multi parameter neuromechanical models have reproduced this phenomenon, but due to the simplification of the model, the origin of the NPL is difficult to identify. By incorporating accurate hydrodynamic and inertial effect, we tried to build a model of high fidelity to describe the dynamics of undulatory fish swimming. The hydrodynamic torque is obtained by the accurate DNS simulation. Meanwhile, the inertial torque is introduced by incorporating the reasonable density distribution and detailed undulatory motion. In our study, we studied cases with three different wave numbers on the fish body, with the swimming pattern ranges from anguiliform to carangiform. The results show different muscle actuation patterns with different wave number on body. This study might provide a beneficial guidance on the future fish-like robot design. [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D19.00005: Evolutionary Optimization of Non-Continuous and Non-Sinusoidal Gaits of a Self-Propelled Swimmer Fatma Ayancik, Emre Akoz, Keith Moored Animals propel themselves through the oceans with a wide variety of swimming gaits. However, it is typically assumed that biological propulsion is achieved by using continuous, sinusoidal motions. Yet, animals have been observed using non-continuous or intermittent swimming gaits and at many times non-sinusoidal motions. Through the use of an evolutionary algorithm, optimal swimming gaits that can be both nonsinusoidal and intermittent are determined. Both the non-dimensional cost of transport and swimming speed are optimized for a virtual body combined with a two-dimensional self-propelled pitching and heaving foil within a boundary element method numerical framework. Nonsinusoidal motions are varied from a triangle-wave to a square-wave motion and the intermittency of the gait is varied by changing the duty cycle of the active phase to the coasting phase during swimming. Both pure pitching, and combined heaving and pitching motions are examined. The Pareto front of optimal solutions is investigated for trends in the optimally efficient swimming gait as the swimming speed is increased. The variation in the wake structures produced by optimally efficient swimmers is probed. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D19.00006: Vortical structures responsible for delayed stall in an idealized humpback whale flipper model Heesu Kim, Jooha Kim, Haecheon Choi In this study, we investigate how the tubercles on the leading edge of an idealized humpback whale flipper model delay the stall. Oil-surface visualization is performed to see the surface flow pattern on the suction surface, and PIV is conducted in several streamwise and crossflow planes at different attack angles ($\alpha$). Without tubercles, leading edge separation first occurs near the tip region and progresses inboard with increasing $\alpha$. With tubercles, however, two types of vortical motions are observed at the mid-span. The first is streamwise vortex arrays which are dominant at $\alpha \leq 9^\circ$, and they are observed downstream of small separation bubbles near the leading edge. The second is asymmetric counter-rotating streamwise vortex pairs that become dominant at $\alpha > 9^\circ$, and these structures appear near the trailing edge. These two types of vortical motions delay flow separation at the peak regions of the mid-span, eliminating the spanwise stall progression and resulting in delayed stall. At $\alpha$ = $16^\circ$ at which the tubercle model stalls, a large-scale streamwise vortex is originated from flow separation near the root region. This structure delays flow separation at the mid-span, leading to higher lift coefficient. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D19.00007: Cetacean Swimming with Prosthetic Limbs Ayodeji Bode-Oke, Yan Ren, Haibo Dong, Frank Fish During entanglement in fishing gear, dolphins can suffer abrasions and amputations of flukes and fins. As a result, if the dolphin survives the ordeal, swimming performance is altered. Current rehabilitation technques is the use of prosthesis to regain swimming ability. In this work, analyses are focused on two dolphins with locomotive impairment; Winter (currently living in Clearwater Marine Aquarium in Florida ) and Fuji (lived in Okinawa Churaumi Aquarium in Japan ). Fuji lost about 75{\%} of its fluke surface to necrosis (death of cells) and Winter lost its tail due to amputation. Both dolphins are aided by prosthetic tails that mimic the shape of a real dolphin tail. Using 3D surface reconstruction techniques and a high fidelity Computational Fluid Dynamics (CFD) flow solver, we were able to elucidate the kinematics and hydrodynamics and fluke deformation of these swimmers to clarify the effectiveness of prostheses in helping the dolphins regain their swimming ability. Associated with the performance, we identified distinct features in the wake structures that can explain this gap in the performance compared to a healthy dolphin. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D19.00008: Sensing and exploitation of vortices for a schooling fish Amy Gao, Audrey Maertens, Michael Triantafyllou The question of whether fish are capable of actively sensing and using individual vortices while schooling has long been debated. Prior research has shown that fish can gain a hydrodynamic benefit when swimming in the wake of another fish. However, it remains unclear if lateral line feedback is necessary, and if so, how a fish may adjust its motion to maximize its energy savings. To begin to address this, we study though numerical simulations the hydrodynamic interactions between two fish swimming in tandem, focusing on the interaction of individual vortices with the following fish. Using a potential flow model, we show that the pressure sensed by the following fish can be captured with a low number of states, which provide information that allows the fish to locate near-field vortices and phase its undulating motion accordingly. We will discuss how vortex interactions along the fish can be beneficial, the signals they induce, and which strategies a fish may use to save the most energy. [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D19.00009: Individual nectophore kinematics during multi-jet swimming by the siphonophore Nanomia bijuga Kelly Sutherland, Brad Gemmell, Sean Colin, John Costello The siphonophore N. bijuga is a colonial marine organism comprised of multiple swimming units that coordinate forward and reverse swimming as well as maneuvering. Though colonies can be cms long, individual swimming units (nectophores) are mms in length. To better understand swimming kinematics and jet-wake properties at the scale of individual nectophores, we collected high speed microvideography and micro particle image velocimetry at the nectophore scale. Nectophores exhibited high pulse frequencies (3 Hz) and a rapid refill time that was roughly equal to the jet time. Forward and reverse swimming were achieved using a maneuverable velum with a triangular opening (jet nozzle) that directed flow forward or backward. Detailed velum kinematics can be applied to the design of multijet underwater vehicles with varying nozzle geometries and cross sectional areas for control of exit flow properties. [Preview Abstract] |
Sunday, November 20, 2016 4:54PM - 5:07PM |
D19.00010: Effects of varying inter-limb spacing to limb length ratio in metachronal swimming Hong Kuan Lai, Rachael Merkel, Arvind Santhanakrishnan Crustaceans such as shrimp, krill and crayfish swim by rhythmic paddling of four to five pairs of closely spaced limbs. Each pair is phase-shifted in time relative to the neighboring pair, resulting in a metachronal wave that travels in the direction of animal motion. The broad goal of this study is to investigate how the mechanical design of the swimming limbs affect scalability of metachronal swimming in terms of limb-based Reynolds number (Re). A scaled robotic model of metachronal paddling was developed, consisting of four pairs of hinged acrylic plates actuated using stepper motors that were immersed in a rectangular tank containing water-glycerin fluid medium. 2D PIV measurements show that the propulsive jets transition from being primarily horizontal (thrust-producing direction) at Re of order 10 to angled vertically at Re of order 100. The ratio of inter-limb spacing to limb length among metachronal swimming organisms ranges between 0.2 to 0.65 (Murphy et al., Mar. Biol. 158, 2011). 2D PIV will be used to examine the jets generated between adjacent limbs for varying inter-limb spacing to limb length ratios. The effect of increasing this ratio to beyond the biologically observed range will be discussed. [Preview Abstract] |
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