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 P27: Biological Fluid Dynamics: High Re Swimming II |
Hide Abstracts |
Chair: Jennifer Franck, U Wisconsin Room: 609 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P27.00001: Combined Heaving and Pitching Propulsors of Non-Uniform Flexibility Amin Mivehchi, Tianjun Han, Mehdi Saadat, George V. Lauder, Keith W. Moored Many swimming animals propel themselves efficiently through water by oscillating of their fins with combined heaving and pitching motions. Contrary to most research on flexible propulsors, these fins are not homogenously flexible, but rather their flexibility varies along their chord and span. Here, using a simple flexibility model we experimentally examine the effect of the distribution of flexibility on the performance of a three-dimensional propulsor using combined heaving and pitching motions. We manufacture propulsors with a combination of rigid and flexible materials where their proportion compared to the chord length is determined by the flexion ratio. The experiments are conducted in a recirculating water channel by varying the frequency of motion at $Re=10^4$, with the pitching motion lagging the heaving motion by 90 degrees. Both the effective flexibility and the flexion ratio of the propulsors are varied independently and force, power and amplitude data are recorded for each experiment. We find peak efficiencies greater than $60\%$ and we detail the dependency of the performance on the variation in the structural properties of the propulsor. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P27.00002: Tailoring the Bending Pattern of Non-Uniformly Flexible Pitching Propulsors Enhances Propulsive Efficiency Tianjun Han, Melike Kurt, Amin Mivehchi, Keith W. Moored Aquatic animals swim rapidly and efficiently by using flexible propulsors. It has been observed that bio-propulsors typically have non-uniform flexibility with increasing flexibility towards the trailing edge. However, most previous research has examined the effect of uniform flexibility on bio-propulsion. Here, we conduct experiments on three-dimensional propulsors with non-uniform chordwise flexibility. We used a simple step function distribution where there is a rigid leading-edge section and a finite flexibility trailing-edge section. This piecewise distribution is defined by the flexion ratio, that is, the ratio of the rigid section length to the chord length. The forces and moments are measured for purely pitching propulsors with various flexion ratios and effective flexibilities. Peak efficiencies for these purely pitching propulsors reach as high as $56\%$ and occur above the first resonant frequency of the system. Additionally, a scaling relation for the resonant frequency of non-uniformly flexible propulsors is determined. This work highlights the result that not only is the resonance condition important for high efficiency performance, but also the bending pattern of a propulsor. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P27.00003: Efficient optimization of swimming gaits Daniel Floryan, Xuanhong An, Clarence W. Rowley We study a simplified model of fish swimming---namely a rigid foil undergoing periodic motion---seeking motions that are optimal in regards to a particular objective (e.g. maximal thrust production). We use an immersed boundary method, and develop an adjoint formulation that allows us to efficiently calculate the gradient of the objective function that is used with gradient-based optimization. Moreover, the adjoint field provides sensitivity information which can be used to elucidate the physics responsible for optimality. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P27.00004: Hydrodynamic performance of a self-propelled ray with oscillatory locomotion Young Dal Jeong, Jae Hwa Lee Mylobatoid rays have dorsoventrally flattened diamond-shaped bodies with expanded pectoral fins, and they swim by oscillating their large pectoral fins. This oscillatory locomotion utilizes the lift-based propulsion, which is specialized for efficient propulsion. Inspired by the high efficient rays, we perform numerical simulations of a self-propelled oscillating ray in a viscous quiescent flow. To consider the fluid-structure interaction between the oscillating ray and surrounding fluid, the penalty immersed boundary method is adapted. From references for the biological ray kinematics, the oscillatory locomotion in the vertical and spanwise directions is actively given at the leading edge, although the chordwise moving motion is freely movable by the fluid-flexible body interaction. Moreover, three-dimensional motion of the rest part is passively determined, and the propulsion performance is influenced by the elastic properties. The effects of the elastic properties on the cruising speed and the input power are investigated systematically. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P27.00005: Intermittent locomotion of a self-propelled plate. Jaeha Ryu, Hyung Jin Sung Many fish and marina animals swim by using a combination of the active bursting phase and the passive coasting phase, which is known as the burst-and-coast swimming. The immersed boundary method is applied to explore the intermittent locomotion of a three-dimensional self-propelled plate. The degree of the intermittent locomotion is captured in a duty cycle (\textit{DC }$= T_{b}/T_{f})$, which is the ratio of the interval of the burst phase ($T_{b})$ to the total flapping period ($T_{f} \quad = \quad T_{b} \quad + \quad T_{c})$. Here, \begin{figure}[htbp] \centerline{\includegraphics[width=0.13in,height=0.17in]{250720191.eps}} \label{fig1} \end{figure} $T_{c}$ is the interval of the coast phase. The averaged cruising speed ( \begin{figure}[htbp] \centerline{\includegraphics[width=0.16in,height=0.17in]{250720192.eps}} \label{fig2} \end{figure} $\bar{U}_{C})$, the input power ($\bar{P}$ \begin{figure}[htbp] \centerline{\includegraphics[width=0.09in,height=0.17in]{250720193.eps}} \label{fig3} \end{figure} ), and the swimming efficiency ($\eta )$ are analyzed as a function of the duty cycle (\textit{DC}). The maximum \begin{figure}[htbp] \centerline{\includegraphics[width=0.16in,height=0.17in]{250720194.eps}} \label{fig4} \end{figure} $\bar{U}_{C}$ is obtained at \textit{DC} $=$ 0.9, while the maximum $\eta $ is at \textit{DC} $=$ 0.3. The hydrodynamics by the intermittent locomotion is scrutinized by using the superimposed flag and the phase map. The characteristics of the flapping motion are demonstrated at the bursting and coasting phases, respectively. The modal analysis is performed to examine how the flapping motion plays a role in the propulsion mechanism. The velocity map and the vortical structures are visualized to show the influence of the intermittent locomotion qualitatively and quantitatively. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P27.00006: CFD-Based Multi-Objective Controller Optimization for Soft Robotic Fish with Muscle-like Actuation Andrew Hess, Xiaobo Tan, Tong Gao Soft robots take advantage of rich nonlinear dynamics and large degrees of freedom to perform actions by novel means beyond the capability of conventional rigid robots. Nevertheless, there have been considerable challenges in analysis, design, and optimization of soft robots due to their complex behaviors. This is especially true for underwater soft robotic swimmers whose dynamics are determined by highly nonlinear fluid-structure interactions. We present a holistic computation framework that employs a multi-objective evolutionary method to optimize feedback-based controllers of a soft robotic fish prototype subjected to artificial muscle actuation. The resultant nonlinear fluid-structure interactions are fully solved by using a novel fictitious domain/active strain method. Compared to the conventional approaches that specify the entire-body curvature variation, we demonstrate that imposing contractile active strains locally can produce various swimming gaits using far fewer control parameters. It also facilitates feed-back controller design for muscle actuation schemes using high-fidelity CFD simulation data. We optimize the controller coefficients via several "thought" experiments where we seek optimal swimming performances of the robotic fish tracking moving targets. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P27.00007: Scaling Laws for Three-Dimensional Combined Heaving and Pitching Propulsors Fatma Ayancik, Keith Moored The underlying physics of oscillatory swimming can be captured with simple models based on the scaling of the added mass and circulatory forces. Here, by considering both of these forces, we present new scaling relations for three-dimensional combined heaving and pitching propulsors with varying aspect ratios. Classic linear theory is augmented by additional nonlinearities and modified for three-dimensional effects by considering the added mass of a finite-span propulsor, the downwash/upwash effects from the trailing vortex system and the elliptical topology of shedding trailing-edge vortices. We verified the scaling relations by using experiments and self-propelled inviscid numerical simulations over a wide range of variables including the dimensionless amplitude, dimensionless heave-to-pitch ratio, Strouhal number, and aspect ratio. The developed relations are found to be in excellent agreement with the numerical and experimental data. These scaling laws are used to identify physical mechanisms that influence thrust and efficiency, and as a guide for improving performance. [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P27.00008: Geometric Influence on Force and Frequency Response of a Bioinspired Undulated Cylinder Kathleen M. Lyons, Christin T. Murphy, Andrew Guarendi, Jennifer A. Franck The unique three-dimensional geometry of seal whiskers has been shown to significantly change the turbulent structures directly downstream, resulting in reduced forces and dampened vibrations when compared with circular cylinders. Biomimicry gives an opportunity to apply the unique whisker geometry to other areas of engineering that require vibration suppression, frequency tuning, or force reduction. This computational investigation isolates the complex geometric parameters of the seal whisker via an undulated cylinder model prescribed by seven non-dimensional parameters including undulation wavelength, thickness, slenderness, amplitudes in the streamwise and transverse flow directions, as well as a peak-shift and a symmetry parameter that induce a non-sinusoidal periodic undulation. Using a two-factor fractional factorial design of experiments, these simulations demonstrate the geometric parameters and two-parameter interactions that are most influential for reducing drag, root-mean-square lift force, and shifting the frequency spectra. It is shown that both transverse and streamwise undulation amplitudes have a notable impact on the downstream turbulent vortex structures, thus impacting the frequency spectra and recirculation region via different mechanisms. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2020 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700