Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session H17: Biofluids: Locomotion VI - Swimming and Flapping Models |
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Chair: Oscar Curet, Florida Atlantic University Room: 305 |
Monday, November 25, 2013 10:30AM - 10:43AM |
H17.00001: Simple asymptotic results for the role of flexibility in flapping propulsion Matthew N.J. Moore Wing or fin flexibility in flapping propulsion is important to our understanding of bio-locomotion and may be used to engineer devices based on similar principles. Laboratory experiments and numerical simulations have been used extensively to examine effects of wing flexibility, but useful analytical results seem to be lacking. Here we use a small-amplitude calculation to determine the forces produced by a thin wing flapping in an inviscid, 2D fluid and shedding a vortex-sheet wake. We represent flexibility in a simple way by considering a torsional spring located at the root of a rigid wing. The wing moves according to an imposed heaving motion and pitches passively in response to the fluid and spring forces. Remarkably, closed-form expressions are obtained for the kinematics and thrust produced by the wing. Though limited to small amplitude, the results capture a variety of behaviors that are consistent with previous experimental and numerical observations. For small frequencies, thrust is enhanced by torsional compliance and peaks at a resonant frequency, while for larger frequencies the compliant wing underperforms when compared to a clamped, rigid wing. The wing can even produce negative thrust, i.e. drag, if the wing's mass is sufficiently large. [Preview Abstract] |
Monday, November 25, 2013 10:43AM - 10:56AM |
H17.00002: Predicting Fruit Fly's Sensing Rate From Insect Flight Simulations Jane Wang, Song Chang Without sensory feedbacks, flies cannot fly. Exactly how sensory feedback controls work in flying insects is a complex puzzle to solve. What do insects measure in order to stabilize their flight? What kinds of neural computations and muscle activities are involved in order to correct their flight course or to turn? How often and how fast do animals adjust their wings to remain stable? To understand the algorithms used by insects to control their dynamic instability, we have developed a simulation tool to study flapping flight, where motions of the insect body and wings are coupled instantaneously. To stabilize the flight in the simulation, we construct a control algorithm that modulates wing motion based on discrete measurements of the body-pitch orientation. Our simulations give theoretical bounds both on the sensing rate and the delay time between sensing and actuation. Interpreting these findings together with experimental results on fruit flies' reaction time and sensory motor reflexes, we give a sharper bound on the sensing rate and further reason that fruit flies sense their kinematic states every wing-beat in order to stabilize their flight. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:09AM |
H17.00003: Insect flight on fluid interfaces: a chaotic interfacial oscillator Haripriya Mukundarajan, Manu Prakash Flight is critical to the dominance of insect species on our planet, with about 98 percent of insect species having wings. How complex flight control systems developed in insects is unknown, and arboreal or aquatic origins have been hypothesized. We examine the biomechanics of aquatic origins of flight. We recently reported discovery of a novel mode of ``2D flight'' in Galerucella beetles, which skim along an air-water interface using flapping wing flight. This unique flight mode is characterized by a balance between capillary forces from the interface and biomechanical forces exerted by the flapping wings. Complex interactions on the fluid interface form capillary wave trains behind the insect, and produce vertical oscillations at the surface due to non-linear forces arising from deformation of the fluid meniscus. We present both experimental observations of 2D flight kinematics and a dynamic model explaining the observed phenomena. Careful examination of this interaction predicts the chaotic nature of interfacial flight and takeoff from the interface into airborne flight. The role of wingbeat frequency, stroke plane angle and body angle in determining transition between interfacial and fully airborne flight is highlighted, shedding light on the aquatic theory of flight evolution. [Preview Abstract] |
Monday, November 25, 2013 11:09AM - 11:22AM |
H17.00004: Does dragonfly's abdomen flexion help with fast turning maneuvers? Geng Liu, Chengyu Li, Haibo Dong Dragonflies are able to achieve fast turning maneuvers during take-off flights. Both asymmetric wing flapping and abdomen flexion have been observed during the fast turning. It's widely thought that the asymmetric wing beats are responsible of producing the aerodynamic moment needed for the body rotation. However, the dynamic effect of the abdomen flexion is not clear yet. In this study, an integrated experimental and computational approach is used to study the underlying dynamic effect of dragonfly abdomen flexion. It's found that dragonfly abdomen tended to bend towards the same side as the body reorienting to. Quantitative analysis have shown that during take-off turning maneuver the abdomen flexion can modulate the arm of force by changing the position of the center of mass relative to the thorax. As a result, roll and yaw moments produced by the wing flapping can be enhanced. This work is supported by NSF CBET-1313217. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:35AM |
H17.00005: Swimming near deformable membranes at low Reynolds number Marcelo A. Dias, Thomas R. Powers Microorganisms are rarely found in Nature swimming freely in an unbounded fluid. Instead, they typically encounter other organisms, hard walls, or deformable boundaries such as free interfaces or membranes. Hydrodynamic interactions between the swimmer and nearby objects lead to many interesting phenomena, such as changes in swimming speed, tendencies to accumulate or turn, and coordinated flagellar beating. Inspired by this class of problems, we investigate locomotion of microorganisms near deformable boundaries. We calculate the speed of an infinitely long swimmer close to a flexible surface separating two fluids; we also calculate the deformation and swimming speed of the flexible surface. When the viscosities on either side of the flexible interface differ, we find that fluid is pumped along or against the swimming direction, depending on which viscosity is greater. [Preview Abstract] |
Monday, November 25, 2013 11:35AM - 11:48AM |
H17.00006: On the interactions between two undulatory swimmers and between a swimmer and a boundary Jinzhou Yuan, Haim Bau We study numerically and experimentally the interactions between a low-Reynolds number, undulatory swimmer, such as C. elegans, and a non-slip wall and the interactions between two swimmers in an unbounded domain. The Stokes equation with collision avoidance potential was solved using finite elements to obtain the translational and rotational drag coefficients of the swimmers. The swimmers' instantaneous linear and angular velocities were determined by requiring the swimmers to be subject to zero net forces and torques and using the method of superposition. A swimmer proximate to a wall is attracted to the wall and eventually assumes a trajectory that is parallel to the wall and a speed that is twice that of a comparable swimmer distal from the wall. The theoretical predictions are in qualitative agreement with experimental observations. Under certain circumstances, two swimmers in an unbounded domain attract one another and eventually achieve an equilibrium distance between their centers of mass and an equilibrium phase difference. The equilibrium distance between the swimmers and the phase difference between their gaits are functions of the swimmers' initial positions and orientations. [Preview Abstract] |
Monday, November 25, 2013 11:48AM - 12:01PM |
H17.00007: Symmetry breaking of rigid/flexible plates in bluff body wakes generates rotation and drift Nicolas Brosse, Ugis Lacis, Fredrik Lundell, Shervin Bagheri, Francois Ingremeau, Hamid Kellay, Andrea Mazzino Bluff body wakes have historically been important for understanding nature and aiding industry. For Reynolds numbers above approximately $Re\approx 10$, a recirculation bubble develops behind the bluff body. If a solid or elastic appendage is attached to the bluff body, it may exert a torque and a side force on the body. We use theory, numerical simulations and experiments to investigate and explain this phenomenon. More specifically, numerical simulations are carried out for a freely falling cylinder with an attached splitter plate for $Re \approx 50$. Experiments of a fixed cylinder with an attached elastic filament are preformed using a vertical soap-film tunnel for $Re \approx 2000$. Both experiments and simulations reveal that if a body has an appendage smaller than or of the same order as the body it is attached to, the body rotates and drifts. We explain our findings with a simple model and discuss the implications for propulsion. [Preview Abstract] |
Monday, November 25, 2013 12:01PM - 12:14PM |
H17.00008: On the role of reduction by symmetry in understanding swimming at mid-Reynolds Henry Jacobs A number of numerical and experimental studies suggest suggest that swimming can be characterized as an emergent phenomena arising from time-periodic internal body forces. In particular, it seems reasonable to surmise that swimming can be characterized as a relative limit cycle. A relative limit cycle is a system trajectory with a time-period, wherein each period is related to the previous by the action of a Lie group. In the case of swimming in $R^n$ this Lie group is the set of rotations and translations, ${\rm SE}(n)$. In this talk we will describe a class of dissipative systems which admit relative limit cycles. Unfortunately, the Navier-Stokes equations coupled to a solids in $R^n$ are not within this class of. However, a Navier-Stokes-$\alpha$ fluid on the $n$-sphere, $S^{n}$, could resolve this issue. The relative limit cycles would be with respect to the group ${\rm SO}(n)$. In a very precise sense, the group ${\rm SO}(n)$ is to the $S^n$ as ${\rm SE}(n)$ is to $R^{n}$. As a result, the relative limit cycles obtained on $S^n$, can be characterized as spatially localized manifestations of trajectories for systems in $R^n$ wherein each period related to the next by a rigid rotation and translation. [Preview Abstract] |
Monday, November 25, 2013 12:14PM - 12:27PM |
H17.00009: Efficient kinematics for jet-propelled swimming Silas Alben, Laura Miller, Jifeng Peng We use vortex sheet and viscous simulations and an analytical model to search for efficient jet-propelled swimming kinematics at large Reynolds numbers (~1000 and above). We prescribe different power-law kinematics for the bell contraction and expansion. In the simulations, two types of efficient kinematics are found: a bell radius velocity which is a nearly linear function of time, and a ``burst-and-coast'' kinematics. The analytical model studies the contraction phase only, and finds that the efficiency-optimizing kinematics transition from a nearly linear bell radius velocity (similar to the numerics) for small-to-moderate output power to an exponentially-decaying bell radius velocity for large output power. [Preview Abstract] |
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