Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E23: Biofluids: Fluid-Structure Interaction |
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Chair: Harishankar Manikantan, UCSD Room: 300 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E23.00001: Stretch-coil transition of a semiflexible filament in extensional flow Harishankar Manikantan, David Saintillan We present a theoretical model for the fluctuation-rounded buckling transition of a semiflexible polymer placed in extensional flow. The competition between elastic rigidity and line tension developed in the polymer backbone can trigger a buckling instability, and the effect of thermal fluctuations on this bifurcation has recently gathered significant attention. While this problem has been studied experimentally and computationally before, the exact nature of the stochastic transition is yet to receive a full quantitative treatment. Motivated by the findings of recent experiments and our own numerical simulations, we approach this analytically by expanding a slender-body equation for the polymer around the first deterministic buckled mode at the onset of the instability. This leads us to a Ginzburg-Landau model for the amplitude of the buckled shape, solving which reveals an expression for a stochastic supercritical bifurcation. This solution captures the smooth transition from a stretched state to a buckled state as the extensional flow strength is increased. It matches excellently with full numerical simulations, and corroborates the conclusions drawn from recent microfluidic experiments. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E23.00002: Elastohydrodynamics of contact in adherent sheets Andreas Carlson, Shreyas Mandre, L. Mahadevan The dynamics of contact between a thin elastic film and a solid arises in many scientific and engineering applications, from the simple saran-wrap to cellular adhesion to grounding lines in ice sheets. Here, we use a mathematical description of the multi-scale processes associated with microscopic adhesion, fluid flow and elastic thin film deformation to deduce the dynamics of the onset of adhesion, as well as the speed and the shape of the adhesion zone. Our analysis is consistent with prior experimental observations, provides new testable predictions for the shape, size and dynamics of adherent contact in thin sheets and in addition provides a broadly applicable prescription for the boundary conditions at elastic contact lines. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E23.00003: Dynamics and topology of a flexible chain: knots in steady shear flow Agnieszka Slowicka, Steve Kuei, Maria Ekiel-Jezewska, Eligiusz Wajnryb, Howard Stone Dynamics of particles in a water-base liquid is a very important subject of research from the point of view of biological, medical and industrial applications. Motion of microorganisms, biopolymers, proteins or artificial particles immersed in a flowing liquid is complex and such systems have numerous applications but, on the other hand,the dynamics has not been yet very well understood. I our paper we performed numerical simulations of a bead-spring model chain to investigate the dynamics of long and flexible elastic fibers in a steady shear flow. For a class of rather open conformations and different parameters of flexibility, we identify two district conformational modes with different final size, shape, and orientation. Through further analysis we identify slipknots in the chain. We also analyzed evolution of the fibers which initially form ``open'' trefoils for different chain flexibilities and initial orientations with respect to the flow direction. We found examples, which illustrate that the shear flow can unknot a flexible chain and then knot it again; this phenomenon sometimes repeats several times. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E23.00004: Flow-Induced Stiffness Enables Torsional Oscillations in a Two-Degree-of-Freedom, Flexibly-Mounted and Free-to-Rotate Rigid Plate Pariya Pourazarm, Yahya Modarres-Sadeghi We study flow-induced oscillations of a flexibly-mounted rigid flat plate placed in water, for a plate with two degrees of freedom in the torsional and transverse directions, with no torsional spring, i.e., no structural stiffness in the torsional direction. At low flow velocities, the plate rotates in the clockwise or counterclockwise direction several times while oscillating in the transverse direction. The frequency of these full rotations converges to a constant number for the majority of flow velocities. At higher flow velocities, the full rotations stop and the plate starts to oscillate in the torsional direction as well, as if there existed a torsional spring. It is concluded that these oscillations in the torsional direction are made possible due to the flow-induced stiffness, since there is no structural stiffness in that direction. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E23.00005: Self-propulsion of a heaving and pitching flexible flag Boyoung Kim, Sung Goon Park, Hyung Jin Sung Flapping motions of flexible flags 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. In the present study, a self-propelled flexible flag with heaving and pitching motions in a quiescent flow has been simulated by using the immersed boundary method. The flexible flag can move freely in the horizontal direction and the body of the flexible flag moves passively along the head. The motion of the head of the flag was described as a harmonic heaving oscillation in the vertical direction. The motion of the angle of the head was described as a harmonic oscillation with a moving clamped condition for the heaving and pitching flag. The cruising speed and the swimming efficiency of the self-propelled flag were determined as functions of the bending coefficient ($\gamma )$, the heaving amplitude (A$_{\mathrm{h}})$, the pitching amplitude (A$_{\mathrm{p}})$, the heaving frequency (\textit{St}), and the phase difference ($\Delta \phi )$ between A$_{\mathrm{h}}$ and A$_{\mathrm{p}}$. We conducted a parametric study on the optimized the cruising speed and the swimming efficiency with respect to $\gamma $, \textit{St}, A$_{\mathrm{h}}$, A$_{\mathrm{p}}$, and $\Delta \phi $ [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E23.00006: Fluid-Structure Interaction Study on a Pre-Buckled Deformable Flat Ribbon Lauren Fovargue, Ehsan Shams, Amy Watterson, Dave Corson, Benjamin Filardo, Daniel Zimmerman, Bob Shan, Assad Oberai A Fluid-Structure Interaction study is conducted for the flow over a deformable flat ribbon. This mechanism, which is called ribbon frond, maybe used as a device for pumping water and/or harvesting energy in rivers. We use a lower dimensional mathematical model, which represents the ribbon as a pre-buckled structure. The surface forces from the fluid flow, dictate the deformation of the ribbon, and the ribbon in turn imposes boundary conditions for the incompressible Navier-Stokes equations. The mesh motion is handled using an Arbitrary Lagrangian-Eulerian (ALE) scheme and the fluid-structure coupling is handled by iterating over the staggered governing equations for the structure, the fluid and the mesh. Simulations are conducted at three different free stream velocities. The results, including the frequency of oscillations, show agreement with experimental data. The vortical structures near the surface of the ribbon and its deformation are highly correlated. It is observed that the ribbon motion exhibits deviation from a harmonic motion, especially at lower free stream velocities. The behavior of the ribbon is compared to swimming animals, such as eels, in order to better understand its performance. [Preview Abstract] |
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