Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B48: Fluid-Structure Interactions (FSI) IFocus
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Sponsoring Units: DFD GSNP Chair: Yahya Modarres-Sadeghi, Univ of Mass - Amherst Room: BCEC 251 |
Monday, March 4, 2019 11:15AM - 11:51AM |
B48.00001: Wave interaction with flexible vegetation: connecting individual blade dynamics to meadow scale wave decay Invited Speaker: Heidi Nepf Flexible plants move in response to wave orbital velocity, which diminishes wave decay relative to rigid plants. The impact of reconfiguration and blade motion on wave decay has been characterized using an effective blade length, le, which represents the length of a rigid blade that generates the same drag as the flexible blade of length l. The effective blade length depends on the Cauchy number, which represents the ratio of hydrodynamic drag to blade stiffness, and on the ratio of blade length to wave orbital excursion. This laboratory study considered how scaling laws determined for individual blades could be used to predict the wave decay over a meadow of multiple plants. First, the drag force on and motion of individual model blades was studied for a range of wave conditions to provide empirical coefficients for the theoretically determined scaling laws for effective blade length, le . Second, the effective blade length predicted for individual blades was incorporated into a meadow-scale model to predict wave decay over a meadow. Third, wave decay was measured over meadows of different plant density (shoots per bed area), and the measured decay was used to validate the wave-decay model. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B48.00002: An Eulerian method for mixed soft and rigid body interactions in incompressible fluids XIAOLIN WANG, Ken Kamrin, Christopher Rycroft Fluid-solid interaction problems are encountered in many engineering and biological applications, but are challenging to simulate due to the coupling between the two material phases. Here, we propose a fully Eulerian approach for solving fluid-solid interactions that is simple to implement and capable of simulating complex multi-body interactions. When the solid is rigid, a projection step is formulated as a composite linear system that simultaneously enforces the rigidity and incompressibility constraints. When the solid is soft, a reference map technique is applied to characterize the body deformation in an Eulerian framework. Several examples including a single body, multiple bodies, and soft-rigid combinations will be presented, with potential applications to biological systems. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B48.00003: A Method for Deriving Fluid-Structure Interaction Reduced-Order Models for Cerebral Aneurysms Suyue Han, Yahya Modarres-Sadeghi A Reduced Order Modeling (ROM) method is discussed for Fluid-Structure Interaction problems in cerebral aneurysm. In this method, we first conduct training CFD simulations with pre-defined structural motion using the fixed mesh method, and then use the snapshot POD method to generate POD modes for both the flow field and the structure. Instead of using traditional topology-changing method, the CFD simulation is enhanced by a fixed mesh method to handle large-amplitude displacements or structural deformation without changing the mesh connectivity, thus consuming much less time. The POD ROM method is also enhanced by the same fixed mesh method, so that the training CFD simulation could be combined with the ROM smoothly. Besides, by implementing a fixed mesh method into the ROM, there is no need for iteratively calculating the forces acting on the structure for every time step. After generating POD modes for both the fluid and the structure using a fixed mesh, we couple these fluid and structure POD modes to create the FSI ROMs. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B48.00004: Flow-induced vibration of an inclined flexible cylinder in tandem arrangement Banafsheh Seyed-Aghazadeh Flow-induced vibration (FIV) of a flexible inclined circular cylinder placed in the wake of a stationary cylinder is studied, experimentally. A highly flexible circular cylinder with an aspect ratio of 47 and a mass ratio of 120 was held fixed at both ends and placed inclined at 45° to the incoming flow in the test-section of a subsonic wind tunnel. The inclined flexible cylinder lied in the wake of an upstream stationary cylinder of equal diameter and inclination. The dynamic response of the downstream cylinder is studied for center-to-center spacing range from 3 to 7 times the cylinder diameter, in the reduced velocity range of U*=3.6-48.5 and the Reynolds number range of Re = 260-3750. |
(Author Not Attending)
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B48.00005: Numerical study on the flow-induced vibrations of a flexibly-mounted cavity at the rear of a bluff body José I Jiménez-González, Carlos García-Baena, Javier F. Aceituno We carry out a computational study on the flow-induced vibrations (FIV) of a rigid cavity, flexibly mounted at the rear of a D-shaped body of height H, subject to a cross-stream of velocity u∞. Simulations are performed for laminar Reynolds numbers to characterize the interaction between wake and parallel rotary plates, connected to the rear edges of the body using torsional hinges. The FIV amplitude response and the effect on force coefficients are investigated for several values of hinge's torsional stiffness k, which provide with different natural oscillation frequencies fn and reduced velocities U*=u∞/fnH. A large FIV response is found for U*>2, where plates oscillate in phase at the shedding frequency. Such response increases the mean drag and fluctuating lift, although reductions are found U*<2, where a weaker FIV response is characterized by oscillation of plates in counter-phase. Finally, to validate the results, we develop a multibody model that allows to retrieve the local aerodynamic forces and torque acting on the plates, using the motion obtained from simulations as input. A final analysis is performed in terms of torque's components and phase between wake forcing and plates' response. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B48.00006: Flutter control using nonlinear tuned magnetic vibration absorbers Xavier Amandolese, Arnaud Malher We will talk about the effects of nonlinear tuned magnetic vibration absorbers on the instability threshold and post-critical flutter of two-degrees-of-freedom « pitch-plunge » wing section. Two post-critical scenarios will be examined: a coupled-mode flutter scenario exhibiting limit cycle oscillations characterized by moderate amplitude in plunge and low amplitude in pitch, and a more complex flutter scenario exhibiting a second post-critical bifurcation from coupled-mode flutter to high amplitude symmetric stall flutter. Magnetic vibration absorbers have been used in plunge, in pitch or in both, and tuned as nonlinear vibration absorbers with cubic stiffness. Their efficiency will be examined in the light of wind tunnel tests and simulations. The latter have been obtained using an analytical aeroelastic model, including a nonlinear unsteady aerodynamic formulation, coupled with the vibration absorbers. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B48.00007: Flutter instability of a reconfiguring beam Mohammad Tari, Frederick Gosselin, Eric Laurendeau Reconfiguration refers to static and dynamic aeroelastic deflections of structures to flow that provide benefits, such as reduced aerodynamic drag. Assuming small structural deformations, the linear theory is used predominantly in engineering applications. However, large deformations of the trees and aquatic plants can only be explained through large deformation theory. The aim of this research is to study experimentally and numerically the flutter instability in slender structures which deform with great amplitude. In particular, we extend the reduced order model of Leclercq & de Langre1 to a RANS coupled with a nonlinear beam model handling large displacements. Since the flutter in such flexible structures arises from the strong interaction of the physics of the fluid and the structure domains, we use a partitioned strongly coupled approach with our in-house structural and fluid solvers. This approach enables us to study flutter and provides insights into the drag reduction mechanisms of flexible structures. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B48.00008: To leak or not to leak: deformation of perforated elastic strips driven through a viscous fluid Pedro Reis, Matteo Pezzulla, Lorenzo Siconolfi, Francois Gallaire From dandelions and insect wings to wire fences and parachutes, there are numerous natural and technological instances of porous flexible structures that deform due to fluid loading. Whereas fluid flow through bulk porous media has been studied extensively, the interaction between a perforated, deformable object and a surrounding viscous fluid has received much less attention. Here, we microfabricate flexible, porous, and slender strips containing a precisely designed array of voids that target set permeabilities. We then drive these perforated strips through a fluid, at low Reynolds number conditions, and quantify the extent of deformation due to viscous loading. We use a reduced theoretical model based on Kirchhoff-Euler beam theory coupled with a description of the fluid loading to deduce the drag force from the deflected shape of the strip. In parallel, we perform ad-hoc numerical simulations to capture the details of the fluid-structure interaction, thereby uncovering a nontrivial effect of permeability on the drag experienced by the porous structure. We hope that the gained insight may guide the design of flexible structures that optimize their porosity and permeability to enhance drag, towards light-weight high-drag slender objects. |
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