On the wake-induced vibration of tandem circular cylinders: the vortex interaction excitation mechanism

Assi, Gustavo R. S.; Bearman, P. W.; Meneghini, Júlio Romano

doi:10.1017/s0022112010003095

Cited by 299 publications

(143 citation statements)

References 44 publications

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“…At the two closest distances, all three shapes the cylinder, the elliptical cylinder, and the whisker show signs of wake induced response, which is similar to trends reported in the literature for cylinders in tandem at similar distances d x /d = 2 to 5.6 [65,5,4,3].…”

Section: Comparison Between the Whisker And The Cylinder And Ellipticsupporting

confidence: 86%

“…Most research has been conducted in studying two interacting circular cylinders of equal or comparable diameter [65,102,5,4] and it is shown that the upstream cylinder has significant effect on the amplitude and frequency of motion of the downstream cylinder even when it is placed at 25 diameters apart. It was also found that the vortical wake of the upstream cylinder causes a restoring force on the downstream cylinder, which is equivalent to a linear spring, hence affecting its natural frequency [3].…”

Section: Motivationmentioning

confidence: 99%

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Passive wake detection using seal whisker-inspired sensing

Beem¹

2015

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This thesis is motivated by a series of biological experiments that display the harbor seal's extraordinary ability to track the wake of an object several seconds after it has swum by. They do so despite having auditory and visual cues blocked, pointing to use of their whiskers as sensors of minute water movements. In this work, I elucidate the basic fluid mechanisms that seals may employ to accomplish this detection. Key are the unique flow-induced vibration properties resulting from the geometry of the harbor seal whisker, which is undulatory and elliptical in cross-section.First, the vortex-induced vibration (VIV) characteristics of the whisker geometry are tested. Direct force measurements and flow visualizations on a rigid whisker model undergoing a range of 1-D imposed oscillations show that the geometry passively reduces VIV (factor of > 10), despite contributions from effective added mass and damping. Next, a biomimetic whisker sensor is designed and fabricated. The rigid whisker model is mounted on a four-armed flexure, allowing it to freely vibrate in both in-line and crossflow directions. Strain gauges on the flexure measure deflections at the base. Finally, this device is tested in a simplified version of the fish wake -seal whisker interaction scenario. The whisker is towed behind an upstream cylinder with larger diameter. Whereas in open water the whisker exhibits very low vibration when its long axis is aligned with the incoming flow, once it enters the wake it oscillates with large amplitude and its frequency coincides with the Strouhal frequency of the upstream cylinder. This makes the detection of an upstream wake as well as an estimation of the size of the wake-generating body possible. A slaloming motion among the wake vortices causes the whisker to oscillate in this manner. The same mechanism has been previously observed in energy-extracting foils and trout actively swimming behind bluff cylinders in a stream. Dave, Jason, Gabe, Pablo, Remi, and Yahya were postdocs when we first met.Thank you for being approachable and sharing much needed advice all along the way.Your love of science has inspired me to be more inquisitive.Brandon, Chris, Matthew, and Patrick were undergrads or high school students who spent their summers working in the Tow Tank with me. Thanks for giving me the chance to practice being a mentor, moving this research forward a lot faster than I could do on my own, and helping me lift the mega-whisker in and out of the tank! May you all keep on building and exploring.Thanks to Kathy Streeter and the New England Aquarium staff for helping me understand more about real harbor seals. They graciously collected shed whisker specimens and allowed me to take many close-up pictures of their seals.Thanks to all the people who helped me prepare for and make it through research cruises: Eric Hayden, Terry Hammar, and Hanu Singh for contributing their expertise 5 to help me make my first ocean-ready sensor, all parties involved in the first UNOLS Chief Scientist Training Cruise se...

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Section: Comparison Between the Whisker And The Cylinder And Ellipticsupporting

confidence: 86%

Section: Motivationmentioning

confidence: 99%

Passive wake detection using seal whisker-inspired sensing

Beem¹

2015

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“…Most research has addressed the problem of two interacting circular cylinders of equal or comparable diameter (Hover & Triantafyllou 2001;Papaioannou et al 2006;Assi et al 2006Assi et al , 2010, in which it was shown that the upstream cylinder has significant effect on the amplitude and frequency of motion of the downstream cylinder even when placed 25 diameters apart. The upstream cylinder continues to have significant effect on the downstream cylinder's response when the two are of unequal diameter and at relatively small distances apart (Sayers & Saban 1994;Lam & To 2003;Assi 2014b;Gao et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Wake-induced ‘slaloming’ response explains exquisite sensitivity of seal whisker-like sensors

Beem

Triantafyllou

2015

J. Fluid Mech.

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Blindfolded harbor seals are able to use their uniquely shaped whiskers to track vortex wakes left by moving animals and identify objects that passed by 30 seconds earlier, an impressive feat as the flow features have velocities as low as 1 mm/s. The seals sense while swimming, hence their whiskers are sensitive enough to detect small-scale changes in the flow, while rejecting self-generated flow noise. Here we identify and illustrate a novel flow mechanism, causing a large amplitude "slaloming" whisker response, which allows artificial whiskers with the identical unique undulatory geometry as those of the harbor seal to detect the features of minute flow fluctuations when placed within wakes: Whereas in open water the whisker responds with very low amplitude vibration, once within a wake, it oscillates with large amplitude and, importantly, its response frequency coincides with the Strouhal frequency of the upstream cylinder, making the detection of an upstream wake and an estimation of the size and shape of the wake-generating body possible. This mechanism has some similarities with the flow mechanisms observed in actively controlled propulsive foils within upstream wakes and trout swimming behind bluff cylinders in a stream, but there are also differences caused by the unique whisker morphology, which enables it to respond passively and within a much wider parametric range.

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“…Numerous studies focused on the classical case of flow past two stationary circular cylinders with various arrangements (Meneghini et al 2001;Kang 2003;Sharman et al 2005;Carmo et al 2008;Mussa et al 2009;Sumner 2010). Additionally, the free vibrations (Prasanth and Mittal 2009;Assi et al 2010;Huera-Huarte and Gharib 2011;Carmo et al 2013;Cui et al 2014) and forced vibrations Yang and Zheng 2010;Bao et al 2012;Bao et al 2013;Yang et al 2014) involving two circular cylinders have also been investigated extensively. It was found that the arrangement type and gap spacing have great influences upon the flow dynamics of two-cylinder system.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Flow Past Two Transversely Oscillating Triangular Cylinders in Tandem at Low Reynolds Number

Zhai

Wang

2017

JAFM

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Flow past two tandem triangular cylinders forced to oscillate transversely in a uniform flow, is numerically investigated at a Reynolds number Re = 100. The incompressible Navier-Stokes equations in ArbitraryLagrangian-Eulerian formulation are solved by four-step fractional finite element method. The two cylinders are oscillated in phase and their motions are limited to low amplitudes with a wide frequency range. This study focuses on two typical spacings between the two cylinders, corresponding to vortex suppression (VS) regime and vortex formation (VF) regime respectively for flow past two stationary cylinders. Numerical results show that the response characteristics of two cylinders are significantly affected by the spacing, oscillation amplitude and frequency. For the VS spacing, both cylinders have a wider lock-on region, especially at relatively larger amplitude and higher frequency; the downstream wake patterns are mainly 2S and a combination of 2S* and 2S. However, for the VF spacing, the lock-on frequency range of the cylinders is even slightly narrower than that of a single oscillating cylinder; the wake field is more complex since it may comprises 2S, P+S and 2S* structures at some higher frequencies. Additionally, the hydrodynamic forces are also discussed in terms of mean and root mean square quantities, and reveal large differences between oscillating and stationary cylinders.

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On the wake-induced vibration of tandem circular cylinders: the vortex interaction excitation mechanism

Cited by 299 publications

References 44 publications

Passive wake detection using seal whisker-inspired sensing

Passive wake detection using seal whisker-inspired sensing

Wake-induced ‘slaloming’ response explains exquisite sensitivity of seal whisker-like sensors

Numerical Study of Flow Past Two Transversely Oscillating Triangular Cylinders in Tandem at Low Reynolds Number

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