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# Drag cancellation by added-mass pumping

Giorgio-Serchi, Francesco and Weymouth, Gabriel (2016) Drag cancellation by added-mass pumping. Journal of Fluid Mechanics, 798 (R3), 1-11.

Record type: Article

## Abstract

A submerged body subject to a sudden shape-change experiences large forces due to the variation of added-mass energy. While this phenomenon has been studied for single actuation events, application to sustained propulsion requires studying periodic shape-change. We do so in this work by investigating a spring-mass oscillator submerged in quiescent fluid subject to periodic changes in its volume. We develop an analytical model to investigate the relationship between added-mass variation and viscous damping and demonstrate its range of application with fully coupled fluid-solid Navier-Stokes simulations at large Stokes number. Our results demonstrate that the recovery of added-mass kinetic energy can be used to completely cancel the viscous damping of the fluid, driving the onset of sustained oscillations with amplitudes as large as four times the average body radius $r_0$. A quasi-linear relationship is found to link the terminal amplitude of the oscillations $X$, to the extent of size change $a$, with $X/a$ peaking at values from 4 to 4.75 depending on the details of the shape-change kinematics. In addition, it is found that pumping in the frequency range of $1-\frac{a}{2r_0}<\omega^2/\omega_n^2<1+\frac{a}{2r_0}$ is required for sustained oscillations. These results on the unsteady fluid forces produced by shape-changing bodies provide a foundation for the design and control of soft-bodied underwater vehicles.

Text
1604 02663v2.pdf - Accepted Manuscript

Accepted/In Press date: 21 May 2016
e-pub ahead of print date: 8 June 2016
Published date: 10 June 2016
Organisations: Fluid Structure Interactions Group

## Identifiers

Local EPrints ID: 398372
URI: http://eprints.soton.ac.uk/id/eprint/398372
ISSN: 0022-1120
PURE UUID: 9f954581-054e-4dbf-a244-d28c1ef6819a
ORCID for Francesco Giorgio-Serchi: orcid.org/0000-0002-5090-9007
ORCID for Gabriel Weymouth: orcid.org/0000-0001-5080-5016

## Catalogue record

Date deposited: 25 Jul 2016 10:08

## Contributors

Author: Francesco Giorgio-Serchi