Assessing the performance of underwater undulatory swimming techniques with computational fluid dynamics

Abstract

Underwater Undulatory Swimming (UUS) is of a major importance in modern competitive swimming. This technique follows a dive or a push off the wall. It consists in reproducing the way of locomotion of marine mammals: a wave travels along the body of a swimmer, from the fingers to the toes, accelerating the flow in its vicinity, and thus propelling them forward. Understanding ways to maximise performance of such a technique is essential to give the leading edge to an athlete. Past studies have looked at ways to maximise swimming speed or ways to observe the flow in the wake and in the vicinity of an athlete (e.g. Computational Fluid Dynamics (CFD), Particle Image Velocimetry). These studies often overlooked real race conditions and did not consider when UUS is not performed at maximum effort or when UUS is performed in over-speed (i.e. greater velocities than an athlete can maintain). In order to study both these aspects, the need for fast computation in order to estimate hydrodynamic forces in various configurations arose.

It appeared that a methodology using an immersed boundary method with unsteady implicit-LES applied to UUS could provide fast and reliable simulations. With the combination of an accurate kinematics gathering methodology using optoelectronic motion capture and such computations, it was possible to estimate, with acceptable precision, the fluid forces, the instantaneous swimming velocity and deceleration trends of a large number of kinematics data (58 in total). Three short studies applying the methodology developed ensued.

The first one consisted in observing a sample of seven swimmers performing UUS at different instructed pace (maximum effort, 100 m pace and 200 m pace). Two groups of athletes were identified and separated regarding the way they adapted their swimming motion to the pace. The first group, in order to reduce their swimming speed, simply reduced their movement frequency while keeping a similar technique form. The second group modified their undulation wavelength significantly when performing UUS at slower paces. The implicit-LES simulations provided useful information to understand how the fluid forces were affected by the change of technique. The second study proposed two possible approaches for modifications of UUS techniques: increasing or reducing an athlete's body segments angular range of motion, or forcing a linear wave propagation along the body. A case study showing insight on how these modifications could affect performance of a university level athlete was undertaken. Results provided by simulations with modified kinematics show insights on the potential direction of training for this athlete in order to maximise their UUS speed. A third and final study observed how quickly various UUS techniques decelerate during the over-speed phases of underwater swimming. It shows the potential benefits of taking advantage of a slower deceleration phase. Additionally, a case study where kinematics of an elite swimmer were modified and inputted in the CFD methodology provides insight on the potential role of the knee flexion on deceleration performance.

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Identifiers

ORCID for Dorian Alexandre Guillaume Audot: orcid.org/0000-0003-1538-7562

ORCID for Dominic Hudson: orcid.org/0000-0002-2012-6255

ORCID for Joseph Banks: orcid.org/0000-0002-3777-8962

ORCID for Martin Warner: orcid.org/0000-0002-1483-0561

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