Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
dIscussIon
These results must be carefully considered because variability increases at
each proximal joint. This increase in variability may explain the absence
of significant difference in amplitude between activities at the hip joint,
despite graphical proof. The inverse dynamic model allows us to compute
knee and hip torques. But modelling torques show a double oscillation
whereas measured torque on ankle shows a single oscillation. The first half
cycle of swimming activities is the down kick of foot and first a positive,
then a negative torque on the knee can be observed. Probably the drag
forces of each segment were underestimated, which needs further research.
Fin swimmer kinematics is influenced by the body position during
fin swimming activities. For each fin swimming activity, kick frequency
and amplitude are different but also depth of the kick foot. Thanks to
this new method, we can assess to three-dimensional forces and torques
on the ankle for the three fin swimming activities. These three practices
show main differences in amplitude but not in the timing pattern.
conclusIon
This method has the main advantage of allowing us to measure the effect
of fin blade on ankle joint, and also to compute the amount of torque
on the knee and hip. However, the muscular capacity of the subjects as
a function of both the swimmer level and fin swimming activities needs
to be clarified.
reFerences
Nakashima, M., Zatou, K. & Mioura, Y. (2007). Development of swimming
human simulation model considering rigid body dynamics and
unsteady fluid forces for whole body, Journal of Fluid Science and Technology,
2(1), 56-67.
Zamparo, P., Pendergast, D. R., Mollendorf, J., Termin, B., & Minetti, A.
M. (2006). Economy and efficiency of swimming at the surface with
fins of different size and stiffness. Eur J Appl Physiol, 96, 459–470.
52
3D Computational Fluid-structure Interaction Model
for the Estimation of Propulsive Forces of a Flexible
Monofin
Bideau, n. 1 , razafimahery, F. 1 , Monier, l. 1 , Mahiou, B. 1 ,
nicolas, G. 2 , Bideau, B. 2 , rakotomanana, l. 1
1Institut de Recherche Mathématique, University of Rennes 1, Rennes,
France
2M2S, University of Rennes 2, Rennes, France
The goal of this study was to analyse the dynamic performance of a
monofin for a given kinematics. The problem is formulated within the
framework of a 3D fluid-structure interaction model. The numerical solution
is computed using the finite element method. Namely, the role of
the added mass is highlighted by the modal analysis of the coupled problem.
Moreover, instantaneous propulsive forces and torques are calculated.
Both qualitative and quantitative results were obtained. In particular, the
effect of its deformability and the influence of added mass are pointed out.
Key words: Monofin, Propulsion, Finite elements, Fluid-structure
Interaction
IntroductIon
The current paper contributes to the investigations of biomechanical
aspects of propulsion in monofin swimming. The estimation of the dynamical
response of the fin is one of the key points of the performance in
monofin swimmers. This can be achieved through dynamic measurement
or modelling. Throughout the history of swimming research, different attempts
have been made to measure accurately the propulsive forces, using
experimental or modelling approaches. The dynamic understanding
in monofin-swimming motion was introduced by Rejman (1999) from an
experimental point of view. Using strain gauges glued on each side of the
fins surface, the author put in relation the local forces during up and down
motions with swimming speed. However this approach is not sufficient
to describe the flow over the fin. More recently, (Zamparo et al., 2005)
used a methodology previously applied to fish locomotion to calculate efficiency
for fin swimming at low speeds. While energy flows were precisely
quantified, it remains very difficult to evaluate the influence of the fin on
global performance. To compensate for this drawback, recent approaches
based on computational modelling can be used. In that sense, two major
approaches have been proposed in the literature. The Finite Element
Method (FEM) has been intensively used to model the foil and swimmer
dynamics (Von Loebbecke, 2009). Most of them, based on Computational
Fluid Dynamics (CFD) neglected the elasticity of the foil. Indeed, no constitutive
law is considered for the structure. Some authors have studied
the mechanical properties of fin without fluid (Bideau et al., 2003). To our
knowledge, there is no study considering de dynamical behaviour of the
whole continuum model (solid and fluid features at the same time). In this
paper, a new method that is devoted to computation of propulsive forces
generated by a flexible monofin is described. From this method, the added
mass is calculated, and shows the great impact of this parameter.
Figure 1. Example of the mesh of the solid domain (monofin) and the
fluid domain (pool) used in the FEM simulation