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AcKnoWledGeMents
Esther Morales would like to thank the University of Granada for the
grant that enabled her to carry out this research. She would also like to
thank the Physical Education and Sports Department and the Research
Group “CTS-527: Physical Activity and Sports in Aquatic Environment”
of the University of Granada for the use of equipment and help
in preparing this paper and the research on which it is based.
132
Advanced Biomechanical Simulations in Swimming
Enabled by Extensions of Swimming Human
Simulation Model “SWUM”
nakashima, M. 1 , Kiuchi, h. 1 , Maeda, s. 1 , Kamiya, s. 1 , nakajima,
K. 1 , takagi, h. 2
1 Tokyo Institute of Technology, Tokyo, Japan
2 University of Tsukuba, Tsukuba, Japan
Since the authors presented the simulation model “SWUM” and its
implementation software “Swumsuit” in BMS-2006, major extensions
have been successively made on SWUM, such as optimizing calculation,
musculoskeletal simulation, and multi agent/object simulation, in order
to extend its capability of analysis. In this paper, these three extensions
are explained and the various recent results from their implementation
presented. The usefulness of the extensions was confirmed since many
reasonable results were obtained.
Key words: Biomechanical Simulation, Optimization, Musculoskeletal
model, SWUM
IntroductIon
There are many biomechanical problems to be solved in human swimming.
In order to discuss such problems quantitatively, numerical
simulation is becoming a powerful and useful tool. The authors have
developed a simulation model, “SWUM,” (SWimming hUman Model)
(Nakashima et al., 2007b) and a free software, “Swumsuit,” as the implementation
of SWUM (Nakashima, 2005, 2006). By SWUM, it is possible
to analyze the dynamics of the whole swimmer’s body with a short
computation time due to modeling the fluid force acting on the swimmer.
Since it was reported in the last symposium (Nakashima 2006),
major extensions have been successively made on SWUM, such as optimizing
calculation, musculoskeletal simulation, and multi agent/object
simulation, in order to extend the capability of analysis. In this paper,
these extensions are explained and the various recent results by them are
presented in order to examine their usefulness.
Methods
All analyses in this paper were carried out using SWUM. It was designed
to solve the six degrees-of-freedom absolute movement of the whole
swimmer’s body as a single rigid body by the time integration method, using
the inputs of the swimmer’s body geometry and relative joint motion.
The swimming speed, roll, pitch and yaw motions, propulsive efficiency,
joint torques and so on, are computed as the output data. The swimmer’s
body is represented by a series of 21 rigid body segments. Each body segment
is represented by a truncated elliptic cone. The unsteady fluid force
and gravitational force are taken into account as the external forces acting
on the whole body. The unsteady fluid force is assumed to be the sum
of the inertial force due to the added mass of the fluid, normal and tangential
drag forces and buoyancy. These components are also assumed to
be computable, without solving the flow, from the local position, velocity,
acceleration, direction, angular velocity and angular acceleration for each
part of the swimmer’s body at each time step. The coefficients in this fluid
force model were identified using the results of an experiment with a limb
model and measurements of the drag acting on swimmers taking a glide
position in the previous studies (Nakashima et al., 2007b). For the simulation
example of six beat crawl stroke in the previous study, the swimming
speed of the simulation became a reasonable value, indicating the validity
of the simulation model. With respect to the six beat crawl stroke, the authors
have already analyzed contributions of each fluid force component
and of each body part to the thrust, effect of the flutter kick, estimation of
the active drag, roll motion, and propulsive efficiency (Nakashima, 2007a).
Analyses of the other three strokes and comparison among four strokes