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NUMERICAL INVESTIGATION OF UNDERWATER UNDULATORY DOLPHIN SWIMMING
S636
Presentation 1789 − Topic 41. Sport biomechanics
NUMERICAL INVESTIGATION OF UNDERWATER UNDULATORY DOLPHIN SWIMMING Steffen Pacholak (1), Christoph Brücker (1)
1. Institute for mechanics and fluid dynamics - TU Bergakademie Freiberg, Germany
Introduction
Results
Propulsion at human dolphin swimming in underwater phase is gained by performing an undulatory motion similar to the movement of fishes. The stiffness of upper and lower extremity parts is resulting in significant vortex structures around the swimmer that are not very well investigated yet. This paper describes the walkthrough starting with a real swim champion as template, movement implementation and the data interpretation of CFD simulation results.
The numerical results were validated by experiments with the same swim champion consisting of a two-dimensional particle image velocimetry (2D-PIV), polyamide seeding particles with water similar density and a fixed high speed camera system [Hochstein, 2011]. To identify vortex structures at numerical calculation results the standard Q-Criterion was modified by relative velocity of vortex. Colouring an iso-surface of the modified Q-Criterion with values of Q leads to a suitable visualisation of vortex evolution and fusion at the swimmers wake (figure 1). Already released vortices are transported along the body surface by the undulatory swim motion and the feet are kicking into these structures to gain additional propulsion. The effect of this vortex recapturing is increasing equally from motion period one to period six because of increasing size and intensity of the involved vortex structures.
Methods The template for creating a realistic geometry is a female swim champion who was scanned by a 3D body scanner from four spatial directions. Her data was saved into a stereolithography file (STL) and missing parts were reconstructed with a recursive Oct-Tree smoothing algorithm. Redundant surface structures and unused details were simplified with a Delauney Triangulation method [Pacholak, 2012]. To assign a natural movement onto this surface model, main pivots were identified as reference points for motion implementation. The matching functions for each pivot were gained by fitting data sets from video footage of the same swim champion. She was prepared with self luminous marker to trace her movement with a high speed camera system [Hochstein, 2011]. The governing equation in fluid dynamics, the equation for mass conservation (1) and NavierStokes-Equation for momentum conservation (2) are solved for a newtonian and incompressible fluid with constant density with OpenFOAM.
G ∇⋅v = 0 (1) G G G G ∂v 1 + (v ⋅∇)v = − ∇p +νΔv (2) ∂t ρ This open source CFD program calculates the
G
pressure p and velocity v around or inside of versatile shaped, multi-element and moving bodies at a fine resolved dynamic mesh of about 1 million hexahedral cells with FVM methods. The motion functions of the pivot points are implemented as moving mesh boundary conditions at the swimmers surface. Journal of Biomechanics 45(S1)
Figure 1: Visualization of vortex structures with modified Q-Criteria at human dolphin swimming
Discussion The numerical results show differences in vortex generation over several motion periods. At world competitions like the Olympic games swimmers performe 5 to 8 strokes in underwater phase. Each period has an individual vortex design that influence the following motion cycles by vortex preformation and vortex recapturing. Comparing numeric results and experiment findings offers some disadvantages when using swimmers midline slices for experimental laser sheet set up.
References Hochstein et al, J Human Movm. Science, 2011. Pacholak et al, J Sports Biomechanics, 2012.
ESB2012: 18th Congress of the European Society of Biomechanics
Presentation 1789 − Topic 41. Sport biomechanics
NUMERICAL INVESTIGATION OF UNDERWATER UNDULATORY DOLPHIN SWIMMING Steffen Pacholak (1), Christoph Brücker (1)
1. Institute for mechanics and fluid dynamics - TU Bergakademie Freiberg, Germany
Introduction
Results
Propulsion at human dolphin swimming in underwater phase is gained by performing an undulatory motion similar to the movement of fishes. The stiffness of upper and lower extremity parts is resulting in significant vortex structures around the swimmer that are not very well investigated yet. This paper describes the walkthrough starting with a real swim champion as template, movement implementation and the data interpretation of CFD simulation results.
The numerical results were validated by experiments with the same swim champion consisting of a two-dimensional particle image velocimetry (2D-PIV), polyamide seeding particles with water similar density and a fixed high speed camera system [Hochstein, 2011]. To identify vortex structures at numerical calculation results the standard Q-Criterion was modified by relative velocity of vortex. Colouring an iso-surface of the modified Q-Criterion with values of Q leads to a suitable visualisation of vortex evolution and fusion at the swimmers wake (figure 1). Already released vortices are transported along the body surface by the undulatory swim motion and the feet are kicking into these structures to gain additional propulsion. The effect of this vortex recapturing is increasing equally from motion period one to period six because of increasing size and intensity of the involved vortex structures.
Methods The template for creating a realistic geometry is a female swim champion who was scanned by a 3D body scanner from four spatial directions. Her data was saved into a stereolithography file (STL) and missing parts were reconstructed with a recursive Oct-Tree smoothing algorithm. Redundant surface structures and unused details were simplified with a Delauney Triangulation method [Pacholak, 2012]. To assign a natural movement onto this surface model, main pivots were identified as reference points for motion implementation. The matching functions for each pivot were gained by fitting data sets from video footage of the same swim champion. She was prepared with self luminous marker to trace her movement with a high speed camera system [Hochstein, 2011]. The governing equation in fluid dynamics, the equation for mass conservation (1) and NavierStokes-Equation for momentum conservation (2) are solved for a newtonian and incompressible fluid with constant density with OpenFOAM.
G ∇⋅v = 0 (1) G G G G ∂v 1 + (v ⋅∇)v = − ∇p +νΔv (2) ∂t ρ This open source CFD program calculates the
G
pressure p and velocity v around or inside of versatile shaped, multi-element and moving bodies at a fine resolved dynamic mesh of about 1 million hexahedral cells with FVM methods. The motion functions of the pivot points are implemented as moving mesh boundary conditions at the swimmers surface. Journal of Biomechanics 45(S1)
Figure 1: Visualization of vortex structures with modified Q-Criteria at human dolphin swimming
Discussion The numerical results show differences in vortex generation over several motion periods. At world competitions like the Olympic games swimmers performe 5 to 8 strokes in underwater phase. Each period has an individual vortex design that influence the following motion cycles by vortex preformation and vortex recapturing. Comparing numeric results and experiment findings offers some disadvantages when using swimmers midline slices for experimental laser sheet set up.
References Hochstein et al, J Human Movm. Science, 2011. Pacholak et al, J Sports Biomechanics, 2012.
ESB2012: 18th Congress of the European Society of Biomechanics