Case Studies
Analyzing the Dolphin Kick of Top Olympic Competitors
The image shows isosurfaces of pressure around the swimmer's body. Red
indicates higher pressure, blue indicates lower pressure. Also visible is
the triangular unstructured surface mesh used to represent the body.
The Researcher
Rajat Mittal, PhD, heads up the team of 10 researchers that make up the
Flow Simulations and Analysis Group (FSAG) at George Washington University.
The group's primary focus is analyzing the physics of complex flows
using numerical simulations. Alfred von Loebbecke, a graduate student
and key researcher in this project, says the group's research is motivated
by the quest to answer fundamental questions as well as specific flow-related
issues encountered in practical applications. The simulation of complex
flows often requires specialized computational tools and the development
of such tools is another area of focus for the group.
Dr. Mittal first began using Tecplot in 1991. In combination with the
FSAG's proprietary Navier-Stokes immersed boundary solver VICAR3D, Tecplot
is being used to analyze complex datasets for research projects that
range from analyzing synthetic jets to fish swimming and dragonfly wings.
The group collaborates with many outside partners, including NASA, Army
Research Office, Office of Naval Research, Air force Office of Scientific
Research and National Institutes of Health.
These images depict three instances of the cycle, with streamribbons
indicating flow direction. Streamribbons are colored by pressure levels;
red indicates areas of high pressure, blue indicates areas of low pressure.
The body is represented here by the triangular unstructured mesh.
Understanding the Fluid Dynamics of Swimming
In 2003 Mittal approached USA Swimming to find out if it would be interested
in collaborating on a research project on competitive swimming which
leveraged some of his work for the Navy on fish swimming for which
FSAG had developed a general-purpose CFD code. The organization was
indeed interested in pursuing the research and provided Mittal and
his team with 3D body scans of two elite swimmers, Lenny Krayzelburg
and Gabrielle Rose, for use as input for simulations.
For one phase of the three-year project, the team analyzed the fluid
dynamics of the dolphin kick, a strategically crucial underwater segment
permitted at the start as well as turn of each lap. Underwater swimming--when
it is undulating and rhythmic in a way that most closely mimics a dolphin--is
now understood to be more efficient that surface stroking.
Alfred uses Alias Maya® software to create an animation that basically
matches the 3D body scans frame-by-frame to video of the dolphin kicks
of two Olympic swimmers, Natalie Coughlin and Michael Phelps. Both swimmers
are considered excellent dolphin kickers, which gave them a tremendous
advantage over competitors.
"The goal of this project is to understand what makes swimmers
like Phelps and Coughlin such great dolphin kickers both of who get a
significant advantage during the dolphin kick phase," says Mittal. "They
usually come out of the water about half a body length or more ahead
of the competition. We're trying to understand the fluid dynamics behind
this."
These images depict isosurfaces of the magnitude of the imaginary part
of the eigenvalues of the deformation tensor. This gives a measure of
the vorticity around the body. A ring of vorticity can be clearly seen
in the third image as it is shed off the feet of the swimmer. Again visible
is the triangular unstructured surface mesh used to represent the body.
View the animation (3 MB, swf).
How GWU Researchers Use Tecplot
To create the animation, von Loebbecke breaks one dolphin kick into 32
frames, which are then used as input for the VICAR3D code. The CFD
software interpolates between those 32 frames and creates 2,000 or
more frames, which were then used to create the flow simulation. An
unstructured mesh was generated for the processed body-scan data, and
was then analyzed to produce both static and dynamic simulations. The
animation was processed by FSAG's three 16-CPU Beowulf clusters, each
comprised of 2.8 GHz Pentium IV CPUs with approximately 16 GB of memory.
Using Tecplot, researchers were able to study the resulting simulations
to more closely examine the 3D vortex topology of the flow around the
swimmer's body. The animated isosurface plots, which were created using
contour and iso-surface manipulation, enable the researchers to better
understand the complex fluid dynamics involved. Researchers also want
to understand how much thrust was being generated by the swimmer and
from where it was being generated. "To do that," says Mittal, "we
look at the plots created in Tecplot that show the surface contours of
pressure on the 3D surface of the body to determine where the high- and
low-pressure zones are that create the thrust. Is it the legs? Is it
the toes? Or is it the thighs?"
One result of the project might be computer-calculated instructions
for the mechanically perfect stroke, the one that science has determined
will produce the lowest turbulence, the optimal arrangement of invisible
eddies, and the swiftest route through the water.
This image illustrates the surface pressure on the swimmer's body at
one instant during the dolphin-kick cycle. Higher pressure is colored
red, and lower pressure is colored blue.
Plotting and Fluid Dynamics
"Fluid dynamics is one of the most visual of all engineering fields,
not just because it looks good but because visualization is key to understanding
fluid dynamics. That is why Tecplot is very crucial to us," says
Mittal. "It's really the only way we can take apart many of these
complex flows and study them. 3D flow fields are an order-of-magnitude
more difficult to understand than 2D flows and so anything you can do
to dissect these flows is tremendously helpful."
Aside from its excellent visualization capabilities, Mittal says that
Tecplot also provides an effective means of debugging code. When trying
to find a bug, the researchers will often use Tecplot visualizations
to quickly pinpoint problems. "We use Tecplot as much in the debugging
phase as we do in the post-processing phase," says Mittal.
According to Mittal, the software's greatest strength is that it enables
him to do everything from simply X-Y plots to complex 3D surface contours-all
in one package. He also credits Tecplot for its ability to run well on
all platforms, from Windows to Linux to UNIX-based machines, as well
as its user-friendly menu system.
Mittal fondly remembers the day he was introduced to Tecplot and believes
it has significantly increased the ability of his team to understand
the complexities of fluid behavior. "Tecplot has provided an incredible
boost to our productivity in term of our research output and the insights
we are able to obtain."
Other people who are contributing to this project are Professor James
Hahn (CSE Dept, GWU), Russell Mark (USA Swimming), Dr. Haibo Dong (FSAG),
Meliha Bozkurttas (FSAG) and Hersh Singh (TJ High School). |
RSS Feeds
System Requirements
