Researchers in the Flow Simulations and Analysis Group at George Washington University (GWU, project.seas.gwu.edu/~fsagmae/) in collaboration with USA Swimming, the main governing body for swimming rules and training in the United States, are using Tecplot (www.tecplot.com) to analyze the stroke cycles of elite swimmers in order to develop more effective training procedures based on a swimmer’s specific body profile. Full 3D body scans of Olympic swimmers Lenny Krayzelburg and Gabrielle Rose were obtained from USA Swimming and used as prototypes of typical elite swimmers.

The Researcher

Pressure isosurfaces around the swimmer”s body. Red indicates higher pressure, blue indicates lower pressure.

Rajat Mittal, Ph.D., heads the team of 10 researchers that make up the Flow Simulations and Analysis Group (FSAG). The group’s primary focus is analyzing the physics of complex flows using numerical simulations. Alfred von Loebbecke, a graduate student and key researcher for the USA Swimming 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, the Army Research Office, the Office of Naval Research, the Airforce Office of Scientific Research, and the National Institutes of Health.

Fluid Dynamics of Swimming

Isosurfaces of the imaginary part of the eigen values of the deformation tensor. Provides a measure of the vorticity
around the body.

In 2003, Dr. Mittal approached USA Swimming to find out if it would be interested in collaborating on a research project that leveraged some of his work for the Navy on fish swimming for which FSAG had developed a general-purpose CFD (computational fluid dynamics) code. The organization was indeed interested in pursuing the research and provided Dr. Mittal and his team with 3D body scans 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 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 than surface stroking.

Von Loebbecke uses Alias Maya (www.alias.com) 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, Nancy Coughlin and Michael Phelps. Both swimmers are considered excellent dolphin kickers, which gives 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 whom typically get a significant advantage during the dolphin-kick phase of a race,” 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.”

Using Tecplot

Surface pressure on the swimmer”s body at one instant during the dolphi-kick cycle.

To create the animation, von Loebbecke broke one dolphin kick into 32 frames, which were then used as input for the VICAR3D code. The CFD software interpolated between those 32 frames and created 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 processors 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, enabled the researchers to better understand the complex fluid dynamics involved. Researchers also wanted to understand how much thrust was being generated by the swimmer and from where it was being generated. “To do that,” says Mittal, “we looked 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 were that created 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.

Plotting & Fluid Dynamics

Stream ribbons indicating flow direction.

“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 Dr. 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, Dr. 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 Dr. Mittal.

According to Dr. Mittal, the software’s greatest strength is that it enables him to do everything from simple 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.

Dr. 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 terms 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).

For More Information: www.tecplot.com