CFD modelling showing velocity vectors around a
swimmer as they move through the water.
Image by WAIS

Computational fluid dynamics (CFD) is the science of understanding fluid flow. It has many applications for WA's oil and gas industry and, increasingly, for sport.

A research project by the Western Australian Institute of Sport (WAIS) and the University of Western Australia is looking to enhance the performance of Australian Olympic Swimming Team members by using CFD to model stroke performance.

“From an energy cost perspective, it is more efficient to change a swimmer’s technique to reduce drag forces rather than solely increase the force applied by the swimmer,” said WAIS sports biomechanist Dr Andrew Lyttle.

“In this respect, the more informed a swim coach is on the propulsive and resistive mechanisms of swimming movements, the greater the potential for performance increases.”

The project, based at UWA Sports Park, is advancing existing applications of CFD to new levels by testing swimmers’ movement in dynamic positions. Previously the technology was viable only in static positions, such as the streamlined glide.

“There is a dramatic increase in the complexity of using CFD when performing the analysis on an athlete who is actively moving their body segments,” Dr Lyttle said.

CFD programmer and UWA PhD student Matt Keys and WAIS initially pioneered dynamic CFD modelling with the underwater dolphin kick, seeking to discriminate between the active drag and propulsion (known as ‘net thrust’) generated in various underwater dolphin kicking techniques.

Changes in performance, as a result of varying the techniques, were precisely measured to identify the optimum technique.

For example, the trial revealed differences in propulsive forces generated from the feet versus those from the thighs and calves.

It highlighted the generation of drag that occurred with certain body movements, such as when the knees are dropped too low on the downsweep, and the beneficial effects of increased ankle flexion on propulsion.

“This takes the ‘trial and error’ approach out of technique prescription, as we can determine whether a change is beneficial without spending weeks changing a swimmer’s technique,” Dr Lyttle explained.

To provide inputs into a dynamic CFD model, an accurate 3D shape of the swimmer is made using a whole body laser scanner that describes the swimmer’s geometry.

It is also necessary to input the 3D kinematics (body movements) of the swimmer to animate the model based on how the subject moves in the water.

The dynamic CFD model then calculates the way the water moves around this 3D animation to calculate the drag and propulsion that result from the movement.

The dolphin kick study essentially formed a proof-of-concept for the CFD methodology and the researchers have now moved on to more complex applications.

“We are now almost at the stage where we can analyse full body stroking and are currently looking at Eamon Sullivan’s freestyle stroke,” Dr Lyttle said.

“The ultimate will be a totally interactive system that would be coach run and driven. Our top swimmers’ body shapes and kinematics would be stored in a database to allow a coach to adjust the technique parameter of interest.”

To see a video of how the technology can model 50m freestyle world-record holder Eamon Sullivan’s stroke, visit the original story.