Saturday, 01 November 2014
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Finite element analysis for designing and developing tennis rackets

Sheffield Hallam University, Prince Sports

Tennis rackets have changed almost beyond recognition over the past 30 years, from the modestly sized wooden rackets used by players from Fred Perry to Björn Borg, to the large-headed, carbon-fibre beasts wielded by the likes of Roger Federer and the Williams sisters.

Despite these advances, relatively little is known about how tweaking the material properties or geometry of a racket affects its performance; R&D is very much a matter of firing a ball at a test model and observing what happens.

Leading racket-maker Prince Sports joined forces with the Sports Engineering Research Group (SERG) of Sheffield Hallam University to devise a tool to design and fine-tune a racket to best suit individual player styles.

The model uses finite-element (FE) analysis to model the five milliseconds in which the ball is in contact with the racket, during which time it compresses, deforms and rebounds; exactly how it rebounds depends on the complex three-dimensional deformation imparted by the angle, trajectory and force of its impact with the racket.

To accomplish this, the SERG team designed an FE model of the racket featuring 35 tensioned strings all of which can move independently; this allows the model to simulate the oblique spinning impacts of tennis balls in real games. This has been validated by comparing the results of the model to high-speed video analysis of real shots.

Monitoring system for training elite swimmers

UK Sport, Loughborough University

Elite swimmers have to perfect their techniques in three different phases of their events — the start, the actual swimming part and the turn at the end of each length.

However, most of the methods used to analyse technique come down to the practiced eye of a coach watching the athlete in the pool or studying video. UK Sport was anxious to incorporate objective analysis methods using digital sensors and turned to Loughborough University’s Sports Technology Institute for help.

The team needed to incorporate different types of sensor into the monitoring system, looking at parameters such as pressure, multiple axis acceleration, angular velocity and position, as well as input from vision systems.

These have to be incorporated into the form that the athletes can wear without impeding their swimming; they have to transmit data wirelessly, from underwater to above water, over a distance of 50m. Moreover, the system had to include data-reduction algorithms and filters to reduce the traffic on the network and more algorithms to extract the key features of the data and present them on a laptop in a form that the athletes and coaches can use to improve performance.

Project Blackroc: Engineering a gold medal-winning skeleton bob

University of Southampton, British Skeleton Association, UK Sport; Sheffield Hallam University, BAE Systems

When British skeleton bob slider Shelley Rudman won a silver medal at the 2006 Winter Olympics in Turin, the race was on to improve for the next games in Whistler, Canada in 2010. With all bob sliders using different kit, the task to find out which features were crucial and how the skeleton bob could best be optimised for the combination of athlete, track and weather was a tricky one.

Amy Williams uses a custom-designed bob

Amy Williams uses a custom-designed bob

The British Skeleton Association (BSA) sponsored two Ship Science graduates from Southampton, Rachel Blackburn and James Roche, to work with skeleton slider Amy Williams to custom-design a bob for her to race on in the run-up to and at the Whistler games.

Working closely with Williams and with sports engineers at Sheffield Hallam and aerospace specialists at BAE Systems, Blackburn and Roche designed a sled with interchangeable structural parts and adjustable components to fit to individual athlete’s bodies and sliding styles, improving its responsiveness to the subtle body movements the athlete uses to steer; it also has a ratchet mechanism to set up the runners. The sled was originally known by the codename Blackroc, after its primary designers, but Williams, who competed on it from 2008, renamed it ’Arthur’.

Williams won the gold medal on Arthur, with a winning margin of 0.56 seconds over four runs; she broke the course record twice. The BSA has now equipped its squad of sliders with Blackroc sleds.

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