CFD software explains how Beckham bends it

In the run-up to the FIFA World Cup, Fluent has published the results of pioneering work at the University of Sheffield.

The fast approaching 2006 FIFA World Cup in Germany next month heralds the arrival of another festival of the beautiful game.

This year's competition promises to showcase swerving kicks which defy explanation and which often decide the outcome of the match.

Some of the world's greatest goalkeepers have been beaten by unusual swerving balls which move to the left and the right before hitting the back of the net, even though they have little or no spin applied to them.

The new research has found that the shape and surface of the ball, as well as its initial orientation, is critical in terms of its trajectory through the air.

A team of researchers, led by Dr Matt Carre at the Department of Mechanical Engineering at the University of Sheffield, used advanced computational fluid dynamics (CFD) software to simulate the physics of airflows in and around objects.

They studied and compared airflows around four balls, all with different panel designs, each having been used at different periods over the past 36 years, up to, and including the new Adidas ball to be used in the 2006 World Cup.

University PhD student and Sheffield FC player Sarah Barber, alongside Dave Mann, Principal Engineer at Fluent, used a 3D laser scanner, similar to those used in Formula 1 motor racing, to obtain accurate surface detail of each individual ball, including their stitches and seam patterns.

They demonstrated that the shape, surface and asymmetry of the ball, as well as its initial orientation, has a profound effect on how the ball moves through the air after it is kicked.

The side force varies according to the orientation of the ball relative to its flight, meaning that for a kick where the ball is slowly rotating, the side force could fluctuate causing it to swerve.

Ultimately the nature of the swerve is affected by the initial orientation of the ball before it is kicked.

In collaboration with Dr Takeshi Asai at the University of Tsukuba in Japan, the team used wind tunnel measurements to verify their CFD studies and demonstrated that in match conditions the drag of nonspinning footballs has fallen by as much as 30% over the last 36 years.

Newer balls, like the one to be used in the FIFA World Cup this summer, which manufacturers claim to be rounder and which have more uniform seam geometry, have been found to be more consistent in high speed kicks with little or no spin.

Commenting on these new findings, Dr Carre said: "Our work clearly points to the fact that any nonuniformity of design of soccer balls, or asymmetry of manufacture, will have a dramatic effect on the side forces of the ball when there's little or no spin applied to it, and hence its swerve through the air".

"We believe that our findings go a long way to explain the phenomenon observed when some players kick the ball with little or no spin, yet get it to swerve in a seemingly erratic manner - possibly producing an S-shape trajectory".

Barber added: "As a soccer player I feel this research is invaluable in order for players to be able to optimise their kicking strategies".

"This knowledge could further be utilised by manufacturers to design future balls which will ultimately enhance the overall experience for players and spectators at all levels of the game".

The aerodynamics of the ball is not the only science to be examined in the weeks leading up to the World Cup.

The first game of the 2006 World Cup on 9th June will take place in the purpose built FIFA World Cup Stadium in Munich, home to both Bayern Munich FC and TSV Munich 1860.

The stadium was designed by the Swiss architects Jacques Duke and Pierre de Meuron, with the quality of the pitch in mind, because of a desire to have uniform airflows going over the turf when the stadium doors are open.

These air movements help to ensure that the pitch grass will have optimal growing conditions between matches.

Dresden based consultant, Dr Peter Vogel of GTD used CFD software from Fluent to study the airflow in the stadium to validate its design.

He was able to verify that the stadium experience is the best possible for the crowd and that the architects' visionary design conforms to high safety standards.

His detailed virtual flow simulations illustrate perfectly the relatively gentle airflow patterns players will experience near the pitch surface in the space above the playing area during a game.

Commenting on all these studies from around the world, Dr H Ferit Boysan, Vice President and General Manager at Fluent's parent company Ansys, suggests: "It is becoming more and more obvious that the aerodynamic performance of a soccer ball is very closely linked to its design and manufacture as witnessed by these initial Sheffield studies".

"Dr Carre and Dr Vogel's work is clearly pointing towards modern computer based simulation techniques permitting us to model any kick, of any ball, in any stadium, such that we will be able to get a prediction of what will happen before a ball is even kicked".

"This will open up whole new directions for the design and development of soccer balls as well as stadia".

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