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.

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.

High speed airflow pathlines colored by local velocity over the Adidas Teamgeist 2006 soccer ball

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 non-spinning soccer balls has fallen by as much as 30% over the last 36 years. Newer balls, like the one to be used in the 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 Carré said: “Our work clearly points to the fact that any non-uniformity 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.”

CFD predictions of surface shear stress patterns on the rear of the Fevernova Ball (left) and Teamgeist Ball (right) for a zero degree tracking orientation (red = high shear, blue = low shear)

Sarah 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 soccer 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 9 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 GmbH 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.

Air flow pathlines colored by local velocity inside the Allianz Stadium in Munich with doors open (red = 1.5m/s)

Commenting on all these studies from around the world, Dr. H. Ferit Boysan, vice president and general manager at ANSYS, suggests that: "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 Carré 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.”

Dr Carré’s Sports Engineering research group is hosted in the Mechanical Engineering Department at the University of Sheffield, England. The group has world-class expertise in sports ball and pitch aerodynamics using various experimental and computer modelling techniques and is closely involved with the International Sports Engineering Association (ISEA) and SportsPulse.

Fluent, Inc., a wholly owned subsidiary of ANSYS, Inc., (Nasdaq: ANSS), is the world's largest provider of Computational Fluid Dynamics (CFD) software and consulting services. Fluent's software is used for simulation, visualization, and prediction of fluid flow, heat and mass transfer, and chemical reactions. It is a vital part of the computer-aided engineering (CAE) process for companies around the world and in almost every manufacturing industry including aerospace, automotive and process industries. Fluent's CFD software has been used extensively in competitive sports ranging from Motor Racing through Olympic Sports to America’s Cup Yachting. Additional information on Fluent's products can be obtained on the World Wide Web at www.fluent.com.

ANSYS, Inc., founded in 1970, develops and globally markets engineering simulation software and technologies widely used by engineers and designers across a broad spectrum of industries. The Company focuses on the development of open and flexible solutions that enable users to analyze designs directly on the desktop, providing a common platform for fast, efficient and cost- conscious product development, from design concept to final-stage testing and validation. The Company and its global network of channel partners provide sales, support and training for customers. Headquartered in Canonsburg, Pennsylvania, U.S.A. with more than 40 strategic sales locations throughout the world, ANSYS, Inc. and its subsidiaries employ approximately 1,400 people and distribute ANSYS products through a network of channel partners in over 40 countries. Visit http://www.ansys.com for more information.