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STEVE HAAKE TECHNOLOGY UNIVERSITY OF SHEFFIELD ts por S engin eering Sports engineering has emerged in Introduction The economics of sport the last two decades as a legitimate ou may have only just heard of I am often told that sport is big business area of research. However, some are sports engineering but it is not a and a few years ago, when grants were still not sure what sports engineering Ynew topic by any means. Over scarce, I wondered where the money is all about and, if it does work, isn’t three hundred years ago, a mechanical was spent. The pie chart in Figure 1a it just cheating? Steve Haake, of the line call device was introduced to Real shows that consumer expenditure in University of Sheffield, has looked at Tennis, whilst in 1672 Newton sport in the UK exceeded £15 billion in the economics of sport to see why discussed the way spinning tennis balls 2001. Going clockwise from the top, the it’s so popular and discusses its deviated in flight. More recently, in 1910, first three portions of the chart show attraction to students. Some Sir J.J Thompson gave an explanation that £5.5 billion was spent on products, examples from tennis, football and of the dynamics of golf ball flight in i.e. clothes and footwear, equipment, wheelchair racing are described to Nature, using the analogy of electron boats and publications. Equipment and show how mainstream engineering beam trajectories. In the last decade or apparel – usually associated with sports principles can be used to analyse so, sports engineering has become very engineering – make up about £4.5 and redesign sports equipment. popular across the world, particularly in billion per annum of consumer the UK. So what is fuelling this interest expenditure. These sectors saw and is sport ‘big business’ as many significant growth in the 1970s and people say? There is a lot of hype 1980s due to public sector sports surrounding sport, often in the claims of provision and local government equipment manufacturers. So does investment in sports centres. Since the sports engineering work and, if it does, 1990s, however, public investment has isn’t the application of engineering to stopped and participation has remained static. Luckily for sports equipment sport simply cheating? ingenia manufacturers, sports participants now 23 TECHNOLOGY Other Expenditure engineering. Loughborough and Birmingham have well established Sport Related Travel courses on sports technology and Sport Clothing and sports and materials science, Footwear respectively. These three institutions alone currently represent yearly intakes Sports TV and video of around 100 students and teach courses such as sports equipment design, ergonomics, vibration and dynamics, aerodynamics and sports materials. At the University of Sheffield, Sport Equipment the elective on Sports Engineering on Health and Fitness the MEng programme in Mechanical Engineering is the most popular final Sport Related year option, with over 80% of the class Publications choosing to take the subject. Combining Spectators sport with engineering is, therefore, an Boats extremely attractive option for students. Participation Figure 1a Breakdown of UK consumer spending on sport Research in sports (Source: Sport market forecasts, Sports Industries Research Centre, engineering 2001) So what kind of research is there in sports engineering that makes it so interesting? Nearly every university spend more than they did 10 to 15 are currently around 20 undergraduate engineering faculty will have produced years ago, possibly because equipment courses involving the technology or work relating to sport. At Sheffield, the costs almost 30% less in real terms engineering of sport. The University of Department of Mechanical Engineering than it used to. Bath has recently set up BEng and has carried out research into the In the UK, interest in sport has been MEng programmes in sports dynamics of tennis, the aerodynamics fuelled in the last decade by football and by its television coverage (worth around £1.6 billion over three years). With government spending on sport for this decade approaching £750 Sport related publications (b) million, participation is set to rise, Boating which will in turn boost expenditure on Participation equipment and apparel. This is seen in Sports gambling the chart in Figure 1b, which shows that the sale of sports equipment Sport clothing and footwear should grow by more than 30% Sport related travel between 2000 and 2005. This is over Sports TV and video twice that predicted for the economy Health and fitness as a whole. Sport is, indeed, very Spectator spending healthy and research in sports Sports equipment engineering should benefit through the General consumer spending growth in sports equipment sales. Sport total Undergraduates and sports 051015 20 25 30 35 engineering ingenia Percentage growth in sport spending 2000 to 2005 Over the last decade, academia has woken to the realisation that sport can Figure 1b Predicted growth in sport compared to the growth in general consumer be used to enhance students’ interest in spending. mainstream engineering. In the UK there (Source: Sport market forecasts, Sports Industries Research Centre, 2001) 24 TECHNOLOGY of football, the design of ice skates, over a simpler rigid body model, is that Tennis courts mountaineering ice axe design and it can mimic the real-life vibrations of a Another set of experiments studied the wheelchair athletics. Some of these are tennis racket which contribute to both effect of the surface on ball rebound outlined below to give a flavour of the energy loss in the ball and poor feel by (see Figure 2(c)). The work showed that sort of work that is being done in the the player. all court surfaces can be considered UK. rigid in comparison to tennis balls, Tennis ball aerodynamics even ‘soft’ surfaces such as grass and Tennis research with the Figure 2 (b) shows an image of clay. This simplifies the modelling of the International Tennis Federation streamlines passing over a rotating impact, which allows the surface to be Figure 2 shows some of the work that tennis ball. Research in wind tunnels (at characterised purely by a coefficient of has been carried out at the University Sheffield, Cambridge and NASA) has friction measure. The ball’s interaction of Sheffield on behalf of the shown that the drag coefficient of is dominated, therefore, by the International Tennis Federation. The tennis balls is approximately 0.6, with dynamic stiffness and damping of the project’s remit was to determine the lift coefficients of up to 0.2, depending ball, and by the momentum flux of the important design parameters for upon the amount of spin. Drag shell during impact. This flux is the equipment in relation to its coefficients of smooth spheres are localised mass of the ball, which performance. generally around 0.5 at low speeds and appears as a wave travelling around values can drop to around 0.1 at high the ball and causing the characteristic Rackets and balls speeds, depending upon the surface dimple in the ball during impact seen in Impacts were carried out using different roughness of the sphere. The transition Figure 2 (c). tennis ball designs in a variety of impact from high to low drag coefficient is Grass surfaces generally have a low positions on different rackets with a caused by a change from laminar flow coefficient of friction, which allows a ball variety of string tensions (see at low Reynold’s numbers (equivalent to to rebound with about 70% of its initial Figure 2(a)). One of the problems in this low speed) to turbulent flow at high speed at low angles. Clay, on the other area involves keeping the number of Reynold’s numbers. Interestingly, tennis hand, has a high coefficient of friction variables to a minimum; this experiment balls show no such transition and the which reduces the ball’s rebound to had five (ball type, string tension, racket drag coefficient remains roughly less than 65% of its impact speed and type, impact position and velocity). constant for all speeds. This is causes the ball to rebound steeply. Other experiments have included angle, contrasted with golf balls where the Manufacturers try to optimise the spin, string type, string configuration, dimples cause transition at quite low construction of balls for different mass and moment of inertia. The work Reynold’s numbers. The drag surfaces. For instance, dynamically stiff has resulted in a mathematical model of coefficient is therefore low for the balls have been used on clay courts to impact based upon a viscoelastic majority of a golf ball’s trajectory which try to reduce energy losses during model of the ball and a flexible beam makes it fly a lot further than if it were impact and cause the ball to rebound model of the racket. The stiffness and smooth. This was actually found out by lower and faster, nearer in performance damping for the ball are found by accident early on in the development of to hard court surfaces. measuring contact times and rebound golf balls when players found that worn velocities in controlled tests. The and cut-up golf balls flew a lot further A complete model of tennis stiffness and damping of the ball than the newer smooth ones. Three analytical models were therefore increase with deformation, which is Returning to tennis balls, it is clear created, one for the ball/racket impact, dominated by the velocity of the that the felt is the main parameter to one for aerodynamics and one for the impact. The parameters required to influence their flight. Tennis balls fresh ball/surface impact. These were model the racket are found through out of the can tend to fluff up after a combined to create a unified model of direct measurement of mass and few shots which can increases the drag tennis dynamics, written in Visual Basic, dimension and through vibration coefficient by up to 10%.

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