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Publications (56)
Stereo camera systems have been used to track markers attached to a racket, allowing its position to be obtained in three-dimensional (3D) space. Typically, markers are manually selected on the image plane, but this can be time-consuming. A markerless system based on one stationary camera estimating 3D racket position data is desirable for research...
In short track speed skating, the relay exchange provides an additional strategic component to races by allowing a team to change the skater involved in the pack race. Typically executed every 1½ laps, it is the belief of skaters and coaches that during this period of the race, time can be gained or lost due to the execution of the relay exchange....
In team invasion sports, tactical behaviour can be examined using spatio-temporal data, i.e. the position of the players at a given time. A review of the spatio-temporal metrics used in team invasion sports performance analysis indicated that thousands of variations of metrics being used. Information about the distribution of metrics' individual ef...
Background subtraction is a classic step in a vision-based localization and tracking workflow. Previous studies have compared background subtraction algorithms on publicly available datasets; however comparisons were made only with manually optimized parameters. The aim of this research was to identify the optimal background subtraction algorithm f...
In short track speed skating, the relay exchange provides an additional strategic component to races by allowing a team to change the skater involved in the pack race. It is thought that during this period of the race, time can be gained or lost due to the execution of the relay exchange. However, the only temporal measurement reported in short tra...
Lowfield Park in Sheffield, UK is a green recreational space maintained by the City Council. Lowfield Park was selected as the primary Sheffield FieldLab for the ProFit project which ended in 2015. The ProFit project was European Interreg IVbNWE funded with the aim of encouraging physical activity through innovations in products, services and ICT s...
INTRODUCTION: A team's tactical behaviour is often quantified using metrics that relate to player locations at a given time. This spatio-temporal data is easily translated into many metrics that describe the point, line and surface relations of players and the ball over time. This study reviews the spatio-temporal metrics used in invasion game spor...
INTRODUCTION: Sports performance analysts have many metrics they can use to investigate athletic performance. The multifactorial nature of sport performance means that interactions between these metrics are potentially important. Methods typically used by sports performance analysts cannot handle many variables and their interactions - especially w...
The measurement of foot-surface contact position would aid the understanding of player movement and step strategy in sports such as tennis. However during competition, it is impracticable to instrument players. A markerless, view-independent, foot-surface contact identification (FSCi) system was developed and validated. The FSCi system analysed sta...
Splash size is an important factor in competitive diving and is considered to have a large effect in final judged scores. The aim of this research was to develop a system to determine the splash size during different stages of the dive entry. One diver was recorded during a training session and their dives analysed using the developed system. Three...
Simple and bifilar pendulum were used to measure the mass moments of inertia of three tennis rackets. The pendulum setups were filmed using an off-the-shelf camcorder, with a stopwatch in view to provide timing data. The measurement accuracy was assessed using calibration rods of known mass moment of inertia. The simple pendulum method was found to...
This research is concerned with tracking tennis racket movements. Previously, stereo camera systems have been used to track markers attached to rackets, which allows for racket movements to be obtained in three-dimensions. Typically, markers are manually selected on the image plane but this can be time consuming and inaccurate. This paper discusses...
A primary aim of the ProFit FieldLab project is to encourage physi-cal activity through innovations in products, services and ICT systems. User in-teractions with newly installed prototype play and exercise equipment within a FieldLab needs to be monitored so that its value and effectiveness can be as-sessed. Real-time feedback of activity level an...
A primary aim of the ProFit FieldLab project is to encourage physical activity through innovations in products, services and ICT systems. User interactions with newly installed prototype play and exercise equipment within a FieldLab needs to be monitored so that its value and effectiveness can be assessed. Real-time feedback of activity level and l...
The monitoring and videoing of a user's movement within a "FieldLab" recreational facility is required to study the effectiveness of innovative equipment designed to increase physical activity. A low cost alternative to current tracking systems based around the Global positioning system (GPS) was trialed for use within the Sheffield FieldLab. This...
Researchers are often interested in tracking object movement in sport. This could be useful to identify equipment designs that match the technique of players. Previously, stereo camera systems have been used to track markers attached to striking implements to measure their movement in three dimensions. However, manual selection of markers on the im...
Tennis players report anecdotally that the choice of string material affects the amount of spin applied to the ball by the racket. Previous research on the effect of the coefficient of friction of tennis strings has concluded that ball rebound is mostly, but not always, independent of the string friction. To understand this better, tennis balls wer...
There has been little three-dimensional (3D) analysis of the interaction of a tennis ball and racket during realistic play
conditions. This paper is a descriptive study of elite players in practice conditions. The method used records racket and
ball movement in 3D, intrudes minimally into the player’s environment and has a high level of portability...
Composite materials have given manufacturers the freedom to develop a broad range of tennis rackets, allowing them to change key parameters such as the structural stiffness, mass, and position of the balance point. The aim of this research was to determine how changing these parameters could affect ball resultant rebound velocity and spin for a sim...
Different types of tennis injury have been associated with play on different court surfaces and current knowledge of tennis player and court interactions is limited. This paper provides a brief overview of tennis injury incidence, player movements and the biomechanics of slips. The discussion proposes a new direction for assessing tennis player-sur...
Previous experimental studies into the dynamics of a ball–racket impact have recorded ball velocities and trajectories in one or two dimensions. These studies were limited in terms of possible impact positions and the ability to represent realistic impact conditions. As the number of dimensions in an experiment increases, it becomes difficult to is...
There are currently no restrictions on the coefficient of friction of tennis courts or strings. The aim of this paper was to determine the effect of friction on tennis ball impacts. Finite element models were used to determine the effect of friction for oblique spinning impacts both between a tennis ball and a rigid surface and between a tennis bal...
Analysis of springboards in elite diving have been limited to the measurement of the variation of material characteristics along the length of the board and it appears that dynamic models of the board's motion have not been carried out because of its complex nature. The purpose of this paper is to develop a simple mechanical model to (i) understand...
Software designed to quickly and easily calculate the 3-dimensional speed and the spin rate of a tennis ball from high speed video footage from a single camera was validated. The software values were compared to speed values from light gates and spin rate values found by manually tracking the ball logo. The respective ranges were 18–31 ms−1 and 65–...
An explicit finite element (FE) model of a tennis ball impact on a freely suspended racket was produced in Ansys/LS-DYNA 10.0. The geometry for the racket frame was reproduced in the FE model using a non-contact laser scanner. The model was validated against experimental data obtained using the fully automated International Tennis Federation Racket...
An explicit finite-element (FE) model of a pressurised tennis ball was produced in Ansys/LS-DYNA 10.0 and validated at room
temperature. This model was successfully updated to simulate temperatures of 283.15 and 313.15 K (10 and 40 ºC), by adjusting
the internal pressure and material properties of the ball’s rubber core. The validation experiment w...
An explicit finite-element (FE) model of a tennis racket string-bed was produced in Ansys/LS-DYNA 10.0. This model was used
to simulate a range of impacts between a tennis ball and string-bed, which were validated against experimental data. The laboratory
validation was undertaken by firing balls, with backspin in the range from 0 to 600 rad·s-1, f...
Performance in starts and turns is a major contributor to success in swimming and is influenced greatly by the glide efficiency and the timing of commencing the post-glide action (including kick in all strokes and the underwater pull in breaststroke starts and turns). The main aim of this research is to develop and test ‘user friendly’ software for...
Modern tennis rackets are manufactured from composite materials with high stiffness-to-weight ratios. In this paper, a finite
element (FE) model was constructed to simulate an impact of a tennis ball on a freely suspended racket. The FE model was in
good agreement with experimental data collected in a laboratory. The model showed racket stiffness t...
The International Tennis Federation (ITF) monitors all aspects of tennis for their role of protecting the nature of the game. One area in which there is limited documented data is ball spin in match play. In previous work, the ball spin generated in the 2007 World Group Davis Cup tie between Switzerland and Spain, played indoors on Taraflex carpet,...
This paper contains the recorded shot movements of 13 players in practice conditions at the Wimbledon 2006 Qualifying Tournament.
A 2-camera 3D system was used to track the racket and ball for a period of 0.02 seconds for each recorded shot. Custom-written
analysis software was used to extract the required co-ordinates from the ball and racket posi...
Tennis can be played on a variety of surfaces including clay, grass and acrylic. The performance of each surface is currently
classified using the surface pace rating (SPR). This measurement is meant to quantify the speed of a tennis court. The current method of measuring SPR involves the use of an air cannon to propel the ball onto the surface at...
An explicit finite-element (FE) model of a tennis racket string-bed was produced in Ansys/LS-DYNA 10.0. This model was used to simulate a range of impacts between a tennis ball and string-bed, which were validated against experimental data. The laboratory validation was undertaken by firing balls, with backspin in the range from 0 to 600 rad·s−1, f...
Performance in starts and turns is a major contributor to success in swimming and is influenced greatly by the glide efficiency and the timing of commencing the post-glide action (including kick in all strokes and the underwater pull in breaststroke starts and turns). The main aim of this research is to develop and test ‘user friendly’ software for...
A new analysis is presented of the major findings in sports ball aerodynamics over the last 20 years, leading to a new method for defining surface roughness and its effects on the aerodynamic performance of sports balls. It was shown that the performance of balls in soccer, tennis, and golf are characterized by the position of the separation points...
We succeeded in obtaining PSP (Pressure-Sensitive Paint) measurements for a rugby ball. It was found that the seam of the ball is the trigger for initiating low pressure. Therefore, a slower spinning ball fluctuates during flight because of the asymmetrical pressure distribution on the sides of the ball. Based on the results from PSP measurements,...
A series of experiments were carried out in which a spinning tennis ball was projected obliquely at a head clamped racket.
In each experiment a different string was used in the racket frame. An automated image analysis algorithm was used to measure
the velocity and spin of the ball. It has been found that, for the majority of impacts, the magnitude...
Although qualitative shot analysis and rudimentary 2D player testing has been performed in the past, a comprehensive 3D study
has yet to be done. This paper outlines a method that has been used to record player baseline shots and serves in 3D. The
method allows accurate tracking of racket velocity (any point on racquet), ball velocity, impact insta...
A model is presented in which the normal impact of a thick walled pressurized sphere, such as a tennis ball, is modelled as a non-linear viscoelastic spring and damper, coupled with momentum-flux forces where the shell wall deforms with high stiffness and damping. These momentum-flux forces are only present in the impact phase and do not appear dur...
The aerodynamic properties of an association football were measured using a wind tunnel arrangement. A third scale model of a generic football (with seams) was used in addition to a 'mini-football'. As the wind speed was increased, the drag coefficient decreased from 0.5 to 0.2, suggesting a transition from laminar to turbulent behaviour in the bou...
An explicit finite-element (FE) model of a pressurised tennis ball is presented. The FE model was used to model an oblique
impact between a tennis ball and a rigid tennis surface, to further the understanding of this impact. Impacts were also conducted
in the laboratory and the results from the FE model were in good agreement with this experimental...
A viscoelastic model of a tennis ball impact at normal incidence on a rigid surface is presented in this study. The ball model has three discrete elements that account for the structural stiffness, material damping and momentum flux loading. Experiments using a force platform are performed to determine the force that acts on the ball during impact,...
The aerodynamic properties of a tennis ball are obtained using wind tunnel measurements. In the first phase of this study, the drag coefficient of a variety of new and used non-spinning tennis balls was measured. The measurements were conducted in the Reynolds number range of 85×10³<Re<250×10³, which corresponds to a velocity range of 20<U<60 ms⁻¹...
In this paper, we describe an experimental investigation of the oblique impact between a tennis ball and head clamped tennis
racket. It was found that the magnitude of the ball rebound spin was not a function of the material, gage or tension of the
string used in the tennis racket. Furthermore, it was concluded that all strings exhibit a sufficient...
The dynamic properties of six types of tennis balls were measured using a force platform and high-speed digital video images of ball impacts on rigidly clamped tennis rackets. It was found that the coefficient of restitution reduced with velocity for impacts on a rigid surface or with a rigidly clamped tennis racket. Pressurized balls had the highe...
Analysis of results from the four major tennis tournaments shows that the percentage of tie breaks in the men’s game has been increasing over the last 30 years. It is hypothesised that this is due to the increasing speed of the serve in the game. There was found to be a significant difference in tie breaks between slower clay surfaces and faster gr...
A model has been derived that determines the ball, stringbed and racket frame motion for an impact between a tennis ball and racket. This paper describes the model and methods used to verify it experimentally. The model incorporated parameters such as racket mass, moment of inertia and ball stiffness. The work was conducted to produce a tool that c...