6 research outputs found
A study of the relationship between surface features and the in-flight performance of footballs
Football is widely regarded as the most popular sport in the world involving over 270 million
people from different countries and cultures. It can be argued that the football is one of most
important aspects of the game and hence the flight of the ball, if unexpected, can alter the
outcome of the game. This thesis provides an engineering perspective and contribution to the
continued understanding and improvement of the in-flight performance of FIFA approved
footballs.
Skilful players will impart spin onto a ball to induce a curve in-flight to try and deceive
opponents. This flight is generally smooth, although subtle variations in the orientation and spin
rate may cause conditions that affect the path and final ball position, in a manner considered to be
unpredictable due to aerodynamic effects. Ball designs and manufacturing techniques are
evolving and certain seam configurations are known to induce asymmetric pressure distributions
resulting in lateral movement during flight.
Aerodynamic research of sport balls has primarily focused on drag and the effects of high spin
rates. Studies have shown the introduction of surface roughness affects the boundary layer state
compared to a smooth sphere. Surface roughness on a football takes many forms including seam
configurations and micro surface textures. The influence of changing the density, distribution and
dimensions of the surface roughness with respect to the aerodynamic behaviour has been
researched. The principle focus of this thesis is concerned with the influence on the lateral
component as a result of applying surface roughness to the outer surfaces.
The influence of the surface roughness on the drag and lateral components were determined using
established wind tunnel techniques. Real balls and full size prototypes were tested. A
mathematical flight model was employed to simulate realistic multiple flight trajectories based on
empirical aerodynamic data. Mathematical and statistical techniques, including R.M.S and AutoCorrelation
Functions were used to analyse the data. The results from this research showed how
small variations in surface texture affected the complex nature of the lateral forces. Trajectories
varied significantly depending on initial orientation and slow spin rate sensitivities. In conclusion,
ball characterisation techniques were developed that identified lateral deviation and shape
measures and considered a gradient profiling approach. Application of these novel parameters
through multiple trajectory analysis allowed for an in-flight performance measure of footballs
designs
The application of simulation to the understanding of football flight
This paper demonstrates the value of using a flight model in the analysis of the flight of a football, and explores the complexity
of the model required to produce useful results. Two specific aspects of the simulation are addressed: the need
to include a model of spin decay and the requirement to include a full aerodynamic drag profile as a function of Reynolds
number rather than a single indicative value. Both are aspects of the ball performance that are experimentally intensive
to obtain.
The simulated flights show that the inclusion of spin degradation is important if flight validation is the objective, but
that it may be unnecessary in a comparative study. The simple analytical model of spin degradation is shown to overestimate
the reduction in lateral deviation when compared to experimentally acquired data. Therefore, the experimental
method is preferred.
The analysis of the shape of the drag profile (drag coefficient against Reynolds number) is explored, and it is shown
from the simulated flights that post-critical coefficients of drag have the greatest effect on trajectories, and an average
drag value is sufficient for most modelled scenarios
The aerodynamic performance of a range of FIFA-approved footballs
Much discussion surrounds the flight of a football especially that perceived as irregular and is typically done so with little understanding of the aerodynamic effects or substantive evidence of the path taken. This work establishes that for a range of FIFA approved balls there is a significant variation in aerodynamic performance.
This paper describes the methods used for mounting stationary and spinning footballs in a wind tunnel enabling accurate force data to be obtained, and the analysis techniques used. The approach has been to investigate a number of scenarios: Non-spinning Reynolds Sweep, Unsteady Loads, Orientation Sensitivity (Yaw Sweep) and Spinning Reynolds Sweep. The techniques are applied to a number of footballs with differing constructions and the results reported. To put the aerodynamic data into context the results are applied in a flight model to predict the potential differences in the behaviour of each ball in the air.
The paper concludes that although the drag characteristics are different for the different balls tested the simulation suggests that this has only a limited effect on the flight of the ball. It is also shown that the unsteadiness of the aerodynamic loads is unlikely to be responsible for unpredictable behaviour. However, it is also shown that there are significant differences in the lateral aerodynamic forces for a range of FIFA approved match balls, and that these aerodynamic differences have a significant effect on the flight path for both spinning and for slowly rotating balls
Maps Showing the Potential Distribution of Four Species of Mosquitoes in the United States
<p>Distribution predicted using satellite derived environmental data is in red, and recorded distribution is outlined in yellow. Image courtesy: TALA Research Group–University of Oxford.</p
Arthropod Vectors That Are Discussed in This Paper
<p>Arthropod Vectors That Are Discussed in This Paper</p
Atomic Layer Deposition of l‑Alanine Polypeptide
l-Alanine polypeptide thin films were synthesized via
atomic layer deposition (ALD). Instead of using an amino acid monomer
as the precursor, an l-alanine amino acid derivatized with
a protecting group was used to prevent self-polymerization, increase
the vapor pressure, and allow linear cycle-by-cycle growth emblematic
of ALD. The successful deposition of a conformal polypeptide film
has been confirmed by FTIR, TEM, and Mass Spectrometry, and the ALD
process has been extended to polyvaline