A model of tennis balls impacting obliquely on tennis courts was developed in this study.udBalls were impacted normally on a force plate to read impact force data, and filmed at highudspeed during oblique impacts. A normal model was created and then extended to coverudoblique impacts. The experimental data was used to verify the model in each case.udA study of surface testing methods found that tennis courts are significantly stiffer thanudtennis balls; so much so that they can be considered rigid. A coefficient of friction betweenudball and surface was all that was necessary to define a surface.udNormal impacts were performed on a force plate for four different ball constructions atudspeeds between 3 and 20 ms-Iud. Impact speed had a significant effect on coefficient ofudrestitution (ratio of rebound speed to inbound speed) - for example for a pressurised ball,udfrom about 0.8 at an impact speed of 3 msIudto about 0.6 at 20 msI. Pressureless ballsudbounce at a similar speed to pressurised balls at low impact speeds, but slower at highudimpact speeds. Punctured balls bounce slower throughout the range of impact speeds. Alludballs showed a rapid increase in force during the initial part of the impact.udAn iterative model was created to simulate normal impact. A numerical method was usedudto find the effect of deformation shape on the relationship between centre of massudmovement and ball deformation. A total force during impact was created by combiningudstructural stiffness, material damping and impulsive reaction forces. This model workedudwell for all ball types and used quasi-static compression data and a low speed drop test toudfind the parameters. The impulsive force simulated the initial increase in force well.udA thorough experimental study of oblique impacts was performed by isolating in turn eachudof the key incoming properties of impact. The incoming speed, spin and angle, togetherudwith the ball and surface construction were individually varied in turn and the effect onudoutgoing characteristics measured using high speed video footage. In most cases there wasuda distinct change in rebound properties when rolling happened. Footage at up to 7000udframes per second was used to qualitatively explain the effect of deformation shapes onudenergy losses. It was found that impacts with backspin caused more deformation and anudincreased energy loss compared to normal impacts with the same vertical velocity. Impactsudwith topspin had a reduced vertical energy loss.udThe normal model was extended to include the horizontal and rotational forces necessaryudto simulate an oblique impact. A damping compensation factor was included to adjust theudvertical energy losses at different spin rates. The oblique test data was used to verify theudmodel, and there was a very good correlation. ud
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