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16:00   Golf; acoustic and mechanical modelling Chair: Paul Wood 16:00 20 mins FINITE ELEMENT ANALYSIS OF THE ACOUSTICS OF A GOLF BALL IMPACTING A TITANIUM PLATE Tom Allen Abstract: The sound a driver makes on impact with a ball can influence the user’s perception of its quality. This research applied Finite Element (FE) techniques to predict the acoustic response of a golf ball impacting a titanium plate. The objective was to further our understanding of how best to model this scenario, as a first step towards simulating a ball-club impact. A golf ball was dropped from 2.5 m onto a USGA COR plate positioned face up in a free-free boundary condition. Impacts were recorded three times at two locations - 0 and 20 mm from the plate centre - using a microphone sampling at 44,100 Hz. Matlab was used to subtract background noise and convert the signal to the frequency domain via a Fast Fourier Transform. The mean frequency and mean relative amplitude from the three trials was obtained for each excited mode of vibration. The experiment was replicated within ANSYS LS-DYNA, with the Boundary Element Method (BEM) used to predict the acoustic response. Medium and fine mesh densities were investigated for the plate. Acoustic predictions of Exact BEM and approximate Rayleigh computation methods were compared to experimental recordings in both the time and frequency domain. The ability of the simulations to predict the acoustic response of the plate was independent of the impact location. The finer mesh density provided better agreement with the experiment in terms of excited frequencies and sound duration, regardless of the computation method. All models over-predicted the relative amplitudes of the experimental frequency spectrum. The Rayleigh method unpredicted true acoustic pressure in the frequency domain in comparison to the BEM method. For both methods, true acoustic pressure in the frequency domain decreased with mesh density. This research provides a methodology to characterise and compare experimental and simulated impact sounds for ball-plate impacts. Further investigation needs to be performed regarding relative amplitudes and time domain response before considering the simulation of impact acoustics for a golf driver. 16:20 20 mins THE INFLUENCE OF INERTIA OF A GOLF CLUB FOR SHAFT MOVEMENT DURING THE GOLFER’S SWING Kenta MATSUMOTO, Nobutaka TSUJIUCHI, Tkayuki KOIZUMI, Akihito ITO, Masahiko UEDA, Kosuke OKAZAKI Abstract: In order to hit a golf ball correctly, a golfer is particularly concerned with the characteristics of its driver. Therefore, a golf club is designed to satisfy the golfers’ demand. However, the United States Golf Association has placed restrictions not only on the volume of the club head, but also on the coefficient of the golf club under the spring effect rule. It is therefore difficult to differentiate these specifications. Golf club developers use a variety of methods to customize clubs to individual golfer. One such technique is “database fitting,” established by Sumitomo Rubber Industries, Ltd. (SRI). In the future, golf club developers would like to provide shafts customized to fit each individual golfer. In order to do so, it is necessary to predict shaft movement during a golf swing via simulation. Therefore, we focused our attention on the conditions for modelling the golf club. We began with 3D modelling of the golf club followed by inputting data demonstrating the swing in order to analyze club movement. Our previous study simulating golf club movement during the golf swing demonstrated 3D club movement via a FEM model with shaft flexibility. As for modelling a golf club, a head was attached to a FEM model of a shaft as a simplified rigid model. Moreover, to take the golfer’s grip into consideration, we modelled the grip using potential energy in grip during the swing. Using this simulation model, we simulated shaft movement while taking into account the golfer’s swing. And resolving inertia force into each term, we simulated shaft movement. In this study, we could obtain below results. Firstly, magnitude of deflection in each direction generated by only inertia of the shaft showed one-tenth of magnitude of deflection in each direction generated by the inertia of the club head. Secondly, each term of inertia force generated influence on deflections. Acceleration term generated the lag deflection and the toe up/toe down deflections. In addition, angular velocity term generated the lead/lag deflections and the toe up deflection. Moreover, angular acceleration term generated the lead deflection and the toe up/toe down deflections. 16:40 20 mins EFFECT OF CLUBHEAD INERTIAL PROPERTIES AND DRIVER FACE GEOMETRY ON GOLF BALL TRAJECTORIES William McNally, Daniel Balzerson, Daniel Wilson, John McPhee Abstract: There are many factors that influence the amount of side-spin imparted to a golf ball during impact with a driver. In general, the best golf drives are launched with minimal side-spin, producing a straight ball trajectory with maximum carry distance. During off-centre impacts, side-spin is generated due to a phenomenon known as the “gear effect.” The extent of the gear effect depends on clubhead design parameters such as the moment of inertia and centre of gravity location. The bulge of a driver is a design feature implemented to counter-act the side-spin produced by the gear effect. In this investigation, an impulse-momentum impact model and an aerodynamic ball flight model are used to (i) examine the effect of the centre of gravity depth (distance from clubface) on ball trajectory during off-centre impacts, (ii) test the efficacy of movable weight technology, and (iii) optimize the bulge radius in relation to the clubhead’s centre of gravity depth and moment of inertia. In the first study, it is qualitatively shown that side-spin increases linearly with increasing centre of gravity depth. In the second study, it is found that movable weights can have a significant effect on ball trajectory, especially at higher swing speeds. In the third study, a relationship between the bulge radius, centre of gravity depth, and moment of inertia is developed, and an equation for calculating the optimum bulge radius is fit to the simulation results.