The Investigation of high quality surfing waves generated by a moving pressure source

This thesis reports on an investigation into a novel method for generating surfable waves. This is a new surf pool concept to generate continuous surfable waves, with one or more pressure sources being rotated within an annular pool to generate waves. The circular channel has sloping bathymetry with the outer side being deeper; the waves are generated in the deep water and break in the shallow water on the inner island. Whilst previous experimental studies proved that it is possible to generate the surfable waves with this method, due to a lack of knowledge concerning waves generated in such a restricted environment, the influence of many parameters on the generated waves required investigation. The research was conducted to better understand the wave generated by moving pressure sources, the waves’ propagation and the effect of bathymetry on the wave quality for surfing. Studying all these parameters by experimental means would be exceptionally time consuming and expensive, so computational fluid dynamics was proposed as an effective alternative approach. Since previously proposed numerical methods were not able to predict the behaviour of these waves accurately, the main aim of the research described within this thesis was to investigate whether a new numerical method could be used as a research tool to gain insight into the production of highly controlled waves suitable for surfing and subsequently for proposed designs. Experimental tests were conducted at the Australian Maritime College’s towing tank and model test basin to investigate wave generation, improve the wave quality for surfing and provide validation data for the numerical investigation. A brief description of these experiments and the derived conclusions are presented. The towing tank test series mainly focused on the pressure source effect on the wave generated and the model test basin series considered the bathymetry effect on the wave propagation and control breaking point. To investigate whether a numerical method could be used as a design tool for proposed designs, the finite volume approach was chosen to predict the wave generation and breaking characteristics. The accuracy and stability of the numerical scheme were firstly investigated. The numerical results for different configurations were compared with the experimental data. It was found that the numerical approach used is capable of accurately predicting wave height, propagation and forces on the pressure sources. A grid study was conducted to optimise the simulation cost and accuracy. In this mesh study, the effect of aspect ratio, the number of cells per wave length and wave height were also investigated. It was shown that mesh quality has a significant effect on wave height prediction. To better understand the effect of channel bathymetry on the wave breaking location, wave breaking intensity, peel angle and wave wall length for different channels were numerically examined at full scale. It was shown that high quality continuous breaking waves with the desired plunging shape and long wave length were able to be generated and it is possible to create waves suitable for surfers from beginner to expert level by changing the pressure source speed. From the channels studied it was concluded that channel shape does not have a significant effect on the maximum wave height, but the width of the deep section of the channel has a significant influence on the breaking location and the channel slope has an effect on the breaking intensity. The wave wall length was longest in the channel with the widest deep-section. To determine the influence of the pressure source parameters on generating high quality surfable waves, different pressure source shapes were modelled. By comparing the results, the effects of wavedozer parameters were investigated. The effects of wavedozer parameters such as draught, angle of attack and beam were investigated and it was shown that increasing the draught, angle of attack and beam increases the height of the generated waves. It was showed that increasing the beam is more effective than increasing draught in terms of increasing the wave height. The waves generated by a higher attack angle wavedozer were found to be larger than the lower attack angle, but the quality of the waves generated by the lower angle of attack was better.