Developing a methodology for the assessment of wave energy along the South African Coast

[摘要] ENGLISH ABSTRACT : Ocean wave energy can become one of the alternative energy resources for fossil-fuelledpower generation in South Africa. Due to global warming, several studies about thegeneration of wave energy have been done to find cleaner and sustainable renewableenergy resources. An array of Wave Energy Converters (WECs) in a form of a wave farmmay be used to harness the energy resource to generate electricity. Nearshore wavefield effects due to the presence of a wave farm must be investigated particularly at thecoastline as it will be affected. The principal objective of this thesis is to investigate theimpacts induced by a wave farm on the nearshore wave field region through numericalmodelling. Another objective is to give guidance about some of the parameters andinput conditions for numerical modelling of wave transformations.In the present study, wave conditions have been assessed at selected locations of theSouth African coast. The JONSWAP model, which is the most frequently used spectralmodel to describe wind-generated waves, was used to represent wave energy spectrumalong chosen locations. The JONSWAP model was fitted into the measured data alongthe coast to obtain the peak enhancement factor (gamma) values for chosen locations.The measured data was found to consist of bimodal spectra, local winds and distantstorms and also multiple peaks in the spectra were observed. The spectral decompositionmethod was then applied to split the data into wind sea and swell to assess a morerealistic description of the wave system. It was found that the method is effective insplitting bimodal spectra but is not successful in multi-peaked spectra.Saldanha Bay was chosen as the case study for installation of a wave farm due toits abundance of wave energy. A nested numerical wave model, referred to as SWAN(SimulatingWAves Nearshore), was used to simulate the nearshore wave field conditionsin Saldanha Bay. The obtained gamma value for Saldanha Bay was used to set the wavemodel. Two model simulations in the study were considered, model simulations in thepresence of a wave farm and model simulations in the absence of a wave farm. Thedifference in significant wave height and wave energy spectrum with and without thewave farm was assessed. The results show a reduction in significant wave height and a change in wave energyspectrum at the selected output locations. A gradual redirection of waves induced bythe presence of wave farm has been observed for all selected boundary wave directionconditions. The overall results of the study indicate the change in the nearshore wavefield during the presence of wave farm. A sensitivity assessment was conducted toinvestigate the change in wave energy due to the orientation of the original wave farmlayout and the addition of two devices in the original wave farm layout.A proposed methodology for the assessment of wave energy was presented to evaluatethe wave energy resource along the South African coast. The proposed methodology isbased on analysis that was conducted in the study.

[发布机构] Stellenbosch University