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UBC Theses and Dissertations

Wave reflection effects within a harbour O’Sullivan, Enda Joseph


This thesis summarizes a numerical model used to predict the wave field in a harbour of constant depth with partially reflecting boundaries, and describes laboratory tests undertaken to assess the numerical model and the importance of partial reflection effects. The numerical model is based on linear diffraction theory, and involves the application of a partial reflection boundary condition. The extension to general harbour configurations that includes breakwaters is made by utilizing a wave doublet representation of the fluid boundaries instead of the usual wave source representation. The numerical model is initially compared to closed-form results for the fundamental case of a straight impermeable offshore breakwater, and the method is found to compare well for this case. Further comparisons are made for a semi-circular harbour with a pair of symmetrical protruding breakwaters, and for a rectangular harbour with a pair of symmetrical protruding breakwaters. The boundaries of the semi-circular harbour were perfectly absorbing and the numerical model predicts the wave field within the harbour realistically. For the later configuration cases which are considered include perfectly absorbing, perfectly reflecting and partially reflecting harbour boundaries, and in all cases the numerical model predicts the wave field within the harbour realistically. Experiments were conducted at the Ocean Engineering Centre at BC Research, Vancouver. Duringthe experiments the wave field within a model harbour was measured under different conditionscorresponding to changes in the wave period, incident wave direction, incident wave height, andreflection coefficients of the harbour boundaries and breakwaters. The experimental results arecompared to those of the numerical model and agreement is generally good. In general the waveheights within the harbour are slightly underpredicted, while the wave heights outside the harbourare slightly overpredicted. Overall, the numerical model is found to provide a reasonably reliable means of predicting the wave field within a harbour of constant depth and arbitrary shape with partially reflecting boundaries.

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