| Popis: |
The damage caused to many coastal structures during storms is suspected to be due to very high pressures from steep and breaking water waves. In this thesis we restrict attention to block work seawalls with vertical faces, with the aim of interpreting the type of violent flows measured and photographed by E.S. Chan and W.K. Melville, in a study reported in Proc. R. Soc. Lond. A, 147: 95-131, 1988. We use two different approaches to model the impact of a sea wave against a coastal structure. The first approach involves applying pressure impulse theory, the integration of pressure over time, to the two dimensional model of a wave with a vertical face impacting a vertical wall. Fourier solutions are found for the pressure impulse, and convergent series are used to express the distribution of the pressure impulse on the wall and the bed. The location and value of the maximum pressure is demonstrated to be strongly dependent on the height of the impacting wave front. For the second approach we use potential flow theory applied to two-dimensional and axisymmetric flows in infinite depth. The two dimensional flow is also considered in finite depth. The velocity potential is prescribed on the free surface for an initial time and for finite depth the seabed forms a rigid boundary. We use a Maclaurin series in time for the velocity potential, where the series coefficients satisfy a Dirichlet problem with a flat free surface, and solve the boundary value problem analytically using a Greens function approach. In the two-dimensional infinite depth case, we also apply complex function theory when the boundary data is a rational function. Analytical results are achieved for all cases, and it is established that both the presence of the bed and the axisymmetric effects are significant in the predicted pressures. Comparisons with experimental results show some agreement |
