Mound Breakwaters under Wave Attack

Research on rubble mound breakwaters when confronted with waves. The rapport covers the flow characteristics and mound stability under regular waves and under oblique wave attack. The authors find a formula for rough, permeable slopes, flow characteristics under the action of a regular wave train by a function of the type. Furthermore they conclude that the distribution of flow characteristics in sea state can be obtained on the basis of interaction curves and joint probability density function of wave heights and periods. The conclusions on the mound stability of breakwaters are: -Stability conditions of an undefined, rough, permeable slope are governed by the stability function. -The stability function depends only on Iribarren's number. -Randomness can be accounted for by using confidence bands for the stability function. -For each type of armour unit, an optimum slope of maximum stability exists. The greater the interlocking among armour units the steeper the optimum slope and the more peaked the stability maximum. -Given a rubble mound breakwater a minimum sea state exists which produces a significant failure probability. If a sea state is presented which is the same or higher than this minimum, failure of the structure is only a question of the duration of the sea state. Conclusions on the characteristics and stability of rubble mound breakwaters under oblique wave attack: -There is a dangerous lack of experimental data on the subject. -Run-up and run-down under small oblique incidence of waves (angle lower than 45 degrees) are function of Ir.cos(theta). For higher incidence angles the hypothesis is unreliable. -The stability of steep slopes under oblique wave attack is not worse than under perpendicular wave incidence. For milder slopes the opposite may be true. -The failure of probability of a rubble mound breakwater under a sea state with oblique incidence, can be calculated by taking into account the breaking limit, the interaction curve and a joint distribution of wave heights and periods