STABILITY ANALYSIS OF LOW CRESTED AND SUBMERGEDRUBBLE MOUND BREAKWATERS: RELATIONSHIP BETWEENFLOW CHARACTERISTICS AND MEASURED DAMAGE ANDSTABILITY FORMULAE FOR LOW CRESTED AND SUBMERGEDBREAKWATERS

摘要

This paper analyzes the correlation between the flow characteristics and the observed damage on low crested and submerged rubble-mound structures and provides design formulas for both types of rubble mound structures. Using laboratory tests, the geometrical characteristics of armour layer damage on these structures has been obtained. Four types of damage, depending on the structure freeboard, are described. The analysis of flow around and inside these structures is carried out with the help of a numerical flow model that solves the VARANS equations with a VOF free surface tracking technique. Different parameters have been considered, i.e. the Mobility Parameter; the Shields Parameter; the Morison Drag Force parameter and the Morison Lift Force parameter. Using the numerical model, the evolution of some characteristic flow parameters around the structure is obtained. This evolution is then compared with the damaged geometry, being the Mobility Parameter that better describes the observed damage geometry on submerged breakwaters. This correlation is used to provide design formulas for these structures. In the case of low-crested breakwaters, other factors, different from the maximum values of flow parameters, should be taken into account for the description of damage: turbulence generated by breaking over the units; the water jet created by plunging waves and forces originated by the down - rush at the seaward slope. That means that a more empiric approach based on the stability number is used to provide stability formulas in these cases.