Stability of Armor Units for a Leeward Mound of Composite Breakwaters

The armor units on the rubble mound foundation of a composite breakwater should be of sufficient mass to ensure stability against storm waves. Toward this, the stability mass of seaward units has been calculated by an equation developed from hydraulic model tests and the mass of leeward units has been designed empirically as half mass of seaward units. This study uses numerical simulation to show that large eddies generated by wave overtopping results in a rapid caissonward flow above the leeward mound crown and that the velocity of this flow is a very important factor in the stability of armor units. Hydraulic model tests were used to formulate a function of wave conditions and structural geometry. From the balance of forces acting on an armor unit, the stability number N_s in the Hudson formula was formulated to allow design of armor units on the leeward mound.