Simulation of the Rubble Mound Breakwater Response to the Underwater Explosion and Assessment of Failure Modes

Breakwaters are of great importance as coastal protection structures, but the double importance of breakwaters in our country is due to the creation of small and large shelters for different vessels. In addition, marine structures, including breakwaters, are subject to a variety of threats, including air, sea and submarine attacks. Therefore, attention to passive defense considerations is important in designing and operating breakwaters against threats and damage. One of the most important of these threats is the terrorist and explosive threats from the sea. In this research, the response of rubble mound breakwaters and their failure modes subjected to the underwater explosion was evaluated. Thus AUTODYN finite element software was used for the simulation and analysis of breakwater responses under the underwater blast loading. The used simulation and analysis method were the Coupling Euler-Lagrange process and explicit dynamical solving, respectively. For verification, first, the wave propagation from underwater explosion and its damaging effect on a concrete dam structure were evaluated. Then, The proposed model response of the breakwater using the software under the variation of explosive mass, water depth, event explosive depth, structure breakwater slope and size of armor layer blocks were investigated. The results showed, the greater the depth of the explosion and the shorter the scaled distance was less than 0.533 kg/m1/3, the geater the short-term damage would be. In the medium time simulation, was observed that by increasing the dimensions of concrete blocks of Armor layer from 2.4 m to 0.6 m, percentage failure decreased from 47% to 23%, and as well as for the structural slope of breakwater, with reducing the angle from 45 degrees to 26 degrees, the failure amount was reduced by about 50%. Generally, within the scope of this research, the critical explosion range was less than 8 meters from the structure.