Effects of attenuation and mitigation of underwater explosion by porous foam layers are investigated experimentally and numerically. When gas bubble generate near the rigid wall, a gas bubble travels to the wall side and collides with the wall surface by the jet in the strong upward flow. Peak pressure of bubble pulsations on rigid wall increases to about 13 times of the hydraulic shock pressure. In the case of foam layer, a gas bubble travel to downward and apart from a foam surface. The foam body extends by strong downward flow. The duration of stresses increase slowly in comparison with the rigid wall. The numerical computation of bubble motion and shape simulates the experimental results well.
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