A flap-type gate for protecting against storm surge and tsunami is the mobile barrier hinged along a sea-bottom axis. Present paper describes the motion characteristics of the gate rising to the water surface or sinking to the bottom. Extensive experiments are performed with the scale model of the rising or sinking gate in a water tank. The effects of the air chamber volume in the gate and the side wall beside the gate on the motions are investigated.
Further, a simple mathematical model is derived for the dynamics of rising motion of the gate. The rising motion predicted numerically using the mathematical model compares well with experiment motion, if the coefficients for the equation of the motion in the mathematical model can be suitably determined.