Forces on a semi-submersible in internal solitary waves with different propagation directions

Abstract

Experiments were conducted to study the forces acting on a semi-submersible platform induced by internal solitary waves (ISWs) with different propagation directions. The ISW propagation directions range from 0 deg to 180 deg at the interval of every 30 deg. A series of depression ISWs were generated by a laboratory piston-type wave-maker in a two-layer fluid system. Conductivity probes are used to obtain the ISW profiles at the interface of the two-layer fluid. Experimental results show that the force peak on both columns and pontoons part induced by ISWs increases linearly with wave amplitude under all the propagation directions. The force peak is also influenced significantly by propagation direction. The inline force peak on the pontoons part reaches the maximum in the 90 deg direction, while that of the columns part is the largest in the 30 deg direction at the same wave amplitude. The transverse force on pontoons part is almost zero in the 0 deg and 90 deg direction. The force peaks of 30 deg and 150 deg have no obvious difference because of the symmetrical semi-submersible, so are 60 deg and 120 deg. Besides, effects of propagation direction on the vertical force peak are negligible.