Researches on Wave Forces Acting on Offshore Structures and Motions in Waves

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Through studies on wave forces acting on an offshore structure and on response of it in waves following conclusions have been obtained. 1. Drag component of viscous forces acting on an oscillating cylinder is sometimes affected the angle of attack. 2. Viscous forces acting on an oscillating semisubmersible can be predicted by summing up the viscous forces acting on the member cylinders if the angle of attack for the incident flow is taken into account. 3. Steady flow increases the drag coefficient and decreases the added mass coefficient of an oscillating cylinders. This is because increase of the relative velocity of the incident flow and increase of Kc number. 4. Viscous forces acting on an irregularly oscillating cylinder are affected by vortices shedding in previous oscillations as well as vortex shedding in the present swing. 5. Wave forces acting on a cylinder submerged horizontally in regular waves rapidly decreases at very low Kc number. This is because the circulation flow rounding the cylinder due to viscosity. 6. Wave forces acting on a semisubmersible fixed in regular waves decreases at relatively high wave height. 7. A simulation program for non-linear motions of a semisubmergible has been developed. 8. Viscous forces acting on a bluff body starting from rest depend on the displacement of the cylinder from the start. 9. A prediction method of the damping for low frequency oscillation has been derived.