Hydrodynamic Loads and Dynamic Behavior of Offshore Structures in Current and Waves

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In order to clarify the hydrodynamic loads and dynamic behavior of offshore structures placed in complicated natural environment, it is necessary to establish a reasonable and accurate method of evaluating the hydrodynamic forces caused by simultaneous action of wave, wind and current. Especially, it is important and urgent to establish a method of predicting the hydrodynamic forces acting on offshore structures in current and waves.Meanwhile, it is not easy to make current and wave at the same time in water basin. Therefore, in the present investigation, the current movement was substituted by moving an offshore structure at a prescribed slow speed corresponding to current velocity. For this purpose, a new control apparatus of towing carriage, which is able to make the towing carriage move at very low speed (0-0.2m/sec), was developed by the aid of the present Grant-in-Aid for Scientific Research and then installed on the existing towing carriage in 1991.In 1992, the hydrodynamic forces on an oscillating articulated column were investigated. The forced oscillation consisting of tow different harmonic components was realized by making simultaneous use of the towing carriage with the new control apparatus, and an existing planar motion mechanism. As the result, it was found that the inertia force coefficients for two kinds of harmonic motions are fairly equal to each other, and they are exactly the same as the inertia force coefficient obtained by the simple harmonic forced oscillation.In addition, the hydrodynamic characteristics of a permeable offshore structures were investigated by making use of the above-mentioned towing carriage.