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

为了弄清复杂自然环境中海洋结构物的水动力载荷和动力特性，有必要建立一种合理、准确的计算方法来计算波、风、流共同作用下海洋结构物所受的水动力。尤其是在水流和波浪共同作用下，海洋结构物所受水动力的预测方法的建立显得尤为重要和迫切，同时，在水域中，水流和波浪不容易同时产生。因此，在本研究中，通过以与流速对应的规定低速移动海上结构物来代替海流运动。为此，在1991年利用科研资助研制了一种能使拖架以极低速度（0 ~ 0.2m/s）运动的新型拖架控制装置，并安装在现有拖架上。1992年对摆动铰接柱的水动力进行了研究。通过同时使用具有新控制装置的牵引小车和现有的平面运动机构，实现了由两个不同谐波分量组成的强迫振动。结果表明，两种简谐运动下的惯性力系数相当，与简谐强迫振动下的惯性力系数完全相同。此外，利用上述拖架对透水海洋结构物的水动力特性进行了研究。

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.