|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1994 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 1993 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Ocean structures, most of which are constructured by multiple vertical cylinders, are working in an environment of both waves and current. In order to evaluate the hydrodynamic forces acting on the ocean structures, the interaction between the waves and current as well as between multiple cylinders has to be considerded. Once the wave drifting force caused by waves and current is calculated, we can obtain the wave drift damping which plays an important role in the slow drift motion of floating body moored in irregular waves. In the present research, the current velocity is assumed to be small (compared with the phase velocity of waves). The effect of the current and the importance of the interaction waves near the cylinders are investigated. The research results are as follows.
1.A mathematical model is established, which takes account of interaction among multiple cylinders fixed or oscillating in both waves and current. A semi-analytical solution is obtained. A computer program based
on the above theory is developed, which can calculate the first and second order hydrodynamic forces for different current velocity, wave frequencies, wave direction, cylinder number and arrangement.
2.In order to verify the theory and calculated results, experiments in wave tanks were carried out. The experimental results are in good agreement with the calculated ones.
3.The steady disturbance flow (caused by the current) has a strong effect on the second order forces such as wave drift force and wave drift damping.
4.The effect of evanescent waves scattered from cylinders can not be neglected.
5.The oscillation of the floating body has a strong effect on the second order forces near the resonance of the oscillation.
6.In a certain range of wave frequencies and wave heights (Kc number), the wave drift damping (calculated by the potential theory) is very important in the damping of slow drift motion.
In the future, the above theory is expanded to be applied to the arbitrary shaped bodies. The computer program will be developed and experiments will be carried out to verify the theory and calculated results. Less