¹Port and Airport Research Institute Yokosuka, Kanagawa, JAPAN

shiraishi@pari.go.jp

　

²Kobe University of Mercantile Marine Kobe, Hyogo, JAPAN

　

It is important in berth planning and port operation to be accurately estimated moored ship oscillations in especially long period components at ports facing the open sea. The phenomenon of moored ship oscillations has been studied for decades by model experiments, field observations and numerical simulations. This paper shows the comparison of numerical simulation result and field observations referring former studies to discuss how we get more accurate result by numerical simulations on ship motions. To evaluate surging motion more accurately by the numerical simulations, it has been more clear the characteristics of mooring ropes after repeated usage and damping factor in loge-period motions in waves. Then, we discussed the effect of characteristic of mooring system by use of observed data on ship oscillation at several ports in Japan. Through the comparison the simulation and observation on surge motion, it is concluded that it is very important to be estimated correctly the load-deflection characteristics of mooring ropes after repeated usage. As for damping factors for long-period component, the free vibration test and the forced vibration test in calm water condition are carried out and evaluate the contribution of linear and non-linear damping effect and the effect of damping due to the hysteresis of load-deflection characteristics of mooring ropes.

　

　

Disaster Prevention Research Institute, Kyoto University Uji, Kyoto, JAPAN

yoshioka@kaigan.dpri.kyoto-u.ac.jp

　

The effect of long period oscillation (LPO) is usually neglected for storm surge prediction because it is hidden behind high waves. We observed a big LPO (amplitude was about 0.5m and period was about 5 minutes) at Shimohaya Bay in Wakayama Prefecture, JAPAN in a storm surge condition. The LPO would raise the water level of 0.5m in high wave condition, which causes the increase of wave overtopping and wave force on coastal structures. Wind and wave were observed by the oceanographic tower standing off shore of the bay. Power spectra of wind and wave were compared with that of LPO. Periods of around 5 minutes are predominant in sea wind, wave group and LPO, and they are same as the resonance period of Shimohaya Bay.

　

　

¹Department of Civil Engineering, Ajou University Suwon, KOREA

dhyoo@madang.ajou.ac.kr

　

²Delis Construction Co. Seoul, KOREA

　

This paper presents a recent investigation for the design of rubble-mound breakwaters. Existing theories and empirical equations have been reviewed and a new relation is proposed for the determination of optimum weight of armor unit of rubble-mound breakwaters. An empirical parameter is introduced into the new semi-theoretical equation, which is closely related with the surface particle velocity of wave motion. The theoretical approach produces a new physical number, which is called 'action slope'.

　

The action slope reflects the wave steepness and the ratio of wave length to the water depth on the stability of armor unit of rubble-mound breakwater, of which the importance has widely been known to practical engineers and proved by conducting laboratory experiments. The final form is found relatively simple and does not need any grouping. The laboratory data reported by various workers were employed for the estimation of proper values of empirical parameters introduced into the new relation.