3.3 COMPARISON OF THE NUMERICAL OPERATION EFFICIENCY WITH THE ACTUAL ONE
According to the actual operation report, the interruption ratio caused by waves and winds amounts to 5.2%. Then the operation efficiency is derived as 94.8%. On the other hand, according to the present evaluation method with the ordinary inside harbor wave, the operation efficiencies for 696GT and 15,OOODWT ship are derived as almost 100%, respectively. That is to say, the actual efficiency derived from the wharf operation report has the smaller value.
It is necessary for the evaluation of the operation efficiency to reproduce the moored ship motions at the interruptions. However, it is found that the ship motions are notrepresented well in the calculations.
4. EVALUATION METHOD OF OPERATION EFFICIENCY CONSIDERING LONG PERIOD WAVES
4.1 NECESSITY FOR NUMERICAL SIMULATION OF MOORED SHIP MOTIONS CONSIDERING LONG PERIOD WAVES
As mentioned above, it is obvious that the calculation results of the operation efficiency differ from the actual ones and the moored ship motions at the interruptions are not reproduced well on the calculations. In order to understand the weather conditions, inside and outside harbor waves and the moored ship motions in detail, we carried out hearings from the pilots and the operators of the berth. Noticeable points from the hearings are summarized as follows.
(1) Surge amounts to ±2.0m at the interruptions.
(2) Moored ships begin to run at the berth suddenly.
(3) Large ship motions are generated even if no winds and a fine weather.
(4) In spite of a calm sea state, the ships are moved by a bottom swell.
(5) When the offshore waves are as high as climbing up breakwaters, the ships are moved and the interruptions happen.
The maximum wave heights and periods of offshore and in front of the berth used in the calculations are H1/3=5.25m. T1/3=15.7s and H1/3=0.72m. T1/3=15.7s, respectively. The surge motions of 15,000DWT ship are +0.96m and -l.14m at the maximum, even if the wave condition at the berth is H1/3=1.Om,T1/3=16s. It is found that the ship motions at the interruptions can not be reproduced by considerable higher waves. In accordance with the above noticeable points, namely the large ship motions are generated in spite of small wave heights, it is considered that a longer period wave influences the moored ship motions.
It is well-known that long period waves whose period is about eleven times of the original wave in the Pacific Ocean and seven times in the Sea of Japan exist7). They consist of three big Waves and eight small ones or of three big waves and four small ones, respectively. The model harbor is facing to the Pacific Ocean. For example, when the offshore wave period is 13s, the long period wave is T=13 ×11=143s. The wave height of the long period wave is estimated as 10% of the offshore waves7).
On the other hand, the berth is located at the entrance of a slip as shown in Fig.-4. The natural periods of the slip are shown in Table-S. From the above investigations, it is considered that long period waves with T=140s or the seiche in the slip induce the moored ship.
Table-5 Natural periods of the slip
Fig.-4 Layout of the berth
We try to calculate the operation efficiency of cargo handlings considering the above long period waves again. The long period wave inside harbor is estimated as eleven times of the ordinary wave period and 10% height of the wave when the offshore waves become greater than 3m height and longer than l0s period. Then the exciting forces for the ship are given by considering the long period wave added to the ordinary inside waves in Table-2. The wave direction of the long period wave is supposed to be a head
