4.2 COMPARISON OF THE NUMERICAL OPERATION EFFICIENCY WITH THE ACTUAL ONE
At first, we try to confirm whether the numerical simulation considering the long period wave can reproduce the moored ship motions at the interruptions.
Case1: August 2 UNmaru by standing off
The weather condition in front of the berth on August 2 at 6:00 is shown as below.
Wave: H1/3=0.58m, T1/3=13.4s,ω＝85deg
Wind: U10=10.3 m/s, SSW( ψ=15deg)
The ship size is uncertain. However, it is estimated as about 10,000GT ship in accordance with the operation situation. The results of the numerical simulation for the ship motions are shown in Fig.-5(a). Either the ship motions are over the allowable motions for the operation of cargo handlings in spite of strong winds. Also the numerical results with the long period wave (H=0.4m,T=143s) are shown in Fig.-5(b). Concerning about sway, pitch, roll and yaw, no differences appear in both of the results, which are not shown in Fig.-5. On the other hand, considerable differences appear in heave and surge. Especially in surge, the large ship motions at the interruptions, over ±2.0m surge, are generated in case of considering the long period wave. It is clear up that thenumerical simulation with the long period wave can reproduce the moored ship motions at the interruptions.
Fig.-5 The calculated ship motions at interruption for 15,000DWT at 6:00. Aug.2
Case2: September1 ACmaru (499GT) by swell
The weather condition in front of the berth on September 1 at 6:00 is shown as below.
Wave: H1/3=0.31m, T1/3=15.7s, ω=85deg
Wind: U10=1.4 m/s, NNW(ψ=l50deg)
The results of the numerical simulation for 696GT ship, similar to 499GT ship are shown in Fig.-6(a). The large ship motions are generated. However, they don't attain the allowable motions. The time series results with the long period wave are also shown in Fig.-6(b).
Fig.-6 The calculated ship motions at interruption for 696GT at 6:00, Sept.1
Considering the long period wave, the large ship motions appear in especially surge and heave. However, the considerable increasing of the motions dcesn't appear different from Case1. The results of 15,000DWT ship under the same external forces are shown in Fig.-7. The large ship motions, namely ±2.0m surge, are generated. On the other hand. the surge motions for 696GT ship are almost ±1.0m. It is considered that the differences of the natural periods of surge and the inertia give the above phenomena. The natural period of surge for 696GT and 15,000DWT ship are Tsu(696GT)=36s and Tsu(15,000DWT)=67s, respectively. The natural period of 15,000DWT ship is near the period of the long period wave rather than 696GT ship one. Also once the moored ship begins to move, the inertia of 15,000DWT ship is so big that the mooring rope tensions can not keep the ship quietly. Despite the ship sizes, the
