Influence of long period waves on evaluation method
for operation efficiency of cargo handling
Masayeshi Kubo* and Shigeki Sakakibara**
Kobe University of Mercantile Marine*
The Yokohama Rubber Co., Ltd**
ABSTRACT
Recently, a harbor tranquility is becoming to be evaluated not only by wave heights at a berth but also moored ship motions directly. On the other hand, large and long period moored ship motions and rope cutting accidents are caused by seiche or long period waves in spite of a calm weather condition in some harbors. In an evaluation of the operation efficiency from the view of moored ship motions, neither the present calculation method of inside harbor waves nor the numerical simulation of moored ship motions consider the above long period waves. So it is afraid that the numerical simulation of moored ship motions doesn't reproduce the actual ship motions at the interruptions. In this paper. influences of long period waves on the evaluation method for operation efficiency of cargo handlings are described by using an actual cargo handling report at a berth of a model harbor. Situations of the interruptions are investigated in details. From the investigations, the long period wave inside harbor is estimated as eleven times of the ordinary wave period and 10% height of the offshore waves when the offshore waves become greater than 3m height and longer than 10s period. And it is clarified that it is necessary to consider the long period waves for reproducing the ship motions at interruptions of cargo handling and the evaluation method for the operation efficiency.
Keyword: Moored ship motions, Numerical simulation,Operation efficiency of cargo handling, Long period wave.
1. INTRODUCTION
Recently, a harbor tranquillity is becoming to be evaluated not only by wave heights at a berth but also wave periods. namely. moored ship motions directly It is an importantrequirement for harbors to achieve more advanced transport efficiency. On the other hand, it is well-known in various harbors that large and long period moored shipmotions are caused by seiche or long period waves in spite of cairn weather conditions. namely. small wave heights and weak winds2).
An evaluation of the operation efficiency from the view of moored ship motions is carried out as follows. Firstly. calculating wave spectra at the berth from the offshorewave and secondly. calculating the moored ship motions under the estimated external forees. then the calculated ship motions are compared with the allowable ship motionsfor the operation of cargo handlings. Neither the present calculation method of inside harbor waves nor the numerical simulation of moored ship motions consider theabove long period waves for evaluating the operation efficiency. So it is afraid that the numerical simulation of moored ship motions doesn't reproduce the actual shipmotions at the interruptions.
In this paper, influences of long period waves on the evaluation method for operation efficiency of cargo handlings are described by using an actual cargo handling report at a berth of a model harbor. Situations of the interruptions are investigated in details. And we show necessity of considering the long period waves for reproducing the large ship motions at the interruptions and for the evaluation method on the operation efficiency from the view of ship motions.
