Van Oortmevssen 



ducted with a tanker moored behind the tank in ir- 

 regular seas, while the tanker motions and the for- 

 ce in the bowhawser were measured. 

 The results of these tests will be compared with 

 the results of tests conducted with existing mooring 

 systems. 



I. INTRODUCTION 



The increasing importance of remote offshore oil fields has 

 created a need for very large unconventional structures for production 

 and storage of oil or liquid natural gas. Some very large structures 

 are now in use, as for instance the floating oil storage 'Pazargad' and 

 the submerged tank in Dubai, while others are under construction, as 

 for example the large concrete tank for the Ekofisk field in the North 

 Sea. Besides structures for exploitation and storage of minerals, the 

 use of very large offshore structures is considered for a variety of 

 future purposes. Plans exist to build polluting or dangerous plants on 

 artificial islands, far from the living areas, to prevent a deterioration 

 of the environmental conditions in densely populated industrial coun- 

 tries. Fear for calamities and a need of plenty of cooling water was 

 the reason to study the possibility to build offshore nuclear power 

 plants, and there is even talk of constructing a floating intercontinen- 

 tal airport. 



With regard to the design and construction of a large uncon- 

 ventional offshore structure, a lot of problems arise. The structure 

 has to be strong enough to survive the severest weather conditions. 

 In the case of floating structures, it is a problem to design a proper 

 anchor system. When the structure is fixed, the entire construction 

 has to be stable. In most cases, such artificial islands require trans- 

 shipment of goods from ships to island or vice versa. Consequently, 

 attention has to be paid to the mooring of ships to the island. If a cons- 

 truction on the sea bottom is considered, its behaviour during immer- 

 sion has to be studied carefully. 



In order to be able to cope with future developments, a re- 

 search program has been performed at the Netherlands Ship Model 

 Basin. A computer program has been developed for the calculation of 

 wave loads on objects of arbitrary shape, using a three-dimensional 

 source technique, while the effects of the free surface and of finite 

 water depth were taken into account. With this program it is also pos- 

 sible to calculate the wave pattern around the structure. Subsequently 

 model experiments were carried out to check the theoretical results. 



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