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The mooring system is assessed by the classification societies in terms of three limit states:

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Ultimate Limit State: mooring lines need to have sufficient strength in the extreme loading cases. Statistical methods are used to determine the extreme       loading (e.g. statistical 100 year wave) while partial safety factors are used to determine the required strengths.

 
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Accidental Limit State: mooring system needs to have sufficient reserve capacity In case one of the lines breaks. Also for the A.L.S. partial safety factors apply.

 
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Fatigue Limit State: each mooring line should have a sufficient fatigue life as they are subject to cyclic loading. Line degradation due to wear and corrosion need to be considered. Sea states occurring during the lifetime and their associated induced stress ranges and frequencies  are to be used as fatigue is an accumulative process.

   Figure 3.2: Example of S-N curve from DNV Standard DNV-OS-E301

The following classification standards are generally used in the design of moorings:

American Petroleum Institute: API RP 2SK

Det Norske Veritas: DNV-OS-E301

       

                                                                     

 

 

 

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Last modified: 10/16/06