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Used at initial stages, is an iterative process.

Fluid forces in lines neglected.

Uni-directional environment assumed. (waves, current and wind all from same direction)

 

For the Catenary equation click here.

 

Semisub is displaced in each mooring line direction to find total restoring force and tension in most loaded line as a function of displacement.

This way the following mooring stiffness curve can be constructed:

 

 

 

 

 

 

 

 

 

 

                 Figure 3.1: Mooring stiffness curve

 

The equivalent stiffness of the mooring system is calculated as follows: 

 Now the following equation holds: 

 

This way the forces at the maximum allowable/required  dynamic offset can be estimated.

 Checks:

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No upward force component at anchor?

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Most heavily loaded line not loaded too much (as % of break strength)?

OK    à              analysis for system in which one line is broken

NOT OK  à     re iterate

Disadvantages of this method:

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Conservative assumptions

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Large safety factors

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Important dynamics not accounted for

       

                                                                     

 

 

 

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Last modified: 10/16/06