with the possible fetch effects. Different spectra are available for a 

 specific selection. An important question here is that these spectra 

 are verified mainly for the North Atlantic conditions. Solitary waves 

 cannot and should not be used for the calculation even though they might 

 generate a more serious mooring condition. 



Wind and current force and moments are approximated by functions of 

 the form: 



F = A sin P and M = B cos 2 p 



using the experimental data in DM-26 for Naval ships. 



MOORING SYSTEM LOADS 



These forms are observed to be more complex to describe than the 

 previous ones. They are usually linearized, and the major new assump- 

 tions are the symmetry in the mooring system and continuity in mooring 

 load. Elastic characteristics of the mooring line are reported to be of 

 the form: 



"^ m 



= R e m S 1.7 



%lt 



R and m values are usually assumed to be constant. R is reported to 

 change for wet, dry, new, and old mooring lines except for chains. 

 Fenders are not always preloaded and cannot be studied by these equations 

 as, in general, their responses are nonlinear and discontinuous. Such 

 systems, on the other hand, have very important dynamic responses as 

 they generate jumps and subharmonics (Wilson, 1973). 



Lines are assumed to be pretensioned, and a geometric "catenary" 

 description is used to find the "quasi-static" tension in the lines. 

 For fixed anchor points, the maximiun horizontal distance from anchor 

 points to line connection points on the ship is calculated using the 

 solution of dynamic equations. Line vibration stress is obtained by 

 multiplying the quasi-static stress by a dynamic load factor. 



Based on the survey of the above assumptions and built in the 

 model, one can claim that a mooring system load calculation can be 

 successfully computed by this computer program if: 



1. The mooring system is symmetric and pretensioned. 



2. The ship is in an environment where the sea can be represented 

 by a spectrum, and the wind and current are constant in 

 magnitude and direction. 



3. The influence of other boundary and initial conditions is not 

 significant, such as very shallow water or other ships in 

 proximity. 



151 



