The paper notes three important results : 



First - Contrary to the assumption made in many mooring analyses, the 

 mooring has significant influence on the dynamics of the moored vessel. 

 This can be seen in the moored and free frequency response curves (Figures 

 3-6, 9, 10, OTC) . For example, there is a significant reduction in peak 

 response and a shift in the frequency where this occurs. This means it is not 

 appropriate to analyze mooring legs by simply imposing the free ship motions 

 at the upper end of the line. 



Second - Contrary to the assumption made by some to get from 6 to 3 degrees 

 of freedom, the use of mooring buoys and hawsers does not effectively isolate 

 the moor from the heave/pitch/roll motions of the vessel. See OTC Table 4 

 and the discussion. This is due to the geometric stiffening effect of the 

 hawser preload. 



Third - At some frequencies, the mooring legs act in a nearly linear 

 fashion while at others the dynamic behavior is decidedly nonlinear (see 

 Figures 13 and 14, OTC). This particular phenomenon is quite difficult to 

 predict and probably involves multi-frequency responses and resonances along 

 with other large displacement effects. This calls into question the validity 

 of the entire frequency domain solution procedure. The OTC paper suggests 

 there is general qualitative agreement with the results obtained with the 

 frequency domain solution and established mooring design procedures (DM-26) , 

 but the calculation of specific responses may be erroneous or difficult to 

 interpret. 



34 



