When the displacements are not small, the changes in position of the 

 line and the changes in magnitude of P must be accounted for in the 

 equations of motion. 



Material Nonlinearity - Most mooring lines exhibit a nonlinear relation- 

 ship between load and elongation (i.e., Hooke's Law does not hold). 

 Even when the effect is linearized, one must contend with differing 

 behavior in tension and compression. The slenderness of mooring lines 

 usually results in such low compressive load resistance that it is 

 assumed to be zero. In most mooring lines (particularly with synthetic 

 materials) , the material damping or hysteresis is also an important 

 effect. 



Non- conservative/Nonlinear Loading - The dominant environmental loads 

 on mooring lines are of the distributed pressure type (e.g., drag loading). 

 This is typically dependent on the square of the relative velocity between 

 the line and the fluid. It is also highly sensitive to the orientation 

 of the velocity vector relative to the line. Dynamic effects produce 

 additional non-conservative loads proportional to the relative acceleration 

 (re Morrison's equation). It is common practice to neglect change of 

 acceleration effects and to treat the acceleration terms with an added 

 mass. The added mass is ususally assumed to be zero for acceleration 

 parallel to the line. 



Position Dependent Constraints - Limits must be imposed on the mooring 

 components to prevent movement out of the water or below the bottom. 

 The bottom interaction of catenary type lines is an important effect in 

 moors of moderate to shallow depths. 



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