28.1.1.2. Example 2

Example (2) Calculation of a force-excursion characteristic with Fairlead attachment 820 m above seabed. 3 segment line: Chain/ Polyester / Chain: Studless ground chain Vicinay R4S 147 mm: Breakload 18852 kN, weight 376 kg/m, EA ~ 1725 MN, length 300 m Polyester section Bridon Superline 254 mm: MBL 18639 kN, weight 10,9 kg/m, length 1425 m, EA ~ 13 * MBL = 242 MN Topchain segment Vicinay R4S 147 mm: Breakload 18852 kN, weight 376 kg/m, EA ~ 1725 MN, length 60 m

Example shows: Tension starts picking up once first 50 m of chain has lifted from the seabed The stiffness of the system is fairly linear (semi-taut system) Use of polyester in deeper water but also to linearize the system

What is the stiffness?

Stiffness at pretension of 700 kN equals ~ 15 kN/m

Using example (2) a 12 line 3-segment system in deep water creates a force-excursion characteristic as shown below. Offset is from the mean position. Pretension in each line 700 kN

The resulting stiffness is (refer curve): Kmooring = 1000 / 10 = 100 kN/m (Which is slightly higher than 6 x 15 kN/m)