19.7. The ECAX Data Record - Nonlinear Axial Stiffness Polynomial

This data record is used to define nonlinear axial stiffness and should be input after an ECAT data record (The ECAT Data Record). If this data record is omitted for a particular section of a mooring line the axial stiffness will be constant, using the value of EA from the ECAT data record.

      2   5  7   11    16    21    26    31         41         51         61        
    - --- -- ---- ----- ----- ----- ----- ---------- ---------- ---------- -
   |X|   |  |ECAX|XXXXX|XXXXX|XXXXX|XXXXX|          |          |          |
    - --- -- ---- ----- ----- ----- ----- ---------- ---------- ------------
       |  |   |                               |__________|__________|
       |  |   |                               |     
       |  |   |                               |_(2)-(4) Coefficients of the polynomial (E10.0)
       |  |   |
       |  |   |_(1) Compulsory Data Record Keyword(A4)
       |  |
       |  |_Optional User Identifier (A2)
       |
       |_Compulsory END on last data record in Data Category (A3)

(2)-(4) These coefficients define a nonlinear variation in axial stiffness. The stiffness is calculated using the formula

EA(ε) = EA(const) + k1.ε+ k2.ε2 + k3.ε3     (0 ≤ ε ≤ εtmax)

EA(ε) = EA(εtmax) + {k1 + 2.k2.εtmax + 3.k3.εtmax 2}.(ε-εtmax)     (ε > εtmax)

where

EA(ε) = EA as a function of strain

EA(const) = the EA value on the ECAT data record (The ECAT Data Record)

k1, k2, k3 = coefficients input on the ECAX data record (The ECAX Data Record - Nonlinear Axial Stiffness Polynomial)

ε = linear strain δL/L

εtmax = strain at Tmax

Tmax = maximum tension specified on the preceding ECAT

Note:

  • The stiffness must increase monotonically over a tension range from zero to the maximum tension specified on the preceding ECAT data record (Tmax).

  • For tension greater than Tmax, the stiffness is assumed to increase linearly with strain, with slope equal to the slope at Tmax.