Dear Jason.Jonkman,
Thank you so much for your prompt response. I rechecked my calculation, and the difference might result from the added mass matrix, which is computed by strip theory and the method of computing mass matrix. My structural mass is spar mass with the lumped mass matrix from the superstructure. I don’t use the same technique like you in OC3-Hywind RAOs - #23 by Jason.Jonkman. Below are my mass matrices and stiffness matrices.
M_structural =
[8065975.57351049 0 0 0 96047931.0553377 0
0 8065975.57351049 0 -96047931.0553377 0 -96101
0 0 8065975.57351049 0 96101 0
0 -96047931.0553377 0 19922216225.0856 0 0
96047931.0553377 0 96101 0 19925853675.2147 0
0 -96101 0 0 0 169608940.129100]
M_addedmass =
[7981568.18556329 0 0 0 222274267.649286 0
0 7981568.18556329 0 -222274267.649286 0 0
0 0 0 0 0 0
0 -222274267.649286 0 15164062100.0025 0 0
222274267.649286 0 0 0 15164062100.0025 0
0 0 0 0 0 0]
K_mooring =
[41181.1776176891 0 0 0 -2906608.23246224 0
0 41181.1776176891 0 2906608.23246224 0 0
0 0 11941.5064526553 0 0 0
0 2906608.23246224 0 310785043.914555 0 0
-2906608.23246224 0 0 0 310785043.914555 0
0 0 0 0 0 11566677.9908399]
K_hydrostatic =
[0 0 0 0 0 0
0 0 0 0 0 0
0 0 333550.146410852 0 0 0
0 0 0 1575800183.54207 0 0
0 0 0 0 1575800183.54207 0
0 0 0 0 0 98340000]
f=
[0.00801929726094901
0.00801929746514019
0.0323647474682099
0.0374444408562521
0.0374468019191301
0.121188604319519]
My mooring stiffness matrix is similar to report 47535, page 23/31. Hydrostatic restoring stiffness considers the restoring effects of body weight. There is a slight difference in the natural frequency, f(Hz). Do you have any idea that helps me improve my code? Thank you so much for your time.
Best regards,
Hoa Nguyen