Reply To: why after adding a mooring system to a ship, there are multiple damping values

[Yu Bi]

Okay, therefore we can exclude the possible causes of the mooring line settings. It then could be caused by the small stiffness in the sway and yaw directions. You can find the mooring stiffness matrix in the EQUILIBRIUM.LIS or EQUILIBRIUM.MFK file. Given the mooring line position in this model, I expect the diagonal stiffness for sway-sway and yaw-yaw to be small while the non-diagonal stiffness for sway-yaw coupling probably could be negative. You can also have a check of the non-diagonal sway-yaw value of added mass and radiation damping. As these two mooring lines don't prove much stiffness in the sway and yaw direction, the negative stiffness/damping/added mass of the sway-yaw coupling term could result in an unstable natural mode in the sway-yaw coupled direction. To prove stiffness for yaw and sway motion, you could add two more cables on the other side of the structure and ensure the cables are not slack at the structure equilibrium position, and then the system could be more stable.