If there are no additional restoring coefficients for surge, sway, and yaw motions, the equation of motion of a structure traveling in waves may become singular at a small enough magnitude of encounter frequency while its associated incident wave frequency is relatively high.

In Aqwa frequency domain simulation, the fictitious damping coefficients are introduced when the incident wave frequency is greater than 0.1 rad/s but the magnitude of the associated encounter frequency is less than or equal to 0.1 rad/s:

(4–90)

where are the structure mass and moment of inertia of yaw motion.

From the above equation, it is observed that if rad/s:

(4–91)