Study on the Nonlinear Dynamic Characteristics of a Truss Spar

The heave-pitch coupled equation of Truss Spar platform under random waves is established considering the static stability and drainage volume changes, including higher order nonlinear term and the effects of instantaneous free surface. The motion responses are calculated, and the impact of damping factor is analyzed. The results show that, when the characteristic frequency of stochastic wave is close to the heave natural frequency of heave, the large amplitude pitch motion is induced under the random parametric-forced excitation, when the significant wave height reaches a certain value. Increasing the heave damping or increasing the pitch damping is the most effective mean to suppress the pitch instability. Therefore, when design the platform, the number and the structure of heave plate and the reasonable arrangement of spiral side plates are important.