Abstract: Offshore wind power structure is the system of superstructure-foundation-infinite domain soil. Dynamic response of structure system is directly affected by transmitting boundary of the model and seismic motion input mode. Firstly, finite element models of tower tubes-foundation-soil-transmitting boundary and tower tubes-foundation-soil-fixed boundary are established. Then, the reason why force instead of acceleration, velocity and displacement is used for seismic input in the model while transmitting boundary is briefly clarified. At last, the following modes are analyzed, i.e. (1) seismic input of fixed boundary; (2) external source wave motion is considered only; (3) external source wave motion and scattering force caused by endogenous oscillation are both considered. Analysis results show that: (1) the reason why force is used for seismic motion input in the model with transmitting boundary is clarified; and the method of seismic motion input is in accord with the actual situation; (2) a convenient method of the generation of stiffness force and damping force is proposed for the foundation of circular cross-section; and it can greatly reduce the workload; (3) the reason that dynamic response of offshore wind power structure is smaller using transmitting boundary than using fixed boundary is explained from the viewpoint of vibration characteristics of model and the damping; (4) the indispensability of endogenous oscillation in seismic response and failure modes of structure using transmitting boundary is pointed out.

Key words: offshore wind power structure, transmitting boundary, scattering force, modes of failure