Dynamic Response of Submerged Vertical Cylinder with Lumped Mass under Seismic Excitation

An analytical approach is presented to assess the response of offshore structures under seismic excitation. This paper evaluates the impacts of different fluid field models and the mass of equipment at the top of offshore structure which is simulated as lumped mass on the responses of offshore structures. To do this, two and three dimensional fluid field models are developed. In three dimensional models different approximation regarding the free surface boundary condition associated with high and low frequency excitations are adopted. Then the alternation of response of structure with changing in the value of lumped mass is calculated. Finally the impacts of different models on the value of maximum displacement for Kobe earthquake are evaluated. It is shown that different approximations regarding the fluid field could largely change the value of maximum displacement evaluated by the models.