Approximate Models for Off-Shore Concrete Gravity Structures.

摘要

This thesis is concerned with the dynamic response of off-shore concrete gravity structures to the loading imposed by random ocean waves in deep water. The purpose and scope is to study previous, present, and future platforms for a general understanding of what has been developed and why. An attempt to model a hypothetical structure with specific dimensions and parameters representative of the present offshore construction industry is then made using a computer program. The model is a hollow, tapering concrete column fixed as a cantilever atop a bottom-sitting caisson and having an axial load imposed by a typical deck for a concrete oil drilling and production platform. In this model, two degrees of freedom (translational and rotational) at each node in one plane only, beam theory with a cubic expansion for concrete column deflection, and linear wave theory with a drag coefficient equal to zero is used. Wave forces are derived from a spectrum of waves with a distribution of energies over all wave frequencies. This spectrum is then condensed to a small number of frequencies due to cost and storage limitations in the computer.