RESPONSE OF TENSION-LEG PLATFORMS TO VERTICAL SEISMIC EXCITATIONS (HYDRODYNAMIC, ADDED-MASS, DAMPING)

The purposes of this report are (1) to set up an analysis model for the determination of Tension-Leg Platform (TLP) response when subjected to vertical earthquake excitation, (2) to find the hydrodynamic added mass and damping coefficients of a moving cylinder resting on the sea-bed surface and (3) to set up a simple model for determining the slope response of the TLP tendon at its connection with the foundation when the TLP is subjected to horizontal seismic excitation.; Presented is a systematic approach, for analyzing the vertical platform motion, tendon force, and foundation uplift when subsea soil is excited by vertical seismic waves. This complex problem of multiple interactions among the soil, foundation, fluid and platform can be mathematically modelled using substructure technique. Each substructure has its own set of frequency dependent impedance functions. Having obtained the impedance functions, the total system is then solved in frequency domain. A specific TLP is analyzed to show the application of the procedures developed and the importance of response to vertical seismic excitation.; To obtain the hydrodynamic added mass and damping coefficients induced by vertical, translational and rocking motions of the cylinder resting on sea-bed, the entire fluid domain is divided into an exterior region outside the cylinder and its vertical projection and an interior region inside the cylinder projection. The potential function in Laplaces' equation is solved by the technique of matching eigen functions at the interface of the exterior and interior regions. It is shown that the method is efficient and accurate.; A model, simulating flexural waves propagating in the tendons as produced by horizontal earthquake motions is formulated and analyzed to determine the maximum tendon slope at their base connection point with the foundation. This maximum slope is required to properly design the connection details.