Effect of Static Offset on TLP Modeling

A tension leg platform (TLP) is a compliant offshore structure that experiences large horizontal displacements under the action of wind and current loads. The presence of a static offset does affect the dynamic characteristics of the TLP in that the geometry of the structure changes, the tendon loads increase due to increased buoyancy associated with platform setdown, and the individual tendons tend to sag under the action of their own weight. An accurate prediction of the static offset requires that the catenary behavior of the tendons and risers be accounted for in the analysis. Presented in this paper is an effective analytical tool for the analysis of the static equilibrium configuration of a TLP under the action of prescribed wind and current loads acting on the platform and for the determination of the dynamic characteristics of the TLP for small dynamic oscillations about a large static offset configuration. Once the static or dynamic response of a TLP has been determined, localized bending stresses near the supports of tendons and risers can be determined routinely from simple asymptotic formulas developed by the writer.