Wind‐Induced Response Analysis of Tension Leg Platforms

Abstract

A procedure is presented for estimating the wind‐induced response of tension leg platforms (TLP). Spatiotemporal characteristics of the wind velocity field over the ocean are discussed. It is shown that the wind spectra generally used for land‐based structures may not adequately represent wind velocity fluctuations at very low frequencies associated with the compliant modes of a TLP. A new spectral description of the longitudinal wind velocity fluctuations over the ocean is proposed. The wind approaching a TLP is treated as a single‐point and a multiple‐point random field. Expressions for the wind loads in the surge, yaw, and pitch degrees of freedom are formulated in both time and frequency domains for subsequent dynamic analysis. To account for the nonlinear behavior in the frequency domain, the mean response of a TLP is computed using nonlinear stiffness characteristics of the system. For unsteady response due to the wind fluctuations, the TLP is assumed to oscillate linearly above the static equilibrium position produced by the mean wind loading. A numerical example illustrates the methodology outlined for predicting the response statistics of a typical TLP. It is verified that the TLP response estimates based on frequency and time domain analyses show good agreement for the platforms investigated. The frequency domain analysis is recommended for estimating the wind‐induced response at the preliminary design stages, to be followed by the time domain analysis in the final stages.