Stochastic response of a double hinged articulated leg platform under wind and waves

The displacement response of an articulated leg platform (ALP) is mainly governed by its rigid body mode of vibration which has a very low frequency. Since the fluctuating component of the wind velocity has very low frequency energy content, the wind induced vibration of the platform may be significant. In this paper, the response of an ALP to wave alone, wind alone, and correlated wind and waves are investigated. The fluctuating component of the wind is modeled by Simiuʹs spectrum, while the sea state is characterized by Pierson–Mosokowitz (P–M) spectrum. Random wind and waves are simulated by Monte Carlo simulation technique. For comparative studies of the platform responses, wind spectra suggested by Kareem, Davenport and API-RP2A are employed. The nonlinear dynamic equations of motion are derived by Lagrangian approach considering nonlinearities due to variable submergence, instantaneous tower orientation and drag force. The response of ALP is determined by a time domain iterative method using Newmarkʹs- β integration scheme. It is concluded that response estimates based on the Davenport spectrum are lower than those based on the Simiu, Kareem and API RP 2A spectra due to higher energy available in these spectra at low frequencies. Furthermore, average hinge rotation of the platform under all cases is within permissible limits for platform operations.