Stochastic Control of Single Legged ALP Using Stochastic Averaging

Abstract

Articulated Leg Platform (ALP) is a compliant offshore structure. The static and dynamic stability of ALP depends on buoyancy force, mainly generated by buoyancy chamber. It is highly flexible in surge and sway direction. Due to high flexibility in these degrees of freedom, sometime response exceeds working comfort. Depending on nature of excitation, it can create unfavorable working condition on the platform too. Response control device can help to reduce the response of platform and can create favorable working conditions. ALP is mathematically modeled as an inverted pendulum. Excitation force on ALP is generated due to fluid structure interaction due to random waves. Generally, structure dimensions are such that Morisons equation is valid for obtaining the excitation forces. Probabilistic approach, which can handle non linearity, is suited to obtain response of such a problem. Stochastic averaging technique along with Fokker Planck equation is one such technique which can handle ALP problem easily, subjected to normalized forces which are small enough to minimize the error. An optimal feedback control along with stochastic averaging technique for ALP is developed, in order to control the response of ALP under wave loads.