Open-Close Loop Active Control of Articulated Leg Platform

Abstract

A method is presented for the active control of the articulated leg platform (ALP) idealized as a single-degree-of-freedom (SDOF) system, using a combined feedforward and feedback (open-close loop) algorithm. The linear active control strategy is adopted to obtain the controlled response. The control law is derived by minimizing a quadratic performance function of the state variables and the control force. The state variables include not only the structural responses but also the sea-surface elevation and its integrands. The controlled responses are determined by a frequency domain iterative technique that duly accounts for the different kinds of nonlinearities present in the system. A single-hinge ALP in a random sea state is analyzed to obtain the controlled responses using the proposed method under a set of parametric variations. The controlled responses are compared with those obtained by the conventional feedback active control (close loop) strategy to investigate the relative merits of the proposed algorithm.