Modified-transformation-based Networked Controller for Offshore Platforms under Multiple Outloads

In the paper, we study the problem of vibration control for offshore platform in nonideal network environment under wave and current forces based on the modified transformation. We consider the wave and current synchronously and give a dynamical system for the outside loads. The problem of time delay, packet dropouts and disordering due to nonideal network are taken into account. In the networked control model, two buffers output the received packets according to time stamps and upper bound of time delay. Based on a transformation, we reduce the time delay system into an equivalent delay-free system. Taking the nonideal network communication conditions into account, we design a modified transformation based on the past time data, wave and current loads, and received packets through network at current time. The networked controller is presented to depress the vibration of structure in nonideal network communication environment based on the modified transformation. An algorithm is given to simplify the computation of control law by recurrence. The system stability under presented networked controller is analyzed based on Lyapunov functional. Through the simulation results and comparison with other networked controllers, we can see that the presented controller can reduce the oscillation of offshore platform effectively.