Research On Control Method Of Underactuated Multi-module Floating Platform Under Unknown Wave Disturbanc

The demand for offshore engineering equipment is increasing with the continuous development of offshore resources,while the safety and stability of the equipment also put forward higher requirements.Multi-module floating platform is one of the main forms of offshore engineering equipment,which can be used for deep-sea resource development,leisure tourism,biochemical processing,transportation and storage,floating airports and movable military bases,etc.It is a major high-end marine engineering equipment with foresight and exploratory nature.The scale of multi-module floating platform is huge,and it is subject to complex wind and wave currents,and the working environment is variable and harsh,so it is necessary to implement stability control for the floating platform to ensure its safe and smooth operation.At the same time,because the multi-module floating platform is located in the remote sea,the manufacturing,operation and maintenance costs are very high,so the control needs to take into account the complexity of the structure and maintenance costs in order to improve its economic performance.In this paper,a time-varying terminal sliding mode control(TVTSMC)strategy is derived based on a multi-module floating platform network dynamics model with unknown wave disturbances.The under-actuated control method based on this strategy can realize multi-objective control of a single actuator and reduce the number and complexity of actuators while ensuring the stability of the multi-module floating platform.From the perspective of control strategies and methods,the cost of multi-module floating platform motion stability control is reduced.The specific work of the paper is as follows:The network dynamics method is used to establish the dynamics model of the multi-module floating platform.Each module of the floating platform is regarded as a network node,and the dynamics model of each module is established separately,including the hydrodynamic model and the anchor chain constraint model;the inter-module connectors are regarded as network connections,and the dynamics connector model is established;finally,the topological matrix is used to combine the models of each node into the dynamics model of the multi-module floating platform system.The dynamics modeling method of this network can be applied to the modeling of floating platform with arbitrary topology.Based on the TVTSMC strategy,an under-actuated multi-module floating platform control method with fewer actuators than modules is developed for the longitudinal motion under the excitation of unknown waves.To implement the motion control,the actuators are installed between the floating platform modules and the actuator dynamics model is derived;a nonlinear wave load observer is established to estimate the wave load in the longitudinal direction;for the longitudinal motion of the platform,the actuator control output is calculated based on the TVTSMC strategy and the PID strategy,and the stability of the control method is proved by Lyapunov’s stability theorem;finally,the effectiveness of the control method is verified by numerical simulation.Based on the TVTSMC strategy,a control method is developed for under-driven multi-module floating platform pendulum and longitudinal rocking motion.This control method,which controls multi-directional motion with a single actuator,can reduce the difficulty of multi-module floating platform actuator design.To implement the multi-directional motion control,the tilting actuator is installed at the bottom of each module and its dynamics model is derived;a nonlinear wave load observer is used to evaluate the load acting on the pendulum and longitudinal rocking directions;based on the TVTSMC strategy,the pendulum and longitudinal rocking motion of the floating platform is controlled and the stability of the control method is proved by Lyapunov’s stability theorem;finally,the control method is verified by numerical simulation.