Motion Control System for Offshore Lifting Operations

Abstract

This MSc thesis presents an investigation into motion control systems aimed at reducing swing motion of a lifting load during offshore heavy lifting operations. Two distinct models are developed for this objective. Subsequently, an analysis is done to assess the impact of various control aspects.

First, an assessment of the offshore heavy lifting market is performed. Following this, diverse motion control systems designed for offshore heavy lifting operations are examined. Special attention is given to the principle of the current damping tugger system used on vessels of Heerema Marine Contractors. Subsequent to this examination, multiple alternative aspects for this current damping tugger system are suggested.

Thereafter, a detailed model is developed, capable of simulating an offshore lifting operation with the use of a motion control system. For this model, the equations of motion are derived and used as the foundation for numerical MATLAB models. These MATLAB models are subsequently transformed into a Simulink model, which serves as the basis for designing the required controllers and setpoints. This model serves as a tool for investigation of the dynamics of offshore lifting operations when using a motion control system, but due to excessive computation time, it was not suitable for analyzing the effects of different control aspects of a motion control system.

Therefore, a simplified version of the model for offshore lifting operations with the use of a motion control system is developed, aiming to reduce the computation time of the model compared to the detailed model. This simplified model is called the analysis model. This analysis model is used for an analysis on the effects of different control aspects of a motion control system during an offshore lifting operation. These aspects comprise two different motion sensors are controller input along with three distinct control methods. The two sensors in question are one for measuring the motion of the winch and another for measuring the motion of the load. The first two control methodologies encompass two divergent setpoint calculation methods, one based on a linear equation and another founded upon a PID controller, both coupled with a winch controller. The third control method includes a controller that combines the setpoint and winch controller to one single, combined controller.

Throughout this analysis, the performance of each control aspect is evaluated across 24 unique scenarios. From these results it is concluded that the use of a load motion sensor result in superior system performance in comparison to employing a winch motion sensor in almost all scenarios. Furthermore, it was found that in combination with a load sensor, the setpoint calculation method based on a PID controller appeared to be the optimal choice in most scenarios, while, when using the winch sensor, both the linear setpoint calculation method and the combined controller method yield the best outcomes in most cases.